GB2360752A

GB2360752A - Helicopter without tail rotor

Info

Publication number: GB2360752A
Application number: GB0007969A
Authority: GB
Inventors: Glyn Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-04-01
Filing date: 2000-04-01
Publication date: 2001-10-03
Also published as: GB0007969D0

Abstract

In order to balance the reactive torque of the lifting rotor 1, the helicopter is provided with a variable pitch fan 9, driven in a direction opposite to the direction in which the rotor 1, is driven, and located in a duct 4. The fan rim 8, defines the rotor of an A.C. generator the stator 5, of which is located in the duct wall. Current produced by the generator is supplied to the helicopter's electrical control and distribution system. By varying the strength of the electro-magnetic couple between the rotor 8, and stator 5, of the generator, yaw control and stability can be achieved. Airflow produced by the fan may be guided by adjustable vanes 15, to produce vectored thrust.

Description

1 2360752 DUCTED FAN ASSISTED, TAIL ROTOR-LESS HELICOPTER CONCEPT This

invention relates to a helicopter concept that uses, in addition to a conventionally configured Main rotor system, a Ducted fan arrangement as a means of Torque correction, instead of a tail rotor system. Utilising contrarotating Angular Momentum, Electro-magnetic coupling, and variable vane thrust directors it will provide Yaw stability, directional control and augmented thrust.

Conventional helicopter configurations can be categorised in two forms, those with tail rotors for torque correction and yaw control, and those without. Of those without, their main applications are directed towards machines of the heavy lift variety or those that are designed for a specific function, eg. Chinook (Tandem rotor system), Kaman (meshing rotors) and older, non-production experimental craft from Sikorsky and Hiller with Contra-rotating systems. In all cases, their specifications are such that speed, manoeuvrability and performance are sacrificed to a degree, in favour of their increased disc loading and greater lift capacity. Perhaps the only exceptions are the 'NOTAX' machines that use ducted airflow over the tailboorn surfaces and ducted thrust in place of a tail rotor. One main physical disadvantage that conventional tail-rotor equipped aircraft all face is the loss of between 10 and 20% of the available motive power to drive the torque correcting tail rotor, and the additional penalties that accompany this feature being vibration, weight and presenting a rotating hazard in close ground proximity. Another principle feature of helicopter dynamics, (although very complex), is that they essentially dictate that both lift and propulsion are developed from the main rotor disc by virtue of the Collective control for lift, and the Cyclic control for directional propulsion. Consequently, these complex forces acting on the Main rotor blades in flight, and the corresponding complexity of Main rotor head design, lead to a situation where the forward airspeed of the machine is restricted, and limited by the dynamic capabilities of the retreating Main rotor blades, as it is designed to fulfil both lift and propulsive functions. If another system of flight was devised such that the propulsive function of the Main rotor was significantly relieved, the Main rotor system would then be left to provide mainly lift and therefore unloading these retreating blades of their propulsive obligation. Therefore it could be that the forward airspeed of the machine would not be so limited, and the aircraft could achieve much higher cruising velocities than conventional helicopters, as a consequence, the Main rotor hub design would be less complex too.

This invention utilises a modified conventional main rotor drive and control system, designed within the constraints of known and established technology, and through a specific system of transmission driving a contra-rotating, variable pitch fan below, and on the same axis of rotation as the main rotor. The design and physical and dynamic properties of the fan being such that, at operating speed, the angular momentum will be slighly less than that of the main rotor system, thereby it will approximately counter the torque re-action induced in the airframe by the main rotor system. The fan will be designed so that the blade pitch will be variable between a minimum and a maximum, this pitch control will be linked directly with the main rotor 2 collective control, so that a maximum collective pitch input will correspond with a maximum fan blade pitch, and vice-versa. This will ensure that variations in control inputs are equally matched by both Main Rotor and Ducted Fan systems in terms of Torque demand. Ducted fan input airflow will be derived from the relatively still and inert air mass beneath and passing through the main rotor head, in forward flight it will be supplemented by the moving airflow beneath the main rotor disc. Ducted Fan output airflow will be directional, via a system of variable vanes, to give vertical thrust in the hover, and progressively more rearwards thrust as the machine transits into forward flight. Thrust vane control will be achieved through a control system linked to the collective and cyclic control functions of the main rotor system.

Using ducted fan thrust as the propulsive element in this concept, the main rotor system will be significantly relieved of this function, and therefore the design effort on the Main rotor could be more focussed on achieving greater lift and disc-loading capacity.

This invention specifies that the Variable pitch ducted fan design will incorporate the means of establishing an Electromagnetic couple between the Fan in rotation and the static Fan duct (housing). This Electromagnetic coupling will be of variable strength, and will provide the main element in establishing Yaw control and stability. This will be achieved by making the Fan outer extremity become a continuous ring with identical Electro-physical properties to that of an A.C. generator rotor, and the corresponding area of proximity to the fan rim on the inside of the Fan duct, to assume identical Electro-physical properties to that of an A.C. generator stator. The electrical status of the fan will be maintained in rotation through a slip-ring arrangement somewhere on the Fan hub. Once the Rotor and Fan system is in rotation, the generator function will be energised by self excitement of the stator components to produce an electrical output, and the Electro-magnetic couple will be established. There will be an on board electrical control system designed to electronically change the Flux density of the couple and/or the current drawn from the generator, to alter the strength of the Electro-magnetic couple. This will increase or decrease the value of torque demanded by the Fan in rotation, and will therefore be used as a means of providing Yaw control and stability. This invention will also provide a means of generating electrical power for on-board electrical systems without using engine driven devices.

A specific embodiment of the above invention will now be described by way of example in one possible configuration, with reference to the accompanying drawings in which:

Figure 1. Shows a side view detailing the relationships between the major components within the concept.

Figure 2. Shows a view facing Forward to illustrate the arrangement of the Ducted airflow passage each side of the central support structure.

Figure 3. Illustrates the Fan/Duct interface arrangement where the Electro-magnetic 3 Couple will be achieved.

Figure 4. Illustrates a general arrangement of a possible Fan assembly.

Figure 5. Illustrates an example of a suggested Aircraft Configuration within the constraints of the invention.

Figure 6. Illustrates the Torque distribution and management between the Main rotor and Ducted fan systems.

Because of the complex and conceptual nature of this invention, the overall function and description will best be achieved, initially, by following the power transmission route, starting at the source.

In this example, there will be a pair of Gas Turbine turboshaft engines mounted side by side Fig 1, 13, and their output shafts coupled together via freewheel units (not shown), torque transducing devices (not shown) and first stage reduction gearing contained within the first transmission unit 12. Which divides the drive into two outputs. One output leaves the first stage transmission unit 12, along driveshaft 11 a, and enters a secondary transmission unit 10, where the drive becomes a high speed transmission driving the fan hub 7. The second output leaves the first stage transmission 12 along driveshaft 11 b which is lower speed than the shaft 11 a drive, and is rotating in the opposite direction, this drives the main rotor transmission unit 6.

The main rotor transmission unit 6 is mounted within the main duct assembly 4, and supported by four support assemblies 3. The main duct assembly 4 is primary airframe structure and consequently provides all the structural strength and rigidity required to ensure complete stability of the whole main rotor and fan drive assemblies. The four support assemblies 3, will also be of sufficient designed strength to ensure stability and rigidity of the main rotor and fan transmissions, and will be of streamlined cross section to allow smooth airflow over them from above, but have sufficient area contained within to enable them to serve as conduits for control linkages, hydraulic and electrical services (not shown), and Main rotor driveshaft 11 b The main rotor transmission 6 will also contain the mechanics required to give full main rotor system directional control in both collective and cyclic senses, by means of a swashplate or any other suitable mechanism, (not shown). The control linkages (not shown)from which will be shrouded for aerodynamic purposes within the mast assembly 2, and finally connect to the main rotor hub and blade assembly 1.

The main rotor hub and blade assembly 1 will be as aerodynamically clean as possible in its external shape and appearance, and conventional in design in that the latest technology available be used for its dynamic and physical properties. Whereby the primary function of the main rotor system will be to provide lift, and propulsive effort to be of secondary consideration. It is vital to this invention that the entire central drive and transmission assemblies, Items 1, 2j 6 7 and 10, together create with their relationship to each other, a smooth and uniform aerodynamic shape in order to maximise the efficiency of the airflow entering the ducted fan, indicated by Arrow X. Similarly, the internal contour of the duct assembly 4 must be so designed to complement the shape of the central drive and 4 transmission assemblies, and both shapes together will generate the most efficient ducted fan configuration possible within the physical and dynamic constraints imposed.

To support the entire central drive and transmission assemblies (items 1, 2,6,7,10), the secondary transmission unit 10 will be located on a surface of primary aircraft structure 14, which should ideally provide the basis of support for the power plants and primary transmission 12. This platform 14 will be of narrow design running fore and aft through the duct housing 4, just wide enough to support the secondary transmission 10, but to give sufficient clearance each side to allow the free passage of downward ducted airflow. This central platform 14 will be used to accommodate the main fuel tank installation 19 because of its virtually neutral CofG position.

The ducted airflow, having been generated by the fan assembly will be directed downwards into the variable control vane system 15. These vanes will be centrally pivoted and located on each side of the central support platform/fuel tank 14, and linked so that they all move together in the same sense and proportion from one single control input (not shown) coupled with the Aircraft cyclic control system. The vane sense and range of movement be so designed to achieve proportional control from airflow directed vertically downwards, Arrow Y( minimum forward cyclic control), to airflow directed fully rearwards, Arrow Z ( maximum forward cyclic control). This ducted airflow is there to supplement and augrnent the lift already produced by the main rotor system, giving additional vertical thrust in the take off and hover and progressively more rearwards thrust as the aircraft transits into straight and level forward flight.

Central to this invention is the ducted fan assembly, it will have a central hub assembly 7, which is driven in the opposite direction to the main rotor system, and at a higher speed which will enable the angular momentum of the fan assembly to be slightly less than the main rotor system. The hub assembly 7 will contain a collective pitch change mechanism (not shown) linked to each fan blade, which will pivot about a bearing system Fig 4 item 16, to give equal control changes to all fan blades simultaneously. This fan pitch change mechanism will be externally linked to the aircraft collective flying controls via the mechanisms contained within the main transmission 6 and through control conduits located in the main supports 3. The fan hub assembly 7 will also contain an electrical slip-ding arrangement (not shown), which will ensure electrical continuity between the aircraft electrical system via supports 3 and transmission 6, to the Power generating source at the fan rim extremity. At the outboard end of each fan blade will be another bearing system 16 housed within the fan rim housing Fig 3 item17, which is a continuous ring that connects all the fan blades together and maintains structural rigidity of the whole fan assembly.

Mounted externally to the fan rim assembly 17, are the Alternating Current (A,C.) generator rotor segments 8. The design, material, dimensions, quantity and general specification of these segments are to be determined by further research and development. Essentially they are to be designed to assume identical electro-physical properties to those of a conventional A.C. Generator rotor assembly that is to move within an electro-magnetic field to generate an Alternating current.

Once the Main rotor and contra-rotating fan assembly are in rotation, and the generation function is energised, the generated current will be drawn from the rotor segments 8, via the fan blades 9 and slip-rings (not shown), from the hub 7, through the transmission 6 and supports 3 and into the aircraft electrical control and distribution system.

To provide the electro-magnetic field to enable the fan rotor to achieve this function, there will be a corresponding stator assembly 5 mounted within the fan duct assembly 4. This stator assembly will need to be the subject of further research and development to achieve identical electrophysical properties to that of an A.C. generator stator assembly, that will be able to produce a variable strength/density electro-magnetic flux field indicated by arrow A in Fig 3.

Once the fan and rotor mechanics are operating, and the A. C. generating system is energised, the relationship between A.C. rotor 8 and A.C.stator 5 will induce between them an electro-magnetic couple, this will appear to the A.C.rotor as a force to be overcome during the course of it's rotation through the stator field. The strength of this electro-magnetic couple will also determine the amount of force that will be required by the A.C. rotor ( and consequently the ducted fan), to continue rotation at constant speed within this force field.

It can now be seen that the amount of driving force (or torque) that is demanded by the Ducted fan assembly can be varied electrically by adjusting the strength of the electro-magnetic couple between the Fan assembly (A. C. rotor) and the airframe (A.C. stator), while maintaining the Fan rotation at a constant speed. It is the differential between the torque demanded by the Main rotor System and the contra-rotating Ducted Fan system which will supply directional control and stability in Yaw, therefore, with this invention, we now have a concept of giving Yaw directional control and stability by varying the strength of the electromagnetic couple of the Fan/Duct A.C. generating system.

Figure 5 illustrates one example of a typical application of this concept to an aircraft configuration. It is accepted that the aircraft type and application using this concept will be limited because of the physical features of the main rotor and ducted fan being located on the same axis with provision required for the free flow of ducted air through the whole assembly. This will prevent the centre section of the main airframe below the centre line of the main rotor being used for other purposes such as passenger compartment, freight etc.

Figure 6 illustrates the way in which the Torque balancing between the main rotor system and the Ducted fan system will be achieved.

(This is a very simplistic analysis for purposes of explanation only. In practice, the "Equilibrium" datum will also be variable through changes in the Main rotor torque, and corresponding Ducted fan torque settings, this is because of the linkage between the Main-rotor Collective/Cyclic controls and the Ducted Fan blade pitch controls.) 6 Point X on the diagram shows the start point for the Main rotor system, initially at rest, then the torque increases as the rotors speed up to operating levels, indicated by the Equilibrium line drawn through the centre of the graph. Point Y represents the Ducted fan assembly at rest, which then increases at the same rate as the Main rotor, but due to the physical differences between the two systems, the ducted fan assembly will not achieve the same torque figure as the main rotor. Then the A.C generating system is electrically energised and the electro-magnetic couple established. The effect of this will be to cause the Ducted fan to demand an increase in torque to drive it, and this increase will bring both Main rotor and fan closer together at a point of equilibrium. The effect of the electro-magnetic coupling will allow the ducted fan torque demand to be variable within the grey band indicated on the diagram, and this variable torque will give the Yaw stabilisation and directional control required to control the aircraft in flight. Another datum indicated on the diagram is the Min A.C. Power line, this is the level of electrical power output that is the Minimum required to power all of the aircraft systems, it will be noted from the diagram that this level should not be encroached upon with the variations in electro-magnetic couple required that gives the Yaw control.

Claims

CLAIM 1. A tail-rotorless helicopter concept, that uses a contra-rotating, variable pitch ducted fan system on the same axis as, and below, a conventional main rotor system. The design and physical and dynamic properties ofthe fan being such that at normal operating speeds and conditions, a combination of the angular momentum and Electro-magnetic coupling of the Fan system will demand a driving torque almost equal and opposite that of the Main rotor system, thereby giving a virtually zero torque re-action induced in the airframe by the main rotor system. This Electro-magnetic coupling force will be variable in it's strength to induce a torque imbalance between the Main rotor system and the contrarotating ducted fan system to give Yaw direction and control. It will be generated by components located on the ducted fan rim outer extremity having identical electro-physical properties to that of an A.C. Generator rotor system, and corresponding components located on the internal face of the fan duct assembly that possess identical electro-physical properties to that of an A.C. Generator stator system. The ducted airflow output of the fan system is volurnetrically controlled by variable pitch blades on the fan assembly, coupled to work with the aircraft collective flying controls, and directionally controlled by the implementation of guide vanes below the fan assembly, that are linked together to direct the airflow proportionally between vertically down (zero forward speed - max collective input) and fully rearwards (max forward speed - some collective input). The vane control linkage system is to form part of the collective and cyclic flying control system.
CLAIM 2. A tail-rotor-less helicopter concept as specified in claim 1 wherein, the aircraft on board Electrical supply and distribution system contains, in addition to the requisite conventional system components, the components required for electronic control and management of the A.C Generating system formed by the Ducted Fan/Fan duct generator. This electronic control and management system will be required to interface between physical Yaw flying control inputs, automatic flight control system and automatic stabilisation system requirements and their corresponding influence on the Electro-magnetic flux field. The power output of the Fan/Fan duct generator is to be managed in such a way that sufficient energy is available for full Yaw control and stability simultaneously with full power available for the remainder of the aircraft onboard electrical systems.
CLAIM 3. A tail-rotor-less helicopter concept as specified in claims 1 and 2, wherein the whole assembly comprising: main rotor hub, main rotor mast assembly, main rotor transmission, Ducted Fan hub and the Secondary transmission (hereafter called the "Central drive group"), forms in its assembly together, a smooth and harmonious aerodynamic contour, that when placed in its relative position in the centre of the Fan duct assembly, combines with the Fan duct assembly to give the most efficient airflow possible within the constraints of established Ducted Fan technology.
CLAIM 4. A tail-rotor-less helicopter concept as specified in claim 3, wherein the Central Drive group will be located on primary airframe structure, which will contain the main fuel tank directly beneath the C of G position. The aircraft structure will also provide primary support for the power plant installation and the first transmission unit.
CLAIM 5. A tail-rotor-less helicopter concept as specified in claim 1, wherein the ducted fan guide vane system will be designed to provide variable airflow each side of the Airframe central support structure.
CLAIM 6. A tail-rotor-less helicopter concept as specified in claim 3, wherein the Main rotor mast assembly will be shrouded to contain all main rotor pitch change linkage mechanisms within a smooth, aerodynamic shell, to limit the drag co-efficient.
CLAIM 7. A tail-rotor-less helicopter concept as specified in claim 3, wherein the main rotor hub assembly will present a uniform and smooth aerodynamic shape to oncoming airflow to limit the drag co-efficient.
CLAIM 8. A tail-rotor-less helicopter concept as specified in claims 1 and 3, wherein the Fan duct assembly will be of primary aircraft structure, and provide the main basis of support and rigidity for the Central drive group through streamlined support struts.
CLAIM 9. A tail-rotor-less helicopter concept as specified in claim 8, wherein the four main central drive group support struts will have a secondary function of providing conduits for flight control linkages, hydraulic system, electrical system functions, and the rear-most to accommodate the main-rotor transmission driveshaft.
CLAIM 10. A tail-rotor-less helicopter concept as specified in claims 1, 2, and 3, wherein the electrical continuity between the A.C generating function of the Ducted fan Rim assembly and the aircraft electrical supply and distribution system, will be maintained through a slip-ding mechanism housed within the secondary transmission that accommodates the fan hub.

R CLAIM
11. A tail-rotor-less helicopter concept as specified in claims 1 and 2 wherein the Ducted Fan construction will allow collective blade pitch adjustment about bearing mechanisms on both inboard and outboard ends of each blade.
CLAIM 12. A tail-rotor-less helicopter concept as specified in claims 1 and 11, wherein the Ducted Fan blades and their bearing assemblies will be designed to accept an electrical conduit through their centres, to enable continuity between the AC generator segments on the fan rim assembly and the slip ring arrangement within the Fan hub assembly.
CLAIM 13. A tail-rotor-less helicopter concept as specified in claims 10, 11, and 12, wherein the Ducted Fan rigidity is maintained through a continuous ring assembly that connects all the individual fan blade outboard bearing assemblies together, and provides a mounting for the A.C rotor segments.
CLAIM 14. A tail-rotor-less helicopter concept as specified in claims 1, 3 and 6 wherein the main rotor transmission is designed to incorporate within its aerodynamic external shape, the necessary mechanics to provide both power transmission to the main rotor mast and hub, but also the main rotor control mechanisms required to give full collective and cyclic flight control to the main rotor system. There will also be the provision for these flight control mechanisms to be inter-linked to the Ducted Fan blade pitch change mechanism and the Variable thrust director vane system.
CLAIM 15. A tail-rotor-less helicopter concept as specified in all preceding claims wherein the first stage transmission that receives the power output from the power plants will have the capacity to modify the engine power inputs to give two separate drive outputs. One of a specific speed to drive the Main rotor transmission, and the other, of a higher speed than the first and rotating in the opposite sense, to drive the Ducted Fan transmission. This first stage transmission assembly will also have the provision to freewheel an engine output in the event of only one engine drive being available. There will also be a monitoring system for engine output torques.