Fixing the trim tab

I’m going to fast forward to the present for this post. I think I’ll be alternating with the last thing that happened and filling in some history of the plane.

Last Saturday, I finally got a chance to fix the rudder trim tab. Folks who fly N194SP will appreciate that it now flies straight in cruise without any annoying pressure to be kept on the rudder pedals. I flew it from Tampa with the ball wanting to swing a quarter-ball left for 26 hours! That resulted in a very sore left leg.

Like most control surfaces, the rudder needs a bit of trim to keep it right where it should be without effort. On many aircraft, a control in the cockpit allows for changes to the rudder trim. However, the 172, being a simple, slow aircraft does with a small metal tab at the tail end of the rudder that may only be adjusted from the outside:rudder trim tab

To adjust this tab, you fly the aircraft straight and level at cruise speed to determine if the ball is centered with no rudder pressure. Whichever way the ball swings in cruise, the tab must be bent the opposite direction. Hop out of the plane and squeezing it between two blocks of 2×4, smoothly bend the tab the correct direction. Fly it again to test; repeat until flying straight.

Although this is a pilot-adjustable piece as far as the FAA is concerned, it isn’t a renter-adjustable piece per our insurance requirements. So, if you rent the plane and it isn’t flying ball-centered, just note it in the book and I’ll come out and fix it.

Maintenance can fix it, too, but the fact that it requires flying the plane makes it very expensive to adjust that way. It took me one hour of flight to fix, or about $100. Having a mechanic do it would also be one hour on the plane and about two hours of a flying mechanic’s time, or about $350 total.

I’d like to thank the great controllers at Reid-Hillview Airport for accommodating my requests. With their help, I was able to get three climbs to 3000′, three 5-minute straight-and-level sections, three landings, and two shutdowns in the run-up for adjustment done in only one hour of Hobbs time. This included a go-around for a helicopter dawdling on 31L!

Next post will be a little about me. I realize I haven’t really introduced myself!

Fixing the trim tab

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