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  #1  
Old 04-14-2017, 08:33 PM
WrightsRV7 WrightsRV7 is offline
 
Join Date: Aug 2015
Location: Hurricane Utah
Posts: 148
Default Dual Servo Electric Elevator Trim

Well N56GZ has flown through phase I and out of the coral, now the fun phase. I installed dual electric servos on the elevator trim and have found them to be quite nice, effective, and from all indications working extremely well and safely. At least for my style of landings, with two forward occupants, 2/3 full fuel, and a case of oil in the baggage compartment, I have about 1/4" of up trim (trailing edge) on each tab (and yes, they move and stay well in sync) at landing with full flaps. In cruise, the trim tab is neutral. I do not trim out all stick forces on final, I prefer to have some light back pressure on the stick, so I am sure others will or may have more "up" trim in play than I. These are very big trim tabs for a small and light plane and it is no wonder most find them very sensitive. I may look at testing out one trim tab down the road, appears from my flying of the RV10 a very small fraction of the dual trim tab movement is utilized.

I will start to collect some video of the trim tab, with particular interest in the servo attach bracket, looking for any significant flexing as the trim tab is placed in more demanding positions (simulating a runaway trim etc...). Beefing up the attach plate (as done in the RV14) will be a rather easy task, if needed.
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  #2  
Old 04-14-2017, 10:56 PM
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stringfellow stringfellow is offline
 
Join Date: Mar 2015
Location: Aurora
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How are they synced? I've wanted to do this too but can't help but think that unless they were synced via some position "brain" that they'd diverge from each other over time.
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  #3  
Old 04-15-2017, 06:46 AM
Gary 40274 Gary 40274 is offline
 
Join Date: Dec 2007
Location: Conyers GA
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Exclamation Soapbox

I am sorry but this is a very bad idea. With no way to sync the tabs or deal with a single tab servo failure it is not if you will have a scary/deadly situation but when. I think this idea needs more cognitive work before it is ready for prime time.

Gary Specketer
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  #4  
Old 04-15-2017, 08:33 AM
rocketman1988 rocketman1988 is offline
 
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Location: Sunman, IN
Posts: 720
Default But...

Just another perspective...

Many, many aircraft out there use only a single trim tab.

I should think that syncing the trim tabs with dual servos would not be an issue, as the system that is stock on the -10 does not "sync" the tabs either.

Kudos for trying something different! Keep us updated on how it is working out...
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  #5  
Old 04-15-2017, 09:17 AM
WrightsRV7 WrightsRV7 is offline
 
Join Date: Aug 2015
Location: Hurricane Utah
Posts: 148
Default tabs "out" of sync issue

Good question...Ray Allen supplied me with two servos having very close, but not identical run speeds. What I have found that after a flight of many touch & goes, some cruise (2 h), and then landing, they are still very very close to identical L/R trim tab positions. They can be reset easily by running to full down trim, then back to take off position (~neutral for me, I like to pull the airplane nose up and off the runway).

I am certainly NOT claiming this is a done deal, I did build an experimental aircraft, and I do think my "ideas" through, and carefully, and with 35 years of Ph.D. research in chemistry, explosives, composites, and polymers, AND take safety very, very seriously. Have an equal number of years flying single (conventional & three-leg), twin engine aircraft, and have worked under a host of very talented IAs and A&Ps, with great respect for their experience and knowledge and the FAA's AC 43. AND still learning and listening as time goes on. If any believes or thinks a "std RV10" trim installation DOES NOT have up to 20 deg of trim tab mismatch then they need to run it to full down trim and take a look. The fact is with the std trim installation (single servo) rarely are the trim tabs in alignment and this is fine by design. We ALL need to consider a "runaway" trim and having one versus two is different for sure, but having one "runaway" trim tab move is less demanding in the cockpit than dealing with both moving (e.g. to full up...).
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  #6  
Old 04-15-2017, 09:53 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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Six years ago I contacted Van's about doing the same thing. Both elevators are set up to take a servo just like the other RVs, and the unnecessarily complicated RV-10 trim tab set up with cams and cables violated my engineer eye.

The short story - I got my head handed to me by Van's. It seemed I hit a sore point with them.

I did follow up on why on earth this design came about. The second/third/fourth hand story was the RV-10 was originally to have one elevator trim tab with a standard servo set up just like the other RVs. The other elevator trim tab was to have a servo that operated only with the flaps - so when you put the flaps down a fixed amount of nose up trim would come in. I don't know why it was changed out.

That's the story I pieced together - anyone else?

Carl
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Old 04-15-2017, 11:00 AM
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Auburntsts Auburntsts is offline
 
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Location: Dumfries, VA
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I guess my question is what is the benefit of going with 2 servos over the stock setup of one servo (esthetics aside)? The stock setup works just fine so I don't understand the problem. If someone was going to mod the elevator trim system I'd have bet it would have been to ditch the 2nd tab, not add a 2nd servo.
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  #8  
Old 04-15-2017, 12:22 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Quote:
Originally Posted by Carl Froehlich View Post
The other elevator trim tab was to have a servo that operated only with the flaps - so when you put the flaps down a fixed amount of nose up trim would come in. I don't know why it was changed out.

That's the story I pieced together - anyone else?

Carl
I heard the same story.
I can only guess at the issues, but one guess would be that airloads help the flaps retract a bit faster than extend - and over time the servo would walk to one end of its range.
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  #9  
Old 04-15-2017, 08:12 PM
WrightsRV7 WrightsRV7 is offline
 
Join Date: Aug 2015
Location: Hurricane Utah
Posts: 148
Default Very Good points...Thank You....

I too got an ear full from Vans, and I fully listened and appreciated their point of view. We all appreciate Vans gives us incredible support and what a superb plane, no matter what model. In fact I downloaded the RV14 "beef up" and have it ready. Most Cessna aircraft use a single trim tab, my twin aero commander (6000 lb aircraft) uses a single trim tab and with less surface area than the two RV10 tabs...

Why do it? Good question Todd... I was a bit bothered having two trim tabs working out of sync...just seemed wrong...and your right...it works well and will continue to do so, no doubt. Vans is full of bright and sharp guys and gals. I will test out what one trim tab does, now I can just unplug one connector at the back fairing and go for it...will be an interesting set of data points and I will post, and I am sure I will get some "feedback", but I am science guy, I like to think things through, and then push a bit forward, even when people say I might fail. From my data and flight experience to date, which has covered very forward CG limits (109.3), I just see no need for the two trim tabs.

Always appreciate the caution, questions, and dialog, makes us a great community of builders and pilots!!! Lets face it, Vans Aircraft has changed general aviation forever, and in such a positive way.

Cheers, Mike

Last edited by WrightsRV7 : 04-15-2017 at 08:17 PM.
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  #10  
Old 04-15-2017, 09:29 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Quote:
Originally Posted by WrightsRV7 View Post
From my data and flight experience to date, which has covered very forward CG limits (109.3), I just see no need for the two trim tabs.

Cheers, Mike
I have a 'stock' 10 with a fairly forward empty cg. Solo and part fuel, I need to carry 15 lbs ballast. On a full flaps landing I end up with full nose up trim, and still nose heavy (but manageable). That's with two stock trim tabs.
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