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  #1  
Old 01-24-2021, 05:18 PM
dwollen89 dwollen89 is offline
 
Join Date: Feb 2020
Location: Austin, MN
Posts: 2
Default Trim and Auto Pilot

After about two years of researching and recently taking a builder's course, I'm ready to pull the trigger on a 7A. I initially thought that I wanted electric trim, but after lots of thought, I think I'm going to go with the manual trim. I've never had/needed electric trim before and frankly I'm concerned about runaway trims. With that being said, when ordering my tail kit, electric trim is an option. I plan to add auto pilot to the plane at some point, probably after the build. Is the electric trim kit separate from the auto pilot? Are there any issues with having a manual trim and an auto pilot?
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  #2  
Old 01-24-2021, 05:26 PM
Darin Watson Darin Watson is offline
 
Join Date: May 2011
Location: Calgary, AB
Posts: 164
Default

Quote:
Originally Posted by dwollen89 View Post
After about two years of researching and recently taking a builder's course, I'm ready to pull the trigger on a 7A. I initially thought that I wanted electric trim, but after lots of thought, I think I'm going to go with the manual trim. I've never had/needed electric trim before and frankly I'm concerned about runaway trims. With that being said, when ordering my tail kit, electric trim is an option. I plan to add auto pilot to the plane at some point, probably after the build. Is the electric trim kit separate from the auto pilot? Are there any issues with having a manual trim and an auto pilot?
Yes, trim is separate from AP. No, there is not an issue with AP and manual trim.
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Darin
C-GULF RV-7 located in Calgary, AB
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  #3  
Old 01-24-2021, 06:06 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,145
Default

All (I think) autopilots designed for RVs act directly on the elevator, not the trim tab. If you have manual trim and an autopilot engaged, and you change the airspeed (either with throttle or by initiating a climb, etc) you will get a message from the autopilot to Ďtrim upí (or down). Now, some autopilots have Ďauto-trimí, e.g., if they detect an out of trim condition they will just fix it, no pilot intervention required. This only works with electric trim. e.g., I have a -10 with electric trim, and a Trio Pro autopilot with auto-trim. I can let the autopilot intercept the glide slope (ILS or LPV) at 130 knots. As I descend I can smoothly reduce the throttle and/or add flaps, until Iím at 80 kias and partial flaps. Runway in sight, I disengage the autopilot - and the plane is in perfect trim. Probably more important for a plane with heavier controls (like a -10) than for the two-seaters, but, still, nice.
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  #4  
Old 01-24-2021, 06:08 PM
andrewtac andrewtac is offline
 
Join Date: May 2014
Location: Friendswood TX
Posts: 314
Default

However, consider electric trim as it can integrate with the autopilot. I can start an approach at 180 kts, and click the autopilot off at 70 kts getting ready to flare and the trim is set. If you don't integrate the trim you will need to be in the loop, or the servos will get overloaded and let go (with trim change requirements). When I got my 8 there was no autotrim, I have since changed it and really enjoy the upgrade.
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RV8 N189DK
RV10 in progress
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  #5  
Old 01-24-2021, 10:52 PM
wnplt wnplt is offline
 
Join Date: Feb 2013
Location: Idaho
Posts: 198
Default

I have auto trim and it trims the electric elevator trim. Auto trim is sweet...
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  #6  
Old 01-25-2021, 07:56 AM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,312
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Quote:
Originally Posted by wnplt View Post
I have auto trim and it trims the electric elevator trim. Auto trim is sweet...
Auto trim is sweet.

Not required, but very nice.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 750 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #7  
Old 01-25-2021, 08:37 AM
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Dugaru Dugaru is offline
 
Join Date: Jan 2016
Location: Richmond VA, USA
Posts: 494
Default Agree on both

I flew for a number of years in my Warrior with an S-Tec 30 that required manual trim changes. It would alert you by flashing a light and sounding a tone. Definitely not a dealbreaker.

But it certainly is nice to have the AP handle trim changes. The Garmin (possibly among others) adds a handy feature where it can run the trim at different speeds based on your airspeed. Very slick, since the stock electric trim on my -9A could sometimes be hard to tune just right at higher speeds. IIRC (and I really should know this already....), this feature is active even when the AP isn't.

Cheaper autopilots with crazy good functionality are one of the huge benefits of flying experimental, so I'd think hard about including automatic trim with an autopilot installation.

Quote:
Originally Posted by airguy View Post
Auto trim is sweet.

Not required, but very nice.
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Based W96: New Kent International Aerodrome
(near Richmond, VA USA)
2021 Dues Paid
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  #8  
Old 01-25-2021, 12:24 PM
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Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,838
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Auto trim is so nice I can't imagine not having it anymore.
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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, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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  #9  
Old 01-25-2021, 02:11 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,145
Default

Quote:
Originally Posted by Dugaru View Post
The Garmin (possibly among others) adds a handy feature where it can run the trim at different speeds based on your airspeed. Very slick, since the stock electric trim on my -9A could sometimes be hard to tune just right at higher speeds. IIRC (and I really should know this already....), this feature is active even when the AP isn't.
.
The Trio does this as well, and yes, you can use the autopilot knob to trim even when the servos are not engaged. Runs at high speeds when IAS is low, and progressively changes to low trim speed when IAS is high. Very handy for fine tuning the trim at cruise.
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  #10  
Old 01-26-2021, 06:55 PM
dwollen89 dwollen89 is offline
 
Join Date: Feb 2020
Location: Austin, MN
Posts: 2
Default

Thanks for the info everyone! Definitely will be getting electric trim. I read the complete thread on the gentleman with the runaway trim on his Rv8. The replies helped to put my mind at ease. I've never had electric trim, but it sounds like it'll be nice to have with the AP.
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