FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesMedium
A mechanic examines turbine blades removed from an engine and notes that the airfoil passages between adjacent blades converge, causing gas pressure to drop and velocity to increase as the gas passes through the moving blade itself. This blade design is best classified as a(n)
- AImpulse blade
- BCompressor blade
- CStator vane
- DReaction blade
Show answer & explanationAnswer & explanation
Correct answer: D. Reaction blade
In a reaction turbine blade, the passage between blades acts like a small nozzle, so pressure continues to drop and velocity increases as gas flows through the rotating blade. Impulse blades, by contrast, have a constant-area passage where pressure drop occurs only in the fixed nozzle guide vanes ahead of the rotor.
Why the other options are wrong
- A. Impulse blades change flow direction at essentially constant pressure; the pressure drop occurs in the stationary nozzle, not the rotor blade.
- B. Compressor blades compress air; they are not classified as impulse or reaction turbine blades.
- C. Stator vanes are stationary compressor components, unrelated to turbine rotor blade classification.
Impulse vs. Reaction Turbine Blades
Impulse blades redirect gas flow at constant pressure using energy from the stationary nozzle; reaction blades have converging passages that continue to accelerate and drop pressure within the rotating blade.
- Most engines use a combined impulse-reaction blade
- Reaction blades act like small nozzles
- Impulse blades rely on nozzle guide vanes for pressure drop
Memory trick: 'Reaction blades React by narrowing the path' — converging shape keeps accelerating gas.