MISSILE EXPULSION MOTOR

Abstract: An annular explusion motor (14) is secured around the main nozzle casing (12) of a missile by means of shear bolts (28). The expulsion motor expels and spins up the missile prior to ignition of the missile main motor whereupon the expulsion motor is jettisoned from the missile by the efflux of the main motor.

Description: This invention relates to an expulsion motor for a missile and to self-propelled missiles incorporating an expulsion motor. In many applications it is desirable to use a missile system in which the missile is initially launched from a launch tube by means of an expulsion motor prior to ignition of the missile main motor. For example when the missile is to be launched from a shoulder launcher it is necessary to ensure that the missile has been expelled from the container a safe distance away from the operator prior to ignition of the boost motor to avoid injury to the operator or damage to the equipment associated with the missile. A similar need may arise for helicopter launched missiles. In a conventional form of expulsion motor propulsive charges are located directly behind the missile but this arrangement means that a longer container launch tube is required for the missile. Other arrangements make use of a cannister attached to the missile and containing a propulsive charge. However, particularly where the missile is to accelerated to very high speeds by the boost motor, the mass associated with the empty cannister constitutes dead weight which must be accelerated together with the missile itself and consequently the velocity of the missile is reduced. U.S. Patent Specification US-A-2968245 discloses a spin cartridge releasably secured behind a missile, thus blocking the main propulsion outlet of the missile, and also increasing the length of the arrangement. U.S. Patent A-4198896 shows a two stage motor in which the rearward stage is arranged adjacent the aft end of the missile. However the rearward stage does not have a core region through which efflux from the forward motor may exhaust. U.S. Patent A-3167016 shows a two stage motor having an inner (main) motor and an outer (expulsion) motor surrounding the inner motor. The outer motor includes a spherical segment aft of the main motor outlet. The expulsion motor does not include a core region through which efflux may exhaust. According to one aspect of the invention there is provided a missile including a main body, a propulsion motor, a propulsion outlet in the aft end region of the main body for exhausting the propulsion efflux rearwardly, and an expulsion motor separably arranged adjacent the main body for imparting a forward thrust thereto, the expulsion motor being of generally annular form surrounding said propulsion outlet and including a propellant charge and an expulsion outlet, wherein said expulsion motor includes a central core region through which propulsion efflux generated in use by said propulsion motor passes rearwardly to exhaust aft of said expulsion motor. By this arrangement it will be appreciated that the expulsion motor may be fitted around the missile main body structure, thus not contributing significantly to the axial length of the missile. Also the expulsion motor may be detached on ignition of the missile propulsion means so that energy is not used up in imparting further acceleration to the expended expulsion motor casing. Preferably, said expulsion motor outlet is adapted to cause fluid exhausting therefrom to have a tangential component of thrust thereby to impart to said missile a spin torque together with a forward thrust. Preferably, said expulsion motor includes obturator means disposed adjacent the rear end portion of said missile arranged such that said propulsion efflux impinges thereon and imparts sufficient rearward thrust on the expulsion motor to cause separation. According to another aspect of this invention, there is provided an expulsion motor for a missile of the type comprising a main body, a propulsion motor and a propulsion outlet in the aft end region of the main body for exhausting propulsion efflux rearwardly, said expulsion motor comprising a housing, a propellant charge contained within said housing, expulsion motor outlet means for exhausting efflux generated by said charge, and means for releasably attaching said expulsion motor to a missile wherein said expulsion motor is of generally annular form surrounding said propulsion outlet, defining a central core region through which propulsion efflux generated in use by said propulsion motor may pass. Further aspects will become apparent from the following description, which is by way of example only, reference being made to the accompanying drawings in which:- Figure 1 is a part-sectioned side view of the rearward portion of a missile showing the location of an expulsion motor; Figure 2 is a detailed longitudinal section view on the motor; Figure 3 is a rear end view of the expulsion motor of Figures 1 and 2, and Figure 4 is a front end view of the expulsion motor. The arrangement illustrated in the drawings is intended for expelling a high velocity missile from its launch container a sufficient distance from the launcher to allow its boost motor to be ignited safely, and for imparting spin to the missile to assist in stabilising the missile. Referring initially to Figure 1, there is shown the rear end of a missile. The missile includes a body portion 10 of generally cylindrical form housing at its rear end the main motor 11 of the missile and the main motor nozzle 12. Four fins 13 project transversely of the body and terminate a short distance away from the end of the missile. An expulsion motor assembly 14 of generally annular cross-section is located rearwardly of the fins and surrounds the end of the missile body. The assembly 14 comprises an outer tube 15 of high strength aluminium alloy overwrapped with Kevlar fibre 16 to resist hoop loads. The rear end of the outer tube 15 is locally thickened and internally threaded to receive an externally threaded nozzle plate 17 (see Figure 3) also of high strength aluminium alloy and which has two series of sixteen nozzle holes 18 on two pitch circle diameters. Alternate nozzles 18' on the outer pitch circle diameter are canted to impart a clockwise spin to the missile as viewed from the rear. The throats of the nozzle holes 18 may be treated or fitted with metal inserts to resist erosion. The nozzle plate 17 also includes a central aperture 19 having an annular lip 19' which protrudes into the efflux of the main missile motor 11 when ignited. The aperture 19 is internally threaded to receive the externally threaded rear end of the inner hollow cylindrical tube 20 of the expulsion motor. Referring now in particular to Figure 2, the forward end of the inner tube 20 passes through an aperture in the front end of the outer tube 15 and is externally threaded to engage an internally threaded locking ring 21 which locks the inner tube 20 to the outer tube 15 which is bottled over as shown. An annular collar 22 is secured to the outside of the locking ring by screws passing through the collar 22 into the locking ring. The forward surface of the collar 22 is castellated to provide four lugs 23. The missile is provided with a complementarily castellated collar 24 so that the torque induced by the canted nozzles 18' may be transferred from the expulsion motor casing to the missile body. The expulsion motor includes a propellant charge 25 and associated igniter 26 located between the inner and outer tubes and spaced from the nozzle plate by a spacer 27. During assembly the expulsion motor is slid over the end portion of the missile body and the complementary castellated collars 23 and 24 are engaged. The castellated collar of the expulsion motor is releasably attached to the missile body by means of four nylon shear screws 28 each passing through a lug 23 into the missile body. At launch, the propellant charge within the expulsion motor is ignited thus imparting both a forward thrust and a clockwise torque to the missile. The forward thrust and the torque are transmitted from the expulsion motor to the missile via the complementary castellated collars. After a predetermined delay, ignition of the main motor 11 occurs and the efflux generated thereby impinges on the annular collar 19 of the nozzle plate 17 thus applying a load which tends to drive the expulsion motor rearwardly with respect to the missile. The nylon shear screws 28 then break and the expulsion motor is jettisoned, with little or no forward velocity. In this arrangement, the expulsion motor surrounds a part of the missile body; thus it does not increase the length of the launch container required. In addition, the motor is of similar outside diameter to the fins and thus does not require a larger diameter container. The dead mass of the exhausted expulsion motor is jettisoned instantaneously with or shortly after ignition of the boost motor. Thus no thrust developed by the boost motor is expended in accelerating the exhausted expulsion motor.

Claims: A missile including a main body (10), a propulsion motor (11), a propulsion outlet (12) in the aft end region of the main body for exhausting the propulsion efflux rearwardly, and an expulsion motor (14) separably arranged adjacent the main body for imparting a forward thrust thereto, the expulsion motor (14) being of generally annular form surrounding said propulsion outlet (12), and including a propellant charge (25) and an expulsion outlet (18), characterised in that said expulsion motor is arranged adjacent the aft end region of the main body (10) and includes a central core region through which propulsion efflux generated in use by said propulsion motor (11) passes rearwardly to exhaust aft of said expulsion motor (14). A missile according to Claim 1, wherein said expulsion motor outlet (18) is formed to cause fluid exhausting therefrom to have a tangential component of thrust thereby to impart to said missile a spin torque. A missile according to Claim 1 or 2, wherein said expulsion motor (14) includes obturator means (19') disposed such that on actuation of said propulsion motor (11) said propulsive efflux impinges on and imparts sufficient rearward thrust on said obturator means to cause separation of said expulsion motor (14). A missile according to Claim 3, wherein said obturator means (19') projects inwardly adjacent the expulsion outlet (18). A missile according to Claim 3 or 4, wherein said obturator means (19) is selected having regard to the propulsive efflux such that on actuation of said propulsion means said expulsion motor (14) separates from the main body (10) with substantially reduced forward velocity. A missile according to any preceding Claim, wherein said expulsion motor (14) is releasably attached to said missile by means of frangible connection means (28). A missile according to any preceding Claim, wherein said expulsion motor (14) includes a castellated collar portion (23) for engaging a complementary castellated portion (24) on said main body (10). An expulsion motor (14) for a missile of the type comprising a main body (10), a propulsion motor (11) and a propulsion outlet (12) in the aft end region of the main body (10) for exhausting propulsion efflux rearwardly, said expulsion motor comprising a housing (15), a propellant charge (25) contained within said housing, expulsion motor outlet means (18) for exhausting efflux generated by said charge, and means (28, 23) for releasably attaching said expulsion motor to a missile, characterised in that said expulsion motor is of generally annular form surrounding said propulsion outlet (12), defining a central core region through propulsion efflux generated in use by said propulsion motor (11) may pass.

Inventors: DRANSFIELD, ALFRED EDWARD BRITISH AEROSPACE P.L.C., FENTON, GEORGE H.A. BRITISH AEROSPACE P.L.C.
Applicants: BRITISH AEROSPACE PUBLIC LIMITED COMPANY
Application year: 1986
Main classification: F42B15
IPC codes: F42B15, F02K9, F42B10