Sanding or Waxing - PIK 20 Question

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...72135?v=glance

Happy learning,

Erik Mann (P3)

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.

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