Différence entre un Autogire et un Hélicoptère


One of the most difficult part to understand is how the gyrocopter differs from the helicopter. Basically, the gyrocopter has a simpler construction than the helicopter, with a simplified rotor.

On an helicopter, the rotor is powered, and ensures both lift and propulsion. The helicopter rotor is simply acting as a big variable-pitch propeller. As such, the air attacks the rotor from above, giving it its « nose down » attitude in flight (exaggerated in the drawing for demonstration purposes). The powered rotor accelerates the air mass towards the ground.

Flash animation: helicopter vs. gyrocopter

On a gyrocopter, the rotor is free (unpowered), and only ensures the lift. Propulsion is ensured by a conventional tractive or propulsive propeller. The air attacks the rotor from below, giving a slight « nose up » attitude. By fleeing trough the rotor, the air maintain its permanent rotation. This is a complex phenomenon too long to describe here.

This is known as autorotation. In an helicopter, autorotation only happens when engine quits. In a gyrocopter, autorotation is permanent, it is its natural way of flying, with our without engine.

To start the autorotation phenomenon, a gyrocopter will, when stopped on the ground before take-off, prerotates its rotor, until it reaches sufficient RPMs to ensure lift after a short roll. After that… it is automatic, and the relative wind / weight combination will ensure permanent rotation – therefore lift – for the aircraft, rotor RPMs varying automatically as needed to maintain the needed lift along all phases of the flight.

So the main differences between gyrocopters and other aircraft kinds are the following, for the same MTOW:

Cannot hoover Can hoover Don’t try to hoover
Cannot take-off vertically Can take-off vertically Cannot take-off vertically
Cannot land purely vertically Can land vertically Cannot land vertically
Needs very short take-off strip Take-off strip not needed Needs a take-off strip
Needs its length to land Needs its length to land Needs a landing strip
Very little sensibility to turbulences Medium sensibility to turbulences Sensible to turbulences
Larger flight envelope than fixed wings Larger flight envelope than fixed wings Limited flight envelope
Easy to pilot Complex to pilot Rather easy to pilot
Excellent manoeuvrability Superior manoeuvrability Average manoeuvrability
Easy for maintenance Relatively heavy maintenance Relatively easy for maintenance
Less expensive than helicopter Rather expensive Slightly less expensive than gyrocopter
Needs more power than fixed-wing / trikes Needs a lot of power Needs less power than gyrocopter

From this comparison, it is easy to extract that, where the specific hoover and take-off capabilities of an helicopter are not needed, a gyrocopter will do the same job at only a fraction of the expense. Gyrocopter excel in the watch and camera-plateform areas, at a much lower cost than helicopters. And of course as leisure aircrafts.

The increase of power needed by the gyrocopter compared to fixed-wings / trikes comes from the fact that the free rotating rotor generates about 70% of the total drag of the aircraft – this being compensated by more power, only really needed for the take-off part of the flight.

The private gyrocopter pilot will enjoy very quiet ride in turbulent conditions, and will fly when his mates are stuck in the airfield’s bar due to strong winds, with a manoeuvrability comparable to the one of an helicopter. A light two-seater gyrocopter can usually fly as slow as 40 km/h, and in excess of 160 km/h.

Of course, comparing gyrocopters to fixed-wings or trikes is difficult, as this is really a matter of taste: some prefer rotary wings, other prefer fixed- or flex-wings.

All what we can say is: if you have never tried it, just try with a professional gyrocopter instructor. You may find it addictive.

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