Pic 20's in the rain

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

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?

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".)

Mine did!

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

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.

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?

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

Si

"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

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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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