Define penetration.

[Bruce Greeff]

Hi

I was recently challenged to define Penetration.
We failed to find a suitable definition - although I have my own opinions.

Views presented on the subject include:
Glider penetration is represented by the polar curve.
Penetration is proportional to wing loading.
Penetration is the "real world L/D" taking into account the energy
reserves over drag to overcome upsets caused by turbulence etc.
Penetration is related to weight only. (variant ratio of- weight and
frontal area * Coefficient of Drag)

I know we must be missing the point so -
Any takers from our learned aerodynamicist types?

What exactly is "penetration" as applied to gliders and how does it
differ from the polar curve.

[John Galloway]

>Bruce Greeff wrote:
>
>What exactly is 'penetration' as applied to gliders
>and how >does it differ from the polar curve.

I don't think I have heard anyone refer to penetration
as a glider performance concept since the seventies!
It referred to the performance in the medium to high
speed part of the polar curve.

John Galloway

[Shawn Curry]

Bruce Greeff wrote:
> Hi
>
> I was recently challenged to define Penetration.
> We failed to find a suitable definition - although I have my own opinions.
>
> Views presented on the subject include:
> Glider penetration is represented by the polar curve.
> Penetration is proportional to wing loading.
> Penetration is the "real world L/D" taking into account the energy
> reserves over drag to overcome upsets caused by turbulence etc.
> Penetration is related to weight only. (variant ratio of- weight and
> frontal area * Coefficient of Drag)
>
> I know we must be missing the point so -
> Any takers from our learned aerodynamicist types?
>
> What exactly is "penetration" as applied to gliders and how does it
> differ from the polar curve.

In the glider sense at least:
Being able to go fast and still keep it up.
Hope this helps.

Cheers,
Shawn

[tango4]

K8's, PW5's and Libelles don't 'penetrate' well because flying fast just
brings 'em down faster. Going cross country in anything but a gentle breeze
becomes seriously hard work.

ASW27's full of H2O penetrate like darts. You can get round the task with
20kt breezes on the nose all day.

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


Ian


"Shawn Curry" > wrote in message
link.net...
> Bruce Greeff wrote:
> > Hi
> >
> > I was recently challenged to define Penetration.
> > We failed to find a suitable definition - although I have my own
opinions.
> >
> > Views presented on the subject include:
> > Glider penetration is represented by the polar curve.
> > Penetration is proportional to wing loading.
> > Penetration is the "real world L/D" taking into account the energy
> > reserves over drag to overcome upsets caused by turbulence etc.
> > Penetration is related to weight only. (variant ratio of- weight and
> > frontal area * Coefficient of Drag)
> >
> > I know we must be missing the point so -
> > Any takers from our learned aerodynamicist types?
> >
> > What exactly is "penetration" as applied to gliders and how does it
> > differ from the polar curve.
>
> In the glider sense at least:
> Being able to go fast and still keep it up.
> Hope this helps.
>
> Cheers,
> Shawn

[Stewart Kissel]

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.

[Mark James Boyd]

In article >,
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'd say it's how flat the polar curve is past the
best L/D point. I've often used 80 knots as
a standard speed where I look at the sink rate
of a polar and I compare gliders based on that
sink rate.

For a comparison of how this works into the wind,
with a 30 knot headwind, a PIK20 or LS-4 has a
20:1 effective glide, while a SGS 2-33 has a
9:1 effective glide, when flown at the "best
glide for 30 knot headwind airspeed."

Quite a difference. Some of my past experiences
fighting 20+ knot headwinds in a glider, while
thermalling, have caused a few "moments of great
concern." Drifting downwind, not frequently enough
checking the landing spot, and having my thermal get
all blown out, has gotten my attention...

Then pushing over the nose and seeing the vario go
way down and the ASI and ground not doing much is
even worse...

If it weren't for ground effect I don't know
WHAT I'd do :PPP

[Andy Durbin]

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

[ISoar]

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

[Ted Wagner]

> 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 ;)

[BGMIFF]

Don't tell this to the guy who won sports class nationals last year in a
standard Libelle. He may have a differing opinion!!!

Brian

"tango4" > wrote in message
...
> K8's, PW5's and Libelles don't 'penetrate' well because flying fast just
> brings 'em down faster. Going cross country in anything but a gentle
breeze
> becomes seriously hard work.
>
> ASW27's full of H2O penetrate like darts. You can get round the task with
> 20kt breezes on the nose all day.
>
> I suppose it relates to how flat the polar curve is above 100 kph.
>
>
> Ian
>
>
> "Shawn Curry" > wrote in message
> link.net...
> > Bruce Greeff wrote:
> > > Hi
> > >
> > > I was recently challenged to define Penetration.
> > > We failed to find a suitable definition - although I have my own
> opinions.
> > >
> > > Views presented on the subject include:
> > > Glider penetration is represented by the polar curve.
> > > Penetration is proportional to wing loading.
> > > Penetration is the "real world L/D" taking into account the energy
> > > reserves over drag to overcome upsets caused by turbulence etc.
> > > Penetration is related to weight only. (variant ratio of- weight and
> > > frontal area * Coefficient of Drag)
> > >
> > > I know we must be missing the point so -
> > > Any takers from our learned aerodynamicist types?
> > >
> > > What exactly is "penetration" as applied to gliders and how does it
> > > differ from the polar curve.
> >
> > In the glider sense at least:
> > Being able to go fast and still keep it up.
> > Hope this helps.
> >
> > Cheers,
> > Shawn
>
>

[Bruce Greeff]

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?

[Chris OCallaghan]

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.

[K.P. Termaat]

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.
>
>
>

[bumper]

> (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."

[whbush]

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]

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.
>
>
>

[Shawn Curry]

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

[tango4]

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...
>

[JJ Sinclair]

>I was recently challenged to define Penetration.

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


JJ Sinclair

[Mark James Boyd]

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.

[Mark James Boyd]

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...

[Mark James Boyd]

>> 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...

[Mark James Boyd]

>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"...

[Shawn Curry]

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

[Doug Taylor]

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. :o\
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 et>...
> 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

[Bruce Greeff]

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

[Chris OCallaghan]

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.

[Mark James Boyd]

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?