Van's Air Force
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Mechanical or electric trim
- Thread starter FrenchRV8
- Start date
My RV-3 has 3 axis electric trim. It’s the first small airplane I’ve flown with all 3 axis. Any plane I build will have 3 axis electric trim and electric flaps.
This being said, if I really wanted a minimalist plane (for cost or weight considerations) the only electric trim I’d consider nearly mandatory would be pitch trim.
I’m sure this question will garner almost as many opinions as the infamous primer discussions, so please view my response as only my opinion.
This being said, if I really wanted a minimalist plane (for cost or weight considerations) the only electric trim I’d consider nearly mandatory would be pitch trim.
I’m sure this question will garner almost as many opinions as the infamous primer discussions, so please view my response as only my opinion.
Mine is a -6 but shouldn't be too different - I went with manual elevator trim, and my thinking at the time was KISS. I'm used to it and it's worked okay but it's also one of the few things I'd probably do different next time. Reasons include: slop in the cable, big knob, constantly adjusting. Might be different for the -8 but that's my take.
I'm okay with my spring aileron trim. It's definitely stone simple and lightweight. Though I suppose I might consider electric for that too if I were to build another plane.
I'm okay with my spring aileron trim. It's definitely stone simple and lightweight. Though I suppose I might consider electric for that too if I were to build another plane.
wcalvert
Well Known Member
Elevator trim is super convenient and used all the time in the pattern and while maneuvering. It's simple to install and doesn't add too much cost/weight or complexity.
Like was said earlier, the real driver is the A/P install. If you want and A/P, electric pitch trim will make or break the deal.
Good luck!
Like was said earlier, the real driver is the A/P install. If you want and A/P, electric pitch trim will make or break the deal.
Good luck!
Call me a Luddite:
noun
1. DEROGATORY
a person opposed to new technology or ways of working.
"a small-minded Luddite resisting progress"
Well, that might be me, but sometime I have my reasons why new technology isn't better.
Lot's of reasons to not need electrical pitch trim:
1. Manual trim will never run away.
2. In the event of an electrical failure, the trim will still work, and not runaway.
3. Cheaper
4. Can't possibly run away due to a stuck switch.
4. Meets the designer's criteria
5. At least in my RV-6, I might use the pitch trim 3 or 4 times in a cross-country flight, maybe a bit more in a formation flight.
6. The manual trim can be adjusted much more finely, and slowly than the electrical trim.
7. If you are on autopilot, the autopilot will alert you that it isn't happy with the trim setting, and you can smoothly fix it, allowing the human pilot to better remain in synch with the trim status of the airplane.
PS: I still drive a manual shift pickup truck, for many of the same reasons!
The only reason I can think of for anyone to get electrical trim is because you Want it, and it's cool like a big airliner...........
Same for aileron trim.
And if I ever get around to installing adjustable yaw (rudder) trim, it will be Manual, for all the same reasons.
No doubt YMWV.
noun
1. DEROGATORY
a person opposed to new technology or ways of working.
"a small-minded Luddite resisting progress"
Well, that might be me, but sometime I have my reasons why new technology isn't better.
Lot's of reasons to not need electrical pitch trim:
1. Manual trim will never run away.
2. In the event of an electrical failure, the trim will still work, and not runaway.
3. Cheaper
4. Can't possibly run away due to a stuck switch.
4. Meets the designer's criteria
5. At least in my RV-6, I might use the pitch trim 3 or 4 times in a cross-country flight, maybe a bit more in a formation flight.
6. The manual trim can be adjusted much more finely, and slowly than the electrical trim.
7. If you are on autopilot, the autopilot will alert you that it isn't happy with the trim setting, and you can smoothly fix it, allowing the human pilot to better remain in synch with the trim status of the airplane.
PS: I still drive a manual shift pickup truck, for many of the same reasons!
The only reason I can think of for anyone to get electrical trim is because you Want it, and it's cool like a big airliner...........
Same for aileron trim.
And if I ever get around to installing adjustable yaw (rudder) trim, it will be Manual, for all the same reasons.
No doubt YMWV.
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oaklandaviator
Well Known Member
Runaway worries…
I read a lot about people worrying about trim runaways, probably because of the airliner runaways in recent memory. It’s important to look at the type of trim system the particular plane has. Airliners, at least all of the ones that I know of, use moveable horizontal stabilizers and also have very wide cg envelopes due to the large cabin area and thrust vector effect. For these reasons, and more I’m sure, a runaway is a very bad thing because you really can’t overpower a full trim condition with the much smaller elevator. Our planes use a trim tab with a pretty small cg range. A complete runaway would be nothing but a nuisance and totally controllable, maybe not by the autopilot but all but the weakest pilot should be able to handle it just fine.
Electric pitch trim is much simpler than manual. Very flexible little wires are run in lieu of a giant, long, relatively inflexible teleflex cable. I like the feel of manual trim in sport planes, but electric is lighter, simpler, works better with an autopilot, and in the off chance it runs away you’ll be able to manually overpower it just fine.
Just my ramblings for the morning.
I read a lot about people worrying about trim runaways, probably because of the airliner runaways in recent memory. It’s important to look at the type of trim system the particular plane has. Airliners, at least all of the ones that I know of, use moveable horizontal stabilizers and also have very wide cg envelopes due to the large cabin area and thrust vector effect. For these reasons, and more I’m sure, a runaway is a very bad thing because you really can’t overpower a full trim condition with the much smaller elevator. Our planes use a trim tab with a pretty small cg range. A complete runaway would be nothing but a nuisance and totally controllable, maybe not by the autopilot but all but the weakest pilot should be able to handle it just fine.
Electric pitch trim is much simpler than manual. Very flexible little wires are run in lieu of a giant, long, relatively inflexible teleflex cable. I like the feel of manual trim in sport planes, but electric is lighter, simpler, works better with an autopilot, and in the off chance it runs away you’ll be able to manually overpower it just fine.
Just my ramblings for the morning.
FWIW, according to the G3X manual, you can use a GSA 28 servo as a trim actuator on a manual trim system. So I guess you could have autopilot and manual trim with that setup. I wonder if you could use the servo for electric trim without engaging an autopilot mode to give the pilot both manual and electric trim options.
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Trim
I have flown several RV6 with manual trim and the added electric trim to my RV7 and prefer manual trim . Good feedback feel for correct trim. No failure when electrics down( tricky in a short strip with no EFIS etc ) . So reliable and shouldnt fail. Jeff R Australia
I have flown several RV6 with manual trim and the added electric trim to my RV7 and prefer manual trim . Good feedback feel for correct trim. No failure when electrics down( tricky in a short strip with no EFIS etc ) . So reliable and shouldnt fail. Jeff R Australia
