GB2447641A

GB2447641A - Rotorcraft comprising differential gearing and a CVT arrangement

Info

Publication number: GB2447641A
Application number: GB0704931A
Authority: GB
Inventors: Darren Strevens
Original assignee: WILLOWPOINT TECHNOLOGY Ltd
Current assignee: WILLOWPOINT TECHNOLOGY Ltd
Priority date: 2007-03-14
Filing date: 2007-03-14
Publication date: 2008-09-24
Anticipated expiration: 2027-03-14
Also published as: GB2447641B; GB0704931D0

Abstract

A rotorcraft comprises one or more lift rotor(s) 12 and a tail propulsion rotor 14, the aircraft having an engine 2, a differential 4 and a transmission system operable to transmit torque to the rotors, the transmission system including a continuously variable transmission (CVT) arrangement 6. The differential gearing 4 receives torque from the engine 2 and transmits it to the main rotor 12, and the tail propeller 14. Ideally, the CVT arrangement 6 is located on the transmission to the main rotor 12. By using the CVT system, the speed ratios between the main lift rotor and the tail propulsive rotor can be varied. The rotorcraft may be a compound aircraft, ie., possessing a wing 16 to provide lift during horizontal flight. A second lift rotor may take the form of a contra-rotating rotor. The rotorcraft may be an unmanned aerial vehicle (UAV).

Description

Rotorcraft System The present invention relates to a rotor-powered

aircraft comprising a continuously variable transmission system for controlling and varying relative rotation speeds of one or more lift rotors and a tail propulsion rotor of the aircraft during take off, flight and landing. The aircrafts of the invention, such as immnned aerial vehicles, are able to take off and land vertically and transfer to flight having an improved speed, performance and economy.

Unmanned aerial vehicles (UAVs) are aircraft which do not have an onboard pilot.

UAVs can be remote controlled or fly based upon pre-programmed flight plans or more complex dynamic automation systems. They can be used in a number of military roles, such as reconnaissance, and non-military roles, such as in conducting aerial surveys.

The continuously variable transmission (CVI) is a transmission in which the ratio of the rotational speeds of two shafts, such as output shafts of a vehicle or other machine, can be varied continuously within a given range. This can provide a potentially infinite number of possible ratios. CVTs have been widely used in the engines of a number of terrain vehicles, and most commonly in cars, and have also been used in tanks to control the relative speeds of the treads on each side of the tank.

CVTs have been used to continuously change the rotation speed of a tail rotor of a helicopter, while maintaining a constant engine rotation frequency (JP 10264895). They have also been used in aircraft to drive aircraft power generators for the stable generation of AC power of a fixed flequency irrespective of the speed of the aircraft, in order to supply electric power to electrical equipment such as instruments, communication devices, lighting, air-conditioners and anti-icing heaters.

US 3977812 describes a mechanism for stopping or feathering the tail rotor of a helicopter while driving a propulsion propeller which is adjacent to the tail rotor, or for stopping the propulsion propeller when the tail rotor is in operation. This involves the use of a planetary gear train (including a central sun gear, a plurality of spur-type planetary gears engaging the sun gear and an outer ring gear internally engaging the % . planet gears) and a rotary braking device. It does not use a CVI vaty the relative rotation speeds of the lift rotors and the tail propulsion rotor, and the wing is fixed to the helicopter body.

Therefore, CVTs have never before been used, or envisaged for use, in rotor-powered aircraft to controlling relative rotation speeds of both a lift rotor and a tail rotor to assist in their take oft', their subsequent transfer to horizontal flight, and their landing.

Therefore, in accordance with the present invention, there is provided a rotor-powered aircraft having one or more lift rotors and a tail propulsion rotor, the aircraft further being provided with a power source, a differential and a transmission system operable to transmit torque from the power source to the rotors, wherein the transmission system includes a continuously variable transmission arrangement operable to vary the relative rotation speeds of the one or more lift rotors and the tail propulsion rotor.

Preferably, the continuously variable transmission arrangement is mounted in parallel with the differential. Also, it is preferred that the one or more lift rotors comprises a pair of contra-rotatable lift rotors.

The rotor-powered aircraft can be equipped with a wing which, when the aircraft is in the take-off position, is substantially perpendicular to the ground. Preferably, the wing is rotatably connected to the aircraft. More preferably, as the wing is able to rotate from a position perpendicular to the ground towards a horizontal position relative to the ground, a biasing device can be used to restrict rotation in the last 15 relative to the horizontal. This biasing device can be a compressible resisting device, such as a spring.

While the method of the invention is primarily intended for unmanned aerial vehicles, it could also be equally applicable to other rotor-powered aircraft, such as helicopters.

Also provided in accordance with the invention is a method of controlling and varying relative rotation speeds of one or more lift rotors and a tail propulsion rotor of a rotor-powered aircraft comprising: providing a power source and a differential; providing a transmission system connected to the power source; providing output shafts connecting the trnsmicsion system with the one or more lift rotors and a tail propulsion rotor; transmitting respective required torque from the power source to the one or more lift rotors and tail propulsion rotor; wherein the transmission system includes a continuously variable transmission arrangement operable to vaiy the relative rotation speeds of the one or more lift rotors and the tail propulsion rotor.

The present invention will now be explained in more detail with reference to the accompanying Figures.

Figure 1. This shows a view of the aircraft engine, differential and CVT and the output shafts connecting them to the lift rotors and tail propulsion rotor.

Figure 2. This shows a closer view of the aircraft engine, differential and CVT and the output shafts connecting them to the lift rotors and tail propulsion rotor.

Figure 3. This shows a view of a craft in its vertical ifight configuration.

Figure 4. This shows a view of a craft in its normal flight configuration.

The output from an aircraft engine 2 is transferred into a differential 4 (Figures 1 and 2). One output shaft 8 from the differential provides the source of power for the lift rotors 12, while the other output shaft 10 provides the source of power for the tail propulsion rotor(s) 14 at the rear of the craft. In parallel with the diffrrenfial is a CVT unit 6. This controls the relative ratio of the revolutions of the two output shafts 8 and from the differential. In this way the direction of the power can be controlled. When the engine 2 is running while the craft is on the ground and preparing for take-off, substantially all of the power is directed towards output shaft 8 and the lift rotors 12 and the rotational speed of the output shaft S is much greater than that of output shaft leading to the tail propulsion rotor(s) 14. This enables the craft to take off vertically with minimal energy wastage. Once the craft is in the air and as it prepares for horizontal flight, the power is gradually transferred to output shaft 10 so that the rotational speed of the output shaft 10 becomes significantly greater than that of output shaft 8. The power is therefore then applied to the tail propulsion rotor(s) 14 at the rear of the craft to provide forward momentum.

The benefits of using a CVT in rotor-powered aircraft are that it enables the craft to achieve a greater efficiency, speed and economy as the power is being directed specifically to where it is required for each part of the take off and flight thus minimising energy wastage. Additionally, it allows the smooth transfer of power to and from the lift rotors or tail propulsion rotor during the transitions to and from horizontal flight and the total power output required for a given weight is reduced from that required from a stepped' or switched transmission. It also eliminates the need for power sources dedicated to either lift or propulsion.

While the craft of the invention can be run with a single rotor, it is preferred they are run with a pair of contra-rotating rotors. This would enable it to lift a heavier payload in vertical take-off and be more stable at high speeds. Additionally, having a pair of lift rotors would also eliminate the requirement for the anti-rotation tail rotor that is seen on all helicopters.

In addition to the CVI system, the craft can be provided with a main wing 16 which, when the craft IS is taking off, is in its vertical flight configuration as shown in Figure 3. In this configuration, the main wing 16 is substantially perpendicular to the ground.

Ns reduces the air resistance during a vertical take ofi It therefore requires still less power and hence less fuel to take off using such a system in combination with a CVI driven rotor-powered aircraft, this msiking the aircraft more economical, which is an important consideration in present times. Alternatively, the aircraft would be able to take off with a significantly increased payload in comparison with known similar aircraft while only requiring the same amount of fuel. This is in stark comparison with conventional aircraft, such as UAVs, which have their wings oriented such that the larger surface area surface of the wings faces the ground.

The wing is preferably rotatably attached to the main body of the craft, so once in flight, air resistance encountered by the wing rotates it to a position towards the horizontal to the ground. This allows it to support the craft during flight, and is shown in Figure 4. The greater the degree of air resistance, the greater the degree of rotation of the wing to the horizontal. If desired, the last 10-15 of this rotation to the horizontal flight position may be restricted by use of a spring or other biasing device which allows for a greater angle-of- attack' for the wing when the craft is not fully loaded.

Claims

Claims I. A rotor-powered aircraft having one or more lift rotors and a

tail propulsion rotor, the aircraft further being provided with a power source, a differential and a transmission system operable to transmit torque from the power source to the rotors, wherein the transmission system includes a continuously variable transmission arrangement operable to vary the relative rotation speeds of the one or more lift rotors and the tail propulsion rotor.
2. The rotor-powered aircraft according to claim 1, wherein the continuously variable transmission arrangement is mounted in parallel with the differential.
3. The rotor-powered aircraft according to claim 1 or claim 2, wherein the one or more lift rotors comprises a pair of contra-rotatable rotors.
4. The rotor-powered aircraft according to any of claims 1-3, wherein there is provided on the aircraft a wing which, when the aircraft is in the take-off position, is substantially perpendicular to the ground.
5. The rotor-powered aircraft according to claim 4, wherein the wing occupies a position substantially perpendicular to the ground due to its own weight.
6. The rotor-powered aircraft according to claim 5, wherein the wing is rotatably connected to the aircraft.
7. The rotor-powered aircraft according to any of 1itn 4-6, wherein the wing is rotatable from a position perpendicular to the ground towards a horizontal position relative to the ground during flight.
8. The rotor-powered aircraft according to claim 7, wherein the wing is equipped with a biasing device to restrict rotation in the final 150 relative to the horizontal.

9. The rotor-powered aircraft according to claim 7, wherein the biasing device is a compressible resisting device.
9. The rotor-powered aircraft according to any of claims 1 to 8, wherein the aircraft is an unmanned aerial vehicle.
10. A method of controlling relative rotation speeds of one or more lift rotors and a tail propulsion rotor of a rotor-powered aircraft comprising: providing a power source and a differential; providing a transmission system connected to the power source; providing output shafts connecting the trnmicsion system with the one or more lift rotors and the tail propulsion rotor; transmitting respective required torque from the power source to the one or more lift rotors and tail propulsion rotor; wherein the transmission system includes a continuously variable transmission arrangement operable to vary the relative rotation speeds of the one or more lift rotors and the tail propulsion rotor.
11. The method according to claim 10, wherein the continuously variable transmission arrangement is mounted in parallel with the differential.
12. The method according to claim 10 or claim 11, wherein the one or more lift rotors comprises a pair of contra-rotatable rotors.
13. The method according to any of claims 10-12, wherein the aircraft is an uiimniicd aerial vehicle.
14. A craft substantially as herein described and illustrated in the drawings.