52/1 Performance in a 15M ship at half the weight.

On Feb 27, 6:00*pm, Frank wrote:
Soaring magazine should be leading the charge here, with
photos of the factory floor and interviews with the builder, but
instead it seems to be ignoring the whole thing.

My own high-performance carbon fiber sailplane project got coverage in
the national soaring press last year.

In Canada:

http://www.sac.ca/index.php?option=c... 398&Itemid=88

Thanks, Bob K.
www.hpaircraft.com

wrote:

It would seem that the Duckhawk would have more international appeal
as a Standard class (15m no flaps) ship - wonder how it would perform
without flaps?

It sure wouldn't need that 200 knot Vne, would it? Flaps are essential
to get the wide speed range that makes the the 200 knot Vne useful. My
understanding is the airfoil is optimized for climbing and very high
speed flight.

--
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

On Feb 27, 8:55*pm, Eric Greenwell wrote:

My understanding is the airfoil is optimized for climbing and very high
speed flight.

Eric, that kinda stretches the meaning of the word "optimize" a bit.

Thanks, Bob K.

Bob Kuykendall wrote:
On Feb 27, 8:55 pm, Eric Greenwell wrote:

My understanding is the airfoil is optimized for climbing and very high
speed flight.

Eric, that kinda stretches the meaning of the word "optimize" a bit.

Thanks, Bob K.


It is an optimized compromise.

If you design for high Clmax and stall at high alpha (to give good climb
performance) and very low drag at the high speed end, without worrying
about L/D ratio in the middle, then that fills Eric's statement
definition. Doing it is another matter........

At 06:54 28 February 2009, Greg Arnold wrote:
Bob Kuykendall wrote:
On Feb 27, 8:55 pm, Eric Greenwell wrote:

My understanding is the airfoil is optimized for climbing and very
high
speed flight.

Eric, that kinda stretches the meaning of the word "optimize" a bit.

Thanks, Bob K.


It is an optimized compromise.

The DuckHawk wing IS optimised for high speed and low speed flight. A
tremendous amount of effort went into creating a wing that would work
well at slow speeds with the flaps down, and also work very well at
high speeds with flaps up.

Additionally, Greg did a lot of analysis of how to maximize the cross
country speed. To simplify greatly, the result was to climb really
fast and run really fast. That actually simplified things a little
with the flaps. Basically, one would fly with flaps down while
climbing and then transition directly to flaps up and run fast to find
the next thermal. Intermediate speeds and flap positions were not
that necessary. So, the flaps up/high speed case and the flaps down/
low speed point were optimized. Of course, in the real world, there
might be times when you don't want to do exactly what the theory says,
so last I heard, the flaps will just have 3 positions: up, zero, and
down (a landing position was discussed, but I don't know if it is
incorporated). Quite a lot of effort was also made to give a fairly
wide performance range to each position. So, while it is optimized
for run and climb, there won't be a big hole in the middle of the
polar.

Doug T.

On Feb 28, 6:46*am, Bob Kuykendall wrote:
On Feb 27, 8:55*pm, Eric Greenwell wrote:

My understanding is the airfoil is optimized for climbing and very high
speed flight.

Eric, that kinda stretches the meaning of the word "optimize" a bit.

Thanks, Bob K.

I just checked last months issue of SOARING. There was an article on the
ARCUS - a sailplane that has yet to fly.

I've also recently been reading back thru old issue of SOARING from our club
library. In the late '70s and early '80s it appears every issue has an
article on the latest homebuilt news. Nearly all of this is about
sailplanes that had yet to be built or fly.

I think the article should have been published by SOARING.

John

On Feb 28, 6:54*am, wrote:
The DuckHawk wing IS optimised for high speed and low speed flight. *A
tremendous amount of effort went into creating a wing that would work
well at slow speeds with the flaps down, and also work very well at
high speeds with flaps up.

Additionally, Greg did a lot of analysis of how to maximize the cross
country speed. *To simplify greatly, the result was to climb really
fast and run really fast. *That actually simplified things a little
with the flaps. *Basically, one would fly with flaps down while
climbing and then transition directly to flaps up and run fast to find
the next thermal. *Intermediate speeds and flap positions were not
that necessary. * So, the flaps up/high speed case and the flaps down/
low speed point were optimized. *Of course, in the real world, there
might be times when you don't want to do exactly what the theory says,
so last I heard, the flaps will just have 3 positions: up, zero, and
down (a landing position was discussed, but I don't know if it is
incorporated). *Quite a lot of effort was also made to give a fairly
wide performance range to each position. *So, while it is optimized
for run and climb, there won't be a big hole in the middle of the
polar.

It seem they are simply taking the historical trend to the next
logical step. For 20 years or more now designers have be trying to
optimize around a design point that represents typical cruise speed,
rather than trying to increase best L/D, for instance. With advances
in materials you can make a lighter, smaller wetted area glider that
has less form drag and therefore pushes the "knee" in the polar to a
higher speed. If you can find some magic in the airfoil/flap design
then maybe you can push the overall design even further along these
same lines, but that is harder to do I think. For a current generation
15M gilders the knee is around 90kts.

Keep in mind that the polar of any glider is a continuous curve and
the designer will still optimize flap settings, etc. to match a
specific climb rate (and McCready setting) that will get you to a
specific cruise speed that is optimal to maximize cross-country
speed. If you pick a planform/airfoil/flap arrangement to suit a
particularly high cruise speed you are implicitly designing the glider
around stronger soaring conditions. Dick Schreder tried this in 1969
with the HP-15, (although without benefit of materials/construction
innovations at play with the Duckhawk).

When people say that the Duckhawk is "optimized" for very high speed
cruise I immediately wonder how high? I can see somewhat higher speeds
(maybe 100-110kts) driven by the construction innovations. I can maybe
see going a little higher to optimize around stronger conditions - but
you need to be careful about going too far and having a glider that
does poorly in weak weather, a la HP-15. I don't see the point in
setting things up for ultra-high cruise speeds unless you want a
glider that is optimized around wave record flying - but that was
another thread...

I am intrigued - can't wait to see it fly.

9B

For those of you who haven't been around forever, only two HP-15s were
built. The original design called for a 15 meter wing with an extreme aspect
ratio of 33 to 1. As a result of Dick Schreder placing 65th in the US
Nationals both '15s have been re-winged. The prototype now has a HP-16 wing
and the other one sports a HP-18 wing.
The HP-15 fuselage is very similar to the HP-14 except that the 1-inch
square-steel-tubing cockpit framing has been replaced by aluminum tubing.
The cockpit is large enough to provide adequate room for a 6' 4" pilot.

Wayne

HP-14 "6F"

http://www.soaridaho.com/Schreder

wrote in message
...
On Feb 28, 6:54 am, wrote:


.... Snip...

When people say that the Duckhawk is "optimized" for very high speed
cruise I immediately wonder how high? I can see somewhat higher speeds
(maybe 100-110kts) driven by the construction innovations. I can maybe
see going a little higher to optimize around stronger conditions - but
you need to be careful about going too far and having a glider that
does poorly in weak weather, a la HP-15. I don't see the point in
setting things up for ultra-high cruise speeds unless you want a
glider that is optimized around wave record flying - but that was
another thread...

I am intrigued - can't wait to see it fly.

9B

On Feb 25, 5:11*pm, SF wrote:
I wrote the following article and submitted it to Soaring for
publication because it was something I was interested in and I thought
others would be too. *It was rejected because the subject matter
wasn't suitable for soaring. *Greg Cole is doing something
extraordinary at Windward Performance and I feel that Soaring is doing
all of us a disservice by not putting content like this in the
magazine.
******************
My Trip To Windward Performance

At the 2008 SSA convention in Albuquerque, NM I attended Greg Cole’s
presentation on the new 15M sailplane he’s building called the
DuckHawk. * The presentation piqued my interest and I managed to
retain the knowledge that the DuckHawk is an American name for
Peregrine Falcon, the fastest moving creature on earth, and that Greg
Cole’s Sailplane factory is in Bend Oregon.

* * * * Other details stuck with me too, like an L/D of 52/1. *Minimum Sink
is 111 fpm; empty weight is 300 Lbs, and this Hawk has an aspect ratio
of 30.0:1. *The 200 Kt. VNE would make for one hot smoking final
glide.

When business took me to Portland, Oregon last Fall, I realized I’d be
fairly close to Bend. A few phone calls got me an appointment with
Greg Cole, president and creative force behind Windward Performance
Ltd, DuckHawk’s creator as well as builders of 11M span SparrowHawk.

Greg Cole has been building and flying his designs since he was a
kid. *He has a BSME from the University of North Dakota, and a MSAE
from Notre Dame. *He holds a US patent on propeller design. *His work
experience includes the McCauley Propeller Company, Columbia Aircraft
Company (chief Engineer), Cirrus Design, Lancair, and Adam Aircraft.
He has made significant Design contributions to several different
aircraft including: the Lancair Legacy, the Lancair Evolution, The
Columbia 300, The Chanute, The A500, and of course the SparrowHawk
which is the only U.S. designed sailplane to hold a world record in 30
years. *The Columbia 300 bears mentioning again as it was the first
new design certified by the FAA in 17 years, and it was a full
composite airframe from a new company.

For those of us that live in America’s South, the drive from Portland
to Bend is simply amazing. * In South Carolina we drive in one green
tunnel of pine trees after another, and while we have mountains, they
don’t have snow on them in early September like Mount Hood. *The drive
down through the high desert is truly beautiful - just don’t try to
pump your own gas. Oregon gas stations are required by state law to be
full service.

The modern sailplane is one truly amazing piece of machinery. *They
may look simple but they’re among the most sophisticated aircraft
flying. *I learned to fly in a Grob 103. *My first single-place glider
was a 1968 Open Cirrus with massive fiberglass spars, fat wings, and
heavy enough to send everyone on the field running the other direction
any time you pull your trailer into the assembly area.

I moved up to a mid-80’s LS6-a, and began teaching students in a
2-33. *The historical progression from the 2-33 and its flying barn
door performance, to a first generation glass ship like the Cirrus, a
second generation glass ship like the LS6-a, and a modern glider using
knife like laminar-flow wings is exciting to experience firsthand.
One of my friends sums it up saying “these new planes just do what you
want them to do so much easier, and they do it so much better”.

Improvements in modern sailplane performance have been driven by
advances in materials, a better understanding of how to design
aerodynamic structures with these materials, computer modeling, and
leaps in understanding aerodynamic principles. Most modern sailplanes,
with the exception of Windward Performance’s aircraft, are built with
a wet, room temperature cured, epoxy resin lay up using glass, carbon,
or Kevlar fiber reinforcement. *The reinforcing cloth is laid into the
mold by hand and the epoxy squeegeed, or painted on. *This type of
construction process was quite an advance over previous wood and metal
construction and quite a bit better than “fiberglass” or polyester
resins or even the vinyl ester resins but still imposes several
limitations on how strong aircraft parts may be made.

* When the resins cure at room temperature there is fairly short
amount of “out-time” – the number of minutes workers have to craft the
part before the resin’s curing process begins. *Complicated multi-
layer layups have to be done quickly. *Yet fiber orientation and
wetout are important in critical aircraft applications. As a result
room-temperature resin application often means a heavier composite
structure to maintain structural safety. *The room temperature curing
of resins, causes the finished part to lose structural integrity
rapidly at temperatures over 140 F, which is why modern composite
sailplanes are painted white. *If they were painted black or even red
they would heat up under sunlight and loose structural integrity.

Thus Cole’s Windward Performance is the only sailplane manufacturer
I’m aware of to use sophisticated prepreg oven-cured carbon fiber
construction. *Prepreg carbon fiber is produced in a factory by
sandwiching a carbon fiber cloth between two epoxy resin sheets, the
sandwich is then run this between high-pressure rollers. *The high
pressure insures an even and complete epoxy coating of the fabric with
the ability to very precisely control the ratio of resin to fabric.
This allows the composite’s weight to remain low but optimized for
strength with very tight tolerances. *Once the fabric is epoxy coated
it is refrigerated for storage and transport, greatly retarding the
start of the curing process.

Since the resin does not cure at room temperatures there is much more
out-time in which to lay up the prepreg material in, say, a wing-mold
while avoiding mistakes from rushing. There’ more time for forming
complicated multi-layer configurations.

In Windward’s aircraft, the prepreg layup is vacuum-bagged to ensure
all air is squeezed out of the layup and the entire assembly goes into
an oven to cure at high temperatures. The benefits of all this are
lighter, far stronger and stiffer composites with a much larger
temperature operating range than conventional wet layup composites
afford.
Given these advantages, and given Greg Cole’s expertise and obviously
high standards of craftsmanship, it became clear why Windward
Performance uses prepregs, and why they result in the Duck Hawk’s
performance advantages.

A winning 15M racing sailplane moves around the course in the least
amount of time with the highest average cross country speed. *The key
to obtaining that is, naturally, minimizing the time you go slow.
Climbing well and going fast between thermals sounds easy, but
mastering this simple concept is far from easy. *Most of us with
modest skills in this area could use all the help we can get from the
aircraft.

The modeling of average cross country speeds with different
atmospheric conditions allowed performance simulations of different
design iterations to be run and small improvements or losses to be
determined. *The accuracy of modeling new designs was, for Cole,
validated by modeling current designs with known performance
characteristics.

Designs that can be made light with small wing areas offer improved
performance over conventional designs especially in tough conditions.
Tough conditions – small thermals, weak lift, headwinds, etc. - seem
to have a far greater negative impact on my contest results than do
the positives of favorable conditions.

Cole’s calculations show soaring with the ability to fly well with low
lift coefficients can also give the ability to go fast at relatively
low wing loadings, meaning faster average cross country speeds. *The
results of the modeling process indicated an optimum with a wing area
of 80 SQFT, and a wing loading of 8.75 LBS/SQFT.

Determining the optimum airfoil also benefits from Cole’s computer
modeling process. *Structural constraints start as the wing area drops
below 90 square feet, and wing volume available for ballast drops
rapidly as well. *As wing area decreases, the Reynolds number goes
down and achieving low drag at high and low lift coefficients becomes
more and more difficult.

Good stalling behavior is another factor Cole considered. *Amongst all
of the airfoils designed the final airfoil selected for the DuckHawk
is the CS33-18; it allows the aircraft to fly at low lift coefficients
at high speeds as well as at high lift coefficients at low speeds.
Winglets were considered but an evaluation of their negatives and
benefits indicated the DuckHawk would fly better without them when
real world soaring techniques were considered.

State of the art performance is what Cole is after here, plus safety
and relative affordability. *The 30:1 aspect ratio and its razor thin
wings are an obvious clue this is not your generic modern glider.
Eighty-pound wings will be appreciated by everyone during assembly.
Eighteen-meter L/D performance with a 15-meter wing span will result
in lower drag while circling and this plane should climb like a
bandit.

The ship’s lower mass will give it an induced drag advantage of 29%
compared to today’s 15m sailplanes at equivalent wing loadings. That
means better climbing. *Lower wetted area means lower parasitic drag
and improved high speed running. A wing loading range between 6.25 and
10.0 lbs./sq. Ft. will give it ability to adapt to a wide variety of
soaring conditions - a plane that will get you quickly around the
course on the tough days and fly faster than anything else out there
now on really good days.

Before my trip to Windward Performance I was unaware of the complexity
of the sailplane manufacturing process. *The plugs and molds required
to produce a sailplane, fill a good sized warehouse even without
working room around them. *The design and production capabilities of
this small sailplane operation ...

read more »

SF,

Exactly who at the SSA Soaring Magazine said the subject matter
wasn't suitable for soaring.

Richard
www.craggyareo.com