McCulloch 40 hp

 Single & Dual Ignition Systems

The McCulloch engine exhibited here is an example of a single ignition system. There is one spark plug in each cylinder and a wire attached to it that comes from an electrical source. In the majority of small aircraft systems the source of electrical power is a magneto. The magneto has a strong magnet rotating inside a wire coil which generates a voltage that is routed out to the spark plugs on the engine at the proper time. The electrical impulse arcs or jumps across a gap in the spark plug at the instant that there is a fuel and air mixture.

The McCulloch single ignition system

A single ignition system used in an airplane does not allow the engine to continue operating and land safely after an ignition system failure. What is used to correct this situation is the addition of a second complete ignition system. Such an engine is said to have “dual ignition.”

Dual ignition provides two advantages: redundancy in the event of in-flight failure of one ignition system; and more efficient burning of the fuel-air mixture within the combustion chamber. Operation of an aircraft engine on one ignition system (rather than a dual

An Aircraft Magneto

system)A typical aircraft spark plug typically results in an RPM that is about 75 RPM lower than a dual system. The two systems are typically controlled by an ignition switch in the cockpit of the airplane. (Place hand turning mag switch here) This switch arrangement permits both systems to be checked before taking off to ensure that both systems are working properly. During normal operation both systems are operating which provides the aircraft with the most safe and efficient operation and...(page 2)