Pic 20's in the rain

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

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 . com...
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

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

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 . com...
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