FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsMedium
While studying magneto theory, a technician learns about the E-gap angle. What does the E-gap represent?
- AThe position of the rotating magnet past the neutral position where the breaker points open for maximum induced voltage
- BThe gap between the spark plug electrodes measured in thousandths of an inch
- CThe distance between the distributor rotor and the distributor block contacts
- DThe angular clearance between the magneto drive gear and the engine accessory gear
Show answer & explanationAnswer & explanation
Correct answer: A. The position of the rotating magnet past the neutral position where the breaker points open for maximum induced voltage
The E-gap (efficiency gap) is the number of degrees the rotating magnet has moved past the neutral position when the breaker points open, timed to occur at the point of maximum rate of flux change for the strongest induced voltage.
Why the other options are wrong
- B. That describes spark plug gap, a different measurement.
- C. Distributor block clearance is a physical component gap, not E-gap.
- D. Gear clearance is unrelated to magnetic flux timing.
E-gap Angle
The number of degrees the magnet rotor turns past the neutral position before the breaker points open, chosen to coincide with maximum rate of change of magnetic flux for peak voltage output.
- Specified by the magneto manufacturer
- Set during internal timing before magneto installation
- Ensures the hottest possible spark at points opening
Memory trick: E-gap = 'Extra degrees past neutral for Extra voltage'