Thorp Air Command - T18.net

So after rewiring most of my plane and having it back in the air since fall I'm starting to get annoyed wi my slow trim. Prior to moving the battery to the firewall I needed little to no trim. Now I'm adjusting the trim more from take off, cruise and landing. I have plenty of trim although now that I'm using it I have noticed it's very slow. Mine has the normal jack screw with electric motor that is mounted just behind my baggage bulkhead.

I have a 14g power wire running to my stick mounted switch then back to the motor. My first steps are to pull the wires at the motor to verify my voltage drop across those wires although I think a 14g should be plenty. That being said the tiny switch in my control stick could be a bottleneck although it's only a short contact.

Is anyone else using a relay from the control stick switch or just straight from power to switch to motor?


If the voltage looks good my next thoughts are checking the electrical brushes in the motor for wear or even putting a faster motor in. I'll have to verify the model motor mine has. I couldn't find anything with a quick glance when I was wiring.

Thanks all!

I would think 14 gauge wire is heavy enough but need to know how many amps the motor can draw and how long the wire is to verify gauge needed. You could be right about the switch if it wasn’t designed to carry the load.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

For what it's worth, my electric trim is 12 seconds stop to stop - I actually wish I had manual trim, as bumping the electrical trim rarely results in level flight at cruise, which is then needing another change once another 6 lbs has burned off 8 minutes later in the header tank. I think slow trim is a good thing in a T-18.

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

I fly another airplane where I cant ever get the trim where I want it because the trim moves too fast. Makes me appreciate my slow Thorp trim motor.

This looks like the original motor from the build in the 70s but I can't see markings. Next week I'll get pictures and see if there is a stamp somewhere. It hasn't tripped the 5amp breaker so it has to be less than that

The slow trim is nice in flight but I struggle on take off. If the trim isn't perfect I have to hold way too much forward pressure and it takes a good 30 seconds to level out. My trim indicator is skipping teeth so it's not accurate and my landing trim is very tail heavy. So rich and go landings don't have enough time to trim level. I can hold the pressure but if I were to slip or something happen I think there is potential for a safety hazard. It doesn't feel unsafe but I don't like any potential.

It might all balance out once I remove as all my bad stuff as and change lighter avionics as planned here in a few months though. I was just hoping for more like 15 seconds trim travel and not 30+

I prefer manual trim and manual flaps in my planes as well but Thorpe has right tight estate

Using 5 amps and 12 feet as the wire length from the bus to the motor, 18 gauge would carry a continuous load just fine. 14 gauge will carry a continuous load of 5 amps for 25 feet before heavier wire is needed. A trim motor would be intermittent use and allow smaller wire (18 gauge for 25 feet at 5 amps).

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Ya, that's what I thought. I went through all the charts on wire gauge and resistance to make sure I sized everything by the book with breakers designed for wire current safety and not just random amounts.

I'll pull my inspection hole and put s little live in the jackshaft. That might be slowing it down as well since it's so cold and I'm not sure how well it was lubed during the inspection.