another idea for trim tab

[avidflyer]

This isn't my idea, but I saw it and thought it was neat. Probably more applicable to earlier model Kitfoxes. A lot easier than cutting up your elevator and I like the adjustment as well. Someone on another forum mentioned a worry about flutter, not sure why that would be a concern. Any thoughts? JImChuk

Kitfox - Trim Tab Update - YouTube

[Maverick]

I did this very thing on my first homebuilt (not a kitfox) and then did a dive test to 150mph to check for flutter which did not occur. I flew this plane for 20yrs and >450 hours with no problem. I used a vernier control that I bought from an equipment company. It was 14 ft long and was originally for a road grader/maintainer and was much cheaper. I mounted the control knob on the dash. The length of the cable made it possible to make a wide loop routing the cable around and back. The other thing I did was weld a cross member between two of the ribs about 3.5 inches in from the trailing edge so the trim tab was fitted to the shape of the elevator. This was a very easy way to add trim and it was very effective and useful.

[avidflyer]

Thanks for the comment about the road grader throttle. I remembered I have a new long one for a big truck that may just be long enough as well. JImChuk

[Av8r3400]

The concern for flutter comes from the engineering of that cable is such that it's designed to pull, not push.


So that being given, putting a spring around the cable to assist in pushing on the trim tab rather than relying solely on the cable would be very advisable.

[avidflyer]

I went looking for a long throttle cable and found this on Amazon. 25'. Also see a 15' length for almost $20 less. JImChuk
Amazon.com: Buyers Products Venier H.D. Adjustable Throttle Locking Control Cable - 25' : Automotive

[Maverick]

In order to address the strength of the wire for pushing and pulling, I attached the end of the cable housing to that cross member I mentioned in my previous post. The amount of wire that extended from the cable housing was kept to a minimum (1.5"). The push/pull wire was industrial grade and after 450 hrs showed no sign of wear or weakness. Dive testing to 150mph, which was far more than the typical max speed, demonstrated an acceptable strength to resist flutter however, I will say this; my trim tab was quite a bit smaller. One needs very little surface area to trim the elevator. In how I applied this mechanism to my plane, I would do it again but that is not an endorsement of it as anyone else's solution.
Maverick