Define penetration.

whbush wrote:
So you can't penetrate downwind? So going down wind is withdrawing?

Downwind I'd be much happier with a real good floater than a
jumbo jet (or other sinker). If you look at the data with
the 30 knot tailwind, a PW-5 has a better L/D (54:1) than a
Salto 13.6 (53:1) even though the best still air L/D for the
PW-5 is 33:1 vs. salto 35:1.

For the most part it doesn't seem to apply too much, because
the minimum sink rate for a lot of modern gliders is very
similar (a glider with a 2-3 knot minimum sink
doesn't sell well).

Of course none of this has anything to do with airspeed at
minimum sink, which is for thermalling and is another matter entirely...
This speed seems to have quite a variance in modern gliders...

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...

Todd Pattist wrote:

However, more often the way I've heard it used, it includes
an informal assumption that the "good" high speed
performance also includes a "good enough" thermalling
performance that the glider can climb in a wind broken
thermal and resume upwind progress.


I've heard it mean the first part (like a jumbo jet),
but have never heard it used to mean it also has good
enough thermalling performance. A glider which did both
(good L/D at high speeds, and good minimum sink rate)
would be nice, but I'd still use the terms seperately
myself.

Aha! I remember the first time I heard it, at Sunset beach.
It was flying model gliders, and we added ballast to
improve "penetration" into the wind associated with ridge lift.

So I never heard it with any reference to thermals at all.

I'd say Todd's definition refers to "the act of flying a glider
in such a way as to make good progress into the wind" which
is slightly different (and a bit more complex) from simply
gliding well into the wind.

For now, I suppose I'll say "patato" and he'll say "potatoe"...

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

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

Shawn Curry wrote:
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
I was wondering more about the differences in mass, rotational inertia, control
effectiveness...

Cirrus is a lot heavier than a sparrowhawk in percentage terms, so presumably
will tend to fly through minor turbulence with less upset.
Conversely Cirrus has lazy aileron response, so roll upsets take a little longer
with controls deflected - presumably less efficient.
Cirrus has all moving stabilisor - very powerful in pitch, and easy to get
unintentional pitch movements in rough air.
Cirrus wings are like rock - graphite 13% (?) wings on Sparrowhawk presumably
just shrug off a lot of what shakes the first generation glass ships.

Just idle wonderment on my part.
Never flown a Sparowhawk, have some vague idea that what makes a difference in
XC in my Cirrus is flying smoothly.

Cheers
Bruce

Well, since you brought it up, the stronger the tailwind, the more
important your minimum sink rate becomes in establishing the greatest
possible distance over the ground. With a headwind, you are turning
the speed ring clockwise... speeding up. With a tailwind,
counterclockwise... slowing down. So to answer your question, NO, you
don't "penetrate" downwind. High speed glide angle is less important
than the total time you can remain aloft, allowing the wind to carry
you along.

Withdrawing? Only if soaring is a particularly sensual experience.
Hmmm, penetrate rapidly, withdraw slowly. Not a bad perscription all
the way around.

Drifting might be a better label, though it too is loaded with
connotations.


"whbush" wrote in message ...
So you can't penetrate downwind? So going down wind is withdrawing?
"Chris OCallaghan" wrote in message
m...
I'll give it a try....

Penetration: a measure of sailplane performance as a function of Lift,
Drag, and Airspeed such that increase in drag is disproportionately
small compared to increasing airspeed throughout the sailplane's speed
range.

Since penetration is most often used to describe a sailplane's ability
to make progress against a head wind, a "penetration factor" of a
sailplane could be measured by establishing L/D at speeds of 60, 80,
and 100 knots, or, conversely, at some fixed rate of sink. The 300
feet per minute sink rate speed has been used as a de facto
penetration factor in the past. The higher the measured airspeed at
-300ft/min, the better the penetration.

Chris OCallaghan wrote:
Well, since you brought it up, the stronger the tailwind, the more
important your minimum sink rate becomes in establishing the greatest
possible distance over the ground.

The interesting part about this for me is that the min sink rate
of so many modern gliders is so similar (on paper).

But I suppose this doesn't take into account ballast, which I expect
one would drop if in a tailwind and just barely
able to glide back to an airfield. How many of you folks have
dropped ballast at the end of the day when the air goes still
except for a tailwind home?