Pic 20's in the rain

[Matt]

do they fall out of the sky when they get wet?

[Arnie]

Max,

Most gliders of that generation use the Wortmann FX 67 airfoil, which has
degraded performance when wet.
Some examples are :
Kestrel, DG-400, Pik-20, Nimbus 2, Lak-12, LS-3, Janus, HP-18, Jantar 2B

Apparently some are worse than others, I suppose this is due to the fact
that some use this profile on the wing roots only, with another profile
towards the wingtips (these being "better" or more "tolerant"), while some
use only the FX-67 only. But it could be something else.

Apparently the laminar flow is disturbed very easily on this profile, so not
only water, but bugs will degrade their performance as well.

Reading Dick Johnson's flight tests, especially some from the 70s, will tell
you a little bit more about this.
If you go to this link (http://www.ssa.org/Magazines/Johnson.asp) and scroll
down, there are 3 reports about the Pik-20, very illuminating.


"Matt" > wrote in message
...
> do they fall out of the sky when they get wet?
>
>

[MikeYankee]

Apparently one landed out near Ridge Soaring the other day after being caught
in a shower. He was at 6000' msl over Milesburg (less than 10 nm away) and
couldn't make it back to the airport. I wasn't there but heard about it.


Mike Yankee

(Address is munged to thwart spammers.
To reply, delete everything after "com".)

[Doug Turner]

Mine did!

At 00:12 30 April 2004, Matt wrote:
> do they fall out of the sky when they get wet?
>
>
>

[Derrick Steed]

>Apparently one landed out near Ridge Soaring the other day after being caught
>in a shower. He was at 6000' msl over Milesburg (less than 10 nm away) and
>couldn't make it back to the airport. I wasn't there but heard about it.


>Mike Yankee

I have a PIK20B and I have experimented with this aspect of its performance (incidentally, mine is one of those with a different section at the tip - it's FX67K-170 out to the aelerons, then progressively changes to FX67K-150 at the tip). After reading Dick Johnson's articles and noting his assertion that the performance of this sections is strongly dependent on Reynolds number (which is probably why the K21, Nimbus 2, Kestrel, etc. aren't affected so badly - e.g. larger chord). On the basis of his assertion I wandered under a shower cloud (it was virga really) at about 50Kts and around 2Kts sink, the wings got wet and the sink rate went to 8Kts! Following the reasoning about Reynolds number I increased speed to 100Kts, sink rate? Still 8 Kts - it strikes me that you have to accept that there are large changes in the glider's polar and if you don't react to these then you will end up not making it. I think the rule "fly faster when the wings are wet" applies very strongly wi!
th these sections - just remember that they work better at higher Reynolds numbers and there are only two ways to achieve them: put water in it (= flying faster), or fly lots faster when the wings get wet.

Rgds,

Derrick.

[Don Johnstone]

Cant say about the Pik but I can tell you the Kestrel
does, and some. All the aerodynamic qualities of a
housebrick. Grob 103 not much better.
On the plus side an ASW 17 does not appear to be effected,
it climbs with wet wings, bonus if you fly in the UK.

At 02:30 30 April 2004, Arnie wrote:
>Max,
>
>Most gliders of that generation use the Wortmann FX
>67 airfoil, which has
>degraded performance when wet.
>Some examples are :
>Kestrel, DG-400, Pik-20, Nimbus 2, Lak-12, LS-3, Janus,
>HP-18, Jantar 2B
>
>Apparently some are worse than others, I suppose this
>is due to the fact
>that some use this profile on the wing roots only,
>with another profile
>towards the wingtips (these being 'better' or more
>'tolerant'), while some
>use only the FX-67 only. But it could be something
>else.
>
>Apparently the laminar flow is disturbed very easily
>on this profile, so not
>only water, but bugs will degrade their performance
>as well.
>
>Reading Dick Johnson's flight tests, especially some
>from the 70s, will tell
>you a little bit more about this.
>If you go to this link (http://www.ssa.org/Magazines/Johnson.asp)
>>and scroll
>down, there are 3 reports about the Pik-20, very illuminating.
>
>
>'Matt' wrote in message
...
>> do they fall out of the sky when they get wet?
>>
>>
>
>
>

[Sf760]

Mosquito's the same, starts rumbling the instant it gets the slightest bit wet.

Si

[Hank Nixon]

"Matt" > wrote in message >...
> do they fall out of the sky when they get wet?

In a word-Yes
PIK is sensitive to rain and bugs but is a very good glider otherwise.
I used to wash mine with very soapy water solution and let it dry on
front 1/3 of wing. This would allow water to wet out and flow off
wing. Good for about 10 minutes in the rain.
Also found it climbed better if never sanded smoother than 400 grit on
leading edge area. When it stopped climbing, I just roughed it up a
bit.
Standard PIK alarm installation: Rain drop hits canopy- alarm says put
the gear down!
All joking aside they are good value for the money.
Good Luck UH

[COLIN LAMB]

My manual for the Scheibe specifically states that the stall speed will also
increase in rain, which requires higher speed for landing.

Colin


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[Andreas Maurer]

On 30 Apr 2004 09:34:46 GMT, Don Johnstone
> wrote:


>On the plus side an ASW 17 does not appear to be effected,
>it climbs with wet wings, bonus if you fly in the UK.

The 17 uses the FX 62K-131 (as well as the 20).

This airfoil is by far the most docile one concerning bugs and water
that I ever saw. Just as you said - nearly no performance loss with
wet wings or lots of bugs on the leading edge.




Bye
Andreas

[Chris Rollings]

At 00:12 30 April 2004, Matt wrote:
> do they fall out of the sky when they get wet?
>
>My best estimate (I flew them quite a lot in the late
>70's/early 80's) was that in light rain best glide
went from near 1:40 to around 1:20, heavy rain or icing
could be worse. Difficult to be sure because some
(or nearly all) of the observed deterioration could
be sink. However, clean and dry they pretty much stayed
with the ASW 20, slightest hint of rain on the wings
and they dropped very rapidly away.
>

[Steve]

(Hank Nixon) wrote in message

> I used to wash mine with very soapy water solution and let it dry on
> front 1/3 of wing. This would allow water to wet out and flow off
> wing. Good for about 10 minutes in the rain.
> Good Luck UH

I have heard of people doing this. Has anyone tried that new car
washing stuff I have seen advertised on TV? Says it makes it so you
will never have to dry your car again. The water sheets up and runs
off. Dries without spotting. Sounds ideal for those of us flying the
ole 67K 150/170 sectioned gliders.

I have wanted to run a test by flying in a balast dump trail. Prepare
a test section of wing and fly in the dumped ballast. Do a visual
comparison of the standard and prepped sections. I have seen the
dreaded "wall of water" that forms on the top of the wing. Not sure
if it is more depressing to see it on a 15 meter wing, or a 22 meter
wing, though. ;-)

And I don't know if it was just the rain, or some sink, too. But I
was on a 40 mile or so final glide in my Zuni with an ASW-20. GPS
tracks showed neck and neck until I flew through a small shower. He
made it home, and I landed 6 miles short. He said he didn't get wet,
and looks to have been less than half a mile to my side and a bit
behind. A year or so previous, that same 20 was out ahead of me on a
final glide. He found sink and claimed picked up a headwind. Landed
about 6 miles short. I started for home a couple of turns after him
and a bit behind, and made it home. I guess what comes around goes
around.

Steve Leonard
Zuni II (15 meters worth of water spoiler)
604 (22 meters worth of water spoiler)

[Michael McNulty]

"Steve" > wrote in message
om...
> (Hank Nixon) wrote in message
>
> > I used to wash mine with very soapy water solution and let it dry on
> > front 1/3 of wing. This would allow water to wet out and flow off
> > wing. Good for about 10 minutes in the rain.
> > Good Luck UH
>
> I have heard of people doing this. Has anyone tried that new car
> washing stuff I have seen advertised on TV? Says it makes it so you
> will never have to dry your car again. The water sheets up and runs
> off. Dries without spotting. Sounds ideal for those of us flying the
> ole 67K 150/170 sectioned gliders.
>

I would be careful to make sure that any such "miracle product' does not
contain silcone before you try it on your glider.

[Bob Korves]

One thing I found flying my old PIK-20d in the rain and with bugs that
applies to any glider is to not fly too fast when the wings are
contaminated. Most speed to fly information is based on a clean polar and
it will be telling you to fly faster and faster as the sink becomes worse.
You will find the ground quickly. I found that if you just slow down in the
rain or with bugs that your achieved glide will be much better (but, of
course, not good).

If you have a vario with a "bugs" setting, and you think you know where to
set it, you can try that, too.
-Bob Korves

"Steve" > wrote in message
om...
> (Hank Nixon) wrote in message
>
> > I used to wash mine with very soapy water solution and let it dry on
> > front 1/3 of wing. This would allow water to wet out and flow off
> > wing. Good for about 10 minutes in the rain.
> > Good Luck UH
>
> I have heard of people doing this. Has anyone tried that new car
> washing stuff I have seen advertised on TV? Says it makes it so you
> will never have to dry your car again. The water sheets up and runs
> off. Dries without spotting. Sounds ideal for those of us flying the
> ole 67K 150/170 sectioned gliders.
>
> I have wanted to run a test by flying in a balast dump trail. Prepare
> a test section of wing and fly in the dumped ballast. Do a visual
> comparison of the standard and prepped sections. I have seen the
> dreaded "wall of water" that forms on the top of the wing. Not sure
> if it is more depressing to see it on a 15 meter wing, or a 22 meter
> wing, though. ;-)
>
> And I don't know if it was just the rain, or some sink, too. But I
> was on a 40 mile or so final glide in my Zuni with an ASW-20. GPS
> tracks showed neck and neck until I flew through a small shower. He
> made it home, and I landed 6 miles short. He said he didn't get wet,
> and looks to have been less than half a mile to my side and a bit
> behind. A year or so previous, that same 20 was out ahead of me on a
> final glide. He found sink and claimed picked up a headwind. Landed
> about 6 miles short. I started for home a couple of turns after him
> and a bit behind, and made it home. I guess what comes around goes
> around.
>
> Steve Leonard
> Zuni II (15 meters worth of water spoiler)
> 604 (22 meters worth of water spoiler)

[Chris Rollings]

A fair bit of experimenting led me to think that flying
at normal best glide speed with about 2 degrees of
positive flap was least bad. I never tried to think
up theoretical explanations for that, but I'm reasonable
sure it was true.

At 00:06 03 May 2004, Bob Korves wrote:
>One thing I found flying my old PIK-20d in the rain
>and with bugs that
>applies to any glider is to not fly too fast when the
>wings are
>contaminated. Most speed to fly information is based
>on a clean polar and
>it will be telling you to fly faster and faster as
>the sink becomes worse.
>You will find the ground quickly. I found that if
>you just slow down in the
>rain or with bugs that your achieved glide will be
>much better (but, of
>course, not good).
>
>If you have a vario with a 'bugs' setting, and you
>think you know where to
>set it, you can try that, too.
>-Bob Korves
>
>'Steve' wrote in message
om...
>> (Hank Nixon) wrote in message
>>
>> > I used to wash mine with very soapy water solution
>>>and let it dry on
>> > front 1/3 of wing. This would allow water to wet
>>>out and flow off
>> > wing. Good for about 10 minutes in the rain.
>> > Good Luck UH
>>
>> I have heard of people doing this. Has anyone tried
>>that new car
>> washing stuff I have seen advertised on TV? Says
>>it makes it so you
>> will never have to dry your car again. The water
>>sheets up and runs
>> off. Dries without spotting. Sounds ideal for those
>>of us flying the
>> ole 67K 150/170 sectioned gliders.
>>
>> I have wanted to run a test by flying in a balast
>>dump trail. Prepare
>> a test section of wing and fly in the dumped ballast.
>> Do a visual
>> comparison of the standard and prepped sections.
>>I have seen the
>> dreaded 'wall of water' that forms on the top of the
>>wing. Not sure
>> if it is more depressing to see it on a 15 meter wing,
>>or a 22 meter
>> wing, though. ;-)
>>
>> And I don't know if it was just the rain, or some
>>sink, too. But I
>> was on a 40 mile or so final glide in my Zuni with
>>an ASW-20. GPS
>> tracks showed neck and neck until I flew through a
>>small shower. He
>> made it home, and I landed 6 miles short. He said
>>he didn't get wet,
>> and looks to have been less than half a mile to my
>>side and a bit
>> behind. A year or so previous, that same 20 was out
>>ahead of me on a
>> final glide. He found sink and claimed picked up
>>a headwind. Landed
>> about 6 miles short. I started for home a couple
>>of turns after him
>> and a bit behind, and made it home. I guess what
>>comes around goes
>> around.
>>
>> Steve Leonard
>> Zuni II (15 meters worth of water spoiler)
>> 604 (22 meters worth of water spoiler)
>
>
>

[cernauta]

"Matt" > wrote:

> do they fall out of the sky when they get wet?
>
Yes, just like the DG400, 200, LS-3 and many others.
Don't use strange products disigned to give long lasting lustre for
cars: they will produce much larger droplets on the wing surface, and
the problem will be worse.
Don't fly fast in the rain: lower your flaps and your speed as well.
The manual says that stall speed may increase, but any excess in speed
will be transfered to the water instantly: a big energy loss!
(a student has calculated the amount of energy needed to accelerate
100 grams of water from 0 to 60kts in a few seconds: it's about 3
times as much as the energy that would keep you flying level at the
same speed).

Water droplets will affect the tailplane too: you'll feel the stick
has different forces, generally it feels "dead". But it isn't, don't
worry.
Take care to avoid turbulence, as recovery from unusual attitudes will
become... scary!

I tried 40kts with landing (+15°) flaps on my 400, and was able to
avoid losing too much altitude. Stop for a few circles in any dry,
zero (or more) lift area, so you may later proceed gliding only when
the wings are nearly dry.

And generally, steer well clear of rain.

Aldo Cernezzi

[Eric Greenwell]

Matt wrote:

> do they fall out of the sky when they get wet?

Since I didn't see anyone mention it, I'll do so: taking off with rain
(or a lot of bugs) wings can also be troublesome. The manual on most
gliders cautions against it, and that caution is probably even more
important for a glider like the PIK 20.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[Derrick Steed]

Aldo Cernezzi wrote:
>any excess in speed
>will be transfered to the water instantly: a big energy loss!
>(a student has calculated the amount of energy needed to accelerate
>100 grams of water from 0 to 60kts in a few seconds: it's about 3
>times as much as the energy that would keep you flying level at the
>same speed).
>

I'm puzzled by the apparent assumptions here, why would any of the rain drops, other than that hitting the stagnation point on the leading edge, be accelerated to 60 Kts? It's much more likely that a high proportion of the mass of the rain drops would simply bounce off with very little momentum transfer. The rain which stuck, a much smaller proportion, may get accelerated to 60Kts, but there is only a limited amount which the wing could accommodate anyway. When I experimented with rain on the wings, I found the sink remained constant even though the speed increased, in which case my glide angle was getting better as I went faster. I must admit I didn't experiment with flaps, but I will, all these comments I've seen so far provide food for thought on how to get the best out of the glider in poor conditions.

Rgds,

Derrick.

[cernauta]

Derrick Steed > wrote:

>Aldo Cernezzi wrote:
>>any excess in speed
>>will be transfered to the water instantly: a big energy loss!
>>(a student has calculated the amount of energy needed to accelerate
>>100 grams of water from 0 to 60kts in a few seconds: it's about 3
>>times as much as the energy that would keep you flying level at the
>>same speed).
>>
>
>I'm puzzled by the apparent assumptions here,

Dear Derrick,
clearly there are assumptions. But I have deliberately flown my 400
into rain, and kept watching the canopy and the wings, trying to
investigate the behaviour of water droplets.
A wing can get very little or a lot of water per time unit, depending
on many variables. Anyway, 100grams of water (= 0,1 liters) is just
half a drinking glass. Not that much, over 10,xx m2 of wing surface,
plus fuselage and tail. It definitely looked possible, from my
perspective in the cockpit, in anything more than light drizzle.

I have then tried to use my method (extremely slow flying, and parking
in dry, zero lift, before leaving for a glide) in competitions, and
could notice a very big advantage against those who raced to escape
from the rain. No matter if they were flying an 800!

all the above, is IMVHO.

Aldo Cernezzi
now dg600 flyier

[Derrick Steed]

>>Aldo Cernezzi wrote:
>>>any excess in speed
>>>will be transfered to the water instantly: a big energy loss!
>>>(a student has calculated the amount of energy needed to accelerate
>>>100 grams of water from 0 to 60kts in a few seconds: it's about 3
>>>times as much as the energy that would keep you flying level at the
>>>same speed).
>>>
>>
>>I'm puzzled by the apparent assumptions here,
>
>Dear Derrick,
>clearly there are assumptions. But I have deliberately flown my 400
>into rain, and kept watching the canopy and the wings, trying to
>investigate the behaviour of water droplets.
>A wing can get very little or a lot of water per time unit, depending
>on many variables. Anyway, 100grams of water (= 0,1 liters) is just
>half a drinking glass. Not that much, over 10,xx m2 of wing surface,
>plus fuselage and tail. It definitely looked possible, from my
>perspective in the cockpit, in anything more than light drizzle.
>
>I have then tried to use my method (extremely slow flying, and parking
>in dry, zero lift, before leaving for a glide) in competitions, and
>could notice a very big advantage against those who raced to escape
>from the rain. No matter if they were flying an 800!
>
>all the above, is IMVHO.
>
>Aldo Cernezzi
>now dg600 flyier
>
I can assure you that although it maybe doesn't come across that way the are
lots of "V"'s in my "IMHO". I'm just curious about other the experience
other people have, to get the full story it's sometimes necessary to
challenge assumptions.

My reasoning was based on one not being able to "parking in the dry", but
instead having to get out of the wet, it's not clear what is the best option
for this. I am only too well aware of the bad effect the rain has, and I
have tried the wing both polished and unpolished (interestingly, the form of
the water droplets was different in the two instances - unpolished, they
stood like little spikes). The real worry I would have is taking off or
landing with the wings very wet - once when visiting a hill site I called
off the launch on a winch three times before giving up and calling it a day
because of passing rain shower wetting the wings (another pilot stole the
only dry launch possibility I had that day - I'll never forgive him for
that).
I hope to hear more experiences, it all goes into the melting pot.

Rgds,
Derrick.

[Chip Bearden]

I flew an LS-3 for many years, which nominally has the same airfoils
as the PIK. When it was newer, I had some "falling out of the sky"
experiences, too, although not as dramatic as the PIK drivers
reported.

Slowing it down and using more positive flap than normal as suggested
by several PIK pilots seemed to help. I later kept my wings in a 400
grit sanded surface, and once for a few years at 220 (the latter was
very difficult to keep clean, the joke being that one had to sand off
the bugs!). The satin finish seemed to help substantially: the water
didn't bead up; it "sheeted" instead and flowed off. It still came
down faster than usual when it got wet but it wasn't scary and, as one
fellow suggested, sometimes it's difficult to separate the effects of
rain and storm-associated sink anyway.

Chip Bearden

[chris]

I think the PIK-20 may be worse in the rain than other gliders that
use the same airfoil. I remember reading that the late production
runs of the PIK-20s were more sloppily built, and that the 17%
thickness at the root got much thicker 20-21%. The closing of the
wings was less accurate. This innaccurate/thicker warped version of
the FX167 airfoil may not fly as well as the LS-3, DG-200, DG-400,
Mosquito, MiniNimbus etc. This effect may be most noticable when wet.

If the airfoil is not built to specification it could be a mess.

Chris


(Chip Bearden) wrote in message >...
> I flew an LS-3 for many years, which nominally has the same airfoils
> as the PIK. When it was newer, I had some "falling out of the sky"
> experiences, too, although not as dramatic as the PIK drivers
> reported.
>
> Slowing it down and using more positive flap than normal as suggested
> by several PIK pilots seemed to help. I later kept my wings in a 400
> grit sanded surface, and once for a few years at 220 (the latter was
> very difficult to keep clean, the joke being that one had to sand off
> the bugs!). The satin finish seemed to help substantially: the water
> didn't bead up; it "sheeted" instead and flowed off. It still came
> down faster than usual when it got wet but it wasn't scary and, as one
> fellow suggested, sometimes it's difficult to separate the effects of
> rain and storm-associated sink anyway.
>
> Chip Bearden

[Bob Kuykendall]

Earlier, Chris > wrote:

> ...I remember reading that the late production
> runs of the PIK-20s were more sloppily built,
> and that the 17% thickness at the root got much
> thicker 20-21%...

According to this Dick Johnson report, there was a thickness error,
but to a much smaller degree:

http://www.ssa.org/Johnson/26-1979-01.pdf

Where Dick writes:

: The PIK-20D factory brochure data
: indicate that the wing thickness-to-chord
: should be .170 tapering to .150 at the tip.
: Our measurements of N19YZs wing showed .176
: at the wing root, .184 at the aileron root,
: and .161 at the wing tip, This averages
: about .01 t/c greater than it should be,
: and perhaps is the reason for the higher drag.

Guessing that the PIK-20 side-of-body chord is nominally about 35",
the difference in depth between 17.0% and 17.6% amounts to 0.21"
(5.3mm). On the other hand, if the actual side-of-body thickness
really were on the order of 21%, the difference between 17% and 21%
times the estimated 35" chord would be around 1.4" (36mm). I cannot
imagine any production sailplane could ever be built with _that_
degree of sloppiness.

For me, the real surprise is reading that the aileron root thickness
had creeped out to 18.4%. Guessing that the taper from 17% at
side-of-body to 15% at the tip is supposed to be distributed linearly,
and that the aileron root falls at about the 0.5 semispan, the
thickness there should have been about 16%. Guessing further that the
chord at the aileron root is about 27.5", the percentage difference
amounts to a depth error of around .66" (17mm). Now that's a large
error.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

[chris]

Bob,

Wouldn't the Dick Johnson report just report on one example/Serial
Number? The one example may not be representative of the worse ones.
Maybe the ones built close to specification are similar to the other
gliders with the same airfoil, and possibly the thickest ones are the
ones that perform really poorly in the rain.

Chris

(Bob Kuykendall) wrote in message >...
> Earlier, Chris > wrote:
>
> > ...I remember reading that the late production
> > runs of the PIK-20s were more sloppily built,
> > and that the 17% thickness at the root got much
> > thicker 20-21%...
>
> According to this Dick Johnson report, there was a thickness error,
> but to a much smaller degree:
>
> http://www.ssa.org/Johnson/26-1979-01.pdf
>
> Where Dick writes:
>
> : The PIK-20D factory brochure data
> : indicate that the wing thickness-to-chord
> : should be .170 tapering to .150 at the tip.
> : Our measurements of N19YZs wing showed .176
> : at the wing root, .184 at the aileron root,
> : and .161 at the wing tip, This averages
> : about .01 t/c greater than it should be,
> : and perhaps is the reason for the higher drag.
>
> Guessing that the PIK-20 side-of-body chord is nominally about 35",
> the difference in depth between 17.0% and 17.6% amounts to 0.21"
> (5.3mm). On the other hand, if the actual side-of-body thickness
> really were on the order of 21%, the difference between 17% and 21%
> times the estimated 35" chord would be around 1.4" (36mm). I cannot
> imagine any production sailplane could ever be built with _that_
> degree of sloppiness.
>
> For me, the real surprise is reading that the aileron root thickness
> had creeped out to 18.4%. Guessing that the taper from 17% at
> side-of-body to 15% at the tip is supposed to be distributed linearly,
> and that the aileron root falls at about the 0.5 semispan, the
> thickness there should have been about 16%. Guessing further that the
> chord at the aileron root is about 27.5", the percentage difference
> amounts to a depth error of around .66" (17mm). Now that's a large
> error.
>
> Thanks, and best regards to all
>
> Bob K.
> http://www.hpaircraft.com/hp-24