Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
1999-08-20
2001-10-16
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
C244S060000, C416S1700HM
Reexamination Certificate
active
06302356
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the design and construction of a speed reduction gearbox for transmission of power from a gas turbine engine to a helicopter rotor. More particularly, the present invention relates to a two-stage reduction main gearbox for a twin-engine helicopter.
To use gas turbine engines to drive helicopters, it requires speed reduction gearboxes between the engines and the helicopter rotors. This is true because gas turbine engines are high speed rotary equipment having components including an output shaft revolving at speeds from about 5,000 to 50,000 revolutions per minute. Many modern helicopters have two horizontally-spaced gas turbine engines with parallel, horizontally-spaced output shafts. To deliver the power from the output shafts of both engines to the main rotor, right-angle, speed-reducing “nose” gearboxes are used, each having an input shaft coupled to an engine output shaft. Each nose gearbox has an output shaft. A main gear reduction gearbox is coupled to the nose gearbox output shafts to harness the power from both engines, provide further speed reduction and increase output torque. Main gear reduction gearboxes include gear sets therein for reducing the shaft speed during the transmission of power from the nose gearboxes to the output devices. The transmission of power from the gas turbine engines to the output devices, which include the main rotor, the tail rotor, and various accessories, imparts substantial loads on the bearings and gears of the main reduction gearbox.
The application of gas turbine engines as a propulsion means for a helicopter often creates design parameter conflicts, such as the need for a durable long life gear train and the necessity to minimize the volume and weight of the transmission. Prior designers of gas turbine engine gear reduction gearboxes for helicopters have generally used multi-stage, main reduction gearboxes to effectuate significant shaft speed reduction. For smaller helicopters, two-stage reductions have been used. The first stage reduction has been limited to an input/output speed ratio of 5 to 1, i.e. 5:1. To the best of my knowledge, that has been the maximum first-stage reduction ratio considered acceptable in the helicopter industry. In efforts to deal with that limitation, and handle greater power inputs as developed by more powerful engines for larger helicopters, the typical practice has been to provide additional stages of gear reduction in the main gearbox. While a second stage has been acceptable for small helicopters, addition of a third stage has been the usual direction taken to handle larger helicopters with more powerful engines. Another approach has been to work within the generally-accepted 5:1 first stage reduction limit, by using a torque-splitting technique, but with attendant weight and cost penalties. Also, depending upon the proposed torque-splitting arrangement, failure to achieve true 50—50 torque splitting can result in overloading one of the two power paths, with attendant early gear failure.
The present invention is addressed to the continuing need for a simpler and lighter helicopter gearbox for handling more power.
SUMMARY OF THE INVENTION
One form of the present invention contemplates a combination comprising: a helicopter having a main rotor; a pair of gas turbine engines mounted to the helicopter, each engine of the pair of gas turbine engines having a first power output shaft; a pair of nose gearboxes mounted to the helicopter, each gearbox of the pair of nose gearboxes having an input coupled to one of the first power output shafts, and each gearbox of the pair of nose gearboxes having a second power output shaft; and a two stage main reduction gearbox mounted to the helicopter and having a first stage coupled with said second power output shafts and a second stage coupled with said main rotor, wherein said first stage defines a face gear reduction greater than 5:1 and said second stage defines an epicyclic gear train reduction to the helicopter rotor.
Another form of the present invention contemplates a combination comprising: a helicopter having a main rotor; a pair of gas turbine engines mounted to the helicopter, each engine of the pair of gas turbine engines having a first power output shaft; a pair of nose gearboxes mounted to the helicopter, each gearbox of the pair of nose gearboxes having an input coupled to one of the first power output shafts, and each gearbox of the pair of nose gearboxes having a second power output shaft; and a two stage main reduction gearbox mounted to the helicopter and having a first stage coupled with said second power output shafts and a second stage coupled with said main rotor, wherein said first stage defines a bevel gear reduction greater than 5.1 and said second stage defines an epicyclic gear train reduction to the helicopter rotor.
Yet another form of the present invention contemplates a combination comprising: a helicopter having a main rotor; a pair of gas turbine engines mounted to the helicopter, each engine of the pair of gas turbine engines having a first power output shaft; a pair of nose gearboxes mounted to the helicopter, each gearbox of the pair of nose gearboxes having an input coupled to one of the first power output shafts, and each gearbox of the pair of nose gearboxes has a second power output shaft; and a two stage main reduction gearbox mounted to the helicopter and having a power input portion first stage reduction and a power output portion second stage reduction, the power input portion coupled to the pair of second power output shafts and providing a speed reduction ratio greater than 5:1, the power output portion being coupled to the main rotor.
One object of the present invention is to provide a helicopter having a two-stage main reduction gearbox handling more power from engines to main rotor than has been considered feasible heretofore.
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Cylkro Gears®—A New Challenge, Guus Basstein, 4 pgs.
Computer Methods In Applied Mechanics and Engineering, I.H. Seol & F.L. Litvin, Department of Mechanical
Barefoot Galen L.
Rolls-Royce Corporation
Woodard Emhardt Naughton Moriarty & McNett
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