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-   -   Another misaligned elevator (https://vansairforce.net/community/showthread.php?t=147940)

seattleworm 03-23-2017 11:43 AM

Another misaligned elevator
 
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!

mikeyj350 03-23-2017 01:42 PM

Quote:

Originally Posted by seattleworm (Post 1160146)
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!

Tankerpilot75 03-23-2017 02:35 PM

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.

Tom023 03-23-2017 03:13 PM

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.

Tankerpilot75 03-23-2017 03:55 PM

How much is too much?
 
Quote:

Originally Posted by Tom023 (Post 1160200)
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.

MFMarch 03-23-2017 03:56 PM

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.

seattleworm 03-23-2017 04:59 PM

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).

A-Ron 03-23-2017 05:44 PM

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

rvbuilder2002 03-23-2017 10:42 PM

Quote:

Originally Posted by Tankerpilot75 (Post 1160191)
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.

DanH 03-24-2017 05:48 AM

"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.


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