The Cessna 120-140 Association Forum

My 140 had the early trim tab actuator and was very sloppy. I am installing the latest superseded unit. pn. 1260074-1. It fits fine but does stick further out the back of the spar than the original one. This limits the nose up trim to 24 degrees vs the spec of 33 degrees.
The push rod is not adjustable.
It is about 3/16 too long.
Has anyone seen a adjustable rod?
Has anyone made one? What did you use.
I have seen old posts complaining of not being able get more than 24 degrees with the poster being told to adjust the rod.
Thanks
Joe

Maybe a dumb question, but can you screw the end of the actuator in further?

If it sticks out more then the geometry won't be the same and the tab will move differently when you move the elevator. Maybe not a good thing...

Thanks for the reply.
The actuator is already fully retracted.
Good thought regarding the geometry. I’ll take some measurements at travel stops.
I’m going to make a correct length rod and see what happens.
On landing I am often at full nose up trip (33) degrees.
Joe

6641 wrote: ↑Wed Jan 20, 2021 7:25 amThe actuator is already fully retracted.

On the original there are two ways to retract. One is by turning the chain wheel, but the other is by screwing the clevis end of the actuator into the body. The latter shortens the overall length and is independent of the trim movement.

Understood
She's in as far as in can be.
Joe

Any chance the snap rings are on the wrong side of the two saddle clamps .... meaning could the jack screw itself be too far aft? IIRC, on mine the jack screw goes in with the snap ring up against one of the saddle clamps, but would fit on either side (of the clamp). Threw the starting point way out of position. Just something else to investigate. Jim S

Hi Joe. Just found my notes when I reinstalled my jack screw. I'm fairly sure it's original to the aircraft. Center to center on the rod is 12", max jack screw stroke is 1.5" taking 15 full revolutions, meaning .10" linear movement per turn. For me that translated to 2 to 4 degs. per complete turn. Don't know if that helps but gives you some kind of reference, your superseded unit might be different. Jim S

Thanks Jim
The replacement actuator is the C150 unit and is a bit longer than the original. The two snap rings do nestle nicely into he mounting bracket as do the saddle clamps.
The sprocket end is a bit more forward making it necessary to relieve the holes in the adjacent rib due to slight chain rub.
Thanks for the rod dimensions they are the same as mine.
I'll post some dimensions when I can compare the actuators side to side and when I figure out what the rod length needs to be.
Joe

Elevator trim does slightly reduce elevator effectiveness, so full up trim will reduce the amount of elevator force you have, not by much of course, but some.

I learned on my Maule which had a big ole motor to not use as much up elevator trim for an approach , the reason was if a go-around was attempted, the force required to hold the nose down was excessive.

I’ve not tried on my 140, but full up nose trim may made an unplanned go -around exciting, or it may not, not sure. Try a go-around with full up trim and see?

But also I don’t believe our trim tabs are also servo tabs, so a reduction in throw will only effect amount of trim available

Full nose up trim go arounds are not a problem on the 140 though I can see where they could be on a heavier bird like the maul.
I am collecting parts to make a replacement rod will be sure to post a final result.
Joe