GB1570283A

GB1570283A - Ejector seats

Info

Publication number: GB1570283A
Application number: GB48260/75A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1975-11-24
Filing date: 1975-11-24
Publication date: 1980-06-25
Also published as: FR2332177B1; DE2653369A1; CA1074761A; SE7613028L; SE422916B; FR2332177A1

Description

(54) IMPROVEMENTS IN OR RELATING TO EJECTOR SEATS (71) 1, SECRETARY OF STATE FOR DEFENCE, London, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to ejector seats for ejecting personnel from cockpits of vehicles and craft such as aircraft. It is concerned with means for restraining the arms of the user during the ejection sequence so as to prevent injury thereto due to sudden exposure to the air while travelling at high speeds.

Various forms of arm restraining apparatus are known which employ cords or tapes to reel in and restrain the arms during ejection from an aircraft. These form part of or have to be fitted to the wearer's clothing and have to be connected to and disconnected from the aircraft and/or seat on entry and normal egress from the aircraft, thus adding to the number of operations which have to be performed before the aircraft can take off.

They have also entailed some difficulty of access to such manually operable devices as seat/occupant manual separation and emergency air or oxygen supplies.

By the present invention is provided an arm restraint system which is seat mounted so that no connecting or disconnecting action has to be taken whenever a user occupies the seat, no prefitting or special clothing is required and which, without loss of effectiveness and safety, allows the user to operate manually operable devices when he needs to.

According to the present invention an ejector seat has an arm restraint apparatus for restraining the arms of a user during an ejection sequence and comprising two nets attached and normally stowed one each side of the seat, and means for deploying the nets early in an ejection sequence including net casting means operable to cast a side of the nets laterally outwards whereby in the course of an ejection sequence the nets encompass the user's elbows and prevent his arms from being deleteriously affected by external air blast. The nets may also serve to prevent the arms fouling any part of the aircraft during ejection.

For the purposes of the present specification the word 'net' describes the function rather than the construction of that item, i.e.

to catch arms. Preferably, however, the nets have a mesh, so that they are relatively immune from blast damage.

According to a preferred feature of the invention the nets may be concave, that is shaped like a hammock or sling, so that in use the user's arms may be somewhat enveloped thereby and be held in the net by inertia and air pressure. Preferably each net is anchored at one side thereof to back, and possibly also at another side thereof to armrest, regions of the seat. The nets may thus be substantially triangular, be made of a fabric and be normally stowed in frangible or openable covers extending along the sides of the back-rest portion of the seat, and possibly along arm-rest portions also.

The nets have preferably a mesh size, at least in a forward region thereof, small enough not to permit the user's fingers to pass therethrough and entangle in the net.

The rear and upper regions of the nets may have a larger mesh but this should not be so large as to permit protrusion therethrough by, and entrapment thereby of, the user's elbows.

According to another feature of the invention the net deployment means may in dude a line attached to a free side of each net and forming part of a draw line releasably attachable to a fixed datum, e.g. the floor of the vehicle, and a snubber block through which the draw line passes in a normally non-returnable manner whereby ejection of the seat brings about deployment of the nets.

As an alternative to using the ejection of the seat to deploy the nets, capstan means may be provided on the floor or seat portion or head-rest region of the seat to wind in the draw line. It will be appreciated that the nets must be effectively deployed before the user leaves the aircraft in an ejection sequence. Furthermore, of course, they must not foul any part of the aircraft but preferably are cast as wide as possible to ensure encompassing the user's arms, which they must not damage, bearing in mind that if the seat is already in motion there will be a considerable 'downward' force on the arms.

Even if capstan means is used to deploy the nets it will generally be preferred that this is arranged to cause no delay in getting the man out of the aircraft If the capstant means are located on a fixed datum such as the floor of the cockpit the connection between the snubber block and the aircraft via the draw line will need to be releasable.

The release of the draw line from the aircraft in the case of any such attachment, that is (a) in the case of using the ejector seat motion to deploy the nets, (b) in the case of a capstan mounted on the aircraft as distinct from the seat, and (c) in the case of the draw line passing around a pulley attached to the floor, may be accomplished frangibly.

For example the attachment to the floor may be via a frangible rivet or bolt or the draw line itself may be frangible at a position which will be downstream of the snubber unit at any final configuration.

For faster deplostment of the nets the draw lines may, as indicated above, pass through pulley means. The draw lines are preferably tapes and made, for example, of nylon.

The operative datum for the upper end of each draw line is preferably as far forward of the head rest region of the seat as possible to maximise the ability of the nets to catch the arms. Each net may also be arranged in this way to support the whole arna and to restrain the user's corresponding shoulder as well. The anchorage of the draw lines and the operation of the net casting means are preferably arranged so that the draw lines and hence the associated free sides of the nets clear the shoulders during deployment.

With most ejector seats the portion thereof upon which the user sits is adjustable in height. Adjustment of the length of the draw lines and the anchorage points may be obtained in inertia reels and inertia catches of the type which lock upon sensing a predetermined acceleration of the line. Alternatively a ratchet and pawl system may be used or the draw lines may be slidably attached to the nets and net casting means so that upon adjustment of the height of the seat portion the draw lines adjust to a new position with respect to the net.

The upper end of each draw line is advantageously anchored to a release unit associated with a seat release mechanism, which may be both manual and automatic and which may free or cut the line. The apparatus can be arranged so that release of the unit is sufficient to ensure release of the arms from the nets. Alternatively the whole attachment of each net to the seat can be releasable, using loops, fairleads and a draw thread Insofar as controls and supplies, e.g. for manual seat/man release and emergency air or oxygen supply, are not mounted so that the user can operate them from the restrained configuration the snubber blocks may have a manual release.

The net casting means may include on each side an arm pivotally attached to the seat at one end hereinafter called the seat end, attached at the other end hereinafter called the net end to the net outer side or the draw line or both, and normally stowed with the net end to the rear of the seat end, the arrangement being such that tension on thes drawn line to deploy the net rotates outwards the arm and hence the line and associated net side, then at or just beyond the maximum cast of the net, pulls the associated net side inwards and forwards. The net to arm attachment means is preferably releasable, perhaps by means of a bolt member attached to the draw line.The pivotal axis of the arm may be tilted laterally inward from the vertical so that the arm is inclined upwards at the point of maximum cast of the net, and may also be tilted forward of the vertical to encourage the released arm to continue to rotate forwards after release of the net.

In another alternative the net casting means comprises pulley and/or slide means associated with, e.g. detachably attached to, the cockpit sides.

It will be appreciated that in embodiments of the invention where the draw lines are immovably attached to the nets and which have net casting means of the pivoting arm type, the swivel axis of the arm is preferably substantially normal to the line of tension in the draw line. Such an arrangement where the arm is pulled by the draw line from a lower datum as distinct from the head rest region permits that slack in the portion of the draw line between the pivoting arm and the upper anchorage can by centrifugal action effectively increase the cast of the net.As aircraft cockpits tend to have side consoles in a large configuration at about seat portion level, such an arrangement where the draw line is wound in from the upper anchorage, where the pivoting arm has to some extent to rotate upwards, is likely to require that commencement of net deployment does not occur until the seat is high enough for the pivoting arm to clear the side consoles. Embodiments of the invention which on the other hand employ draw lines which are slidably attached to the nets may not need to have the plane of swinging of the pivoting arm aligned with a source of tension in the draw line. The advantage of slackness may in such a case be lost but it may increase the scope for avoidance of damage to personnel by the pivoting arm.

In one pivoting arm arrangement a bolt member attached to the draw line and net is retained at the free end of the arm until a predetermined configuration is reached during swinging, when the bolt member is pulled away from the arm by the combined tension in the portions of the draw line on either side thereof. In another arrangement a bolt member attached to the draw line as above is so releasably mounted on the free end of the arm as to be partly pulled therefrom by tension in the draw line and partly ejected therefrom centrifugally, thereby increasing the cast of the net. The arm may be stowed by means of a spring clip or tie which can be arranged to increase the speed of swinging of the arm and hence the centrifugal force on the bolt member.The arm may be kinked or dog-legged to impart a toggle action thereto for commencement of swinging and, in the case of bolt members releasable centrifugally, to ensure release in a forward and laterally outward direction.

Insofar as seat height adjustment needs to be catered for in arm restraint apparatus according to the invention this may be ao complished using inertia reel devices of the type which readily permit low tension adjustment of the draw line length but which lock upon sensing a predetermined draw line acceleration.

An injection seat provided with arm restraint nets in accordance with the invention may have knee wings, one each side pm- truding upwards from the forward region of the seat part of the seat, and to each of which is attached a fairlead for the draw line. With this arrangement the throw of the nets can further be maximised. Moreover the user's arms can readily be supported with the hands not far from such controls as manual seat release and snubber block release controls. The snubber blocks may, of course, be most conveniently mounted on the knee wings.

The ejector seat may also have leg restraint means for pulling in, restraining and supporting the user's legs during an ejection sequence. Though perhaps of known types these may be associated with the winding in and release means of the arm restraining apparatus.

Arm restraint apparatus in accordance with the invention is particularly suitable for use on ejector seats whereon the ejection handle is sited on the front of the seat pan between the user's legs. As the operation of this handle terminates the user's elbows are usually laterally spread out, and the arm tension the user requires to pull the handle may not have been relaxed before the ejection has got under way; The nets can readily be arranged to encompass the elbows on this position and to protect them while leaving the vehicle.

Arm restrain apparatus in accordance with the present invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 illustrates one embodiment of the invention in a stowed configuration, Figure 2 depicts in detail a casting arm shown in Figure 1, Figure 3 illustrates the embodiment in a maximum cast configuration, Figure 4 illustrates it in a fully deployed configuration, Figure 5 illustrates a second embodiment of the invention in a stowed configuration, Figure 6 depicts in detail a casting arm of the second embodiment, and Figure 7 illustrates the second embodiment in a fully deployed configuration.

The ejector seat 10 illustrated in Figures 1 to 4 has a back-rest portion 11, a headrest portion 12, seat side portions 13 and knee wings 14. Two arm restraint nets 15 are attached to the back and side portions 11 and 13, one net at each side. Each net 15 is attached along an upper free edge to a draw line 16, formed of nylon tape, a top end of which is anchored to a release unit 17 on the side of the head-rest portion 12.

Near the lower end of the free edge of the net the draw line 16 carries a toggle 18 which in combination with a toggle arm 19 provides net casting means. Thereafter the draw line 16 passes through a fairlead 20 mounted on the knee wing 14 in such a manner as to afford manual access between the deployed net and the knee wing to a wind-in unit 21.

The ejection seat also has a leg restraint apparatus which, being of known type, is illustrated generally at 22.

The toggle arm 19 is pivotally attached to the seat side portion 13 in such a manner that in stowed and outstretched positions it is inclined upwards. As shown in Figure 2 the arm 19 has a cavity 26 and slot 27 arranged at its outer, free, end for releasably holding the toggle 18. A pin 28 mounted on the arm 19, in the cavity, serves as a guide for the rotation and release of the toggle 18. The toggle comprises jaws 29 for attachment to the drawline 16, a catchment bar 30 the breadth and length of which are slightly less than those of the slot 27 and the depth of which is slightly less than the breadth of the cavity 26, and a trunk 31 connecting the jaws 29 and the bar 30. There is a hole in the bar 30 and trunk 31 to accommodate the pin 28 as a slide fit. The long axis of the bar 30 is normal to that of the jaws and the draw line 16.The arrangement is such that the cavity 26 and slot 27 arranged on the arm 19 will retain the bar 30 of the toggle 18 until the maximum lateral throw of the arm 19 when the bar 30 is aligned with the slot 27, when tension in and configuration of the draw line 16 will cause the toggle to withdraw from the arm.

The lower and upper regions of each net have a mesh size of 1 cm and 4 cm respectively and the net is concave in form. It is normally stowed in tubular fabric reinforced rubber housings 32, 33 split longitudinally to permit the nets to be drawn out thereof by their free edges, and attached to the seat back and side portions respectively. In the stowed configuration the arm 19 is in its fully rearward position, actually with the free end laterally proud of the pivoted end.

The draw line 16 between the toggle 18 and the fairlead 20 is also detachably attached at intervals to the seat side.

Also mounted on the seat side portion are the emergency oxygen supply 34 (starboard side) and the emergency manual- seat separation unit 35 (port side).

The operation of the restraint system is as follows. When the user pulls the ejection handle, the wind-in unit 21 pulls the draw lines 16 through the fairleads 20 and the arms 19 are thereby swung outwards and forward. The nets 15 are thereby caused to break out of the housings 32, 33 and the free edge of each net is cast beyond the user's elbows.

At the position of maximum lateral throw of the arms 19 shown in Figure 3 and thus of maximum cast of the nets the toggles 18 and hence the draw lines 16 and the nets are released from the arms 19 which continue their forward swing freely. The draw lines then spring laterally inwards until they are taut.

The configuration will then be that illustrated in Figure 4, with the draw lines passing over the shoulders of the user, so that the nets encompass the user's arms.

The ejector seat will not begin to leave the cockpit until the deployment of the nets is substantially complete. Operation of the leg restraint system, however is brought about by the passage of the seat.

If the user desires emergency oxygen he can reach between the starboard net and the knee wing 14 to gain access thereto.

When the automatic seat separation unit operates, the release units 17 are opened along with other user restraining device rerelease units, and unimpeded seat/man separation is thereby allowed. If the automatic unit fails to operate, the manual release unit 35 can be operated from within the port side net.

In the embodiment shown in Figures 5 to 7 an ejector seat having a seat portion 50, and a head-rest portion 51, and mounted on an aircraft cockpit floor 52, has an arm restraint system comprising nets 53, draw tapes 54, pivoting arms 55, bolt members 56, fairleads 57, snubber blocks 58, inertia reel units 59 and intertia reel/release units 60. The nets 53 and tapes 54 are normally stowed in sleeves 61a, b. The seat also -has leg restraint apparatus indicated generally at 62.

The seat portion 50 is adjustable in height with respect to the back of the seat and the head-rest portion 51. Each draw tape 54 is attached immovably to a net 53, the stowage sleeve 61a wherefor is mounted on a lower back rest part of the seat portion 50.

The fairleads 57 and snubber blocks 58 are mounted as far as forward as possible on the seat portion 50. The draw tape 54 between the arm 55 and the fairlead 57 is stowed in a sleeve 61b on the base side of the seat portion 50. The sleeve 61 a, b are constituted by fabric flaps held in place by Velcro (Trade Mark) touch and close fasteners.

The nets 53 are somewhat similar to those of the Figures 1-4 embodiment.

The inertia reel release units 59 are mounted as far forward as possible on the head-rest portion 51, and each comprise an inertia reel element and a guillotine unit.

The reels 60 are mounted on the cockpit floor 52 beneath the snubber blocks 58 by a frangible anchorage. The inertia reels, which are of the type which lock on a given tape acceleration, are to cater for slack in the draw tapes 54 which might otherwise arise when the seat height is adjusted.

The pivoting arm arrangement is shown in some detail in Figure 6. Each arm 55 is mounted on the lower back-rest part of the seat portion 50 and held back by a spring clip 66. It is dog-legged toward the free end which thus projects somewhat laterally of the seat and pivoted mounting. An axial hole in the end of each arm accommodates freely the bolt member 56 which is attached to the tape 54. Retention of the member 56 in the arm 55 during stowage is ensured by a degree of tension in the tape 54 between the member 56 and the stowage sleeve 61b.

The sequence of operations required by the user upon entry to his seat includes the fastening of his seat harness and leg restraint cords 63, and the adjustment of the height of the seat portion 50, which involves taking up of slack or paying out of tape 54 by the inertia reels 59, 60, as appropriate.

Upon ejection the passage of the seat from the cockpit brings about the pulling of the tapes 54 through the appropriate snubbers 58. The tapes 54 are pulled- out of the stowage flaps 61b and commence the swinging of the arms 55 out of the clips 66 and hence the removal of the nets 53 from the flaps 61a.

This removal is arranged to be completed soon enough for nets as a whole to be to some extent flung sideways centrifugally, and when the arms have swung a little way from its maximum lateral extension the bolt members 56 are partly flung and partly pulled therefrom and the tape 54 becomes drawn inward and taut, The anchorage of the reels 60 to the cockpit floor then breaks. Mean while the leg restraint apparatus has also operated to restrain the user's legs.

The user's arms are thus cradled in the nets 53 and his legs restrained before the seat leaves the aircraft. If he needs to obtain emergency oxygen this can be effected via a control 67 accessible from within. the net.

Upon the usual automatic seat/man separation, the guillotine elements of the units 59 cut the tapes 54 at the same time as other restraints and are released. Should these fail the man can release himself manually by operating a manual release (not shown).

In a third embodiment, not illustrated in the drawings, the net casting means comprises fairleads releasably attached to a cockpit datum such as the walls, the draw lines extending from the nets via these fairleads to the forward part of the seat and then the line tensioning means, and the arrangement being such that pulling the draw lines first pulls the nets out towards the fairleads,.

which are then released allowing the nets to close in. The releasable fairleads in this third embodiment may be part of sliders associated with runners mounted on the said datum. The alignment of the slide means can be arranged to effect a predetermined net trajectory, the sliders detaching from the runners by running off the ends thereof. The runners may be substantially vertically aligned in a seat operated net system or substantially horizontally aligned in a reel-in net deployment system.

In yet another embodiment not illustrated in the drawing the net casting means includes a rod member constrained to slide laterally outwards from the seat back, the draw lines being attached to the outer ends of the rod members, and the arrangement being such that tension on the lines pulls the rod members outwards and casts the nets. The rods may be made of a resilient material whereby the outer ends thereof are pulled forward to some extent as the rods are being withdrawn.

A metal or plastics rod of suitable cross section, for example a stiff metal wire, may be used. Alternatively or additionally the rods may be fitted with a forward component to their initial disposition. The constraint may be provided by tubes, perhaps somewhat flexible or resilient, or by distinct fairleads.

WHAT I CLAIM IS:- 1. An ejector seat having arm restraint apparatus for protecting the arms of a user during an ejection sequence and comprising two nets attached and normally stowed one each side of the seat, and means for deploying the nets early in an ejection sequence and including net casting means operable to cast a side of the nets laterally outwards whereby in the course of the sequence the nets encompass the user's elbows to prevent his arms from being deleteriously affected by external air blast.

2. An ejector seat as claimed in claim 1 and wherein the nets are concave.

3. An ejector seat as claimed in claim 1 or claim 2 and wherein each net is anchored' at one side to a back region of the seat.

4. An ejector seat as claimed in any one of claims 1 to 3 and wherein each net is normally stowed in openable covers extending down a back-rest portion of the seat.

5. A ejector seat as claimed in any one of the preceding claims and wherein a forward portion of each net has-a small rtesh and a rearward portion a large mesh. 6. An ejector seat as claimed in any one of the preceding claims and wherein the net deployment means includes a draw line attached to a free side of each net, and a snubber block through which the draw line passes in a normally non-returnable manner.

7. An ejector seat as claimed in claim 6 and wherein the draw line is releasably attachable to a fixed datum whereby ejection of the seat operates the net deployment means.

8. An ejector seat as claimed in claim 7 and wherein the releasable attachment is frangible.

9. An ejector seat as claimed in claim 6 and wherein the net deployment means includes capstan means for winding in the draw line.

10. An ejector seat as claimed in any one of claims 6 to 9 and wherein the draw line is a tape.

11. An ejector seat as claimed in any one of the preceding claims and including an automatic release unit for releasing the user's arms from the nets at a seat/man separation stage of an ejection sequence.

12. An ejector seat as claimed in any one of the preceding claims and including manual release means for slackening the nets.

13. An ejector seat as claimed in claim 12 and wherein the manual release is a snubber override device.

14. An ejector seat as claimed in any one of the preceding claims and wherein the net casting means includes on each side an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tapes 54 through the appropriate snubbers 58. The tapes 54 are pulled- out of the stowage flaps 61b and commence the swinging of the arms 55 out of the clips 66 and hence the removal of the nets 53 from the flaps 61a. This removal is arranged to be completed soon enough for nets as a whole to be to some extent flung sideways centrifugally, and when the arms have swung a little way from its maximum lateral extension the bolt members 56 are partly flung and partly pulled therefrom and the tape 54 becomes drawn inward and taut, The anchorage of the reels 60 to the cockpit floor then breaks. Mean while the leg restraint apparatus has also operated to restrain the user's legs. The user's arms are thus cradled in the nets 53 and his legs restrained before the seat leaves the aircraft. If he needs to obtain emergency oxygen this can be effected via a control 67 accessible from within. the net. Upon the usual automatic seat/man separation, the guillotine elements of the units 59 cut the tapes 54 at the same time as other restraints and are released. Should these fail the man can release himself manually by operating a manual release (not shown). In a third embodiment, not illustrated in the drawings, the net casting means comprises fairleads releasably attached to a cockpit datum such as the walls, the draw lines extending from the nets via these fairleads to the forward part of the seat and then the line tensioning means, and the arrangement being such that pulling the draw lines first pulls the nets out towards the fairleads,. which are then released allowing the nets to close in. The releasable fairleads in this third embodiment may be part of sliders associated with runners mounted on the said datum. The alignment of the slide means can be arranged to effect a predetermined net trajectory, the sliders detaching from the runners by running off the ends thereof. The runners may be substantially vertically aligned in a seat operated net system or substantially horizontally aligned in a reel-in net deployment system. In yet another embodiment not illustrated in the drawing the net casting means includes a rod member constrained to slide laterally outwards from the seat back, the draw lines being attached to the outer ends of the rod members, and the arrangement being such that tension on the lines pulls the rod members outwards and casts the nets. The rods may be made of a resilient material whereby the outer ends thereof are pulled forward to some extent as the rods are being withdrawn. A metal or plastics rod of suitable cross section, for example a stiff metal wire, may be used. Alternatively or additionally the rods may be fitted with a forward component to their initial disposition. The constraint may be provided by tubes, perhaps somewhat flexible or resilient, or by distinct fairleads. WHAT I CLAIM IS:-

1. An ejector seat having arm restraint apparatus for protecting the arms of a user during an ejection sequence and comprising two nets attached and normally stowed one each side of the seat, and means for deploying the nets early in an ejection sequence and including net casting means operable to cast a side of the nets laterally outwards whereby in the course of the sequence the nets encompass the user's elbows to prevent his arms from being deleteriously affected by external air blast.

2. An ejector seat as claimed in claim 1 and wherein the nets are concave.

5. A ejector seat as claimed in any one of the preceding claims and wherein a forward portion of each net has-a small rtesh and a rearward portion a large mesh.

6. An ejector seat as claimed in any one of the preceding claims and wherein the net deployment means includes a draw line attached to a free side of each net, and a snubber block through which the draw line passes in a normally non-returnable manner.

arm pivotally attached to the seat at one end and attached to a free side of the net at the other, and normally stowed with the net holding end to the rear of the pivotal attachment to the seat, the arrangement being such that tension on the draw line to deploy the net rotates outward the arm and hence the line and associated net side, and then beyond the maximum cast position of the arm and net side draws the net side forwards, inwards and taut.

15. An ejector seat as claimed in claim 14 and wherein each net side is releasably attached to the casting arm.

16. An ejector set as claimed in claim 15 and wherein the releasable attachment is effected by means of a bolt member.

17. An ejector seat as claimed in any one of claims 14 to 16 and wherein the arm is bent whereby it is ensured that the tension of the lines does not act only through or seatward of the arm pivot.

18. An ejector seat as claimed in any one of claims 1 to 13 and wherein the net casting means includes fair leads releasably attached to cockpit datum, the draw lines extending from the nets via these fairleads to the forward part of the set and then to line tensioning means.

19. An ejector seat as claimed in claim 18 and wherein the releasable fairleads form part of runners associated with slide means mounted on the said datum.

20. An ejector seat as claimed in any one of claims 1 to 13 and wherein the net casting means includes a rod member constrained to slide laterally outwards from the seat, the draw lines being attached to the outer ends of the rod members, and the arrangement being such that tension on the lines pulls the rod members outwards and casts the nets.

21. An ejector seat as claimed in claim 20 and wherein the rod members are resilient in flexure.

22. An ejector seat as claimed in either claim 20 or claim 21 and wherein the rod members are fitted with a forward component to their initial disposition.

23. An ejector seat as claimed in any one of the preceding claims and having means for taking up slack in or paying out draw line during seat height adjustment.

24. An ejector seat as claimed in claim 23 and wherein the said means comprise inertia devices which lock upon sensing a predetermined draw line acceleration.

25. An ejector seat as claimed in any one of the preceding claims and substantially as hereinbefore described.

26. An ejector seat substantially as hereinbefore described with reference to Figures 1--4 of the accompanying drawings.

27. An ejector seat substantially as hereinbefore described with reference to Figures 5-7 of the accompanying drawings.