High altitude flutter - Vne

From experience, sustained 10-12 knot wave lift for 100km or longer
sections of the Sierra wave is common enough so that a 200knot redline
can make a significant difference. Doing the math, so long as I have
about 10:1 glide @ Vne that's good enough for me. Selecting a target
indicated cruise speed of say, 120 knots at 17.5K ft. (true 160 knots)
I can push over to 145 knots to handle the lift spikes of 12-16 knots
before having to go upwind to reduce the climb rate. This then allows
me to track straight and modulate altitude with airspeed-only making
for a better net ground speed. Without a Class A clearance, IMHO this
is the only way that a 3000km flight is going to be done in the
Sierra.

Kemp

On Jan 5, 10:49*am, Kemp wrote:
From experience, sustained 10-12 knot wave lift for 100km or longer
sections of the Sierra wave is common enough so that a 200knot redline
can make a significant difference. *Doing the math, so long as I have
about 10:1 glide @ Vne that's good enough for me. *Selecting a target
indicated cruise speed of say, 120 knots at 17.5K ft. (true 160 knots)
I can push over to 145 knots to handle the lift spikes of 12-16 knots
before having to go upwind to reduce the climb rate. *This then allows
me to track straight and modulate altitude with airspeed-only making
for a better net ground speed. *Without a Class A clearance, IMHO this
is the only way that a 3000km flight is going to be done in the
Sierra.

Kemp

That's good enough for me - almost no one knows the XC Sierra wave
like Kemp. I wonder if this is the design point they had in mind for
the Duckhawk or if the high Vne happened for other reasons.

Kemp, would you consider the Duckhawk (I can't say I like that name)
as the glider to do a 3,000 km flight in, or if not, why not? There
are already acro gliders that have very high redlines, but for some
reason no one that I know about uses them for big time XC wave flying.

Stay warm up there.

Andy

On Jan 3, 7:46*pm, Eric Greenwell wrote:
...High temperature cured pre-preg allows significantly lighter
weight than wet layups done by hand, too...

Cite?

On Jan 5, 6:16*am, DRN wrote:
On Jan 4, 2:35*pm, wrote:

No, polars are typically fit for the region of "normal" flight,
not for blown final glides or high-speed wave...
Don't know if any instruments try to model high-speed
polars really accurately.

Us western pilots don't think of a 110 kt final glide as "blown"
Dave ;-). Truth be told, I typically find that I am underperforming
the glide ratio in the computer at most speeds, but it really picks up
above 90 knots. I guess I can start moving points on the polar around
until it starts to "feel right" but given all the variables at play
that seems painful.

A "learn mode" is not practical. The *only* way to get reasonably
accurate polar information is by parallel measurement using a
super-well-calibrated reference glider. To my knowledge, this
is *only* done periodically by the Idaflieg group.

Yeah, I figured. Thanks. I'll check what they've got.

9B

Bob Kuykendall wrote:
On Jan 3, 7:46 pm, Eric Greenwell wrote:
...High temperature cured pre-preg allows significantly lighter
weight than wet layups done by hand, too...

Cite?

I'm not the best person to ask, since all I can do is repeat what Greg
Cole tells me. Here's where he gets his pre-preg:

http://www.toraycompam.com/index.php...14&Itemi d=32

They are in Tacoma, WA. Summarizing as best I can from conversations
with Greg:

"Hand layup requires carbon fiber and epoxies that can be applied by
hand and at room temperature, and will reliably "wet" under those
conditions. Applying by hand makes it difficult to exactly the right
amount of epoxy, which means too much is always applied to compensate
for the variations of hand layup and the difficulty of testing the final
product.

By impregnating the carbon fiber at the factory,the epoxy is applied by
machine to a very close tolerance so there is no excess weight. This
allows a much wider choice of carbon fibers and epoxies to be used.

The product (fiber + epoxy) can be inspected and tested before delivery
to the customer, so tolerances are tighter. As a result, you can have a
stronger, stiffer material for the same weight. Or, use less material
(less weight) for the same strength."

The high temperature cure (250F) used for these pre-pregs is probably an
important part of getting the better strength and stiffness per pound,
but I don't recall what he's said about it.

--
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

Eric Greenwell wrote:
Bob Kuykendall wrote:
On Jan 3, 7:46 pm, Eric Greenwell wrote:
...High temperature cured pre-preg allows significantly lighter
weight than wet layups done by hand, too...

Cite?

I'm not the best person to ask, since all I can do is repeat what Greg
Cole tells me. Here's where he gets his pre-preg:

http://www.toraycompam.com/index.php...14&Itemi d=32


They are in Tacoma, WA. Summarizing as best I can from conversations
with Greg:

"Hand layup requires carbon fiber and epoxies that can be applied by
hand and at room temperature, and will reliably "wet" under those
conditions. Applying by hand makes it difficult to exactly the right
amount of epoxy, which means too much is always applied to compensate
for the variations of hand layup and the difficulty of testing the final
product.

By impregnating the carbon fiber at the factory,the epoxy is applied by
machine to a very close tolerance so there is no excess weight. This
allows a much wider choice of carbon fibers and epoxies to be used.

The product (fiber + epoxy) can be inspected and tested before delivery
to the customer, so tolerances are tighter. As a result, you can have a
stronger, stiffer material for the same weight. Or, use less material
(less weight) for the same strength."

The high temperature cure (250F) used for these pre-pregs is probably an
important part of getting the better strength and stiffness per pound,
but I don't recall what he's said about it.


And if you are vacuum bagging, excess resin is forced out of the
laminate. High end sailboats have used such techniques for years, and
reportedly save a lot of weight. The light weight of the Sparrowhawk is
another datapoint that suggests you can save a lot of weight.

On Jan 5, 4:31*pm, Bob Kuykendall wrote:
On Jan 3, 7:46*pm, Eric Greenwell wrote:

...High temperature cured pre-preg allows significantly lighter
weight than wet layups done by hand, too...

Cite?

My estimate is that the prepregs save about 10% per square.
On other 15% due to the smaller wing. The biggest saving would be on
the spar due to use of pulltrusion which could be as High as 40%.
Allowing for a thinner airfoil, smaller root chord and an higher
aspect ratio the saving on the spar would be cut down to only 5%.
There other weight savings, hardware in the wing is lighter (made from
carbon) also a thin poly coat of paint.
In all a weight saving of 35% on the wing is doable, maybe even more.

Example The total weight of an ASW 27 is 230lb.
If you add the savings up, the weight of a wing of a new design like
the Duck Hawk, could end up near a 150 lb or 75 lb per panel.
The fuselage also can come in at 150lb.
Regards
Udo

Fourth line from the bottom should read:
the total weight of an ASW27 "wing" is ~ 230 lb

My estimate is that the prepregs save about 10% per square.
On other 15% due to the smaller wing. The biggest saving would be on
the spar due to use of pulltrusion which could be as High as 40%.
Allowing for a thinner airfoil, smaller root chord and an higher
aspect ratio the saving on the spar would be cut down to only 5%.
There other weight savings, hardware in the wing is lighter (made from
carbon) also a thin poly coat of paint.
In all a weight saving of 35% on the wing is doable, maybe even more.

Example The total weight of an ASW 27 is 230lb.
If you add the savings up, the weight of a wing of a new design like
the Duck Hawk, could end up near a 150 lb or 75 lb per panel.
The fuselage also can come in at 150lb.
Regards
Udo

On Jan 5, 7:15*pm, Udo Rumpf wrote:
Fourth line from the bottom should read:
the total weight of an ASW27 "wing" is ~ 230 lb

My estimate is that the prepregs save about 10% per square.
On other 15% due to the smaller wing. The biggest saving would be on
the spar due to use of pulltrusion which could be as High as 40%.
Allowing for a thinner airfoil, *smaller root chord and an higher
aspect ratio the saving on the spar would be cut down *to only 5%.
There other weight savings, hardware in the wing is lighter (made from
carbon) also a thin poly coat of paint.
In all a weight saving of 35% on the wing is doable, maybe even more.

Example The total weight of an ASW 27 is 230lb.
If you add the savings up, *the weight of a wing of a new design like
the Duck *Hawk, could end up near a 150 lb or 75 lb per panel.
The fuselage *also can *come in at 150lb.
Regards
Udo

Thanks for the correction Udo - I was starting to feel bad about my
grossly overweight -27.

9B

Kemp, would you consider the Duckhawk (I can't say I like that name)
as the glider to do a 3,000 km flight in, or if not, why not? There
are already acro gliders that have very high redlines, but for some
reason no one that I know about uses them for big time XC wave flying.

Stay warm up there.

Andy

I looked at some acro ships and the highest redline I could find was
180 knots (Windex I think), which, yes is better than 150knots, but
the lightweight is really a nice benefit. Yes, the Duckhawk is very
interesting and for me, esp. with a self-launch version, a very
compelling machine. Easy assembly due to light wings, high Vne, good
enough performance even allowing for some marketing. I've visited
Greg's facility twice and am impressed with the approach and the
Sparrowhawk too. I have a 3 view printout with specs tacked to my
office wall as a reminder........

Kemp