The following instructions provide details on how to Track a Wooden Aircraft Propeller.
|Tracking is the procedure for making sure that your prop spins entirely in one plane. When you turn the prop from one end to the other end, both ends of the prop should pass through the same points in space. Here’s how to do it.
First, make sure that your magneto switches are off. Next, chock your wheels to make sure that the airplane doesn’t roll forwards or backwards during this procedure. It would be a shame to think that there was something wrong with your prop when in fact the airplane was moving.
|Torque your prop to the manufacturer’s recommendations. For props from Thompson Aeronautical you can use 10 - 12 foot lbs. Use a cross pattern as you tighten the bolts first tightening a bolt on one side and then the one on the opposite side. Torque the bolts to about 75% of their final torque value on your first trip around the prop, then make a second pass to bring them up to the final torque value.|
|Next, place something solid behind the prop, in a position so that it almost, but don’t quite touch the trailing edge of the tip of the prop.
|It doesn’t really matter exactly what you use to do this as long as you have some way of measuring the difference between the track of one blade and the track of the other blade or blades.|
The idea is to have the blades almost but not quite touch as the prop passes. Rotate the prop slowly by hand and measure the gaps between the prop and the paint can. If the gaps are identical, then you are done. If moving the prop into the second position would make it hit the paint can, then readjust the position of the paint can and repeat the procedure.
The maximum acceptable distance between the paint can and the prop from blade to blade is 1/8 or 3 mm. Ideally, you’d like it have it down to be 1/16 or 1 ½ mm or less.
If you’re satisfied with how your prop is tracking, then you are done, but if not, here are several things you can check. Look for fiberglass backing plates that may be made of a non-uniform thickness. Look for anything else that may be keeping the prop from mounting flush to the engine hub.
If your prop still isn’t tracking well, you can take it off and either sand away some of the wood under the hub or add extra varnish to improve the tracking. If you have a hardwood European Beech prop or a mahogany prop from Thompson Aeronautical, you can increase the torque on one side of the prop up to 15 foot lbs; however, don’t try this on props made of softer woods like spruce.
For more details on propeller making and repair read, “How to Design, Build and Repair a Wooden Aircraft Propeller.