Helicopter Piston Engine Maintenance

Helicopter Piston Engine Maintenance By Greg Napert April 2000 For the most part, piston-powered helicopters are a relatively rare breed. Turbine-powered helicopters are more popular because of their increased utility and also for what many...

"Further, we don't have any shock cooling issues with the engine either because there is no ram air cooling. Instead, there is a centrifugal blower that is always blowing air over the engine. If you chop back the throttle, there is not as much air, so the engine is not Ôshock-cooled.' Additionally, our blower provides more than adequate cooling."

Cox adds, "We are very specific in our 100-hour inspection criteria to make sure the cooling baffles aren't cracked and are in place, because we do rely quite a bit on the fan for cooling. On the R-44, the blower cools your muffler, your battery, your hydraulic reservoir, main rotor gearbox, alternator, magnetos, drive belts, etc. There is really no significant cooling effect from the rotor downwash."

In terms of oil changes, Robinson recommends oil changes every 25 hours, which is much more often than on a fixed-wing installation. The reason is that the helicopter is exposed to a considerable amount of dust while in hover. But just as important, the Robinson models don't come standard with an oil filter. Cox says, "You can get the R-44 with a filter or you can adapt an aftermarket filter kit to the R-22. But our recommendation, based on experience is to change the oil every 25 hours and filter or no filter."

Cox als o says, "Change the air filter at least every 100 hours, and in some applications where low-level, dusty environments are encountered, we recommend increasing the frequency of filter changes."

In terms of general troubleshooting and other maintenance items on the helicopter, Cox says that Robinson tries to generally follow in-step with Lycoming's recommendations. "Our approach to engine installations is to make it simple, light, and economical."


By contrast, Enstrom helicopter piston engines require a quite different approach. Lee Burdue, Technical and Training coordinator for Enstrom, explains that piston installations in their helicopters are somewhat unique in the marketplace.

First, the engines in their "C" and "F" models are turbocharged by Enstrom under an STC in order to produce the rated horsepower to a given altitude. Second, the configuration of the helicopter is such that the engine compartment does operate at elevated temperatures when compared to fixed-wing installations.

"These higher temperatures," Burdue explains, "can do such things as cause the diaphragm in the fuel servo to become stiff and brittle or can cause premature magneto point wear. If the fuel diaphragm becomes stiff, it will affect the fuel flow and the engine take more fuel to do the same job. You can tell when this is a problem by checking the manifold pressures versus fuel flows." He adds, "A typical indication that you have a problem with the diaphragm would be a manifold pressure of, say, 28 inches, with an associated fuel flow of 130 to 140 pounds, instead of the correct 102 to 105 pounds of fuel flow."

The result of these higher than normal temperatures means there is a requirement for more frequent maintenance intervals as well as attention to specific areas of the engine that are affected by the heat. Enstrom does have a non-turbocharged "A" model helicopter that runs a bit cooler but does not offer the advantages of the turbocharged "C" and "F" models.

All engines used on Enstrom's helicopters are HIO-360 Lycoming engines that are designed specifically for helicopters.

Enstrom offers a class to maintenance personnel in which it teaches some of the basics of maintaining its engines.

Burdue says, "We begin by addressing the fuel servos that we use on our engines. Much of the troubleshooting of the fuel servo can be done by knowing what the fuel flow should be depending on specific manifold pressures."

He continues, "For instance, if you're pulling 28 inches of manifold pressure and you're indicating a fuel flow of 105 pounds per hour, they're okay; there is no fuel problem, so you can eliminate the fuel servo and fuel related items. We also feel it's important for the technician to understand fuel flows and how the fuel is distributed throughout the engine."

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