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Stabilizer Cracking sound

I purchased a RV-6 at the begging of the year and have been enjoying it tremendously. I am learning a great deal with small challenges popping up from time to time. The other day I was putting the airplane in the hangar and I noticed a cracking like sound when I lifted up on the left Stab. Lifting on the right stab dose not produce the same sound. I inspected the stab thoroughly. Pulled the fairing and inspected inside the stab with scope camera. I could see absolutely NO cracks, wrinkles, loose rivets, deformations or separations inside or out. I compared the left to the right and they looked the same.

I'm thinking it might be the stab skin against the fuselage but I cannot tell. Does anybody have any inputs or suggestions?
 
Welcome to VAF!!!!

Raymond, first post I see, welcome to VAF:D

I dont think lifting the plane by the elevator is a good thing to do, but then I am not a builder/owner of a 6 either.

I would pull the tail fairing and inspect the hold down hardware for tightness, and signs of movement.

Have someone gently lift the stab while you are looking around, and see if you can pinpoint the source.

Hopefully someone else will jump in here with better info, but this seems to be something you really should get to the bottom of.

Good luck, and again, welcome aboard.
 
I'm sure you are not going to fly it until you find the source

The pitch trim is unique to the left side. I can't think of anything except the structure of the stabilizer or the elevator that would sound like stabilizer cracking when I am standing right there applying the force on the item that sounds like it is cracking. I would ground the airplane until I solved that problem but you probably have done that already. Do you also feel the cracking along with the sound? You could isolate further By disconnecting the pushrod, the trim tab and the the elevator, testing after each disassembly. If you are down to the bare stabilizer, the sound is still present and using visual inspection methods you have not been able to detect the source you may be able to get someone to use nondestructive test methods for crack detection to find it for you.

Bob Axsom
 
I second two things already said here... One, do not lift the tail with the horizontal stabilizer. If you really, really have to lift the tail, grab the stinger and lift. Two, ground the plane until you figure this out. Losing one side of your HS will ruin your day.

If I couldn't isolate it on the plane, I would remove the fairings, rudder, vertical stab, elevators, and finally the horizontal stab. It sounds like major surgery but its not that hard. Then I could check the mounting point in the fuselage where the HS attaches. Maybe you've got some cracked rivets along the longeron there?
 
Noise

These planes did not have pre punched skins. Each hole had to be manually marked and drilled.

Possible noise source could be 'oil canning' from a poorly fitted skin????
 
There's a lot of loose English flying around in here. First, the only production RV to have a stabilator is the 12. Second, lifting on the stabilizer is not the same as lifting on the elevator, Mike.:rolleyes:

Ok, now that I've had my fun, I don't see what the problem is with lifting on the stabilizer. In fact, I wouldn't fly in an aircraft where you couldn't do that. The HS should be solid enough to the aircraft to apply force to change it's pitch. When you rotate, it's the HS that's pushing down on the tail hard enough to raise the nose (or, in a TD, the tail lifts first by forces on the HS). I was taught to pre-flight hands on, move the control surfaces, test the attachments, and so on. I always give the wings and tail a push; if something goes 'clunk' then I'd rather find out on the ground. That said, I don't expect that lifting the tail and pushing is the easiest way to ground-handle a TD, any more than pushing down on the tail of a Cessna is easier than using a towbar.

As for the sound the OP is hearing, I'd suggest getting a second set of eyes (ears?) on the problem; preferably an experienced builder or A&P. Speaking only for myself, I only get hinge noises and a clunk when the controls hit the stops but otherwise my tail surfaces are silent. I have manual trim and the cable makes no noise as the controls move. And there should not be enough flex at the fuselage to make the fairing make a sound.
 
Could be stab against the tail fiberglass fairing. Mine does that.

Yep, I suspect it is merely a mechanical rubbing of a couple of components that is causing the sound. The original post stated Raymond did a comprehensive visual inspection and didn't find anything amiss.

My RV-6 has a particular sound in the rear of the fuse when pushing it around with the towbar and I've never been able to completely find the source. It only take a tiny amount of movement between a bulkhead and skin or something similar to make a noticeable noise.
 
I don't see what the problem is with lifting on the stabilizer. In fact, I wouldn't fly in an aircraft where you couldn't do that.
You should avoid flying in Cessnas, then. The 150/152 series, in particular, is prone to the forward spar on the HS cracking due to people pushing down on it to spin the tail around on the ground. Granted, that is a Cessna, not an RV.

I think the distinction is between lifting on the stabilizer to test security, vs. lifting on it to lift the tail off the ground and move the airplane around. I grab the tip of mine on each side and pull and push before every flight to test security, but I wouldn't consider lifting the tail off the ground that way. The distributed load of the aerodynamic forces is much more gentle than the point load that my hand would apply to do the same work.
 
Second, lifting on the stabilizer is not the same as lifting on the elevator, Mike.:rolleyes:

Ouch, got me on that one:eek:

The distributed load of the aerodynamic forces is much more gentle than the point load that my hand would apply to do the same work.

Which is why I made the statement in the first place.

When you lift the stab (got it right this time;)) you are most likely lifting only one side. This is inducing a rocking motion to the mounting structure, which is designed to deal with a vertical load.
 
Check for Fiberglass Fairing Interference

I encountered a similar thing as I was finishing my first annual. Couldn't figure out where the clicking sound was coming from on the right elevator. Then I realized I hadn't completely attached the emp fairing and the lower right tab wasn't properly positioned. Completed attaching fairing and sound went away.
 
Ok, I get the asymmetrical load thing but I still think that an aircraft rated for aerobatic G-loads should be less touchy than that. Granted, most of the forces are at the wing spar. And I am guilty of horsing a Cessna around by the tail but I've never seen one fail or even be loose. Many of these were flight school aircraft (Sierra Academy), so the maintenance wasn't the best and the airframe hours were high. I don't push the tail on my RV (love my bogie bar), but I am confident it is solid enough to take it if I needed to; I recheck the attachment every annual or if the fairing gets removed for any reason.

And so I stand corrected about the fairing. I don't think I could get enough movement out of my tail to make the fairing cause a sound, but if others are experiencing it, it is worth checking out.
 
The damage caused by lifting or pushing on the horizontal stab is frequently a squeezed leading edge.
Most people don't think about centering the force on the spar. So the leading edge skin takes most of the abuse. :eek:
It leaves an ugly spot!
 
Thank you all for your inputs, this website and forum is awesome.

I am going back out to the airport to re inspect. Just to clarify I have not / do not lift the tail by the stab. I do push it back holding the vertical stab and horizontal stab attempting equal pressure. this is not much force at all though. I have grounded the plane and will get some local a/p and builders to look at it.

As far as I can tell now is to perform 3 things.
1. Torque bolts down
2. Inspect with another person applying light force
3. Perform some type of micro crack investigation, non destructive testing (have no idea about that )

It just seems if things were moving around a visual inspection would reveal it. As I stated before I could find no deformations. The rivets look just a smooth as could be', and nothing on the inside.

I'll post what I find out.

Thanks all !
 
Problem Solved

The culprit was the lower trim strip just under the stab on the fuselage. Removing it caused the sound to cease.

Thanks all for the inputs.

Scott
RV-6
 
Glad you found the cause, hope there was not a lot of damage to the surface where it was interfering.
 
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