Debunking Glider Spoiler Turns Causing Spin Thinking

[[email protected]]

Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.

Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky. :)

https://youtu.be/tC-Yqp-uHo0

Here is the description of the video:
I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?

I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. :) Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.

Thanks for your insights and comments to try to help clarify the confusion.
Bruno - B4

[Bill T]

I've never heard of this. YGTBSM!
17 years flying gliders, 12 years as an instructor, moving the spoliers at will, turns or no turns, no problems.

I've never read anything in any glider flying manual, FAA handbook, or aerodynamic study.
Better warn the airlines, no spoiler actuation during turns!

I love to do a flight review with some of those pilots and watch them when I use the spoliers.
BillT

[JS]

In Australia there is a definite fear of using the blue handle during turns in the pattern (circuit).
Seems unjustified to me.
Jim

[[email protected]]

On Monday, June 1, 2015 at 10:12:22 PM UTC-6, Bill T wrote:
> I've never heard of this. YGTBSM!
> 17 years flying gliders, 12 years as an instructor, moving the spoliers at will, turns or no turns, no problems.
>
> I've never read anything in any glider flying manual, FAA handbook, or aerodynamic study.
> Better warn the airlines, no spoiler actuation during turns!
>
> I love to do a flight review with some of those pilots and watch them when I use the spoliers.
> BillT

Wait and you will see. I am already starting to get pilots defending this on the comments section of the video! That's why I brought it up. Wait till Europe wakes up tomorrow, sees the video and starts commenting. Should be very interesting! :)

Bruno - B4

[[email protected]]

I can't remember the last time my airbrakes were closed during a final turn in a high performance glider - and I live in Europe.

[Kevin Neave[_2_]]

Hi John,

If you're having to use the airbrakes everytime have you considered opening
up the circuit? Or is there something at Portmoak that prevents this?

I'm quite happy to use (or have my pupils use) airbrakes during final turn
if they were using them on base leg. Less happy for pupils to open them
during the turn. The final turn probably takes about 5 seconds so why not
wait 'til wings are level and the picture has stabilised before opening the
brakes. Why increase the workload for the sake of a few seconds?

KN

At 06:26 02 June 2015, wrote:
>I can't remember the last time my airbrakes were closed during a final
turn
>in a high performance glider - and I live in Europe.
>

[Per Carlin]

It is all about speed, attitude and banking.

When you are flying with high alfa, close to stall and then deploy brakes trouble are not far away.
If you fly in correct speed (1,5x stall + ½x wind) deploying brakes are safe. As long as you not change attitude and speed (glider specific behavior) when the brakes goes out.

[Surge]

South Africa appears to follow the "no spoiler during turns" rule as well.
On two occasions I was told by instructors not to use spoilers/air brakes while in banked turns onto base or onto finals.

Once was during a 30 degree bank to finals at 120km/h (64 knots) in an Twin Astir at about 300 feet AGL with spoilers half extended.
I deliberately flew faster to compensate for the increase in G-loading and loss of lift due to the spoilers being half out but it wasn't an acceptable answer to the instructor so I adjusted my flying style.

The "no spoilers during turns" rule makes sense if you're flying the turn too slowly and not taking the increased stall speed into account.

Example: According to the POH, a 650kg (1430lbs) Twin Astir stalls at about 90km (49 knots) with spoilers fully deployed. Add a 45 degree bank and the stall speed increases to 126 km/h (68 knots).
This is usually above the normal approach speed flown during circuits so I can conceive that a pilot who is not "ahead of the glider" could possibly fly too slowly during the turn. Throw in an uncoordinated turn and things could go wrong very quickly depending on glider type.

Maybe those grey beards have merit in their reasoning however the use of spoilers during turns closer to the ground can certainly help with altitude control during off field landings where there isn't a 1000+ foot runway available and there may be obstacles that can only be avoided with a turn to very short finals (e.g. high voltage power lines blocking the approach to a field and the field is too short to go over the top of 55 meter (180 foot) high power lines).

[Paul B[_2_]]

"In Australia there is a definite fear of using the blue handle during turns in the pattern (circuit).
Seems unjustified to me.
Jim "

I have flown in Australia for some 15 years, instructing for the last six, yet I have never heard such nonsense. Sure if you are very slow pulling g and then open air brakes, you may have problem, but that problem stems from the slow speed.

Paul

[Jonathon May[_2_]]

At 08:44 02 June 2015, Paul B wrote:
>
>
>"In Australia there is a definite fear of using the blue handle during
>turns in the pattern (circuit).
>Seems unjustified to me.
>Jim "
>
>I have flown in Australia for some 15 years, instructing for the last
six,
>yet I have never heard such nonsense. Sure if you are very slow pulling g
>and then open air brakes, you may have problem, but that problem stems
from
>the slow speed.
>
>Paul
>

I have heard of problems changing flap settings in aborted approaches ,but
I always thought the increased wing loading steadied every thing and
increased aileron response.
It is probably prudent to leave the brakes where they are during the turn,
then sort out the approach on the old "one thing at a time " theory, but I
would be reluctant to shutting the brakes for the turn then opening them
after.

[[email protected]]

On Tuesday, June 2, 2015 at 8:15:06 AM UTC+1, Kevin Neave wrote:
> Hi John,
>
> If you're having to use the airbrakes everytime have you considered opening
> up the circuit? Or is there something at Portmoak that prevents this?
>
> I'm quite happy to use (or have my pupils use) airbrakes during final turn
> if they were using them on base leg. Less happy for pupils to open them
> during the turn. The final turn probably takes about 5 seconds so why not
> wait 'til wings are level and the picture has stabilised before opening the
> brakes. Why increase the workload for the sake of a few seconds?
>
> KN
>
I respect the standard teaching for pupils and it is a sensible approach for them and for low performance gliders and others with very powerful airbrakes - but take a look at pictures of experienced pilots in high performance gliders turning onto finals and see how many of them have the airbrakes cracked open. I am not alone. BTW I didn't say I opened them during the final turn - for me on a normal circuit pattern the height judgement and adjustment starts somewhere on the base leg. During the final turn my attention is devoted to airspeed and lookout rather than height as I have already been thinking about that. I believe that is a safer practice for me.

JG

[Jonathan St. Cloud]

I was taught to open the airbrakes to a certain point ⅓-½ at the right time in the pattern to not change the setting , unless of course necessary. If you fly a power plane, do you pump the throttle in the pattern?

[[email protected]]

On Tuesday, June 2, 2015 at 2:42:53 AM UTC-5, Surge wrote:

>
> The "no spoilers during turns" rule makes sense if you're flying the turn too slowly and not taking the increased stall speed into account.
>
> Example: According to the POH, a 650kg (1430lbs) Twin Astir stalls at about 90km (49 knots) with spoilers fully deployed. Add a 45 degree bank and the stall speed increases to 126 km/h (68 knots).
> This is usually above the normal approach speed flown during circuits so I can conceive that a pilot who is not "ahead of the glider" could possibly fly too slowly during the turn. Throw in an uncoordinated turn and things could go wrong very quickly depending on glider type.

This is just the expected % increase in stall speed due to the loading imposed by the turn, right? But remember, the turn doesn't really "impose" the extra loading. The extra loading (lift) is imposed by either an increase in airspeed (safe), or by the pilot moving the stick aft to try to maintain the old airspeed (unsafe). If the pilot doesn't move the stick aft as he increases the bank angle, it will take a bit of time (a few seconds) for the airspeed (and loading) to increase, but there will be no risk of stall. During these few seconds, the flight path will curve slightly downward because the wing is not producing the full load "required" by the bank angle. The same would happen if the pilot opened the spoilers while holding a constant (or zero) bank angle-- the wing won't stall unless the pilot increases the angle-of-attack.

I guess what I'm trying to say is-- one of the key points of Tom Knauff's books is that turns aren't unsafe as long as you don't move the stick aft. The same could be said of spoiler usage. Opening the spoiler won't produce a stall as long as the pilot doesn't move the stick aft to increase the wing's angle-of-attack.

Banking and opening spoilers aren't completely analogous though. As you increase bank angle, you must move the stick further aft just to hold the SAME angle-of-attack that you had at a shallower bank angle. To actually increase the angle-of-attack, you have to move the stick even FURTHER aft. This is a point in the pilot's favor, in terms of avoiding accidental stalls, so long as the pilot has some awareness of what he is doing with the stick. Again this comes up in Knauff's books and seminars. This has to do with the curving nature of the airflow in a turn, and the resulting change in airflow at the tail. The same is not true when you increase loading per unit wing area in other ways-- like by adding water ballast, or by "removing" part of the wing (opening spoilers).

I guess there's another factor that could be relevant. In some gliders, opening the spoilers creates a large trim change, forcing you to move the stick just to hold the same angle-of-attack that you had before opening them. If you have plenty of airspeed-- no problem. If you have less airspeed and you are going by the theory that you won't stall because you aren't doing the wrong thing with the stick, maybe you could have a problem. Even if angle-of-attack tends to stay constant as the spoilers are opened, the resulting downcurve of the flight path could tempt a pilot to haul back on the stick to arrest it. At the end of the day I guess you'd better have plenty of airspeed if you are making radical changes in spoiler setting.

S

[Charlie M. (UH & 002 owner/pilot)]

Hmmm.... never heard of this either. Flying for ~40 years (in sailplanes) & a CFIG for 8 years.
Maybe the "original issue" was sailplanes that had a noticeable pitch attitude change with change in spoliers/dive brakes (add spoliers, nose pitches up, thus slower/higher AoA?). Rather than point that out, the decision was made to not use them in a turn.

Kind of like training that, "Go fast in the pattern so you don't stall/spin", rather than stall/spin training & recognition.

[Bill D]

On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>
> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky. :)
>
> https://youtu.be/tC-Yqp-uHo0
>
> Here is the description of the video:
> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>
> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. :) Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>
> Thanks for your insights and comments to try to help clarify the confusion.

[jfitch]

On Tuesday, June 2, 2015 at 7:52:00 AM UTC-7, Bill D wrote:
> On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
> > Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
> >
> > Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky. :)
> >
> > https://youtu.be/tC-Yqp-uHo0
> >
> > Here is the description of the video:
> > I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
> >
> > I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. :) Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
> >
> > Thanks for your insights and comments to try to help clarify the confusion.
> > Bruno - B4
>
> This is what I told Bruno earlier in a phone call.
>
> Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.
>
> A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.
>
> So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.
>
> Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.
>
> So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed..
>
> That's my $0.02

I would never fly a pattern at so slow a speed that opening the spoilers (or 4 knots error in airspeed) would cause a stall. If you do so, some day you are very likely to stall or spin, spoilers or no spoilers, in anything but perfectly calm conditions. Are 4 knot gusts so uncommon in the world?

[Dan Marotta]

That's a pretty good $0.02, Bill.

There's a trend to teach people to stay out of trouble by being overly
conservative rather than to teach proper theory and practice.
Disappointingly this leads to a bunch of mediocre pilots and, I believe,
more accidents.

As to using dive brakes, I open them as I begin my final turn (a
descending 180 deg turn to final) and I use them during the turn as I
see fit. Once on final I use them less, maybe 1/2 to 3/4 until just
before touchdown when I open them fully. I pick my touchdown point on
downwind and fly to that point. Never do I fly to a landmark and then
make a turn to base, fly to another landmark and turn to final. That's
just asking for trouble.

My $0.02.

On 6/2/2015 8:51 AM, Bill D wrote:

> On Monday, June 1, 2015 at 9:09:34 PM wrote:
>> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>>
>> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.
>>
>> https://youtu.be/tC-Yqp-uHo0
>>
>> Here is the description of the video:
>> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>>
>> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>>
>> Thanks for your insights and comments to try to help clarify the confusion.
>> Bruno - B4
> This is what I told Bruno earlier in a phone call.
>
> Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.
>
> A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.
>
> So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.
>
> Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.
>
> So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.
>
> That's my $0.02


On 6/2/2015 8:51 AM, Bill D wrote:
> On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
>> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>>
>> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky. :)
>>
>> https://youtu.be/tC-Yqp-uHo0
>>
>> Here is the description of the video:
>> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>>
>> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. :) Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>>
>> Thanks for your insights and comments to try to help clarify the confusion.
>> Bruno - B4
> This is what I told Bruno earlier in a phone call.
>
> Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.
>
> A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.
>
> So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.
>
> Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.
>
> So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.
>
> That's my $0.02

--
Dan Marotta

[Dan Marotta]

I noted in one of the responses to Bruno's video, and I'm paraphrasing
here, that you should never use spoilers in the base turn unless
something unusual happens, i.e., an unexpected thermal. I submit that
doing something only seldomly in an unusual case is more dangerous than
doing it all the time and being well-practiced.

On 6/2/2015 9:47 AM, Dan Marotta wrote:
> That's a pretty good $0.02, Bill.
>
> There's a trend to teach people to stay out of trouble by being overly
> conservative rather than to teach proper theory and practice.
> Disappointingly this leads to a bunch of mediocre pilots and, I believe,
> more accidents.
>
> As to using dive brakes, I open them as I begin my final turn (a
> descending 180 deg turn to final) and I use them during the turn as I
> see fit. Once on final I use them less, maybe 1/2 to 3/4 until just
> before touchdown when I open them fully. I pick my touchdown point on
> downwind and fly to that point. Never do I fly to a landmark and then
> make a turn to base, fly to another landmark and turn to final. That's
> just asking for trouble.
>
> My $0.02.
>
> On 6/2/2015 8:51 AM, Bill D wrote:
>> On Monday, June 1, 2015 at 9:09:34 PM wrote:
>>> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>>>
>>> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.
>>>
>>> https://youtu.be/tC-Yqp-uHo0
>>>
>>> Here is the description of the video:
>>> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>>>
>>> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>>>
>>> Thanks for your insights and comments to try to help clarify the confusion.
>>> Bruno - B4
>> This is what I told Bruno earlier in a phone call.
>>
>> Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.
>>
>> A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.
>>
>> So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.
>>
>> Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.
>>
>> So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.
>>
>> That's my $0.02
>
>
> On 6/2/2015 8:51 AM, Bill D wrote:
>> On Monday, June 1, 2015 at 9:09:34 PM wrote:
>>> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>>>
>>> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky. :)
>>>
>>> https://youtu.be/tC-Yqp-uHo0
>>>
>>> Here is the description of the video:
>>> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>>>
>>> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. :) Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>>>
>>> Thanks for your insights and comments to try to help clarify the confusion.
>>> Bruno - B4
>> This is what I told Bruno earlier in a phone call.
>>
>> Opening spoilers increases the stall speed something like 4 knots. Most flight manuals provide specific guidance to this effect.
>>
>> A moderately banked turn sets up a speed difference across the wing span (the outside wing tip is going faster than the inside tip in a turn). This difference is in the range of 10 knots. This can be determined mathimatically from airspeed and bank angle.
>>
>> So, with the inside wing tip flying at roughly 5 knots less than the ASI says and the spoiler on that wing increasing the stall speed roughly 4 knots, you have reduced your stall margin on the inside wing tip about 9 knots. That can be significant.
>>
>> Whether that matters depends on the airspeed. A low airspeed turn to final with spoilers open can put the inside wing right on the edge of a stall. If you fly patterns at the speed your instructor taught you to, you'll have adequate stall margin even with the spoilers open. Pull the speed down below the yellow triangle in that turn and you could be in trouble. Add gusty winds and it gets much worse.
>>
>> So, it is correct to teach "no spoilers in a turn"? I think that's an over reaction based on a misunderstanding. A better approach is to teach airspeed control and using that control to maintain at least 1.5 x Vso + 1/2 the gust speed until stabilized on the final approach with wings level. Only then can airspeed be safely reduced to the yellow traingle approach speed.
>>
>> That's my $0.02
>
> --
> Dan Marotta

--
Dan Marotta

[Martin Gregorie[_5_]]

On Tue, 02 Jun 2015 09:47:50 -0600, Dan Marotta wrote:

> Never do I fly to a landmark and then make a turn to base, fly to
> another landmark and turn to final. That's just asking for trouble.
>
Surely that can only work for a pilot who never has and never will land
anywhere but his home field.

UK training specifically warns against that trick.

My 2p.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Bill D]

On Tuesday, June 2, 2015 at 9:47:56 AM UTC-6, Dan Marotta wrote:
> That's a pretty good $0.02, Bill.
>
> There's a trend to teach people to stay out of trouble by being overly
> conservative rather than to teach proper theory and practice.
> Disappointingly this leads to a bunch of mediocre pilots and, I believe,
> more accidents.
>
> As to using dive brakes, I open them as I begin my final turn (a
> descending 180 deg turn to final) and I use them during the turn as I
> see fit. Once on final I use them less, maybe 1/2 to 3/4 until just
> before touchdown when I open them fully. I pick my touchdown point on
> downwind and fly to that point. Never do I fly to a landmark and then
> make a turn to base, fly to another landmark and turn to final. That's
> just asking for trouble.
>
> My $0.02.
>
> On 6/2/2015 8:51 AM, Bill D wrote:
>
>
> On Monday, June 1, 2015 at 9:09:34 PM UTC-6, wrote:
>
>
> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>
> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky.
>
> https://youtu.be/tC-Yqp-uHo0
>
> Here is the description of the video:
> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>
> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>
> Thanks for your insights and comments to try to help clarify the confusion.

[Kevin Neave[_2_]]

Hi Dan

It obviously works for you but I'm interested in why you do this.

If you're doing a 180 to finals and opening the airbrakes at the start of
the turn are you not pointing away at this point with the landing area out
of sight behind you?



At 15:47 02 June 2015, Dan Marotta wrote:
>That's a pretty good $0.02, Bill.
>
>
>As to using dive brakes, I open them as I begin my final turn (a
>descending 180 deg turn to final) and I use them during the turn as I
>see fit. Once on final I use them less, maybe 1/2 to 3/4 until just
>before touchdown when I open them fully. I pick my touchdown point on
>downwind and fly to that point. Never do I fly to a landmark and then
>make a turn to base, fly to another landmark and turn to final. That's
>just asking for trouble.
>
>My $0.02.
>

[kirk.stant]

On Tuesday, June 2, 2015 at 11:48:56 AM UTC-5, Bill D wrote:

> When watching the video I grimaced when I saw the spoilers open on downwind and base on every landing even though the glider was well below normal pattern altitude. In this situation, the spoilers should remain closed until the glider is stabilized on a short final approach.

It's fascinating reading about all the different ways people are taught to land gliders.

I was taught to check spoilers on downwind (so you can adjust if either the lock full open, or don't open at all), then about abeam the touchdown point, pull on 1/3 to 1/2 spoilers (depending on how effective they are) and fly the pattern, trying to not change spoiler setting until landing. BUT - If low, less or close, if high, more and slip. In my LS6, I set the flaps to landing (or less, if the wind is strong) on downwind and don't worry about them anymore until after touchdown.

I also like the military style "180" single turn pattern, especially if the pattern is low and tight (like say after a "low pass").

I also prefer a fast pattern, slowing down once on final - but again that is glider-specific.

And of course, ALWAYS adjust for your actual altitude/energy state and do what is needed to land safely!

Bottom line, I think it helps to get everything set on downwind (gear, flaps, initial spoiler setting, airspeed) then concentrate on flying a safe pattern. To me, messing with flaps and spoilers while making base and final turns and changing aircraft configuration throughout the pattern is asking for trouble (see all the ASW-20s that crashed early on with the gear cycling on final, ex-Libelle pilots thinking they were pulling the spoilers!)

Finally - I detest big, high, long final patterns. Why? The longer the pattern, the more chance something can get messed up. 1000' on downwind is absurd! Get in tight at 600' or so, two (or one) tight turns to final, land.

Because when you start landing out, at 1000' you should still be trying to thermal away (with a field picked out), and when you do have to set up your pattern, you will be low and close - so you can see what you are getting into!

Kirk
66

[kirk.stant]

On Tuesday, June 2, 2015 at 12:00:06 PM UTC-5, Kevin Neave wrote:
> Hi Dan
>
> It obviously works for you but I'm interested in why you do this.
>
> If you're doing a 180 to finals and opening the airbrakes at the start of
> the turn are you not pointing away at this point with the landing area out
> of sight behind you?

Kevin, Dan is just doing what he was taught as an Air Force pilot - single steep 180 turn from downwind to final.

In many ways the easiest way to land a plane - when combined with an overhead pattern (which doesn't really work well with gliders, unfortunately) results in the exact same pattern at every landing.

A shame civilian pilots are not exposed to it.

Works great in a Pawnee - 120mph at 500 agl on initial, pitch out just past the numbers, configure on downwind, pull off some power and a nice descending 180 turn will put you on the numbers in minimum time - and it looks good from the ground!

Kirk
66

[Charlie M. (UH & 002 owner/pilot)]

On Tuesday, June 2, 2015 at 12:00:12 PM UTC-4, Martin Gregorie wrote:
> On Tue, 02 Jun 2015 09:47:50 -0600, Dan Marotta wrote:
>
> > Never do I fly to a landmark and then make a turn to base, fly to
> > another landmark and turn to final. That's just asking for trouble.
> >
> Surely that can only work for a pilot who never has and never will land
> anywhere but his home field.
>
> UK training specifically warns against that trick.
>
> My 2p.
>
>
> --
> martin@ | Martin Gregorie
> gregorie. | Essex, UK
> org |

At our field, we teach "angles, what does it look like?", then again, most of our CFIG's are cross country/competition pilots.
Landmarks "can" work at a constant fixed location, but is no help in "Farmer Browns back 40". Heck, even an altimeter is rather useless (in an off airport landing) since you don't know field elevation.

[Tango Eight]

On Tuesday, June 2, 2015 at 1:24:53 PM UTC-4, kirk.stant wrote:

> Bottom line, I think it helps to get everything set on downwind (gear, flaps, initial spoiler setting, airspeed) then concentrate on flying a safe pattern. To me, messing with flaps and spoilers while making base and final turns and changing aircraft configuration throughout the pattern is asking for trouble (see all the ASW-20s that crashed early on with the gear cycling on final, ex-Libelle pilots thinking they were pulling the spoilers!)

What helps even more is starting with the POH before developing your own type specific procedures :-).

For instance: Landing flaps in the 20 are reserved for final approach, per the POH, for a whole bunch of very good reasons.

-Evan Ludeman / T8

[[email protected]]

Bruno, thanks for a thought provoking post and video.

You made me think about what I do when in the landing pattern. I fly a standard pattern, flaps in landing configuration, spoilers cracked on downwind, spoilers adjusted to achieve the right angle on down wind, base and final as required. I'm fairly certain I don't adjust the spoilers during turns.. I don't remember ever hearing anything about no spoiler adjustments during turns. However ---never really thought about it, but moving the stick, and adding rudder during the turn seems like enough workload without adjusting the spoilers too. BTW I use 1.5Vso + 1/2 gust speed. I'm going to try, at altitude (like you) turning near Vso (stall) and adjusting the spoilers to see the effect.

Chuck Zabinski

[Martin Gregorie[_5_]]

On Tue, 02 Jun 2015 10:37:23 -0700, Charlie M. (UH & 002 owner/pilot)
wrote:

>
> At our field, we teach "angles, what does it look like?", then again,
> most of our CFIG's are cross country/competition pilots.
> Landmarks "can" work at a constant fixed location, but is no help in
> "Farmer Browns back 40". Heck, even an altimeter is rather useless (in
> an off airport landing) since you don't know field elevation.

Yes, that precisely how I was taught.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Monday, June 1, 2015 at 11:09:34 PM UTC-4, wrote:
> Either a large majority of us are unaware that we are on the verge of death every time we adjust our spoilers while landing, or some people are being taught this and causing them to unnecessarily fear spoilers and using them to their full degree of helpfulness and effectiveness.
>
> Here's a video I made trying to demonstrate what happens when you use spoilers while turning...nothing! I was a little bit of a punchy mood while taking the video - sorry for being a little bit snarky. :)
>
> https://youtu.be/tC-Yqp-uHo0
>
> Here is the description of the video:
> I had been flying gliders for almost 20 years before someone on the internet wrote to me that adjusting spoilers while turning to land can kill you. What?!?! Supposedly, because your inside wing is flying so much slower than the outside in a turn, a little spoiler can spoil the whole day. I have been freely adjusting my spoilers as needed during landing my entire flying career. Why have none of the glider manuals I have ever read warned about this?
>
> I've asked multiple CFI-G's (glider instructors) and they are also baffled this is being taught to students. I've now heard from 4-5 different people (all pilots outside of USA) that have been taught this by their instructors. Time to try to debunk this. :) Glider is an ASW-27B flown dry at the time of this video out of Cedar Valley, Utah.
>
> Thanks for your insights and comments to try to help clarify the confusion.

[kirk.stant]

On Tuesday, June 2, 2015 at 1:37:48 PM UTC-5, Tango Eight wrote:
> On Tuesday, June 2, 2015 at 1:24:53 PM UTC-4, kirk.stant wrote:
>
> > Bottom line, I think it helps to get everything set on downwind (gear, flaps, initial spoiler setting, airspeed) then concentrate on flying a safe pattern. To me, messing with flaps and spoilers while making base and final turns and changing aircraft configuration throughout the pattern is asking for trouble (see all the ASW-20s that crashed early on with the gear cycling on final, ex-Libelle pilots thinking they were pulling the spoilers!)
>
> What helps even more is starting with the POH before developing your own type specific procedures :-).
>
> For instance: Landing flaps in the 20 are reserved for final approach, per the POH, for a whole bunch of very good reasons.
>
> -Evan Ludeman / T8

Obviously, type-specific procedures specified in the POH take precedence. In the case of the LS6, it pretty much just says "for landing, put flaps in L". Having flown the 20, I totally agree with the POH procedure!

My point is that it's possible to make a landing pattern procedure so complicated that the pilot's attention is distracted "by doing everything in the right sequence at the right time" - forgetting that the most important thing is to arrive on short final at a suitable airspeed and height, and at the desired location!

Kirk
66

[Surge]

On Wednesday, 3 June 2015 01:37:42 UTC+2, Bruce Hoult wrote:
> I think you'll find that's more like 58 knots.
>
> In a 45 degree turn, the G loading is 41% higher, but it only takes 20% more speed to produce that G loading, not 41% more speed.

You're right.
G-loading would be 1.41G in a 45 degree bank but the stall speed would increase by 1.19 so that would make it 58 knots (107km/h).

[Dan Marotta]

It would take a lot of writing to totally describe the pattern. Of
course I make allowances for cross wind (crab), lift/sink (altitude),
head/tail wind (airspeed, flap setting), thermal/sink (dive brakes,
shifted touchdown point), etc. It's a dynamic process. Most pilots can
do it some can't. What I described is the nominal method. I do not fly
by rote as some pilots apparently do or are instructed to do...

On 6/2/2015 5:34 PM, son_of_flubber wrote:
> On Tuesday, June 2, 2015 at 6:31:07 PM UTC-4, Dan Marotta wrote:
>> I can see the
>> landing area slightly over my shoulder as I begin the turn and I
>> keep my eyes on that spot with occasional glances inside and out on
>> final for other aircraft.
> So you initiate the turn from downwind at the right time/point regardless of sink/wind conditions?
>
> With your one turn method, the length of the glideslope to touchdown is set when you initiate the turn from downwind and so you make all corrections to touchdown point with more/less airbrakes (keeping airspeed constant)?

--
Dan Marotta

[Dan Marotta]

How come nobody ever states that these G loading increases are for level
flight? Since the glider is always descending, wouldn't it be better to
include something about the descent rate being maintained? What about a
climbing turn? Maybe some trig including the flight path angle?

Curious minds... And it's a slow morning before going to tow at the
Moriarty encampment.

On 6/2/2015 11:48 PM, Surge wrote:
> On Wednesday, 3 June 2015 01:37:42 UTC+2, Bruce Hoult wrote:
>> I think you'll find that's more like 58 knots.
>>
>> In a 45 degree turn, the G loading is 41% higher, but it only takes 20% more speed to produce that G loading, not 41% more speed.
> You're right.
> G-loading would be 1.41G in a 45 degree bank but the stall speed would increase by 1.19 so that would make it 58 knots (107km/h).

--
Dan Marotta

[[email protected]]

The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.

Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.

S

On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
> How come nobody ever states that these G loading increases are for
> level flight?* Since the glider is always descending, wouldn't it be
> better to include something about the descent rate being
> maintained?* What about a climbing turn?* Maybe some trig including
> the flight path angle?
>
>
>
> Curious minds...* And it's a slow morning before going to tow at the
> Moriarty encampment.
>
>

[Bruce Hoult]

On Wednesday, June 3, 2015 at 4:58:36 PM UTC+3, Dan Marotta wrote:
> How come nobody ever states that these G loading increases are for
> level flight?* Since the glider is always descending, wouldn't it be
> better to include something about the descent rate being
> maintained?* What about a climbing turn?* Maybe some trig including
> the flight path angle?

The speed at which the wing stalls depends only on the G loading, not on the attitude with respect to gravity or the earth. Of course if you're in an unusual attitude then your speed may be changing.

As long as you keep the angle of attack constant (which pretty much means the elevator and therefore stick position), you don't have to think about how the speed or the G loading are changing -- they'll change together in sync. As long as you stay below the speed at which the G loading will break your wings off anyway.

[jfitch]

On Wednesday, June 3, 2015 at 10:32:35 AM UTC-7, wrote:
> The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.
>
> Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.
>
> S
>
> On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
> > How come nobody ever states that these G loading increases are for
> > level flight?* Since the glider is always descending, wouldn't it be
> > better to include something about the descent rate being
> > maintained?* What about a climbing turn?* Maybe some trig including
> > the flight path angle?
> >
> >
> >
> > Curious minds...* And it's a slow morning before going to tow at the
> > Moriarty encampment.
> >
> >

It doesn't matter if the glider is descending - the wing loading is the same. The only thing that will change that is accelerated flight. That is an increasing or decreasing rate of descent (not constant) or a change in velocity (that includes turns which are a change in velocity by definition). A sustainer glider will have the same wing loading in level (unaccelerated) flight as it does in a glide.

It is best not to think of the "speed at which the wing stalls". That can be anywhere from 0 to beyond redline, depending on a bunch of conditions. You should think of "the angle of attack at which the wing stalls" which is for all intents invariant on a glider. The only way to unstall a wing is to reduce its angle of attack, fortunately that is usually easy. This may have consequences (normally, an increased rate of descent) which may have to be dealt with later, but at least you are in control of it.

[Dan Marotta]

Thanks! Most appreciated.

On 6/3/2015 11:32 AM, wrote:
> The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.
>
> Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.
>
> S
>
> On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
>> How come nobody ever states that these G loading increases are for
>> level flight? Since the glider is always descending, wouldn't it be
>> better to include something about the descent rate being
>> maintained? What about a climbing turn? Maybe some trig including
>> the flight path angle?
>>
>>
>>
>> Curious minds... And it's a slow morning before going to tow at the
>> Moriarty encampment.
>>
>>

--
Dan Marotta

[[email protected]]

PS that's for level flight-- for a turn the effective glide ratio is worse than the L/D and so the trig is more complicated and there's more unloading of the wing (compared to horizontal flight at the same bank angle) than you'd have at the same L/D in level flight, but the unloading is still quite small until we start talking about really steep bank angles or really poor L/D ratios.

Examples: G-load (lift / weight) at various bank angles and L/D ratios:

L/D Infinite-- 0 deg 1.00 30 deg 1.15 45 deg 1.41 60 deg 2.00
L/D 10:1-- 0 deg .995 30 deg 1.15 45 deg 1.40 60 deg 1.97
L/D 5:1-- 0 deg .981 30 deg 1.13 45 deg 1.36 60 deg 1.87
L/D 2:1-- 0 deg .894 30 deg 1.00 45 deg 1.15 60 deg 1.41
L/D 1:1-- 0 deg .707 30 deg .756 45 deg .817 60 deg .894

(if my math is right....)

S

On Wednesday, June 3, 2015 at 12:32:35 PM UTC-5, wrote:
> The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.
>
> Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.
>
> S
>
> On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
> > How come nobody ever states that these G loading increases are for
> > level flight?* Since the glider is always descending, wouldn't it be
> > better to include something about the descent rate being
> > maintained?* What about a climbing turn?* Maybe some trig including
> > the flight path angle?
> >
> >
> >
> > Curious minds...* And it's a slow morning before going to tow at the
> > Moriarty encampment.
> >
> >

[[email protected]]

I might've paid attention in math class if I had known it could save lives

[jfitch]

On Thursday, June 4, 2015 at 5:50:31 AM UTC-7, wrote:
> PS that's for level flight-- for a turn the effective glide ratio is worse than the L/D and so the trig is more complicated and there's more unloading of the wing (compared to horizontal flight at the same bank angle) than you'd have at the same L/D in level flight, but the unloading is still quite small until we start talking about really steep bank angles or really poor L/D ratios.
>
> Examples: G-load (lift / weight) at various bank angles and L/D ratios:
>
> L/D Infinite-- 0 deg 1.00 30 deg 1.15 45 deg 1.41 60 deg 2.00
> L/D 10:1-- 0 deg .995 30 deg 1.15 45 deg 1.40 60 deg 1.97
> L/D 5:1-- 0 deg .981 30 deg 1.13 45 deg 1.36 60 deg 1.87
> L/D 2:1-- 0 deg .894 30 deg 1.00 45 deg 1.15 60 deg 1.41
> L/D 1:1-- 0 deg .707 30 deg .756 45 deg .817 60 deg .894
>
> (if my math is right....)
>
> S
>
> On Wednesday, June 3, 2015 at 12:32:35 PM UTC-5, wrote:
> > The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.
> >
> > Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.
> >
> > S
> >
> > On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
> > > How come nobody ever states that these G loading increases are for
> > > level flight?* Since the glider is always descending, wouldn't it be
> > > better to include something about the descent rate being
> > > maintained?* What about a climbing turn?* Maybe some trig including
> > > the flight path angle?
> > >
> > >
> > >
> > > Curious minds...* And it's a slow morning before going to tow at the
> > > Moriarty encampment.
> > >
> > >

Are you saying that the wing loading goes down in a turn because the glide ratio deteriorates?

That is incorrect. Wing loading and glide ratio, as you are using them here, are unrelated.

In steady state, unaccelerated flight, Lift = Mass and the wing loading is constant. It does not matter what your sink rate is. The wing loading is the same with flaps, gear, and spoilers out as it is clean. If Lift <> Mass then the glider is accelerating, either up, down or by changing direction. If Lift > Mass then the wing loading is higher, for example a turn or pull up. If Lift < Mass then the wing loading is lower, for example a push over..

[[email protected]]

We have one old timer instructor in my club who insists on airbrakes fully in during turns. The only good reason I can think of for doing this is if you have a student who is in the early stages of learning the circuit and landing. Early on they may have trouble reliably determining whether they are above or below glidepath while turning or may be overwhelmed by adding the modulation of the brakes to the demands on their attention during the base and final turns.

If you are flying the pattern at the approach speed recommended by the manual for an approach in which full airbrakes might be deployed (which in my opinion is every approach) you should have a safe margin above the stall speed in the sort of well banked turns you should be using in the circuit whether the brakes are in or out. The brakes are there to put you on your desired glide path. Use them as necessary, you paid for them!

As an experiment try this at altitude: trim to the recommended approach speed with full airbrakes or recommended approach speed found in the AFM (or if it's not specified use the formula you were taught for choosing an approach speed), roll the glider into a good coordinated 40 degree bank turn then move the elevator progressively back. In every glider I've flown the elevator hits the stop without provoking a stall. I tried this after reading a Derek Piggott article suggesting it.

[[email protected]]

On Thursday, June 4, 2015 at 10:41:59 AM UTC-5, jfitch wrote:
..

>
> Are you saying that the wing loading goes down in a turn because the glide ratio deteriorates?

Yes, I am. The worse the glide ratio (horizontal distance covered per vertical distance covered), the less lift the wing must generate, for any given bank angle. As L/D approaches 1:1 and glide ratio approaches something really terrible (worse than 1:1, if the aircraft is banked), the lift vector becomes less than the weight vector. Because much of the aircraft weight is being supported by the drag vector. See my table from previous post. As we start at any given bank angle, and hold that bank angle constant, and degrade the L/D ratio by increasing the drag coefficient, the flight path will end up aiming more and more steeply downward into a descending helix, with the ultimate end point being a vertical rolling dive at 0:1 L/D and 100% of the aircraft weight supported by the drag vector. (The drag coefficient must be infinite, and the airspeed must be zero, to achieve this so we never get there in real life.)

See my table from previous post.
>
> That is incorrect. Wing loading and glide ratio, as you are using them here, are unrelated.
>
> In steady state, unaccelerated flight, Lift = Mass and the wing loading is constant.

No-- see my table from previous post. Lift does not equal weight in unbanked gliding flight, unless L/D is infinite. Do you know how to draw the lift -drag- weight vector triangle for unbanked gliding flight? It appears in most sailplane instructional materials-- I should hope!

S

[[email protected]]

On Thursday, June 4, 2015 at 11:34:35 PM UTC-5, wrote:

> As an experiment try this at altitude: trim to the recommended approach speed with full airbrakes or recommended approach speed found in the AFM (or if it's not specified use the formula you were taught for choosing an approach speed), roll the glider into a good coordinated 40 degree bank turn then move the elevator progressively back. In every glider I've flown the elevator hits the stop without provoking a stall. I tried this after reading a Derek Piggott article suggesting it.

What is the result of the same test with airbrakes closed?


What do you need to do with the stick to hold a constant airspeed as you open the spoilers in wings-level flight?

Is the heart of the matter simply that for a given airspeed in wings-level at any given bank angle, including zero degrees bank, the stick needs to be positioned further aft with the spoilers open than with the spoilers closed?

S

[[email protected]]

On Thursday, June 4, 2015 at 11:34:35 PM UTC-5, wrote:

>
> As an experiment try this at altitude: trim to the recommended approach speed with full airbrakes or recommended approach speed found in the AFM (or if it's not specified use the formula you were taught for choosing an approach speed), roll the glider into a good coordinated 40 degree bank turn then move the elevator progressively back. In every glider I've flown the elevator hits the stop without provoking a stall. I tried this after reading a Derek Piggott article suggesting it.

In other words is the heart of the matter that the airbrakes make the glider trim to a lower angle-of-attack, for a given elevator position? Possibly because of changes in airflow over the tail?

I guess I'm simply suggesting that in wings-level flight, the glider may stall with the stick further aft with airbrakes open than with airbrakes closed. Yes? Airbrakes probably decrease downwash over the tail, causing the glider to trim to a lower a-o-a.

The need for progressively more aft stick to command a given angle-of-attack (e.g. the stall angle-of-attack) as we progressively increase the bank angle is not unexpected, but I've never done a side-by-side comparison of airbrakes closed vs airbrakes open. Perhaps you have the same demand for extra back stick to maintain a given angle-of-attack as you increase the bank angle in both cases, but in the airbrakes-open case, you are starting with the stick further aft, so you and up hitting the stop sooner.

S

[[email protected]]

On Thursday, June 4, 2015 at 10:41:59 AM UTC-5, jfitch wrote:

> Are you saying that the wing loading goes down in a turn because the glide ratio deteriorates?

Well-- of course I'm not saying that holding L/D constant and increasing the bank angle will decrease the wing loading! That would be very silly.

I am saying that holding bank angle constant and decreasing L/D will decrease the wing loading due to the deterioration in glide angle.

See previous posts and especially the table of wing loading for various L/D ratios and bank angles. The table says it better than I can say it in words.

S

[JS]

Bruno must have had a laugh using the term "Debunking" on RAS.
Jim

On Monday, June 1, 2015 at 8:09:34 PM UTC-7, wrote:
>
> Thanks for your insights and comments to try to help clarify the confusion.
> Bruno - B4

[jfitch]

On Friday, June 5, 2015 at 7:01:27 AM UTC-7, wrote:
> On Thursday, June 4, 2015 at 10:41:59 AM UTC-5, jfitch wrote:
>
> > Are you saying that the wing loading goes down in a turn because the glide ratio deteriorates?
>
> Well-- of course I'm not saying that holding L/D constant and increasing the bank angle will decrease the wing loading! That would be very silly.
>
> I am saying that holding bank angle constant and decreasing L/D will decrease the wing loading due to the deterioration in glide angle.
>
> See previous posts and especially the table of wing loading for various L/D ratios and bank angles. The table says it better than I can say it in words.
>
> S

This is a unique use of the term "wing loading". By that definition, an HP with 90 degree flaps, pointing straight at the ground in steady state, has zero wing loading, and parachutes always have zero canopy loading.

[Jim Lewis[_2_]]

"Lift does not equal weight in unbanked gliding flight, unless L/D is infinite."

I confess this one stumps me. I'll have to think about it a while.

Disregarding drag (maybe I shouldn't), if lift does not equal weight the result is unbalanced forces, which result in acceleration (in a vector sense). The glider will either accelerate or fly an increasingly steep glide; maybe both.

Maybe it's like an optical illusion.

[[email protected]]

>>This is a unique use of the term "wing loading".

In my table I referenced g-loading, not wing loading, but they are not unrelated. Assuming you define g-loading as lift / weight. Another reasonable way to define g-loading is net aerodynamic force / weight-- that's a useful definition for orbital re-entry dynamics and such, but that's not what you'd be reading on a conventional panel-mounted aircraft g-meter.

>>By that definition, an HP with 90 degree flaps, pointing straight at the ground in steady state, has zero wing loading

If the flight path is directed straight down, the wings must be at the zero-lift angle-of-attack. The g-meter on the panel will read zero, and there is no lift generated by the wings.

>> and parachutes always have zero canopy loading.*

I'm not very interested in parachutes, but if I were, I don't think I would define my terms as you seem to be suggesting.

Once again-- you don know how to draw the lift-drag-weight vector triangle for unbanked gliding flight, right?

S

[Dan Marotta]

Without drawing any pictures -

At constant speed the glider is descending, therefore the lift vector
(perpendicular to the wing) is canted forward. Adding in the drag
vector (opposite the glider's longitudinal axis) yields a vector which
is directly opposite to gravity. It is this resultant vector (the sum
of the lift and drag vectors) which offsets the weight vector.

Did I say that well enough?

On 6/5/2015 9:33 AM, Jim Lewis wrote:
> "Lift does not equal weight in unbanked gliding flight, unless L/D is infinite."
>
> I confess this one stumps me. I'll have to think about it a while.
>
> Disregarding drag (maybe I shouldn't), if lift does not equal weight the result is unbalanced forces, which result in acceleration (in a vector sense). The glider will either accelerate or fly an increasingly steep glide; maybe both.
>
> Maybe it's like an optical illusion.

--
Dan Marotta

[[email protected]]

Can someone help educate these folks by posting a link to a nice illustration of the lift-drag-weight vector triangle for straight-line gliding flight?

S

[Jim Lewis[_2_]]

Thank you for your interest in educating us.

[Jim Lewis[_2_]]

Yes, thank you.

At an L/D of 45:1 I suppose the drag vector would be significant?

[Bob Whelan[_3_]]

On 6/5/2015 9:01 AM, jfitch wrote:
<Snip>

> This is a unique use of the term "wing loading". By that definition, an HP
> with 90 degree flaps, pointing straight at the ground in steady state, has
> zero wing loading...

Maybe some of the confusion stems from terminology? It's been a long time
since my college days when I learned the definition of 'wing loading' (and I
haven't bothered to look it up now!), but I still think of it as simply a
mathematical construct: aircraft weight/wing area (including that projected
through the fuselage).

As such, it's a simple, static concept; the definition says nothing about
aircraft attitude, dynamic loading, load distribution, etc. Complexity enters
the picture when dynamic/structural 'stuff' needs to be considered, e.g.:
non-steady-state flight conditions (turns, spirals, changing flight
trajectories, ...), wing-borne loads, etc.

Considering the flight condition above, the wing's structural loading (even in
the lift-plane perpendicular to the wing chord) of a glider under that
condition will be quite different from the wing's definitional wing loading.
Imagine a glider descending at a zero-lift AOA (which the above example is not)...

HTH,
Bob W.

[Dan Marotta]

How about this? Lift weight drag of a glider
<https://www.google.com/search?q=lift+drag+weight+vector+diagram&espv=2&biw=1280&bih=675&tbm=isch&imgil=P0lMoDrEgSfJCM%253A%253BhJTVL_XvdI7R2M%253Bh ttp%25253A%25252F%25252Fwww.kitestrings.org%25252F topic10-250.html&source=iu&pf=m&fir=P0lMoDrEgSfJCM%253A%252ChJTVL_XvdI7R2M%252C_&usg=__qfFN38kSGKUAQBuynNOaDmlnsAE%3D&ved=0CDMQyjc&ei=NdlxVdafA4WlsAXkh4PQAw#tbm=isch&q=lift+drag+weight+vector+diagram+glider&imgdii=htd7GlKMM3-dPM%3A%3Bhtd7GlKMM3-dPM%3A%3BGHSbBYUdPbo61M%3A&imgrc=htd7GlKMM3-dPM%253A%3BlbPHPYZSArLXbM%3Bhttps%253A%252F%252Fww w.grc.nasa.gov%252FWWW%252Fk-12%252Fairplane%252FImages%252Fglidvec.gif%3Bhttps %253A%252F%252Fwww.grc.nasa.gov%252FWWW%252Fk-12%252Fairplane%252Fglidvec.html%3B709%3B531>

On 6/5/2015 10:56 AM, wrote:
> Can someone help educate these folks by posting a link to a nice illustration of the lift-drag-weight vector triangle for straight-line gliding flight?
>
> S

--
Dan Marotta

[[email protected]]

Re NASA diagram linked above in recent post--

That doesn't cut the mustard!

A) they didn't draw L, D, and W in the form of a closed vector triangle, so it's unclear that the net force equals zero

B) If you look closely at the three force vectors, you see that they COULD NOT FIT into a closed vector triangle of the appropriate shape (right angle between L and D).

Don't feel bad guys, NASA evidently doesn't get it either...

Don't the SSA instructional materials include a good diagram showing L, D, and W as a closed vector triangle of the appropriate shape?

S

[[email protected]]

"What is the result of the same test with airbrakes closed? "

About the same - you run out of elevator authority before the ship stalls. Ships I've personally tried this on: Grob 102 CS-77, Grob 102 Standard III, Grob Twin Astir (RG), Grob Twin II Acro, Let L-13 Blanik, LET L-23 Super Blanik (short wingspan version only), LET L-33 Solo, PW-5, Standard Jantar 1, DG-505 (20 and 18 meter configuration), Twin Lark, Schempp-Hirth Duo Discus, Schweizer 1-26, Schweizer 1-23, Schleicher ASW-15B.

Boiled down: if spoilers being extended during causes a problem during a base or final turn you've already seriously screwed up by flying the circuit and approach at far too low a speed and not using well banked turns. For more information go to Knauff or Piggott. They've got a hell of a lot more experience and knowledge than almost anybody.

[Charlie M. (UH & 002 owner/pilot)]

All the math is fine......
But, if your head is up your arse (Sorta British spelling), it does not matter if you leave a "dent in the ground".

I learned by/taught, "What does it sound like, what does it feel like, what does it look like?".
Period.

Either you were not taught well, or you, "Missed part of the discussion."

Can we please now close this thread? The horse has been whipped so many times, there is nothing left to whip............
Sigh..........

PS, off-field landing a ASW-20C with a full load of water (unknown to me until too late) I would have NOT made a decent landing. But the "feel" was wrong so I added speed.......

[[email protected]]

"For more information go to Knauff or Piggott. They've got a hell of a lot more experience and knowledge than almost anybody.*"

Yes and no... for example I heard Tom Knauff explain to a seminar that the wing reaches the stall angle-of-attack with the stick further aft in a turn than in wings-level flight, but he was unable to explain why. He offered an explanation that it had to do with the increased wing-loading-- which would suggest that we ought to see the same effect when we load up with water ballast.

This is a sincere question that I'll explore myself the next time I fly-- in wings-level flight, and it shallow bank angles where we can stall the wing before running out of aft stick travel, do most ships reach the stall angle-of-attack with the stick further aft with the airbrakes open than with the airbrakes closed?

S

[Sarah[_2_]]

I'm coming in at the end of a long ...er discussion, so excuse me if I"m missing something.
But I believe the diagram is correct. Regardless of how it's "drawn", the vector math for forces is simple.

L cos(a) + D sin(a) - W = 0
L sin(a) - D cos(a) = 0

Are necessary & sufficient for gliding without net force (acceleration) in the horizontal and vertical directions.



On Friday, June 5, 2015 at 12:29:01 PM UTC-5, wrote:
> Re NASA diagram linked above in recent post--
>
> That doesn't cut the mustard!
>
> A) they didn't draw L, D, and W in the form of a closed vector triangle, so it's unclear that the net force equals zero
>
> B) If you look closely at the three force vectors, you see that they COULD NOT FIT into a closed vector triangle of the appropriate shape (right angle between L and D).
>
> Don't feel bad guys, NASA evidently doesn't get it either...
>
> Don't the SSA instructional materials include a good diagram showing L, D, and W as a closed vector triangle of the appropriate shape?
>
> S

[[email protected]]

On Friday, June 5, 2015 at 5:35:29 PM UTC-5, Sarah wrote:
>
> ... But I believe the diagram is correct. ...

Hi Sarah. First of all I erred in referring to a link to a google search as if it were a link to a single diagram. But these educational diagrams from NASA came up near the top of the search:

http://www.grc.nasa.gov/WWW/k-12/airplane/glidvec.html
http://www.grc.nasa.gov/www/K-12/airplane/ldrat.html

I have no quarrel with the math on those pages-- I haven't looked at it closely.

To me, a vector diagram conveys a concept much more intuitively and concisely than an equation, and the vector diagrams in these drawings immediately leap out to the viewer as being hopelessly screwed up. There is no way you could re-arrange those three vectors into a closed triangle. In relation to L, W is much too small and D is much too large. The glider cannot be in a steady-state-- it must be accelerating upwards and aftwards. So those diagrams are an embarrassment to NASA, and an obstacle rather than an aid to the children they are hoping to educate.

What I really don't understand, is why they chose to draw the diagram with the tail end of each arrow at the CG of the glider, rather than drawing the diagram with the arrows arranged head-to-tail into a closed triangle. A closed triangle of three force vectors elegantly and instantly conveys the idea that the forces on the body are perfectly balanced, never mind about sines and cosines.

It seems bizarre that the first one hundred images on a google image search for "Lift weight drag of a glider" didn't include a single diagram drawn as I have described above-- with the force vectors arranged head-to-tail into a closed right triangle. It seems to me that such a diagram ought to be near the beginning of any description of how a glider works.

Here's a diagram that's correct, but less elegant than a simple closed triangle of three vectors drawn head-to-tail:

http://www.recreationalflying.com/tutorials/groundschool/umodule1b.html#descent_forces

S

[Martin Gregorie[_5_]]

On Fri, 05 Jun 2015 09:56:48 -0700, platypterus101 wrote:

> Can someone help educate these folks by posting a link to a nice
> illustration of the lift-drag-weight vector triangle for straight-line
> gliding flight?
>
> S

Try this: http://www.av8n.com/how/htm/4forces.html - the
Lift, Thrust, Weight, and Drag section of http://www.av8n.com/

Better yet, read the whole site. Its its explanations are always clear
and relatively non-mathematical, preferring to use diagrams rather than
formulae. Yes, its about powered light aircraft and aimed at GA pilots,
but none the worse for that.

Alternatively, get yourself a copy of "Stick and Rudder" by Wolfgang
Langewiesche. Its equally non-mathematical and presents a pilots-centric
view of how wings work and the effect of control inputs. IMO it belongs
in a glider pilots library alongside George Moffat's "Winning on the
Wind" or its second edition, "Winning II" and, if you're pre-solo or
early solo, you may also want a copy of Derek Piggott's "Gliding".


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Martin Gregorie[_5_]]

On Fri, 05 Jun 2015 06:35:11 -0700, platypterus101 wrote:

> What do you need to do with the stick to hold a constant airspeed as you
> open the spoilers in wings-level flight?
>
That's dependent in what glider you're flying:

- If you're in a Puchacz you give the stick a healthy shove forward as
you open the brakes. If you don't, it will loose at least 5 kts almost
instantly.

- if you're in a Libelle, SZD Junior or an ASK-21 there's little
immediate speed change.

- in a Grob G103 you pull back a bit because these drop their nose and
pick up speed when you open the brakes.

> Is the heart of the matter simply that for a given airspeed in
> wings-level at any given bank angle, including zero degrees bank, the
> stick needs to be positioned further aft with the spoilers open than
> with the spoilers closed?
>
No. The main effect of well-designed airbrakes is to reduce effective
lifting surface, but, as a side effect is to add drag, most gliders will
need the stick to be eased forward a little to keep the airspeed
constant. However, the wind gradient and turbulence will probably be more
significant: you'll think you're correcting for these factors rather than
for the extra drag from the brakes. But, as I said above, it does depend
on the glider. For the G103 to behave as it does, its drag must reduce
along with the lift as you open the brakes. Conversely, the Puchacz has
huge speed-limiting upper and lower surface brakes: so much so that it
would be surprising if shoving those out in the breeze didn't show it
down.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Saturday, June 6, 2015 at 7:59:13 AM UTC-5, Martin Gregorie wrote:

> No. The main effect of well-designed airbrakes is to reduce effective
> lifting surface, but, as a side effect is to add drag, most gliders will
> need the stick to be eased forward a little to keep the airspeed
> constant. However, the wind gradient and turbulence will probably be more
> significant: you'll think you're correcting for these factors rather than
> for the extra drag from the brakes. But, as I said above, it does depend
> on the glider. For the G103 to behave as it does, its drag must reduce
> along with the lift as you open the brakes. Conversely, the Puchacz has
> huge speed-limiting upper and lower surface brakes: so much so that it
> would be surprising if shoving those out in the breeze didn't show it
> down.
>
One could steer this conversation in the direction of transient versus steady-state effects. For example, if we start with a typical sailplane L/D ratio (say 30:1), and then we deploy some device that doubles the drag coefficient and halves the lift coefficient, we'll experience a temporary deceleration due to the sudden drag, but as the flight path curves downward, it must be the case that we'll finally come to equilibrium at a much higher airspeed than we started with.

Because "scaling up" the L and D vectors, by increasing the airspeed, is the only way to create a closed vector triangle of L D and W.

Assuming that angle-of-attack is held constant throughout.

When we open airbrakes without moving the stick, there's no reason to assume that angle-of-attack stays constant. We're killing the lift over one part of a wing which has twist (washout), so we're making a change in the average incidence of the "working" part of the wing. And we may be changing the airflow over the tail as well.

So a question of interest remains-- let's forget about airspeed entirely-- in wings-level flight or at some shallow bank angle, does the stick need to be further aft (closer to the aft stop) to induce a stall with airbrakes open than with airbrakes closed?

S

[Dan Marotta]

We can beat up theory all day, but what about practice?

I don't give a sh!t what I do with the stick when I open the brakes, nor
what is the arc hyperbolic cosine of the angle of the dangle, nor what
the glider does in response. When I deploy the boards, I also operate
the flight controls to make the flight path do what I want.

Or you can be debating theory as you proceed merrily towards the ground.

On 6/6/2015 7:32 AM, wrote:
> On Saturday, June 6, 2015 at 7:59:13 AM UTC-5, Martin Gregorie wrote:
>
>> No. The main effect of well-designed airbrakes is to reduce effective
>> lifting surface, but, as a side effect is to add drag, most gliders will
>> need the stick to be eased forward a little to keep the airspeed
>> constant. However, the wind gradient and turbulence will probably be more
>> significant: you'll think you're correcting for these factors rather than
>> for the extra drag from the brakes. But, as I said above, it does depend
>> on the glider. For the G103 to behave as it does, its drag must reduce
>> along with the lift as you open the brakes. Conversely, the Puchacz has
>> huge speed-limiting upper and lower surface brakes: so much so that it
>> would be surprising if shoving those out in the breeze didn't show it
>> down.
>>
> One could steer this conversation in the direction of transient versus steady-state effects. For example, if we start with a typical sailplane L/D ratio (say 30:1), and then we deploy some device that doubles the drag coefficient and halves the lift coefficient, we'll experience a temporary deceleration due to the sudden drag, but as the flight path curves downward, it must be the case that we'll finally come to equilibrium at a much higher airspeed than we started with.
>
> Because "scaling up" the L and D vectors, by increasing the airspeed, is the only way to create a closed vector triangle of L D and W.
>
> Assuming that angle-of-attack is held constant throughout.
>
> When we open airbrakes without moving the stick, there's no reason to assume that angle-of-attack stays constant. We're killing the lift over one part of a wing which has twist (washout), so we're making a change in the average incidence of the "working" part of the wing. And we may be changing the airflow over the tail as well.
>
> So a question of interest remains-- let's forget about airspeed entirely-- in wings-level flight or at some shallow bank angle, does the stick need to be further aft (closer to the aft stop) to induce a stall with airbrakes open than with airbrakes closed?
>
> S

--
Dan Marotta

[Martin Gregorie[_5_]]

On Sat, 06 Jun 2015 06:32:10 -0700, platypterus101 wrote:

> On Saturday, June 6, 2015 at 7:59:13 AM UTC-5, Martin Gregorie wrote:
>
>> No. The main effect of well-designed airbrakes is to reduce effective
>> lifting surface, but, as a side effect is to add drag, most gliders
>> will need the stick to be eased forward a little to keep the airspeed
>> constant. However, the wind gradient and turbulence will probably be
>> more significant: you'll think you're correcting for these factors
>> rather than for the extra drag from the brakes. But, as I said above,
>> it does depend on the glider. For the G103 to behave as it does, its
>> drag must reduce along with the lift as you open the brakes.
>> Conversely, the Puchacz has huge speed-limiting upper and lower surface
>> brakes: so much so that it would be surprising if shoving those out in
>> the breeze didn't show it down.
>>
> One could steer this conversation in the direction of transient versus
> steady-state effects.
>
Kindly stop changing the subject. You asked about transient effects when
the brakes are opened. I passed on personal experience of flying gliders
with a range of behaviour when the brakes are opened, which is what you
asked about.

There is only valid answer: "what happens depends on which glider you're
flying", i.e. there is no single universal answer. Live with it.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Martin Gregorie[_5_]]

On Sat, 06 Jun 2015 08:42:02 -0600, Dan Marotta wrote:

> We can beat up theory all day, but what about practice?
>
> I don't give a sh!t what I do with the stick when I open the brakes, nor
> what is the arc hyperbolic cosine of the angle of the dangle, nor what
> the glider does in response. When I deploy the boards, I also operate
> the flight controls to make the flight path do what I want.
>
> Or you can be debating theory as you proceed merrily towards the ground.
>
Well put, sir.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Saturday, June 6, 2015 at 9:42:10 AM UTC-5, Dan Marotta wrote:
> When I deploy the boards, I
> also operate the flight controls to make the flight path do what I
> want.

Wouldn't it be analogous to say that when I bank the glider, I also operate the flight controls to make the flight path do what I want, so there's no significance to the fact that I have to get the stick way aft to reach the stall angle-of-attack while steeply banked?

I'm having a little trouble understanding why people are getting steamed up....

S

[Dan Marotta]

Not getting steamed up. Only trying to lighten up the conversation and
remind the newer guys that theory is great in the classroom but there's
no time in flight to plan the minute details of operating the flight
controls. I still recall how liberating it was the first time I flew
the aircraft without having to think about how to move the controls to
get the desired reaction. After that it was more like dancing than like
digging a ditch.

But to answer directly - yes, in a steeply banked turn in a glider (at
least in mine) I can hold the stick at the aft stop without stalling. I
never do that during the final turn, by the way...

On 6/7/2015 7:47 AM, wrote:
> On Saturday, June 6, 2015 at 9:42:10 AM UTC-5, Dan Marotta wrote:
>> When I deploy the boards, I
>> also operate the flight controls to make the flight path do what I
>> want.
> Wouldn't it be analogous to say that when I bank the glider, I also operate the flight controls to make the flight path do what I want, so there's no significance to the fact that I have to get the stick way aft to reach the stall angle-of-attack while steeply banked?
>
> I'm having a little trouble understanding why people are getting steamed up...
>
> S

--
Dan Marotta

[OG]

Hi Surge, which club and instructor was that? It certainly is not normal practice in SA

[George Haeh]

Piggott pointed out that the airflow over
the tailplane in a turn comes at an angle
that requires more elevator than normally
available to stall the glider.

On one of my spin checks, we found that
the Puchaz will spin out of a 45 degree
banked turn.

[Surge]

On Sunday, 7 June 2015 17:05:05 UTC+2, OG wrote:
> Hi Surge, which club and instructor was that? It certainly is not normal practice in SA

Hi Oscar

It was with two very experienced instructors at MGC (Orient) but I'll refrain from mentioning their names as they're not on this newsgroup to defend their point of view.

[[email protected]]

Exactly-- in turning flight, the flight path is curved, and therefore the relative wind (direction the airflow would come from if not disturbed by glider) is curved too-- at any given instant, the nose of the glider is moving in a different direction than the tail. In the real world there is downwash etc but the horizontal tail is still meeting the air at a different angle in a turn than it would in wings-level flight. So is the vertical fin.

For an extreme case of curvature of the relative wind in the yaw dimension, just visualize the relative wind at different points on a glider that is flat-spinning! Different parts are moving in different direction and experiencing different relative wind directions.

S

On Sunday, June 7, 2015 at 10:00:08 PM UTC-5, George Haeh wrote:
> Piggott pointed out that the airflow over
> the tailplane in a turn comes at an angle
> that requires more elevator than normally
> available to stall the glider.
>
> On one of my spin checks, we found that
> the Puchaz will spin out of a 45 degree
> banked turn.

[[email protected]]

On Thursday, June 4, 2015 at 11:34:35 PM UTC-5, wrote:

>> As an experiment try this at altitude: trim to the recommended approach speed with full airbrakes or recommended approach speed found in the AFM (or if it's not specified use the formula you were taught for choosing an approach speed), roll the glider into a good coordinated 40 degree bank turn then move the elevator progressively back. In every glider I've flown the elevator hits the stop without provoking a stall. I tried this after reading a Derek Piggott article suggesting it. <<

In recent tests (happened to be in a Ka-6) I couldn't tell that the airbrakes had any effect on the stick position and stick force at the stall angle-of-attack, in wings-level flight as well as in turning flight. The stick had to be much further aft to bring the wing to the stall angle-of-attack when the glider was substantially banked, as expected.

On the other hand I seem to recall noting once that the airbrakes had a powerful nose-down trim effect on a 1-26. I.e. that the glider tended to trim to a much lower angle-of-attack/ much higher airspeed. It's been a while since my last flight in one so check it out for yourself rather than taking my word for it...

S

[Andreas Maurer]

On Fri, 5 Jun 2015 06:17:43 -0700 (PDT),
wrote:



> Lift does not equal weight in unbanked gliding flight, unless L/D is infinite.

It does.
Otherwise a glider would fly a ballistic arc, not a straight line.


Regards
Andreas

[[email protected]]

On Tuesday, June 9, 2015 at 8:05:23 AM UTC-5, Andreas Maurer wrote:
> On Fri, 5 Jun 2015 06:17:43 -0700 (PDT), platypterus101
> wrote:
>
>
>
> > Lift does not equal weight in unbanked gliding flight, unless L/D is infinite.
>
> It does.
> Otherwise a glider would fly a ballistic arc, not a straight line.
>
>
> Regards
> Andreas

Still on with this misconception? See my previous posts, especially the table of G-loading at various L/D ratios and bank angles. Multiply the G-loading values by the glider weight and you transform the table into lift force in pounds, for various L/D ratios and bank angles.

Take a moment to learn how to draw the L - D - W vector triangle for unbanked gliding flight, and then you'll see the light...

Here's an illustration of L D W vectors in an unbanked glide, though it would be clearer if they were re-arranged into a closed triangle:

http://www.recreationalflying.com/tutorials/groundschool/umodule1b.html#descent_forces

This SHOULD be near the front of any good book on learning to pilot gliders..

Wish we were addressing this in a new thread instead of confusing the airbrake discussion with this...

There's really not much to say about this that hasn't already been addressed...

At normal sailplane glide angles the lift vector is ALMOST as large as the weight vector, in unbanked flight, but not quite. If you don't understand why, then you also don't understand why the L/D ratio is the same as the glide ratio (forward distance / vertical distance or horiztonal speed / vertical speed) in still air.

A glider pilot ought to know these things-- or at least ought to know enough to avoid posting statements to the contrary on a sailplane discussion forum!

We ought to change the SSA logo to a picture of the L-D-W vector triangle, since it is what makes gliding flight possible...

All in the spirit of a good discussion...

S

[Andreas Maurer]

Hi "S",

On Tue, 9 Jun 2015 07:11:21 -0700 (PDT),
wrote:

>
>On Tuesday, June 9, 2015 at 8:05:23 AM UTC-5, Andreas Maurer wrote:
>> On Fri, 5 Jun 2015 06:17:43 -0700 (PDT), platypterus101
>> wrote:
>>
>>
>>
>> > Lift does not equal weight in unbanked gliding flight, unless L/D is infinite.
>>
>> It does.
>> Otherwise a glider would fly a ballistic arc, not a straight line.
>>
>>
>> Regards
>> Andreas
>
>Still on with this misconception?

No misconception, but probably simply a different use of terms.

In my opinion "Lift" is not the force that is generated perpendicular
to the ldirection of flight, but lift (read: the force that keeps the
glider in the air on a straight, non-accelerated flight path) is the
sum of the "lift" vector created by the wing and the drag vector,
hence the "Resultant Force" in the drawing you mentioned:

>http://www.recreationalflying.com/tutorials/groundschool/umodule1b.html#descent_forces



>This SHOULD be near the front of any good book on learning to pilot gliders.

In Germany it is one of the most important chapters in the books, but
explained a lot simpler than on the website you mentioned.


>Wish we were addressing this in a new thread instead of confusing the airbrake discussion with this...
>
>There's really not much to say about this that hasn't already been addressed...
>
>At normal sailplane glide angles the lift vector is ALMOST as large as the weight vector, in unbanked flight, but not quite. If you don't understand why, then you also don't understand why the L/D ratio is the same as the glide ratio (forward distance / vertical distance or horiztonal speed / vertical speed) in still air.

Don't worry, I understand that pretty well since a couple of decades.
:)

>A glider pilot ought to know these things-- or at least ought to know enough to avoid posting statements to the contrary on a sailplane discussion forum!


>We ought to change the SSA logo to a picture of the L-D-W vector triangle, since it is what makes gliding flight possible...

Germany here, I don't care about SSA... ;)


Greets
Andreas

[[email protected]]

Re the above post: Andreas, if you define lift as the NET vertical aerodynamic force, then you have no room left for drag.

What you are really doing, is defining "lift" as the vector sum of what most people call "lift", and what most people call "drag".

That is the dashed vertical line in this diagram http://www.recreationalflying.com/tutorials/groundschool/umodule1b.html#descent_forces .

By your system of definitions, there is can be no drag vector (unless it happens to equal zero in magnitude), and the glide ratio is no longer equal to arctan (D/L). The L/D ratio ceases to be a meaningful concept.

So... maybe you want to rethink that?

S

[Jim Lewis[_2_]]

Mostly very helpful but isn't atan(D/L) the glide angle rather than the glide ratio? Maybe once again it's largely a matter of vocabulary. I certainly don't know. Thankfully, being fairly dumb about these things has not seemed to diminish my flying skills - wishful thinking?

[[email protected]]

On Wednesday, June 10, 2015 at 12:06:04 PM UTC-5, Jim Lewis wrote:
> Mostly very helpful but isn't atan(D/L) the glide angle rather than the glide ratio? Maybe once again it's largely a matter of vocabulary. I certainly don't know. Thankfully, being fairly dumb about these things has not seemed to diminish my flying skills - wishful thinking?

It's all good. I still say my answer to Dan Marotta's question
"How come nobody ever states that these G loading increases are for level flight? Since the glider is always descending, wouldn't it be better to include something about the descent rate being maintained? What about a climbing turn? Maybe some trig including the flight path angle?"

was correct. Including the table of G-loading for various bank angles and L/D ratios. The decrease in G-loading (or lift force) due to the flight path through the airmass being descending, not level, is very small for typical sailplane glide ratios, but it is still very real and fundamental to understanding the theory of gliding. And yes you are absolutely right of course, on my last post I meant to type "glide angle" not "glide ratio". Glide ratio (in still air) would be simply L/D. If you are defining lift correctly. If you are using lift to mean the total VERTICAL aerodynamic force, than you can no longer say that the still-air glide ratio equals the L/D ratio. The L/D ratio and the W/D ratio are very close to each other, for flat glide angles, but they are not exactly the same.

OK, enough on that. Really!

S

[Tango Whisky]

G-load has absolutely nothing to do with L/D or (stationary) speed of airmass.

Bert TW

[Andreas Maurer]

On Wed, 10 Jun 2015 11:58:39 -0700 (PDT),
wrote:

> Including the table of G-loading for various bank angles and L/D ratios.

G-load has absolutely nothing to do with L/D or with airmass movement.


Andreas

[Andreas Maurer]

On Wed, 10 Jun 2015 12:13:08 -0700 (PDT), Tango Whisky
> wrote:

>G-load has absolutely nothing to do with L/D or (stationary) speed of airmass.


Oops Bert.... sorry for copying your posting. Didn't see yours until
now. ;)


CU
Andreas

[jfitch]

On Wednesday, June 10, 2015 at 11:58:41 AM UTC-7, wrote:
> On Wednesday, June 10, 2015 at 12:06:04 PM UTC-5, Jim Lewis wrote:
> > Mostly very helpful but isn't atan(D/L) the glide angle rather than the glide ratio? Maybe once again it's largely a matter of vocabulary. I certainly don't know. Thankfully, being fairly dumb about these things has not seemed to diminish my flying skills - wishful thinking?
>
> It's all good. I still say my answer to Dan Marotta's question
> "How come nobody ever states that these G loading increases are for level flight? Since the glider is always descending, wouldn't it be better to include something about the descent rate being maintained? What about a climbing turn? Maybe some trig including the flight path angle?"
>
> was correct. Including the table of G-loading for various bank angles and L/D ratios. The decrease in G-loading (or lift force) due to the flight path through the airmass being descending, not level, is very small for typical sailplane glide ratios, but it is still very real and fundamental to understanding the theory of gliding. And yes you are absolutely right of course, on my last post I meant to type "glide angle" not "glide ratio". Glide ratio (in still air) would be simply L/D. If you are defining lift correctly. If you are using lift to mean the total VERTICAL aerodynamic force, than you can no longer say that the still-air glide ratio equals the L/D ratio. The L/D ratio and the W/D ratio are very close to each other, for flat glide angles, but they are not exactly the same.
>
> OK, enough on that. Really!
>
> S

It's good to know I can reduce my G-loading by opening the spoilers, or dropping the landing gear. ;)

[JS]

Holding your breath does the same thing.
Try it, you'll feel lighter.
Jim

On Wednesday, June 10, 2015 at 9:19:14 PM UTC-7, jfitch wrote:
>
> It's good to know I can reduce my G-loading by opening the spoilers, or dropping the landing gear. ;)

[[email protected]]

"Holding your breath does the same thing.
Try it, you'll feel lighter.
Jim "

Wow! That really works, just tried it hear in my chair!

[Bob Whelan[_3_]]

> "Holding your breath does the same thing.
> Try it, you'll feel lighter.
> Jim "
>
> Wow! That really works, just tried it here in my chair!

What's wrong?!? I did it, but right up until I turned blue and passed out, I
actually felt heavier...air from the big breath I took first?

[[email protected]]

It is always amusing listening to pilots discuss aerodynamics.

It's proof that the monkey does not need to know how the machine works, as long as they know what button to push and when.

I'll remember to use the breath hold in the future.

Todd Smith
3S
Educated and practicing aeronautical engineer.

[[email protected]]

On Thursday, June 11, 2015 at 1:44:11 PM UTC-4, wrote:
> It is always amusing listening to pilots discuss aerodynamics.
>
> It's proof that the monkey does not need to know how the machine works, as long as they know what button to push and when.
>
> I'll remember to use the breath hold in the future.
>
> Todd Smith
> 3S
> Educated and practicing aeronautical engineer.

Such an individual has no place on this site!
UH

[[email protected]]

It's always good to consider extreme cases.

Consider a terminal velocity dive, where the flight path is vertical.

I stand by every word I've said so far, so I won't say them again.

I get the impression some folks are reading this in the form of individual emails and missing the context of the whole thread? Because points that have already been answered keep getting raised over and over again. Here is the whole thread: https://groups.google.com/forum/#!topic/rec.aviation.soaring/svCmIstyZPU

S

[[email protected]]

The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight. That's quite close to what we'll read on a panel-mounted G-meter. I won't quarrel if you want to use G-loading to mean something else, that's fine, there is at least one other very reasonable definition of G-loading, but if the parameter of interest is lift force or lift force/ weight, then absolutely you do it reduce it, in the long run (steady-state case), by deploying spoilers or landing gear.

Again consider the terminal velocity vertical dive-- what will your panel-mounted G-meter read?

Why people are suddenly talking about airmass movement is beyond me-- I wasn't.

S

[[email protected]]

I am convinced that the airbrake is the least understood of the glider controls.
In order to give an opinion on the subject of airbrake use in turns, perhaps we should go back to their use as a glidepath control device.
I've heard many pilots explaining how the airbrakes work saying something like "When you open the airbrakes, the lift on that part of the wing is reduced or eliminated. Since you have less lift now, your vertical speed will increase and you will sink faster". Wow. And wrong, except for an instant after you open the airbrakes.
When you open the airbrakes, the lift on that part of the wing is gone, true. But only for a few moments, after that, the angle of attack, the airspeed, or both have to increase to create enough lift in the rest of the wing in order to hold the weight of the glider. Otherwise the glider would keep accelerating in the vertical direction.
If you try to keep the same airspeed when you open the airbrakes, the angle of attack has to increase. That means that you are closer to the stall, or conversely, that the stall speed increases.
Right when you open the airbrakes the total lift is reduced. This gives a nose down pitch tendency, but the extra drag causes some nose-up pitch tendency. The net effect is that some gliders tend to accelerate and some tend to deccelerate when opening the airbrakes. After a couple of seconds the glider is stable again in a steeper glidepath.
It is never a good idea to make big changes in the airbrake position on the flare because you risk a heavy landing or a ballooning.
Now, to their use in turns...

[[email protected]]

Definitely opening the airbrakes increases the stall speed. Combine it with the increase of the stall speed in a well-banked turn and your margin of safety gets reduced. However, in most gliders you run out of aft elevator before the stall in a well-banked turn (there are some exceptions).If you keep a good pattern speed through the turn you shouldn't have any problem.
The problem I see is that opening the airbrakes causes a temporary "instability", in other words, the glider may drop a few feet before getting in a stable turning configuration. That may create some problema as you try to adjust your flight in a turn, since now you have more dimensions to deal with, your curve in 3 dimensions is not as nice and stable as if you had kept the same amount of airbrake or no airbrake at all.
My suggestion is: if you really have to open or close them, by all means do.. But if there is not such a need, I think it is better not to change the airbrake lever position during the turn, or not make a big change. And by the way, just crack-opening the airbrakes is a big change of settings (as the total lift is reduced for a short period of time).
The problem as I see it is not whether the airbrakes are open or not. The problem is the additional changes in pitch and elevation in a curving descending path close to the ground, created when you make big changes in your airbrake settings. It is better to arrive to final in a stable curving configuration and then transition to a stabilized final approach where it is much easier to play with the airbrakes.

[Tango Whisky]

What is this - war on physics ?!

LOL
Bert TW

[Martin Gregorie[_5_]]

On Thu, 11 Jun 2015 21:26:29 -0700, Tango Whisky wrote:

> What is this - war on physics ?!
>
Total misunderstanding of high school physics is more likely, coupled
with the sort of subject changing typical of trolls.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Thursday, June 11, 2015 at 5:38:16 PM UTC-7, wrote:
> The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight.


Maybe this is a clearer system of terminology:

Total g-loading = net aerodynamic force / weight

Lift-wise g-loading = lift / weight. This is the g-loading component that acts in the direction of the lift vector, i.e. perpendicular to the flight path. A conventional panel-mounted g-loading measures something very close to this. Excess amounts of this kind of g-loading is usually the reason pilots pull the wings off in clouds.

Drag-wise g-loading = drag / weight. This is the g-loading component that acts in the direction of the drag vector, i.e. parallel to the flight path. This component of g-loading is large in very steep dive. This component of G-loading has little effect on a conventional panel-mounted g-meter.

In unbanked steady-state flight in a glider, L D and W form a closed vector triangle. Thus the magnitude of L is dependent on the L/D ratio, and increasing the drag coefficient by opening spoilers or lowering landing gear does decrease L and also does decrease the lift-wise component of g-loading.

I don't know if the recent reference to trolls was aimed at me, but see my June 3 post and my June 4 post presenting the table of lift/weight at various bank angles and L/D loadings-- I was responding directly to Dan Marotta's question. I was not trolling for contradictory responses. Nonetheless several people disagreed with these posts, and away the discussion went in a typical internet spiral.

For high L/D ratios, we can substantially increase D and cause only a tiny decrease in L, unless the bank angle is really extreme. I never said otherwise-- the table I posted on June 4 shows it-- yet there is still SOME reduction in L, and to say otherwise is to ignore the L D W vector triangle. For much poorer L/D ratios, increasing D makes a much larger reduction in L, especially when the bank angle gets above 45 degrees or so. The terminal-velocity dive is an interesting extreme case where L/D is zero, and thus either L is zero or D is infinite. It the real world it is always the former case.

All this is kind of peripheral to looking at the immediate effects of deploying the spoilers, because the decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio, and I said as much in my June 3 reply to Dan. If folks hadn't wanted to argue, the discussion wouldn't have spiralled so far away from the original topic.

S

[[email protected]]

On Friday, June 12, 2015 at 6:16:31 AM UTC-7, wrote:

>
> All this is kind of peripheral to looking at the immediate effects of deploying the spoilers, because the decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio,

Better would have been written "All this is kind of peripheral to looking at the long-run or steady-state effects of deploying the spoilers, because the final or steady-state decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio."

The immediate or short-term decrease in L can be much larger, as was well explained in the couple of posts by "sant..." immediately above.

S

[[email protected]]

On Friday, June 12, 2015 at 6:16:31 AM UTC-7, wrote:
> On Thursday, June 11, 2015 at 5:38:16 PM UTC-7, wrote:
> > The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight.
>
>
> Maybe this is a clearer system of terminology:
>
> Total g-loading = net aerodynamic force / weight
>
> Lift-wise g-loading = lift / weight. This is the g-loading component that acts in the direction of the lift vector, i.e. perpendicular to the flight path. A conventional panel-mounted g-loading measures something very close to this. Excess amounts of this kind of g-loading is usually the reason pilots pull the wings off in clouds.<

Key point-- this is the g-loading component that is normally of greatest interest to pilots, because this is the g-loading component that affects the stall speed. When someone says that doubling the g-loading increases the stall speed by 1.4, they really ought to specify that they are talking about the lift-wise component of g-loading. We don't often use this language in actual practice. So when a pilot talks about g-loading, the listener ought to suspect that he may be talking about the lift-wise component of g-loading. As was the case in many of my previous posts.

It's really simplest to just leave g-loading out of it and simply talk about L and D and L/ weight and D/ weight. Then there is no possibility of confusion. So long as we understand the L D W vector triangle.

S

[jfitch]

On Friday, June 12, 2015 at 6:16:31 AM UTC-7, wrote:
> On Thursday, June 11, 2015 at 5:38:16 PM UTC-7, wrote:
> > The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight.
>
>
> Maybe this is a clearer system of terminology:
>
> Total g-loading = net aerodynamic force / weight
>
> Lift-wise g-loading = lift / weight. This is the g-loading component that acts in the direction of the lift vector, i.e. perpendicular to the flight path. A conventional panel-mounted g-loading measures something very close to this. Excess amounts of this kind of g-loading is usually the reason pilots pull the wings off in clouds.
>
> Drag-wise g-loading = drag / weight. This is the g-loading component that acts in the direction of the drag vector, i.e. parallel to the flight path. This component of g-loading is large in very steep dive. This component of G-loading has little effect on a conventional panel-mounted g-meter.
>
> In unbanked steady-state flight in a glider, L D and W form a closed vector triangle. Thus the magnitude of L is dependent on the L/D ratio, and increasing the drag coefficient by opening spoilers or lowering landing gear does decrease L and also does decrease the lift-wise component of g-loading..
>
> I don't know if the recent reference to trolls was aimed at me, but see my June 3 post and my June 4 post presenting the table of lift/weight at various bank angles and L/D loadings-- I was responding directly to Dan Marotta's question. I was not trolling for contradictory responses. Nonetheless several people disagreed with these posts, and away the discussion went in a typical internet spiral.
>
> For high L/D ratios, we can substantially increase D and cause only a tiny decrease in L, unless the bank angle is really extreme. I never said otherwise-- the table I posted on June 4 shows it-- yet there is still SOME reduction in L, and to say otherwise is to ignore the L D W vector triangle. For much poorer L/D ratios, increasing D makes a much larger reduction in L, especially when the bank angle gets above 45 degrees or so. The terminal-velocity dive is an interesting extreme case where L/D is zero, and thus either L is zero or D is infinite. It the real world it is always the former case.
>
> All this is kind of peripheral to looking at the immediate effects of deploying the spoilers, because the decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio, and I said as much in my June 3 reply to Dan. If folks hadn't wanted to argue, the discussion wouldn't have spiralled so far away from the original topic.
>
> S

The L/D/W vector triangle is a construct of convenience, not a Holy Trinity.. It carries accuracy but no further insight than any other interpretation. Physically, it is most intuitive to think of the aerodynamic forces on a wing section as the sum of the pressures on its surface. This is mathematically complex though, and for the purposes of Newtonian motion they can be most simply represented as two vectors: a resultant force and a moment vector.. Aerodynamicists have often found it convenient to further split the former vector into two, one parallel to the incident flow (that they call Lift) and one perpendicular (that they call Drag). This is as accurate, but no more correct, than any other collection of vectors that properly sum to the result.

It is perfectly accurate to think of there being two force vectors acting on a sailplane in steady state unaccelerated flight: aerodynamic and gravitational, of equal magnitude acting through a single point in opposite directions. Any change in those three conditions results in accelerating motion.

To enumerate the changes between L and D in various flight conditions as somehow representing the Truth of Flight is an act of Faith, promoting an arbitrary construct into some sort of Enlightenment. Among other things, it leaves out the moments from wing and tailplane, AOA of the wing, and many other things which may be more important to structure and stability (for example) than any minor changes in L and D. I can fly at a glide ratio of 40 at 40 knots and at 80 knots, total lift and drag are the same but a whole lot of things are different I assure you, and opening the spoilers will have a very different effect.

Just to keep the thread going :).

[BobW]

On 6/12/2015 10:00 AM, jfitch wrote:
<Snip...>
> The L/D/W vector triangle is a construct of convenience, not a Holy
> Trinity. It carries accuracy but no further insight than any other
> interpretation. Physically, it is most intuitive to think of the
> aerodynamic forces on a wing section as the sum of the pressures on its
> surface. This is mathematically complex though, and for the purposes of
> Newtonian motion they can be most simply represented as two vectors: a
> resultant force and a moment vector. Aerodynamicists have often found it
> convenient to further split the former vector into two, one parallel to the
> incident flow (that they call Lift) and one perpendicular (that they call
> Drag). This is as accurate, but no more correct, than any other collection
> of vectors that properly sum to the result.
>
> It is perfectly accurate to think of there being two force vectors acting
> on a sailplane in steady state unaccelerated flight: aerodynamic and
> gravitational, of equal magnitude acting through a single point in opposite
> directions. Any change in those three conditions results in accelerating
> motion.
>
> To enumerate the changes between L and D in various flight conditions as
> somehow representing the Truth of Flight is an act of Faith, promoting an
> arbitrary construct into some sort of Enlightenment. Among other things, it
> leaves out the moments from wing and tailplane, AOA of the wing, and many
> other things which may be more important to structure and stability (for
> example) than any minor changes in L and D. I can fly at a glide ratio of
> 40 at 40 knots and at 80 knots, total lift and drag are the same but a
> whole lot of things are different I assure you, and opening the spoilers
> will have a very different effect.
>
> Just to keep the thread going :).
>

Well stated. This (part of) this thread is a good example of the limitations
of an international-in-scope information-exchange of mathematically-complex
ideas and concepts, when limited entirely to the written word. It's even
possible some readers may've been motivated to improve their own
understandings of 'stuff' related to the O.P.'s thesis! In the spirit of
keeping the thread going... :)

[[email protected]]

On Friday, June 12, 2015 at 9:01:01 AM UTC-7, jfitch wrote:

> The L/D/W vector triangle is a construct of convenience, not a Holy Trinity. It carries accuracy but no further insight than any other interpretation. Physically, it is most intuitive to think of the aerodynamic forces on a wing section as the sum of the pressures on its surface. This is mathematically complex though,

Hmmm.. every time I try to introduce more complexity I'm accused of changing the subject and trolling.

I agree that splitting the aerodynamic forces into L and D is in some sense arbitrary. I disagree that is not enlightening. Every time we talk about effect of G-load on airspeed at the stall angle-of-attack, etc, we are making use of that split, i.e. we are talking about the lift-wise component of G-loading. It is a useful thing to do.

I say she IS a Holy Trinity and I intend to worship at her altar again very soon!


You said some days ago: "In steady state, unaccelerated flight, Lift = Mass and the wing loading is constant. It does not matter what your sink rate is. The wing loading is the same with flaps, gear, and spoilers out as it is clean. If Lift <> Mass then the glider is accelerating, either up, down or by changing direction."

I say no, in an unbanked unpowered glide, in the steady-state condition, Lift is less than Weight, and Lift changes whenever the L/D ratio changes.


You said: "It doesn't matter if the glider is descending - the wing loading is the same. The only thing that will change that is accelerated flight. That is an increasing or decreasing rate of descent (not constant) or a change in velocity (that includes turns which are a change in velocity by definition). A sustainer glider will have the same wing loading in level (unaccelerated) flight as it does in a glide. "

But I say not so. I say the lift-wise component of the G-loading-- i.e. the Lift/Weight-- is slightly less in a descending glide than in level flight (all relative to the airmass of course.)


You said "It is best not to think of the "speed at which the wing stalls". That can be anywhere from 0 to beyond redline, depending on a bunch of conditions. You should think of "the angle of attack at which the wing stalls" which is for all intents invariant on a glider."

I say that's all true, and it's also true that the airspeed we see at the stall angle-of-attack is highly dependent on the square root of the lift-wise component of the G-loading, and that's why we ought to care about the lift vector or the lift-wise component of the G-loading or whatever we want to call it.

The L D W concept IS useful and enlightening, because airspeed at stall is highly related to the magnitude of L. Not to the total aerodynamic force. If we care about airspeed at stall, then we care about the lift-wise component of the G-loading.

S

[[email protected]]

All this discussion seems to have been started by my posts on June 3 and June 4. After having gone around a few times, maybe it is more clear where I was coming from. Does anyone have any problems with this table? IF so, can you clearly explain why?

> Examples: G-load (lift / weight) at various bank angles and L/D ratios:
>
> L/D Infinite-- 0 deg 1.00 30 deg 1.15 45 deg 1.41 60 deg 2.00
> L/D 10:1-- 0 deg .995 30 deg 1.15 45 deg 1.40 60 deg 1.97
> L/D 5:1-- 0 deg .981 30 deg 1.13 45 deg 1.36 60 deg 1.87
> L/D 2:1-- 0 deg .894 30 deg 1.00 45 deg 1.15 60 deg 1.41
> L/D 1:1-- 0 deg .707 30 deg .756 45 deg .817 60 deg .894

[[email protected]]

Yes, at typical sailplane glide ratios, changes in the drag vector (due to landing gear, spoilers, etc) have little effect on the magnitude of the Lift vector. (As I said on June 3.) Yes, Lift is almost the same magnitude as Weight, and the lift-wise component of the G-loading vector is almost the same magnitude as the total G-loading vector. For all practical purposes, there's nothing to argue about here. But in theory, there is a difference, and if you start looking at really extreme cases, the difference becomes large. The more of the total weight is supported by the drag vector, the smaller the lift vector must be.

S

[jfitch]

On Friday, June 12, 2015 at 10:20:53 AM UTC-7, wrote:
> On Friday, June 12, 2015 at 9:01:01 AM UTC-7, jfitch wrote:
>
> > The L/D/W vector triangle is a construct of convenience, not a Holy Trinity. It carries accuracy but no further insight than any other interpretation. Physically, it is most intuitive to think of the aerodynamic forces on a wing section as the sum of the pressures on its surface. This is mathematically complex though,
>
> Hmmm.. every time I try to introduce more complexity I'm accused of changing the subject and trolling.
>
> I agree that splitting the aerodynamic forces into L and D is in some sense arbitrary. I disagree that is not enlightening. Every time we talk about effect of G-load on airspeed at the stall angle-of-attack, etc, we are making use of that split, i.e. we are talking about the lift-wise component of G-loading. It is a useful thing to do.
>
> I say she IS a Holy Trinity and I intend to worship at her altar again very soon!
>
>
> You said some days ago: "In steady state, unaccelerated flight, Lift = Mass and the wing loading is constant. It does not matter what your sink rate is. The wing loading is the same with flaps, gear, and spoilers out as it is clean. If Lift <> Mass then the glider is accelerating, either up, down or by changing direction."
>
> I say no, in an unbanked unpowered glide, in the steady-state condition, Lift is less than Weight, and Lift changes whenever the L/D ratio changes.
>
>
> You said: "It doesn't matter if the glider is descending - the wing loading is the same. The only thing that will change that is accelerated flight.. That is an increasing or decreasing rate of descent (not constant) or a change in velocity (that includes turns which are a change in velocity by definition). A sustainer glider will have the same wing loading in level (unaccelerated) flight as it does in a glide. "
>
> But I say not so. I say the lift-wise component of the G-loading-- i.e. the Lift/Weight-- is slightly less in a descending glide than in level flight (all relative to the airmass of course.)
>
>
> You said "It is best not to think of the "speed at which the wing stalls".. That can be anywhere from 0 to beyond redline, depending on a bunch of conditions. You should think of "the angle of attack at which the wing stalls" which is for all intents invariant on a glider."
>
> I say that's all true, and it's also true that the airspeed we see at the stall angle-of-attack is highly dependent on the square root of the lift-wise component of the G-loading, and that's why we ought to care about the lift vector or the lift-wise component of the G-loading or whatever we want to call it.
>
> The L D W concept IS useful and enlightening, because airspeed at stall is highly related to the magnitude of L. Not to the total aerodynamic force.. If we care about airspeed at stall, then we care about the lift-wise component of the G-loading.
>
> S

What you have discovered is merely a quirk of the (arbitrary) definition of the vector L. How it may change with changes in L/D ratio over the normal performance envelope will have no effect on what a pilot does or should do. It has less effect on the airframe structure than many other factors and I doubt any designer considers this as an independent problem.

We should worry less about the airspeed at stall (a wing will stall at ANY airspeed, at ANY wing loading) and worry more about angle of attack. In most regimes of flight, AOA is the one thing you can immediately affect - airspeed, lift, drag, etc. are consequences of it and will settle to steady state after some time goes by. You will have much better insight starting with that, than L and D vectors. If you are stalled or near stall, specifically you must reduce the angle of attack and let L, D, W, airspeed, wing loading, and pretty much everything else fall where they may.

[[email protected]]

Well, if you don't think very steep descent angles (relative to airmass) are relevant to soaring, how about very steep climb angles (relative to airmass)?

In the future we can look forward to motorgliders with powerful electric (or rocket?) motors that will afford very steep glide climb angles, such as is currently the case in the world of RC soaring.

A large glide angle (poor L/D ratio, steep glide path relative to airmass) reduces the magnitude of the lift vector, and the lift-wise component of the G-loading vector. Likewise, a large climb angle (steep climb path relative to airmass) also reduces the magnitude of the lift vector, and the lift-wise component of the G-loading vector.

(The lift-wise component of the G-loading vector is simply Lift / Weight).

For wings-level flight-- 40:1 L/D ratio--

The three numbers in each line of the table are:

a) Thrust to Weight ratio,
b) Lift to Weight ratio (i.e. liftwise component of G-loading vector),
c) stall speed in powered climb, divided by stall speed in exactly horizontal flight.

The first line (0 T/W) is a descending case; all the following lines are climbing cases.


T/W L/W Stall speed / stall speed in exactly horizontal flight
0 -- .99969 -- .99984
..1 -- .9972 -- .9986
..5 -- .878 -- .937
..75 -- .680 -- .825
1 -- 0 -- 0

In the last case, where thrust equals weight, setting the wing to the zero-lift angle-of-attack yields a steady-state climb regardless of airspeed, so the concept of stall speed becomes meaningless.

In the motorgliders of the future, we'll gain a hands-on feel for the way that a steep glide or climb angle reduces the lift-wise G-loading component, and the stall speed!

S

[Tango Whisky]

Ok, one last try:
The force created by the wing is usually described as a vector, wich can be decomposed into a vector perpendicular to the flight path (lift), and a vector antiparallel to the flight path (drag). The sum of the two, i.e. the total vector of the wing, is exactly opposed to the weight vector of the aircraft and rules the g-load. In non-accelerated flight it exactly equals the weight, ruling in 1 g - regardless of L/D ratio.

Now if you suppose that it's the lift part which is opposed to the weight, then L/D would influence g-load. But this is just not how physics works on this planet.

Bert TW

[[email protected]]

"In the last case, where thrust equals weight, setting the wing to the zero-lift angle-of-attack yields a steady-state climb regardless of airspeed, so the concept of stall speed becomes meaningless.*"

Sorry , I was a bit sloppy there. If thrust = weight and l/d 40:1, airspeed must be xxx. If we hold thrust = weight and unoaqd L to zero, so L/D becomes 0, ....

[[email protected]]

Re "one last try" immediately above-- please take a moment to re-read my previous post. It is the lift-wise component of the G-loading vector-- closely related to what your panel-mounted G-meter reads-- not the total G-loading vector-- which is determined by the L vector, or the L/D ratio, whichever way you want to look at it. In previous posts I spent some time discussing the difference betweeb the total G-loading vector, and the lift-wise component of the G-loading vectorm

I stand by the tables I posted today and on June 4. Do you have a specific correction to offer?

S

[[email protected]]

Phone-phart, disregard second-to-last, will repost. S

[[email protected]]

"In the last case, where thrust equals weight, setting the wing to the zero-lift angle-of-attack yields a steady-state climb regardless of airspeed, so the concept of stall speed becomes meaningless.*"

Sorry, that was a bit sloppy. If thrust=weight, no thrust is available to counteract drag, and so airspeed must be zero in the steady-state case. Angle-of-attack is undefined, so the wing cannot be considered to be stalled. Progressively higher T/W ratios (greater than 1:1) allow for progressively higher airspeeds, with the wing held at the zero-lift angle-of-attack, as the aircraft climbs straight up. Obviously we have abandoned the concept of a 40:1 L/D-- we have shoved the stick forward to unload the wing to zero lift as we climb straight up, so L/D is zero.

[[email protected]]

"Now if you suppose that it's the lift part which is opposed to the weight, then L/D would influence g-load. But this is just not how physics works on this planet.*"

A key point is that g-load is really just an expression of force. That's all it is. It is the vector sum of all the real forces acting on the aircraft, except gravity. Then we divide by weight to get a dimensionless expression.

When we talk about g-load, we really aren't saying anything that we couldn't express just as well by talking about the actual aerodynamic and thrust forces generated by the aircraft.

In a glider, where there is no engine, the g-load is the vector sum of all the aerodynamic forces generated by the glider. In coordinated flight, this would simply be the vector sum of lift and drag.

When we say that g-load affects stall speed, we really should say that the lift-wise component of the g-load vector affects stall speed. Not the total g-loading vector. But all we're really saying is that the magnitude of the lift vector affects stall speed. No extra information or content is added by bringing the concept of "g-loading" into the discussion.

The L/D ratio affects the magnitude of the lift vector, and also affects stall speed. In a powered climb, the T/W ratio affects the magnitude of the lift vector, and also affects stall speed. As per the tables I posted on June 4, and yesterday.

S

[jfitch]

On Wednesday, June 17, 2015 at 6:14:09 AM UTC-7, wrote:
> "Now if you suppose that it's the lift part which is opposed to the weight, then L/D would influence g-load. But this is just not how physics works on this planet.*"
>
> A key point is that g-load is really just an expression of force. That's all it is. It is the vector sum of all the real forces acting on the aircraft, except gravity. Then we divide by weight to get a dimensionless expression.
>
> When we talk about g-load, we really aren't saying anything that we couldn't express just as well by talking about the actual aerodynamic and thrust forces generated by the aircraft.
>
> In a glider, where there is no engine, the g-load is the vector sum of all the aerodynamic forces generated by the glider. In coordinated flight, this would simply be the vector sum of lift and drag.
>
> When we say that g-load affects stall speed, we really should say that the lift-wise component of the g-load vector affects stall speed. Not the total g-loading vector. But all we're really saying is that the magnitude of the lift vector affects stall speed. No extra information or content is added by bringing the concept of "g-loading" into the discussion.
>
> The L/D ratio affects the magnitude of the lift vector, and also affects stall speed. In a powered climb, the T/W ratio affects the magnitude of the lift vector, and also affects stall speed. As per the tables I posted on June 4, and yesterday.
>
> S

You discuss the "lift G-load" as if it was a thing in itself. It is not, it is a mathematical construct of several derived values. When the load on the wing changes many other things change - and perhaps the lift also increases. Let us suppose you are in an unaccelerated glide and a magic wand causes the glider's weight to double. After some time and control input, you return to an unaccelerated glide at the same speed. You will discover that the angle of attack has doubled, the induced drag has quadrupled, the angle of the resultant forces on the wing spar has changed, as has the bending moment. And the L/D is reduced.

As a second thought experiment, I fly my glider at 40 knots, it gets an L/D about 40. I then increase the speed to 80 knots, and still get an L/D of 40. But: the angle of attack is reduced by 75%, the induced drag on the wing reduced even more, the parasitic drag of the fuselage increased by 4x, the angle of the resultant forces on the wing spar changed again. My L/D and "lift G-load" are identical, but nothing else on the glider is. At 40 knots I am very close to stall, at 80 no where near it.

As a third thought experiment, I will take the resultant aerodynamic force on my wing, and split into two vectors: one at 30 degrees above the angle of attack which I will call Lift, one at 120 degrees above the angle of attack which I will call Drag. This is every bit as natural and valid as your Lift and Drag, which are similarly arbitrarily defined. When I am in a high drag configuration and my glide ratio is 2:1, I discover that Lift has disappeared completely. My Lift G-load is 0. Yet I am still in steady state flight, and there is still 1G bending load on the spar.

You cannot take an arbitrary mathematical construct, deal with it in isolation, and draw any momentous (or perhaps even any valid) conclusions.

[Jim Lewis[_2_]]

My admittedly incomplete understanding of the effect of weight on L/D is that increasing weight does not change the
L / D but will change the IAS required.

I suppose if you require the airspeed pre and post weight increase to be unchanged, the L / D will vary, but this is usually not the way we exploit the usefulness of added weight, as far as I know anyway.

[[email protected]]

Re the recent post above from jfitch--

Thanks for your continued engagement. There are some interesting and fundamental ideas at play here. Here are some thoughts-- you might want to read all the way to the end before responding to anything, as I've come around somewhat closer to your viewpoint. This is REALLY LONG, but I think there are some interesting points here.

I agree that L and D can be argued to be arbitrary constructs. As can Cl (lift coefficient) and Cd (drag coefficient). But that doesn't mean they are un-useful. A given value of L and a given value of D will result in a given net aerodynamic force vector. (Assuming for the moment that we are talking about coordinated flight in an unpowered glider.) L and D are useful because they are tools to allow us to specify a net aerodynamic force vector. But other coordinate systems could serve the same purpose.

Let's think more fundamentally about what determines stall speed. Stall speed is just whatever airspeed you happen to have at some particular moment, when you place the wing at the stall angle-of-attack. It could be a very high airspeed, or a very low airspeed. The net aerodynamic force generated by the airflow around the aircraft (excluding thrust from the engine if present) will be proportional to the square of whatever airspeed you happen to have when you place the wing at the stall angle-of-attack. L and D will both vary in relation to the square of this airspeed.

We often think of stall speed as being proportional to the square root of the g-loading, at least when weight is fixed. In some previous posts I was suggesting that it is more appropriate to focus on the lift-wise component of the g-loading vector. IF angle-of-attack and Cl and Cd are constant, and L/D is therefore constant, but we have a motor and we are varying the thrust in a powered climb, then the more of the aircraft's weight is carried by thrust, the less is carried by L, and the stall speed goes down in proportion to the square root of the reduction in L. This is what the table I posted on June 16 is showing. It would be equally valid to say that the stall speed goes down in proportion to the square root of the reduction in D. Remember, L/D is constant in this thought experiment--I specified an L/D of 40:1 in the table I posted on June 16. However, the dragwise component of the G-loading vector is also influenced by the Thrust vector, which complicates everything. So in this particular case-- which is certainly not a glider-- the stall speed does in fact vary according to the square root of the liftwise component of the G-loading vector, but not according to the square root of the dragwise component of the G-loading vector, and not according to the total G-loading vector, which in this particular case is always 1G. The reason L has gained this privileged position, is that we are varying the Thrust force, which acts parallel to Drag and purely perpendicular to Lift, at least for this purposes of this simplified discussion. That's the only reason Lift has become a "privileged" force-- because our engine is bolted on in such an orientation as to make thrust that acts parallel to the flight path.

In the table I posted on June 16, I was imagining that angle-of-attack, Cl, and Cd were all staying constant. I should have said that explicitly. It would be equally valid to use some other arbitrary set of axes, but much more complicated, because then T would no longer act parallel to the direction of one of our chosen axes.

Back to the pure glider case-- and the table I posted on June 6. If we are decreasing the L/D, the obvious question is "how?"

Are we increasing Cd while leaving Cl unchanged? If so, the airspeed that will yield a steady-state condition in wings-level flight right at the stall angle-of-attack, will be decreased, especially if we are talking about steep glide angles where the drag vector is supporting much of the aircraft weight. Imagine a gigantic parachute letting the whole glider come nearly straight down.

Or are we deceasing Cl while leaving Cd unchanged? If so, the airspeed that will yield a steady-state condition in wings-level flight right at the stall angle-of-attack, will be increased, especially if we are talking about flat glide angles where the lift vector is supporting nearly all of the aircraft weight. This is usually the scenario we're talking about, when we talk about deploying spoilers.

So I absolutely agree that if we are varying the lift coefficient and/or the drag coefficient, we can't say that the stall speed will vary according to the square root of the lift force, i.e. the square root of the lift-wise component of the G-loading vector. We need more information.

So it really wasn't appropriate for me to suggest that the variable-thrust case described in the table I posted on June 16 had much to do with the glider case described in the table I posted on June 4, if we're interested in how the stall speed varies in each case. The June 4 table doesn't have enough information to tell us how the stall speed varies, while the June 16 table does.

I'm trying to remember exactly how we got on this track. Opening a new browser window and scrolling back through the thread--

See Dan Marotta's question of June 3. Dan was asking about how the increase in G-loading due to banking was different in a descending glide than in horizontal flight. My table of June 4 answered that. I wasn't trying to claim that we could make any deductions about how the stall speed changed as we move up and down in the table (different L/D ratios, different Cl values, different Cd values, different angle-of-attack values). I was just showing that the lift-wise component of G-loading varied DIFFERENTLY as we change the bank angle, when the L/D is high than when the L/D is low. I still stand by that table.

I'm not saying that in the glider case (no thrust), L has a privileged position in determing the stall speed. It would be equally valid to say that stall speed varies according to the square root of the lift-wise component of the G-loading vector, or according to the square root of the lift vector, or according to the square root of the drag-wise component of the G-loading vector, or according to the drag vector, or according to the square root of the net aerodynamic force vector, or according to the square root net G-loading vector. All those things would be true, at least if we are holding angle-of-attack and Cl and Cd all constant. Which is what we should be doing, if we are going to the left or right in any given line on the table I posted on June 6, and intending to learn something about stall speed.

Key point-- KEY POINT-- in the case of an unpowered glider, not only is the lift vector or the lift-wise component of the G-loading vector less in a 60-degree bank with a 1/1 L/D than in a 60-degree bank with a 50/1 L/D -- so too is the NET G-loading vector and NET aerodynamic force vector less in a 60-degree bank with a 1/1 L/D than in a 60-degree bank with a 50/1 L/D. And the same is true of the drag vector. I'm not putting the Lift vector in a privileged position here. The worse the L/D ratio, the more of the aircraft's weight is supported by the drag vector. As a result, a high bank angle makes causes LESS increase in the L vector than it would in horizontal flight or in a flatter glide with a better L/D ratio. Likewise, when the L/D ratio is poor, a high bank angle also makes LESS increase in the net aerodynamic force vector or total G-loading vector than it would in horizontal flight or in a flatter glide with a better L/D ratio.

The extreme case is this: at L/D ratios near zero, we're nearly in a terminal-velocity vertical dive, with nearly all the weight supported by the drag vector, and the bank angle has very little effect on anything. When the flight path is truly vertical, the bank angle becomes undefined, and Lift is zero.

So I still say I answered Dan's question correctly.

Did I ever suggest that simply decreasing the L/D ratio would necessarily decrease the stall speed, due the decrease in the L vector? If so that would be inappropriate due to the reasons given above. But scanning back through my past posts, I don't see that I ever said that. My June 6 post beginning "One could steer this conversation in the direction" specifically referenced changes to the Cl and Cd values-- I was not assuming that stall speed varied in lockstep with changes in the L/D ratio.

OK, I do see that on June 12--DEEP into the discussion and AFTER several folks had already objected to many of my previous posts which I still say were 100% accurate-- I did make a post that said "Key point-- this is the g-loading component that is normally of greatest interest to pilots, because this is the g-loading component that affects the stall speed." That's true in the powered case, where we are varying thrust, as illustrated by the table I posted on June 16. But in the glider case where there is no thrust, if angle-attack is constant and Cl and CD are constant, there's nothing "privileged" about L-- as you have pointed out. That fact in no way invalidates anything I posted before that point, including the table I posted on June 6 in answer to Dan's question. The June 6 table was meant to be a table of G-loading, not stall speed, and the discussion didn't drift over into the topic of stall speed until many days after I posted that table. But the fact is that the June 6 table DOES tell us something about stall speed. Remember again, L/D was meant to be constant, going from left to right on any given line. IF we want to expand our conception of the table to encompass something about stall speed, then we ALSO have to specify that angle-of-attack, and therefore Cl and Cd, are held constant as we go to the left or right on any given line of the table. As long as we agree that that's what we're thinking of, then the table DOES tell us how stall speed varies with bank angle-- but NOT because there is anything uniquely privileged about the L vector. We could come to the same conclusion by looking at the D vector or the Net Aerodynamic Force vector-- they all must vary in exactly the same way.

I want to emphasize once more that the NET G-loading or NET aerodynamic force vector varies in exactly the same way as the lift-wise G-loading or Lift force varies, in the table I posted on June 6, because L/D is constant. The NET G-loading is less in a 60-degree bank with a 1:1 L/D ratio, than in a 60-degree bank with a 50:1 L/D ratio.

You've raised the issue that we can have the same L/D ratio at more than one angle-of-attack. I.e. holding L/D constant doesn't hold angle-of-attack or Cl or Cd constant. That doesn't matter, as far as the concepts illustrated in the table I posted on June 6 are concerned. Again, it wasn't originally meant to say anything about stall speed. IF we want the table to tell us how stall speed varies when we move right or left on any given line of the table, THEN we do have to specify that Cl and Cd are staying constant, on any given line of the table.

In summary-- I erred in saying that in the glider case, the liftwise component of the G-loading vector was uniquely privileged in determining the airspeed at the stall angle-of-attack. In the glider case, the dragwise component of the G-loading vector, or the total G-loading vector (i.e. the net aerodynamic force vector) would serve just as well. But I didn't make this statement into deep into the discussion, and I still stand by my answer to Dan Marotta's original question of June 3.

Sorry for getting a bit carried away in exalting the L-D-W vector triangle.... S

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Substitute the words "table of June 4" for "table of June 6", sorry.

S

[[email protected]]

A bit more concisely now--

See Dan Marotta's question of June 3, and the discussion of whether or not L/D ratio affects "wing loading" in subsequent posts.

My table of June 4 was directly relevant to this discussion.

The take-home message of the table was as follows:

If we are holding L/D constant, then then L, D, and Na (net aerodynamic force) are fixed in proportion to each other.

If we are holding L/D constant and degrading the glide angle by banking, the magnitude of L, D, and Na (net aerodynamic force) must all increase as the bank angle increases, but the increase in these force vectors is much smaller if the L/D ratio is very poor than if the L/D ratio is very high.

Whether you define wing loading as N/W or L/W, there is much less increase in wing loading with increasing bank angle when the L/D ratio is very poor, than when the L/D ratio is very high.

For typical sailplane L/D ratios-- even with spoilers open-- the effect is likely too small to ever be noticed-- as I said to Dan-- but it is a real effect.

If we are not only holding L/D constant, but we are also holding angle-of-attack and Cl and Cd all constant, then we can see that for any given angle-of-attack-- including the stall angle-of-attack-- as we degrade the glide angle by banking, the airspeed must increase, because the airspeed is proportional to the square root of L, or the square root of D, or the square root of Na. (Remember that L and D and Na are fixed in proportion to each other.) The increase in airspeed with increasing bank angle will be much less when the L/D ratio is very poor, than when the L/D ratio is very high.

Again, for typical sailplane L/D ratios we'll probably never notice this, but it is a real effect.

The extreme case of a very poor L/D ratio is a terminal-velocity vertical dive, in which case the bank angle is undefined (or defined to be zero?) and thus has no effect on airspeed, L, D, and Na at all.

Any suggestion that opening the spoilers will reduce the stall speed, by degrading the L/D ratio, was in error-- when we open the spoilers, we change Cl.

We can't draw conclusions about the how stall speed varies as we move vertically (rather than horizontally) in the table I posted on June 4, because we haven't specified why the L/D ratio is changing-- whether due to changes in Cl, Cd, or both. But we can still see how the wing-loading (L/W or Na/W) varies as we move vertically through the table.

Here is the table one more time, but I've modified it to included Na/W (net aerodynamic force / weight) as well as L/W at various bank angles. Take your pick of which one you prefer to call the "G-loading". I could have also added the D/W, but you can easily calculate that from L/W. I've also added a line for the L/D =0 case.

Gliding flight (no thrust.) A table of (lift / weight), followed by (net aerodynamic force / weight), at various bank angles and L/D ratios:

Bank angle, L/W, Na/W:
L/D Infinite--
0 deg 1.000,1.000 30 deg 1.155,1.155 45 deg 1.414,1.414 60 deg 2.000,2.000
L/D 10:1--
0 deg .995,1.00 30 deg 1.147,1.153 45 deg 1.400,1.407 60 deg 1.966,1.976
L/D 5:1--
0 deg .981,1.00 30 deg 1.125,1.147 45 deg 1.361,1.388 60 deg 1.869,1.906
L/D 2:1--
0 deg .894,1.00 30 deg 1.000,1.118 45 deg 1.155,1.291 60 deg 1.414,1.581
L/D 1:1--
0 deg .707,1.00 30 deg 0.756,1.071 45 deg 0.817,1.155 60 deg 0.894,1.264
L/D 0/1
0 deg 1.00,1.00 30 deg 1.00,1.00 45 deg 1.00,1.00 60 deg 1.00,1.00

S

[[email protected]]

****Re-posted-- the only change is in the last line of the table****

A bit more concisely now--

See Dan Marotta's question of June 3, and the discussion of whether or not L/D ratio affects "wing loading" in subsequent posts.

My table of June 4 was directly relevant to this discussion.

The take-home message of the table was as follows:

If we are holding L/D constant, then then L, D, and Na (net aerodynamic force) are fixed in proportion to each other.

If we are holding L/D constant and degrading the glide angle by banking, the magnitude of L, D, and Na (net aerodynamic force) must all increase as the bank angle increases, but the increase in these force vectors is much smaller if the L/D ratio is very poor than if the L/D ratio is very high.

Whether you define wing loading as N/W or L/W, there is much less increase in wing loading with increasing bank angle when the L/D ratio is very poor, than when the L/D ratio is very high.

For typical sailplane L/D ratios-- even with spoilers open-- the effect is likely too small to ever be noticed-- as I said to Dan-- but it is a real effect.

If we are not only holding L/D constant, but we are also holding angle-of-attack and Cl and Cd all constant, then we can see that for any given angle-of-attack-- including the stall angle-of-attack-- as we degrade the glide angle by banking, the airspeed must increase, because the airspeed is proportional to the square root of L, or the square root of D, or the square root of Na. (Remember that L and D and Na are fixed in proportion to each other.) The increase in airspeed with increasing bank angle will be much less when the L/D ratio is very poor, than when the L/D ratio is very high.

Again, for typical sailplane L/D ratios we'll probably never notice this, but it is a real effect.

The extreme case of a very poor L/D ratio is a terminal-velocity vertical dive, in which case the bank angle is undefined (or defined to be zero?) and thus has no effect on airspeed, L, D, and Na at all.

Any suggestion that opening the spoilers will reduce the stall speed, by degrading the L/D ratio, was in error-- when we open the spoilers, we change Cl.

We can't draw conclusions about the how stall speed varies as we move vertically (rather than horizontally) in the table I posted on June 4, because we haven't specified why the L/D ratio is changing-- whether due to changes in Cl, Cd, or both. But we can still see how the wing-loading (L/W or Na/W) varies as we move vertically through the table.

Here is the table one more time, but I've modified it to included Na/W (net aerodynamic force / weight) as well as L/W at various bank angles. Take your pick of which one you prefer to call the "G-loading". I could have also added the D/W, but you can easily calculate that from L/W. I've also added a line for the L/D =0 case.

Gliding flight (no thrust.) A table of (lift / weight), followed by (net aerodynamic force / weight), at various bank angles and L/D ratios:

Bank angle, L/W, Na/W:
L/D Infinite--
0 deg 1.000,1.000 30 deg 1.155,1.155 45 deg 1.414,1.414 60 deg 2.000,2.000
L/D 10:1--
0 deg .995,1.00 30 deg 1.147,1.153 45 deg 1.400,1.407 60 deg 1.966,1.976
L/D 5:1--
0 deg .981,1.00 30 deg 1.125,1.147 45 deg 1.361,1.388 60 deg 1.869,1.906
L/D 2:1--
0 deg .894,1.00 30 deg 1.000,1.118 45 deg 1.155,1.291 60 deg 1.414,1.581
L/D 1:1--
0 deg .707,1.00 30 deg 0.756,1.071 45 deg 0.817,1.155 60 deg 0.894,1.264
L/D 0:1-- (vertical dive) (bank angle could also be considered to be undefined)
0 deg 0.00,1.00 30 deg 0.00,1.00 45 deg 0.00,1.00 60 deg 0.00,1.00

[[email protected]]

> You cannot take an arbitrary mathematical construct, deal with it in isolation, and draw any momentous (or perhaps even any valid) conclusions.<

The great thing about defining L as acting perpendicular to the flight path, and D as acting parallel to the flight path, is that it is so easy to relate the L/D ratio to the glide angle or glide ratio. (Easier when wings-level than when banked, but do-able in either case.) Knowing the glide angle or glide ratio unlocks the door to knowing the actual value of the L vector, the D vector, and the Net Aerodynamic Force vector, assuming coordinated, steady-state flight.

Keep in mind that at very steep bank angles, the glide ratio is much lower than the L/D ratio. The resulting steep glide angle allows the Drag vector to support much more of the aircraft's weight than it does in wings-level flight at the same L/D ratio, so that the Lift vector and the Net Aerodynamic Force vector both end up being smaller than they would at the same bank angle with an infinite L/D ratio. This effect is more pronounced when the L/D is very low than when the L/D is very high.

Even with an L/D of 40:1, we can see that the Net Aerodynamic Force generated at extreme bank angles is slightly less than we'd see if L/D were infinite (i.e. if drag were zero).

Here is the table expanded to cover 40:1 L/D, and also to cover 80 and 85 degrees of bank:

If the L/D ratio given in some particular line of the table happens to correspond to the L/D ratio at the stall angle-of-attack of some particular glider in some particular configuration (flaps, spoilers, landing gear), then the stall speed of that glider in that configuration would be expected to vary with bank angle according to the square root of the L/W or Na/W values given in that line of the table. (For most real-world sailplanes there will be no discernible difference from the way the stall speed varies with bank angle in the infinite L/D case; if we're talking about a glider shaped like the space shuttle (L/D as low as 1:1 at hypersonic speed -- see https://en.wikipedia.org/wiki/Space_Shuttle ), it will be a different story!)

Gliding flight (no thrust.)
A table of (lift / weight), followed by (net aerodynamic force / weight), at various bank angles and L/D ratios:

Bank angle, L/W, Na/W:
L/D Infinite--
0 1.000,1.000 30 1.155,1.155 45 1.414,1.414 60 2.000,2.000, 80 5.759,5.759
85 11.478, 11.478

L/D 40/1
0 1.000,1.000 30 1.154,1.155 45 1.413,1.414 60 1.998,1.998 80 5.700,5.702
85 11.029,11.032

L/D 10:1--
0 0.995,1.000 30 1.147,1.153 45 1.400,1.407 60 1.966,1.976 80 4.990, 5.015
85 deg 7.54,7.58

L/D 5:1--
0 0.981,1.000 30 1.125,1.147 45 1.361,1.388 60 1.869,1.906 80 3.776,3.851
85 4.58,4.67

L/D 2:1--
0 0.894,1.000 30 1.000,1.118 45 1.155,1.291 60 1.414,1.581 80 1.889,2.112
85 1.97,2.20

L/D 1:1--
0 0.707,1.000 30 0.756,1.071 45 0.817,1.155 60 0.894,1.264 80 0.986,1.394
85 0.996,1.409

L/D 0:1-- (vertical dive) (bank angle could also be considered to be undefined)
0 0.00,1.00 30 0.00,1.00 45 0.00,1.00 60 0.00,1.00 80 0.00,1.00
85 0.00, 1.00

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> Example: According to the POH, a 650kg (1430lbs) Twin Astir stalls at about 90km (49 knots) with spoilers fully deployed. Add a 45 degree bank and the stall speed increases to 126 km/h (68 knots).
> This is usually above the normal approach speed flown during circuits so I can conceive that a pilot who is not "ahead of the glider" could possibly fly too slowly during the turn. Throw in an uncoordinated turn and things could go wrong very quickly depending on glider type.

Do you have a source for a stall speed of 68 knots at 45 degrees? PHAK and other sources say the stall speed increases with the square root of the load factor. A 45 degree bank has a load factor of 1.41; the square root of this is 1.189. So a 45 degree bank results in a 19% increase in stall speed, or in this case 58 knots.

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Ditto the above question-- unless the L/D ratio is really poor, the stall speed in a 45-degree banked turn ought to be about 1.189* the stall speed in the same configuration in wings-level flight. S

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And if the L/D ratio IS really poor, the increase in stall speed with increasing bank angle is even less. S

[Jim Lewis[_2_]]

On Friday, June 26, 2015 at 12:36:00 PM UTC-7, wrote:
> Ditto the above question-- unless the L/D ratio is really poor, the stall speed in a 45-degree banked turn ought to be about 1.189* the stall speed in the same configuration in wings-level flight. S

This is probably an unneeded addition, but for the sake of completeness, I would change "45-degree banked turn" to "45-degree banked LEVEL turn in still air". Lots of us fly 45-degree banked turns in thermals without pressing the stick back much.

[[email protected]]

On Friday, June 26, 2015 at 7:57:19 PM UTC-7, Jim Lewis wrote:
> On Friday, June 26, 2015 at 12:36:00 PM UTC-7, wrote:
> > Ditto the above question-- unless the L/D ratio is really poor, the stall speed in a 45-degree banked turn ought to be about 1.189* the stall speed in the same configuration in wings-level flight. S
>
> This is probably an unneeded addition, but for the sake of completeness, I would change "45-degree banked turn" to "45-degree banked LEVEL turn in still air". Lots of us fly 45-degree banked turns in thermals without pressing the stick back much.

Is there some suggestion here that the glider behaves differently in an updraft? Surely not.

Re "level"-- in a glider? If the flight path is horizontal with respect to the airmass, you are decelerating, not in a steady-state situation. To maintain horizontal flight, you'll have to keep moving the stick aft at a certain rate, as the airspeed bleeds off. Will the glider reach the stall angle-of-attack at a different airspeed than if you just ease the stick ever-so-slowly aft, so that the rate of deceleration is negligible, and you stay very close to a steady-state glide?

At any given instant of time where the glider is at some given angle-of-attack, the L/W and Na/W values (Na=Net Aerodynamic Force) will be slightly smaller in the steady-state glide than in decelerating level flight, so the airspeed at the stall angle-of-attack will be slightly less in the steady-state glide than in decelerating horizontal flight, but the difference will be trivial for normal sailplane L/D ratios. In the decelerating level flight case, the L/W value will be the same as it is on the top line (infinite L/D) of the table I posted on June 25, and the Na/W ratio will be slightly larger. For any given glider at some given angle-of-attack, the ratio between L, D, and Na will be the same in the decelerating level flight case as in the steady-state glide case. Looking at the table I posted June 25, for glide ratios of 10:1 or better you can see that there is no discernible difference between L and Na. There's also no discernible difference between the value of L, or Na, at a 10:1 L/D, and L, or Na, at an infinite L/D. So I'd say there's no way you'll be able to tell the difference between the stall speed at the slow deceleration rate required to maintain exactly horizontal flight in still air, versus the extremely slow deceleration rate you'd use to reach the stall angle-of-attack while staying very close to a steady-state glide.

S

[Jim Lewis[_2_]]

I'm afraid I don't know enough to really understand your posting.

I can address a couple of your statements though ( I think ):

Does a glider perform differently in an updraft? Seems like it, at least in the degree of back stick needed to maintain a circle. This is no surprise, I'm sure. The "updraft" contributes to the force needed to reduce the downward acceleration of the glider, so less lift force is needed for the job, so less increase in AoA is needed. I'm probably missing your points here and just describing what you already know. I'm sorry about that.

What about a "level" turn in a glider? As far as my very limited experiences have shown me, a "level" turn - a turn during which the glider does not loose altitude - is what I hope for in a thermal. Actually, I hope to gain altitude in a thermal but that doesn't happen for me very often. Does the glider's airspeed decrease in such a "level" thermal? Not if the "updraft" is adequate.

I'm sorry I don't follow your statements about approaching stall speed gradually or slowly. Over my head I'm afraid.

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>>Does a glider perform differently in an updraft? *Seems like it, at least in the degree of back stick needed to maintain a circle. *This is no surprise, I'm sure. *The "updraft" contributes to the force needed to reduce the downward acceleration of the glider, so less lift force is needed for the job, so less increase in AoA is needed.<<

An updraft is a velocity, not an acceleration. What you are saying, is much like saying a glider handles differently in a headwind, crosswind, or tailwind. Remember the famous "walking slowly down on a rising escalator" analogy-- does it feel any different as you walk downward, on an escalator that is rising than on an escalator that is stopped?

All unaccelerated reference frames are equally legitimate-- it doesn't matter whether the escalator is stopped or moving up or moving down, it feels the same to walk on in each case. It only feels "funny" for a second or two when you step off the escalator into a new reference frame.

Food for thought...

I'm at a loss to explain your perception. Nothing comes to mind that would create that illusion-- unless it's just that when you are rising rapidly, you relax a bit and are no longer so worried about maintaining the absolute minimum sink rate relative to the airmass.

S

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PS re recent few posts above-- there might be a correlation between your not getting that stick well aft while thermalling, and your experience of rarely gaining altitude while thermalling! When you are at a safe altitude, gently take it all the way to the stall buffet while thermalling, and then back it off a bit.

Then try the exact same thing at the same bank angle, when no longer in the thermal. If you are expecting some difference in airspeed, pitch attitude, or stick position, then you might be surprised at what you discover.

S

[Jim Lewis[_2_]]

Thank you. I'll give it a try.

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I think the issue was made murky by stipulations. Any aircraft IN A TURN that stalls is prone to spin - much more so if it is uncoordinated. The turn to base or final is the last place you want this to happen. Not adding flaps while turning was part of my pilot training in the 70's. The combination of turning (higher G loading) increases stall speed, and if you add drag while doing it, you can inadvertently loose too much airspeed for the bank angle, add to this the possibility of an uncoordinated turn. To error is human, to error close to the ground offers the answer to one of mankind's greatest debates; what happens to your soul when you die!

In the USA a pilot must consistently recover from a stall with less than 50ft altitude loss in order to get a license. Do we do stalls at 150ft? Heck no; we do them at 2000ft. We know a mistake close to the ground will kill us. The same is true for screwing with the aircraft while it is in a turn.

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On Tuesday, June 2, 2015 at 9:55:37 AM UTC-6, Dan Marotta wrote:
> I submit that doing something only seldomly in an unusual case is
> more dangerous than doing it all the time and being well-practiced.


Do you stall the aircraft on final frequently so you can be good at it?

[[email protected]]

On Tuesday, June 2, 2015 at 12:37:48 PM UTC-6, Tango Eight wrote:
> What helps even more is starting with the POH before developing your own type specific procedures :-).
>
> -Evan Ludeman / T8

Great comment!

We have a generation of pilots that has never seen (or forgotten) the folks that died learning what not to do.

[Dan Marotta]

An aircraft recovers from a stall at any altitude, in the same manner
and with the same loss of altitude, given the same initial conditions
and recovery controls.Â* Of course, closer to the ground a pilot is more
inclined to pull harder on the stick as the ground rushes up, preventing
recovery.Â* Practicing at altitude will train the pilot to use the
correct amount of pressure, minimizing altitude loss.

Of course, practicing NOT stalling is more beneficial.Â* Learning how far
you can push your aircraft without stalling is, in my opinion, the
better way.Â* And, to address the subject line, I use spoilers throughout
the turn as needed.Â* I think a pilot who applies a particular amount of
spoiler and holds that throughout the pattern to landing is leaving a
lot of performance on the table.

On 1/4/2018 11:35 PM, wrote:
> On Tuesday, June 2, 2015 at 9:55:37 AM UTC-6, Dan Marotta wrote:
>> I submit that doing something only seldomly in an unusual case is
>> more dangerous than doing it all the time and being well-practiced.
>
> Do you stall the aircraft on final frequently so you can be good at it?

--
Dan, 5J

[[email protected]]

On Friday, January 5, 2018 at 1:32:08 AM UTC-5, wrote:
> I think the issue was made murky by stipulations. Any aircraft IN A TURN that stalls is prone to spin - much more so if it is uncoordinated. The turn to base or final is the last place you want this to happen. Not adding flaps while turning was part of my pilot training in the 70's. The combination of turning (higher G loading) increases stall speed, and if you add drag while doing it, you can inadvertently loose too much airspeed for the bank angle, add to this the possibility of an uncoordinated turn. To error is human, to error close to the ground offers the answer to one of mankind's greatest debates; what happens to your soul when you die!
>
> In the USA a pilot must consistently recover from a stall with less than 50ft altitude loss in order to get a license. Do we do stalls at 150ft? Heck no; we do them at 2000ft. We know a mistake close to the ground will kill us. The same is true for screwing with the aircraft while it is in a turn.

Could you please provide the reference from which you got the 50 foot standard.
UH

[SoaringXCellence]

As a currently appointed glider DPE I can say with some certainty the there is no documented minimum altitude loss in the current US FAA Glider Practical Test standard.

The current standards were published in 1999, prior to that time there were many elements that are no longer tested or for which the tolerances have changed.

Mike

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NOTE: Entering a stall/spin does not require the airbrakes being extended, nor does having them extended increase the likelihood of a stall/spin (because we all know that stall speed increases when they are extended).

In 10 years of flying gliders in the U.S. in everything from 2-33's, 1-26's, Blaniks, Grobs, Krosnos, Discus, PW-6, Duo Discus, Pegase, HpH304, ASG-32 and others with a wide variety of instructors at a wide variety of soaring sites, whether flying with me or giving a pre-flight checkout, the only mention of airbrake use during landing I ever heard from a CFI-G was to check them on downwind to ensure they were working. This started when I was a student with my first glider flights. I have and do use the airbrakes during landing (including during my biennial checks and area checkouts with no comments from any CFI-G about this) - in downwind, base, and final - in all these gliders with no adverse effects. The basic training mantra was airspeed, airspeed, airspeed, along with coordinated turns and TLAR) - the airbrakes were secondary and used to control rate of descent regardless of position in pattern to help maintain TLAR - and that was what I was taught, and how I use them - (and that does not require much use once the pattern is established (but there are those gusty, shear laden days with surprises ...)). Position in the pattern is not a factor - airspeed, coordinated turns, and TLAR were the gospel preached to me. There are times to come in high and get down fast, and times to come in low and hold off - the airbrakes are an integral part of handling a variety of (out)landing situations - but all depend on maintaining adequate airspeed, and coordinating turns.

[Sig_ZA]

I was taught that there is nothing inherently dangerous in using spoilers in the circuit, provided that the correct speeds are maintained.

With spoilers out, even just cracked open, during base and finals turns safe speed margins are reduced, i.e. inside wing flying slower, reduced lift from deployed spoilers and wind shear (again inside wing flying slower).

However, I was advised NEVER to use them on the base and finals turns (unless absolutely necessary and me paying full attention) and here is why:

Imagine that you normally use spoilers during these turns, with no problems at all, but one day you are returning from a 9 hour cross country flight, it’s been a long final glide and energy is low. Also the weather has changed and the wind is gusting from an approaching storm front.

So you are fatigued, the glider is in a low energy state and wind is gusting. The holes in the cheese line up and you crack the spoilers during a steep base turn with speed too low. The end.

[Andy Blackburn[_3_]]

I haven't read every comment in this thread from the beginning, so maybe someone has observed this previously. If so, apologies for the repetition.

There's nothing inherent about turning that will cause a stall or spin. There's nothing inherent about deploying the spoilers that will cause a stall or spin. There's noting inherent about putting out the landing flaps that will cause a stall or spin. There's noting inherent about turning low that will cause a stall or spin. There's nothing inherent about doing them all at once that will cause a stall or spin. But, the more moving parts there are in your approach maneuvers the more attention it will take to keep everything in proper order. A few examples:

Turning below a few hundred feet presents the pilot with a very different peripheral scene because the inside wing tip traces a circle against the ground that is in the direction of travel rather than the opposite direction at higher altitudes. This tends to make it feel as though you are slipping and over-ruddering the turn can become a risk. Not a problem if you fly the airplane properly.

When you deploy the spoilers two things happen. First, you spoil the lift on the portion of the wing spanned by the spoiler (that's why they're called spoilers). This means to maintain unaccelerated flight the rest of the wing needs to produce more lift, which the pilot may compensate for by increasing angle of attack. Not a problem if you fly the airplane properly, but if you are too close to the angle of attack for stall, you can end up on the wrong side of the Cl vs alpha curve.

Second, deploying spoilers increases drag so the descent angle needs to increase to keep from bleeding off airspeed. The net effect between loss of lift and increase in drag depends a bit on the glider and the airspeed and g-load, but suffice to say that airspeed and AOA will have additional influences inflicted on them. Not a problem if you fly the airplane properly, but a bunch of rates and angles are going to change when you tug on the spoiler of flap handle.

I, for one, try not to change too many things too quickly all at once in the pattern, or if I do, I tend to push the nose over a bit in case I get distracted by, you know, looking out the window. Can you yank aggressively on all the handles at once and not create a problem? Absolutely, but it helps to pay good attention if you do.

The FAA preaches stabilized approach for a reason:

https://www.faa.gov/news/safety_briefing/2016/media/SE_Topic_16-11.pdf

Andy Blackburn
9B

[John Foster]

On Saturday, January 6, 2018 at 1:38:02 AM UTC-7, Andy Blackburn wrote:
....
> Second, deploying spoilers increases drag so the descent angle needs to increase to keep from bleeding off airspeed. The net effect between loss of lift and increase in drag depends a bit on the glider and the airspeed and g-load, but suffice to say that airspeed and AOA will have additional influences inflicted on them. Not a problem if you fly the airplane properly, but a bunch of rates and angles are going to change when you tug on the spoiler of flap handle.
....
> Andy Blackburn
> 9B

This, I believe is the key that people are not considering. The physics of it is such that when the air brakes/spoilers are deployed, they disrupt not only the lift, but increase the drag. As such, if you kept the aircraft in the same attitude, you would increase the AOA and are more likely to stall.

However, if you maintain your airspeed, to do this and deploy the spoilers, you would need to change the attitude of the aircraft into a more nose-down position. This would decrease the AOA, thus compensating for the decreased lift and increased drag, and the net effect would be no significant change to the stall speed, whether you are turning or flying level wings. The AOA remains the same, and IAS and stall speed also remain the same.