If Gary Osoba is flying the SparrowHawk in turbulent conditions, he
has a nearly infinite L/D. He can do the dynamic soaring thing and
extract energy from the turbulence and just keep going. I've seen him
do it and it is amazing.

If it is me flying, I don't know how to do dynamic soaring, so I
tighten my belts and press on. The SparrowHawk is very stable and,
while it has very low inertia, it has fairly high damping in all axes,
so requires relatively little input from the pilot in turbulence so
there would not be much additional drag from control deflections.
Never have flown a Cirrus so I can't comment about it in this regard.

The varying angles of attack will make a difference depending how much
time is spent out of the drag bucket. No idea how it would compare on
this example. At the speeds you would be flying into a headwind, you
would have to have an incredibly strong shear to increase angle of
attack to the point of stall so that wouldn't be much of a worry. If
it is that strong, nothing flies very well.

The stiffness issue is a little complex. If the energy from a
vertical gust is used to bend the wing, less gets transferred to the
glider. The glider can gain energy from both up and down gusts (and
side gusts but that is more complicated). Taras Kiciniuk (I am really
sorry if I spelled the last name wrong) has a great presentation on
dynamic soaring that explains this with vector diagrams. One should
actually pull the instant you hit an upward gust and push the instant
you hit a downward gust. This is half of what Gary Osoba does. It is
also backwards to what you work really hard at flying powered
airplanes so the retraining is taking a while. \
Other aeroelastic effects would also make a difference. Generally,
wings are designed to wash out a bit as positive load is applied
(leading edge twists down as tip goes up). This prevents divergence
which is bad - if the wing twists the other way (washes in), a.o.a.
increases with positive load which increases a.o.a. which makes more
positive load and so on - BANG. The more flexible wing will probably
twist more, relieving more load and thus, transferring less energy to
the glider. Therefore, I think the stiffer glider will have the
advantage over the more flexible one, everything else being equal.

Is any of this enough to notice (without using the dynamic soaring
techniques)? I've no idea. The results would certainly be highly
variable with the conditions.

Doug Taylor

Shawn Curry wrote in message link.net...
Mark James Boyd wrote:
Say a Sparrowhawk and a Cirrus. Guess is the Cirrus will penetrate
better and hence be able to achieve longer flights in windy and / or
turbulent conditions?


Wow. Now THERE is an interesting question. How does a glider
with super stiff wings do going through turbulence vs. one
with flexing wings? I'd suspect the stiffer wings would
lose (they'd stall more cleanly instead of absorbing the impact)
but the difference may be too small to be important.

Any guesses on this one? This is pretty far out of my
field...

Don't think its stiff vs. flexy. Rather, how well laminar flow is
maintained (less drag) with less than perfect flow over the wings.
Apparently some airfoils do better than others. This belief with the
ASW-24 (which I've heard is suspect) probably cost more sales than
races. Why a Cirrus would be better than a Sparrowhawk in this regard
is beyond my understanding. BTW Ventii have very stiff wings and do
well in turbulence and headwinds.

Conjecturally Yours,
Shawn