Define penetration.

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 don't think the wind or turbulence has something to do with penetration.
Penetration is the ability to proceed forward (fast) without much of a
(height) penalty. So to my idea for a glider it is typically L/D as a
function of speed beyond the speed for best L/D.
Especially the newer designs show quite flat polar curves for the higher
speeds, meaning that at the higher speeds L/D does not worsen very much.
Ideally L/D should not divert from best L/D for the higher speeds, i.e. a
completely flat polar curve coïnciding with the tangent from the origin of
the polar diagram. Then you would always fly with Vne and have the best
possible penetration for your glider. Another pilot would do the same, but
when the L/D for his glider is better he would penetrate better.

Karel, NL

"Stewart Kissel" schreef in
bericht ...
SNIP

I suppose it relates to how flat the polar curve is
above 100 kph

SNIP

Okay, I'll bite. If glider penetration describes the
ability of a ship to make progress into the wind without
falling out of the sky, is it soley a matter of looking
at the polar at the indicated airspeed? Intuition
tells me that is it, but an aeronautical engineer type
might make be look like a big dummy here.

Bruce Greeff wrote in message ...
Hi

I was recently challenged to define Penetration.

A measure of the ratio of forward progress to altitude lost when
flying into a head wind.

The ability to make forward progress against a headwind while engaging
is sawtooth profile thermalling flight.

What a 1-26 hasn't got.

I'm glad I didn't dump the water!

With inadequate pentration the top of current climb is no further down
course than the top of the last one. The further down course it is,
the better the penetration.


Andy

A 2-33 penetrates like mashed potatoes thrown at a screen door.

A 2-33 penetrates like mashed potatoes thrown at a screen door.

True, but for what it's designed to do, a 2-33 is as good as an ASW-27

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.

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.

Always fascinating to see where these northern winter threads end up...

whbush wrote:
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.

Hang about Bruce, *you* started this thread! Shouldn't you be out flying?

:-)
Ian

"Bruce Greeff" wrote in message
...
Always fascinating to see where these northern winter threads end up...

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...