GB2432650A

GB2432650A - Missiles

Info

Publication number: GB2432650A
Application number: GB8228426A
Authority: GB
Inventors: Ronald Peter Bartlett; John Frank William Crane; Robert Gregory Daniels; David Houldcroft; Stanley Leek; Derek Herrington Peckham
Original assignee: British Aerospace PLC; UK Secretary of State for Defence; Matra Bae Dynamics UK Ltd; MBDA UK Ltd
Current assignee: BAE Systems PLC; Matra Bae Dynamics UK Ltd
Priority date: 1981-10-09
Filing date: 1982-10-05
Publication date: 2007-05-30
Anticipated expiration: 2002-10-05
Also published as: IT8249237A0; FR2897679A1; GB8228426D0; SE8205757D0; SE8205757A; GB2432650B

Abstract

A missile (10) having a longitudinal axis (11) parallel to a design direction of flight has a window (16) of radiation transmissive material aligned at an angle to the longitudinal axis, through which radiation emitting and/or receiving apparatus (17) eg. a passive infrared, semi-active laser or television device, may emit or receive radiation. When the missile is in flight, jet producing means, which may be in the form of a forward facing intake (19), air passage (20) and slit nozzle (21), produce a jet of fluid forwardly of the window (16) so that the airflow is caused to separate from the missile body upstream of the window and is prevented from reattaching in front of or on the window, so as to limit the aerodynamic heating of the window.

Description

MISSILES

The present invention relates to missiles of the type which carry radiation emitting and/or receiving apparatus, for example passive infra-red, semi-active laser or television devices.

Such apparatus must include a window transmissive to its activating signal (which might be, for example radar, visible light or infra-red radiation), through which a target may be viewed. The window is often located in the structure of the nose portion; at this location the window is subject, according to well-known aerodynamic laws, to aerodynamic heating. The amount of heating can be reduced by orienting the window at a relatively small angle with respect to the direction of motion of the missile. However, the angle between the window and the direction of motion is limited by the need for the target to be viewed through the window when the missile and the target are on, or are approaching collision courses.

The effect of aerodynamic heating is particularly important for missiles using infra-red detection apparatus.

The noise generated by an infra-red window increases with temperature, and a stage can be reached where the speed of the missile is limited by the noise generated by its window. Moreover, aerodynamic heating can lead to thermal stress, oxidation and even structural modification of the material of the window. In this last respect, where the window is to pass infra-red radiation, it could be made of Zinc Sulphide, but there is evidence that its lattice structure may alter at 6000 C. There is therefore a need to limit the aerodynamic heating of a window in a missile.

According to this invention, there is provided a missile having a longitudinal axis parallel to a design direction of steady flight, which includes a first surface extending rearwardly from a fore-portion of the missile, a second surface extending from the first surface at an angle to the longitudinal axis, the second surface including a window member of radiation transmissive material, jet producing means for producing a jet of fluid forwardly of the window member so that, in use, the local airflow over the missile body is caused to separate from the body up- stream of the window member and is prevented from re-attaching to the body in front of, or on the window member.

Preferably, the jet producing means includes an air intake facing forwardly relative to the design flight direction and connected by an air passage to a jet outlet located forward of the second surface.

The first surface is preferably plane and parallel to the longitudinal axis and the second surface is preferably plane.

The missile preferably further includes spaced side wall surfaces upstanding from the first surface which together with laid first and second surfaces define a recess, and the side wall surfaces may protrude from the local surface of the missile to assist stabilization.

Advantageously the air intake is arranged with respect to the jet outlet so that as the angle of incidence of the projected free stream on the window increases, so the mass flow through the air intake increases.

When the missile is intended for supersonic motion, the air passage is preferably arranged to reduce the supersonic flow through the air intake to a high pressure subsonic flow and thereafter to cause the flow to issue from the jet outlet at supersonic speed.

The fore-portion of the missile conveniently includes a fore-surface extending rearwardly from the apex of the missile, the rearmost edge of the fore-surface together with the foremost edge of the first surface defining said air intake.

The jet outlet is preferably in the form of a slit nozzle. The slit nozzle is preferably straight, but may alternatively be curved, and it may be disposed to direct air flow outwardly with respect to the first surface either substantially normally or at an angle relative to the longitudinal axis. The slit nozzle may comprise a single slit, or a plurality of slits.

-4' -The missile may include one or more further first and second surfaces and associated window members, symmetri-cally disposed about the longitudinal axis, further jet producing means being associated with the or each window member.

By way of example only, certain specific embodiments of this invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is an elevation, in section, of a forward part of a first embodiment of missile; Figure 2 is a plan view in the direction of Arrow Y in Figure 1; Figure 3 is an elevation in the direction of Arrow X in Figure 1; Figure 4 is a general perspective view of a forward part of a second form of missile; Figure 5 is an elevation, in section, of the part of the missile of Figure 4; Figure 6 is a plan view of the part of the missile of Figure 4; and Figure 7 is an elevation, in section, of a forward part of a third form of missile.

Referring initially to Figures 1 to 3, a guided missile, of which a forward part only is shown at 10, is of generally circular section normal to a longitudinal axis 11 except for a first plane surface 12 which extends rearwardly parallel to the axis 11 from adjacent a nose 13 and a second plane surface 14 which extends from the first surface 12 at an angle to the axis 11 (see Figure 1) to meet a main body 15 of the missile.

A window 16 translucent to infra-red light is positioned in the second plane surface 14. An infra-red sensor and missile control system, shown generally at 17, is positioned within the body 15.

A nose portion 18 extending from the nose 13 to the junction of first 12 and second 14 plane surfaces is of generally solid construction apart from a forward facing air intake 19 which is connected by an air passage 20 to a slit nozzle 21 in the first plane surface 12.

In use the missile is fired (from, for example, an aircraft) and is driven forward by drive means (not shown) in a direction parallel to the longitudinal axis 11.

Infra-red light passing through the window 16 is detected by the sensor and control system 17 which activates directional controls (not shown, but which might be, for example, aerodynamic surfaces or vectored thrust means,) which orientate the missile to head towards the strongest infra-red light source. Ram air passing through the air intake 19 passes via air passage 20 to slit nozzle 21 from which is ejected substantially normally relative to the longitudinal axis 11. In this way the airflow over surface 14 is modified to reduce aerodynamic heating of the window 16.

It will be realised that missile drive means, directional control means, and guidance means are all well-known in the art, as such form no part of the present invention, and are therefore not herein described. The invention has been described as for use with an infra-red guidance system, but it can of course be used for other guidance systems using, for example, radar or visible light.

It will also be realised that many variations of the embodiment herein described with reference to and illustrated in Figures 1 to 3. For example, it might be found advantageous to have a curved slit nozzle 21, to have slit nozzle 21 directing air other than normal to longitudinal axis 11, or both. The nose portion 18 might be hollow to contain, for example, an explosive warhead.

Referring now to Figures 4 to 6, the forward part 10 of a missile is provided with a recess 30, defined by a first plane surface 12, a second plane surface 14 upstand-ing therefrom, and spaced sidewalls 31 which protrude beyond the local surface of the forward part to give a stabilising effect to be described below.

The nose is formed as a chisel lip 32 having a ramp surface 33 extending rearwardly therefrom to form, with the foremost lip portion 34 of first plane surface 12 an air intake 19, to receive air under ram air pressure when the missile is in motion. An air passage 20 connects the intake with a slit nozzle 21 positioned so that, in use, fluid is exhausted outwardly with respect to the first plane surface 12 and substantially normal thereto.

The air passage 21 diminishes in cross-section to a minimum whence it increases in cross-section to provide a plenum chamber 35 within which the flow may be expanded.

When the missile is in supersonic flight, the full stream air passes through an oblique shock S,, attached to lip 32 and preferably also lying on lip 34, and is deflect-ed into air intake 19. The lip 34 is angled to the incident stream so that a second oblique shock S2 is generated from lip 34. The flow therefore passes into air passage 20 where it is decelerated to subsonic speed and then expands out into plenum chamber 35 until a normal shock S3 forms.

At this station, the supersonic flow has been reduced to a high pressure subsonic flow. The reduction in the super- sonic flow may have been achieved in three stages; alter-natively, there may be more or less changes depending on the particular design of the air passage. The flow is then turned through an angle to the longitudinal axis 11, enters a converging choke 36 and passes through a sonic throat at the slit nozzle 21 and emerges as an expanding supersonic jet, which is partly confined by side walls 31 to prevent lateral spillage and to seal the window oblique jet corner.

The jet causes the local airflow to be detached from the surface of the forward part 12 before it impinges upon window member 16 and prevents re-attachment of the airflow in front of or on the window 16, and consequently aero-dynamic heating can be reduced.

In the form of nose assembly shown in Figures 4 to 6, when the nose is pitched downwardly, the window 16 becomes more exposed to the airstreain and the tendency for aero-dynamic heating becomes greater. For this reason, the intake 19, which is depicted as a two-dimensional wedge type, is placed to the same side of the nose as the window 16, and located so that mass flow into the intake increases with nose down incidence.

It may be necessary to provide a variable geometry intake 19, to ensure good starting and efficient running.

This may be effected for example by causing pivotal move-ment of first surface 12 by means of a bi-metallic strip.

Since the nose is inclined to the longitudinal axis of the weapon, a small yaw of the missile will induce a rolling moment; this may be offset by the protruding portions of the side walls 31.

For some forms of flight vehicle, the intake/duct system may be replaced by gas supplied from an internal source; but for high speed missiles of a reasonable diameter, the total mass of gas required over the whole flight of the vehicle is generally too great.

Referring now to Figure 7, there is shown a nose assembly for a missile of relatively large diameter. In this case, two windows 16 are provided, with associated intakes 19, one to each side of the longitudinal axis 11 of the missile respectively. As illustrated, this could provide 1800 field of view and also would be aerodynami-cally symmetrical at zero degrees incidence and so would tend to reduce the overall zero incidence drag co-efficient.

As a further extension of this principle, the windows/intakes may be cylindrically symmetrical. In this case, the nose would be in the form of a cone and the window would be annular. In order to maximise the jet flow on the windward side of the missile, the intakes and air passages would have to be circumferentially partitioned so that cross flow between the air passages was prevented.

Claims

-10 -CLAIMS: 1. A missile having a longitudinal axis parallel to a

design direction of steady flight, which includes a first surface extending rearwardly from a fore-portion of the missile, a second surface extending from the first surface at an angle to the longitudinal axis, the second surface including a window member of radiation transmissive material, jet producing means for producing a jet of fluid forwardly of the window member so that, in use, the local airflow over the missile body is caused to separate from the body upstream of the window member and is prevented from re-attaching to the body in front of, or on the window member.

2. A missile according to Claim 1, wherein the jet producing means includes an air intake facing forwardly relative to the design flight direction and connected by an air passage to a jet outlet located forward of the second surface.

3. A missile according to Claim 1 or Claim 2, wherein the first surface is plane and parallel to the longitudinal axis.

4. A missile according to any of the preceding Claims, wherein the second surface is plane.

-11 - 5. A missile according to any of the preceding Claims, which further includes spaced side wall surfaces upstanding from the first surface which together with said first and second surfaces define a recess.

6. A missile according to Claim 5, wherein said side wall surfaces protrude from the local surface of the missile to assist stabilization.

7. A missile according to any of Claims 2 to 6, wherein the air intake is arranged with respect to the jet outlet so that as the angle of incidence of the projected free stream on the window increases, so the mass flow through the air intake increases.

8. A missile according to any of Claims 2 to 7, and intended for supersonic motion, wherein the air passage is is arranged to reduce the supersonic flow through the air intake to a high pressure subsonic flow and thereafter to cause the flow to issue from the jet outlet at supersonic speed.

9. A missile according to any of Claims 2 to 8, wherein the fore-portion of the missile includes a fore-surface extending rearwardly from the apex of the missile, the rearmost edge of the fore-surface together with the fore- -12 -most edge of the first surface defining said air intake.

10. A missile according to any of the preceding Claims, wherein the jet outlet is in the form of a slit nozzle provided in the first surface.

11. A missile according to Claim 10, wherein the slit nozzle is straight.

12. A missile according to any of the preceding Claims, wherein the jet producing means is arranged to produce a jet substantially normal to the longitudinal axis.

13. A missile according to any of the preceding Claims, wherein the missile includes one or more further first and second surfaces and associated window members, symmetrically disposed about the longitudinal axis, further jet producing means being associated with the or each window member.

14. A missile substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.

Amendments to the claims have been filed as follows 1. A missile having a longitudinal axis parallel to a design direction of steady flight, which includes a first surface extending rearwardly from a fore-portion of the missile, a second surface extending from the first surface at an angle to the longitudinal axis, the second surface including a window member of radiation transniissive material, jet producing means for producing a jet of fluid forwardly of the window member so that, in use, the local airflow over the missile body is caused to separate from the body upstream of the window member and is prevented from re-attaching to the body in front of, or on the window member.

2. A missile according to Claim 1, wherein the jet producing means includes an air intake facing forwardly relative to the design flight direction and connected by an air passage to a jet outlet located forward of the second surface.

3. A missile according to Claim 1 or Claim 2, wherein the first surface is plane and parallel to the longitudinal axis.

4. A missile according to any of the preceding Claims, wherein the second surface is plane.

LL

5. A missile according to any of the preceding Claims, which further includes spaced side wall surfaces upstanding from the first surface which together with said first and second surfaces define a recess.

6. A missile according to Claim 5, wherein said side wall surfaces protrude from the local surface of the missile to assist stabilization.

7. A missile according to any of Claims 2 to 6, wherein the air intake is arranged with respect to the jet outlet so that as the angle of incidence of the projected free stream on the window increases, so the mass flow through the air intake increases.

8. A missile according to any of Claims 2 to 7, and intended for supersonic motion, wherein the air passage is arranged to reduce the supersonic flow through the air intake to a high pressure subsonic flow and thereafter to cause the flow to issue from the jet outlet at supersonic speed.

9. A missile according to any of Claims 2 to 8, wherein the fore-portion of the missile includes a fore-surface extending rearwardly from the apex of the missile, the rearmost edge of the fore-surface together with the fore-most edge of the first surface defining said air intake.

10. A missile according to any of the preceding Claims, wherein the jet outlet is in the form of a slit nozzle provided in the first surface.

11. A missile according to Claim 10, wherein the slit nozzle is straight.

12. A missile according to any of the preceding Claims, wherein the jet producing means is arranged to produce a jet substantially normal to the longitudinal axis.

13. A missile according to any of the preceding Claims, wherein the missile includes one or more further first and second surfaces and associated window members, symmetrically disposed about the longitudinal axis, further jet producing means being associated with the or each window member.

14. A missile according to any of Claims 1 to 12, wherein said first surface comprises the surface of a cone and said second surface comprises a generally annular window member disposed coaxially with respect to said cone.

15. A missile substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.