Full Fwd/Aft Trim

MadseasoN

MadseasoN

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MadseasoN
In a typical single engine trainer (C150, C172, Cherokee, Arrow). You're within CG @ GW and the trim sticks [stops working] full fwd or full aft. Power settings and configuration obviously matter, considering this do you still have enough yoke travel to maintain level flight and eventually land safely? Has anyone encountered this?
 
Trim doesn't affect yoke travel. It affects yoke FORCES.

So, yes, you always have enough travel for level flight and a landing. What you may not have is enough upper body strength to do it at all throttle positions and configurations.
 
For a healthy person, yes.
 
Not even sure you need to be healthy to land a 182 with full nose up trim. That's where it ends up or close to it, anyway, if you've got the flaps down and the power at idle. Big huge yawn there.

The other direction is a little tougher but I know someone who got the "joy" of taking off with a newer 182 with electric trim reverse-rigged. He said it was heavy. Went around the pattern and landed.
 
denverpilot said:
Not even sure you need to be healthy to land a 182 with full nose up trim. That's where it ends up or close to it, anyway, if you've got the flaps down and the power at idle. Big huge yawn there.

The other direction is a little tougher but I know someone who got the "joy" of taking off with a newer 182 with electric trim reverse-rigged. He said it was heavy. Went around the pattern and landed.
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I had the electric trim in a 182T wind the trim all the way nose down while at the hold short line for a long takeoff delay. I attempted a takeoff, and it felt ridiculously wrong at rotation, so I aborted the takeoff, pulled off the runway, and then noticed where the trim was.

I might have been able to struggle with the airplane airborne, but it would have taken a whole hell of a lot of effort, and I wasn't exactly in the mood to test that (and on a 7000 foot runway, it would have been utterly unnecessary).

I also had a different 182T autopilot glitch while airborne, where engaging it in pitch mode resulted in runaway nose down trim. It didn't make it all the way to the stop (but it got further than one might expect, because the AP button didn't turn it off), but it took a stupid amount of effort to fight the trim while I wound it back off.
 
MAKG1 said:
I had the electric trim in a 182T wind the trim all the way nose down while at the hold short line for a long takeoff delay. I attempted a takeoff, and it felt ridiculously wrong at rotation, so I aborted the takeoff, pulled off the runway, and then noticed where the trim was.

I might have been able to struggle with the airplane airborne, but it would have taken a whole hell of a lot of effort, and I wasn't exactly in the mood to test that (and on a 7000 foot runway, it would have been utterly unnecessary).

I also had a different 182T autopilot glitch while airborne, where engaging it in pitch mode resulted in runaway nose down trim. It didn't make it all the way to the stop (but it got further than one might expect, because the AP button didn't turn it off), but it took a stupid amount of effort to fight the trim while I wound it back off.
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I had the electric trim in my Comanche wind all the way nose down and then jam. Flying at speed wasn't too tough, but landing was hard - not too bad with both hands, but it was quite a pull for one hand. Something that needs to be repaired right away.
 
MAKG1 said:
Trim doesn't affect yoke travel. It affects yoke FORCES.

So, yes, you always have enough travel for level flight and a landing. What you may not have is enough upper body strength to do it at all throttle positions and configurations.
Click to expand...
While this is true, elevator trim implemented with tabs does affect control "effectiveness" but in the opposite direction one might expect. IOW if you apply full nose UP trim the elevator will become more effective with the wheel fully forward (nose down) and less effective with the wheel/stick fully aft (nose up). The trim tab acts similarly to a flap on a wing, increasing the camber for part of the elevator.

Some Twin Comanche pilots claim that dialing in nose down trim helps with landings when the CG is near the forward limit by making the elevator more effective near stall speeds in the nose up direction.
 
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denverpilot said:
Not even sure you need to be healthy to land a 182 with full nose up trim. That's where it ends up or close to it, anyway, if you've got the flaps down and the power at idle. Big huge yawn there.

The other direction is a little tougher but I know someone who got the "joy" of taking off with a newer 182 with electric trim reverse-rigged. He said it was heavy. Went around the pattern and landed.
Click to expand...
Because he didn't follow the checklist and verify the trim worked correctly, first flight after maintenance.

If we're referring to the same person, of course.
 
gismo said:
While this is true, elevator trim implemented with tabs does affect control "effectiveness" but in the opposite direction one might expect. IOW if you apply full nose UP trim the elevator will become more effective with the wheel fully forward (nose down) and less effective with the wheel/stick fully aft (nose up). The trim tab acts similarly to a flap on a wing, increasing the camber for part of the elevator.

Some Twin Comanche pilots claim that dialing in nose down trim helps with landings when the CG is near the forward limit by making the elevator more effective near stall speeds in the nose up direction.
Click to expand...

Maybe, maybe not. Barry Schiff did this experiment and found that the trim tab alone has zero or close to zero pitching moment on a C172. That said the 172 has a somewhat small tab.
 
dmspilot said:
Maybe, maybe not. Barry Schiff did this experiment and found that the trim tab alone has zero or close to zero pitching moment on a C172. That said the 172 has a somewhat small tab.
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I would certainly expect this effect to be somewhat proportional to the size of the trim tab relative to the elevator and IME it's not a huge effect on most airplanes. It also seems contrary to safety to use full nose down trim in the landing flare given that this means you have to pull really hard and if you relax just a bit you'd probably touch down nose first.
 
Nobody's mentioned that some aircraft use anti-servo tabs... ;-)

It's quite aircraft-specific...
 
I had the primary electric trim in a BE99 runaway aft on me once. That got my attention....
 
I had a Cessna 210L have a runaway trim issue on final at Baltimore Friendship years ago and lit with it that way. Turned out I had hit the altitude hold on the Cessna 400 autopilot and it was correctly trying to climb a 1,000 feet. Good lesson to double check that the autopilot is off. A 210 control pressure gets pretty heavy with full trim! Don't mean to be sexist but I am not sure all pilots would have been able to overpower it.

Another trim story. The year I started working at Cessna they were testing the new 340 airframe. A fiber lock nut on the elevator trim tab actuator failed, the bolt fell out and the trim tab rod jammed the tab full up. This created full down elevator. The test 340 did 1/2 of an outside loop, stalled inverted and went into an uncontrollable inverted flat spin. Pilot had a chute but could not get to the door in time and perished with the airplane. I will never do a preflight and forget to check for a cotter pin correctly installed in a castellated nut, nor will there ever be a fiber lock nut used on my airplane trim tab!
 
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