Tip jet

The blade tip drive (English Tip Jet and tip driven rotor ) is a design for helicopters, in which the rotor is driven by a tangentially acting on the tip of each rotor blade force. Since the driving force is not transmitted via a shaft ( rotor shaft ), there is no reaction torque on the cell, and a tail rotor or the second rotor to the main torque compensation is not needed. Also, no need for a costly gearbox and rotor head are simpler in construction. To control about the vertical axis while hovering but additional control devices are needed.

Development

The basic principle was developed in 1909 by Girop. In order to drive the rotor at the blade tip, various techniques have been tried with time: initially set to small piston engines with propellers at the leaf tips. The development consisted of an internal engine which generated compressed air by means of compressor. This was pressed through a hollow rotor shaft and hollow rotor blades, streamed from nozzles at the end of the leaves and produced by recoil thrust for rotating the rotor - the so-called cold blade tip drive.

Aircraft equipped with this drive were about the Dornier Do 32, Dornier and lapwing as more recent development, the Boeing X - 50th

To increase the performance, was injected and ignited in other models at the nozzle fuel - the hot tip drive. This also includes variants with ramjet engines, wherein the first rotor is mechanically accelerated, in order to achieve the required start-up speed for these engines. However, the efficiency of the ramjet engines proved to be due to the low speed as unfavorable.

Blade tip drives were also used in compound auto gyros by the rotor was driven only for vertical take-off. When cruising it stays the same as when the Giro without drive in rotation and generates lift, and possibly also with wings, while the propulsion is generated by a separate engine. This design was used in the McDonnell XV -1 and the Air Screwdrivers Fairey Rotodyne.

However, all driving techniques showed a high noise and high fuel consumption in comparison with mechanically driven rotors. Therefore, to date, no approach has been pursued, capable of flying devices are available only with UAVs and model sport.

So far, only one man carrying the blade-tip helicopter went into serial production - the Sud -Ouest SO 1221 Djinn who carried out the first flight on 16 December 1953. He used a compressor for cold blade tip drive and still scored 1953 the then world altitude record for helicopters with 4,789 meters.