Sanding or Waxing - PIK 20 Question

[culverflyer]

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 .

[[email protected]]

The Wortmann FX-67-K-170 airfoil that the PIK-20 and Nimbus 2 use is
very sensitive to bugs, and even a very small amount of rain. With a
waxed wing surface the rain drops tend to stand tall, severely
separation the top surface air flow. Leaving the wings sanded and
unwaxed allows the rain drops to flow more smoothly on the wing
surface; significantly reducing drag.
However, only a bug wiper system appear to help the bug problem.

[Udo Rumpf]

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.

As to the question, sanding or waxing,

I have some empirical experience, and I can make a deduction.
If any one has a better insight please let us know.

The reason to sand an airfoil shape, that has shown to be
sensitive to being polished, could be as follows.

The laminar flow on a polished surface, at the transition point, turns into
a large transition bubble due to an unfavourable pressure gradient.
This bubble is large enough to cause a noticeable drag increase.
By sanding one maintains most of the designed laminar flow over that
region but the transition is forced sooner and it has enough energy to
keep the bubble small. Hence less laminar flow but overall reduced drag.

I would not be surprised if the same could be achieved with a thin
turbulator ahead of the transition as is done on many, but not all airfoils
on the bottom surface. This would keep the cleaning shores to a
minimum, as the polished surface can be maintained

The advantage of the sanding would be that the transition could take place
anywhere in the critical range, automatically, since the transition
position
will change with speed. A turbulator will give you one position only and
one
speed, hence the placement of the turbulator strip has to be conservative
to cover all ranges.
Regards
Udo



> wrote in message
oups.com...
>
> The Wortmann FX-67-K-170 airfoil that the PIK-20 and Nimbus 2 use is
> very sensitive to bugs, and even a very small amount of rain. With a
> waxed wing surface the rain drops tend to stand tall, severely
> separation the top surface air flow. Leaving the wings sanded and
> unwaxed allows the rain drops to flow more smoothly on the wing
> surface; significantly reducing drag.
> However, only a bug wiper system appear to help the bug problem.
>

[Chris Nicholas]

Udo R. wrote 11.9.05: [snip] The reason to sand an airfoil shape, that
has shown to be

sensitive to being polished, could be as follows.



The laminar flow on a polished surface, at the transition point, turns
into a large transition bubble due to an unfavourable pressure gradient.

This bubble is large enough to cause a noticeable drag increase.

By sanding one maintains most of the designed laminar flow over that
region but the transition is forced sooner and it has enough energy to
keep the bubble small. Hence less laminar flow but overall reduced drag.

[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.

Hoping for education, not flames or sarcasm.

Chris N.

=======================




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[Bob Korves]

"culverflyer" > wrote in
:

> 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 .
>
>

I had a PIK-20d and the performance loss with bugs or rain was memorable.
The drag increase could be heard and the sink felt before rain was wisible
on the canopy.

I never waxed the glider, hoping that might help the droplets to lay flat
on the wing. The urethane finish also didn't need to be waxed to protect
it. I always wondered if a thin layer of some sort of surfactant (like
soap, maybe?) might help the problem. Never tried it, though...

I finally solved the problem by selling the PIK and co-owning a LAK-17a.
It has a urethane finish for easy care and flies just fine in the rain. It
also does't drop wings, handles great, has automatic hookups, and has
outstanding performance. Yes, it does cost a bit more.
-Bob Korves

[Bill Daniels]

> wrote in message
oups.com...
>
> The Wortmann FX-67-K-170 airfoil that the PIK-20 and Nimbus 2 use is
> very sensitive to bugs, and even a very small amount of rain. With a
> waxed wing surface the rain drops tend to stand tall, severely
> separation the top surface air flow. Leaving the wings sanded and
> unwaxed allows the rain drops to flow more smoothly on the wing
> surface; significantly reducing drag.
> However, only a bug wiper system appear to help the bug problem.
>

I sand the wings on my Nimbus 2 and they seem to deliver the advertised L/D.
I have tried surfactant on a few gliders and, by appearance only, it seems
to work. A capful or two of dishwasher "rinse clear" or "spot free" or
something like that in a bucket of water seems to be enough.

As for the bugs, as slow as I fly, they have time to get out of the way.

Bill Daniels

[culverflyer]

What grit do you use on the Nimbus 2 do you sand top and bottom and how far
back??


"Bill Daniels" > wrote in message
...
>
> > wrote in message
> oups.com...
> >
> > The Wortmann FX-67-K-170 airfoil that the PIK-20 and Nimbus 2 use is
> > very sensitive to bugs, and even a very small amount of rain. With a
> > waxed wing surface the rain drops tend to stand tall, severely
> > separation the top surface air flow. Leaving the wings sanded and
> > unwaxed allows the rain drops to flow more smoothly on the wing
> > surface; significantly reducing drag.
> > However, only a bug wiper system appear to help the bug problem.
> >
>
> I sand the wings on my Nimbus 2 and they seem to deliver the advertised
L/D.
> I have tried surfactant on a few gliders and, by appearance only, it seems
> to work. A capful or two of dishwasher "rinse clear" or "spot free" or
> something like that in a bucket of water seems to be enough.
>
> As for the bugs, as slow as I fly, they have time to get out of the way.
>
> Bill Daniels
>

[Marc Arsenault]

I owned the Pik 20B for three years now. I usually never fly in rain since
there is never some around. The horror stories narated will only mean that
my glider would descend like a Cessna 150 in rain. No big deal. I have had
quite a bit of bugs on the leading edge as we tend to manufacture them in
Canada. I pratically did not see any traumatic difference in the flight
characteristics.

Finally, I would not worry one bit about this wounderfull glider. In fact, I
wax it every spring. It gives it a great look and is much easier to clean
after a long day. I would not spend any time sanding the wings unless you
have a serious bump bear the spar.

I see that a fortunate fellow flew his Pik on the Ridge in april for 1 000
km. Can't be that bad, would you not agree?

Best regards, keep the blue side up!

Marc Arsenault
"74"

[Bill Daniels]

I use 400 grit up through 1200 grit and sand all the way to the trailing
edge top and bottom using a 20mm thick bar of super flat Plexiglas as a
sanding block.

I'm battling aging and cracked gelcoat that must be replaced someday. I've
used matching white lacquer primer to stabilize the old gelcoat and provide
a good sanding base. The Lacquer primer also replaces the gelcoat lost to
sanding. The whole prime and sand operation takes about a day and I only
have to do it once a year in the spring. So far, it seems to be a good
solution for an old glider.

Maybe it's the condition of the wing but I don't see much degradation in
rain or with modest bug buildups. If you are interested, I uploaded a
flight to the OLC for September 2nd - you can download the IGC file and
analyze the performance for yourself. The wing got wet a couple of times in
that flight.

Bill Daniels


"culverflyer" > wrote in message
...
> What grit do you use on the Nimbus 2 do you sand top and bottom and how
far
> back??
>
>
> "Bill Daniels" > wrote in message
> ...
> >
> > > wrote in message
> > oups.com...
> > >
> > > The Wortmann FX-67-K-170 airfoil that the PIK-20 and Nimbus 2 use is
> > > very sensitive to bugs, and even a very small amount of rain. With a
> > > waxed wing surface the rain drops tend to stand tall, severely
> > > separation the top surface air flow. Leaving the wings sanded and
> > > unwaxed allows the rain drops to flow more smoothly on the wing
> > > surface; significantly reducing drag.
> > > However, only a bug wiper system appear to help the bug problem.
> > >
> >
> > I sand the wings on my Nimbus 2 and they seem to deliver the advertised
> L/D.
> > I have tried surfactant on a few gliders and, by appearance only, it
seems
> > to work. A capful or two of dishwasher "rinse clear" or "spot free" or
> > something like that in a bucket of water seems to be enough.
> >
> > As for the bugs, as slow as I fly, they have time to get out of the way.
> >
> > Bill Daniels
> >
>
>

[P. Corbett]

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 .
>
>

[[email protected]]

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

[Udo Rumpf]

> [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

[Marc Arsenault]

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 .
>>
>>
>
>

[Chris Nicholas]

Udo, thanks. Chris N.





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[Maule Driver]

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.

[Udo Rumpf]

"Maule Driver" > wrote in message
m...
> 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

[Alan Garside]

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.

[Alan Garside]

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.

[Maule Driver]

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)

[01-- Zero One]

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.

[Papa3]

Chris Nicholas wrote:
> U
> 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.
>
> Hoping for education, not flames or sarcasm.
>
> Chris N.

Chris,

I highly recommend you run, don't walk, to the book store and purchase
the Illustrated Guide to Aerodynamics by Skip Smith. All of this stuff
and a whole lot more is covered in a very easy to read format aimed at
the layman. It doesn't dumb things down too much, so you still need to
think and maybe even scribble some numbers from time to time. You can
find it online at any of the usual places:

http://www.amazon.com/exec/obidos/tg/detail/-/0830639012/102-7974159-6672135?v=glance

Happy learning,

Erik Mann (P3)

[Chris]

Some time ago, I saw a table comparing various gliders with clean vs. dirty
(I remember somthing like 20 bugs per meter) wings. In that comparission
especially the PIK-20 was very bad with the dirty wing. IMO a wet wing with
water drops multiple times as big as bugs the performance is "comparable" to
the dirty wing.

Much to my surprise (I think) a DG-400 which should have the same profile
wasn't that bug-sensitive.

Anyone knows the source for that table?

Christian


"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.
>
>
>

[Ian]

On Wed, 14 Sep 2005 23:55:40 +0000, 01-- Zero One wrote:

> 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.

I can't talk for the Pik, but I used to own a share in a Nimbus 2 and I
currently own a share in an LS3a. Supposedly all of these have rain
sensitive airfoils.

In over 800 hours in the Nimbus, I never noticed a problem when the wings
got wet.

However in the LS3a I have had the experience of flying in wave, just in
front of a wave cloud. The wave seemed very weak and I could not gain
hight but a K7 joined underneath and quietly out climbed me. Then I
noticed that water droplets had formed along the leading edge of the LS3a
wing. This must have been due to condensation in the wet layer, as the
canopy remained dry. There was also a slight vibration which was just
detectable in the very smooth wave conditions.

I persevered and eventually climbed above the moist layer. As the wings
dried the vibration stopped and the rate of climb increased. Then as I
gained hight the lift got stronger, I enjoyed that afternoon ;-).


Ian