Chapter 5 : Helicopter Powerplant

Model radio controlled helicopter is often powered by a two cycle internal combustion engines but there are other types like four-cycle internal combustion engine. Most of the internal combustion engine for models are fueled by methyl alcohol called the "glow engines" and the other one is unleaded gas whic his usually a four cycle or four stroke engines. ( see also Airplane Powerplant Fig. 19 , Fig. 20a ) These engines are powerful which can supply the demand for the needed power to fly the helicopter. But because of continious development of lighter and stronger materials, powerful electric motors and light but powerful batteries, it is possible now to fly a helicopter using electric motors.

Whichever engines you use, the drive mechanism to rotate the blades are basically the same design. Main gear, pinion gear, clutch assembly and the engine or motor ( see Fig. 24 ). The only difference between the internal combustion engine powered versus the electric type is the clutch. Electric powered type doesn't use clutch. The motor is directly connected to the pinion gear without the clutch unlile the I.C.E. ( Internal Conbustion Engine ). ( See Fig. 25 )

A feature, which is called auto rotation, the main gear connected to the main shaft is free wheeling so in an event the engine malfuctions or stopped, the main rotor will continue to rotate.

Fig. 24 RC Helicopter Powerplant

Fig. 25 RC Electric Model Helicopter Exploded View

In a model radio controlled helicopter, two type of internal combustion engines are usually employed with regards the fuel they use. There are other types like two stroke and four stroke engines but we will tackle only on the most common types.

1) Glow engine - engine that uses methanol for fuel and castor oil for lubricant. The igniter is called the glow plug, shaped like a miniature spark plug but uses coil for combusting the fuel and air mixture ( see Fig.26 ). Power source for the glow plug is 1.5volts NiCad (Nickel Cadmium) battery or dry cell with high ampere. Usually 75% methanol and 25% castor oil is the fuel mixture. Castor oil readily mixes with methanol unlike the petroleum based motor oil. But for more speed, nitromethane is added depending on the type of aircraft flyer desire (e.g. pylon racing, sport flying or pattern flyer).

Figure 26: Typical two cycle glow engine

2) Gas engine - Gas engines are commonly used by larger RC helicopters because this type has larger displacement. It uses ordinary unleaded gasoline and petroleum based motor oil. You can compare its size with an ordinary handheld chainsaw.

Electric powerplant used by model helicopters are straight forward. The electic motor wires are connected to a speed controller. The speed controller is connected to the rechargable batteries and radio control receiver. ( See Fig. 27 )

Figure 27: Electric Heli Powerplant Components