GB2077399A

GB2077399A - Missile accuracy improvement

Info

Publication number: GB2077399A
Application number: GB8115013A
Authority: GB
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1980-05-20
Filing date: 1981-05-15
Publication date: 1981-12-16
Also published as: BE888869A

Abstract

A weapon system for launching a missile 1 from an airborne helicopter 3 includes launching means 2 associated with the helicopter and a missile, the missile having stabilising fins 5 and means (6, 7) to render the fins inoperative during a predetermined flight period subsequent to launch of the missile when the missile passes through at least a major portion of the disturbed flow associated with the wash of the helicopter rotor 4 after which said means (6, 7) are actuated to allow the fins to become operational. The means rendering the fins inoperative may comprise a sleeve 6 attached to a lanyard 7, or a sleeve or band formed of combustible or ablative material. <IMAGE>

Description

SPECIFICATION Missile accuracy improvement This invention relates to the improvement of accuracy of missiles launched from helicopters, the missiles being of the unguided but fin stabilised type.

Hitherto when such missiles have been launched from helicopters their accuracy has been poor. This is known largely to be due to the disturbed flow associated with the helicopter rotor wash reacting with the stabilising fins at a time when the missile is particularly susceptible to disturbances and thus causing the missile to materially diverge from its desired flight path; since the missiles are unguided, once they have diverged their course cannot be corrected even when clear of the distrubed flow. Moreover, if the missiles are angularly displaced they will continue to diverge from the desired flight path.

According to one aspect of this invention, there is provided a weapon system for launching a missile from a helicopter when airborne which includes launching means associated with the helicopter and a missile, the missile having stabilising fins and means to render the fins inoperative during a predetermined flight period subsequent to launching of the missile from the helicopter in which the missile passes through at least a major portion of the disturbed flow associated with the helicopter rotor wash after which said means are actuated to allow the fins to become operational.

In one embodiment, the fins of the missile are deployable between an inoperative retracted position and an operational extended position and said means render fins inoperative by retaining them in a retracted position. In an alternative embodiment, the missile has fixed fins and said means render the fins inoperative by preventing their exposure.

The means to render the fins inoperative may be actuated by lanyard means, one end of which is secured to a part of the helicopter, the other end of which is secured to an actuation position of said means, the length of the lanyard being such that the means are actuated after the missile has passed through a major portion of the helicopter rotor wash. Alternatively said means may include retardation means adpated to effect actuation of said means after elapse of a sufficient period of time for the missile to pass through a major portion of the helicopterdownwash. Said means may conveniently include a sleeve which surrounds the fins to render them inoperative.In this case, the sleeve may be of an ablatable material and the missile may be propelled through at least a portion of its flight by means of a rocket, the efflux of said rocket acting to ablate said sleeve.

In another arrangement, said means may include restraining band means adpated initially to retain the fins in a retracted position.

In another aspect of this invention, there is provided a method of improving the accuracy of an unguided missile when launched from a helicopter, said missile including a plurality of fins, which includes the steps of: (a) rendering the fins inoperative during launch; (b) maintaining the fins inoperative for a predetermined flight period subsequent to launch during which the missile passes through at least a major portion of the disturbed flow associated with the helicopter rotor wash, and (c) subsequently allowing the fins to become operative for flight stabilisation.

Some examples of the invention are described with reference to the accompanying drawings in which Figure 1 is a representation of a folding fin missile, with means for temporarily rendering the fins inoperative, being launched from a helicopter, not necessarily to scale, Figure 2 is a view of the rear part of a folding fin missile showing alternative means for rendering the fins inoperative, Figure 3 is a similar view of a folding fin missile showing further alternative means for rendering the fins inoperative, and Figure 4 is a similar view showing a fixed fin missile with means for rendering the fin inoperative.

Referring to Figure 1 a rocket powered, unguided but fin stabilised missile 1 is required to be launched from a launcher 2 carried by a helicopter 3. The helicopter has a rotor shown generally at 4, the wash from which creates a region of disturbed air flow. The missile 1 must travel through this flow on its way to a target. Particularly when the helicopter is at low forward speed or in hover this disturbed flow is found to cause the launched missile to diverge from its desired flight path.

It is thought that the divergence is caused by the disturbed flow reacting with the stabilising fins of the missile since the fins are exposed to the air flow in the critical early stages of flight after launch. Even when, as shown in Figures 1, 2 and 3, the missile 1 has folding fins 5 instead of fixed fins, which are folded for housing within the launcher 4 and unfolded subsequent to leaving it for stabilisation purposes, it is found that the fins unfold too early to clear the disturbed flow. Means are accordingly provided to render the fins, whether fixed or folding, inoperative for a predetermined period subsequent to the missile leaving the launcher.

In Figure 1 wherein the missile has folding fins 5, such means take the form of a restraining sleeve 6 which fits around the previously folded fins and a lanyard 7 connected between it and the launcher, the length of the lanyard being such that the sleeve 6 is drawn away from the missile to allow fin unfolding at a predetermined distance from the helicopter, this distance being determined by the characteristics of both the region of influence of the rotor wash and the intial flight of the missile.

In Figure 2, wherein the missile again has folding fins 5, such means take the form of a restraining band 8 holding the fins in the folded condition, the band being cut by burning and/or the ablative effects of rocket exhaust or mechanically by a time delay actuated guillotine. It may also be removed by a lanyard similar to that referenced 7.

In Figure 3, wherein the missile again has foldable fins 5, a sleeve 9 of combustible and/or ablatable material could be used to hold the fins in the folded condition. If the sleeve is of non combustibie material and is therefore similar to that referenced 6, it could be ejected mechanically after a suitable delay or removed after the manner of Figure 1.

In Figure 4, wherein the missile has fixed fins 10, a covering sheath is provided to render the fins inoperative by shielding them from any transverse airflow, the sheath being removable by any of the methods previously mentioned. Naturally such a sheath when used with folding fins may advantageously reduce any residual effectiveness the fins may have when folded.

The embodiments described with reference to the figures are exemplary only: many other ways of delaying the effectiveness of fins are possible.

For example, the unfolding of fins or the removal of a sheath may be delayed by dashpot means, fusible plug means in a gas supply duct, cordite charge, or pyrotechnically delayed igniter means.

The matter is merely one of engineering choice depending largely on the design of the missile.

A typical delay for restraint or sheath removal from the fins is about 0.1 seconds after leaving the launcher, in distance about 5 meters.

During the first 5 meters of flight the average speed of a missile is about 60 m/sec. and the wash from the rotor is about 30 m/sec. The delay envisaged by the invention, after which the fins are rendered operative, is sufficient to allow the missile to clear at least the majority of the disturbed flow due to rotor wash and for the missile to have accelerated to a speed far greater than that of the disturbed flow.

Claims

1. A weapon system for launching a missile from a helicopter when airbourne which includes launching means associated with the helicopter and a missile, the missile having stabilizing fins and means to render the fins inoperative during a predetermined flight period subsequent to launching of the missile from the helicopter in which the missile passes through at least a major portion of the disturbed flow associated with the helicopter rotor wash after which said means are actuated to allow the fins to become operational.

2. A weapon system according to claim 1, wherein the fins of the missile are deployable between an inoperative retracted position and an operational extended position and said means render the fins inoperative by retaining them in a retracted position.

3. A weapon system according to claim 1, wherein the missile has fixed fins and said means render the fins inoperative by preventing their exposure.

4. A weapon system according to any of the preceding claims, wherein said means is actuated by lanyard means, one end of which is secured to a part of the helicopter, the other end of which is secured to an actuation position of said means, the length of the lanyard being such that the means are actuated after the missile has passed through a major portion of the helicopter rotor wash.

5. A weapon system according to any of claims 1 to 3, wherein said means include retardation means adapted to effect actuation of said means after elapse of a sufficient period of time for the missile to pass through a major portion of the helicopter downwash.

6. A weapon system according to any of the preceding claims, wherein the means includes a sleeve which surrounds the fins to render them inoperative.

7. A weapon system according to claim 6, wherein the sleeve is of an ablatable material and the missile is propelled through at least a portion of its flight by means of a rocket, the efflux of said rocket acting to ablate said sleeve.

8. A weapon system according to claim 2, wherein said means includes restraining band means adapted initially to retain the fins in a retracted position.

9. A method of improving the accuracy of an unguided missile when launched from a helicopter, said missile including a plurality of fins, which includes the steps of: (a) rendering the fins inoperative during launch; (b) maintaining the fins inoperative for a predetermined flight period subsequent to launch during which the missile passes through at least a major portion of the disturbed flow associated with the helicopter rotor wash, and (c) subsequently allowing the fins to become operable for flight stabilization.

10. A weapon system substantially as hereinbefore described, with reference to, and as illustrated in, any of the accompanying drawings.

11. A method of improving the accuracy of an unguided missile when launched from a helicopter substantially as hereinbefore described, with reference to and as illustrated in, any of the accompanying drawings.