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Elevator trim tab play

Chris Cooper

Active Member
Fixed the elevator trim tab to the hinge and attached the motor and actuator. With the clevis pin in place I have about 0.5mm of play. The pin is very slightly loose in the trim tab horn. Is this acceptable?
 
After couple thousand hours of flying I had considerable play in elevator trim tab due to an elongated hole. I fly an RV9A. A good friend of mine machined a bushing out of a rivet. Fits perfect feels tight. Thanks Julian! :)


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"No"

Fixed the elevator trim tab to the hinge and attached the motor and actuator. With the clevis pin in place I have about 0.5mm of play. The pin is very slightly loose in the trim tab horn. Is this acceptable?

I think the consensus would be "no - get it fixed". There are various ways to bush the hole in the arm to get a better fit at the pin.

Good catch, by the way!

Best,
Mark
 
When you say 0.5 mm play, is that at the trailing edge? I had about a 1/16 inch play at the trailing edge after 390 hours. I found the trim tab hole was about 3 one thousands inch larger than the clevis pin diameter. After reading your post, I fabricated a press fit clevis pin and now have no trailing edge play. I will be interested to see if its easier to hold altitude accurately.
 
After couple thousand hours of flying I had considerable play in elevator trim tab due to an elongated hole. I fly an RV9A. A good friend of mine machined a bushing out of a rivet. Fits perfect feels tight. Thanks Julian! :)

Any time comaradishe!!!!
 
In service experience and GVT testing (on an airplane that for the test had ~ 1/16" play) has shown it to not be very critical with even quite a bit of play assuming aircraft VNE limits are complied with.
I think a conservative limit would be .032 or 1/32".
 
If my math is correct .5 mm is less than .020 "
.020 " free play at the the trailing edge is totally fine.

A millimeter is actually 0.03937 inch - interestingly, the same number as the number of inches in a meter. For quick calculations, for those of us who must make the conversion in our head, because we don't think in metric, we always just use 0.040 inch (40 mils) as "close enough for government work." :D
 
.020 " free play at the the trailing edge is totally fine.

I've examined the trim tabs on several RVs with the mechanical push/pull cable control system and I was surprised how much play they had...it's been years now since I looked at one, but I want to say the TE of the tabs had something like 1/4" of play, maybe more. I remember thinking they could be at risk for flutter, but there are a lot of older RV's flying around like that and I've never heard of it being an issue on any of them.

So yeah, .020 is probably a long way from having anything to worry about.
 
After reading this post and living with a 1/16 th inch play at the trailing edge for a long time, I fabricated a clevis pin with no play. Flew today for the first time since making the modification and noticed a difference in the plane holding altitude as opposed to hunting. Very pleasant to fly hands off, rudder only and not have any significant altitude excursions
 
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