Thin Airfoil and Climb Performance

[Krzysztof Kubrynski]

Some time ago there was a discussion about influence of (thin) airfoil on
climb performance of sailplane. I am not a regular reader of the group, so
my post is slightly delayed.
Influence of airfoil characteristics on climb performance and final
cross-country speed was the main objective studied during design of Diana-2
sailplane. The paper on this subject was presented at OSTIV Congress and
published in Technical Soaring. The paper can be download now from
http://www.dianasailplanes.com/Tech_Soar_KK.pdf
May be someone will find it interesting.
In my opinion there is nearly no room for further improvement of sailplane
performance measured by e.g. max. L/D. But there is a relatively large
space for improving final cross-country speed by better utilization of
thermals. Diana-2 was just an attempt to perform this.

Krzysztof Kubrynski

[sisu1a]

> In my opinion there is nearly no room for further improvement of sailplane
> performance measured by e.g. max. L/D.


Wow, how many times has THAT old line embarrassed someone in the past?
(rhetorical..)

Perhaps this may be true for CURRENT traditional materials and
established dogma, but besides Windward Performance (who now has the
DuckHawk turning from a 'paper airplane' to a flying machine) who
makes eintire gliders out of PREPREG carbon, you will only find an
occasional aileron or rudder made out of this VERY UNDERUTILIZED
spaceage material. Considering that prepregs have appx double the
strength of the traditional wet layup construction that just about
every composite glider is made with (including the lovely Dianna 2), I
see much room for improvement in ALL aspects of soaring performance
enhancement. And this is even with materials that have already been
discovered (but as mentioned, other than some fancy trim parts have
been studiously ignored by 'most' designers).

In case the significance of what double the strength to weight ratio
means when applied to sailplane structures is not grasped by someone
out there, it is this: The structural minimum just got that much
closer to the aerodynamic optimum. Personally, I see no end to
improvements since our materials will continue to advance, thus
continuing to push the all important structural minimum closer to that
(also ever advancing) theoretical aerodynamic optimum.

How about once carbon nanotube fabric is available, then in prepreg
form? Still no room for improvement then?

Paul Hanson

"Free your mind and your a$$ will follow"--George Clinton

[noel.wade]

Paul -

You're missing out on a key point: Changing materials to a lighter
structure does not change the aerodynamics of the wing.

It changes the wing-loading - but that's no different from adding or
removing water ballast. As long as the wing SHAPE remains the same, a
different weight/wing-loading simply shifts the polar. It doesn't
create an improvement.

Wing efficiency is affected by the shape of the airfoil, the wing
planform (and how the two add together to become a total 3-d package),
the smoothness of the skin/surface, the surface-area/skin drag, and
numerous other smaller factors.

Existing composite materials can be made to follow complex curves and
result in an extremely smooth surface, so changing to a fancier
material does nothing to improve the efficiency of the wing.

The reason that Pre-Preg and other fancy/costly exotic materials
aren't commonly in use is because they aren't NEEDED to achieve
aerodynamic optimums. Fancy materials are mostly used for
manufacturing reasons, to carry higher loads, to have more specific
stiffness in a particular load direction, etc. Aerodynamics doesn't
enter into the equation.

Small, incremental advances in overall performance have been made over
the last 20 years; but they are pretty tiny in comparison to the
performance jumps that were seen from the 50's to the late 70's (when
glide ratios doubled or tripled). We're down to the point where we're
fighting physics every step of the way in order to see any
improvements. And in order for theoretical gains to be realized in
actual flight, the tolerances are getting so tight that normal
manufacturing techniques cannot be applied. And with tolerances that
tight you also end up fighting the fact that the air gliders move
through is not sitting still. At some point the turbulence and
natural air movement disrupts the pristine theoretical predictions of
how the air will behave as the sailplane passes through it, rendering
supposed performance gains null (and in some cases causing an actual
performance penalty - see the part of the Diana 2 paper where they
talk about lift minimums in certain airfoils at high Cl).

Take care,

--Noel

[noel.wade]

P.S. Note that in the paper that they talk about little improvement
in basic airfoils or passive boundary layer control. They leave the
door open to performance improvements via active boundary layer
control methods (turbulators, Sinha's "de-turbulator" tape, etc). The
trick to active boundary layer control is in making it both reliable
and efficient over the wide speed band and aerodynamic conditions that
sailplanes fly.

[sisu1a]

On May 5, 9:23 am, "noel.wade" > wrote:
> Paul -
>
> You're missing out on a key point: Changing materials to a lighter
> structure does not change the aerodynamics of the wing.

I did not miss the original point, I just don't agree with it. Clearly
you miss mine though. If structure does not change the aerodynamics of
a wing, then why are modern hot ships still made of wood, or metal?
The fact of the matter is that the aerodynamic optimum will never
agree with the structural minimum, but the more that materials
advance, the closer to that optimum designers can get. It most
certainly does affect the areodynamics of a wing, so long as the wing
is designed specific to the materials it is made from.

> It changes the wing-loading - but that's no different from adding or
> removing water ballast. As long as the wing SHAPE remains the same, a
> different weight/wing-loading simply shifts the polar. It doesn't
> create an improvement.

Huh? Wing loading? Again, you are way off my point. Advances in
structure ALLOWS changes in shape, which most certainly can lead to
improvement. Any racing ship will have the ability to change it's wing
loading with ballast, but since we're on the subject of wing loading,
by using prepreg your dry weight can be significantly lower, thus
'possibly' allowing a wider range in wing loading and thus a ship
adaptable to a wider range of conditions.

> Wing efficiency is affected by the shape of the airfoil, the wing
> planform (and how the two add together to become a total 3-d package),
> the smoothness of the skin/surface, the surface-area/skin drag, and
> numerous other smaller factors.

Precisely. And by using prepregs a designer can go with a less
compromised foil since the material is so much stronger, not to
mention they have the ability to be smoother (and stay that way!),
much less affected by weather/heat (they are not room temp cured so
at normal runway temps are not even close to getting soft and you will
never be complaining about the dreaded 'spar hump' for that matter).
This all means nothing of course if the design blows...


> Existing composite materials can be made to follow complex curves and
> result in an extremely smooth surface, so changing to a fancier
> material does nothing to improve the efficiency of the wing.

As can prepregs, although it is a good bit more work. However
'fancier' materials allow the designer to make a wing that looks a lot
more like the airfoil they really wanted to use, instead of the one it
had to be mutated into to allow for the safe amount of structure.

> The reason that Pre-Preg and other fancy/costly exotic materials
> aren't commonly in use is because they aren't NEEDED to achieve
> aerodynamic optimums. Fancy materials are mostly used for
> manufacturing reasons, to carry higher loads, to have more specific
> stiffness in a particular load direction, etc. Aerodynamics doesn't
> enter into the equation.

Absolutely incorrect. The reason they are not used is because their
significance is not widely recognized enough for customers to expect
any different. Most big manufacturers have their entire infrastructure
built around traditional wet layup. In fact some of them even were the
original pioneers of these now widely utilized, current industry
standard materials and techniques. They are not about to fire all
their workers, sell off all their equipment and revamp their entire
existence around this "new" material, and anything short of that would
yield no results. It is a completely different ballpark, and there is
only one manufacturer who is setup for it, although it is now becoming
commonplace to be used in flight control surfaces for obvious
aerodynamic reasons (flutter?).

> Small, incremental advances in overall performance have been made over
> the last 20 years; but they are pretty tiny in comparison to the
> performance jumps that were seen from the 50's to the late 70's (when
> glide ratios doubled or tripled). We're down to the point where we're
> fighting physics every step of the way in order to see any
> improvements. And in order for theoretical gains to be realized in
> actual flight, the tolerances are getting so tight that normal
> manufacturing techniques cannot be applied. And with tolerances that
> tight you also end up fighting the fact that the air gliders move
> through is not sitting still. At some point the turbulence and
> natural air movement disrupts the pristine theoretical predictions of
> how the air will behave as the sailplane passes through it, rendering
> supposed performance gains null (and in some cases causing an actual
> performance penalty - see the part of the Diana 2 paper where they
> talk about lift minimums in certain airfoils at high Cl).

I agree that the performance leaps will probably never be as rapid as
the transition from wood/metal to glass period (which was essentially
due to "new fancy materials" allowing the structures to come much
closer to the aerodynamic optimums and thus allowing the new
aerodynamic advances of the time to enter the equation, leading to
more aerodynamic research...), and I am not saying otherwise. I AM
saying though, that L/D WILL continue to improve, especially at higher
speeds. The initial L/D's will be slowly creeping up while the polars
are getting flatter. As new materials come along, so do new design
possibilities that were once ruled out due to structural
considerations. Not to mention possible advances in aeroelastic skins
(morphing wing/fuse shapes) and as mentioned de-turbulation. I guess
it comes down to the simple fact that I just think we have more to
look forward to in the future than others may.

Paul Hanson

PS. In the late 50's, the world's leading aerodynamicists dismally
predicted L/D's around the 40 mark were thought to be "the plateau"
designers and ships would get stuck at. Luckily new designers came
along that hadn't heard the rules so were not bound by them...

[[email protected]]

On May 5, 10:26 am, sisu1a > wrote:
> On May 5, 9:23 am, "noel.wade" > wrote:
>
> > Paul -
>
> > You're missing out on a key point: Changing materials to a lighter
> > structure does not change the aerodynamics of the wing.
>
> I did not miss the original point, I just don't agree with it. Clearly
> you miss mine though. If structure does not change the aerodynamics of
> a wing, then why are modern hot ships still made of wood, or metal?
> The fact of the matter is that the aerodynamic optimum will never
> agree with the structural minimum, but the more that materials
> advance, the closer to that optimum designers can get. It most
> certainly does affect the areodynamics of a wing, so long as the wing
> is designed specific to the materials it is made from.
>
> > It changes the wing-loading - but that's no different from adding or
> > removing water ballast. As long as the wing SHAPE remains the same, a
> > different weight/wing-loading simply shifts the polar. It doesn't
> > create an improvement.
>
> Huh? Wing loading? Again, you are way off my point. Advances in
> structure ALLOWS changes in shape, which most certainly can lead to
> improvement. Any racing ship will have the ability to change it's wing
> loading with ballast, but since we're on the subject of wing loading,
> by using prepreg your dry weight can be significantly lower, thus
> 'possibly' allowing a wider range in wing loading and thus a ship
> adaptable to a wider range of conditions.
>
> > Wing efficiency is affected by the shape of the airfoil, the wing
> > planform (and how the two add together to become a total 3-d package),
> > the smoothness of the skin/surface, the surface-area/skin drag, and
> > numerous other smaller factors.
>
> Precisely. And by using prepregs a designer can go with a less
> compromised foil since the material is so much stronger, not to
> mention they have the ability to be smoother (and stay that way!),
> much less affected by weather/heat (they are not room temp cured so
> at normal runway temps are not even close to getting soft and you will
> never be complaining about the dreaded 'spar hump' for that matter).
> This all means nothing of course if the design blows...
>
> > Existing composite materials can be made to follow complex curves and
> > result in an extremely smooth surface, so changing to a fancier
> > material does nothing to improve the efficiency of the wing.
>
> As can prepregs, although it is a good bit more work. However
> 'fancier' materials allow the designer to make a wing that looks a lot
> more like the airfoil they really wanted to use, instead of the one it
> had to be mutated into to allow for the safe amount of structure.
>
> > The reason that Pre-Preg and other fancy/costly exotic materials
> > aren't commonly in use is because they aren't NEEDED to achieve
> > aerodynamic optimums. Fancy materials are mostly used for
> > manufacturing reasons, to carry higher loads, to have more specific
> > stiffness in a particular load direction, etc. Aerodynamics doesn't
> > enter into the equation.
>
> Absolutely incorrect. The reason they are not used is because their
> significance is not widely recognized enough for customers to expect
> any different. Most big manufacturers have their entire infrastructure
> built around traditional wet layup. In fact some of them even were the
> original pioneers of these now widely utilized, current industry
> standard materials and techniques. They are not about to fire all
> their workers, sell off all their equipment and revamp their entire
> existence around this "new" material, and anything short of that would
> yield no results. It is a completely different ballpark, and there is
> only one manufacturer who is setup for it, although it is now becoming
> commonplace to be used in flight control surfaces for obvious
> aerodynamic reasons (flutter?).
>
> > Small, incremental advances in overall performance have been made over
> > the last 20 years; but they are pretty tiny in comparison to the
> > performance jumps that were seen from the 50's to the late 70's (when
> > glide ratios doubled or tripled). We're down to the point where we're
> > fighting physics every step of the way in order to see any
> > improvements. And in order for theoretical gains to be realized in
> > actual flight, the tolerances are getting so tight that normal
> > manufacturing techniques cannot be applied. And with tolerances that
> > tight you also end up fighting the fact that the air gliders move
> > through is not sitting still. At some point the turbulence and
> > natural air movement disrupts the pristine theoretical predictions of
> > how the air will behave as the sailplane passes through it, rendering
> > supposed performance gains null (and in some cases causing an actual
> > performance penalty - see the part of the Diana 2 paper where they
> > talk about lift minimums in certain airfoils at high Cl).
>
> I agree that the performance leaps will probably never be as rapid as
> the transition from wood/metal to glass period (which was essentially
> due to "new fancy materials" allowing the structures to come much
> closer to the aerodynamic optimums and thus allowing the new
> aerodynamic advances of the time to enter the equation, leading to
> more aerodynamic research...), and I am not saying otherwise. I AM
> saying though, that L/D WILL continue to improve, especially at higher
> speeds. The initial L/D's will be slowly creeping up while the polars
> are getting flatter. As new materials come along, so do new design
> possibilities that were once ruled out due to structural
> considerations. Not to mention possible advances in aeroelastic skins
> (morphing wing/fuse shapes) and as mentioned de-turbulation. I guess
> it comes down to the simple fact that I just think we have more to
> look forward to in the future than others may.
>
> Paul Hanson
>
> PS. In the late 50's, the world's leading aerodynamicists dismally
> predicted L/D's around the 40 mark were thought to be "the plateau"
> designers and ships would get stuck at. Luckily new designers came
> along that hadn't heard the rules so were not bound by them...

Paul,

You have some nerve.....when Mr. Kubrynski is talking most of people
familiar with his work are listening....well, maybe you need to become
aerodynamicist and prove us all wrong....the field is wide open.

Jacek
Pasco, WA

[Bob Whelan[_2_]]

sisu1a wrote:
> On May 5, 9:23 am, "noel.wade" > wrote:
>> Paul -
>>
>> You're missing out on a key point: Changing materials to a lighter
>> structure does not change the aerodynamics of the wing.
>
> I did not miss the original point, I just don't agree with it.

<Point/counterpoint snipped...>

Perhaps it may be useful to imagine using the material 'Unobtainium' to
design sailplanes having zero structural restraints/considerations (e.g.
infinitely thin airfoils, tailbooms, vertical stabs, whatever...)
influencing its aerodynamics...in other words, imagining 'the perfect
aerodynamics' designed to extract soarable energy from the atmosphere
while still enclosing a pilot.

Such a plane will probably be instantly recognizable to our eyes today
as a 'sailplane'...simply because the design will still have to deal
with physics...but my money is on it looking 'different' too. Maybe the
Bruce Carmichaels and Al Bowers of the world already have such ship in
their back pockets waiting for the material to arrive! (Remember that
'wonderfoil' designed by [I think it was] someone at Douglas or Boeing
with startlingly high 2D L/D values for its time [late '70's/early
'80's?]...but which couldn't be built for lack of Unobtainium?)

Regards,
Bob W.

[Bob Kuykendall]

On May 5, 8:58*am, sisu1a > wrote:
> Considering that prepregs have appx double the
> strength of the traditional wet layup construction...

To the extent that that is true, it's also largely irrlevant to glider
design. The reason we use carbon has much more to do with its
stiffness than its strength. And prepregs offer only a rather modest
stiffness/weight or stiffness/volume advantage over conventional
vacuum-bagged carbon. However, they usually require the use of a high-
temperature, high-pressure autoclave, and also specially-made high-
temperature molds to go with it. Tooling like that can be quite
expensive to buy and operate, and is quite difficult to amortize in
the very marginal economics of sailplane development and manufacture.

Thanks, Bob K.
http://www.hpaircraft.com/hp-24

[Andy[_1_]]

On May 5, 9:23*am, "noel.wade" > wrote:

>Existing composite materials can be made to follow complex curves and
>result in an extremely smooth surface, so changing to a fancier
>material does nothing to improve the efficiency of the wing.

Maybe someone will come up with an affordable combination of new
materials and new processes that will give us sailplanes that keep the
complex curves intended by the designer for more than a few months
after delivery.

Andy

[sisu1a]

> Such a plane will probably be instantly recognizable to our eyes
today
> as a 'sailplane'...simply because the design will still have to deal
> with physics...but my money is on it looking 'different' too. Maybe the
> Bruce Carmichaels and Al Bowers of the world already have such ship in
> their back pockets waiting for the material to arrive! (Remember that
> 'wonderfoil' designed by [I think it was] someone at Douglas or Boeing
> with startlingly high 2D L/D values for its time [late '70's/early
> '80's?]...but which couldn't be built for lack of Unobtainium?)
>
> Regards,
> Bob W.

Thanks Bob, perhaps your clarifying and endorsing of my point will
hold more water than my untrained/unprofessional/non-aerodynamicist
opinion will (Bob Whelen IS an aerodymicist as well as a published
author for those who don't know). In quite typical fashion, your post
cuts right to a point that was attempted but with far less clutter.

Jacek, relax. I'm not knocking Polish gliders or aerodynamics FWIW, I
love Diana 2, and own an SZD-59 that I'm quite happy with. I'm just
saying I think there is more hope on the horizon than predicted, thats
all. We ALL have things to look forward to, it's a good thing.
Mebelieves the Dianna 2 represents the plateau for traditional wet
layup (or very very close to it at least) and is a wonderful machine.
My drool has had to be wiped off of the wings of the Diana 2 at the
convention on more than one occasion. Once we do have "Unobtanium"
though, there will be better ships yet! I'm sure the Pols' will be in
on it too! ; )

With Respect,
Paul Hanson

[Eric Greenwell]

sisu1a wrote:

> If structure does not change the aerodynamics of
> a wing, then why are modern hot ships still made of wood, or metal?

When the shift from wood and metal to fiberglass occurred, a huge factor
was cost: it was much cheaper to build a glider to the tolerances
required in molded fiberglass than the other materials, and it retained
the shape better. At that time, you could build a lighter aluminum
glider of the same performance, but it was a constant effort to keep the
airfoil correct. I don't know if this is still true for carbon fiber
versus aluminum; regardless, I think the cost would still favor the
molded construction.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[noel.wade]

Paul -

I don't argue that there isn't room for improvement and that the newer
materials have benefits.

But the bottom line is that the increases in L/D and *aerodynamic
performance* aren't likely to change by large amonths. And the new
materials have little or no effect on the aerodynamic performance or
the shape of the wings.

With all due respect (I'm not trying to be antagonistic), please read
Fred Thomas' "Fundamentals of Sailplane Design" book or go study
aerodynamics before trying to lecture about the subject.

--Noel

[sisu1a]

> When the shift from wood and metal to fiberglass occurred, a huge factor
> was cost: it was much cheaper to build a glider to the tolerances
> required in molded fiberglass than the other materials, and it retained
> the shape better. At that time, you could build a lighter aluminum
> glider of the same performance, but it was a constant effort to keep the
> airfoil correct. I don't know if this is still true for carbon fiber
> versus aluminum; regardless, I think the cost would still favor the
> molded construction.

No arguments here! Still a case for material advances improving
sailplanes (by making laminar capable wings affordable and
maintainable), but still a poor point for me to have tried to use to
advance my hypothisis for current improvements...you got me.

> But the bottom line is that the increases in L/D and *aerodynamic
> performance* aren't likely to change by large amonths.

I don't think I quantified the amount, just stated that many have said
"it wont get better than X amount" and have been proven wrong as
aerodynamics AND materials improve.

>And the new materials have little or no effect on the aerodynamic performance or
> the shape of the wings.

Now we really part ways. I was only citing that even currently
available materials offer more room for improvement, but I'm certainly
not limiting my thoughts on this to prepreg carbon. Do you not think
that once OTHER materials are advanced enough to have a super-smooth
uber-laminar wing that can change in airfoil/incidence/planform/etc
while in flight (like a bird's wing. but much slicker) will not yield
significant performance improvements? We do not yet have the materials
to construct such a thing, but when (if?) the "Unobtanium" to
construct such a wing comes about I think there will be a major leap
in performance capabilities, but perhaps you do not see it this way.

> With all due respect (I'm not trying to be antagonistic), please read
> Fred Thomas' "Fundamentals of Sailplane Design" book or go study
> aerodynamics before trying to lecture about the subject.

Lecturing? Hardly. (not feeling antagonized ; ) I simply felt the need
to counterpoint some things from my post you clearly misinterpreted
(equating strength/weight ratio of construction with wing loading for
example). I appreciate your endorsement of Fred Thomas' book, and I
will continue to read my copy. I do not profess to be an
aerodynamicist and my opinions are mostly based on intuition, which
leaves much room for learning I am open to. My original point was
actually that the "this is all we have to look forward to" type
statement are words that thankfully have been eaten many times over,
and I think (hope?) they will have to be eaten again (also pointing
out that they can 'possibly' eaten sooner than thought using current
materials, but not that it would be practical to do...).

Is this discussion group not for the exchange of ideas and a place to
learn? I have no problem being wrong, as I all too often am. I however
do not discourage anyone from posting about things they are truly
interested in, whether they have a degree in that subject or not.
Counter to that school of thought and historically speaking, many very
important discoveries were made by people that luckily were ignorant
to the "facts" that something was impossible so they dared to leap.

Paul Hanson

[sisu1a]

> But the bottom line is that the increases in L/D and *aerodynamic
> performance* aren't likely to change by large amonths. And the new
> materials have little or no effect on the aerodynamic performance or
> the shape of the wings.

Nasa doesn't seem to agree with you either: http://www.gizmag.com/go/2242/picture/3073/
(there are links to the rest Aero Elastic Wing article along with more
pics)
Perhaps they should read Fred Thomas' book and get over
themselves! ; )

In Jest,
Paul

[[email protected]]

On May 5, 3:28*pm, sisu1a > wrote:
> > But the bottom line is that the increases in L/D and *aerodynamic
> > performance* aren't likely to change by large amonths. *And the new
> > materials have little or no effect on the aerodynamic performance or
> > the shape of the wings.
>
> Nasa doesn't seem to agree with you either:http://www.gizmag.com/go/2242/picture/3073/
> (there are links to the rest Aero Elastic Wing article along with more
> pics)
> Perhaps they should read Fred Thomas' book and get over
> themselves! *; )
>
> In Jest,
> Paul

Just for the 'what if' pile..... What if a new material becomes
available that would allow a true variable airfoil / camber wing to be
built. (like the Aero Elastic Wing on steroids) Not just the last 10%
or so of the chord, but truly changing the airfoil in flight to
whatever is best suited to the immediate circumstances? Yes, this is
JUST a fantasy, but so was aviation in general 105 years ago.

[Frank Whiteley]

On May 5, 5:04 pm, wrote:
> On May 5, 3:28 pm, sisu1a > wrote:
>
> > > But the bottom line is that the increases in L/D and *aerodynamic
> > > performance* aren't likely to change by large amonths. And the new
> > > materials have little or no effect on the aerodynamic performance or
> > > the shape of the wings.
>
> > Nasa doesn't seem to agree with you either:http://www.gizmag.com/go/2242/picture/3073/
> > (there are links to the rest Aero Elastic Wing article along with more
> > pics)
> > Perhaps they should read Fred Thomas' book and get over
> > themselves! ; )
>
> > In Jest,
> > Paul
>
> Just for the 'what if' pile..... What if a new material becomes
> available that would allow a true variable airfoil / camber wing to be
> built. (like the Aero Elastic Wing on steroids) Not just the last 10%
> or so of the chord, but truly changing the airfoil in flight to
> whatever is best suited to the immediate circumstances? Yes, this is
> JUST a fantasy, but so was aviation in general 105 years ago.

How about a passive nano-unobtanium surface that smoothed and
roughened at different speeds/loadings to prevent flow separation,
along with the airfoil elasticity?

Frank W

[[email protected]]

On May 5, 4:09*pm, Frank Whiteley > wrote:
> On May 5, 5:04 pm, wrote:
>
>
>
>
>
> > On May 5, 3:28 pm, sisu1a > wrote:
>
> > > > But the bottom line is that the increases in L/D and *aerodynamic
> > > > performance* aren't likely to change by large amonths. *And the new
> > > > materials have little or no effect on the aerodynamic performance or
> > > > the shape of the wings.
>
> > > Nasa doesn't seem to agree with you either:http://www.gizmag.com/go/2242/picture/3073/
> > > (there are links to the rest Aero Elastic Wing article along with more
> > > pics)
> > > Perhaps they should read Fred Thomas' book and get over
> > > themselves! *; )
>
> > > In Jest,
> > > Paul
>
> > Just for the 'what if' pile..... * What if a new material becomes
> > available that would allow a true variable airfoil / camber wing to be
> > built. (like the Aero Elastic Wing on steroids) Not just the last 10%
> > or so of the chord, but truly changing the airfoil in flight to
> > whatever is best suited to the immediate circumstances? *Yes, this is
> > JUST a fantasy, but so was aviation in general 105 years ago.
>
> How about a passive nano-unobtanium surface that smoothed and
> roughened at different speeds/loadings to prevent flow separation,
> along with the airfoil elasticity?
>
> Frank W- Hide quoted text -
>
> - Show quoted text -

YES! I'll buy one as soon as I'm not the weak link in my Speed
Astir's performance! Oh... never mind.

[noel.wade]

> > How about a passive nano-unobtanium surface that smoothed and
> > roughened at different speeds/loadings to prevent flow separation,
> > along with the airfoil elasticity?

Hey hey, I *did* say "passive boundary layer control"!! ;-)

Lemme try to be clearer, and not as abrasive as perhaps I came across
earlier:

Aerodynamicists have gotten really good at figuring out optimum static
shapes of airfoils and 3d wings for a desired "mission" or set of
aerodynamic circumstances.

Airfoil effectivness and pressure distributions are affected by the
precision and smoothness of the external shape - and newer materials
don't bring anything to the table that fiberglass doesn't already
provide.

Weight, in and of itself, doesn't play a part in the actual efficiency
of a wing to extract energy / lift from the stream of air flowing
around it; and weight savings are what things like pre-preg are
generally good for right now (you might say "stiffness" - but you can
usually get an equally stiff part with a much heavier layup of
traditional fiberglass with a good core material; so in the end it
goes back to being a weight issue).

Elastic / flexible materials have already made an appearance before,
at least as coverings over hinges to improve airflow (Speed Astir
flaps, anyone?)... But to get a marked increase in glide efficiency
over an entire flight, things like this are going to have to be able
to react and adapt quite quickly to a wide variety of aerodynamic
situations. Look at the Sinha "De-Turbulator" tape: At very specific
speeds with very specific airflows it is able to momentarily provide a
large boost to the glide ratio/efficiency of a wing. But it doesn't
(yet) appear to be capable of adapting to different airflows and
different flight regimes - so in the end if may not provide a huge
performance boost to an overall flight. Additionally, it has not been
proven that the boosted performance is a sustainable / stable flight
condition - it might just be a momentary / transitionary gain that
cannot be maintained for long enough to make a meaningful difference
during a flight.

When it comes to physics, we have pretty much mathematically solved
the equations to provide the most efficient wing shape for any single
flight condition. We can minimize drag or maximize lift or pick a
middle-point that best matches our desires at that precise moment. An
adaptable wing doesn't help in a static situation (i.e. constant
airspeed, constant angle of attack, no-wind, calm-air, straight-line
best-glide. That's theoretically what we mean when we talk about
"Best L/D"). You can only get as good as you can get with the optimal
wing-shape for that one situation.

Furthermore, there's no getting around the fact that an actual
aircraft flight is a chaotic and ever-changing blend of different
conditions. For an aircraft to fly well overall, it needs to be a
compromise that can work reasonably under all of the disparate
conditions. And with current technology and materials (no matter how
exotic), there's no way to make a wing that can dynamically optimize
its shape in-flight and in reaction to all of the various conditions.
I look forward to the day when such technology exists; but I might
well be dead by that point (and I'm only 30 right now - but even as an
optimistic technology professional I just don't see it being a near-
term possibility).

Take care,

--Noel

[Shawn[_5_]]

noel.wade wrote:

snip


> Furthermore, there's no getting around the fact that an actual
> aircraft flight is a chaotic and ever-changing blend of different
> conditions. For an aircraft to fly well overall, it needs to be a
> compromise that can work reasonably under all of the disparate
> conditions. And with current technology and materials (no matter how
> exotic), there's no way to make a wing that can dynamically optimize
> its shape in-flight and in reaction to all of the various conditions.
> I look forward to the day when such technology exists; but I might
> well be dead by that point (and I'm only 30 right now - but even as an
> optimistic technology professional I just don't see it being a near-
> term possibility).
>
> Take care,

Makes me think of adaptive optics used to correct for atmospheric
turbulence degrading the image generated by large telescopes. The
medium the telescope is adapting to is the same, so I imagine the time
scale is similar to what an adaptive surface of a sailplane would need.
Could be kinda heavy equipping the wing with all those actuators though.
:-o

Shawn

[Sarah Anderson[_2_]]

Maybe the time scale doesn't have to be *that* fast. Simply scale up "eagle cam"'s aerial
virtuosity

http://animal.discovery.com/convergence/spyonthewild/birdtech/birdtech.html?ct=1329.15073148073

to NASA's
http://www.nasa.gov/centers/dryden/news/FactSheets/FS-061-DFRC.html

It would be interesting to hear if this idea went any further. And fun to imagine it's use
in soaring.

--Sarah


Shawn wrote:
snip
>
> Makes me think of adaptive optics used to correct for atmospheric
> turbulence degrading the image generated by large telescopes. The
> medium the telescope is adapting to is the same, so I imagine the time
> scale is similar to what an adaptive surface of a sailplane would need.
> Could be kinda heavy equipping the wing with all those actuators though.
> :-o
>
> Shawn

[Krzysztof Kubrynski]

sisu1a wrote:

>
>> In my opinion there is nearly no room for further improvement of
>> sailplane performance measured by e.g. max. L/D.
>
>
> Wow, how many times has THAT old line embarrassed someone in the past?
> (rhetorical..)
>
> Perhaps this may be true for CURRENT traditional materials and
> established dogma, but besides Windward Performance (who now has the
> DuckHawk turning from a 'paper airplane' to a flying machine) who
> makes eintire gliders out of PREPREG carbon, you will only find an
> occasional aileron or rudder made out of this VERY UNDERUTILIZED
> spaceage material. Considering that prepregs have appx double the
> strength of the traditional wet layup construction that just about
> every composite glider is made with (including the lovely Dianna 2), I
> see much room for improvement in ALL aspects of soaring performance
> enhancement. And this is even with materials that have already been
> discovered (but as mentioned, other than some fancy trim parts have
> been studiously ignored by 'most' designers).
>
> In case the significance of what double the strength to weight ratio
> means when applied to sailplane structures is not grasped by someone
> out there, it is this: The structural minimum just got that much
> closer to the aerodynamic optimum. Personally, I see no end to
> improvements since our materials will continue to advance, thus
> continuing to push the all important structural minimum closer to that
> (also ever advancing) theoretical aerodynamic optimum.
>
> How about once carbon nanotube fabric is available, then in prepreg
> form? Still no room for improvement then?
>
> Paul Hanson
>
> "Free your mind and your a$$ will follow"--George Clinton


I wrote ... that in my opinion there is nearly no room for further
improvement of sailplane performance measured by e.g. max. L/D having in
mind real life. All know that there it is possible to decrease drag and
increase L/D by active boundary layer control (e.g. suction or, more
interesting, active devices for fluctuations damping). Such solutions are
possible, but at least in the next 30 years I do not expect to see
sailplanes utilizing such technology. Such situation is because of: costs,
complexity and inconvenience in daily use.
We can imagine soaring competitions as F1 racing: new sailplane every two
contests, budget of a few hundred M$, many people in service... I am sure
that L/D ratio over 100 could be reached in less than two years. But it
will never happen. Even simpler solutions (but costly) as Eta or Sigma
seams to be impractical... So we must live in the real world.
Better materials could improve slightly characteristics (applying thinner
airfoils) - but at higher lift coefficients we can have problems. Adaptive
wings (especially near the leading edge) with elastic skin (or applying
smart materials) can help - and I am sure such solution will be utilized in
a relatively short period (I am also interested in this). But high speed
drag of current airfoils (having about 80% extend of laminar flow) leads
really to nearly no room for improvement - smooth flat plate at zero angle
of attack have usually lager drag. Reducing cockpit dimensions is an
acceptable solution in F1 cars but not in sailplanes - most pilots prefere
comfort.
On the other hand we can examine a large collection of real flight logs in
order to find correlations: mean_net_climb_in_thermals -
cross_country_speed. Result is very interesting. Diagrams, such as those
presented in my paper - extracted from Diana-2 flight logs, but performed
for other sailplanes show that results for different, but modern high
performance sailplanes, are very similar. Cross-country speed of open class
sailplanes are very similar to that of racing class sailplanes (slightly
better in lower average_net_climb and slightly worse in larger
average_net_climb. Of course all know, that longer wings leads to better
results at the same thermal conditions. I am sure such result is due to
better utilization of thermals by longer sailplanes - so at the same
thermal conditions they have higher net climb rate. So this is the most
convenient way to improve final cross-country performance. Of course
aerodynamic design should be performed as good as possible - and I tried to
do that in the case of Diana-2. I am sure, that it is still possible to
improve aerodynamics of Diana-2, but we must remember, that only new wing
was designed/manufactured. All other elements are nearly exactly the same
as in Diana-1 - and they are rather incorrect in respect to aerodynamics.
Really I am not fully satisfied with Diana-2 aerodynamics and I am sure the
next design should be (much) better. But much better can be measured by
3-4% of the drag and much higher costs.

Krzysztof