Cruise power and what cuts engine power
Cruise setting (manufacturer's recommended):
- Balances reliability, performance, economy of operation, engine life.
- Reliability is the overriding factor.
- Sustained power above it threatens reliability.
What cuts engine power:
| Factor | Effect | Cite |
|---|---|---|
| Rising density altitude (unsupercharged engine) | Power loss immediately: less air intake | PHAK ch.11; FAA AWH 8.4.1.5 |
| Rising density altitude (thin air) | Thrust and lift cut: take-off roll lengthens | FAA AWH 8.4.1.5; TP 1102 Fig. 2-11 |
| High relative humidity | Piston brake horsepower cut significantly | PHAK ch.7; TP 1102 l.1947, l.3426 |
Trap: expecting an unsupercharged engine to hold power to some height; it loses power as soon as density altitude rises.
References
- TP 1102 (Aeroplane Flight Training Manual), ch.3 Engine Handling: Cruise Power
- TP 1102 (Aeroplane Flight Training Manual), l.1947 and l.3426: humidity reduces engine performance
- FAA Aviation Weather Handbook (FAA-H-8083-28), 8.4.1.5, l.3159-3167: density altitude cuts power, thrust, lift; lengthens take-off roll