Vertical Take-Off and Landing (VSTOL)
The name of Igor Sikorsky is to the helicopter as the Wright Brothers are to the airplane.
Sikorsky had been interested in helicopters for decades before he finally succeeded in building a working aircraft. He built his first rotary-wing aircraft in Ukraine as early as 1909. The machine (named H-1), featured two co-axial two-bladed rotors. Powered by a small (18 Kw) Anzani engine, it failed to take off. Sikorsky described his vehicle as a rectangular box.
A model built a year later (H-2) also failed to get into the air, while evidencing serious control problems. The vehicle with its slender propellers … resembled a huge butterfly. Sikorsky gave up the idea for some time and designed fixed-wing aircraft instead.
He might have pondered over the problem. His first working concept came 30 years later, with the Vought-Sikorsky VS-300 model, that made its first tethered flight in September 1939. The helicopter was officially invented, and VSTOL technology made rapid progress since Sikorsky’s maiden flight. The first commercial helicopter to enter service was the Bell 47 model (1946).
Between the years of Sikorski’s first trial and first successful flight (1909-1939) a number of other engineers attempted to build a practical helicopter. These include de Bothezat (1922), Florin (1929), d’Ascanio (1930), Breguet (1935), and others. Technical publications documenting developments started to be relatively widespread in the 1920s (for example: Glauert, 1921; von Karman, 1921; Klemin, 1925).
How it Works
The basic idea is to create an upward thrust with an airscrew. This was relatively easy from the beginning. Problems come with the control and the forward flight. Landing is not easy, either, because it requires navigation in a slipstream of self-induced vortices (vortex rings). One important step in control was the introduction of the tail rotor (as the vertical tail of the airplane).
Forward flight is created by tilting the rotor, so as to give an axial component to the thrust. This axial component must overcome the total drag of the vehicle. However, forward flight created at least two major additional problems: a rolling moment on the aircraft and a rotor stall (under particular conditions) on the retreating elements.
The balancing of the rolling moment is achieved with special technical solutions on the shaft, while stall is a serious limit to forward speed.
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