GB2301566A

GB2301566A - Launching air vehicles or projectiles

Info

Publication number: GB2301566A
Application number: GB9511203A
Authority: GB
Inventors: Dennis Griffin
Original assignee: Airscrew Howden Ltd
Current assignee: Ametek Airtechnology Group Ltd
Priority date: 1995-06-02
Filing date: 1995-06-02
Publication date: 1996-12-11
Also published as: IL118537A0; GB9511203D0

Abstract

An unmanned air vehicle or other projectile is launched by an apparatus comprising a flywheel 3 and a twin fusee drum or pulley 4 coupled to the flywheel. A length of belting 8 is windable onto the drum or pulley as the drum or pulley rotates. The belting is arranged to be releasably coupled to the unmanned air vehicle or other projectile. Energy stored in the flywheel is released by winding the belting onto the drum or pulley, thereby accelerating the unmanned air vehicle or other projectile to launch velocity, at which point the releasable coupling is released. The thickness of the belting may vary along its length so as to achieve substantially constant acceleration of the vehicle or projectile.

Description

LAUNCHING PROJECTILES This invention is concerned with launching projectiles, such as (but not restricted to) remote piloted vehicles (RPVs), also known as unmanned air vehicles (UAVs) and as unmanned aircraft (UMAs).

Assisted take off for unmanned air vehicles is normally achieved by means of high power catapults, or rocket packs, which accelerate the aircraft to flying speed usually from a purpose made launcher structure.

Other systems have been proposed such as the flywheel operated launcher described in GB-A-2132577 and various designs of bungee launchers and gas guns. The flywheel system involves the use of heavy masses to provide in effect a store of inertial momentum but such systems tend to be relatively more expensive than the technically simpler bungee and gas gun systems. These rely on release of stored energy but suffer from a lack of control of the initial rate of change of accelerating forces (the "jerk") which change can prove excessive and damage the UMA. Even with prior art flywheel systems, there is an initial jerk. As the flywheel spins and energy is transferred to the mass of a UAV, it is lost from the flywheel resulting in a progressive reduction in its rate of spin.It has proved difficult in prior flywheel systems to provide for a predictable and especially a virtually constant acceleration of the mass following initial engagement of the flywheel.

The present invention has arisen from our work seeking to overcome the difficulties inherent in prior launching systems.

This is achieved, as we explain in detail below by the use of a relatively simple mechanical device, namely a drum or pulley of the single or multiple (and preferably twin) fusee form.

In accordance with one aspect of the present invention, we provide apparatus for launching an unmanned air vehicle or other projectile, comprising a flywheel and a drum or pulley coupled to the flywheel (preferably via a clutch) and a length of belting windable onto said drum or pulley as said drum or pulley rotates and being adapted to be releasably coupled to an unmanned air vehicle or other projectile to be launched.

Preferably the flywheel is coupled to a prime mover.

In the preferred embodiment described in detail hereinbelow with reference to the accompanying drawings, the drum or pulley is of the twin fusee type comprising a pay-out spool and a take-up spool mounted on the same axle, the belt passing from the pay-out spool over a remote single pulley connectable to the unmanned vehicle or other projectile to be launched before passing back to the take-up spool.

As will be appreciated, other pulley systems with differing mechanical advantage could be substituted.

The invention is hereinafter more particularly described with reference to the accompanying generally schematic drawing, the single figure of which shows the preferred embodiment of apparatus constructed in accordance with the present invention.

Referring to the drawing, a prime mover 1 (which may take any convenient form) is coupled by belt and gearing to a flywheel 3. Flywheel 3 is connectable to a drum or pulley (here a pulley) 4 via a clutch 5 of suitable torque rating.

The flywheel 3 and pulley 4 are mounted on the same axle so that when the clutch is fully engaged, flywheel and pulley will rotate at the same speed. Pulley 4 is of the double fusee type comprising a take-up spool 6 and a pay-out spool 7. Relatively flat belting 8 is mounted on the pulley so that, as it is paid out from the pay-out spool 7, it is taken up on the take-up spool 6, passing over a remote single pulley 9 at a remote position. Pulley 9 is connectable to the load such as the unmanned air vehicle or other projectile. The belt is preferably flat and should be of suitable tensile strength and flexibility so as to take the strains produced and to wind on the pulley or drum. The belt preferably has a high compressive stiffness so as to maintain its thickness even under high tensile stress.

In an alternative, and somewhat similar arrangement, the twin fusee pulley is replaced by a single fusee pulley or drum, and in that case the remote end of the belting would simply be connectable to the load. It is deemed unnecessary to illustrate this alternative arrangement, the construction of which will be entirely clear from the above description taken together with the accompanying single figure of drawing showing the twin fusee arrangement.

If the relatively flat belting (alternatively described as a strap or tape) is wound on to a drum or pulley, the belt will accumulate and thereby increase the effective diameter of the drum or pulley as layer upon layer of belting is stored. The resultant effective increase in diameter provides for a continuous change in gearing as a considerable length (and therefore thickness of belting on the drum or pulley) of belt is wound on. When the drum is connected to a spinning flywheel, and the remote end of the belt is connected to the load such as the unmanned air vehicle or other projectile, this load is accelerated to a speed equal to the peripheral speed of the belt coil on the drum or pulley. For a constant flywheel speed, this would increase as belt is accumulated on the drum or pulley.

However, as energy is transferred to the accelerating mass, it is correspondingly lost from the flywheel, resulting in a progressive reduction in the rate of spin. By selection of the flywheel inertia, drum or pulley diameter, and thickness of the belt, we can provide for a smooth and continuous transfer of energy from the flywheel to the unmanned air vehicle or other projectile. In one contemplated embodiment, the belt thickness varies along its length and in this way we can achieve a virtually constant acceleration of the mass once the initial engagement of the flywheel to the drum has been effected.

With the single fusee or drum system, there may still be a significant initial jerk and the twin fusee system illustrated in the single figure of drawing and described in more detail below represents a significant improvement, even over the single pulley arrangement. The belt forms a loop from the pay-out spool through a pulley block releasably connected to the UAV or other projectile before passing back to the take-up spool. It will be appreciated that since both spools of the twin fusee pulley travel at the same speed and in the same direction the belt must be wound in opposite senses on the two spools so that rotation of the pulley winds belting off one spool and on to the other.If the belt were of zero thickness, and both spools of the pulley had equal effective diameter, rotation of the pulley would simply transfer belt from one spool to the other with no effect on the load. However, the belt does have a finite thickness and so the effective diameter of the pay-out spool will reduce whereas the effective diameter of the take-up spool will increase with rotation. The subsequent difference between pay-out and take-up is a shortening of the belt loop and consequent acceleration of the load. With the double fusee system we can virtually eliminate the potentially damaging initial snatch or jerk by arranging for the effective diameter of both spools to be initially the same. This represents a significant improvement even over the single fusee or drum arrangement discussed above.Since the effective spool diameters change in opposite senses, the gearing effect which results from the thickness of belt on the drum is enhanced. By graduating the belt thickness or joining lengths of progressively thicker belting together to effect step changes at optimal points in the travel, we can enhance this effect.

In one practical embodiment, we employ two spools with an initial 500mm effective diameter, one spool (the pay-out spool) containing 78m of 2.5mm thick belt, and the other (the take-up spool) having an initial empty 500mm diameter.

The pulley was connected to a 40kg/m2 flywheel spinning at 1000 rpm and the belt loop was attached to a 750kg projectile. The resultant energy transfer resulted in a 32m/s terminal velocity of the mass after a travel of 57m.

This gave a resultant peak acceleration of less than twice the acceleration due to gravity with virtually zero jerk at the start of launch.

Claims

CLAIMS:

1. Apparatus for launching an unmanned air vehicle or other projectile, comprising a flywheel and a drum or pulley coupled to the flywheel, and a length of belting windable on to said drum or pulley as said drum or pulley rotates and being adapted to be releasably coupled to an unmanned air vehicle or other projectile to be launched.

2. Apparatus according to Claim 1, wherein the drum or pulley is coupled to the flywheel via a clutch.

3. Apparatus according to Claim 1 or Claim 2, wherein the flywheel is coupled to a prime mover.

4. Apparatus according to any preceding Claim, wherein the drum or pulley is of the twin fusee type comprising a pay-out spool and a take-up spool mounted on the same axle, the belting passing from the pay-out spool over a remote single pulley connectable to the unmanned vehicle or other projectile to be launched before passing back to the take-up spool.

5. Apparatus according to any preceding Claim, wherein the belting is generally flat, the arrangement being such that, as the belting is wound on to the drum or pulley, the belting accumulates and thereby increases the effective diameter of the drum or pulley as layer upon layer of belting is stored resulting in a continuously changing gearing as a substantial length of belting is wound on said drum or pulley.

6. Apparatus according to Claim 5, wherein the thickness of the belting varies along its length so that the apparatus in use can achieve a virtually constant acceleration of the unmanned air vehicle or other projectile once initial engagement of the flywheel to the drum has been effected.

7. Apparatus for launching an unmanned air vehicle or other projectile, substantially as hereinbefore described with reference to and as shown in the accompanying drawing