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Thread: Fabric problems with Pitts aircraft
Message: Fabric problems with Pitts aircraft
Follow-Up To: ACRO Email list (for List Members only)
From: "Sheldon Apsell" <SHELDONA at FS.MICROLOGIC.COM>
Date: Thu, 06 Mar 1997 11:50:33 UTC
March 6, 1997
In my last post regarding the fabric separating in flight
on Roy Speeg's S-2B, I implied that the problem was with
the fabric itself and that there should be less of a problem
with aircraft covered with dacron (such as Roy's) than with
aircraft covered with cotton (such as mine). I have since
learned that this is probably incorrect. Although in the past
there has been a problem with the quality of fabric on Pitts
aircraft, this probably has nothing to do with the incident
involving Roy's plane.
I have been told that the process by which the dacron is
glued to the wing is very critical. Apparently, the adhesive
used does not adhere to dacron. Consequently, the
adhesive must be applied to the top of the material and then
carefully worked through the weave until it comes out the
bottom. The glue on the bottom adheres to the wing
members, but if there is insufficient glue on the top of the
dacron or if it has been applied incorrectly, the fabric will
separate from the glue. It is the glue on the top adhering
to the glue on the bottom that traps the dacron and keeps
it in place. A fabric punch test will tell you whether or not
the material is good but it doesn't tell you that it has been
properly installed. I don't have any idea what kind of test
(if any) can be performed to confirm that the fabric has been
properly installed.
I would like to emphasize that this can be a very serious
problem. It is believed that this is the failure mechanism
that led to the fatal crash that killed Steve Wittman and his
wife. According to the accident report, Steve did not use
the correct procedure for installing the fabric. It then
separated in flight causing aileron flutter and structural
failure.
Another point to consider regards the appropriate course
of action to take should you experience such a failure in
flight. After the incident with Roy's plane, he asked me why
I didn't bail out. The truth of the matter is that it never
occurred to me. Although I was wearing my own parachute
which I new to be perfect shape, a high quality crash helmet,
and long pants (in spite of the Florida heat and humidity);
I was psychology unprepared to use my emergency
equipment. (I was also right over a pond where earlier in
the day Roy and Mike Goulian had been feeding the
alligators!) I was lucky in that the fabric separated in an
area that did not affect the function of the ailerons. But I
now believe that if the fabric has separated further outboard
the correct response would have been to bail out
immediately (and take my chances with the alligators).
Sheldon Apsell
Newton, MA
Pitts S-2B
P.S. There is absolutely no truth to the rumor that Roy is
recovering his wing with alligator skins!