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Old 05-17-2020, 06:23 AM
Triumph1974 Triumph1974 is offline
Join Date: Feb 2008
Location: Richmond VA
Posts: 97
Default question on A/P aileron control sensitivity/responsiveness post install

For those of you that have flown with and without A/P servos hooked up in your RVs, is there a noticeable reduction on flight control sensitivity after installing the servos? Or if anyone has noticed that a paint job reduces sensitivity?

I have a RV7A, and likely will be adding on the Dynon SV32 A/P servos in the near future.....right now the plane is super responsive to the slightest control much so that other RV 6 and 7 owners that the first thing that say after taking the controls is that is it is much more responsive (one comment was "twitchy" ) than their planes (which are 'fully loaded" planes and weight a bit more than mine which is 1,035 lbs)....

Currently the plane is not fully painted....didn't know if that gives the control input more sensitivity, or if it could be that the A/P servos would have an impact....just wondering the experience others have seen as they start to add more bells and whistles....

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Old 05-17-2020, 07:23 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,865

some servos add a bit of resistance to the controls (dynon/GRT) and some don't (Garmin / Trio). You won't notice in flight, but will on the ground. I have also found that some other planes had stiffer controls than mine and attribute that to care and attention to properly shimming the heim joints in certain areas. Spring based aileron trim will add a fair amount of resistance to the controls on the ground.

I don't think paint would affect this, but not an aero engineer and don't really know.

In the air, the shape of the trailing edge area (sect 5 show examples of over or under bent edges and how they impact the area 6-8" forward of the T/E) makes a big difference in the responsiveness of the control surface (on rounded t/e's). This is likely the differences repoted. When I started IFR training, I spent a good amount of time addressing the elev T/E's and it really helped in reducing pitch sensitivity (some could call it "twitchy" though I don't think it was). Still very responsive, but more stable. I don't believe that these T/E's will end up perfect without attention to detail and therefore expect variability amongst the fleet.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 05-17-2020 at 07:36 AM.
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Old 05-17-2020, 08:56 AM
Walt's Avatar
Walt Walt is offline
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,942

You may want to have a look at this thread about an overly twitchy aircraft:
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1900+ hrs, New Titan IO-370, Bendix Mags
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Old 05-17-2020, 04:34 PM
BobTurner BobTurner is offline
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,285

As noted above, the Trio servos use a clutch, so the servo gear train is disconnected from the controls when the servos are disengaged.
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Old 05-18-2020, 05:47 AM
WingsOnWheels WingsOnWheels is offline
Join Date: Mar 2009
Location: Plano, TX
Posts: 2,129

Sounds like the trailing edge radius on the ailerons is not to spec. You can confirm by checking the aileron surface with a straight-edge. The surface should be flat up to the TE radius. Best to correct that before paint.

The dynon servo added a little drag, but not much.
Colin P.
RV-6A #20603
Complete 5/10/19
I donate every year on my B-Day (in Dec), but donated early in Sep'19.

Last edited by WingsOnWheels : 05-21-2020 at 04:43 AM.
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Old 05-20-2020, 03:19 PM
Triumph1974 Triumph1974 is offline
Join Date: Feb 2008
Location: Richmond VA
Posts: 97
Smile Adjustment on Trailing Edges

Thanks everyone for the tips. I did checks on the ailerons/elevators and found 3 areas that where quite not in line with the straight edge...did some light massaging on the T/E radius and in the first test flight I did notice that the controls where more solid than previously...still light, but I sort of like the responsiveness where it is now.

Haven't gotten a chance to do a 2nd round of evaluation/testing.... probably will leave as is for now and only consider further adjustment if the A/P has difficulty with stability once installed.

By the way...some of the links in a prior detailed thread that Walt shared seemed to refer back to the Vans website and appear to be gone...

Thanks again everyone!
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Old 05-20-2020, 03:23 PM
Bavafa Bavafa is offline
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,517

If twitchy you might want to check the trailing edge of your ailerons. That does have an impact.
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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Old 05-21-2020, 11:02 AM
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dougweil dougweil is offline
Join Date: Jun 2005
Location: Hudson, WI
Posts: 248

Absolutely check your aileron trailing edges. My quickbuilt RV7 was excessively sensitive in roll to the point of being not fun to fly at all. I lived with it for about hundred hours until researching the ?fat? aileron trailing edge issue. Squeezing them down made it a totally different airplane.
Doug Weiler

Hudson, WI
president, Twin Cities RV Builders Group
RV-4, sold
RV-7 completed and flying N722DW, 840 hours
Based Lake Elmo, MN (21D)
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Old 05-30-2020, 05:02 PM
Triumph1974 Triumph1974 is offline
Join Date: Feb 2008
Location: Richmond VA
Posts: 97
Default Post AP install Update

Ok, everyone here is an update post install. Installed the Dynon AP servos the other weekend and was able to do a short 20 min flight test a few days ago- the RV7a is a totally different feeling airplane than what is was prior.....grant it I haven't done any testing yet in bumpy weather as my test flight was done on a calm evening.

A week or so prior to the AP install I did massage the one aileron trailing edge just a bit on two rib lines, did a test flight and the plane was a bit less "twitchy", but still was on the super responsive "light touch" side of the things.....after the AP install, it feels more "solid" in the controls and less twitchy.... so my take is that the AP servos do make a difference in the feel of the controls.

Thanks for the comments,
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Old 05-30-2020, 05:33 PM
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N941WR N941WR is offline
Join Date: Jan 2005
Location: SC
Posts: 12,887

Originally Posted by Triumph1974 View Post
...after the AP install, it feels more "solid" in the controls and less twitchy.... so my take is that the AP servos do make a difference in the feel of the controls.

Thanks for the comments,
Congrats on adding the AP.

On a nice day, when you have some time, go fly, then remove the AP servo to bell crank link and see if you notice a difference. Only if you do back-to-back flights will you be able to tell for sure.

If the AP servo is what is making your airplane more stable, I suggest you continue to look at those trailing edges.
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
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