GB2189752A - Weight-shift aircraft - Google Patents

Abstract

A weight-shift aircraft is provided with steering means operated by a joystick-type control assembly 19 which is mounted on a pilot support airframe 2. The airframe 2 is suspended below a wing airframe 1 of the aircraft and movable relatively thereto, about a joint 20, for steering purposes. For roll control the steering means comprise flying wires 32 which brace the wing and the effective lengths of which vary in complementary fashion according to the position of the joystick 21 of the assembly 19. For pitch control the steering means comprise a push/pull rod and bell-crank system 26,27,29 which connects the control assembly 19 to the wing airframe 1. <IMAGE>

Description

SPECIFICATION Weight-shift aircraft The invention relates to weight-shift aircraft, such as hang gliders and microlight aircraft. Aithough the invention is applicableto weight-shift aircraft generally it is particuiarly, but not exclusively, concerned with microlight aircraft commonly referred to as powered hang gliders.

Aweight-shift aircraft of hang glider type comprises a wing, usually a flexible or so called "Rogallo" wing with a tubular airframe, beneath which is suspended a large mass which for a conventional hang glider is mainly the pilot, and which for a microlight aircraft also includes a pilot support airframe on which is mounted a pusher power unit and an undercarriage, and in which the pilot sits.

Weight-shift aircraft are steered by altering the angle-of-attack or aspect of the wing to the prevailing airflow by moving the position of the large mass relative to the wing by so called weight-shift.

Conventionallyweight-shift is facilitated by the provision of a triangular control frame or a bar, which at its uppermost part is rigidly mounted to a keel spar of the wing airframe and at its lowermost part has a control bar which is grasped and manipulated by the pilot. However, to cause the wing to roll in a given direction it is necessaryforthe pilot to move the control bar in the opposite direction relative to himself, ie to reverse steer. As compared with the joystick control of conventional aircraft this reverse steering characteristic applies in respect of both pitch and roll, so that weight-shift aircraft present learning difficulties and confusion both for novices and for pilots already skilled in flying conventional aircraft.

An additional and importantfunction ofthecontrol frame or bar is to supportthe bottom ends of lower or flying wires/spars of the aircraft. These wires or spars brace the outer regions of the wing spars to the control frame or bar during positive lift.

Whilst the conventional control frame is a suitable arrangement for a hang glider in which the pilot is suspended in the prone position, it has considerable disadvantages for powered microlight aircraft in which the pilot is ordinarily seated. In the latter case the size and position of the control frame prevents adequatefairing ofthe pilotsupportairframeand therefore the pilot in the seated position increases drag and suffers discomfort from the oncoming air flow.

The main object of the invention is to overcome the disadvantage ofthe reverse steering characteristic of present weight-shift aircraft, at the same time removing the need for a control frame and thereby facilitating fairing for the pilot.

According to the invention a weight-shift aircraft is provided with steering means operated by a joystick-type control assembly mounted on a pilot supportairframewhich,duringflight,issuspended below the wing of the aircraft and movable relative thereto for steering purposes.

Preferably the joystick-type assembly comprises a joystick universally mounted to the pilot support airframe and operable for positive steering ofthe aircraft in pitch and roll. The joystick may be connected to the wing airframe, for pitch control, through a push/pull rod and bell-cranksystem ofthe steering means.

Additionally the steering means may provide the bracing required by the wing airframe under positive lift, in place ofthe lower orflying wires of a conventional weight-shift aircraft. Thus the steering means may comprise bracing wires the effective lengths of which,for for roll control, vary in complementary fashion according to joystick position.

The invention will now be further described with reference to the accompanying drawing which illustrates, byway of example and in diagrammatic perspective view, a preferred embodiment of microlight aircraft in accordance with the invention.

The microlight aircraft illustrated in the drawing comprises a wing airframe 1 on which the flexible wing (not shown) is supported in known fashion, and a pilot supportairframe 2. The airframe 1 comprises two wing spars 3 pivotally mounted to the nose end of a keel spar4 by nose plates 5 and angularly located relative thereto by a cross bar 6, the wing being suitably attached to said spars, and a king post 7 to which upper or landing wires 8 are attached. The lower ends ofthewires 8 are attached respectivelyto wing bolts 9,the upper noseplate 5 and the rear portion of the keel spar 4, thereby providing the bracing required by the airframe 1 under negative lift.

The pilotsupport airframe 2 supports a rear power unit 10with pusher propeller 11 and a pilot seat 12.A tricycle undercarriage comprises rear axle struts 13 (only one of which is shown), a longitudinaltubular chassis member 14, rear wheels 15, steering forks 16 with foot rests 17 and a front wheel 18. Weight-shift of the airframe 2 is controlled by a joystick control assembly 19 mounted to the airframe 2 and steering means in accordance with the invention, as will now be described.

The pilot support airframe 2 is suspended from the keel spar4 at a joint 20 allowing pitch and roll rotation thereabout. This movement is controlled by angular displacement of a joystick 21 of the assembly 19. The joystick 21 is fixed to an upper portion of a gimbal 22 of the assembly 19, and a pitch control horn 25 is fixed to a lower portion ofthe gimbal 22. The gimbal 22 is pivotally mounted at 23 on a roll control torque tube 24 which is rotatably mounted and axially located on the chassis member 14. Mechanical stops (not shown) may be provided to limit angular movement of the joystick 21 within a range providing adequate control of the aircraft.

For pitch control the steering means includes a push/pull rod and bell-crank system.A link26 is pivotally connected between the horn 25 of the control assembly 19 and a downwardly projecting limb 27a of a bell-crank lever 27 pivotally mounted at 28 on the torque tube 24. The pivotal axes ofthe gimbal 22 and the lever 27 are mutually parallel, and the other or rearwardly directed limb 27b of the lever 27 is connected to the keel spar 4through a rod 29.

The lower end of the rod 29 is connected to the lever 27 by a universal spherical joint at 30, and the upper end of the rod 29 is fixed to a slip ring 31 which turns freely, and is axially located, on the spar 4 rearwardly ofthe joint 20. Thusfore-and-aft movement ofthe joystick 21 acts, through the push/pull rod and bell-crank system, to rotate the airframe 2 in pitch about thejoint 20.

Roll control utilises two side flying wires 32 which atthe upper ends are secured to the airframe 1 at, or nearto, the wing bolts 9 of the respective wing spars 3. These wires 32 provide the bracing required bythe wing airframe 1 under positive lift, and the lower ends thereof are connected to and extend around a cam drum 33 of the steering means. The drum 33 is rotatably mounted above the chassis member 14 about an axis parallel thereto behind the seat 12, and it is coupled to the torque tube 24through achain and sprocket drive. A chain 34 engages a driving sprocket 35 fixed on the torque tube 24 and a smaller driven sprocket 36 fixed to the drum 33.Thus side-to-side movement ofthe joystick 21 turns the drum 33 to vary the effective lengths ofthe flying wires 32, thereby rotating the airframe 2 in roll about the joint 20. The core of the drum 33 is shaped to provide a cam profile such that as the drum 33 turns the effective lengths ofthe two wires 32 vary in complementaryfashion according to the joystick position and so that neither of these wires becomes slack when the aircraft moves in roll.

In neutral flight conditions the spherical joint 30 is approximately aligned with the chassis member 14 and thus lies on the rotation axis of the torque tube 24. Thus, movementofthejoystickfor roll control does not affect the pitch, and vice versa, so that pitch and roll control are substantially independent of one another in flight.

In flightthe pilot, seated with his feet resting on the foot rests 17, controls the aircraft by manipulating the joystick 21 -fore or aftto pitch the nose of the aircraft down or up respectively, and to right or leftto induce roll to right or left respectively. Thus the aircraft has a positive steering characteristic.

Servo assistance or control, which may be of a conventional and wellknown type, can be added to reduce pilot fatigue in pitch and roll operation.

Claims (12)

1. Aweight-shift aircraft provided with steering means operated by a joystick-type control assembly mountedonapilotsupportairframewhich,during flight, is suspended below the wing ofthe aircraft and movable relative thereto for steering purposes.

2. Aweight-shift aircraft according to claim 1, wherein said control assembly comprises a joystick universally mounted to the pilot support airframe and operable for positive steering of the aircraft in pitch and roll.

3. Aweight-shift aircraft according to claim 2, wherein thejoystick has a gimbal mounting on a roll control torque tube which is rotatably mounted on a longitudinal memberofthepilotsupportairframe.

4. Aweight-shift aircraft according to claim 2 or claim 3, wherein the joystick is connected, for pitch control,through a push/pull rod and bell-crank system to the wing airframe.

5. Aweight-shift aircraft according to claim 3 and claim 4,wherein said system comprises a bell-crank pivotally mounted on said control torque tube and connected buy a universal joint to the lower end of a push/pull rod which is connected atthe upper end to a keel sparofthewing airframe.

6. Aweight-shift aircraft according to claim 5, wherein the upper end of said push/pull rod is connected to a slip ring which turns freely, and is axially located, on said keel spar.

7. A weight-shift aircraft according to claim 5 or claim 6, wherein the pivotal axes of said gimbal mounting and said bell-crankrelativetothetorque control tube are mutually parallel.

8. Aweight-shift aircraft according to any one of claims 5 to 7, wherein the centre of said universal joint is substantially aligned with the rotation axis of said control torque tube in neutral flight conditions.

9. Aweight-shift aircraft according to any one of the preceding claims, wherein the steering means comprises wires which provide the bracing required bythewing airframe under positive lift and the effective lengths ofwhich, for roll control, vary in complementary fashion according to joystick position.

10. Aweight-shift aircraft according to claim 3 and claim 9, wherein said wires are connected to a drum which is rotatably coupled to said torque control tube and the drum core is of varying effective radius, presenting a profile which ensures that neither of the wires becomes slack when the aircraft moves in roll.

11. Aweight-shift aircraft according to claim 10, wherein a chain and sprocket drive between the control torque tube and the drum provides a step-up drive ratio.

11. Aweight-shift aircraft according to any one of the preceding claims, wherein the aircraft is a microlight aircraft.

12. Aweight-shift aircraft substantially as hereinbefore particularly described with reference to the accompanying drawing.