FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
A radial engine's electric starter is connected to the crankshaft through a starter adapter. What two functions does the starter adapter typically provide?
- AA freewheeling clutch to disengage the starter and a shear section to protect against overtorque
- BPropeller feathering and reverse pitch control during start
- COil pressure boost and fuel pressure boost during cranking
- DIgnition timing advance and fuel enrichment during start
Show answer & explanationAnswer & explanation
Correct answer: A. A freewheeling clutch to disengage the starter and a shear section to protect against overtorque
The starter adapter contains a clutch (overrunning or friction type) that allows the starter to disengage automatically once the engine starts and accelerates past the starter's speed, and a shear section (shear pin/section) designed to fail if excessive torque is applied, protecting the starter and gear train from damage.
Why the other options are wrong
- B. Propeller feathering/reverse pitch is a propeller governor function, unrelated to the starter adapter.
- C. Oil and fuel pressure boosting are unrelated to the starter adapter's function.
- D. Ignition timing and fuel enrichment are controlled by the magneto and carburetor/primer system, not the starter adapter.
Starter Adapter
A gear reduction assembly between the starter motor and crankshaft containing a clutch to disengage the starter automatically and a shear section to protect the drive train from overtorque.
- Clutch allows freewheeling once engine starts
- Shear section fails intentionally under excessive torque
- Common on radial and some large reciprocating engines
Memory trick: Adapter = a bodyguard that lets go (clutch) and sacrifices itself (shear) to protect the starter.