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Another misaligned elevator

seattleworm

Well Known Member
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I drilled the elevator horn per instruction (clamping the counterbalance arm "in trail" with HS tip), then noticed the trailing edges of the elevators are not aligned. The left one is about 7/16 higher. I checked with Van's, they told me it's fairly common, most people just make sure the counterbalance arm is "in trail" and accept the where ever the trailing edges at. Sound's like I can just "build on". But I am still surprised to see this much misalignment. When I built my flying RV7, the elevators were perfectly aligned. I checked the HS and elevators individually, they all look straight. Instead of "build on", I drilled out the counterbalance arm, trying to work out this misalignment. But I spent the night for nothing, very difficult to reposition the cbw arm. I then rivet back the cbw arm, with bigger rivets and some additional pop rivets, back to where I started. I guess I have to live with what I have if I don't want to build another elevator. Does anyone have real life experience on flight characteristics and performance with this much elevator misalignment. I know it will be a slower airplane due to added drag, but by how much!
 
I know it will be a slower airplane due to added drag, but by how much!

Somewhere between 0.005 and 10 knots ;)

Seriously though, I really don't think it will make any noticeable difference. I ended up with ours being somewhere around 1/16" off, and as you said it's common that people don't get them EXACTLY right, and without building a new elevator you've got what you've got. 7/16" sounds like a bit much, but if Van's says it's good then by golly I'd say build on. There will be plenty of other opportunities during the build to make the plane faster or slower, lighter or heavier than with this one thing.

If it makes you feel any better, I had a friend with a C182 who flew it for years and ultimately decided to sell it. As part of the process, the buyer took it to his mechanic for an inspection, and discovered the elevators were off from each other by about an inch! One of those things you'd never notice until someone points it out, but it was bad enough that you could see it just looking at it. Best guess was that it came that way from the factory. You'd never know there was a problem though; the plane performed just like any other 182 and flew great.

Best of luck!
 
Flight experience with misaligned elevator

You really, really need to address this misalignment! I bought my airplane (RV7A) from the original builder two years ago. The elevator was misaligned at the rear by about the 7/16" you say your is. To compensate for this misalignment he mis-rigged the ailerons. He sold me the airplane "as is" but did disclose he'd had a prop strike landing at OSH the previous summer. The engine was removed, sent to G&N aircraft for tear down, inspection and rebuild so I felt confident that it would be okay. A new prop was installed. Everything was well documented and no other damage was visible. I had noticed and commented on the elevator/aileron differences but the prebuy inspector gave it a clean bill of health saying these were minor issues and easily corrected. WRONG!

When I first flew it in the pattern at the builder's home field nothing out of the ordinary was felt but the autopilot did not want to stay engaged (I was new to RV flying and greatly impressed by the overall appearance of the aircraft.) therefore too willing to overlook critical build errors.

After exchange of money and bill of sale I flew it from Denver to OKC. That flight opened my eyes to the severity of the elevator/aileron misalignment and the impact of this to high speed flight. The entire three hour flight had me fighting to keep the airplane level and keep it from trying to role upside down and around like a cork screw. I felt really stupid about my purchase decision.

My local A&P/IA contacted Associated Aero and the owner came over, looked over my plane, and immediately pulled off the elevators. Both were welded to fill in the old misdrilled bell crank holes and re drilled to properly align the trailing edges. The ailerons and flaps were re rigged, and and the elevator re balanced. Guess what, it now flies as is was designed to fly.

I honestly believe the prop strike the original builder experienced at OSH was partially caused by an aircraft that couldn't fly straight and had unexpected flight characteristics in high wind and higher speed flight. His advanced age also contributed to his inability to manage challenging flight conditions.

I guarantee your RV will not perform as you want it to with a 7/16" difference in the trailing edge of your elevators. You will be forced to compensate for role with other rigging decisions. The builder of my RV made a lot of excellent build decisions but his greatest build errors were in the empennage and those errors Led to a poor performing aircraft that was just marginally airworthy. This is a critical area - "build it right!"

It's taken me two years to identify and correct the multiple build errors and other issues that I discovered after purchase. Don't cut corners or fail to correct errors. Not only is your life at risk but so are the lives of those people who will fly with you or walk under you.
 
How much is too much?

So how much off would be the threshold for correction? When drilling mine I had both elevators clamped precisely but still have about 1/8" offset with one level, or 1/16" split between the two. As the plane has yet to fly I've decided to wait and make adjustments only if there is a problem.

I honestly don't know. But anytime you have to make compensating corrections I would say is too much. I can only say (not having actually built an RV myself) that I would try real hard to make it as perfect as possible in critical areas that obviously impact how the airplane flys. Remember, "experimental" does not mean "perfection" but "flight safety" does mean as close to design parameters as possible. Error on the side of safety and accept nothing less.
 
I have the same problem. Mine was off by 3/8" and I asked Van's about it.
Their reply:

"I would not consider this a flight critical problem, at worst it could induce a rolling tendency but until you flight test there is no way to know. In some cases aircraft have been intentionally set up with counterbalances being off like yours in order to get the elevator trailing edges aligned (I expect your is not like this). In the end if you decide you want to fix this you can have the bolt hole welded shut on one elevator horn and re-drill."

I've decided to wait for a while an consult my local EAA Tech to get his opinion.
 
Thanks for the input! The misalignment still bugs me after a few days. I tried to correct last night, drilling out the cbw arm but to no avail. What puzzles me is the root cause of this misalignment, individual elevator is straight (as expected for prepunched kit). The RV7 elevators I built per plan were right on when installed. With Jim's real life experience, I feel I need to do some correction. But how? Can anyone share some ideals? The worst case will be spending another $400 for parts and build another elevator, but which one to build? I am not even sure I can get a good match with a new one. Maybe I should just re-fill the hole on one elevator horn, match the trailing edge and redrill, live with "off trail" cbw arm (left side sticking up about 1/2" when elevator trailing edges are aligned and right side "in trail" with HS tip).
 
Another thing to check....

"individual elevator is straight (as expected for prepunched kit)"

I personally would verify this by placing each elevator on a perfectly flat surface to see if it actually is straight. Just because the rivet holes lined up doesn't mean there isn't a twist built into it by the builder if he didn't weight it down. IIRC the (RV-10) plans have you clamp or weight everything down to the workbench when building to insure a perfectly flat elevator. Who knows, maybe the horns are perfectly aligned but it gets out of whack outboard towards the tips. 7/16" , for me, is unacceptable. An 1/8 would drive me nuts...good luck man
 
The ailerons and flaps were re rigged, and and the elevator re balanced. Guess what, it now flies as is was designed to fly.

There are literally hundreds of RV's flying with misaligned elevator trailing edges that don't have any roll trim problem.
I would be willing to bet that it was the work done on the ailerons that corrected your problem.
The span of the horizontal/elevators is rather short and has a much lower moment it can induce to effect roll trim when compared to the wings/ailerons.
 
"Build on" decisions have a whole different feel 5 years and 5000 feet in the future. If you're not entirely happy now, you surely won't be then. Build new parts.
 
corkscrew effect of prop

Wouldn't the corkscrew effect of the prop be a bigger source of roll than 7/16" of offset on the elevators? No idea, just asking.

corkscrewing-slipstream.gif


I have to say, if it were me, I'd fix it. That's one of the reasons I'm not yet flying, I seem to enjoy building every piece 3 times until it's "perfect".
 
I'm in process of final assembly of the elevators of an RV-10 right now. Can someone enlighten me as to which step I need to watch out for if I want to insure my elevators are aligned? (and what to change from stock Van's instructions) Is this during the "attachment" phase? Or do I need to be looking for something now as I assemble spars and skins together?

Any advice from someone who's "learned the lessons" would be very appreciated. May save me some angst down the road. Thanks.
 
I have "re-rigged" a number of miss-aligned elevators on different RV models over the years, including my own. I have never seen any difference in flight characteristics after the change.
 
Re rigging the ailerons helped but!

There are literally hundreds of RV's flying with misaligned elevator trailing edges that don't have any roll trim problem.
I would be willing to bet that it was the work done on the ailerons that corrected your problem.
The span of the horizontal/elevators is rather short and has a much lower moment it can induce to effect roll trim when compared to the wings/ailerons.

I can assure you misaligned elevators DID cause a significant rolling moment! Okay, let's assume for a moment your right and the true cause of my problems were the ailerons. If that's the case where do you set your ailerons to ensure equal control movement on both sides and by the way allow you to trim out differences equally between left and right tank balances?

The problem with what is implied by the above quote is that the elevator, which controls a significant amount of aircraft direction, has less effect than ailerons. I can assure you having demonstrated in the past the effect of a much larger control surface (speed brakes) on the KC-135 which extend on top of the wing, their effect on vertical direction that the elevator wins every time - as it should!

Any twisting moment adversely impacts aircraft control. I've flown large and small aircraft and can assure you that any control surface that is not correctly built or has been overstressed has adverse impacts. Build it right! Compromise is just an "incident" waiting to happen. Remember every accident begins with the first step and any intervention in the process helps to avert it.
 
You could try to see if it was just a mis-drilled elevator horn, which should be easy enough to fix if you know how to weld, or know a good welder.

Just unbolt the elevator horns from the hinge bearing assembly on the horizontal stabilizer, so they can move freely from each other. Then gently clamp each elevator so that the counterweight arms are in trail and see if you still have a mis-alignment issue. If an elevator is still not lining up, that would indicate a twist in that elevator, which is a more difficult to fix.

If the elevators trailing edges are in trail as well as the counterweight arms, then you have an issue with the drilling of the elevator horns where they mount into the horizontal stab bearing assembly, which is pretty simple to fix. The horns would need to have their holes welded up and repainted, and then re-drilled.

I am about to do the horn drilling on my RV-7 in a few days. I'm worried about not getting those horns lined up perfectly, and keeping everything in trail while I drill.
 
I'm in process of final assembly of the elevators of an RV-10 right now. Can someone enlighten me as to which step I need to watch out for if I want to insure my elevators are aligned? (and what to change from stock Van's instructions) Is this during the "attachment" phase? Or do I need to be looking for something now as I assemble spars and skins together?

Any advice from someone who's "learned the lessons" would be very appreciated. May save me some angst down the road. Thanks.

The steps in question are on page 11-3, steps 6-12.
 
Elevator issues have their start in the initial construction. If the V blocks that you used are not perfectly square any misalignment gets doubled as the horns are reversed when building the second elevator but the surface is not.
Also many elevator horns are not identical when placed side to side. There is a bit of wiggle room in the horns but sometimes not enough.
On my rocket there was a half inch difference ,at the wide end of the elevator when measuring to a LEVEL floor. I built a new inner rib and drilled it to the skins when the trailing edges were aligned. I forget how many, but some of the trailing edge rivets had to be drilled as well.
There was no difference in speed, which was my goal, and I can not remember any roll changes.
 
If that's the case where do you set your ailerons to ensure equal control movement on both sides and by the way allow you to trim out differences equally between left and right tank balances?

There is a lot more to dealing with roll trim issues than "setting the ailerons" to a specific amount of movement on both side. In fact that is one of the adjustments that has the least influence on roll trim (There is lots of info here in the forums and on Van's web site).

Back to elevators......
A misalignment of T.E. (when the counterbalance arms are aligned with the H. Stab) can be cause by two things. A twisted elevator, or a counter balance arm that is not aligned with the cord line of the elevator (or some measure of both)
You can easily check for twist with the elevator still installed by measuring with a level at the inboard and outboard end. If there is no twist, both measurements will be the same.
If the elevators are free of twist, but are mis-aligned at the trailing edges, then I could see it having some roll influence, but my experience is that the way they are typically mis-aligned (primarily the inboard ends because of twist), there is no detectable roll influence.
 
Here is the plan!

Last night I spent more time to measure the twist of elevators with digital level, the left elevator is twisted about 1-degree (0.9 to be precise) across the length, higher angle on the outboard. However, a closer look at the trim tab showed a visible twist on the left side. If I just clamp the straight angle (got a longer piece last night) to the non-movable trailing edge, instead of on the trim tab trailing edge, the difference is about 1/4" (drop from 7/16). I guess the 1/4" difference is from the 1-deg twist. With this new finding and the input from everyone (thank you for all the valuable inputs), I will leave the elevator as is, but will build new trim tab. The rest will be left to test flight to find out. Thanks everyone for sharing your thoughts!
 
I certainly have not built an RV and am only a student pilot, but if I am understanding the mis alignment I have another question. The 172 I have flown as a student has elevator trim only on one side. Wouldnt this trim be basically the same as this mis alignment? This would create more lift on one side of the elevator than the other. When trimming the 172 I have not noticed any tendency of the aircraft to roll. How would this be different? How could this create more tendency for roll than the slipstream or the torque of the engine? I could see this adding some drag though. As someone else said earlier, no idea, just asking.
 
I certainly have not built an RV and am only a student pilot, but if I am understanding the mis alignment I have another question. The 172 I have flown as a student has elevator trim only on one side. Wouldnt this trim be basically the same as this mis alignment? This would create more lift on one side of the elevator than the other. When trimming the 172 I have not noticed any tendency of the aircraft to roll. How would this be different? How could this create more tendency for roll than the slipstream or the torque of the engine? I could see this adding some drag though. As someone else said earlier, no idea, just asking.

Not quite. The trim tab only effects the elevator itself, not the aircraft. And the 2 elevators are tied together firmly.
 
Actually I think Cholly has a good point. Every small Cessna generates more force on one side of the elevator than the other whenever the trim is not neutral.
 
So are the 2 elevators on a vans not tied together firmly? And how can you only effect the elevator and not the aircraft since the aircraft can move in 3 dimensions? I understand that if the elevators were wildly mis alligned, say a foot for illustration purposes, they would contribute to roll. But something less than half an inch with very little arm on an aircraft with p factor, torque, and slipstream, it just seems negligible. It seems it would be the lesser of the variables contributing to roll.
 
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Actually I think Cholly has a good point. Every small Cessna generates more force on one side of the elevator than the other whenever the trim is not neutral.

It's put on the left side elevator to counteract the P-Factor. :) During takeoff the trim tab is down. The torque and P-factor on a right-hand turning engine are trying to roll and turn the airplane to the left. The trim tab on the left elevator being in the down position counteracts this force to a degree. That's why airplanes with moveable horizontal stabilizers (instead of trim tabs) will roll more to the right on takeoff, requiring much larger rudder inputs. The RV-10 allows you to fine tune this through the use of two independentaly-adjustable trim tabs, one on each elevator. Those who elect to install left rotating engines, such as in the UK, are shipped a different set of plans depicting the trim tab installed on the right elevator. The RV-12 solves this problem through the use of a trim tab that runs the entire length of the stabilator. And of course the use of a Rotax 912 under the cowl, aka turboencabulator. :)

Oh, wait, it's not April fool's day yet. :)

Vic
 
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Had me going for a while there Vic.......:D

Isn't the problem that people are trying to align the elevator horns rather than the elevator trailing edges? If you clamp the elevators in line and then drill the elevator horns, you have to end up with the trailing edges aligned. OK, the horns might be out a bit and you might have to trim/file the stops a little but I really can't see how this can be a major issue.....
 
Had me going for a while there Vic.......:D

Isn't the problem that people are trying to align the elevator horns rather than the elevator trailing edges?

Maybe for a few (if the instructions are followed it compensates for the horn misalignment that you are describing).

The problem described is when the counter balance arms of each elevator are aligned when drilling the horns (the proper way to do it), but then the inboard ends of the elevators are not aligned (usually the result of one or both of the elevators having a twist in them).
 
One other consideration: The elevator trim tabs on the RV-10 are asymmetrical - they move at different rates and don't stay aligned with each other as they are moved by the trim servo. The difference in trailing edge position of the trim tabs will be a lot more than the offset between the 2 elevators being discussed here. So I would think that if the offset between the trim tabs isn't going to cause problems, that a small offset in the elevators shouldn't either.

I asked Van's about this characteristic of the trim tabs, thinking that I had done something wrong when building the servo bell crank. I was told that the asymmetric tabs was by design, and was correctly built.
 
Is it better to have the counterbalance horns aligned, or the elevator trailing edge. With the trailing edge aligned my counterbalance horns are out by less than 1/4”
 
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