Gasser

From RC Helicopter Wiki

A gasser is a helicopter that uses an internal combustion engine running on regular gasoline (petrol, motor gasoline or aviation gasoline). Typically these are two stroke engines, and so must have lubricating oil (usually bought separately) mixed in with the fuel, unlike nitro fuel which usually comes premixed with oil. Gassers consume much less fuel (and the fuel is much cheaper) than an equivalent nitro helicopter, and do not tend to leave so much oily residue over the airframe.

Gasser engines are spark ignition, with the spark either coming from a magneto (generator) attached to the crankshaft as part of the engine, or by using electronic ignition with power supplied by an external battery.

Gasser engines often do not require a starter motor, instead using a pull-start (recoil starter) than can be unclipped when the engine is running. This helps keep the equipment needed at the field to a minimum. Some users run a small generator off the engine to charge their flight pack and so do not even need to charge the avionics battery!

However, gas engines are not without their downsides. Gasser engines are typically heavier and create more vibration than an equivalent powered nitro engine. Gas engines tend to run substantially slower than nitro engines, and so require a different gear ratio to drive the main and tail rotor. This can also make reliably engaging a centrifugal clutch difficult. Additionally, gasser engines run somewhat hotter than nitro engines, thus making good cooling critical; this is exacerbated by the engine running slower, thus turning the cooling fan slower.