Over shrinking fabric on elevators

Collin Campbell

Collin Campbell

New member
Ran into an issue while covering the elevators on the Model 5 I am currently building. In a recent post by Rob Caldwell, he mentioned checking the fit of the trim tabs after covering the elevators. So, in checking mine out, I found that I had the same problem! Never had an issue like this before, so was wondering what could be the problem. The trailing edge of the elevator at the tab recess had narrowed down significantly (the trim tab would barely fit in there) and also noticed that the elevator spar (1" tube) had bowed about 1/8". The gap between the elevator and the stab is just over 1/8" (5/32") so this was not good...

I figured that somehow the fabric on the elevator was just not up to being shrunk to the full 350 deg. The rudder came out just fine at the full setting, but of course it doesn't have the cut-out in the trailing edge tube for the trim tabs as do the elevators. For reference, in the past I had been using a regular household iron to do the final shrinking. Of course I calibrated it like the instructions say but what I am thinking now is the iron was just not capable of maintaining the setting...(not sufficient wattage to do the job). Well, the difference is, I bought a Fabric Pro iron (like was suggested in another post) and I really like it! Digital setting so it is easy to use and maintains the temp within a couple of deg or so. So it seems with this new iron, I am now able to maintain the full 350 deg temp, while in the past I was not and therefore no overshrinking issues.

So, I recovered both elevators and this time only shrunk the fabric to 300 deg. and stopped. At this temp. there were no deforming issues...spar tubing all straight...trim tabs fit. Plan to talk to Bob about this issue next time I speak to him to get his thoughts on the matter. I am thinking an extra 1/4" tube somewhere might be in order...
 
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Just so I understand. Mark, where is this new 1/4" tube going? Is it between the trim tab hinge tube and the leading edge of the elevator? Something like this (but maybe a straight piece of tube :-)?


elev.png
 
I had the same issue with trim tab clearance during shrinking. I ended up putting in a 1x2 spacer in while shrinking. The spacer length was the length of the trim tab plus allowance for clearance both sides. Worked out ok. Maybe that could help?

The clearance closes as the shrinking fabric forces the curved trailing edge tubes to "straighten" . That is what I saw. I used heavy fabric because I play in the rocks, gravel and sagebrush.
 
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Hey guys -

Don’t see that this was ever tied off. If it’s answered elsewhere, please post a link. Is Collin’s guidance to use less heat the
final solution? I’ll keep looking. Thanks!
 
I had the same issue Collin described at the trailing edge of the trim tab gap. When we shrink the stresses on the H-stab wants to become round like a circle. That reaction will close up the trim tab gap some.

My solution......Before I shrank, I fit the trim tab into position and measured my "Before Shrinking" clearance. I then measured the gap after each shrink....every 25F starting at 250F. At 250F there was no effect. As I shank, I saw the gap closing in on the tab. Collins caution definately needed to be accounted for on my H-stab. I stopped shrinking before I reached 350F due to clearance issues. I had absolutely no surprises shrinking and measuring the gap this way. I could see what was happening and how far it was going.

I think I got it to 300F. I used a digital Iron....forget the name...maybe Fabric Pro from Stewarts. Its a good iron!!
 
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