OK netters I guess I will step off into it.
Wittman Tailwinds do have wooden truss ribs. All Wittman Tailwind wings that I
know of in recent years are glued together with T88. I keep up with the Wittman
guys closely, I know many of them, I attend their get togethers. The older ones
used the powder mix for gluing theirs, I don't rember what you call that stuff.
The Wittman has two wooden spars just like a KR. The ribs are actually 1/2"
wide. The reason is so there is a larger gluing surface for the sheets of
plywood that get glued down and covers the wings. Once all the plywood is
glued, set, sanded smooth the current trend is to cover them with a layer of
fiberglass cloth mostly for sealing but for some strength. Most builders in the
last 8 to 10 years are using the West epoxy system for wetting out the
fiberglass cloth that covers the outside surface of the Wittman wings.
Steve Wittmans plans tell you to cover the wings with doped fabric, as in
Stits/Poly Fiber, but actually the predecessor to the Poly Fiber system.
Unfortunately what killed Steve Wittman was a mix up in technique . Steve had
always used the old covering system which allowed you to lay fabric (I am
talking about fabric covered airplanes type of fabric not fiberglass) on the
wood and wet it out with the dope just like we do with fiberglass cloth. The
dope would penetrate through the fabric and then it was stuck down, no problem,
that is the old way of covering the plywood wings as specified by Mr Wittman.
When he built the O&O Mr Wittman used the Stits system, but he did it wrong, he
did it like the old stuff. What he was supposed to do was paint the new stuff
(Poly Tak) on the plywood first, laying the fabric on top of that while it was
still wet, covering a little at a time to make sure the Poly Tak stays wet when
the fabric is applied to it, then use the second step, paint (Poly Brush) on
top of the fabric.
The fabric on the O&O managed to stay on the plane for about 10 years I think
it was. He had built this plane to carry all of his things to his winter home
in Ocala Fl from Oshkosh, that is why he named it the O&O for those of you who
don't know. The last flight that Steve Wittman made from Ocala headed back to
Oshkosh for the summer of course was his last, the fabric had delaminated from
the plywood, set up flutter and tore the wing off of the airplane. I think EAA
had an article about it, I never read it so I am not sure what they wrote about
it but this is what happened to it.
Bottom line is know your systems, attempt to know what you are doing and by all
means pay attention..
I for one would never use West Epoxy for gluing ribs or a wooden airplane
together. I have never known anyone to have done such. Not saying that there is
not someone who has but I would never do that.
I know a guy who built his wooden truss ribs with model airplane CA glue, I
warned against that but a guy has to do what a guy has to do.
I have known guys who use the wrong stuff to build all kinds of airplane parts.
I will rephrase that and say the wrong stuff as far as I am concerned.
Larry H.
