Ownership: Caring for carbon

Several different companies make composite blades (not to be confused with natural composites, which most of us call wood). Each has its own line of applications and construction methods. MT Propeller primarily uses a wood core surrounded by carbon fiber. Hartzell Propeller uses a low-density foam core on a metal shank. Carbon fiber or Kevlar is then layered on top to produce what engineers describe as a monocoque structure, which is not unlike many airframes.

Regardless of what hides inside, much of the surface propeller maintenance is consistent across brands. Like other maintenance tasks, pilots are allowed to perform some basic work, but most repairs must be done by a technician or authorized repair station.

Cleaning and visual inspections remain the first lines of defense against bigger issues. Cleaning a composite propeller is a fairly straightforward process. Hartzell, which only manufactures constant-speed propellers, recommends a mild soap-and-water solution on the blades. Lather, rinse, repeat. For more stubborn grease or oil, mineral spirits on a rag should do the trick. Although it may be tempting to break out the big guns, never use a pressure washer on a propeller. The force can push water into sensitive areas and lead to corrosion. For the spinner, automotive aluminum polishes are generally allowed, and most do a great job.

Regular lubrication is required for a constant-speed propeller, and whether you as the owner/operator choose to take on that job is up to you. The guidance on preventative maintenance says pilots are limited to “lubrication not requiring disassembly other than removal of nonstructural items such as cover plates, cowlings, and fairings.” That said, in Hartzell’s case, the lubrication instructions are in the owner’s manual, and the process is straightforward. The hub should be greased every 100 hours or 12 months, whichever comes first. And while adding grease might be easy, adding too much is expensive. Doing so can cause vibration issues that only removal and teardown will fix.

Dollars for dings

Running your hand down the leading edge of the propeller isn’t just a great way to be in touch with your machine, it helps catch dings and divots. Many composite propellers have an erosion shield, a strip of metal bonded into the fabric weave that helps protect against chips and other damage. It can become pitted or even delaminate. Take a quick look at the erosion shield, along with the trailing edge and face of the propeller. Damage can happen anywhere, and just like a metal blade, there is specific guidance on how and when to fix it.

So, let’s say you find a small gouge on the leading edge. To whom do you turn? You have a few options at this point. Grab the maintenance manual and refer to the section that describes airworthy versus unairworthy damage. Assuming the blade must be fixed, you will need to turn to one of three places: your local technician, a manufacturer-approved repair facility, or the factory.

The repair level is generally dictated by the amount of expertise required to make the repair and by how much the damage impacts airworthiness. At the bottom end of that scale are minor nicks, face gouges, and other small blemishes. Erosion shields are replaced at overhaul shops, and prop strikes—well, you might as well have the factory on speed dial. If a propeller kissed the pavement and is able to be repaired, the factory is the only place to get it done.

But there is an optimistic way of looking at this. Composite blades can more or less be made new again. They can be reconstructed, repaired, and refinished to pretty much new condition. Hartzell’s Mark Spoltman, the manager of composite engineering, said he’s seen propellers with more than 50,000 hours on the clock. “A metal blade has repair limits, and the props may only last one, two, or three overhauls. That’s not the case with composites,” he said.

Most of the damage Hartzell sees at the factory is hangar rash or “hitting something,” Spoltman said. Overhauls are only required every six years or 4,000 hours on Hartzell propellers, but most of the propellers they see early have been through some form of trauma. Incredibly, many can be rebuilt and saved.

But for the minor stuff, your local technician can do the work. Hartzell produced a series of videos earlier this year that discuss the repair process for minor work. Although it requires some skill and a few special tools, the process is nothing more than grinding away the damage, cutting some repair fabric, and then bonding it to the propeller.

To avoid having to go in for a check-up and quick fix, “Try not to bump them,” Spoltman says. “[Composite propellers] are more sensitive to hits, especially the trailing edges.” In other words, other than to take special care, there’s no special care.

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