Propeller gearbox (aviation)
A propeller gear or air screw gear is a reduction gear with which the speed of a high-revving motor is reduced. This allows, among other things, the use of internal combustion engines with a small displacement to drive a propeller in a suitable speed range.
History and function
The Wright brothers discovered the need for a propeller gear as early as 1903. However, it was only used more generally with the development of larger engines in the 1920s. Large high-performance engines with high crankshaft speeds were equipped with propeller gears, as pilots noticed an improvement in performance in otherwise identical aircraft with and without reduction gears.
Executions
Propeller gears can be designed in one or more stages as follows:
Variations
The 1915 Rolls-Royce Falcon featured an epicyclic transmission with a clutch that limited torque to protect the transmission's gears . The later Rolls-Royce Merlin used counter-rotating reduction gears to drive counter-rotating propellers for twin-engine aircraft - a far cheaper method, in contrast to the development and construction of two engine variants with opposite directions of rotation.
The main challenge when connecting gearboxes to combustion engines is the resonance vibrations that occur at certain speeds. The load of the propeller and the gearbox can change the resonance frequencies of the crankshaft , so that strong torsional vibrations quickly occur at certain rotational speeds . Measures taken by the engine designer to mitigate these vibrations in the engine can become useless if the resonance frequencies are shifted by the transmission. Occasionally, couplings or elastic couplings are installed to limit torsional vibrations.
Motors of Tiara - series of Continental Motors used a single transmission for driving the propeller and the camshaft , to bring the propeller speed to half the engine speed.
application
gear ( helical gear ) on a twelve-cylinder - V-Engine Rolls-Royce Merlin 1942
The use of propeller drives was common in the heyday of piston engines in aviation in the 1930s and 1940s. Essentially all of the high-performance piston engines were equipped with propeller drives.
Today, the use of propeller drives in kit aircraft is common when engines originally intended for use in vehicles are used. These engines have in addition to the lower prices typically a smaller displacement than motors for use in light aircraft were designed and develop their rated power at higher speeds - typically more than 4000 min -1 . Conventional aircraft engines , in which the propeller is attached directly to the crankshaft , develop their rated power in the vicinity of the safe and efficient speed of the propeller at 2500 to 3000 min −1 . This speed range is the typical maximum for a propeller of a single-engine aircraft because of the need the speed of the propeller blade tips under the speed of sound to keep as it is approached the speed of sound at detachment occurs at the blade tips, leading to massive loss of thrust.
However, various type-approved engines have also been designed with propeller drives . The Cessna 175 uses a propeller gearbox that is part of the Continental GO-300 engine . The Helio Courier and various twin-engine models from Beechcraft use the gearbox-equipped Lycoming GO-435 and GO-480 . Furthermore, many Light Sport Aircrafts use BRP-Rotax engines such as the Rotax 912 , which use propeller gears.
Propeller gears are also used in shaft turbines ( helicopter engines ) and turbo-prop drives, for example in the Soviet Kuznetsov NK-12 with up to 15,000 hp (11,032 kW ).
See also
literature
- Flight International . tape 49 , no. 1935 , January 24, 1946 (English).
- Bill Gunston: Development of Piston Aero Engines . Patrick Stephens Limited, Cambridge, England 2006, ISBN 0-7509-4478-1 (English).
- TE Guttery: The Shuttleworth Collection . Wm. Carling & Co, London 1969, ISBN 0-901319-01-5 (English).
Individual evidence
- ^ A b c Bill Gunston: Development of Piston Aero Engines . Patrick Stephens Limited, Cambridge, England 2006, ISBN 0-7509-4478-1 , pp. 82 (English).
- ↑ TE Guttery: The Shuttleworth Collection . Wm. Carling & Co, London 1969, ISBN 0-901319-01-5 , pp. 27 (English).
- ^ Flight International . tape 49 , no. 1935 . Reed Business Information, January 24, 1946, ISSN 0015-3710 (English).
- ^ Bill Gunston: Development of Piston Aero Engines . Patrick Stephens Limited, Cambridge, England 2006, ISBN 0-7509-4478-1 , pp. 191 (English).
- ↑ Prof. Dr.-Ing. Roger Grundmann: Flight Mechanics. (pdf) Technische Universität Dresden , accessed on February 2, 2020 .
- ↑ Richard von Mises, Kurt Hohenemser: Fluglehre: theory u. Calculation d. Airplanes in elementary representation . 6th edition. Springer, Berlin 1957, ISBN 978-3-642-99861-4 , p. 188 .