March 25, 2013
By Ian J. Twombly
Does your airplane fly a little off? Does the ball lie comfortably out of the center, or is one wing always higher than the other to maintain straight flight? Maybe your rudder trim is pegged to one side and you still stomp like crazy on the pedal to keep the nose straight. We were experiencing some of these conditions with this year’s Get Your Glass Sweepstakes Piper Archer, so we called a rigging expert to fix all its alignments.
The first step in assessing any rigging problem is to find the right shop. Many shops claim to know how to rig an airplane, but fewer actually do it right. We called Trevor Janz at the Piper Flyer Association for a recommendation. To our surprise, Janz came back with Hagerstown Aviation Services, a shop we’re familiar with, and it’s only 15 minutes away to boot.
Joe Hart did the work and found there were a number of issues. “The first thing you have to check,” he said, “is the turn coordinator.” Hart said many pilots come in thinking their airplane is wildly out of rig, but end up leaving happy with only a newly leveled TC. “It’s the number-one rigging issue,” he said.
Luckily, there’s an easy way for pilots to check and see if their turn coordinator is level. Hart said to go up on a smooth day and center the ball in the inclinometer. If the airplane starts to turn, it’s impossible the turn coordinator is level. Have it fixed and chances are your problems will be solved.
Assuming the TC is level, Hart flies each airplane to see if he can recreate the pilot’s complaints. Although Hart did find the Archer’s TC to be off, that wasn’t the only issue. Next he looked at the rudder to ensure it was centered when the rudder pedals were centered. Both seemed to agree. Then he went to make sure the nosewheel was centered with the rudder pedals and there Hart found a second problem.
It turns out that a previous owner had done some work on the nose gear rod ends. As Hart explains it, these are adjustable parts that attach to the nose gear’s steering mechanism. The rod ends and torque tube adjustment caused the rudder pedals to be significantly farther back in the cabin than is normally the case. That, combined with a turnbuckle that had the rudder cables attached too tight, meant that the rudder trim was significantly off with no way for the pilot to adjust it farther. Hart loosened the cables and adjusted the system so that the rudder trim is now centered.
Then he went to work on the ailerons and bank characteristics. Once Hart corrected the yaw issue, one wing had a slightly heavier feel than the other. Piper calls for a flap to be adjusted up or down to correct that problem, which Hart did. Now that means the bank pressure should be equal in both directions.
Finally, Hart adjusted what many would think of as the equivalent of an alignment in a car. To get the yokes straight in straight-and-level flight, he did some basic adjustments on the push rods to each aileron. “I shortened the rod on one side and lengthened it an equal amount on the other,” he said.
We first took the airplane to Hagerstown Aviation Services thinking the problems could have been everything from a previously unreported accident that had twisted the fuselage to the benign turn coordinator adjustment. In the end it turns out it was a mixture of a few little problems that had added up to make an airplane that was definitely out of rig.
There seem to be two main reasons an aircraft owner would want to have their airplane properly rigged—optimum performance and harmonized controls. So what did we get? Without question, the airplane has harmonized controls now. Instead of constantly having it with one wing low to keep flying straight, you can let go of the yoke and fly completely hands off. It seems rare to be able to do that in older airplanes, but flying the Archer is even better than it was before.
Performance is a different story. A recent cruise test to compare pre-rig performance with post-rig performance found no gain in speed or efficiency as a result of the work. On the trip to Oshkosh I was seeing around 149 mph at 6,000 feet msl on 70-percent power. That’s analogous to what I saw yesterday at 7,500 msl. So while I’m happy to be doing better than book (about 7 mph more), the rigging procedure didn’t do anything for performance. The reason is simple. The biggest problem was with the turn coordinator and not the structure of the airplane. So when I had previously “centered” the ball in flight, it turns out I was really putting it out of center. That explains why I slowed down after the instrument said the ball was centered.
Next week: Learning to fly a glass-cockpit airplane
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