Optimum thermalling speed display

Evan, it must be nice to have the time and opportunity to fly enough contest to stay on the peak of performance.

However, not everyone has the ability or time to do this. And a newcomer to the sport may be having enough trouble absorbing all that is going on without having to figure out how to determine in real time the optimum airspeed to thermal by trial an error!

For the 47 percent of us who are not yet retired or independently wealthy, every little bit helps - just saying "go out and buy the best nav display and practice a lot and go to a lot of contests and you will figure it out" isn't going to hack it.

There has to be a starting point for thermaling speed. Aerodynamically, that's probably best represented by min sink for the bank angle and wing loading. From then on, you are in the realm of technique and glider idiosyncrasies - where experience and flying time makes the difference. What I'm asking is is it possible to at least display the basics, to make learning the techniques easier.

I think it would be helpful. You hotshots who zen-thermal can continue to do so - having data available doesn't mean it has to be used slavishly!

And in regards to my LS6 comments - it is by far the easiest racing glider I have flown. When thermalling, you can slow down to the point you start to mush without any tendency to drop a wing or spin. But since there is so little pre-stall indications (no buffet, controls stay responsive, etc) it is not practicable (at least not for me - others are welcome to disagree) to just slow down then add a few knots. I like to have an airspeed target to shoot for - usually by setting what I know is the approximate AOA via nose position, then adjusting airspeed as necessary. All while trying to figure out where the center of the thermal went...and dodging the 2-33 blundering around in the middle.

CN looks nice. I've also found that SYM can be customized to display only the info I want, where I want it, when I want it. I like that. I agree that the tendency seems to be to generate and display a lot of data - interesting data sometimes, but mostly just eye-candy, that does nothing to make you go faster.

Keep up the good work with the CN!

Kirk
66

OK. I have that. And I have reviewed my Reichmann, who basically says the
same thing which is to set the turn according to the shape of the thermal.
Interestingly relative to this thread, he goes on to say that for each
turn radius (well, "thermal gradient"), there is a single optimum airspeed
and a single optimum bank angle.

What I was musing about, however, although I didn't really express it very
well, was whether there is always a decrease in turn radius with an
increase in bank angle (assuming that one stays a constant speed above
stall), or if that curve might "invert" in certain cases.

- Jim




At 16:19 29 September 2012, wrote:
On Saturday, September 29, 2012 2:30:04 AM UTC-4, Jim Wallis wrote:
So is the target bank angle always 45 degrees (with slowest safe speed
fo=
r that bank) or would you give up bank angle to slow down more i.e. focus
o=
n speed control. Which gives you the tightest circle? - Jim The key
poin=
t Evan makes (and I totally agree!) is that the strongest lift is
closest
=
to the the center of a thermal, so flying slower smaller diameter
spirals
=
will increase climb rate even though the increased bank decreases the
vert=
ical component of lift. I had opportunity to fly with some paragliders
(wi=
th JS ) and even though the paraglider min-sink isn't good, they
outclimbe=
d us because they can fly such a small circle, and stay in the strongest
l=
ift.

There is no "always". The bank angle for best climb must take into
acoount
=
sink rate of the glider as well as the gradient of thermal strength with
re=
spect to thermal size. Then throw in that many thermals are not round and
r=
equire bank changes. Add to this that, as bank changes, speed should
change=
slightly, while anticipating the next gust or slacking of lift. And,
just
=
to make it a bit more complicated, avoid the angle of attack where the
lift=
vs angle of attack gradient is unfavorable.
Funny how flying for a week or so in concentrated manner makes this
easier
=
to do.
UH

I have answered my own question. I was distracted by my recollection the
axiom that flying slower reduces the radius of the turn but, of course,
that isn't relevant if you are always flying at a fixed amount above stall.
It is clarified in this quote from another forum (pprune.org):

"As the speed is increased from the straight and level stall speed, the
radius of turn can be reduced by increasing the angle of bank. However, a
radius and speed are reached where the load factor is at a maximum for the
structure. Any further increase will overstress the structure. Thus the
radius of turn will increase, as the speed is further increased at constant
angle of bank. The speed corresponding to the minimum radius turn is called
the manoeuvre speed.
At speeds below the manoeuvre speed, the maximum (or limiting) load factor
cannot be produced aerodynamically i.e. the angle of bank is limited by the
maximum lift coefficient. At speeds above the manoeuvre speed, an increase
in the angle of attack to produce maximum lift coefficient, will produce a
load factor higher than the limit load factor i.e. it will overstress the
structure."

It was useful for me to see this discussed starting from the straight and
level stall speed (i.e. the speed that doesn't permit turns at all)

So, (to try to bring my digression back in line with the thread topic!) it
does seem like the most useful information would be how much speed you are
above stall speed for any given bank angle.

- Jim




At 16:19 29 September 2012, wrote:
On Saturday, September 29, 2012 2:30:04 AM UTC-4, Jim Wallis wrote:
So is the target bank angle always 45 degrees (with slowest safe speed
fo=
r that bank) or would you give up bank angle to slow down more i.e. focus
o=
n speed control. Which gives you the tightest circle? - Jim The key
poin=
t Evan makes (and I totally agree!) is that the strongest lift is
closest
=
to the the center of a thermal, so flying slower smaller diameter
spirals
=
will increase climb rate even though the increased bank decreases the
vert=
ical component of lift. I had opportunity to fly with some paragliders
(wi=
th JS ) and even though the paraglider min-sink isn't good, they
outclimbe=
d us because they can fly such a small circle, and stay in the strongest
l=
ift.

There is no "always". The bank angle for best climb must take into
acoount
=
sink rate of the glider as well as the gradient of thermal strength with
re=
spect to thermal size. Then throw in that many thermals are not round and
r=
equire bank changes. Add to this that, as bank changes, speed should
change=
slightly, while anticipating the next gust or slacking of lift. And,
just
=
to make it a bit more complicated, avoid the angle of attack where the
lift=
vs angle of attack gradient is unfavorable.
Funny how flying for a week or so in concentrated manner makes this
easier
=
to do.
UH

On Saturday, September 29, 2012 9:13:23 PM UTC-4, kirk.stant wrote:
Evan, it must be nice to have the time and opportunity to fly enough contest to stay on the peak of performance.



However, not everyone has the ability or time to do this. And a newcomer to the sport may be having enough trouble absorbing all that is going on without having to figure out how to determine in real time the optimum airspeed to thermal by trial an error!



For the 47 percent of us who are not yet retired or independently wealthy, every little bit helps - just saying "go out and buy the best nav display and practice a lot and go to a lot of contests and you will figure it out" isn't going to hack it.



There has to be a starting point for thermaling speed. Aerodynamically, that's probably best represented by min sink for the bank angle and wing loading. From then on, you are in the realm of technique and glider idiosyncrasies - where experience and flying time makes the difference. What I'm asking is is it possible to at least display the basics, to make learning the techniques easier.



I think it would be helpful. You hotshots who zen-thermal can continue to do so - having data available doesn't mean it has to be used slavishly!



And in regards to my LS6 comments - it is by far the easiest racing glider I have flown. When thermalling, you can slow down to the point you start to mush without any tendency to drop a wing or spin. But since there is so little pre-stall indications (no buffet, controls stay responsive, etc) it is not practicable (at least not for me - others are welcome to disagree) to just slow down then add a few knots. I like to have an airspeed target to shoot for - usually by setting what I know is the approximate AOA via nose position, then adjusting airspeed as necessary. All while trying to figure out where the center of the thermal went...and dodging the 2-33 blundering around in the middle.



CN looks nice. I've also found that SYM can be customized to display only the info I want, where I want it, when I want it. I like that. I agree that the tendency seems to be to generate and display a lot of data - interesting data sometimes, but mostly just eye-candy, that does nothing to make you go faster.



Keep up the good work with the CN!



Kirk

66

Kirk,

Who are you calling hotshot? Go look at your own contest record. Kirk, you've done some pretty kick ass contest flying with that LS-6. To do that, you pretty much have to wear the glider. This just doesn't square up with your statements above, leaving me rather puzzled.

I think most of us would agree that as far as overall climb performance goes, the order of importance is 1) path selection, 2) thermal selection, 3) efficient centering, 4) leaving before lift goes soft, 5) optimization of the climb. So I guess what's going on here is that you have mastered #1 - 4 and have only #5 left to work on -- good for you!

FWIW, I think that the behavior you ascribe to the '6 -- essentially being happy to thermal at a very wide range of speeds -- is a good thing. It indicates a broad optimum in the ship's performance curves and allows the pilot to change it up as conditions or personal preference dictates. If that's true, then there probably isn't too much to be gained by trying to zero in on an exact optimum. My speculative $0.02, anyway.

Nav tools: I have learned the hard way -- you don't get to know these things until you fly 'em hard. Anything works for recreational flying. the real bargain out there is XCSoar (free) on a readable android device (I have Dell Streak 5 and it is really good). But I gave up on XCS as a contest tool earlier this year after it $%^&ed up in flight one too many times and the developers indicated that contest flying just wasn't their priority. Contest winners in USA are mostly (my unscientific survey) flying CN and SN-10. These tools are vastly more robust in the contest flying environment. As an example, you can power cycle ClearNav on task and it will recover gracefully with a valid igc log and accurate times and stats. That's the sort of industrial strength you pay the big bucks for.

-Evan Ludeman / T8

Evan, you are making me blush..

To reign this all back to my original question - I guess I'm an AOA freak (comes from years playing around with F-4s and F-15s (real and simulated) where AOA is a constant companion and an important performance indicator.

I like AOA - airspeed in a turning environment only indicates energy, not performance. Ideally, I could do a hard pull into the core of a thermal, looking out the window for traffic in the thermal, roll into the turn, then without looking in get a cue that I'm fast/slow/close to the optimum speed for my WL and bank angle. All heads out.

Since I can't get a helmet mounted display into my cockpit (plus they are heavy and uncomfortable!), and retrofitting an AOA indicator is too complicated and expensive right now - and the ones out there are really stall preventers, not performance indicators - that leaves using some of the processing and sensors already in the cockpit.

Guess I'm enough of a control/tech freak to want another bell and/or whistle!

Would it make me fly better? Late in the season, probably not - for all the excellent reasons you (and others) have stated. But early in the season? I think so. It would be fun to find out.

SN10s rock. Tied to a carefully optimized Oudie, I'm happy.

Perhaps we should all move down under for the winter season and continue this research in the air!

These discussions (virtual post-flight bull**** sessions on the clubhouse deck, really) are fun - I'm amazed we have managed in RAS to keep civil discourse going, compared to most other aviation forums!

Cheers, today I'm off to watch NHRA drag races - about as opposite from soaring as you can get.

Cheers

Kirk
66

Hello fellow glider pilots,

There has been a study of tradeoffs between bank angle and speed.
See the video:

http://www.youtube.com/watch?v=EO9nX...tur e=mh_lolz

Or search for "Analysis of circling flight during thermalling".

Let me know what you tink.

On Saturday, September 29, 2012 5:13:48 PM UTC-4, Skypilot wrote:[color=blue][i]
'Evan Ludeman[_4_ Wrote: ;825243']On Saturday, September 29, 2012 10:49:36 AM UTC-4, kirk.stant wrote: Evan,I wonder if there has been a study done on tradeoffs between sink rate and circle size. Of course, the problem is that thermals are not very consistent...And just to make things clear, I also vary my speed and bank angle until I find what I think is the best climb.But I disagree that the best speed cannot be somewhat quantified. Stall is obviously the slowest - and that speed changes based on at least two variables. How far above stall - up to CL max, or perhaps even faster in a tight, turbulent thermal at 60 degrees of bank) is optimum? Without knowing what stall speed or min sink is, you are guessing or relying on experience or glider feedback. If you are not experienced, or your glide does not give much feedback, you are left with guessing - probably on the high side because of all the "stall spin" stories you have read here on RAS. So if it is easy to display, in real time, what stall/min sink/Cl max is at your current flight condition, that data helps calibrate your "experience" quicker. I find it amusing that we are raving about new technology varios and debating the relative merits of PNA thermal centering displays, while the airspeed cue we display in the cockpit to use all the new info is still just a mechanical airspeed indicator. Some gliders talk a lot, so that monitoring the airspeed is not very necessary. Others, like my ls6, have very little change in feel from the stall up to ridiculously high thermalling speeds - only the nose position relative to the horizon is a givaway to how fast I'm flying, once trimmed up. So the technique of pulling till you feel the stall buffet and easing off doesn't work very well! Anyway- interesting discussion. Cheers f Just ring up Mr Borgelt and get him to design one of these with a bar display system to sit on top of the dash. Attach it to an autopilot attached to a thermal assistant. Plug it all in to a remote control Uav system and fly from the pub. How cool would that be +-------------------------------------------------------------------+ |Filename: AOA.jpg | |Download: http://www.aviationbanter.com/attachment.php?attachmentid=59906| +-------------------------------------------------------------------+ -- Skypilot

fellow glider pilots.

On 10/2/2012 11:56 PM, wrote:
Hello fellow glider pilots,

There has been a study of tradeoffs between bank angle and speed.

The Soaring Flight Manual (sadly no longer in print) had a nice diagram
that showed these tradeoffs:

http://home.comcast.net/~verhulst/GB...TurnRadius.JPG

Tony "6N"

[color=blue][i]
See the video:

http://www.youtube.com/watch?v=EO9nX...tur e=mh_lolz

Or search for "Analysis of circling flight during thermalling".

Let me know what you tink.

On Saturday, September 29, 2012 5:13:48 PM UTC-4, Skypilot wrote:
'Evan Ludeman[_4_ Wrote: ;825243']On Saturday, September 29, 2012 10:49:36 AM UTC-4, kirk.stant wrote: Evan,I wonder if there has been a study done on tradeoffs between sink rate and circle size. Of course, the problem is that thermals are not very consistent...And just to make things clear, I also vary my speed and bank angle until I find what I think is the best climb.But I disagree that the best speed cannot be somewhat quantified. Stall is obviously the slowest - and that speed changes based on at least two variables. How far above stall - up to CL max, or perhaps even faster in a tight, turbulent thermal at 60 degrees of bank) is optimum? Without knowing what stall speed or min sink is, you are guessing or relying on experience or glider feedback. If you are not experienced, or your glide does not give much feedback, you are left with guessing - probably on the high side because of all the "stall spin" stories you have read here o
n RAS. So if it is easy to display, in real time, what stall/min sink/Cl max is at your current flight condition, that data helps calibrate your "experience" quicker. I find it amusing that we are raving about new technology varios and debating the relative merits of PNA thermal centering displays, while the airspeed cue we display in the cockpit to use all the new info is still just a mechanical airspeed indicator. Some gliders talk a lot, so that monitoring the airspeed is not very necessary. Others, like my ls6, have very little change in feel from the stall up to ridiculously high thermalling speeds - only the nose position relative to the horizon is a givaway to how fast I'm flying, once trimmed up. So the technique of pulling till you feel the stall buffet and easing off doesn't work very well! Anyway- interesting discussion. Cheers f Just ring up Mr Borgelt and get him to design one of these with a bar display system to sit on top of the dash. A
ttach it to an autopilot attached to a thermal assistant. Plug it all in to a remote control Uav system and fly from the pub. How cool would that be +-------------------------------------------------------------------+ |Filename: AOA.jpg | |Download: http://www.aviationbanter.com/attachment.php?attachmentid=59906| +-------------------------------------------------------------------+ -- Skypilot

fellow glider pilots.

Check these videos and pass them around.

https://www.youtube.com/watch?v=EO9nXPRkWKk

https://www.youtube.com/watch?v=EO9nXPRkWKk

On Monday, August 14, 2017 at 8:58:21 PM UTC-4, wrote:
https://www.youtube.com/watch?v=EO9nXPRkWKk

Both links above are for part 1.
Part 2 is he
https://www.youtube.com/results?sear...+thermalling+2

Uli
'AS'