NO344389B1

NO344389B1 - A system for variable blade pitch control and autorotation for electrically powered rotorcraft

Info

Publication number: NO344389B1
Application number: NO20181567A
Authority: NO
Inventors: Rolf Olav Flatval
Original assignee: Rolf Olav Flatval
Priority date: 2018-12-06
Filing date: 2018-12-06
Publication date: 2019-11-25

Description

Title

A system for variable blade pitch control and autorotation for electrically powered rotorcraft.

The object of the invention

The invention relates to a system for variable blade pitch change and a potential for safe autorotation designed for electrically powered large rotorcraft in the range of, but not limited to 0.4 to 4 tons.

Variable blade pitch control in rotor systems for heavy rotorcraft is used to achieve the best and most responding way to control the lift of the rotorcraft. Variable blade pitch control is used in all large helicopters, on both main rotor and tail rotor. An other way to control the lift on a rotor system is by using variable rotor speed (rpm) and constant pitch rotor blades. This is the method most used in small drones and quadcopters today, but variable speed and constant pitch blades are not suitable for autorotation due to aerodynamic laws. In case of a malfunction to the electric motor or the power supply, a rotorcraft with constant blade pitch and a variable speed rotor will lose control and fall to the ground.

On the other hand, use of variable blade pitch control and constant speed rotor, as embodied in the invention, will make it possible to obtain control of the rotorcraft in air, after loss of power, by using autorotation (windmilling) to a safe landing in the same manner as a helicopter.

According to an embodiment, the system for variable blade pitch control and potential for autorotation can be achieved from the invention by using an (dual operation) electric linear actuator with clutch to transfer non-rotating vertical motion, through a blade pitch control rod with transition box, to a rotating pitch change plate comprising the blade pitch change links. In addition, a freewheel between the rotor system and the propulsion system (electric motor) can make autorotation possible without any mechanical drag or friction from transmission or motor.

Evolution toward more efficient batteries, hybrid solutions and electric motors with less weight, and development of medium to short length rotor blades with autorotation properties and internal weights towards the blade tip to maintain the rotational kinetic energy in the rotor when entering autorotation, will increase the effort to develop and design certified electrically powered rotorcraft with safe operation in all phases of flight.

Background

First priority in all aviation is safety. This is why all helicopters, in order to be certified, have to demonstrate in real life their ability to autorotate down to a safe landing. This is also one of the reasons why heavy electrically powered rotorcraft today are not certified for commercial use. The most common way to work around this problem is to add more independent rotor systems to the rotorcraft. This is not concidered as a safe solution.

Such leading helicopter manufacturers as Leonardo, Airbus and Bell are all developing, testing or designing electrically powered rotorcraft. Leonardo with Project Zero (https://en.wikipedia.org/wiki/AgustaWestland_Project_Zero), Airbus together with Audi and Italdesign with Pop.Up Next (https://www.italdesign.it/project/pop-up-next/) and Bell together with Uber with Bell Air Taxi (https://www.bellflight.com/company/innovation/air-taxi).

In addition, a multiple of small companies are developing and testing electrically powered rotorcraft: https://www.youtube.com/watch?v=_tFG-uk3WcE .

The invention relates to, and is partly based on, the known technical approach to variable blade pitch control used on tail rotors in helicopters, and especially the award winning Electrical Tail Rotor from Leonardo and Clean Sky:

(http://www.leonardocompany.com/en/-/national-award-innovation-2017-premionazionale-innovazione and https://www.youtube.com/watch?v=-LIH_6581QE ). Other variants of variable blade pitch control can be seen on compressor blades and inlet guide vanes in gas generators in aircraft engines, and blade change control in windmills for power production.

However, blade pitch control on tail rotor blades for large helicopters are normally provided by using hydraulically powered servo actuators and/or mechanical linkages.Tail rotor blades on helicopters do not autorotate by windmilling, as they are driven by the autorotation (windmilling) of the main rotor through a gearbox and tail rotor drive shafts.

Other known technology and documents describing use of electric motor and electric actuators for controlling rotor blade pitch are patent numbers US 2009140095 A1, WO 2015138655 A1, US 2013264412 A1 and US 2013119187 A1. Patent number US 2009140095 A1 (ref section 0011 and claim numbers 1, 8 and 11) mentions an “Electric powered rotary-wing aircraft” where an electromechanical servo system (32) provides blade pitch control for main and tail rotor blades. The electromechanical servo mentioned for the main rotor are located in the rotor hub and thereby exposed to vibration and centrifugal forces and will, as described in the document, need a slip ring system for power supply. The document patent number WO 2015138655 A1 (ref sections 0066 and 0099, and claim 1) describes “Mast dampner and collective pitch in a rotorcraft” including use of electric actuators (142) affixed to the rotor blade or a rotor beam. This solution will also be subject to vibration and centrifugal forces. Document patent number US 2013264412 A1 (ref claim number 1) concerns a “Rotary wing aircraft having a tail rotor, and a method of optimizing the operation of a tail rotor” which decribes the use of a pitch modification device (20) for changing the tail rotor blades. The pitch modification device is not described in detail in the document. The document patent number US 2013119187 A1 (ref section 0068 and claim number 1) describes a “Device for varying blade pitch of a lift rotor” and makes provision for electric actuators (22) controlled by a flight control system. The solution includes a traditional swashplate system using electric actuators instead of hydraulic servo jacks.The rotary part of the swashplate operates and change the angle of flaps, as an integrated part of the main rotor blade, and thus changing the blade pitch.

An alternative and improved solution for variable blade pitch control and autorotation for electrically powered rotorcraft such as heavy drones, multicopters, helicopters, quadcopters or eVTOL is contained in the invention.

The advantages of the invention are a compact solution where an electric linear actuator with clutch for blade pitch change can be located inside an electric motor with a hollow driveshaft. In addition, a freewheel between two hollow driveshafts can permit autorotation of the rotor system. Further, two hollow driveshafts can be coupled for transmission of flightloads by means of a thrust plate.

This system enables the rotorcraft to perform autorotation in the event of:

– One or more of the electric motors should fail to operate normally

– Failure of the main power supply (batteries) to the electric motors

– One of the two rods in the electric linear actuators with clutch should fail In the unlikely event that both of the independent power supply lanes to the dual operation of the electric linear actuator with clutch should fail, the invention includes calibrated springs in the pitch control system that could set the blade pitch to optimum blade pitch (i.e. best angle of attack) for autorotation.This could ensure a pre-controlled slow rate of descent, but will not prevent a hard landing. Design of other rotorcraft systems, including a flotation bag system, could help reducing the impact at landing in this rare case.

Brief Summary

According to an embodiment the invention relates to a system for controlling variable blade pitch and autorotation for electrically powered rotorcraft with at least two rotors. The system comprises at least one electric linear actuator with clutch, located partially inside a rotor with hollow driveshaft which is part of an electric motor, to control variable blade pitch.

Further, the system is comprising at least one thrust plate to transfer vertical loads between two hollow driveshafts.

In addition, one or more freewheel designed for vertical operation to connect or disconnect rotational drive between two hollow driveshafts.

In addition, at least one calibrated spring to mechanically set blade pitch to optimum angle of attack for autorotation in the unlikely event of failure to the electric linear actuator with clutch.

Brief Description of the Drawings

The solution is shown in Fig.1 with electric linear actuator rods extended. The exemplary embodiment of the illustration does not necessarily include all shims, bolts, sealing rings, nuts, bearings or electrical wiring and connections. The size of components may differ from actual size, and the electric motor and electric linear actuator are drawn as examples of the components.

Fig. 1 illustrates an exemplary embodiment of the invention with reference numbers as listed below :

1: Electric linear actuator with clutch (dual operation)

2: Electric motor

3: Stator

4: Rotor with hollow driveshaft No.1

5: Transition box with blade pitch control rod

6: Hollow driveshaft No.2

7: Thrust plate

8: Freewheel

9: Locknut

10: Calibrated spring

11: Hollow driveshaft No.3

12: Conical ring (x2 halves)

13: Anti-twist bolt

14: Blade pitch change link (partial)

15: Rotor hub (partial)

16: Locknut

17: Blade pitch change plate

Detailed description

According to an embodiment of the invention, an electric linear actuator with clutch 1 and with two independent push/pull actuator rods for dual operation, can be attached to the rear end of an electric motor 2, and the main body of the electric linear actuator with clutch 1 can be located inside and in the center of the electric motor 2. This is made possible as the electric motor 2 comprises a rotor with hollow driveshaft No.14. The purpose of the electric linear actuator with clutch 1 is to transform signals from a flight control system (input) to vertical motion of the transition box with blade pitch change rod 5 via a blade pitch change plate 17 and blade pitch change links 14 to the rotor blades (output).

The electric linear actuator with clutch 1 must be powerful enough to overcome aerodynamic- and sentrifugal twisting forces acting on the rotor blades, in addition to the calibrated springs 10.

For safe operation, the purpose of the clutch is to disconnect the affected failed actuator rod in case of power loss (fail/safe operation), and thus allow the rod to float with the operative and working rod.

Power supply to the actuator clutches can be independent and different from the power supply to the actuator motors.

The power supplies to the electric linear actuator with clutch 1 may be different from the main power supply (main batteries) to the electric motor 2, and may be delivered from independent power sources.

Exampel of linear actuator is described here: https://en.wikipedia.org/wiki/Linear_actuator

Large helicopters use hydraulically powered servo actuators, often located remote from the rotors, to change the pitch of the rotor blades, as this is required to overcome the strong forces acting on the blades. For rotorcraft with two or more rotors and shorter rotor blades, the forces acting on the rotor blades will be significantly less and thus require less power to change the blade pitch.

The electric linear actuator with clutch 1 in this invention could also be located remote from the electric motor 2, as this solution may lead to better access to the actuators. However, additional linkages, levers and mountings will increase the total weight and the complexity of the system, increase the number of parts needed, and the actuators could be more exposed to the environment and to damage.

The electric motor 2 mainly comprises a vertical rotor with hollow driveshaft No.1 4 and a stator 3, and may be designed for vertical operation. Other types of electric motors with vertical hollow shaft (VHS) are today often used in pumping operations.

Connected to the upper end of the electric linear actuator with clutch 1 is the transition box with blade pitch change rod 5. The transition box with blade pitch cange rod 5 is located inside of the hollow driveshafts.The purpose of the transition box 5 is to transfer the linear vertical non-rotating motion from the electric linear actuator with clutch 1 to the linear vertical and rotating motion of the blade pitch change rod 5, and eventually to change the blade pitch.

The transition box 5 can include a cylindrical shaped box comprising the lower part of the blade pitch change rod 5, two roller bearings, a retaining plate and a locking ring. Close to the lower end of the blade pitch change rod 5 is a protruding collar to face roller bearings on both the upper and lower side. A circular retaining plate with a center hole with sealing to match the blade pitch change rod 5 can be located on top of the upper roller bearing. A locking ring between the retaining plate and the inner wall of the transition box could keep the unit together. This is similar to a usual manner of designing units for transition from non-rotating to rotating motion on helicopters. The blade pitch change rod 5 may be made hollow (for reduced weight) or solid (for increased strenght), and can be connected at the upper end to the rotating blade pitch change plate 17.

The upper end of the rotor with hollow driveshaft No.14 is connected to the lower end of hollow driveshaft No.26 and are balanced together for vibration. The driveshafts are preferably made as two individual units for maintenance and assembly purposes, but may also be made as one unit.

Hollow driveshaft No.26 has a protruding collar on the outer side at approximately halfway its length to face a thrust roller bearing at the upper side to support the weight of the rotor when it is not rotating (on ground). The bearing can also provide the possibility to manually check the freewheel 8 for correct operation on ground before flight, by rotating the rotor by hand.

Located on top of the thrust roller bearing and outside the hollow driveshaft No.26 is a circular thrust plate 7. The thrust plate 7 can be attached to hollow driveshaft No.3 11. The purpose of the thrust plate 7 is to transfer the vertical flight loads from the rotor to hollow driveshaft No.26, by connecting hollow driveshaft No.311 to hollow driveshaft No.26 through the thrust ball bearings and freewheel 8.

The thrust plate 7 may be made of a solid corrosion resistant material (e.g. stainless steel) to withstand the flight loads.

At the upper side of the thrust plate 7 is according to an exemplary embodiment a thrust ball bearing, a freewheel 8 and another thrust ball bearing located. They can all be held in place by a locknut 9 located at the top end of hollow driveshaft No.2 6.

According to an embodiment of the invention the freewheel 8 provide the possibility for autorotation as it will disconnect hollow driveshaft No.311 from hollow driveshaft No.26 in case of a malfunction of the electric motor 2 or loss of power supply to the electric motor 2.

The freewheel 8 can be of a type with a number of rocking pawls/bearings placed in a retainer (roller cage) and held in place by springs. Due to vertical loads, the side walls and the retainer may have to be reinforced compared to a “normal” freewheel to ensure free operation of the pawls.The freewheel 8 will connect the drive from hollow driveshaft No.26 to hollow driveshaft No.311 during normal operation, and disconnect the two driveshafts if hollow driveshaft No.26 no longer provide drive due to failure of electric motor 2.

According to an embodiment of the invention, the hollow driveshaft No.311 can transfer the rotational drive from hollow driveshaft No.26 through the freewheel 8 to the rotor hub 15. Connected to the thrust plate 7 at the lower end, the hollow driveshaft No.3 narrows in to a smaller diameter, and protruding machined splines on the outer side of hollow driveshaft No.3 11 may transmit the drive to the rotor hub 15 through matching internal splines in the center of the rotor hub 15. The rotor hub 15 can be secured by two semicircular conical rings 12 at the lower side and a locknut 16 at the upper side. Threads at the upper end on the outside of hollow driveshaft No.311 match the internal threads of the locknut 16.

The blade pitch change plate 17 rotates at the same speed as the rotor hub 15 and can be fixed in the rotational plane compared to the rotor hub 15 by means of anti-twist bolts 13. This to ensure that no twisting forces are acting on the blade pitch change links 14. According to an embodiment the anti-twist bolts 13 can go through the blade pitch change plate 17 and the rotor hub 15. Between the lower end of the anti-twist bolt 13 and the lower surface of the rotor hub 16, we can find the calibrated springs 10 that provide the means of presetting the blade pitch for autorotation in case of failure to all rods on the electric linear actuator with clutch 1. Other locations of the calibrated springs 10 could be between the upper end of the anti-twist bolt 13 and the upper surface of the rotor hub 15, or around the antitwist bolts 13 between the lower surface of blade pitch change plate 17 and the upper surface of the rotor hub 15.

At the periphery of the plade pitch change plate 17 may at least two attachment points for blade pitch change links 14 be located. The blade pitch change links 14 may be of either adjustable or fixed type.

The descriptions and terminology used in this document are not intended to be limiting for the invention.

Claims

1. A system for controlling variable blade pitch and autorotation for electrically powered rotorcraft with at least two rotors, the system comprising:

at least one electric linear actuator with clutch (1), located partially inside a rotor with hollow driveshaft (4) as part of an electric motor (2), to control variable blade pitch;

at least one thrust plate (7) to transfer vertical loads between at least two hollow driveshafts (6,11);

one or more freewheel (8) designed for vertical operation to connect or disconnect rotational drive between two hollow driveshafts (6,11);

at least one calibrated spring (10), located between the rotor hub (15) and the antitwist bolt (13), to move the anti-twist bolt (13) and blade pitch change plate (17), to set an optimum angle of attack for autorotation when the electric linear actuator with clutch (1) is decoupled due to failure.

2. The system of claim 1, wherein at least one electric linear actuator with clutch (1) located partially inside an electric motor (2) comprising two actuator rods to work in parallel and independent to each other to maintain safe operation in case of failure to one of the rods.

3. The system of claim 1, wherein at least one thrust plate (7) to transfer vertical flight loads between two hollow driveshafts (6,11) include a robust circular diskshaped plate attached to hollow driveshaft No.3 (11), transfering the loads to hollow driveshaft No.2 (6) through at least one thrust ball bearing, a freewheel (8) and a locknut (9).

4. The system of claim 1, wherein at least one freewheel (8) to connect or disconnect rotational drive from hollow driveshaft No.2 (6) to hollow driveshaft No.

3 (11), thus connecting or disconnecting the electric motor (2) to the rotor hub (15), comprising a reinforced design with strengthend roller cage/retainer and strengthend side walls to withstand the vertical flight loads and ensure free operation of the pawls (sprags) inside the freewheel.

5. The system of claim 1, wherein at least one calibrated spring (10), located between the rotorhub (15) and the anti-twist bolt (13), to move to its neutral relaxed position when the electric linear actuator with clutch (1) is decoupled, and thereby move the anti-twist bolt (13) and the blade pitch change plate (17) to set the blade pitch to the optimum angle of attack for autorotation.