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Elevators not evenly aligned

mikehoover

Well Known Member
Just drilled my elevator horns and am preparing to mount the HS/Elevators on the fuse hopefully within the next week. I noticed that the left elevator seems to be about 3/8"-1/2" lower than the right one at the trailing edge; really noticeable when I clamp a long piece of angle on the trailing edge of the right elevator and it hangs over the top of the left elevator. The elevator counterbalances are clamped to the HS so they are in proper position even with the HS. Has anyone had this happen? How can they be off this much, or is this typical? Thanks!

Mike
 
I believe that you have the same problem that most RV have. My horns didnt line up well either but I aligned the trailing edges before drilling the hole for the control rod eye. If the problem you described is what I think you are saying dont worry about it most RV have the same problem. For the elevator stops on mine one horn hits the stop in the up position and one horn hits the stop in the down postion. I dont recall the exact amount of travel but that is determined after the horizontle is attached to the fueslage. Sorry about the spelling hope this will ease your mind.
Jim

I actually welded the holes shut that I drilled the first time and redrilled them to get it a little closer. Not sure I would recomend welding for everyone but it worked for me.
 
If I understand correctly, you're saying that the front counterbalances are lined up, but the trailing edges are not (or vice-versa too, I guess). I would think that twisted elevators are the most likely explanation. You could lay the elevator on a known flat surface and check this. If it's just the control horns that are a little out of sync with each other I wouldn't worry about it.
 
Elevator Alignment

I had a similar situation, although not to the same degree.

I was advised by Van's and others to insure the elevator surfaces are aligned--even if the counterweights are slightly out of alignment. The logic was that, given the large surface area of the elevators they will have a much greater influence on the flight characteristics of the aircraft than does a counterweight sticking up (or down) slightly. If the rudder is not yet installed you can easily check this by first aligning the trailing edges of the elevators (not clamping the counterweights) and then sighting across the top surfaces of both elevators from one end to insure alignment.

Good Luck and Cheers,

db
 
Missaligned elevators will induce a roll moment which must be conteracted by an aileron input. Now you have 4 control surfaces not in trail, thereby creating drag. If your elevators are missaligned as much as you say, you should correct the problem now.
Mel...DAR
 
are the pushrod holes drilled?

The elevator horns are often mis-aligned. Instructions say to line up the trailing edges on a table (not a direct quote..check the manual). If you have already drilled the holes that you bolt the pushrod to, you may have a problem. The instructions and the drawings both assume the horns will be misaligned slightly. Mine are offset, but the trailing edges are even. If you have already drilled both horns, and your trailing edges are offset, I'd call Vans tech support and see what they say you should do next.
 
Build9A said:
Instructions say to line up the trailing edges on a table (not a direct quote..check the manual).

I wish they did! The manual (page 8-15) says to align the elevator counterbalances with the stabilizer tips and clamp them. Then on to drilling the horns. This is perhaps another of Vans' booby-traps. A mention that the trailing edge alignment takes priority over counterbalances being even with stabilizer tips would have been helpful here.

As it is, if I clamp a length of aluminum angle along both trailing edges to line them up, the left counterbalance is about 3/8" low if the right one is clamped to the HS tip. If the left is clamped, the the right one is 5/8" above the HS tip. So which configuration would be thought of as having the elevators in neutral, or in trail?

Regardless, I have the horns drilled, so I might have to weld patch one hole in the forward-most horn, and redo that hole with the TEs aligned. The aft-most horn's hole will still be okay.

Will be contacting Vans tomorrow. Thanks for all the replies!
 
twist in elevator

Per vans, (mine were off about 3/4 inch) line up the
trailing edge and drill the horns, then see which elevator looks out of alignment, and lock the good side in trail with the horiz stab and drill out the
end rib in the counter balance area and massage
the end rib on the bad side, you may see where the next rib is pulling the rivets and skin, (thats how far the twist goes) the direction you need it to
be in trail (reduce the 1/2 inch) you should be able
to work most of it out.. you will have to use some blind rivets to fix it, but most of it will be in the end rib and you can get solid rivets with the sqeezer.

I ended up with about 3/8
vans said, you won't know it during flight, many rv's have this problem, (we all start on the emp) also he said only you will know it so at the fly in's or when you go somewhere other might see it, just tie the
stick back with the seat belt so they are not aligned
and no one will ever know :) build on..


Danny..
 
Elevator Alignment

Some aircraft purposely misalign the elevator trailing edges in order to eliminate any 'dead-band' effects in the pitch control system (I believe that the Kitfox calls out a 3/8" differential). At least one of the surfaces will always be in 'clean air' by rigging in this fashion.

The resultant differential elevator roll effect is minimal at such close inboard stations. I would guess that most applications stipulate that the left elevator be rigged higher if an engine with American-style prop rotation is used, to theoretically counter any roll-due-to-slipstream effects on the tail group, but I'll bet that any effects of misalignment in the range of 3/8" would be impossible to measure.

Regards,
Hawkeye Hughes
Skyote, RV-3's
 
REHughes said:
Some aircraft purposely misalign the elevator trailing edges in order to eliminate any 'dead-band' effects in the pitch control system (I believe that the Kitfox calls out a 3/8" differential). At least one of the surfaces will always be in 'clean air' by rigging in this fashion.

The resultant differential elevator roll effect is minimal at such close inboard stations. I would guess that most applications stipulate that the left elevator be rigged higher if an engine with American-style prop rotation is used, to theoretically counter any roll-due-to-slipstream effects on the tail group, but I'll bet that any effects of misalignment in the range of 3/8" would be impossible to measure.

Regards,
Hawkeye Hughes
Skyote, RV-3's

When Kitfox's start cruising at 200 mph they will probably change that setup. FWIW when I make small trim adj in my RV3 there is a slight but noticable roll input.

Tom
RV3
2000+ hours
 
Roll Effect of Tab

tin man said:
When Kitfox's start cruising at 200 mph they will probably change that setup. FWIW when I make small trim adj in my RV3 there is a slight but noticable roll input.

Tom
RV3
2000+ hours

It would be interesting to see if the roll effect you describe persists if you move the tab while holding the stick rigidly fixed in roll and pitch... That should remove, or at least reduce, most of the prop gyroscopic effects associated with the trim change.

I would like to try and quantify some of those effects but my -3 is in the middle of an upgrade. Let us know what you find if you try it.

Regards, Hawkeye
 
Hawkeye
I first heard of this happening from John Harmon (multiple RV builder and Rocket guru). I also thought No Way.............. Believe me I'm no expert but after a bunch of hours in my RV3 I started to notice a lot of little nuances one of which was roll input from the trim tab. Trimed straight and level in smooth air if I put a slight pitch trim input in I get a slight but noticeable roll input. I have not tried this at all speeds but @ 180 mph indicated it definately exists. Its not gonna make you loose control and unless your really paying attention I don't think most pilots would even notice it but it happens. On a side note note I think all RV builders should strive to make their RVs as perfect as possible whether it be in trim or what ever. Anyone sho says "it shouldn't matter" is not serving the RV community and its builders. I notice a lot of this advice is comming from posters who have not yet flown their airplanes. If you want to compare results please contact me.
I'm in northern California and can find an excuse to fly almost anywhere within reason.
Cheers
Tom
RV3
 
Not flown yet

Thats true I have not flown yet, but I can repeat
tech support from Scott Risan, I didn't build the
twist in my elevator, I just started with a partly
started emp kit.. and dealing with the problems
of that mistake, and I quoted exactly what Scott
told me to do, in fact I talked with three different
vans Engineers , as I was ordering new elevator parts at time.. still not happy with 1/8 counter balance not being perfect.. I thought we were
helping people, and getting it straight from them
1st hand I figured I would help him feel at ease
a little about the situation and that it could be fixed
sure he needs to call them about it.. have you
looked at how many RV's have this problem ?
I have.. lots.. vans said it wouldn't affect it..

Danny..
 
Last edited:
Is anybody aware of anyway to eliminate the problem before it happens? I've got all of the parts for both elevators, drilled. deburred, dipmpled, primed and ready to assemble on my 9A. I'm starting to get a little gunshy. When all of the prepunched parts line up perfectly during the pre-assembly, it doesn't seem that you have much control of twist when you finally rivet it together.
Mike Doyle, Xenia OH
 
godspeed said:
I didn't build the
twist in my elevator...

I didn't build twist in that is at all visible. Perhaps there is some - it might be hard to not have a little, but the 1/2" is all the way across the left elevator and trim tab relative to the right elevator. When I clamp an angle along the trailing edges of the right and left elevators, the length of the angle that extends along the TE of the left elevator sits 1/2" above the TE along the whole length, as if by design.

mdoyle said:
When all of the prepunched parts line up perfectly during the pre-assembly, it doesn't seem that you have much control of twist when you finally rivet it together....

If it is so easy to mess up the elevators just by following the instructions, it seems Vans would give a little more guidance as it is so early in the building process. I would consider building another left elevator to get it more lined up, but there is no reason to believe the new one would not be off by 1/2" as well. What would I do differently the second time that I did or didn't do the first time? Can't think of anything. It would just be a gamble and a hope that it came out right. This is odd since the Vans kit as a whole so far has really been right on the money on things that would be a lot easier to screw up. For instance, my flaps and ailerons line up so well it is scary. The wings needed very little adjustment to get the angle of incidence right and no adjustment for sweep. Or is there something I will discover is wrong a year or two from now when I am getting much closer to first flight?

Well, I hope to talk with someone at Vans today to discuss this.
da37407f6f62012a066dba847dcf0c1725097_DSC_0212.JPG
 
To far back to remember exactly but on a slow build RV3 kit the jigging and drilling process involved a shim at one end of the spar. If you use a flat table without the shim you will get twisted elevators. Don't know if this applies to your situation but I'm pretty sure all the RV elevators are built the same..
Good luck
Tom
RV3
2000+ hours
 
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