Where are spark plugs fitted in aero engines?

• A. Fitted into each Cylinder head.
• B. Mounted on the crankcase.
• C. Placed in the exhaust manifold.
• D. Embedded in the piston crown.

Answer: (A)

Spark plugs must ignite the air-fuel mixture right where combustion happens. In aviation piston engines, the combustion chamber is formed in the cylinder head, so each cylinder needs a spark plug threaded into the head and projecting into that chamber. This placement ensures the spark occurs at the correct moment within the compression stroke and directly in the combustion chamber. If a plug were in the crankcase, in the exhaust manifold, or embedded in the piston crown, it wouldn’t reach the combustion chamber or would ignite the exhaust, which is ineffective or harmful. So the correct arrangement is one spark plug fitted into each cylinder head.