GB2362450A

GB2362450A - Explosive release unit

Info

Publication number: GB2362450A
Application number: GB8907526A
Authority: GB
Inventors: Robert Ronald Evans; Francis Richard Gordon
Original assignee: ML Aviation Ltd
Current assignee: ML Aviation Ltd
Priority date: 1988-04-13
Filing date: 1989-04-04
Publication date: 2001-11-21
Anticipated expiration: 2009-04-04
Also published as: GB8808712D0; IT8967242A0; SE8901327D0; DE3912079B3; GB8907526D0; GB2362450B; FR2894560A1

Abstract

For controlled release and ejection of stores from aircraft, one or more explosive release units are used, each comprising a combustion chamber (61, fig.1) for an explosive charge (62, fig.1) and a telescopic ram arranged to be extended by high pressure gases generated in the combustion chamber (61, fig.1) during explosion of the charge (62, fig.1). A variable orifice valve 6 is connected in a flow path between the combustion chamber (61, fig.1) and the inside of the ram 1. The variable orifice valve 6 has a needle 8 connected to the ram 1 and arranged so that when the ram is retracted the cross-sectional area of the orifice of the valve is small to throttle the pressure generated in the combustion chamber but, as the ram 1 extends, the cross-sectional area of the orifice is increased. Preferably, an annular chamber 22 is formed on the outside of the ram 1, and a valve (31, fig.6) and pressure storing chamber (30, fig.6) provide and introduce gas under pressure into the annular chamber 22 to retract the ram 1.

Description

2362450 Explosive Release Unit For controlled release and ejection of

stores from aircraft in flight it is usual for the aircraft to include one or more explosive release units by which the stores are carried and which, after being triggered, release the store and positively project it away from the aircraft. Such explosive release units typically include a telescoping ram assembly which, after the explosive charge is detonated, is extended rapidly to drive the store away from the aircraft. This ensures that the store does not get trapped by the airflow passing the aircraft and, for example, collide with the aircraft's tailplane. Store is collective term used to describe bombs, missiles, containers containing a number of weapons, supplies and other equipment suspended from a military aircraft and intended to be released in flight.

The forces applied by the explosive release unit to eject the store should ideally take account of the size, shape and weight of the store, its angle of ejection, the speed of the aircraft, and the mechanical strengths of both the local aircraft structure and of the easing or shell of the store. In practice care is taken that the explosive release unit does not impose too great a loading on the aircraft structure or the casing of the store to cause damage to either of them, and this condition is used to determine the maximum pressure that is applied to the telescopic ram assembly. To limit the pressure that is applied to the store by the explosive release unit the release unit typically includes one or more chokes arranged between the explosive charge and the telescopic ram. The chokes limit the maximum pressure that is applied to the telescopic ram and hence the maximum loading imposed on the casing of the store by the ram and the maximum reaction on the aircraft structure.

Such chokes are effective to limit the maximum loading that is applied to the store but also tend to limit the overall performance of the explosive release unit and limit the maximum ejection force that can be generated by the explosive release unit and hence the store separation velocity is similarly limited.

According to a first aspect of this invention an explosive release unit for ejecting a store from an aircraft in flight comprises a combustion chamber for an explosive charge, a telescopic ram arranged to be extended by high pressure gases generated in the combustion chamber during explosion of a charge, and a variable orifice valve connected in a flow path between the combustion chamber and the inside of the telescopic ram, the variable orifice valve having an operating member connected to the telescopic ram and arranged, so that, when the ram is retracted the cross-sectional area of the variable orifice of the valve is small to throttle the pressure generated in the combustion chamber but, as the ram extends, the cross-sectional area of the variable orifice is increased.

Thus, the variable orifice valve gradually increases the pressure that is applied to the inside of the telescopic ram as the ram is extended. This results in an increasing ejection load being applied to the store with the result that as the store is accelerated away from the aircraft the load applied to the inside of the ram is increased so further accelerating the store. With such an arrangement the pressure initially exerted by the explosive charge inside the combustion chamber is throttled into the ram and kept below a predetermined threshold and thus the initial force exerted by the ram on the store is kept below a threshold at which damage to the store occurs but, as the store begins to accelerate away from the aircraft and the pressure in the combustion chamber passes its peak, the choke progressively opens to increase the pressure inside the telescopic ram with the result that the ram maintains a high force on the casing of the store even though this is accelerating away from the aircraft. Thus, although the force exerted on the case of the store never exceeds a threshold value at which damage occurs the store is urged strongly away from the aircraft with the pressure exerted on the inside of the telescopic ram during ejection exceeding that which, at the start of ejection, would have been likely to have damaged the store. Preferably the profile of the increase in pressure of the telescoping ram is tailored to suit the particular store to be ejected. Thus, by varying the way in which the cross-sectional area of the variable orifice valve increases with extension of the telescopic ram it is possible to tailor the time profile of the ejection force generated by the explosive release unit to take account of the size, shape, weight, angle of deployment and speed of the aircraft on release and take account of the mechanical strength of the aircraft structure or the casing or shell of the store.

The variable orifice valve may be formed by a cylinder having a number of apertures arranged along its length and a piston being a sliding fit inside the cylinder and being connected to the telescoping ram so that, as the ram is extended the piston moves along the cylinder so exposing an increasing number of apertures in the side wall of the cylinder and thus increasing the available cross-sectional area through.which gas can flow through the cylinder and hence through the valve.

Alternatively the variable orifice valve has the form of a needle valve with a shaped needle connected to the telescoping ram and located in an aperture of fixed size. As the telescopic ram is extended, the shaped needle is withdrawn from the aperture and thus, the cross-sectional area of the aperture increases as the needle is withdrawn.

According to a second aspect of this invention an explosive release unit includes a telescopic ram the telescoping sections of which include interengaging longitudinally extending splines to prevent mutual rotation of the telescoping sections during extension and retraction.

The longitudinally extending splines may be located on adjacent surfaces of two adjacent telescoping sections or, alternatively, they may be formed on one of the telescoping sections and a fixed part of the housing of the explosive release unit remote from the telescoping section. The interengaging splines prevent relative rotation between the telescopic sections. This is of prime importance when yokes are fitted to the ram ends for missle ejection since it ensures that the yoke is fitted in a defined angular position. The splines ensure the fixed orientation of the yokes during retraction. 20 Preferably the telescoping ram is retracted by gas pressure and, in this case, an annular chamber with sliding seals is formed on the outside of the ram between adjacent telescoping sections and the explosive release unit includes means to provide and introduce gas under pressure into the annular chamber formed between adjacent telescoping sections to retract the telescoping ram assembly. According to a third aspect of this invention an explosive release unit comprises a combustion chamber for an explosive charge, a telescopic ram arranged to be extended by the introduction of high pressure gases generated in the combustion chamber during explosion of the charge into the inside of the telescopic ram, an annular chamber with axially sliding seals formed on the outside of the telescopic ram between adjacent sections, a pressure storing chamber for storing high pressure generated in the combustion chamber during explosion of the charge, and a valve connected between the combustion chamber, the pressure storing chamber and the annular chamber and having a pressure responsive closure member which is movable between one position in which it shuts off communication between the combustion chamber and the pressure storage chamber and another position in which it shuts off communication between the pressure storage chamber and the annular chamber, the arrangement being such that explosion of the charge in the combustion chamber drives the valve closure member into its other position so that high pressure gases generated in the combustion chamber are introduced and stored in the pressure storage chamber and then, in response to the pressure in the combustion chamber falling, the valve closure member moves to its one position to connect the pressure storage chamber with the annular chamber so that the high pressure stored in the pressure storage chamber is applied to the annular chamber to cause retraction of the telescopic ram.

Preferably the telescopic ram includes a vent which is opened when the telescopic ram is fully extended to vent the inside of the telescopic ram to the atmosphere.

Preferably the vent includes a pin which is urged outwards by the pressure inside the ram and which, in use, engages the surface of the store carried by the explosive release unit so that, when the ram is fully extended and the store is released the pin is then free to move outward under the pressure inside the ram to open the vent and release the pressure from the inside of the telescopic ram.

Preferably the ram includes a housing fixed to the aircraft and at least two axially slidable telescoping sections. In this case preferably the annular chamber is formed between the housing and a first axially slidable telescoping section. Further, it is preferred that the operating member of the variable orifice valve is connected to the innermost sliding telescoping section.

The explosive release unit may also include a spring connected between two of the telescoping portions or one of the telescoping portions and the fixed housing of the explosive release unit to retract the ram. Preferably an explosive release unit includes all three aspects of the present invention.

Preferably the explosive release unit also includes a hook release system of conventional design and the combustion chamber is also connected to a hook release linkage actuated piston and cylinder assembly so that, when the explosive charge is triggered the piston and cylinder initially actuates the hook release linkage to release suspension hooks by which the store is connected to the aircraft.

A particular example of an explosive release unit in accordance with the various aspects of this invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a block diagram of an explosive release unit; Figure 2 is a partly sectioned side elevation of a telescopic ram assembly in a retracted position; Figure 3 is a partly sectioned side elevation of a telescopic ram assembly partly extended; Figure 4 is a partly sectioned side elevation of a telescopic ram assembly fully extended; Figure 5 is a partly sectioned side elevation of a telescopic ram assembly vented to the atmosphere; Figure 6 is a partly sectioned side elevation of a pressure storage chamber and valve during charging; Figure 7 is a partly sectioned side elevation of a pressure storage chamber and valve during discharge and retraction; and, Figure 8 is a partly sectioned side elevation of an alternative variable orifice valve drawn to a larger scale.

This example of explosive release unit includes two similar telescopic ram assemblies 1, a combustion chamber 61 containing three pyrotechnic cartridges 62, a pressure storage chamber and valve assembly 2, and a suspension hook assembly 63. The combustion chamber 62 and suspension hook assembly 63 are conventional in construction and will not be described in detail. The telescopic ram assemblies I each comprise a housing 3 fixed to the airframe of the aircraft, an inner sliding piston 4 and an outer sliding piston 5. A variable orifice valve assembly 6 formed by a valve housing 7 and throttle insert 60 connected to the housing I and a shaped needle 8 are located in the middle of the inner piston 4 and a vent valve 9 formed by a vent valve housing 10 and vent passage 11 formed in the lower end of the needle 8 are located at the bottom of the inner piston 4.

A tension spring 12 is connected between a spider 13 connected to the upper end of the outer piston 5 and a spring holder 14 connected to the lower end of the inner piston 4. Sliding seals 15 and 16 form axial sliding seals between the housing 3 and the outer piston 5 and further sliding seals 17 form axial sliding seals between the inner piston 4 and outer piston 5. Interengaged axially extending splines 18 and 19 formed on the inner piston 4 and outer piston 5 respectively prevent relative rotation between the inner and outer pistons. Further, elongate axially extending splines 20 and 21 formed on the spider 13 and valve housing 7 respectively prevent rotation of the outer piston 5 with respect to the housing and hence with respect to the airframe. The outside surface of the outer piston 5 is relieved to form an annular chamber 22 which is also sealed by the axially sliding seals 15 and 16 and this outer annular chamber 22 communicates via port 23 and inlet 24 with the pressure storage chamber and valve assembly 2. The combustion chamber is connected to an inlet port 25 and then via a feed pipe 26 to a central portion of the valve housing 7.

In use a yoke 28, shown in chain dotted lines and arranged to fit the store 29 to be handled is connected to the lower end of the inner piston 4 and held in place by the vent valve housing 10. The particular profile of the upper end of the needle 8 is also arranged to suit the particular store 29 being handled by the explosive release unit. When changing the type of store to be dropped by the aircraft the armourer merely unscrews the vent valve housing 10 and the yoke 28 and then replaces these components with those designed for a different store or, can merely remove the vent valve housing 10 and needle 8 and then change the needle 8 for a different type before replacing the valve housing 10.

The pressure storage chamber and valve mechanism 2 shown most clearly in Figures 6 and 7 comprises a pressure storage chamber 301, and a side ported shuttle valve 31 having a lower end 32 which closes a lower valve seat 33 which terminates an inlet passage 34 leading from the combustion chamber. The side port 35 in the shuttle valve is connected via port 37 to the inside of the pressure storage chamber 30. The shuttle 31 is urged downwards so that its end 32 is driven against seat 33 by a compressi on spring 38. The other end 39 of the shuttle 31 forms a seal with a valve seal 40 which communicates via pipe line 41 with inlet 24 of the telescopic ram assemblies 1.

Assuming initially that no pyrotechnic cartridges 62 are fitted to the combustion chamber 61 and the combustion chamber 61 is open to the atmosphere, to load the store the yoke 28 and piston assembly are manually extended to the full extent of the outer piston stroke: the spring loaded inner piston remains in the unextended, i.e. retracted, position. The store 29 may then be located onto the extended yoke 28, and, engaging the anti-rotation abutments, raised into its flight position guided by the yokes 28. Engagement of store 29 to yoke 28 raises the protruding exhaust/needle valve 11 into its upper sealing position. The hooks 64 and wedges, not shown, of the locking mechanism 63 are then either manually or automatically closed around suspension hooks or lugs 65 on the store. Note that adjustments may easily be made to the orientation of the store whilst maintaining lateral stability between its loading points. This is of great importance when loading conformal stores, i.e. stores partly contained in the profile of the aircraft and those which are fitted with offset, or open-sided rail suspension lugs. Once the store is loaded into position the pyrotechnic cartridges 62 are fitted into the cartridge holders and screwed into the breeches. In this example three cartridges 62 are used.

In use all three cartridges 62 are fired simultaneously.

To release the store the pyrotechnic cartridges are fired which causes a build-up of pressure in the combustion chamber 61 and the build-up of presure in inlet pipe 25 and feed pipe 26; and in inlet 34 of the pressure storage chamber and valve assembly via connecting pipe 66. This build up of pressure also operates the hook release linkage actuator piston and cylinder assembly 67 to open both suspension hooks 64 simultaneously as the piston head strikes the lobe 68 of the release system actuator cam and drives it against its compression load into its over-centre position. Rotation of an attached bell crank is transmitted by a mechanical link to open both the fore and aft suspension hooks64. The mechanical linkage is illustrated only diagrammatically in Figure 1. As soon as the pressure in the inlet 34 acting on the end 33 of the shuttle valve 31 is sufficient to overcome the bias of the spring 38 the shuttle moves upwards so seating the end 39 against the valve seat 40 and opening a passageway from the inlet 34 via the side port 37 between the combustion chamber and the pressure storage chamber 30 to build up pressure inside the pressure storage chamber 30 and to isolate the chamber 30 from venting.

The high pressure gas in the feed pipe 26 is introduced into the centre of the valve housing 7. A small amount bleeds past the annular orifice defined by the shaped needle 8 and throttle insert 60 to increase the pressure inside the telescopic ram assemblies I causing the pistons to move downwards. As the outer and inner piston assemblies together move downwards so does the needle 8 thus varying the cross-sectional area of the annular orifice defined between the needle and its seat and so, subsequently, allowing a greater quantity of high pressure gas to flow through the variable orifice valve 6. This higher pressure gas then exerts a greater thrust on the piston assemblies and in turn on the store 29 to thrust it away from the airframe. Further movement of the piston assemblies pulls the needle 8 to the end of the valve housing 7. This is the position shown in Figure 3 when the outer piston 5 is fully extended and abuts retaining ring 29.

Continuing pressure acting inside the telescopic ram I then continues to urge the inner piston 4 downwards. After the needle 8 has left the lower end of the valve housing 7 the full pressure inside the combustion chamber is applied to the inside of the telescopic ram assembly to cause maximum acceleration of the telescopic ram assembly 1. The outer piston 5 is prevented from rotating with respect to the housing I by the interengaged splines 20 and 21. This interengagement continues as the outer piston 5 moves with the splines 20 on the spider 13 continuing their interengagement with the spline 21 formed on the outside of the valve housing 7. This process continues until a shoulder on the outside of the outer piston 5 engages a piston retaining sleeve fixed in the end of the housing 2 and carrying the axial sliding seal 16. This is the maximum extension of the telescopic ram and is shown in Figure 4. A choke 69 may be provided in the line connecting the two telescopic rams so that a differential pressure is applied to them. In this way, with a higher pressure applied to the forward ram the store can be launched with a nose-down orientation. The acceleration that has then been applied to the store 29 results in the store having sufficient momentum to continue moving away from the aircraft. As the store moves away from the end of the needle 8 the gas pressure inside the telescoping ram acting on the needle 8 causes it to move downwards into the position shown in Figure 5. In this position then passageway 11 is in communciation both with the inside of the telescopic ram and with the atmosphere and this vents the high pressure from inside the telescopic ram and, in turn, from the combustion chamber 61 to atmosphere. As this high pressure is vented to the atmosphere the spring 38 urges the shuttle valve 31 downwards once again to seat its end 32 against the seat 33 and so shut off communication between the inside of the pressure storage chamber 30 and the combustion chamber.

With no gas pressure inside the telescopic ram 1 to 35 hold the ram into its extended position the spring 12 expanded during the inner piston extension phase and acting between the spider 13 and the spring retainer 14 connected to the lower end of the inner piston 4 pulls the piston inner 4 upwards retracting into the outer piston 5. Again the axial sliding motion of the piston 4 relative to the piston 5 is controlled by the interengaging splines 18 and 19 to prevent relative rotation. Simultaneously as the one end 33 of the shuttle valve 31 seats on seat 32 the end 39 of the shuttle valve moves away from the seat 40 to open a communication passage between the inside of the pressure storage chamber 30, the port 37, the seat 40 and an outlet pipe 41 to the inlet 24 in the housing 1 of the telescopic rams. Thus the pressure stored in the pressure storage chamber 30 is then applied to the annular chamber 22 formed on the outside of the outer piston 5. This pressure acts against the shoulder to drive the piston 5 upwards into the housing 1. This thus retra,cts the outer piston 5 into the housing 1 to return the telescopic ram to the configuration shown in Figure 2 except for the fact that the needle 8 is in its lowermost position with respect to the exhaust valve housing 10 as shown in Figure 5.

Figure 8 shows an alternative variable orifice valve arrangement. In Figure 8 the valve housing 71 includes a number of orifices 51, 52, 53, 54 and 55 in its side wall. The needle 8 in the first example is replaced by a piston 8' which is connected via a piston rod 59 to the exhaust valve assembly 9. Apart from these changes the remainder of the telescopic ram assembly 1 is the same.

In use, as the pressure in the combustion chamber builds up after firing of the pyrotechnic cartridges 62 the high pressure gas from the feed pipe 26 acts on the top face of the piston 8' and leaks around the sides of the piston 8' between the piston 81 and the valve housing 71 to increase the pressure on the inside of the telescopic tube assembly. As the pressure builds up and the inner piston 4 starts to move downwards the piston 81 moves past the orifices 50. The orifices 50 increase the flow path betwen the volume above the piston 8' and the inside of the telescopic ram so allowing the pressure inside the ram to build up more rapidly. This process is repeated for the orifices 51, 52, 53, in turn until the piston 81 leaves the valve housing 7' as the outer piston 5 is moving along the housing 1. In this example it would be necessary to exchange the valve housing 7' to change the extens ion/pres sure profile of the telescopic rams.

Claims

1. An explosive release unit for ejecting a store from an aircraft in flight comprising a combustion chamber for an explosive charge, a telescopic ram arranged to be extended by high pressure gases generated in the combustion chamber during explosion of a charge, and a variable orifice valve connected in the flow path between the combustion chamber and the inside of the telescopic ram, the variable orifice valve having an operating member connected to the telescopic ram and arranged, so that, when the ram is retracted the cross-sectional area of the variable orifice of the valve is small to throttle the pressure generated in the combustion chamber but, as the ram extends, the cross-sectional area of the variable orifice increases.

2. An explosive release unit according to claim 1, in which the variable orifice valve is formed by a cylinder having a number of apertures arranged along its length and a piston being a sliding fit inside the cylinder and being connected to the telescopic ram so that, as the ram is extended the piston moves along the cylinder so exposing an increasing number of apertures in the side wall of the cylinder and thus increasing the available cross- sectional area through which gas can flow through the cylinder and hence through the valve.

3. An explosive release unit according to claim 1, in which the variable orifice valve has the form of a needle valve with a shaped needle connected to the telescopic ram and located in an aperture of fixed size, in use, as the telescopic ram is extended, the shaped needle is withdrawn from the aperture and thus, the cross-sectional area of the aperture increases as the needle is withdrawn.

4. An explosive release unit according to any one of the preceding claims, in which the telescoping sections of the telescopic ram include interengaging extending splines to prevent mutual rotation of the telescoping sections during extension and retraction.

5. An explosive release unit including a telescopic ram the telescoping sections of which include interengaging logitudinally extending splines to prevent mutual rotation of the telescoping sections during extension and retraction.

6. An explosive release unit according to any one of the preceding claims, in which the telescopic ram is retracted by gas pressure and, in which, an annular chamber with sliding seals is formed on the outside of the ram between adjacent telescoping sections, the explosive release unit further including means to provide and introduce gas under pressure into the annular chamber formed between adjacent telescoping sections to retract the telescopic ram assembly.

7. An explosive release unit comprising a combustion chamber for an explosive charge, a telescopic ram arranged to be extended by the introduction of high pressure gases generated in the combustion chamber during explosion of the charge into the inside of the telescopic ram, an annular chamber with axially sliding seals formed on the outside of the telescopic ram between adjacent sections, a pressure storing chamber for storing high pressure generated in the combustion chamber during explosion of the charge, and a valve connected between the combustion chamber, the pressure storing chamber and the annular chamber and having a pressure responsive closure member which is movable between one position in which it shuts off communication between the combustion chamber and the pressure storage chamber and another lonaitudinallv position in which it shuts off communication between the pressure storage chamber and the annular chamber, the arrangement being such that explosion of the charge in the combustion chamber drives the valve closure member into its other position so that high pressure gases generated in the combustion chamber are introduced and stored in the pressure storage chamber and then, in response to the pressure in the combustion chamber falling, the valve closure member moves to its one position to connect the pressure storage chamber with the annular chamber so that the high pressure stored in the pressure storage chamber is applied to the annular chamber to cause retraction of the telescopic ram.

8. An explosive release unit according to claim 6 or 7, 15 in which the ram includes a housing for fixing to an aircraft and at least two axially slidable telescoping sections, in which the annular chamber is formed between the housing and a first axially slidable telescoping section, and in which the operating member of the variable orifice valve is connected to the innermost sliding telescoping section.

9. An explosive release unit according to claim 8, which also includes a spring connected between two of the telescoping portions or one of the telescoping portions and the fixed housing of the explosive release unit to retract the ram.

10. An explosive release unit according to any one of the preceding claims, in which the telescopic ram includes a vent which is opened when the telescopic ram is fully extended to vent the inside of the telescopic ram to the atmosphere.

An explosive release unit according to claim 10, in which the vent includes a pin which is urged outwards by the pressure inside the ram and which, in use, engages the surface of the store carried by the explosive release unit so that, when the ram is fully extended and the store is released the pin is then free to move outward under the pressure inside the ram to open the vent and release the pressure from the inside of the telescopic 5 ram.

12. An explosive release unit according to any one of the preceding claims, which also includes a hook release system of conventional design and in which the combustion chamber is also connected to a hook release linkage piston and cylinder actuator so that, when the explosive charge is triggered the piston and cylinder actuator initially actuates the hook release linkage to release suspension hooks by which the store is connected to the aircraft.

13. An explosive release unit substantially as described with reference to the accompanying drawings.

d Amendments to the claims have been filed as follows 1. An explosive release unit for ejecting a store from an aircraft in flight comprising a combustion chamber for an explosive charge, a telescopic ram arranged to be extended by high pressure gases generated in the combustion chamber during explosion of a charge, and a variable orifice valve connected in the flow path between the combustion cham-er and the inside of the telescopic ram, the variable orifice valve having an operating member connected to the telescopic ram and arranged, so that, when the ram is retracted the cross-sectional area of the variable orifice of the valve is small to throttle the pressure generated in the combustion chamber but, as the ram extends, the cross-sectional area of the variable orifice increases.

10\ 4. An explosive release unit according to any one of the preceding claims, in which the telescoping sections of the telescopic. ram include interengaging longitudinally extending splines to prevent mutual rotation of the telescoping sections during extension and retraction.

5. An explosive release unit according to any one of the preceding claims, in which the telescopic ram is retracted by gas pressure and, in which, an annular chamber with sliding seals is formed on the outside of the ram between adjacent telescoping sections, the explosive release unit further including means to provide and introduce gas under pressure into the annular chamber formed between adjacent telescoping sections to retract the telescopic ram assembly.

6. An explosive release unit according to claim 5, in which the ram includes a housing for fixing to an aircraft and at least two axially slidable telescoping sections, in which the annular chamber is formed between the housing and a first axially slidable telescoping section, and in which the operating member of the variable orifice valve is connected to the innermost sliding telescoping section.

7. An explosive release unit according to claim 6, which also includes a spring connected between two of the telescoping' portions or one of the telescoping portions and the fixed housing of the explosive release unit to retract the ram.

8. An explosive release unit according to any one of the preceding claims, in which the telescopic ram includes a vent which is opened when the telescopic ram is fully extended to vent the inside of the telescopic ram to the atmosphere.

9. An explosive release unit according to claim 8, in which the vent includes a pin which is urged outwards by the pressure inside the ram and which, in use, engages the surface of the store carried by the explosive release unit so that, when the ram is fully extended and the store is released the pin is then free to move outward under the pressure inside the ram 0 to open the vent and release the pressure from the inside of the telescopic ram.

10. An explosive release unit according to any one of the preceding claims, which also includes ahook release system of conventional design and in which the combustion chamber is also connected to a hook release linkage piston and cylinder actuator so that, when the the piston and cylinder the hook release linkage bv which the store is explos,ive charge is triggered actuator initially actuates to release suspension hooks connected to the aircraft.

11. An explosive release unit substantially as described with reference to the accompanying drawings.

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