FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesHard
A turboprop engine's propeller shaft torquemeter indicates 3,000 ft-lb of torque while the propeller shaft is turning at 1,500 RPM. Using the formula HP = (Torque × RPM) / 5,252, what shaft horsepower is being produced?
- AApproximately 857 SHP
- BApproximately 600 SHP
- CApproximately 1,200 SHP
- DApproximately 1,050 SHP
Show answer & explanationAnswer & explanation
Correct answer: A. Approximately 857 SHP
HP = (Torque × RPM) / 5,252 = (3,000 × 1,500) / 5,252 = 4,500,000 / 5,252 ≈ 857 SHP. The torquemeter measures the twisting force on the propeller shaft, and this standard formula converts torque and RPM into shaft horsepower.
Why the other options are wrong
- B. 600 SHP does not match the calculation using the given torque and RPM values.
- C. 1,200 SHP is too high for the given torque and RPM inputs.
- D. 1,050 SHP overstates the result; check the multiplication and division steps.
Torquemeter / Shaft Horsepower
A torquemeter measures twisting force on a turboprop's propeller shaft; shaft horsepower is calculated using HP = (Torque × RPM) / 5,252.
- Torquemeters are essential since turboprop thrust is measured as SHP, not EPR
- Formula: HP = Torque(ft-lb) × RPM / 5,252
- 5,252 is the constant derived from 33,000 ft-lb/min per HP divided by 2π
Memory trick: Remember '5,252' as the magic number that turns torque and RPM into horsepower.