Man vs. machine

On most airplanes, you can trim the elevator by turning a wheel or crank that sets a tab — a flap on a flap — that then redirects the airflow to hold the elevator or stabilator at a certain angle of attack. Elevator trim is fairly important, since it saves you from having to hold constant pressure on the yoke to keep the plane from diving to the ground or going nose up and stalling. Fancier planes also have rudder and aileron trim (the Warrior has a fake rudder trim that’s really just a spring in the control system).

Since I bought my Piper Warrior II in December 2002, the elevator trim wheel has been surprisingly hard to move. Sometimes I almost get used to it, but then I fly another plane and notice that the wheel does not require 20+ lb of force to turn. At every annual inspection, I’ve squawked the trim, and mechanics have replaced the cable, replaced the pulley, and tried various lubricants. It always seemed a bit easier afterwards, but then soon went back to its old self.

This year, I squawked the trim once again, but the mechanic wasn’t satisfied just relubing; instead, he decided to examine the trim tab itself, and he noticed that when you turn the trim wheel, the tab flexes, but that the hinge has seized up with corrosion and does not seem actually to move. I imagine that it has been moving some — since it also acts as an anti-servo tab, the plane would be tricky to control otherwise, and I’m sure that I verified at least some movement on every preflight — but it’s still strange to think that I’ve been flying single-pilot IFR with no autopilot and trimming my plane by flexing aluminum through brute force alone. Man vs. machine, indeed.

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About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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3 Responses to Man vs. machine

  1. Paul says:

    Wild story, Dave. So the anchor point for the anti-servo tab was just flexing? I guess elevator effort has eased up a bit?

    I know that I get tougher elevator trim effort in the cold months, but I chauked it up to bad lube on the lead screw. Good you caught this.

    –paul

  2. John says:

    A 1969 Arrow I used to instruct in had a similar issue. During one flight with another instructor, I found the trim had become very stiff. The other instructor wanted to fiddle with it, but I was in the middle of an approach and thought this was a bad idea. So I just used a little force on the yoke to fly the approach.

    On the ground, we squawked it and I happened to talk to the mechanic a day later. The trim cable that wraps around the jack screw had slipped over time and a turnbuckle had move int a position where it was binding against one of the plastic pulleys. Had we continued to run the trim back and forth, the pulley could have split, the cable gone loose, and we would have lost trim control.

  3. harrier says:

    Different plane with a different trim system but trim experience none the less. I was in a Seneca and had trimmed it nose low for some maneuver I was practicing. When I tried to trim the nose up, I heard a snap and the wheel started free wheeling. I looked down to see the cable hanging loosely. Now, I had already purchased a gym membership for the sole purpose of gaining enough arm strength to land the Seneca with just one hand. The plane is NOSE heavy on landing and we had a tiny strip, so you aren’t going in with much power to help you out. Luckily I had another pilot with me. He held the nose up with both hands, his feet braced against the panel (it took this much to override that trim, and he kinda had geek arms) as I landed. When maintenance pulled the cable out, it was FINE in all spots but one wear spot where it had obviously been rubbing against something.

    It was just another experience that makes you realize no matter how much you preflight, you gotta be ready for anything. I imagine if I had been alone, I would have diverted to the big 10,000′ runway at the nearby international airport.

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