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  #11  
Old 03-24-2017, 06:19 AM
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rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
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Default 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.



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".
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  #12  
Old 03-24-2017, 06:39 AM
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Default

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.
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  #13  
Old 03-24-2017, 06:49 AM
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Mel Mel is online now
 
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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.
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  #14  
Old 03-24-2017, 07:58 AM
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Tankerpilot75 Tankerpilot75 is offline
 
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Location: Oklahoma City, OK
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Default Re rigging the ailerons helped but!

Quote:
Originally Posted by rvbuilder2002 View Post
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.
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  #15  
Old 03-24-2017, 09:15 AM
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CubedRoot CubedRoot is offline
 
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Default

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.
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  #16  
Old 03-24-2017, 09:44 AM
MFMarch MFMarch is offline
 
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Location: Washougal, WA
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Default

Quote:
Originally Posted by rvanstory View Post
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.
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  #17  
Old 03-24-2017, 10:15 AM
Tom Martin Tom Martin is offline
 
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Location: Ontario, Canada
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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.
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  #18  
Old 03-24-2017, 11:02 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Tankerpilot75 View Post
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.
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  #19  
Old 03-24-2017, 02:45 PM
seattleworm seattleworm is offline
 
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Location: Seattle, WA
Posts: 120
Default 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!
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  #20  
Old 03-24-2017, 07:54 PM
Cholley6 Cholley6 is offline
 
Join Date: Dec 2016
Location: Monroe, Louisiana
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Default

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.
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