Manual Trim tab information sought.

rvator51 · #1 02-25-2007, 12:03 PM

Coming back from the RV Rendezvous at Cable Airport, we experienced a violent stick shaking forward and back in our rv-4 while descending from 11,500. Reduction of throttle immediately stopped it.

I am suspecting the trim tab was one of the contributing factors. It is a Vans stock manual trim setup.

For those of you that have the manual setup. How much play do you have in your trim tab? The rear end of our trim tab has about 3/16 in play in it. Looks like most of the slop is at the trim tab connection to the cable end.

Ironflight · #2 02-25-2007, 06:27 PM

Tom,

I'm not sure I can help you much - I have the electric trim on the Val, and no noticeable play - but I'm curious if you looked at your speed when you felt the shaking. I suspect that you are on the right track - play in the tab - and I am just wondering if this was tab flutter. Since you were pretty high, your TAS might have been pretty high....

No flaming intended - I'm just curious if we can learn something!

Paul

rvator51 · #3 02-25-2007, 07:44 PM

Quote:

Originally Posted by Ironflight

Tom,

I'm not sure I can help you much - I have the electric trim on the Val, and no noticeable play - but I'm curious if you looked at your speed when you felt the shaking. I suspect that you are on the right track - play in the tab - and I am just wondering if this was tab flutter. Since you were pretty high, your TAS might have been pretty high....

No flaming intended - I'm just curious if we can learn something!

Paul

Hey Paul,

We had descended to about 6000 ft when the shaking occurred and were doing about 165 kts ground speed.

Paul Thomas · #4 02-25-2007, 09:35 PM

What was IAS and pressure alt? Like Paul, my 1st thought is flutter.

osxuser · #5 02-26-2007, 02:53 PM

Flutter *usually* from what I understand is a much smaller, less noticable event, not a violent shake. Definitely a higher frequency than what you seem to be describing. Now if the trim tab was fluttering, that might cause the violent shakeing on the elevator. My personal thought is:

If you have a control surface that is NOT counterweighted (So it's negatively balenced most likely) like the trim tab, and it's allowed to fly freely, it will unload in whichever direction the relative wind tells it too, which will could cause the elevator to start a harmonic type vibration. Tighten up those rod ends to zero play, and I'll bet you'll have no problem.

N520TX · #6 02-26-2007, 03:19 PM

I just re-read this article today - your situation sounds eerily similar to what Rob details on the 3rd page. http://www.vansaircraft.com/pdf/hp_limts.pdf

billnaz · #7 03-05-2007, 04:56 PM

I checked my man trim tab and found the same 3/8" slop. I just started flying mine, so I've got no experience yet. The flutter scenario sure looks plausable. Man, these planes are awsome!!!

Bill