Trim Control Horn Problem?

Stalldog · #1 07-08-2012, 08:15 PM

Did I do a bad thing? Went to mount the servo and it's slightly off center with the pushrod, so I figured I'd slightly open up the hole in the control horn so the pushrod wouldn't be in a bind. Mind you, I only drilled it out to 1/4", which is the diameter of the clevis pin, but it's no longer tight in the control horn and has an ever so slight amount of play. I read AFTER I did this that I should not open up the hole any, but again, I only drilled it out to 1/4". So, my question, will this be a problem with the trim tab? I don't want to create any type of flutter problem or make the trim tab hard to control.

If it's a problem, I figure I have some options: 1. Drill another undersized hole in the control horn and slowly ream it out until the clevis pin fits tightly like before, then cut off old hole and reshape the end of the control horn. Or, 2. Drill out the control horn and pop rivet a new control horn in it's place. I've got some Cherrymax rivets if needed.

Maybe it's not a problem. What do you think?

frazitl · #2 07-09-2012, 08:30 AM

way too big for the trim servo pushrod pin at the control horn. IIRC, it's more like 1/8". Wonder why the pushrod didn't line up? Might start here.

Mine has no slop, and I think that's important.

I wouldn't do anything that changed the geometry. Maybe a bushing? Not much clearance in the pushrod slot though...

A new trim tab wouldn't be too hard or expensive to build.

aerhed · #3 07-09-2012, 09:14 AM

Go with a new horn and make it line up with the servo rod in a straight shot. If you drilled a new hole further up the horn you'd have excessive tab travel and increased trim sensitivity. I like to set up elevator tabs so that with forward CG full down tab yields a speed a few knots above stall. You really don't want it to trim any slower.

aerhed · #4 07-09-2012, 09:16 AM

Quote:

I like to set up elevator tabs so that with forward CG full down tab yields a speed a few knots above stall.

Oops. Make that AFT CG.

rvbuilder2002 · #5 07-09-2012, 09:34 AM

Quote:

Originally Posted by aerhed

Oops. Make that AFT CG.

I think you had it right the first time. The most fwd GG position will require the most nose up trim.

aerhed · #6 07-09-2012, 09:44 AM

No. You want to run out of trim before stalling and aft CG is the worst situation. If it means a little more stick load on final with forward CG, that's life.

rvbuilder2002 · #7 07-09-2012, 09:49 AM

Quote:

Originally Posted by aerhed

No. You want to run out of trim before stalling and aft CG is the worst situation. If it means a little more stick load on final with forward CG, that's life.

In that context you are correct. I didn't notice you wrote "speed just above stall"
I was thinking relative to FAR23 which I think requires ability to trim to 1.3 above Vs0 at max fwd C.G. (if I remember correctly).

Stalldog · #8 07-09-2012, 10:40 AM

Update. I actually drilled it out to 1/8", not 1/4". Brain was tired when I posted this!

Also, when I mounted the servo, I shifted it over from Van's measurements and it now lines up with the opening AND the horn, so no alignment issue.

The dia of the hole in the horn is actually slightly less than 1/8" so that the pin fits tightly. What I did was to ream it out to 1/8" so that it now has a very tiny amount of play. Will that be a problem?

Mel · #9 07-09-2012, 11:06 AM

Quote:

Originally Posted by Stalldog

What I did was to ream it out to 1/8" so that it now has a very tiny amount of play. Will that be a problem?

A small amount of play in the trim tab is not a problem.
All (RV) manual trim tabs have a small amount of play and it has never been a problem.
Thousands of RVs have been flying this way since the '70s.

rvbuilder2002 · #10 07-09-2012, 11:21 AM

I agree with Mel, if you final drilled with 1/8th, the small amount of play will not be a problem.