I seem to have an aileron trim or aileron rig issue. The control cables were rigged with the proper tension. The only squawk that I have at this point is that the airplane requires left rudder input during cruise. Failure to do so makes the airplane want to slowly turn right. It seems like a constant battle to fly straight.
The prior owner said his A&P suspected that the nose gear was slightly askew once the airplane got airborne. There is a cable on top of the nose gear that is connected to a Spring assembly. The theory is that once the plane is airborne, the spring will center the nose wheel. In his case, they made a slight adjustment to that cable and the airplane no longer needed the left rudder.
Since the top portion of the gear is somewhat aerodynamic, would it make sense that if it were cocked slightly, it could act as a rudder to some degree? Or does it sound like the rigging needs fine-tuning? Or both?
Any recommendations? We’ve already played the “bend the fixed trim tab” game.
Bob Steward, A&P-IA:
Step one in diagnosing any trim issue is to see what input is needed to achieve straight and level flight. If left rudder is needed, when no inputs are made, where does the Turn and Bank show the ball to be sitting? Is it centered? Is it offset to one side (the left?)? Does centering the ball cause the plane to fly straight? Are the wings level on the T&B when the input is made? Without the input?
What we are looking to find is the nature of the problem. It can be an aileron or rudder trim problem. Ailerons bank the plane and will fly it in a circle in a slight slip.
Rudder steers the plane in a circle in a slight skid.
Holding left rudder when the ailerons are causing the plane to fly in a circle will only produce S&L at the expense of a cross control situation with more drag.
The T&B will show if you are wings level with the ball centered.
Its not unusual to have a bent trim tab to fly S&L. The other things to check include the flaps. They might be out of rig allowing one flap to give more lift than the other and this will bank the plane and cause the turning tendency. This again causes a cross control when the rudder is held to center the ball without the wings being level.
Its been suggested that the nose gear acts as a rudder, and it may in fact do that. The slip stream flows over the nose gear at a bit of an angle, since the prop causes the air to rotate around the fuselage. Because of the rotation, the angle of attack of the nose gear is such that it may want to cause a LEFT turning tendency. (Air impinges on the strut from the right side, creating “lift” to the left.)
There is no way to make adjustments to the cable that centers the nose gear with the nose wheel on the ground. The friction in the system prevents you from knowing how much tension is actually present. It might be worthwhile to jack the nose, before you make any changes, and see if the nose strut looks cocked to one side.
EDITOR’S NOTE:
It isn’t a common problem for one of the centering cable bails to jump off the end of the centering spring, but it also isn’t at all rare. Having to apply rudder to center out the resulting half-ball skid isn’t dangerous, but it is a bit uncomfortable for any prolonged length of time. Since the problem virtually always occurs while on the ground, it can take you by surprise at liftoff and climb. Depending on which side came off, it can help or hinder on
climbout. It will always hinder in cruise. The biggest cause for concern is just not knowing what’s causing the need for unusually high rudder pedal pressures to center the ball.
There is a relatively easy (and cheap)preventive measure. With the nose gear centered on the ground, tightly safety wire the left and right cable bails to each other and to the spring eye. That way the tight-side bail always holds the loose side bail on the spring eye, no matter how far the nosewheel gets turned. When you do this, make sure that there will be no interference from the added safety wire, throughout the range of travel in both directions. Assuming you have experience with properly applying safety wire, I believe that this falls under approved activity for the owner-pilot (safety wire and cotter pins).