Electric vs. Manual Trim?

Greetings builder community! I am planning on ordering the empennage kit for an RV8 in the next couple of months. I am still researching and have many questions. In particular, one decision I have to make is around the option for the emp kit regarding manual or electric elevator trim. While electric elevator trim sounds really nice, and I'd really like to have it - my understanding (with confirmation from VANS Builder Support) is that the two options are mutually exclusive. The electric trim replaces the manual trim option.

My concern is, what happens when/if the electric trim fails in flight? Is the aircraft still safely landable in this condition? In a certificated airplane (i.e. the Piper Archers I have been training in) there is usually a manual trim option available if the electric trim is inop (and at the school they usually are). But it sounds like the way the RV8 is designed that is not the case?

My plan is to use the Garmin G3X dual display system with the Garmin 2-axis autopilot. I assume the AP will work with either manual trim or electric trim options - but I'm not sure on that point either.

Any constructive guidance on this topic would be most helpful!

__________________
Damien Currier
Planned RV-8 Builder
2016 Dues Paid

If you are planning an autopilot, you will likely (really) want autotrim. Autotrim requires electric trim. Decision made!

dcurrier said:

My concern is, what happens when/if the electric trim fails in flight? Is the aircraft still safely landable in this condition?
Any constructive guidance on this topic would be most helpful!

__________________
Damien Currier
Planned RV-8 Builder
2016 Dues Paid

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I have an RV7 so may be a bit off base but I think you will find that the airplane would be controllable and landing would be manageable but flying the airplane very far would get tiring. These are good questions and valid concerns that you have. Check this system out. I installed one in my airplane 8 years ago and it works flawlessly.

http://www.tcwtech.com/Safety-Trim%20Page.htm

Joe

Caveman said:

I have an RV7 so may be a bit off base but I think you will find that the airplane would be controllable and landing would be manageable but flying the airplane very far would get tiring. These are good questions and valid concerns that you have. Check this system out. I installed one in my airplane 8 years ago and it works flawlessly.

http://www.tcwtech.com/Safety-Trim%20Page.htm

Joe

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Or, better yet http://store.makerplane.org/m-pwr-2x-dual-channel-variable-speed-trim-control/. No electo-mechanical parts.

I have manual trim and love it ... would not trade it for electric. Major trim changes require no more than 1/4 to 1/2 turn of the knob. Also, my TruTrak 2-axis autopilot works flawlessly; it does NOT require electric trim.

Welcome to the brotherhood Damien!

Get that empennage ordered and get to building You have come to the right place as there are a lot of experienced people on this forum.

One other data point is that the manual trim cable is much thicker - obviously running to the very aft regions of the airplane - which is heavier than the electric wire that runs back there to the servo motor in the elevator (also weighs something). I was told, when I asked the same questions, that a full up/down trim situation would not make the -8 un-flyable as there would be enough elevator to fly/land.

Know that you can always make the decision later...order the emp. without any trim and then later after you have mulled it over in your mind a few hundred times and discussed it with all of your new RV friends, the decision will become clear and you will easily be able to order a trim cable or trim motor and have it shipped for free in the wing kit or replacement part shipment! Nothing is in stone - build the airplane you want to see when you open that hanger door .

Rupester said:

I have manual trim and love it ... would not trade it for electric. Major trim changes require no more than 1/4 to 1/2 turn of the knob. Also, my TruTrak 2-axis autopilot works flawlessly; it does NOT require electric trim.

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Totally agree with this..

Once you've had autotrim, you'll never want to give it up. I developed one of the first autotrim systems for EAB aircraft and it's the best thing I ever did for reducing pilot workload, enhancing safety and preventing inadvertant autopilot disconnects. When you choose to disconnect, the airplane is in perfect trim.

Ironically, I recently had an AP servo fail and my autotrim system flew the aircraft for 100 miles before I noticed it.

The G3X system and garmin autopilot work fine with manual trim. With the AP engaged, If trim forces against the servo are too great a message pops up on the middle of the PFD indicating to "Trim Up" or "Trim Down". And with a 1/4 turn or so the message goes away. With the garmin AP, if you have elec trim you can have auto trim where the AP controls the right amount of trim, which would be nice, couple more things to wire though.

Yes

We have the G3X, electric trim, with auto pilot and speed compensated auto trim. This set-up is for those long flights with some place to go. I think the question you are asking here is can you control the aircraft if you have a runaway trim or the trim goes fault on you. If you are up at speed it can get tiring to fight an out of trim "8", but it is well with-in the control authority of the aircraft to manually override the trim force. I have at times pushed the button on the stick and not noticed that the trim had run to full side or pitch trim positions. When you are up at speed roll trim will not be as noticeable as pitch trim. Pitch will let you know there is force being applied. If you are at pattern speed 90-70 kts. the force that is fed back from an big out of trim setting is not that noticeable and is easily ignored and overridden. You will like it either way, it is just what you want in your personal set-up that counts.
Hope this helps, Yours, R.E.A. III #80888

If the trim dies in cruise flight you will be able to land, no problem. Especially if you have stuff in the back. I rarely even touch the trim in the -8 or Rocket when landing after a cross country with my wife/stuff in the back.

A trim "runaway" will be unwelcome, but I believe it is a manageable event if it happens at speed.

I would not consider any trim failure mode in my decision to install manual or electric.

I would consider weight, real estate and ergonomics however. The manual trim, while simple and effective, does have a hefty lever and cable associated with it. Electric is actuated with a simple toggle which can be placed anywhere in the cockpit easily. Its simple to add a second switch for the back seater as well.

If you are ever going to have anyone one "instruct you" from the back, as much as you can "instruct" in an RV8....then they will wish you had put electric trim in the back as well.