Thorp Air Command - T18.net

i have a t18 that i purchased two years ago from Bruce janzen in Redlands calf and then i imported the aircraft into Australia.it is a fantastic aircraft.I have found that with full tanks i have enough nose down trim but as the fuel reduces i run out of nose down trim and i then have to hold forward stick pressure.The electric trim motor has also given me trouble so i am replacing it so i hope this solves the problem.i would have thought that with a Lyc 360 and CSU that i would not have had this problem.There does not appear to be any adjustments on the actuating arms so the other prospect would be to lengthen the arms to give more trim tab movement.
Can anyone give me details on this problem.
regards,
Warren hill

This is a common problem. You can lengthen the links or more simply bend the arms. It doesn't take much adjustment to make a difference. The reason for the issue in the first place is that the plane was designed for 125/135 HP. With the 180, you are traveling much faster in cruise.

I would suggest you also reaccomplish a weight and balance as our planes tend to "grow" over the years.

Cheers,

_________________
Bob Highley
N711SH
SN 835
KLAL

Thanks for the information Bob.Can you suggest how much longer the arms should be?Thanks Warren Hill

I actually fixed mine by bending the arms on the anti-servo links. Not more than 1/8", I think.

The jackscrew nut in the trim mechanism ideally has 5 1/2 turns lock to lock. That is not much movement to cover the whole trim spectrum. My advice is to make a small adjustment and see how it works.

_________________
Bob Highley
N711SH
SN 835
KLAL

JUST TO ADD MY OPINION TO THE NOSE HEAVY TRIM PROBLEM, I THINK THAT IT'S FOOLISH TO START BENDING AND TWISTING THINGS TO RESOLVE THIS ISSUE. YOUR JUST TRYING TO GO FROM AN UNKNOWN TO AN UNKNOWN. IF THIS WERE MY PLANE I WOULD FIRST CHECK THE WEIGHT AND BALANCE CONFIGURATION. THAN CHECK THE RIGGING USING THE PLANS AND NEWS LETTERS AND MAKE ADJUSTMENTS AS NEEDED. IT'S NOT THAT HARD TO DO, AND IT PROVIDES A GOOD LEARNING EXPERENCE. THERE'S ALL THE EXPERENCE YOU'LL NEED IN THIS GROUP SO YOU CAN CONTACT SOMEONE DIRECTLY AND THEY CAN HELP YOU THROUGH THE PROCESS. THAT INCLUDES ME. PAUL MACMICHAEL

Paul's trim recommendation should be followed. Fortunately we have the Newsletters available on the Forum. See Newsletters #93 and 99(minor correction)for the procedure to check rigging per drawing A-521. Newsletter 136 has John Thorp's weight and balance data. Typically when the weight and balance and tab rigging is brought into compliance, the trim is adequate.
Richard Eklund

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RCE

We made longer trim links and now our O-290 engined Thorp no longer runs out of down trim.

Brent Schultz
N6CM

Can the arms be adjusted cold, or do they need to be heated?

I have the opposite problem. I'm running out of "nose up" when my flaps are down. I have to pull quite a bit to maintain 80 KTS on final. The current rigging matches the drawing. W&B is fine.

D

My links are not as per drawing. I cheated and copied Bob's trim links and bent the arms to match his. The trim works with flaps down or up. I generally trim in flight and very seldom trim on landing with the exception when I have a lot of weight in the trunk. I suggest bending them with heat as cold might run the risk of kinking the tube

With an 0-320 and C/S, with remote filter up front, and oil cooler, when the tank is full and I'm wearing just my shorts, I pull about 5 pounds of back pressure below 100 MPH on the airspeed with full flaps. That's with the 28 lbs of battery behind the baggage area. Two quarts of oil and two 750 ml bottles of a dry Tuscan chianti (clandestinely wrapped in a towel at the very back of the baggage compartment by She Who Eye Wership) will keep the stick pressure to a minimum on landing with about 10 US gallons in the tank. I think I would feel comfy bending the arms a bit.
Honestly, I keep a quart or two of oil at the back of the baggage, as well as the extinguisher and some other sundries and other than the extreme configuration stated above, she's trimmable through the spectrum.

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

Fraser : It might help if you put that trunk monkey back in the baggage compartment where he belongs ! Wait a minute...put the trunk monkey in the pilots seat and you go in the baggage compartment . BOOM !

RB
BaBaLoo

I would not suggest bending the arms. Please make sure W&B is ok. Then rigging is checked. Also make sure you have full travel. Then, if needed, I would shorten or lengthen the links by no more than 1/16" to start.
Cubes

W&B check
Horizontal tail rigging check

I was flying with CG near forward limit, so that's a factor.

I don't plan to make any changes real soon.... need to see what happens with trim at the other end of the speed range first.

Longer links = more range?

D

I cant remember the last time I used full Flaps to Land, it has been awhile, I just use the first notch and all is well. After trimming for nose up I still have to put a little aft pressure on the stick to keep things as they should be but this is not a bother at all......Full Flaps does require quite a little more aft pressure on the stick but again not really an issue....Dan

D,

Longer links changes trim range, does not give more range.

_________________
Bob Highley
N711SH
SN 835
KLAL