Trim and Auto Pilot

[dwollen89]

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?

[Darin Watson]

Originally Posted by dwollen89

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.

[BobTurner]

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 ‘trim up’ (or down). Now, some autopilots have ‘auto-trim’, 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 I’m 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.

[andrewtac]

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.

[wnplt]

I have auto trim and it trims the electric elevator trim. Auto trim is sweet...

[airguy]

Originally Posted by wnplt

I have auto trim and it trims the electric elevator trim. Auto trim is sweet...

Auto trim is sweet.

Not required, but very nice.

[Dugaru]

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.

Originally Posted by airguy

Auto trim is sweet.

Not required, but very nice.

[Walt]

Auto trim is so nice I can't imagine not having it anymore.

[BobTurner]

Originally Posted by Dugaru

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.

[dwollen89]

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.