Crispy Critter Update...

[crispy critter]

Well ill start by saying its been far too long since much work has progressed on Crispy but we have been doing a little. Today I hauled it out of storage in the hangar and home to my garage where I will have a little more time to devote to it this winter, especially on cold days when I cant work at the airport(I have heat in my garage).
As much as it pained me to do it, the first order of business after hauling it home today was to cut open a section of new fabric on the aft end of the fuselage. I had it covered all thru the second cross coat of silver and when I moved it out of the paint both I wasnt thinking when I parked it next to a window in dads hangar. The window always caught the morning sun and would shine directly onto the left side of the vertical stab from sunrise until almost noon....and guess what that did....yep, it tighten the fabric on the left side to the point where it wouldnt allow the vertical to straighten up. I tried shrinking the right side with no luck, in fact the left side is so tight now that if you do force it hard enough(and I mean hard) to straighten the vertical it causes wrinkles in the right side(see pics).
So with all that explained, today I managed to move it to my garage, removed the fabric from the vertical, and get the left side glued back on. I will lighty shrink it in the morning and then glue on the right side sometime tomorrow. Hope to get everything covered & painted this winter and spring but making no promises.

Sorry about the sideways pictures, I tried to delete them and repost but it wouldnt let me delete the first ones....oh well.lol

[Robert Lees]

Re: Crispy Critter Update...

Forgive the obvious question, but why would the sun further shrink the fabric on that side if it was heat-shrunk first?
Lots of aircraft spend years parked on outdoor tie-down always in the same place; do they suffer the same fate?

Rob

[crispy critter]

Re: Crispy Critter Update...

Sometimes they do rob but usually not as bad after they have sufficient uv(silver) on them. Mine only had two thin cross coats on it and it shrank it about as tight as it would shrink.

[Ragwing nut]

Re: Crispy Critter Update...

Either you didn't have it tight enough to start with or did you use taughtening dope on it? It can be tricky to make sure you pull the fabric up evenly on the vertical or you will have that problem.

[crispy critter]

Re: Crispy Critter Update...

It's possible that it may have been a little tighter on one side to start with but unless you shrink it to the point just shy of the Dacron loosing its elasticity it will shrink in the heat if you don't have enough uv on it. I never shrink above 350 and Dacron will continue to shrink up to around 450 at which point it will actually start to go the other way(if it doesn't start to melt). If you have enough uv it will not shrink or at least not much once you've ironed it up to 300+. However if you don't have uv or enough uv it will continue to shrink.

[Ragwing nut]

Re: Crispy Critter Update...

It's possible that it may have been a little tighter on one side to start with but unless you shrink it to the point just shy of the Dacron loosing its elasticity it will shrink in the heat if you don't have enough uv on it. I never shrink above 350 and Dacron will continue to shrink up to around 450 at which point it will actually start to go the other way(if it doesn't start to melt). If you have enough uv it will not shrink or at least not much once you've ironed it up to 300+. However if you don't have uv or enough uv it will continue to shrink.

it will never get that hot in the sun. Black tops out around 200-220*. I have never heard of UV shrinking the fabric, although it will deteriorate it. What paint system did you use?

[lawheelock]

Re: Crispy Critter Update...

Forgive the obvious question, but why would the sun further shrink the fabric on that side if it was heat-shrunk first?
Lots of aircraft spend years parked on outdoor tie-down always in the same place; do they suffer the same fate?

Rob

I don't think it was stated as to what fabric (Ceconite or Polyfibre) was used nor what finishing process (dope or Poly-brush or Poly-spray}
At any rate, even non tautening dope continues to shrink somewhat, though not as much as regular dope. Whether or not the Poly products continue to shrink some, I do not know, but I suspect they do and with heat from the sun this might hasten and enhance the shrinkage of the "paint" product.
I covered my Stinson with Razorback in 1977-78 and the only way Razorback is tightened is with the tautening dope PROVIDED that no dope penetrates the weave of the fabric. Every coat on Razorback is sprayed in order to prevent penetrating the weave.
So, in Kevin's situation, it is probably the paint material on the fabric that caused the shrinkage, not the fabric itself. Two coats of aluminum pigmented "paint" should have been sufficient to protect the dacron from UV damage, but maybe not.
It is normally considered not good to stop with the aluminum coat and wait months or year before applying the final coats because it invites poor bonding of the final coats to the aluminum impregnated material. I suppose it might help to spray a coat of rejuvenator on the aluminum coat before proceeding if it has been more than a week or two since the application of the aluminum.
Larry Wheelock, BC12D N96179 being repaired, Stinson N584LW still flying with the Razorback, Mooney M20C N79806 flying

[barnstmr]

Re: Crispy Critter Update...

Comment related to fabric shrinkage

Lon removed his '39 BC-65 rear struts and sent them out to Wag Aero for refurbishment. He never intended to let the airplane go as long, but it ended up almost 2 years before he got the chance to go re-install those struts. He made a mistake by not providing any extra support of the wings at the rear spar. And so the wings sat for the whole time in this state with gravity acting to put a twist load on the wings. Over the time, the wings relaxed and drooped rather significantly toward the rear.

So recently, on Thanksgiving day, I helped Lon re-install his rear struts. That's when we became aware of the situation. It was concerning at first. In order to align and pin the strut attachment, it took two men (one working at each spar) to twist the wing (one man pulling down on the front spar... one pushing up on the rear) while a third worked to place the pin... So we accomplished the strut installation using a drift to pin to temporarily the struts in place. At this point, we acknowledge that the resulting strain on the wing caused the fabric to wrinkle in every rib bay. We first thought the load to be possibly damaging, but then realized the load was nowhere near the kinds of loads the airplane actually experiences in flight from gusts etc.. The fabric is Poly-Fiber (Stits) installed in 1999.

We discussed the situation and concluded that this condition was probably due to the moisture and temperature changes causing the fabric and the rib lacing to assume a comfortable relaxed state. That day in the Hangar, it was rather cold.... had been around freezing the night before. It was a sunny day, so we decided to push the airplane out on the ramp to soak in some sun. It warmed up to near 50 degrees as we washed the airplane off while sitting out in the sun, and in just 30 minutes many of the wrinkles had subsided. So then we let the airplane soak in the warmth and sunlight while we went hand had our Thanksgiving lunch with the family. We returned in about 3 hours to discover the fabric looked completely normal... absolutely no wrinkles. So we un-pinned the rear struts and found that there was almost no force required to align the holes... the wing was literally back to normal.

My point to all of this is that there is a useful purpose in the way these old fabric covered airplanes are built. These are NOT stressed aluminum skinned structures. The fabric, rib lacing, and dope covering are each intended to flex and conform to the shape of the primary structure and assume the airfoil shape of the aluminum ribs. I think a lot has to do with stretching and skewing of the weave rather than the fibers themselves. It should not be surprising that over time with humidity and temperature changes, etc.... the taughtness of the fabric will most assuredly vary.

[Robert Lees]

Re: Crispy Critter Update...

Terry,

I had exactly the same situation with a Razorback-covered Taylorcraft about 15 years ago. The fiberglass fabric slackened off, and when we put the new rear struts in, over a few hours the fabric sorted itself out. No damage to the paint, either.