Define penetration.

Stewart Kissel wrote:
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.



I don't think it is that simple.

Polars are still air measures. By definition, if you are wanting to know
about penetration into wind the air is not still. Presumably a number of
factors like stability, control authority, drag caused by control
movements, rotational inertia etc. will affect how efficiently the
aircraft flies in turbulent conditions.

This has me wondering how you would quantify the difference in real
world ability to progress cross country for different gliders with
similar polar curves.

Let's take an example - Chose two aircraft with similar polars, but
radically different physical characteristics.
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?

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.

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.

(Andy Durbin) wrote:

I was recently challenged to define Penetration.

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



You guys have it all wrong. On US Navy ships and shore stations too, they
always posted a copy of the Uniform Code of Military Justice. And I
quote - - " . . . penetration, however slight, is sufficient to complete the
offense." Thinking back, don't think they discussed head winds at all.
--
bumper ZZ (reverse all after @)
"Dare to be different . . . circle in sink."

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.

Bruce Greeff wrote:

Stewart Kissel wrote:

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.



I don't think it is that simple.

Polars are still air measures. By definition, if you are wanting to know
about penetration into wind the air is not still. Presumably a number of
factors like stability, control authority, drag caused by control
movements, rotational inertia etc. will affect how efficiently the
aircraft flies in turbulent conditions.

This has me wondering how you would quantify the difference in real
world ability to progress cross country for different gliders with
similar polar curves.

Let's take an example - Chose two aircraft with similar polars, but
radically different physical characteristics.
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?


Your example is hardly an example. Its a guess. Data please.
My "guess" is that you have a bias against US built gliders. However,
thats only a guess. ;-)

Shawn

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...

I was recently challenged to define Penetration.

Kobe Bryant was also asked the same question, check with him for the details.


JJ Sinclair

Todd Pattist wrote:

I've heard the term "penetration" used solely to refer to
good L/D at high speed. Thus, a jumbo jet with a glide
ratio in the mid 20's at speeds above 150 knots might be
considered to have good penetration.

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.