Trim Wheel Froce - Much Ligther @ Cruise

[Alexdangelo]

Hi All..

so I have a new to me J.. I know the trim force is heavy generally. I usually use electric trim in cruise but today I was hand trimming. I noticed when @ 6500' and hand trimming the force was very light, easily half the normal force. Trim was working fine, and pitch control was spot on with it. Just very light force needed, which seemed odd to me!

Once I was lower, the trim force felt heavy and normal again..

Has anyone ever had this experience?

Thanks All

[Will.iam]

I trim 90%+ by hand. Rarely do i use the motor trim as i figure the autopilot uses that motor enough as it is and i want to know if the system is getting stiff. Having said that i have not noticed a difference with trim wheel force with altitude but i have with air loading the elevator. I. E. If I’m out of trim from say bringing up the flaps then the trim will be stiff at first but lighten up as i get the plane back into trim. Or i can let off the elevator momentarily as i trim making the process easier. Lots of times i’ll trim nose up first allow the airplane to slow to 100kts drop the gear and add 10 degrees flaps as it slows to 90 kts then it’s about in trim. Start trimming nose up again before lowering flaps to 30. Can’t do this when IFR and have to maintain a precise altitude but vfr pattern no problem and easier on gear trim and flap systems. 

[N201MKTurbo]

You may find that it has nothing to do with altitude or speed or loading, but where you are on the jack screw. the places where you spend the most time will be the easiest to turn and the places where you rarely go are stiffest. Disassembling, cleaning and greasing the jack screw and gearbox will do wonders for it. It should be done every 20 years or so. Most have never been done.

[rickseeman]

Is this jackscrew under the trim wheel or at the tail? I would like to look at mine. Thanks.

[N201MKTurbo]

26 minutes ago, rickseeman said:

Is this jackscrew under the trim wheel or at the tail? I would like to look at mine. Thanks.

The jackscrew is in the tail, the gearbox is under the trim wheel.

[rickseeman]

Thanks, I will look.

[Hank]

2 hours ago, rickseeman said:

Thanks, I will look.

Take off the large avionics panel on the side, stick your head in and look down to the right.

[rickseeman]

Will do. Thanks

[PT20J]

When you run the trim up on the ground you are actually lifting the empennage against gravity. Conversely when you run the trim down on the ground, gravity is helping you.

I the air, the empennage is designed so that the aerodynamic loads approximately balance and so the trim force can be lighter.

The jackscrew should be inspected and lubed at annual time. You access it by removing the covers beneath the horizontal stabilizer that cover the gap between the empennage and the tailcone. There should be a boot that covers it to keep it from getting dirt in it.

[rickseeman]

Ok, I'll look for the boot. Thanks. I think mine needs some lube because it's kinda stiff.

[PT20J]

24 minutes ago, rickseeman said:

Ok, I'll look for the boot. Thanks. I think mine needs some lube because it's kinda stiff.

If you have a Bendix-King autopilot, there is a needle carrier bearing around the trim shaft where the trim servo sprocket attaches that is supposed to get lubed but never does.

[rickseeman]

I have a Garmin autopilot now. I will at least know what that is if I see it. (In case it wasn't removed.) Thanks

[PT20J]

3 hours ago, rickseeman said:

I have a Garmin autopilot now. I will at least know what that is if I see it. (In case it wasn't removed.) Thanks

The GFC 500 does not require lubrication of the trim bearing.