The propeller: that long-thin spinning object mounted on the engine; generally on the front of the airplane, or on either side in a multiengine aircraft. Except for a few examples like gliders and jets, many aircraft have one or more. There have been aircraft with propellers mounted behind, acting to push the vehicle through the air rather than pull it. Without a properly maintained and functioning propeller the aircraft isn’t going anywhere.
AMT spoke with propeller experts Michael Mayhill, manager of customer service and support, and Kevin Ryan, technical support representative, both with Hartzell Propeller Inc., and asked them what were the most common questions they received from general aviation (GA) maintenance technicians in the field. Mayhill says, “You can place the most common questions into one of about 10 categories. Our technical support staff answers many of the same questions each and every day.” Ryan went on to say, “This is OK, that’s what we are here for; to support the owners and maintainers of our propellers.”
Q. What is the most common question asked by aircraft technicians in the field?
A. How big of a nick can I file out of the leading edge of an aluminum blade propeller? We are asked this almost every day, and it can be a difficult and challenging question to answer. The broad rule-of-thumb on our propellers is 1/16- to 1/8-inch deep nick or gouge can normally be repaired on the aircraft. However, if you have an old prop with blades already approaching the minimum width and thickness limits, you should consider sending it to a prop shop. By simply removing damage in this case, you could easily take the blade below minimum dimensional limits.
The minimum width and thickness criteria are part of the propeller overhaul manuals which are typically only available to an overhaul facility. Also, don’t ignore nicks and gouges on the face and camber sides of the prop blades. These sections of the blade frequently receive damage that is either ignored or simply sanded and repainted without a detailed inspection of the surface. Also, remember that removal of significant damage may result in a propeller imbalance situation requiring fine tuning on the aircraft with a propeller dynamic balance.
Q. What are the repair criteria for blade damage on the new Hartzell GA-class composite blades?
A. Most GA aircraft technicians have little experience dealing with composite blades, as composites have historically been used primarily on airline-class propellers. Hartzell published Service Letter HC-SL-61-294 to provide technicians with clear instructions on composite blade minor field repairs.
Q. What are the ground/object strike criteria? What has to be done and is my propeller repairable?
A. Depending on the nature and severity of the strike, a propeller’s repairability can range from very little needed to a complete restoration. Composite-bladed propellers are typically affected differently because by definition they do not bend like an aluminum blade. The three general criteria for determining whether a prop needs to go to a prop shop after a object strike event are: 1. Is the track or angle of the blade out of tolerance; 2. Has there been a diameter reduction; and 3. Has the pitch change mechanism been damaged, which can be first identified by movement of the blade inside the hub. Also, consult the propeller owner’s manual.
Q. What are the ground run-up procedures? I’m having trouble with low pitch stop and governor adjustments.
A. Mechanics often contact Hartzell to discuss propeller rpm issues, particularly after a new propeller is installed. Static run-up is one area of particular concern and confusion. Many aircraft technicians do not appear to have a solid grasp of the propeller/governor relationship, and how adjusting one affects the other. Lack of basic understanding often results in unnecessary aircraft downtime, needless governor and/or propeller repairs, and excessive troubleshooting labor. This is true on both single and multiengine aircraft. The propeller owner’s manual explains the proper procedures.
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