Sanding or Waxing - PIK 20 Question

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

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

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

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