FAA Private Pilot Helicopter (PRH)Performance and LimitationsMedium
The height-velocity (H/V) diagram published for a helicopter primarily identifies
- Athe maximum gross weight allowed at various altitudes
- Bthe airspeeds where retreating blade stall occurs
- Ccombinations of altitude and airspeed where a safe autorotative landing may not be possible following an engine failure
- Dthe best rate-of-climb speed at each density altitude
Show answer & explanationAnswer & explanation
Correct answer: C. combinations of altitude and airspeed where a safe autorotative landing may not be possible following an engine failure
The H/V diagram, often called the 'deadman's curve,' shows combinations of low altitude and low airspeed (and sometimes high altitude/low airspeed) where insufficient time or energy exists to enter a stabilized autorotation and cushion the landing after an engine failure.
Why the other options are wrong
- A. Gross weight limits are found on weight and balance and performance charts, not the H/V diagram.
- B. Retreating blade stall relates to high forward airspeed, not the H/V diagram.
- D. Best rate of climb speed is a separate performance value, not shown on the H/V diagram.
Height-Velocity Diagram
A chart showing combinations of altitude and airspeed to avoid because a safe autorotative landing may not be achievable if the engine fails.
- Also called the 'deadman's curve'
- Low altitude/low airspeed and low altitude/high airspeed combinations are most critical
- Varies by gross weight, density altitude, and helicopter model
Memory trick: Stay out of the shaded zone or you can't autorotate in time.