When it comes to rotary wing aircraft, there are a wide variety of helicopters to choose from. One helicopter company that has found a niche in the market is Robinson Helicopter. The company's piston engine aircraft are being used for a variety of applications throughout the world. We are going to take a look at one of its helicopters, the R-22, and discuss some basic topics concerning its powerplant -- the Lycoming O-360 series engine.
One of the things that a technician notices when first exposed to R-22s is the fact that they do not have helicopter H-rated engines installed in them such as the Lycoming HIO- or HO-360 series. Instead, they have O-360 series engines installed. These are basically the same engines certificated for fixed wing applications. The differences come with the accessories. That is what sets up the last letters of the designation. The carburetor location, the type of oil sump on the engine, and the accessory pads are accessories that change the designation.
When looking at the engine installed on the R-22, it helps to know a little history on why H-rated engines were developed in the first place. Well, when manufacturers in the 1940s and 1950s began putting piston engines in helicopters, they were no longer limited by the tip speed of a propeller. They could therefore turn the engines at a higher rpm to get more power. H-rated engines were thereby developed by the engine manufacturer in order to handle those increased rpm requirements. With these models, airplane engines that were originally designed to run at from 2,400 to 2,700 rpm were now able to operate at that of a helicopter -- approximately 3,000 to 3,400 rpm. They were also putting out the maximum amount of power possible.
Over time, with the introduction of turbine engines, the popularity of piston powered helicopters began to slide. The turbine engine became the engine of choice. It offered better governing and more power capabilities than its piston counterparts. There was also the perception that turbine engines were more reliable than pistons.
So, how did Robinson end up using O-series engines in its helicopters? When Frank Robinson began designing the R-22, he went back to the drawing board. He wanted to use a piston engine in the helicopter due to the decreased cost of production and lower operating expenses. However, he chose not to go with an H-rated engine. Instead, he decided to design a helicopter that would operate at the lower rpm that the fixed-wing certificated engines were designed for. He felt that the lower operating speeds would lead to increased TBO times and reliability. The original R-22s used Lycoming O-320 engines. The first production R-22s actually operated at 2,650 rpm instead of the 2,700 rpm rating of the engine. The manifold pressure was also flat rated.
When the Beta II versions of the R-22 came out in 1995, they had O-360 engines installed in them. Again, Robinson stuck with the philosophy of de-rating the engine and maintaining lower rpm. One factor in the O-360 engine that caused a slight concern to Mr. Robinson was that it had a slightly faster piston speed than the O-320 engine. This was due to the longer stroke. This factor has turned out to be a non-issue, and the O-360 has turned out to be a very reliable engine.
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