FAA Private Pilot Helicopter (PRH)Performance and LimitationsMedium
A helicopter has 900 shaft horsepower available and requires 750 shaft horsepower to maintain level flight at 60 knots and the current gross weight and density altitude. What is the excess power available, and how does it relate to climb performance?
- A1,650 shp excess power, which increases maximum airspeed only
- B0 shp excess power, since level flight power equals total power available
- C750 shp excess power, which has no effect on climb rate
- D150 shp excess power, which is converted into climb performance
Show answer & explanationAnswer & explanation
Correct answer: D. 150 shp excess power, which is converted into climb performance
Excess power is the difference between power available and power required for level flight: 900 − 750 = 150 shp. This excess power is what allows the helicopter to climb; more excess power results in a greater rate of climb.
Why the other options are wrong
- A. Incorrect math; adding instead of subtracting power available and required.
- B. Incorrect; power available exceeds power required, so excess power does exist.
- C. Confuses power required with excess power; also incorrectly states no effect on climb.
Excess Power and Climb Rate
Excess power is the power available beyond what is needed for level flight; it is used to produce a climb, and more excess power yields a greater rate of climb.
- Excess power = power available − power required
- Best rate-of-climb speed occurs where excess power is greatest
- Excess power decreases as altitude/weight/temperature increase
Memory trick: Leftover power lifts you higher.