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03-24-2017, 08:31 PM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,769
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Quote:
Originally Posted by Cholley6
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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Not quite. The trim tab only effects the elevator itself, not the aircraft. And the 2 elevators are tied together firmly.
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Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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03-24-2017, 08:55 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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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.
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03-24-2017, 10:23 PM
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Join Date: Dec 2016
Location: Monroe, Louisiana
Posts: 15
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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.
Last edited by Cholley6 : 03-24-2017 at 10:34 PM.
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03-24-2017, 11:00 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Yes the elevators are tied together.
RVs have very light roll forces. It doesn't take much to bank them.
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03-25-2017, 06:12 AM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,627
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Quote:
Originally Posted by BobTurner
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.
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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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 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
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Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
Last edited by vic syracuse : 03-25-2017 at 07:35 AM.
Reason: spelling
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03-25-2017, 07:18 AM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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Had me going for a while there Vic.......
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.....
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Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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03-25-2017, 10:18 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by paul330
Had me going for a while there Vic.......
Isn't the problem that people are trying to align the elevator horns rather than the elevator trailing edges?
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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).
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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03-25-2017, 10:48 AM
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Join Date: Jan 2016
Location: Sugar Land, TX
Posts: 406
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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.
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Dave Macdonald
RV-10 First Flight April 1, 2020.  Currently in Phase 1
2020 VAF Dues Paid
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