Scratch-built Trim Hinge Issue to look for

[John Bickham]

Just wanted to give heads up to scratch builders on issue that I came across on the trim tab hinges during covering and installation.

Take this point with the following disclaimers:

• super amateur builder
• decisions made years ago, results today
• not sure what current plans specify
• I covered tail structure with heavy fabric for off field abuse

I ran into a little interference problem with the trim tab hinges and the finished fabric. My plans (#1117) only specified a 3/16" pin. I didn't see any detail regarding the tubing for the hinge. So much time has passed, I can't tell you how I arrived at the decision to use 1/4" x .028" tubing for the hinges, but I did.

Problem is that thin a wall of tubing, I didn't have enough clearance for the thickness of the fabric. I had to eliminate the fabric in the area of the hinge tubes to get a good fit and smooth motion. Even though I covered with heavy fabric, I'm sure I would have the same issue with medium fabric. I would consider going with a thicker wall tubing like 5/16" x .058 next time.

One other little point and this one does have to do with decision to use heavy fabric. When I shrunk the fabric, the bow of the elevator pulled in a bit and caused a bit of clearance issue at the rear edge. So much so, that I had to put a spacer where the trim tab should be while fabric shrinking.

Just relaying my experience based on the decisions I made. Expect others had better results. Hope helpful.

trim tab hinge fabric issue (1).JPGtrim tab hinge fabric issue (2).JPG

[Steve W]

Usually shim the hinge tube off the main tubing with small strips of flat stock. Helps with not blowing through the thin hinge tubing when welding and allows a bitter fit of the clevis pins

[John Bickham]

Thanks Steve, that would be the answer. I am curious, is that one of those "experience educates" things or did I miss that detail somewhere?

[Steve W]

No there isn’t any warning about that kind of stuff. I did the same
thing you did on my first scratch built plane. Had a hard time as you did getting the pins in after the fabric.
So just a heads up on the side window hinges, you will experience the same lack of clearance. I had to grind down the head diameter of the long clevis pins to get them in without cutting into the paint. I shimmed the hinge tubing before welding but obviously not enough.

[John Bickham]

Thanks too much

[Collin Campbell]

To solve this issue, I have been doing the hinges like what is shown in this EAA video. It shows making hinges for an elevator, but can easily be adapted for our situation at the trim tabs. It makes the welding much easier and provides the clearance we need for the fabric. Only thing I might add is to make the jig from steel instead of wood to make it hold up better while welding. https://www.eaa.org/videos/5694283174001

[randyhall99]

Excellent video, thanks for sharing.

[John Bickham]

That a fine, nice method. If I have another plane in me, that would be the way to go. thanks