Inspector Scott
Member
I'm at the point where I have to make a decision on how to power my trim and looking for some input
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manual or Electric trim
- Thread starter Inspector Scott
- Start date
alpinelakespilot2000
Well Known Member
Perhaps if you are wanting to fly coupled IFR approaches electric trim would be ideal, but I have an autopilot and am completely happy with manual trim. Works great for the VFR flying I do. My Dynon lets me know with an indication if I need to adjust the trim up or down. I first purchased the electric trim but switched to manual during the build. It was part of my KISS approach to building that 700 hours later I'm glad I took.
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MacCool
Well Known Member
I have manual trim, no issues. I had a runaway trim occurrence years ago...I remember it as quite inconvenient. As to auto pilot on my RV...trimming is no big deal even on my ancient old TruTrak. I wouldn't have been averse if the builder of my airplane had opted for electric trim, but I don't miss it at all.
PilotjohnS
Well Known Member
electric
fly my check out in a 7 with manual trim. built mine with electric. after flying both electric trim, hands down wins. and if there is an Otto pilot, then electric is a must. For the potential of runaway trim, I put the trim circuit breaker right in front of pilot, near the throttle so I can get to it in a hurry and without changing hands on stick. JMHO
fly my check out in a 7 with manual trim. built mine with electric. after flying both electric trim, hands down wins. and if there is an Otto pilot, then electric is a must. For the potential of runaway trim, I put the trim circuit breaker right in front of pilot, near the throttle so I can get to it in a hurry and without changing hands on stick. JMHO
I flew my transition training in an RV-7A with electric trim and found it too sensitive, could not find the "just right" spot.
Built my plane with manual elevator and aileron trim and have a BK xCruze 110 (Trutrak Gemini) autopilot that tells me when it needs some up or down trim; trim sensing pitch servo. The manual trim may add some weight in the tail due to the heavy cable, and there is a little bit of slop in the vernier cable.
Built my plane with manual elevator and aileron trim and have a BK xCruze 110 (Trutrak Gemini) autopilot that tells me when it needs some up or down trim; trim sensing pitch servo. The manual trim may add some weight in the tail due to the heavy cable, and there is a little bit of slop in the vernier cable.
erich weaver
Well Known Member
Yes, the servo typically moves too fast, making adjustment very sensitive. I had to play around with adding resistors until I found the sweet spot, which turned out to be a voltage just above the point where the servo didn’t respond at all. Trim sensitivity is of course also very dependent on air speed. Just a very quick touch of the button is noticeable at cruise speed, but I need 2-3 seconds to trim the nose up when I slow down to pattern speed.
Walt
Well Known Member
All modern glass panels have auto trim and speed control based on airspeed, so the above problem really does not exist any longer.
"Runaway" trim can be avoided using good wiring practices/components, I believe 100% of those events are builder induced.
(I'm sure someone will say "it happened to me")
I can't imagine building a modern airplane w/glass panel and manual trim, makes no sense.
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Bought an RV4 in 2012. Basic VFR with manual trim and flaps. Quickly converted both to electric. Sold it in 2015 and purchased a flying RV8. Electric flaps and trim, with IFR glass. So I have only one thing to add to the statement above: You'll be happier with electric whether your RV is VFR OR full blown glass IFR.
Scott Hersha
Well Known Member
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MacCool
Well Known Member
Exactly. If my airplane on autopilot needs to be re-trimmed, it tells me and I just give the knob a little tweak. No big deal.
Walt
Well Known Member
Guess it depends on definition of “modern”, Garmin, Dynon/Skyview, AFS all provide auto trim w/speed defined trim speed.
I never said you “need” it, but it’s a very nice feature, take it or leave it.
We don’t “need” lots of features we have these days, but many make flying more enjoyable and safer.
I never said you “need” it, but it’s a very nice feature, take it or leave it.
We don’t “need” lots of features we have these days, but many make flying more enjoyable and safer.
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Anyone have their manual trim on the LEFT side, against the fuselage side? I like to fly aerobatics with my right hand on the stick, and the left hand on the throttle, so will have my trim on the left.
I'm going with a UL engine with fuel injection and electric CS prop, which uses a prop control on the panel and not on the throttle quadrant. So my plan is to have a throttle quadrant on the left, with a second handle on the quadrant that will be the manual trim. Think of a throttle quadrant with a throttle and mixture, but the mixture handle would be the trim, instead.
Mostly I'm wondering how the manual trim cable might get routed. I don't have my fuselage kit, yet, so I don't have anything to look at and scratch my head about.
I'm going with a UL engine with fuel injection and electric CS prop, which uses a prop control on the panel and not on the throttle quadrant. So my plan is to have a throttle quadrant on the left, with a second handle on the quadrant that will be the manual trim. Think of a throttle quadrant with a throttle and mixture, but the mixture handle would be the trim, instead.
Mostly I'm wondering how the manual trim cable might get routed. I don't have my fuselage kit, yet, so I don't have anything to look at and scratch my head about.
Scott Hersha
Well Known Member
My RV4 (that I didn’t build, but bought) had a manual trim lever on the left wall right next to the throttle quadrant. It was standard build per plans. Maybe you can get a copy of the RV4 plans and duplicate for your RV7.
Desert Rat
Well Known Member
You could argue the pros and cons of each until the cows come home and still not come to a consensus. There are just too many variables that have to do with what other magic boxes you have installed.
Personally, I wouldn't want electric trim if I didn't have some way to speed schedule it. I've been there done that in other planes and the trim gets annoyingly sensitive at high speed.
I have a speed scheduling solution via Garmin, so I went with electric for the simplicity of the installation and the weight savings (especially applicable to the elevator trim).
I have zero concerns about a trim runaway. I've heard about this for 30+ years now and still haven't experienced any autopilot or trim system going rogue terminator and trying to kill me. In the unlikely event that it does happen, that's why those breakers are easy to find by feel.
Personally, I wouldn't want electric trim if I didn't have some way to speed schedule it. I've been there done that in other planes and the trim gets annoyingly sensitive at high speed.
I have a speed scheduling solution via Garmin, so I went with electric for the simplicity of the installation and the weight savings (especially applicable to the elevator trim).
I have zero concerns about a trim runaway. I've heard about this for 30+ years now and still haven't experienced any autopilot or trim system going rogue terminator and trying to kill me. In the unlikely event that it does happen, that's why those breakers are easy to find by feel.
Caveman
Well Known Member
Another option
Here is another option if you have older glass or steam gauges. I installed it during the build 15 years ago and it has worked flawlessly.
https://www.tcwtech.com/product/safety-trim-intelligent-servo-controller/
Thanks,
Joe
Here is another option if you have older glass or steam gauges. I installed it during the build 15 years ago and it has worked flawlessly.
https://www.tcwtech.com/product/safety-trim-intelligent-servo-controller/
Thanks,
Joe
This ^^^works. If you’re handy with electronics you can build something like it for just a few dollars. Or, still another option, the Trio autopilot offers speed sensitive auto-trim. e.g., the higher the airspeed, the slower the trim runs (you set the parameters). And you can use it in a manual mode (I frequently do) when hand flying with the servos disengaged.
Side note: I guess I’m getting old, but I find it annoying when internet posters use the expression ‘is a must’ to mean ‘is nice’, when the common English dictionary interpretation of ‘must’ is ‘required’. Looking at the comments I see others are bothered, too.
Richard Connell
Well Known Member
Pedants unite!
I had auto trim in my RV7 15y ago. It’s not new technology.
Now speed scheduling and auto trim is affordable and ubiquitous. I doubt many RVs are built with manual trim these day. The weight alone is worth considering.
Trim runaways are the RV bogeyman. Much discussed but never seen.
For those who have seen it would state that the plane is completely flyable at each extreme. We have all tested that in phase 1 right? It’s not a 737.
Plenty of ways to mitigate that extremely low likelihood failure.
Only if you have the separate A/P knob panels. I was somewhat annoyed when they came out with these after my panel was completed and didn't provide for auto trim in the system without the additional modules, but TBH, I don't have an issue with not having auto trim.
after installing the Dynon a/p panel with my AFS EFIS, I found auto-trim nice because before I often didn't notice the trim suggestions on the a/p. Now they don't show up anymore
The a/p panel also provides time-limited trim actuation to mitigate runaway trim effects.
The a/p panel also provides time-limited trim actuation to mitigate runaway trim effects.
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