January 9th 1923 marked the first officially observed flight of an autogyro. The aircraft, designed by Juan de la Cierva, introduced rotor technology that made forward flight in a rotorcraft possible. Until that time, rotary-wing aircraft designers were stymied by the problem of a rolling moment that was encountered when the aircraft began to move forward. This rolling moment was the product of airflow over the rotor disc, causing an increase in lift of the advancing blade and decrease in lift of the retreating blade. Cierva’s successful design, C4, introduced the articulated rotor, on which the blades were hinged and allowed to flap. This solution allowed the advancing blade to move upward, decreasing angle of incidence and lift, while the retreating blade would swing downward, increasing angle of incidence and lift. By definition the autogyro is an aircraft that achieves lift by a free spinning rotor. Several aircraft used rotor to attain performance not available in the pure helicopter.
A gyroplane is an aircraft that receives the lift it needs for flying from a rotating wing; there is no power transmission and flight is possible thanks to a rotor powered by the engine that supplies the force of traction.
DIFFERENCES BETWEEN GYROPLANES AND HELICOPTERS
Gyroplanes and helicopters are very charming and interesting rotorcraft, furthermore they are capable of different and specific manoeuvring and uses if compared with fix wing aircrafts. Both, gyro and helicopter, receive the lift they need for flying from their rotating wing. This common characteristic [the rotor] makes it difficult for many people to see the difference between them being their appearance pretty similar for the laity. This confusion between the two kinds of rotorcrafts has been enhanced by the reduced spread of gyroplanes compared to helicopters.. Even if the common characteristic is the rotor it is stupefying how many conceptual differences – even up to opposite condition – there are between gyroplane rotor and helicopter rotor. Aerodynamic forces, stresses, angles of incidence and degrees of liberty are different and obviously flight performances and characteristics are different too.
In gyroplanes there is no power transmission to the rotor during flight, it is easy to see this: gyroplanes do not have anti-torque devices as tail rotor to balance main power-driven rotor torque. Lift is given by autorotation granted by the air flowing up through the blades. This condition is allowed by the degree of liberty of movement of the rotor head – and so of the rotor disc – along lateral axis; talking of Magni’s gyroplanes, this excursion is from 0° (horizontally) to 18° towards the rear of the gyroplane. This laying allows the correct passing through of the airflow in all allowed flight condition within gyroplane flight envelope. Pilot’s authority on lateral axis is granted by the use of the stick. Due to the lack of transmission of power the gyroplane can’t keep stationary hovering as helicopters can. As a matter of fact, when speed decrease with nose up attitude, the airflow through the rotor decrease so rotor rpm also slowly but constantly decrease causing a reduction in lift. When rotor rpm are under a certain level – this value is due to weather conditions and weight of the gyro – the gyro will start sinking (2-4 m/s with engine; up to 10 m/s without engine) steeply or vertically if the advancing speed has got to 0 due to the loss of lift. While loosing height the pilot keeps authority on all flight controls and the rotor will be kept “fed” by the airflow from bottom upward generated by the sinking movement. So as soon as descent speed is enough the rotor will keep a number of turns enough for a constant speed descent.
It must be very clear that even if gyroplanes can’t stall as aircrafts’ fixed wings do on the other side it is also impossible to keep stationary hovering conditions for more than a few seconds.
Within gyroplane’s flight envelope rotor rpm will self-stabilize on a value depending on the combined effect of load, type of manoeuvring and weather condition, this makes piloting very easy! Considering again a specific range of gyroplanes, Magni’s one, the only power transmission system is the prerotator. This system is meant and needed just to spin-up the rotor to a minimum number of rpm so to allow take-off, it is then disengaged and no more used during the flight.
It is possible to deduce that gyroplanes, even if capable of operating in narrow spaces, can’t take-off or land vertically as helicopters do.. After prerotation has been disengaged gyroplanes need a short take-off roll to get some acceleration. Always considering a specific range of gyroplanes, Magni’s one, it is possible to quantify the needed space in a range that goes from 40 to 80 m for take-off and approx. 2-5 m for landing.
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