Sanding or Waxing - PIK 20 Question

My experience from 6 years racing the PIK agrees with Bill's. Sand
with 600 at 45 degrees back to high point of airfoil. Clean with water
with generous helping of dish soap. Wipe dry, don't rinse.
Other very important factor in climb of PIK is flap setting. It wants
to fly at a constant AOA with additional lift for tighter turns added
by flap setting. As I recall, I used 6 deg for 30 deg of bank, 8 deg at
45 and changes flap setting whenever bank changed, even recentering. A
lot of work, but it did help performance.
Good Luck UH

[snip]

Sorry to be ignorant, but I don't understand the technicalities of this.
What is the " . . . unfavourable pressure gradient . ." ? One in the
wrong direction, or too large, or what?

And in what sense does a transition have energy? Particularly "enough
energy to keep the bubble small" ? If it had energy, the idiot layman's
thinking is that more means bigger.

The layered airflow (laminar boundary layer) has more energy
near the leading edge. The air closer to the surface moves more vigorously
in a tighter layer. (thin boundary layer) As the air is traveling some
distance the layer that is near the surface gets slower and the shear
that is taken place becomes thicker ( thicker boundary layer). The above
mentioned air structure will break down at some point due to luck of
energetic flow. There are several ways to lengthen this type of flow by
providing a shape (pressure gradient) that favours this type of flow.
(Presently for gliders the max chord length that sustains laminar
flow is 90% at the bottom surface. Top surface have less laminar flow,
mostly between 50% and 65%

In any case, when this flow is tripped early (more energy) the resulting
transition can keep the bubble smaller.
I hope that helps if not, I recommend some further reading on the subject

Regards
Udo

Hello Paul et all,

I also aggree with this. However it appears to work under certain conditions
of lower bank perhaps. At higher bank turns I found no real big difference.
The one thing is assured with the "B" model is that it climbs really well in
small lift. This came also from a more experienced pilot who tried my "74".
Again, I would be quite relinquant to modify the profile of the wing with
sanding unless definite deformation near the spar.

Cheers

Marc
"74"

"P. Corbett" a écrit dans le message de news:
.. .
I take it from your question that your PIK-20 is not climbing well.

When I first began flying this type, I was disappointed with the climb
until I discovered top rudder. If your yaw string is out on the forward
canopy and while circling is in line with the longitudinal axis, you are
in a slight skid. There is some controversy about the magnitude of the
skid and this subject is covered very well by Richard Johnson in the
October 2004 issue of Soaring Magazine.

The climb performance of my PIK-20B improves a lot when I apply top
rudder. When the climb is optimum, the yaw string is displaced about 5-10
degrees toward the outside of the turn. This seems to be a trait of most
gliders that I have flown but my PIK-20 seemed especially sensitive in
this regard.

So before you begin sanding or polishing, you might try this first...if
you haven't already.

Paul
ZZ



"culverflyer" wrote in message
...
Sanding rather than waxing a PIK 20 Question
Has anyone have info on this I was told that when this persons PIK did
not
clime well he would sand the wings with 400 grit .

Udo, thanks. Chris N.





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Udo Rumpf wrote:
I am always surprised when I read comments about sensitivity to rain
or water and I agree water that pearls on the wing surface will have
a negative effect on "all airfoil shapes". When was the last time you flew
through rain and where it mattered in regards to getting home or not.
Either one is cut off and one has to land in any case or one escapes
a light and short duration shower and waits it out. I have no interest
in how my airfoil performs when exposed to water.

In my limited experience, you are generally correct. But the PIK20b in
my experience is *particularly* sensitive to water.

I flew the PIK in a number of eastern US contests. We didn't fly in
much rain but one particular encounter in the mid-80s captured my
attention. I pulled up into a thermal just as a light sprinkle of rain
hit. I stalled out of the pull up! This is the only time I can
remember stalling accidently in any conditions.

It didn't at first occur to me that the rain and the stall were related
but it soon became apparent that I wasn't flying the same sailplane I
was flying before the rain.

I didn't make it home that day and landed at an airport. The anemic
Citabria was sent from Dansville to pick me up at Grand Canyon airport
(NY State). We started the tow just as another light sprinkle fell.
The Citabria lifted off in its normally anemic way but I couldn't get
the unballasted PIK off the ground. I rolled off into the grass at the
end. Anyone familiar with Grand Canyon (in the mid-80s) knows the
reason for the name. Fortunately the ground falls away quickly and I
became airborne.

I would suggest that the PIK is a notable exception to your conclusion.

"Maule Driver" wrote in message
news
Udo Rumpf wrote:
I am always surprised when I read comments about sensitivity to rain
or water and I agree water that pearls on the wing surface will have
a negative effect on "all airfoil shapes". When was the last time you
flew
through rain and where it mattered in regards to getting home or not.
Either one is cut off and one has to land in any case or one escapes
a light and short duration shower and waits it out. I have no interest
in how my airfoil performs when exposed to water.

In my limited experience, you are generally correct. But the PIK20b in my
experience is *particularly* sensitive to water.

I flew the PIK in a number of eastern US contests. We didn't fly in much
rain but one particular encounter in the mid-80s captured my attention.
I pulled up into a thermal just as a light sprinkle of rain hit. I
stalled out of the pull up! This is the only time I can remember stalling
accidently in any conditions.

It didn't at first occur to me that the rain and the stall were related
but it soon became apparent that I wasn't flying the same sailplane I was
flying before the rain.

I didn't make it home that day and landed at an airport. The anemic
Citabria was sent from Dansville to pick me up at Grand Canyon airport (NY
State). We started the tow just as another light sprinkle fell. The
Citabria lifted off in its normally anemic way but I couldn't get the
unballasted PIK off the ground. I rolled off into the grass at the end.
Anyone familiar with Grand Canyon (in the mid-80s) knows the reason for
the name. Fortunately the ground falls away quickly and I became
airborne.

I would suggest that the PIK is a notable exception to your conclusion.


On hind sight I should have realized how bad "moisture" is on the FX 67
airfoil

I had done experiments with this airfoil under the assumption
that it was only related the way it was constructed, as in the HP
technique,
I used turbulators successfully on the top surface to counter some of the
ills of that airfoil.
Wing dropping on take off for one, as well as in landing mode when the
glider with this airfoil
showed stall behaviour well before the stall speed was reached.

One other experiment I conducted, installing a .040" wire, tape down along
the span
about 5% from the leading edge. My surprise was It climbed much better but
the cruise was no better then a K6 which made sense to me.

It seems everything has be just dead on with this airfoil shape for it to
perform to it potential.
One glider I know of is the LS3, which has done just that I never heard of
any complains.
Regards
Udo

Having flown a Pik 20D (same wing section as the B)
for 18 years I can confirm this is one Glider you do
NOT want to fly in rain. The first indication you get
in rain is a vibration through the stick, then any
lift you might have been in becomes sink, I have lost
thousands of feet trying to cross areas of rain (9000'
in Poland). I have had to leave a thermal because a
Glider above decided to dump his water. I have found
increasing the speed to 65kts while flying out of the
rain seems the optimum solution. If you follow the
director then you will be on the ground very quickly.
A pilot from our club flying a B was caught on the
ridge in rain and had to land at the bottom of the
ridge but was unable to select a suitable field as
he just ran out of height/time. The Pik was way ahead
of its time when it first came out but at a price,
the wing section, which needs to be kept clean of bugs
and out of rain. Dick Jhonson's report suggested if
the leading edge was re-profiled so it was not so sharp
it could improve this situation.

Having flown a Pik 20D (same wing section as the B)
for 18 years I can confirm this is one Glider you do
NOT want to fly in rain. The first indication you get
in rain is a vibration through the stick, then any
lift you might have been in becomes sink, I have lost
thousands of feet trying to cross areas of rain (9000'
in Poland). I have had to leave a thermal because a
Glider above decided to dump his water. I have found
increasing the speed to 65kts while flying out of the
rain seems the optimum solution. If you follow the
director then you will be on the ground very quickly.
A pilot from our club flying a B was caught on the
ridge in rain and had to land at the bottom of the
ridge but was unable to select a suitable field as
he just ran out of height/time. The Pik was way ahead
of its time when it first came out but at a price,
the wing section, which needs to be kept clean of bugs
and out of rain. Dick Jhonson's report suggested if
the leading edge was re-profiled so it was not so sharp
it could improve this situation.

Udo Rumpf wrote:
"Maule Driver" wrote in message
(snips)
I would suggest that the PIK is a notable exception to your conclusion.

It seems everything has be just dead on with this airfoil shape for it
to perform to it potential.

That seems to be what Dick Johnson confirmed with his PIK improvement
work back in the 70s or early 80s.

One glider I know of is the LS3, which has done just that I never heard
of any complains.

I didn't know it had the same airfoil but I never heard complaints either.

Thanks
Bill Watson (MauleDriver)

I believe all of you about your experiences in the Pik 20.



However, my glider, a refinished LS-3a with the FX-67-K-170 airfoil, has
little detectable deterioration in the rain. I notice perhaps a very
small performance hit but really nothing like what you all have been
describing. I suppose that during the refinish job several years ago
they hit on the right leading edge profile by chance. Whatever the
case, I have been able to do several nice climbs in rain and virga that
clearly had the wing well disturbed.



Larry










"Alan Garside" wrote in
message :

Having flown a Pik 20D (same wing section as the B)
for 18 years I can confirm this is one Glider you do
NOT want to fly in rain. The first indication you get
in rain is a vibration through the stick, then any
lift you might have been in becomes sink, I have lost
thousands of feet trying to cross areas of rain (9000'
in Poland). I have had to leave a thermal because a
Glider above decided to dump his water. I have found
increasing the speed to 65kts while flying out of the
rain seems the optimum solution. If you follow the
director then you will be on the ground very quickly.
A pilot from our club flying a B was caught on the
ridge in rain and had to land at the bottom of the
ridge but was unable to select a suitable field as
he just ran out of height/time. The Pik was way ahead
of its time when it first came out but at a price,
the wing section, which needs to be kept clean of bugs
and out of rain. Dick Jhonson's report suggested if
the leading edge was re-profiled so it was not so sharp
it could improve this situation.