EAA Sport Aviation - November 2009

it keeps the mechanism operating smoothly, and changing the grease will help eliminate contaminants that can cause corrosion. However, it must be done according to the manufacturer’s exact instructions and only with the specified grease.

Always leave constant-speed propellers in a horizontal or, in the case of three blades, in a “Y” position to avoid water from collecting on the hub. Regular oil changes are also very important in aircraft with constant-speed props. Since engine oil provides the power source for controlling propeller pitch, ensuring that the oil is clean will reduce the chance that the propeller and governor will have problems caused by sludge or water contamination.

Wood propellers are truly works of art and should be treated as such. They should be inspected regularly for damage and delamination. Pay particular attention to the metal tips, looking for loose screws, rivets, or solder. The varnish coating serves a critical role in protecting the propeller from moisture damage and should be carefully maintained. If the propeller is removed for any reason, the bolt holes and hub bore should be inspected for elongation and damage. Then, the holes should be treated with a moisture preventive such as asphalt varnish.

The compressible nature of wood requires that the torque on the propeller bolts be checked regularly. If moisture enters the wood, it can swell and then become loose after drying out. Typically, propeller torque should be checked 25 hours after installation and every 50 hours thereafter.

Finally, regardless of the type of propeller that you have, perform a propeller tracking check. This is a fairly simple procedure that any owner can do. Begin by removing one spark plug from each cylinder so that the propeller can be easily rotated. Next, rotate one of the blades so that it’s pointing down and place a wooden

The technician uses a highly accurate protractor to measure the blade angle at each station.

block under the blade tip, marking the exact spot that the tip passes over on the block. Finally, rotate the propeller, checking the other blades to ensure that the track is within 1/16 inch of the mark. Any variation beyond 1/16 inch is cause for concern. It may be caused by a bent blade and should be inspected and repaired by a propeller maintenance facility.

Propeller Overhauls

Aircraft owners often follow the advice of their wallets when it comes to preventive maintenance. This is especially true with regard to the manufacturer’s overhaul recommendations for propellers.

Many owners of fixed-pitch propellers are unaware that a TBO exists at all for their props. McCauley recommends that its fixed-pitch propellers be overhauled every seven