Thorp Air Command - T18.net

I am considering installing a 4.5 rpm elevator trim motor in my project. Would anyone think 4.5rpm is too slow for elevator trim? I currently have the same gear motor in my flying Thorp, but it is a 17rpm motor, and sometimes I feel like I am hunting for my trim sweet spot.

Here is the one I am considering:
https://www.zoro.com/dayton-dc-gearmoto ... /G3445111/

Others who have electric trim can answer better than I, but I suspect that it will be just fine. Better a little slow than too fast, for trim, in my opinion. It looks like a good motor, and that price is a few bucks cheaper than you can buy it direct from the supplier, W. W. Grainger (unless you have a business account at Grainger, & get a discount).

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

When you say hunting for your "sweet spot" , do you mean you overshoot that magic spot ? It doesn't take much travel of that tab to "trim it out ." I find I just "bump" my coolie hat and it is more than enough to level things out . I have flow a lot of AC with electric trim and I find that is the case for all of them . So I would say yes...slower is better . It may mean you hold the trim switch a 1/10 of a second longer , but probably less likely to overshoot .

RB

Mine turns about 11 rpm and is a little slower than I like, but is acceptable. I would think 15 to 18 would be about perfect.

Jim
N180RG

Yep, I feel like I am overshooting that magic trim spot with the 17rpm trim motor, but based on Jim's post, I may just stick with it for the project too.

When I built my plane, I was flying the F-4 Phantom. I timed the trim system from stop to stop and found it to be 9-10 seconds. The trim screw on the T-18 turns 5 1/2 turns stop to stop. That makes for 33 RPM. I found that to be a bit fast for the T-18 in cruise, due to the sensitivity of the stab trim. The trim motor I found runs about 1/2 that, or 15-17 RPM and is just about right. I found my trim motor in a NASA junk pile at Langley AFB. Probably an actuator from a space craft. Hope it doesn't crump!

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Bob Highley
N711SH
SN 835
KLAL

FWIW, my trim is 12 seconds stop to stop, which is about 27-28 RPM......I find it OK - that sweet spot is pretty narrow, and for those of us with just a header tank, it never lasts very long.

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Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

Bob...did they have any $600 toilet seats or $400 hammers in that NASA junk pile ?

RB

A trip down memory lane: back in 1980 I had bee flying my T-18 for a little while when I got a call from Leroy Holt in McAlester, OK. He was getting close to finishing his and ask me to fly down and look it over and perhaps answer a few questions. I flew down and he picked me up and we went out to his shop. His project was coming right along and we had a good discussion and got to know one another a little. I noticed on his work bench a little "gear box" about the size of a regular pack of cigarettes. The workmanship on it was out of this world! The input shaft had what appeared to be jeweled bearings similar to a Swiss watch, same with the output shaft. I asked him what it was for and he said the little automobile window operating moter for his electric trim was to fast so this gear box was to be a speed reducer. I asked him what it was made for and where he found it. He worked in the US Naval Arsenal near McAlester and he found it in a junk pile there much like Col. Bob did his. It was part of the arming mechanism from a Mark 4 atom bomb!!!
Steve Hawley

I haven't had mine open to examine mine but I will next fall at annual. I actually do not like electric trim. I like to feel the wheel and not have one more electrical component and gear connections to service and wear out.

Mine is way too slow. I often have to hold the button for a few seconds when trimming for pattern altitude and decent base to final. It's quite annoying. When I decide what I'm going to build it will most likely have manual trim.

I'm used to electric flaps in the Cessna planes although I prefer my manual flaps in the thorp. I've oddly had many motor and switch failures through the years on flap motors.

I'm with you, Jeff.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

well my electric trim motor failed.

I'm starting another thread but I figured I would ask here. Does anyone know where this motor is mounted in the plane?

Here you go......
viewtopic.php?f=4&t=6201&hilit=trim+motor+grainger&start=0

Jeff - I used to have a T-18 where the trim motor was mounted just aft of the baggage compartment under the deck, with a long aluminum tube to the jack screw. The advantage to that was that if the motor went T-UP, you didn't have to pull the tail to replace it. Having said that, the tail is easy to remove (mind your torque when re-installing the bolts) and I think that the installation referenced above is superior to the one I had.

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Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

Thank you both!

Seems like each time I visit the hanger during this "minor" upgrade I'm finding many deficiencies with the airplane that need fixed to my liking. I appreciate all the amazing help from you guys here.