Wing Loading / climb rate

[Chris Davison[_3_]]

A questions that I should know the answer to but don't...in a thermal, all
things being equal, will a 15m glider and an 18m glider with the same wing
loading climb at the same rate?

Thanks
Chris

[Tango Eight]

On Wednesday, February 1, 2017 at 1:15:05 PM UTC-5, Chris Davison wrote:
> A questions that I should know the answer to but don't...in a thermal, all
> things being equal, will a 15m glider and an 18m glider with the same wing
> loading climb at the same rate?
>
> Thanks
> Chris

No.

best,
Evan

[[email protected]]

On Wednesday, February 1, 2017 at 10:15:05 AM UTC-8, Chris Davison wrote:
> A questions that I should know the answer to but don't...in a thermal, all
> things being equal, will a 15m glider and an 18m glider with the same wing
> loading climb at the same rate?
>
> Thanks
> Chris

Not if their polars have different sink rates in a bank at min sink speed and the same wing loading. If they were the same it would be a coincidence.

To convince yourself of this imagine two 15/18M gliders of the same type - identical in every way except one has 15M tips and the other has 18M tips. They are ballasted to the same wing loading. In the thermal they are in identical lift. Beyond this the only difference is that the 18M glider has spoilers deployed. Will one glider climb faster? Yes!

Okay, I think your question probably assumes both gliders keep spoilers closed and are identical in every other way, but the same basic idea holds. The 18M glider has different span, aspect ratio and wetted area and therefore a different mix of form and induced drag at any given speed and lift coefficient. Go get a polar for a 15/18M glider and do the ratio of the square root of the wing loadings transformation to equalize the wing loading and you'll see the polars are still different. The 18M ought to have a lower sink rate because of lower induced drag attributable to the higher aspect ratio.. Above a certain speed the polars may cross over as form drag goes up with V-squared. There's actually a lot more going on than just these simple effects, but that ought to give you a basic understanding.

Shorter answer: There's a lot more to aerodynamics and aircraft performance than just wing loading.

Andy Blackburn
9B

[Eric Greenwell[_4_]]

Chris Davison wrote on 2/1/2017 10:14 AM:
> A questions that I should know the answer to but don't...in a
> thermal, all things being equal, will a 15m glider and an 18m glider
> with the same wing loading climb at the same rate?

I'm told thermal climb rate is related to "span loading" (weight/span),
while high speed performance is related to wing loading (weight/wing
area). In your example, the 18m glider will climb better.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Bruce Hoult]

On Thursday, February 2, 2017 at 5:12:27 AM UTC+3, Eric Greenwell wrote:
> Chris Davison wrote on 2/1/2017 10:14 AM:
> > A questions that I should know the answer to but don't...in a
> > thermal, all things being equal, will a 15m glider and an 18m glider
> > with the same wing loading climb at the same rate?
>
> I'm told thermal climb rate is related to "span loading" (weight/span),
> while high speed performance is related to wing loading (weight/wing
> area). In your example, the 18m glider will climb better.

Told by who, I wonder? :-)

Span is important to minimize induced drag, but that's a waste of time unless you have enough wing area to give an acceptable coefficient of lift or AoA at desired circling speeds and radii.

There is probably an intermediate cruising speed range where the dominant factor is wing loading / wing area / wetted area / span*chord. At a guess that might be from midway between min sink and best L/D speeds out to maybe 1.4 or 1.5 times best L/D speed.

At higher speed I'd have thought the dominant factor would be minimizing span*wing thickness, i.e. frontal area. That's what kills the 1960s 40:1 ships at high speed -- or newer short span ones such as the PW5.

[jfitch]

On Wednesday, February 1, 2017 at 8:42:35 PM UTC-8, Bruce Hoult wrote:
> On Thursday, February 2, 2017 at 5:12:27 AM UTC+3, Eric Greenwell wrote:
> > Chris Davison wrote on 2/1/2017 10:14 AM:
> > > A questions that I should know the answer to but don't...in a
> > > thermal, all things being equal, will a 15m glider and an 18m glider
> > > with the same wing loading climb at the same rate?
> >
> > I'm told thermal climb rate is related to "span loading" (weight/span),
> > while high speed performance is related to wing loading (weight/wing
> > area). In your example, the 18m glider will climb better.
>
> Told by who, I wonder? :-)
>
> Span is important to minimize induced drag, but that's a waste of time unless you have enough wing area to give an acceptable coefficient of lift or AoA at desired circling speeds and radii.
>
> There is probably an intermediate cruising speed range where the dominant factor is wing loading / wing area / wetted area / span*chord. At a guess that might be from midway between min sink and best L/D speeds out to maybe 1.4 or 1.5 times best L/D speed.
>
> At higher speed I'd have thought the dominant factor would be minimizing span*wing thickness, i.e. frontal area. That's what kills the 1960s 40:1 ships at high speed -- or newer short span ones such as the PW5.

In classical aerodynamics, induced drag dominates at low speeds (high lift coefficients), and that is inversely proportional to aspect ratio. However if you work through the math, area and wing loading cancel the wing chord out, hence the term span loading (which normalizes for wing loading in effect).

At high speeds profile (and parasitic) drag is dominant. Wing thickness is loosely related to profile drag, but the main thing that kills the 60's ships is the bad behavior of the laminar flow, not the thickness per se. Fuselages have gotten a little cleaner, but it is the wing sections and understanding of laminar flow that is the biggest difference I think.

[Bruce Hoult]

On Thursday, February 2, 2017 at 9:47:29 AM UTC+3, jfitch wrote:
> On Wednesday, February 1, 2017 at 8:42:35 PM UTC-8, Bruce Hoult wrote:
> > On Thursday, February 2, 2017 at 5:12:27 AM UTC+3, Eric Greenwell wrote:
> > > Chris Davison wrote on 2/1/2017 10:14 AM:
> > > > A questions that I should know the answer to but don't...in a
> > > > thermal, all things being equal, will a 15m glider and an 18m glider
> > > > with the same wing loading climb at the same rate?
> > >
> > > I'm told thermal climb rate is related to "span loading" (weight/span),
> > > while high speed performance is related to wing loading (weight/wing
> > > area). In your example, the 18m glider will climb better.
> >
> > Told by who, I wonder? :-)
> >
> > Span is important to minimize induced drag, but that's a waste of time unless you have enough wing area to give an acceptable coefficient of lift or AoA at desired circling speeds and radii.
> >
> > There is probably an intermediate cruising speed range where the dominant factor is wing loading / wing area / wetted area / span*chord. At a guess that might be from midway between min sink and best L/D speeds out to maybe 1.4 or 1.5 times best L/D speed.
> >
> > At higher speed I'd have thought the dominant factor would be minimizing span*wing thickness, i.e. frontal area. That's what kills the 1960s 40:1 ships at high speed -- or newer short span ones such as the PW5.
>
> In classical aerodynamics, induced drag dominates at low speeds (high lift coefficients), and that is inversely proportional to aspect ratio. However if you work through the math, area and wing loading cancel the wing chord out, hence the term span loading (which normalizes for wing loading in effect).

Could you run through that math for me?

As I see it, wing area equals span times (average) chord. Wing loading equals weight divided by wing area, so weight/(span*chord). Not sure I see how chord cancels out of that?

Certainly I agree that for a given wing area and wing loading, more span and less chord is better. 10 sqm has been the traditional benchmark wing area for a single seater, getting smaller with time. Ka6 and Cirrus are both about 12; Std Libelle, Discus, LS8, even PW5 about 10; Diana 2 is 8. If you could build a single-seater with 50m span and 200mm chord (and no more than 20 - 30 mm thickness) without it breaking then it would probably go pretty well in a straight line.

So span loading is a useful figure if you hold the wing loading constant.

But you can't just pick a span loading you like and then reduce or increase the chord to whatever you feel like. A single seater with 15m span with 500mm - 800mm average chord works. 200mm or 2000m would be ridiculous, assuming you want to fly in the speed ranges we fly gliders in. 200mm chord might be interesting if you didn't mind a 70 knot stall speed and 90 knots thermalling :-)

[[email protected]]

I worked some math out on page 15 of this PDF. The section is called drag.

http://spekje.snt.utwente.nl/~roeles/maccready.pdf

[Bruce Hoult]

On Thursday, February 2, 2017 at 11:33:07 AM UTC+3, wrote:
> I worked some math out on page 15 of this PDF. The section is called drag.
>
> http://spekje.snt.utwente.nl/~roeles/maccready.pdf

The requested URL /~roeles/maccready.pdf was not found on this server.

[[email protected]]

Whoops
Make that
http://spekje.snt.utwente.nl/~roel/maccready.pdf

[[email protected]]

Whoops
Make that
http://spekje.snt.utwente.nl/~roel/maccready.pdf

[Bruce Hoult]

On Thursday, February 2, 2017 at 11:33:07 AM UTC+3, wrote:
> I worked some math out on page 15 of this PDF. The section is called drag..
>
> http://spekje.snt.utwente.nl/~roeles/maccready.pdf

Ok, good. What exactly do you wish to point to there?

I see that in general there are a lot of approximations, assuming small angles etc. I didn't check if that always looks like a good simplification, but this did jump out at me:

"Using this formula we can calculate both CD0 and e if we know some data
about the best L/D point of the polar. Since at this point the induced drag
should equal the parasitic drag"

That is certainly wrong.

It's true that in practice where you are looking for a minimum of two different ways to lose, the minimum is likely to be at a point where they are roughly equal, but it's only very rough. The two things could easily be different by, say, a factor or two, or more.

What *is* true at the minimum is that the *derivatives* of the two things are equal in magnitude, and opposite in sign.

Take, for example, the (positive) minimum of 1/x + x^2 (which is something similar in form to induced plus form drag). They are equal when x = 1, and both halves are 1 (so the total is 2).

But the minimum is at x = 1/cubeRoot(2) ~= 0.793701. At this point 1/x is 1.26 and x^2 is 0.63. So in fact the "induced drag" is twice the "form drag" at the minimum.

As you'll know, the derivative of 1/x is -1/x^2, while the derivative of x^2 is 2x. So at x = 0.793701 the derivatives are -1.5874 and +1.5874 (cube root of 4) -- equal and opposite.

At the minimum of a sum, the *slopes* are equal (and opposite), not the *values*.

[[email protected]]

Thanks for the comments. I'll reply by email later on, as not to spoil the thread.

People were referring to the equations regarding drag,in turns .
Therefore I pointed to the drag formula in the pdf.

[Eric Greenwell[_4_]]

Bruce Hoult wrote on 2/1/2017 8:42 PM:
> On Thursday, February 2, 2017 at 5:12:27 AM UTC+3, Eric Greenwell wrote:
>> Chris Davison wrote on 2/1/2017 10:14 AM:
>>> A questions that I should know the answer to but don't...in a
>>> thermal, all things being equal, will a 15m glider and an 18m glider
>>> with the same wing loading climb at the same rate?
>>
>> I'm told thermal climb rate is related to "span loading" (weight/span),
>> while high speed performance is related to wing loading (weight/wing
>> area). In your example, the 18m glider will climb better.
>
> Told by who, I wonder? :-)

Aerodynamics people (Dan Somers and Greg Cole, I recall), and people
intent on handicapping a range of gliders.

>
> Span is important to minimize induced drag, but that's a waste of time unless you have enough wing area to give an acceptable coefficient of lift or AoA at desired circling speeds and radii.

The OP did specify "same wing loading", so we know they both have
"enough" area, even if the area isn't optimum for other reasons.

> There is probably an intermediate cruising speed range where the dominant factor is wing loading / wing area / wetted area / span*chord. At a guess that might be from midway between min sink and best L/D speeds out to maybe 1.4 or 1.5 times best L/D speed.
>
> At higher speed I'd have thought the dominant factor would be minimizing span*wing thickness, i.e. frontal area. That's what kills the 1960s 40:1 ships at high speed -- or newer short span ones such as the PW5.
>
The 18 m ship could choose to fly at a higher wing loading while
retaining a climb equal to the shorter span glider, then reap the
benefits of the higher wing loading the cruise.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications/download-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/Guide-to-transponders-in-sailplanes-2014A.pdf

[Jim[_33_]]

I have had a similar question, with a small difference, for many years.

My question is:

"Using only s single glider and changing only the max flying weight - adding ballast shot bags, whatever - will that glider give its pilot a greater potential thermal climb rate when heavier or lighter?"

I am aware that higher weight will alter airspeeds but that is not my curiosity - other than a higher weight will raise stall speed some - which may add difficulties for the heavier glider using very narrow thermals - turn radius varies as the square of true airspeed, etc.

[Tom Claffey[_2_]]

At 23:39 02 February 2017, Jim wrote:
>I have had a similar question, with a small difference, for many years.
>
>My question is:
>
>"Using only s single glider and changing only the max flying weight -
>addin=
>g ballast shot bags, whatever - will that glider give its pilot a greater
>p=
>otential thermal climb rate when heavier or lighter?"
>
>I am aware that higher weight will alter airspeeds but that is not my
>curio=
>sity - other than a higher weight will raise stall speed some - which may
>a=
>dd difficulties for the heavier glider using very narrow thermals - turn
>ra=
>dius varies as the square of true airspeed, etc.
>


For any glider increasing the weight will reduce it's climb rate.

[Bruce Hoult]

On Friday, February 3, 2017 at 11:15:04 AM UTC+3, Tom Claffey wrote:
> At 23:39 02 February 2017, Jim wrote:
> >I have had a similar question, with a small difference, for many years.
> >
> >My question is:
> >
> >"Using only s single glider and changing only the max flying weight -
> >addin=
> >g ballast shot bags, whatever - will that glider give its pilot a greater
> >p=
> >otential thermal climb rate when heavier or lighter?"
> >
> >I am aware that higher weight will alter airspeeds but that is not my
> >curio=
> >sity - other than a higher weight will raise stall speed some - which may
> >a=
> >dd difficulties for the heavier glider using very narrow thermals - turn
> >ra=
> >dius varies as the square of true airspeed, etc.
> >
>
>
> For any glider increasing the weight will reduce it's climb rate.

The concept is pretty simple :-)

If you double the weight of a glider you increase all the speeds, including the sink rate, by 40%. So maybe you go from 100 fpm sink to 140 fpm.

If the lift is strong enough that an unballasted glider climbs at 10 knots then the ballasted one will climb at 9.5 knots or so. Maybe worse. Maybe 9 knots. So 5% or 10% slower climb.

But then it gets to run 40% faster at the same glide angle.

[Tim Taylor]

You need to factor in the increased thermal speed and larger diameter circles. Unless the core of the thermal is large the climb rate is reduced significantly more than just the glide calculations predict. In the "real world" higher wing loading gives an advantage, but not as much as many think unless you are flying mostly on streets. In the mountains I often do better with a 9.5 to 10 pound wing loading because I can maneuver better and work small diameter thermals.

[Jim[_33_]]

My curiosity has been about the effect of just gross weight vs. wing loading on the

For example, let's stipulate a thermal providing a vertical force ( I avoid using newtons as the SI unit for force. I've never managed to get comfortable with it.) that would provide +5 kt lift to a glider with a gross weight of 800 lbs and a wing loading of 10 lbs / sqft.. I'm just making this stuff up. I am not trying to be realistic!

Now let's invent another glider with a wing loading of just 5 lbs / sqft. but with the same gross weight as the first glider.

Would the second glider, with a wing loading of just 5 lbs / sqft, get a better climb rate than the first glider since it appears it would need only half the lifting force per square foot of wing than would the first glider?

[Tim Taylor]

On Friday, February 3, 2017 at 10:19:00 AM UTC-7, Jim wrote:
> My curiosity has been about the effect of just gross weight vs. wing loading on the
>
> For example, let's stipulate a thermal providing a vertical force ( I avoid using newtons as the SI unit for force. I've never managed to get comfortable with it.) that would provide +5 kt lift to a glider with a gross weight of 800 lbs and a wing loading of 10 lbs / sqft.. I'm just making this stuff up. I am not trying to be realistic!
>
> Now let's invent another glider with a wing loading of just 5 lbs / sqft. but with the same gross weight as the first glider.
>
> Would the second glider, with a wing loading of just 5 lbs / sqft, get a better climb rate than the first glider since it appears it would need only half the lifting force per square foot of wing than would the first glider?

Unfortunately it is not that easy. The short answer is the lighter wing loading glider will climb better, just as the heavier will run better. The long answer is they won't fly at the same speed so the lighter wing loading glider has the advantage additionally of working a tighter core.

[Jim[_33_]]

Thank you Tim. I am beginning to understand it all.

JIm

[Mike the Strike]

On Friday, February 3, 2017 at 7:40:25 AM UTC-7, Tim Taylor wrote:
> You need to factor in the increased thermal speed and larger diameter circles. Unless the core of the thermal is large the climb rate is reduced significantly more than just the glide calculations predict. In the "real world" higher wing loading gives an advantage, but not as much as many think unless you are flying mostly on streets. In the mountains I often do better with a 9.5 to 10 pound wing loading because I can maneuver better and work small diameter thermals.

Exactly what we have found in Arizona - much depends on the thermal profile and especially the ability to stay in a strong, narrow thermal core.

Mike

[[email protected]]

On Sunday, February 5, 2017 at 3:24:58 AM UTC+11, Mike the Strike wrote:
> On Friday, February 3, 2017 at 7:40:25 AM UTC-7, Tim Taylor wrote:
> > You need to factor in the increased thermal speed and larger diameter circles. Unless the core of the thermal is large the climb rate is reduced significantly more than just the glide calculations predict. In the "real world" higher wing loading gives an advantage, but not as much as many think unless you are flying mostly on streets. In the mountains I often do better with a 9.5 to 10 pound wing loading because I can maneuver better and work small diameter thermals.
>
> Exactly what we have found in Arizona - much depends on the thermal profile and especially the ability to stay in a strong, narrow thermal core.
>
> Mike

I often feel like on the exceptionally hot and high Australian days, that it feels like I just can't fit in the thermals at high altitudes. Lighter aircraft don't seem to have the same trouble. My theory is that a thermals diameter doesn't vary substantially with height, however due to density altitude/TAS, my thermalling radius does vary substantially. Or at least that's my excuse.

Any thoughts on whether this is true, that the diameter of thermals remains constant at altitude, or widens slower than the circling radius considering TAS?

[Soartech]

On Friday, February 3, 2017 at 1:26:02 PM UTC-5, Jim wrote:
> Thank you Tim. I am beginning to understand it all.
>
> JIm

Those of us who flew hang gliders/paragliders already understand this relation between weight, area and efficency. Hang gliders have a lower sink rate and better glide than paragliders but the much larger area of PG allows them to slow down and turn very tight circles in lift so they can outclimb HG much of the time.

[Jim[_33_]]

Yes, I have enjoyed slower-flying thermal-working too. It's lots of fun.

My curiosity about wing loading and climb rate really is limited to non-thermalling, non-turning flight. I was wondering about the possible relationship of wing loading to lifting force. Likely an unrealistic circumstance in actual flying though. Just a curiosity.

[Tango Whisky]

Le lundi 13 février 2017 04:52:04 UTC+1, Jim a écritÂ*:
> Yes, I have enjoyed slower-flying thermal-working too. It's lots of fun.
>
> My curiosity about wing loading and climb rate really is limited to non-thermalling, non-turning flight. I was wondering about the possible relationship of wing loading to lifting force. Likely an unrealistic circumstance in actual flying though. Just a curiosity.

Well, on a good soaring day, about 70-80% of the flight is non-thermalling, non-turning flight.
And the lifting force always matches the weight of the glider, regardless of wing loading.

[Jim[_33_]]

>
> Well, on a good soaring day, about 70-80% of the flight is non-thermalling, non-turning flight.
> And the lifting force always matches the weight of the glider, regardless of wing loading.

Yes. I understand that. If the glider is not to accelerate downward the total "lifting force" equals the current gross weight (and drag vector too I guess) of the glider. My silly curiosity has been about exactly the point you make. Everything else being equal ( I know, never happens), does a wing that supports 10 lbs per square foot of wing area require the same TOTAL"lifting force" as a wing that supports 5 lbs per square foot of wing area - but has twice the wing area? IF this is the case it would suggest that the glider with half the wing loading but twice the wing area could be sustained by a smaller "lifting force".

This is just a curiosity. I don't think this has ever entered into my decision making during flight. Not that I understand that either.

[Bruce Hoult]

On Monday, February 13, 2017 at 8:36:35 PM UTC+3, Jim wrote:
> >
> > Well, on a good soaring day, about 70-80% of the flight is non-thermalling, non-turning flight.
> > And the lifting force always matches the weight of the glider, regardless of wing loading.
>
> Yes. I understand that. If the glider is not to accelerate downward the total "lifting force" equals the current gross weight (and drag vector too I guess) of the glider. My silly curiosity has been about exactly the point you make. Everything else being equal ( I know, never happens), does a wing that supports 10 lbs per square foot of wing area require the same TOTAL"lifting force" as a wing that supports 5 lbs per square foot of wing area - but has twice the wing area? IF this is the case it would suggest that the glider with half the wing loading but twice the wing area could be sustained by a smaller "lifting force".

They both need exactly the same total lifting force. The one with twice the wing area needs half the lifting force per square foot.

[Dan Marotta]

If the lifting force exactly matched the weight of the glider then, in
still air, wouldn't the glider not lose altitude? Or are you saying
that the sink rate of the glider is cause by drag?

On 2/13/2017 6:46 AM, Tango Whisky wrote:
> Le lundi 13 février 2017 04:52:04 UTC+1, Jim a écrit :
>> Yes, I have enjoyed slower-flying thermal-working too. It's lots of fun.
>>
>> My curiosity about wing loading and climb rate really is limited to non-thermalling, non-turning flight. I was wondering about the possible relationship of wing loading to lifting force. Likely an unrealistic circumstance in actual flying though. Just a curiosity.
> Well, on a good soaring day, about 70-80% of the flight is non-thermalling, non-turning flight.
> And the lifting force always matches the weight of the glider, regardless of wing loading.

--
Dan, 5J

[Martin Gregorie[_5_]]

On Mon, 13 Feb 2017 09:36:34 -0800, Jim wrote:

> Yes. I understand that. If the glider is not to accelerate downward
> the total "lifting force" equals the current gross weight (and drag
> vector too I guess) of the glider. My silly curiosity has been about
> exactly the point you make. Everything else being equal ( I know, never
> happens), does a wing that supports 10 lbs per square foot of wing area
> require the same TOTAL"lifting force" as a wing that supports 5 lbs per
> square foot of wing area - but has twice the wing area? IF this is the
> case it would suggest that the glider with half the wing loading but
> twice the wing area could be sustained by a smaller "lifting force".
>
Depends how you define 'lifting force'.

If you define it as the total lift generated by the wing, then it will
not vary with the wing area because it will always match the weight of
the glider.

If, OTOH , you define it as the lift generated by a square foot or square
meter of wing, then doubling the wing area will halve the 'lifting forge'
per unit of wing area because, again because the total lift generated by
the wing will match the glider's weight.

What does change as the wing area is varies are a number of factors that
contribute to the wing's total lift and drag, such as skin friction
(varies with wing area) and tip vortex drag (varies inversely with wing
span for a fixed wing area).

For a descriptive treatment, i.e. minimal numbers or equations, of this
and other topics I suggest you read:

Stick and Rudder - Wolfgang Langwiesche

or visit the av8n website, http://www.av8n.com/

Both are written to give a private pilot a better understanding of how
and aircraft flies and both are equally applicable to gliding.


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

[Martin Gregorie[_5_]]

On Mon, 13 Feb 2017 10:50:31 -0700, Dan Marotta wrote:

> If the lifting force exactly matched the weight of the glider then, in
> still air, wouldn't the glider not lose altitude? Or are you saying
> that the sink rate of the glider is cause by drag?
>
> On 2/13/2017 6:46 AM, Tango Whisky wrote:
>> Le lundi 13 février 2017 04:52:04 UTC+1, Jim a écrit :
>>> Yes, I have enjoyed slower-flying thermal-working too. It's lots of
>>> fun.
>>>
>>> My curiosity about wing loading and climb rate really is limited to
>>> non-thermalling, non-turning flight. I was wondering about the
>>> possible relationship of wing loading to lifting force. Likely an
>>> unrealistic circumstance in actual flying though. Just a curiosity.
>> Well, on a good soaring day, about 70-80% of the flight is
>> non-thermalling, non-turning flight.
>> And the lifting force always matches the weight of the glider,
>> regardless of wing loading.

Lift generated must equal the glider's weight. If it didn't, the rate of
sink would not be a constant relative to the air mass for a given trim
setting and airspeed.


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

[Bruce Hoult]

On Monday, February 13, 2017 at 8:50:39 PM UTC+3, Dan Marotta wrote:
> If the lifting force exactly matched the weight of the glider then, in
> still air, wouldn't the glider not lose altitude? Or are you saying
> that the sink rate of the glider is cause by drag?
>
> On 2/13/2017 6:46 AM, Tango Whisky wrote:
> > Le lundi 13 février 2017 04:52:04 UTC+1, Jim a écrit :
> >> Yes, I have enjoyed slower-flying thermal-working too. It's lots of fun.
> >>
> >> My curiosity about wing loading and climb rate really is limited to non-thermalling, non-turning flight. I was wondering about the possible relationship of wing loading to lifting force. Likely an unrealistic circumstance in actual flying though. Just a curiosity.
> > Well, on a good soaring day, about 70-80% of the flight is non-thermalling, non-turning flight.
> > And the lifting force always matches the weight of the glider, regardless of wing loading.

As I'm sure you know, lift = weight is exactly true for a powered aircraft in straight and level flight.

It's only an approximation for a glider, where in fact lift plus drag together exactly equal weight. But as the lift is typically 40 - 60 times the drag we usually take a shortcut and ignore that.

In a glider with airbrakes deployed and in a steady speed 45 degree dive lift and drag are equal and both 70.71% of the weight. But that's not how we fly when trying to maximize performance.

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

I think this is exactly what originally asked. Thus, equal weight gliders, the one with bigger wing area (reduced wing loading) can fly slower and gain altitude better in weaker thermals compared to the glider with a heavier wing loading.
Then again, you WANT wing loading in the case of a ridge where a heavier wing loading glider helps. This from a guy that has time on the PA ridges at max @9lbs in a ASW-20 A and C, vs. heavier 20 B's.
Bigger wing area also adds to surface drag which hurts performance. There is a reason the term "light wing floater" was coined.

[Dan Marotta]

That's what I was thinking. Ignore the small part of the sum. Thanks,
nice refresher!

On 2/13/2017 12:01 PM, Bruce Hoult wrote:
> On Monday, February 13, 2017 at 8:50:39 PM UTC+3, Dan Marotta wrote:
>> If the lifting force exactly matched the weight of the glider then, in
>> still air, wouldn't the glider not lose altitude? Or are you saying
>> that the sink rate of the glider is cause by drag?
>>
>> On 2/13/2017 6:46 AM, Tango Whisky wrote:
>>> Le lundi 13 février 2017 04:52:04 UTC+1, Jim a écrit :
>>>> Yes, I have enjoyed slower-flying thermal-working too. It's lots of fun.
>>>>
>>>> My curiosity about wing loading and climb rate really is limited to non-thermalling, non-turning flight. I was wondering about the possible relationship of wing loading to lifting force. Likely an unrealistic circumstance in actual flying though. Just a curiosity.
>>> Well, on a good soaring day, about 70-80% of the flight is non-thermalling, non-turning flight.
>>> And the lifting force always matches the weight of the glider, regardless of wing loading.
> As I'm sure you know, lift = weight is exactly true for a powered aircraft in straight and level flight.
>
> It's only an approximation for a glider, where in fact lift plus drag together exactly equal weight. But as the lift is typically 40 - 60 times the drag we usually take a shortcut and ignore that.
>
> In a glider with airbrakes deployed and in a steady speed 45 degree dive lift and drag are equal and both 70.71% of the weight. But that's not how we fly when trying to maximize performance.

--
Dan, 5J

[Bruce Hoult]

On Monday, February 13, 2017 at 10:16:11 PM UTC+3, Charlie M. (UH & 002 owner/pilot) wrote:
> I think this is exactly what originally asked. Thus, equal weight gliders, the one with bigger wing area (reduced wing loading) can fly slower and gain altitude better in weaker thermals compared to the glider with a heavier wing loading.

*Only* because at the slower speed it can turn tighter and the thermal might be stronger in the middle.

Note that low wing loading doesn't equate to low sink. Sink comes from the drag and modern construction gives low drag despite high wing loadings.

That classic floater the K8 has a min sink of 132 fpm at 32.4 knots with 4.48 lb/sq ft.
The 1-26 has min sink of 174 fpm (at a speed I couldn't find) with 4.38 lb/sq ft.

An LS8 has min sink of 116 fpm with 6.56 lb/sq ft (dry, 190lb pilot). ASW28 110 fpm. Diana claims 88.6 fpm despite a high wing loading.

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

Oh, I agree. I also noted that the increased wing area adds to drag. We stated the same thing in different ways.