GB2240954A - Lock means for missile control fins - Google Patents

Abstract

Lock means for missile control fins 11 comprise a protruding lock pin 31 for engagement in a mating aperture 32 in the control fin 11 and moans for ensuring that the pin is not completely withdrawn from the aperture until fin actuator means is capable of stabilising the fin against operational loads. The fin is movable by fluid pressure (pneumatic) actuating means 14 including a control piston is in a cylinder 16 and a balance piston 17 in a cylinder 18, the pistons being connected to opposite ends of a lever 13 rigid with the fin 11. A spring 33 acting as a piston 29 carrying the pin 31 holds the pin in the aperture 32 until the pressure in chamber 35, which builds up with some delay after the supply line 21 is pressurized because of a restrictor 24 and small passage 37, is sufficient to overcome the spring force and the force due to pressure in a chamber 24. The pin 31 is then withdrawn from aperture 32 to allow the actuator 14 to move the fin 11. <IMAGE>

Description

Description of Invention Title: LOCK MEANS FOR MISSILE CONTROL FINS This invention relates to lock means for missile control fins particularly for use in missiles in which the control fins are permanently extended and are controlled during flight by a pneumatic actuator.

In such an installation the lock means are necessary in order to retain the control fins in a neutral pitch position during launch of the missile, and lock release means are provided to automatically release the lock means following launch. Conveniently, the pneumatic actuator is supplied from an on-board pressurised gas supply which is also used to operate the lock release means.

To prevent instability it is necessary to restrict the excursion of the individual fins to a minimal angular diversion from the neutral pitch position (say +3.5 degrees) following release of the lock means.

This may be difficult to achieve with a simple pneumatic lock arrangement based on a spring loaded plunger supplied directly from the gas supply especially immediately following release of the lock means.

Thus, with a low spring load the lock means may be withdrawn before sufficient pressure has built up in the pneumatic actuator so that the position of the control fins cannot be effectively stabilised when external aerodynamic loads are applied because the actuator torque capacity is insufficient to react such loads. Alternatively, the spring load could be increased so that the lock means is held in position until the actuator pressure reaches a suitable level but the spring would be large and heavy and the allowable margins on the release load would be small and difficult to control.

It is therefore an objective of this invention to provide a lock means for missile control fins which will release an associated control fin only when the pressure in a control fin pneumatic actuator is sufficient to stabilise the control fin.

Accordingly, in one aspect, this invention provides lock means for a missile control fin pivotally mounted for rotation about a transverse axis, said lock means comprising a piston located in a cylinder and having a protruding lock pin for engagement in an aperture in the control fin and spring means biassing the lock pin into engagement, the piston having a first effective area facing a first chamber in the cylinder at an end remote from the lock pin and selectively connectable directly to a pressurised gas supply, and a second effective area greater than said first effective area facing a second chamber at the other side of the piston and selectively connectable to said pressurised gas supply through a flow restrictor.

In another aspect, this invention provides lock means for a missile having a plurality of radially extending control fins pivotally mounted about transverse axes and operable by a pneumatic control actuator having a fin position control chamber and a balance chamber supplied from an on-board pressurised gas supply, the lock means comprising, for each control fin, a piston located in a cylinder and having a protruding pin adapted for engagement in an aperture in a surface of the control fin to lock the control fin in a neutral pitch position, spring means biassing the pin into locking engagement in the control fin, the piston having a first effective area facing a first chamber in the cylinder at the end of the piston remote from the pin and a second effective area greater than said first effective area facing a second chamber in the cylinder at the other side of the piston, the first chamber being connected during operation directly to said pressurised gas supply and said second chamber being connected to said pressurised gas supply through a flow restrictor Conveniently, said flow restrictor comprises a control orifice controlling the pressurised gas supply into the balance chamber of the pneumatic control actuator so that the gas pressure in said second chamber of the lock means corresponds to that in the actuator balance chamber.

Preferably the lock means is arranged so that prior to complete withdrawal of the pin from the aperture, limited pivotal movement of the control fin about its axis of rotation is permitted. In one form of the invention the lock pin may have a frusto-conical end portion for location in a corresponding tapered aperture in the control fin so that the limited pivotal movement of the control fin is permitted as the lock pin is withdrawn.

Alternatively, the lock pin may have an enlarged diameter end portion and said aperture may comprise an outer diameter of substantially the same size as the end portion and an inner diameter of larger dimension than the end portion, a compression spring in the second chamber of said lock means to balance the biassing spring means in the first chamber so as to position the end portion in locking engagement with the outer diameter portion of the aperture when no gas pressure is supplied whereby initial entry of gas pressure into said first chamber acts on the first effective area to move the lock pin outwardly until the end portion is located in the larger dimension inner diameter of the aperture so as to permit limited pivotal movement of the control fin until gas pressure increases in the second chamber sufficiently to completely withdraw the pin and release the control fin.

Preferably, said lock pin is parallel to the rotational axis so as to protrude from a missile external surface for engagement in its mating aperture in an inner surface of the control fin.

The invention will now be described by way of example only and with reference to the accompanying drawings in which, Figure 1 is a schematic of a lock means for a missile control fin constructed according to the invention, Figure 2 is a fragmentary sectioned view of an alternative form of part of the invention, and Figure 3 is a fragmentary sectioned view of a further alternative form of part of the invention.

Referring now to Figure 1, a missile control fin shown in broken outline at 11 is pivotally mounted about a transverse axis 12 of a missile (not shown). The fin 11 is rotationally fixed to a rocker lever 13 which is positioned by a dual chamber pneumatic control actuator generally indicated at 14. Whilst only one control fin 11 is shown in Figure 1 it will be understood that a plurality (usually four) will be required in each installation, and each fin will have its own control actuator 14.

One arm of lever 13 is connected to a control piston 15 located in a control chamber 16 and the other arm of lever 13 is connected to a balance piston 17 located in a balance chamber 18. An orifice 19 through piston 17 provides fluid communication between the balance chamber 18 and a dapper chamber 20 at the other side of the piston 17 and bounded in part by an effective piston area less than that operative in the balance chamber 18.

Control chamber 16 is connected to a supply of pressurised gas from a duct 21 through a supply valve 22, and is vented to ambient through a vent valve 23. Balance chamber 18 is connected to the supply of pressurised gas in duct 21 through a restrictor in the form of a control orifice 24. Supply and vent valves 22 and 23 are controlled via control lines 38 by an electronic control unit 25 which receives signals from a fin position potentiometer 26 and control signals 27 from a missile control system (now shown).

Duct 21 is supplied from an on-board high pressure gas supply and a pressure regulator (not shown), and branch ducts 40 are provided for connection to the control actuators 14 of the unillustrated control fins.

Lock means 28 is associated with each of the control fins 11.

Whilst illustrated in the schematic drawing in alignment with the chord dimension of control fin 11 in practice the lock means 28 is more likely to be parallel with rotational axis 12 so as to protrude from an external surface of the missile for engagement in an aperture located in an adjacent inner surface of each of the control fins 11.

Each lock means 28 comprises a piston 29 located in a cylinder 30 and having a protruding pin 31 shown engaged in an aperture 32 in a surface of control fin 11 to lock the control fin in a neutral pitch position. A spring 33 is located in cylinder 30 to bias the pin 31 into its locking engagement.

Piston 29 has a first effective area facing a first chamber 34 at the end of the piston remote from the pin 31 and a second effective area greater than the first effective area and facing a second chamber 35 in cylinder 30 at the other side of the piston 29. The first chamber 34 is connected via passageway 36 directly to the supply of pressurised gas in duct 21 and the second chamber 35 is connected through passageway 37 to the interior of the balance chamber 18.

Figures 2 and 3 illustrate different forms of lock pin 31 and aperture 32 both providing for limited pivotal movement of an associated control fin 11 about its axis 12 prior to complete withdrawal of the lock pin 31 from the aperture.

In the embodiment of Figure 2 the end of the pin 31 tapers downwardly and outwardly in the form of a frusto-conical end portion and locates, when locked, in a correspondingly tapered aperture 32.

Pin 31, in the embodiment of Figure 3, has an enlarged diameter end portion 31a for location in a locking position as shown in an aperture 32 having an outer diameter portion 32a of substantially the same dimension and an inner diameter portion 32b of larger dimension than the diameter of the end portion 31a of lock pin 31. In this embodiment, a compression spring (not shown) is located in chamber 35 around lock pin 31 to balance spring 33 and retain lock pin 31 so that the end portion 31a is retained in its locking position in diameter portion 32a when no gas pressure is being supplied.

With no gas pressure in duct 21 such as during initial launch of a missile, the control fins 11 are retained in the neutral pitch position by the respective lock means 28 due to the lock pins 31 being retained in the respective apertures 32 by the spring 33.

Following launch and release of the lock means 28 as hereinafter described, gas pressure supplied to duct 21 from the onboard supply and pressure regulator energise the pneumatic control valves 14 to provide pitch control of the control fins 11 and effect steering of the missile in a known manner by selectively venting and pressurising control chambers 16 using the supply and vent valves 22 and 23 respectively.

The lock means 28 of this invention is released in the following manner. Gas pressure in duct 21 flows directly through passageway 36 into the first chamber 34 and through restricting orifice 24 and passageway 37 into the second chamber 35.

Thus, gas pressure rises rapidly in chamber 34 and acts on the smaller effective area of the piston 29 tending to move the pin 31 further into the aperture 32 in the control fin 11. Gas pressure rises more slowly in the second chamber 35 because it is fed through the restrictor orifice 24 and the chamber 35 has a larger volume; however, the gas pressure in chamber 35 acts on the second, larger, effective area of the piston 29 eventually overcoming the force of spring 33 to withdraw the pin 31 from aperture 32 and release the control fin 11.

Appropriate selection of the ratio between the first and second effective areas of the piston 29 and of the rate of spring 33 ensures that release of the lock means 28 occurs only when the gas pressures in chambers 16 and 18 of pneumatic actuator 14 are sufficiently high to control effectively the location of the control fin 11 within the pre-determined design limits.

This feature is enhanced by the forms of lock means illustrated in Figures 2 and 3 both of which permit limited pivotal movement of the control fin 11 prior to complete withdrawal of lock pin 31 from aperture 32. This limited movement is sensed by the control fin position potentiometer 26 which signals control unit 25 which in turn primes the actuator 14 so as to counter loads that will be encountered on complete withdrawal of the lock pin 31.

In the embodiment of Figure 2 this is achieved due to the frusto-conical end portion of pin 31 which ensures an increasing clearance in tapered aperture 32 as the pin 31 is withdrawn. The embodiment of Figure 3 makes use of the initial rapid build up of gas pressure in the first chamber 34 to move the pin 31 outwardly against the compression spring (not shown) in chamber 35 so that end portion 31a is located in enlarged diameter portion 32b of aperture 32 to permit the limited pivotal movement of fin 11 prior to complete withdrawal of the pin 31 to release the control fin as the gas pressure increases in chamber 35.

Whilst several embodiments have been described and illustrated it will be understood that many modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims (12)

1. Lock means for a missile control fin pivotally mounted for rotation about a transverse axis, said lock means comprising a piston located in a cylinder and having a protruding lock pin for engagement in an aperture in the control fin and spring means biassing the lock pin into engagement, the piston having a first effective area facing a first chamber in the cylinder at an end remote from the lock pin and selectively connectable directly to a pressurised gas supply, and a second effective area greater than said first effective area facing a second chamber at the other side of the piston and selectively connectable to said pressurised gas supply through a flow restrictor.

2. Lock means for a missile having a plurality of radially extending control fins pivotally mounted about transverse axes and operable by a pneumatic control actuator having a fin position control chamber and a balance chamber supplied from an on-board pressurised gas supply said lock means comprising, for each control fin, a piston located in a cylinder and having a protruding pin adapted for engagement in an aperture in a surface of the control fin to lock the control fin in a neutral pitch position, spring means biassing the pin into locking engagement in the control fin, the piston having a first effective area facing a first chamber in the cylinder at the end of the piston remote from the pin and a second effective area greater than said first effective area facing a second chamber in the cylinder at the other side of the piston, the first chamber being connected during operation directly to said pressurised gas supply and said second chamber being connected to said pressurised gas supply through a flow restrictor.

3. Lock means as claimed in Claim 2, wherein said flow restrictor comprises a control orifice controlling the pressurised gas supply into the balance chamber of the pneumatic control actuator so that the gas pressure in said second chamber of the lock means corresponds to that in the actuator balance chamber.

4. Lock means as claimed in Claim 3, wherein said balance chamber is bounded in part by a balance piston having an orifice providing fluid communication between the balance chamber and a damper chamber at the other side of the balance piston.

5. Lock means as claimed in any one of Claims 2 to 4, wherein the pressurised gas supply to the control chamber is controlled by supply and vent valves to provide pitch control of the control fins.

6. Lock means as claimed in any preceding Claim, wherein the lock pin has a frusto-conical end portion for location in a correspondingly tapered aperture in the control fin so as to permit limited pivotal movement of the control fin as the lock pin is withdrawn.

7. Lock means as claimed in any one of Claims 1 to 5 inclusive, wherein the lock pin has an enlarged diameter end portion and said aperture has an outer diameter of substantially the same size as said end portion and an inner diameter of larger dimension than said pin end portion, a compression spring in the second chamber of said lock means to balance the biassing spring means in the first chamber so as to position the end portion in locking engagement with the outer diameter portion of the aperture when no gas pressure is supplied whereby initial entry of gas pressure into said first chamber acts on the first effective area to move the lock pin outwardly until the end portion is located in the larger dimension inner diameter of the aperture so as to permit the limited pivotal movement of the control fin until gas pressure increases in the second chamber sufficiently to completely withdraw the pin and release the control fin.

8. Lock means as claimed in any preceding Claim, wherein said lock pin is parallel to the rotational axis so as to protrude from a missile external surface for engagement in its mating aperture located in an inner surface of the control fin.

9. Lock means for missile control fins substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

10. Lock means as claimed in Claim 9, modified substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

11. Lock means as claimed in Claim 9, modified substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

12. Every novel feature and every novel combination of features disclosed herein.