Glossary
What is autorotation?
A gyroplane rotor has nothing driving it. It turns because air is flowing up through the disc, and it keeps turning for as long as that flow continues. Here is why that works.
The rotor spinning under the force of air flowing up through the disc, rather than being driven by the engine. It is the principle a gyroplane flies on continuously, and the state a helicopter enters after an engine failure.
The short answer
Autorotation is a rotor turning under the force of air passing up through the disc, rather than being driven by an engine. Point a rotor into an upward airflow at the right angle and the air does the work of spinning it.
A gyroplane is in autorotation continuously, by design. Its engine drives a propeller for thrust; nothing drives the rotor in flight. A helicopter is normally the opposite, its rotor driven by the engine, and enters autorotation only when that drive is lost. The mechanism is identical. The difference is whether it is the normal state or the emergency one.
Where the upward airflow comes from
Two things produce it, and usually both at once.
The first is the rotor disc being tilted back relative to the oncoming air. As the aircraft moves forward, air meets the underside of the disc and passes up through it. This is why a gyroplane needs forward airspeed and cannot hover in still air the way a helicopter can: remove the forward motion and the flow that drives the rotor goes with it.
The second is descent. An aircraft coming down is moving through air that is, relative to the aircraft, travelling upward. That is what sustains a helicopter rotor after an engine failure, and it is why a gyroplane descends under control rather than dropping if its engine stops. Losing thrust costs forward speed and altitude; it does not stop the rotor.
Why the rotor keeps turning rather than slowing down
This is the part that is genuinely counter-intuitive, and the answer is that different parts of the same blade are doing different jobs at the same time.
The airflow arriving at a blade is the sum of two motions: the blade rotating through the air, and the air passing up through the disc. Near the hub the blade is moving slowly, so the upward component dominates and the airflow meets the blade from well below. Out toward the tip the blade is moving much faster, so rotation dominates and the flow meets it much closer to edge-on.
That difference splits the disc into regions. Over the inner part, the aerodynamic force on the blade tilts forward of the axis of rotation and pulls the blade around: this is the driving region, and it is what powers the rotor. Over the outer part the force tilts behind the axis and resists rotation: the driven region, which absorbs energy. In steady autorotation the two are in balance, the driving region supplying exactly what the driven region and the drag take away, and rotor speed holds steady.
Disturb that balance and the rotor speeds up or slows down. This is why rotor management is the central skill in flying a gyroplane, and why the acceptable rotor speed range is a type-specific limit that lives in your aircraft flight manual rather than in a reference article.
What this means in practice
- An engine failure in a gyroplane is a descent under control, not a loss of lift. The rotor is already doing what it does.
- A gyroplane cannot hover in still air, because it needs flow through the disc. In a strong enough headwind it can appear to, which is a difference in ground speed rather than in airspeed.
- The rotor must be turning before takeoff. Spinning it up mechanically beforehand is prerotation, and it exists to shorten the ground roll, not to sustain the rotor in flight.
- Unloading the rotor removes the airflow that drives it. That is the mechanism behind a power push over, and it is the reason type-specific instruction matters more than any article.
Autorotation in a gyroplane and in a helicopter
| Gyroplane | Helicopter | |
|---|---|---|
| Rotor in normal flight | Autorotating | Engine driven |
| Autorotation is | The normal state | An emergency procedure |
| Source of thrust | A separate propeller | The rotor itself |
| Hover in still air | No | Yes, under power |
| After an engine failure | Continues as before, descending | Transitions into autorotation |
Where to go for the numbers
Deliberately none here. Rotor speed ranges, descent rates and inflow angles differ by type, by rotor system, by loading and by air density, and a figure quoted without those qualifiers is worse than no figure. Your aircraft flight manual is the authority for the aircraft you are flying.
For the handling itself, an instructor approved for gyroplanes on your type. Our training directory lists schools by country.
