Elevator Bending After Fabric Covering

[SMGlaeser]

I encountered something unexpected when shrinking the fabric on my elevators. The trailing edge deflected inward at the trim tab pocket, to the point where the deflection was very apparent and the trim tabs themselves no longer fit. I should have grabbed some pictures, but I was worried it would set and immediately cut off the fabric. Good news is that the elevators returned to their starting shape. I'm using Superflite 3.7oz fabric with Stewart Systems, should be a regular covering system. I have not experienced deflection to this severity; horizontal stabilizers, flaps, ailerons, and rudder remained true after shrinking the fabric.

Is this a technique issue? I started shrinking fabric at the center of the elevator up against the 1" leading edge tube and worked outwards on both sides. I noticed the deflection after the 2nd shrink at 300F.

I'm also wondering if the elevator itself would benefit from more bracing. The deflection can make sense when you consider the structural integrity of the trailing edge is compromised with the trim tab pocket coupled with a lack of cross bracing. BTW, this is a factory kit.

[Paul Johnston]

The part will be fine - shrink less- maybe skip the second pass at 300.

[Ryan Koeneke]

I haven't covered yet but I recall this post from Collin

https://bearhawkforums.com/forum/model-specific-qb-kit-built/bearhawk-five-quickbuild/69160-over-shrinking-fabric-on-elevators

[Battson]

We have seen this issue a few times before over the years.
There is an agreed solution somewhere on the forum, or maybe it was the old Yahoo group. I can't find it right now.

Mine had a large gap, but it closed up so close that it almost touched once the tapes were applied. I was lucky that I didn't need to recover the trim tabs.
If you leave your trim tabs to last, they can be filed down. But many people do these first as a good way to practice before the move on to larger parts.

[SMGlaeser]

I appreciate the links to other posts. Solidifies in my mind the need for some additional bracing and combine that with a more measured approach to shrinking the fabric.

[Bcone1381]

Measure the gap before you start to shrink. Shrink the skin at 25F intervals and then measure the gap to see how it closes up. Stop shrinking when the gap is still sufficient in size.

The fabric shrinking of the oval shape of the surface makes it move towards a circle-ish shape and so It closes up that gap, but its closure is very predictable and when you stop increasing the heat on the fabric the fabric stops shrinking, so it stays put.

[Collin Campbell]

I found that wedging a piece of wood (3/4" X 3/4") or so in the trim tab gap during shrinking kept things in place.

[Bcone1381]

Colin may be a top ten eab builder in the USA. and so I would prioritize his post ahead of post #6.