WO2000009394A1

WO2000009394A1 - Parachute opening devices

Info

Publication number: WO2000009394A1
Application number: PCT/GB1999/002654
Authority: WO
Inventors: David Richard Jordan Hirst; Peter Beynon
Original assignee: Wardle Storeys (Safety & Survival Equipment)
Priority date: 1998-08-15
Filing date: 1999-08-12
Publication date: 2000-02-24
Also published as: GB9817716D0; HK1025937A1; GB2342326A; GB2342326B; AU5379799A; GB9919061D0

Abstract

An automatic parachute opening device provides the possibility of opening main and reserve parachutes at predetermined heights above the ground. A microcontroller within the device monitors the rate of descent and height above ground level as derived from barometric pressure readings and actuates the main canopy if the rate of descent is above a predetermined level at a predetermined height above the ground. If the speed is also above this predetermined level at a second, lower, height above the ground, the reserve parachute is deployed.

Description

PARACHUTE OPKNTNO DRVTCES

The invention relates to parachute opening devices and in particular to automatic

parachute opening devices.

Parachutes are normally transported in a container and are deployed from the

container to support a load during descent from an altitude. In the context of this

specification, the term "load" includes both a person and an inanimate load. There are

a number of ways of opening the container to deploy the parachute; for example, the

container may be opened by withdrawal of a pin holding the container closed or a

guillotine may cut one or more cords holding the container closed. Where the load is

a person, the container may be opened by the person pulling a cord or actuating a

guillotine. In the case of an inanimate load, or sometimes with people, the container

may be opened by use of a static line attached to, for example, an aircraft from which

the load is dropped.

In the case of a manually opened container, the person carrying the parachute waits

until an appropriate height and then opens the container to deploy the parachute.

There can be occasions, however, where opening does not take place at the correct

height, or does not take place at all under the control of the person. For example, the

person may loose consciousness. In the case of an inanimate load, it may be preferred

not to use a static line to open the container. There is also the problem that the parachute may not deploy correctly, whether

released by a person or by a static line. For this reason, parachute containers also

include a reserve parachute which can be deployed in the event of non-functioning or

malfunctioning of the main parachute. It is, however, possible that, for example, in

the case of unconsciousness of a person using the parachute, the reserve is also not

deployed, or is not deployed in sufficient time to decelerate the load before ground

level.

According to the invention, there is provided an automatic parachute opening device

for use with a pack containing a first parachute and a second parachute and carried by

a load, the device comprising a first actuator for connection to a first release

mechanism for the first parachute, a second actuator for connection to a second release

mechanism for the second parachute, and a control system, the control system

detecting when the load has a rate of descent at a predetermined height above ground

level above a predetermined rate of descent and operating the second actuator

mechanism on said detection.

In this way, the device deploys the second parachute if the first parachute has not been

deployed, on the basis of the rate of descent of the load. The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:-

Figure 1 is a plan view from above of a first form of automatic parachute opening device in an uncocked position,

Figure 2 is a similar view to Figure 1 but showing the first form of the device partially cocked,

Figure 3 is a similar view to Figures 1 and 2 but showing the first form of the device fully cocked,

Figure 4 is a block diagram of a circuit board incorporated in the first form of the

device of Figures 1 to 3,

Figure 5 is a plan view from above of a second form of automatic parachute opening device prior to cocking,

Figure 6 is a similar view to Figure 5 but showing the second form of the device in a cocked position, and

Figure 7 is a similar view to Figure 6 but showing the second form of the device after firing. Referring first to Figure 1, the first form of the device comprises a nickel plated

aluminium alloy casing 10 which, as seen in Figure 1, is generally square in plan

view. The casing has a rectangular back plate 11 surrounded by an upstanding

peripheral wall 12. The wall 12 includes parallel side sections 13a, 13b, a front section

14 and a rear section 15. The casing 10 is closed by a front plate which is the same

shape as the back plate but which, in Figures 1 to 3, is removed to reveal the internal

components of the casing. An electrically conductive O-ring is located between the

casing 10 and the front plate.

The casing defines a bore 16 extending from a blind end along one side section 13a

of the wall 12 and having an open end through the front section 14 of the wall 12. A

tube 17 is coaxial with this bore 16 and projects from the casing 10 at the open end of

the bore 16. The end of the tube 17 remote from the casing 10 is closed by an end cap

52. The bore 16 contains a coil spring 18 and a piston and rod assembly 20. The

spring 19 extends between the end cap 52 and a shoulder of the piston and rod

assembly 20. The rod 20 of the assembly extends axially through the spring 18. The

end of the rod remote from this connection projects from the spring 18 along the tube

19. Thus, by pulling the piston and rod assembly 20 in a direction out of the tube 17,

a spring 18 can be compressed against the end cap 52 and the end of the spring 18

within the bore 16 moves towards the tube 17. A pin 21 is provided on the spring 18 at the connection between the spring 18 and the

rod 20. A plate 22 overlies the tube 20 and is provided with a longitudinal slot 23

through which the pin 21 projects as the spring 18 is compressed.

The first lever 24 is mounted between two retention plates 53,54 within the casing 10

for pivotal movement about an axis normal to the back plate 11. This pivot axis 25

is located adjacent the front section 14 of the wall 12 and also adjacent the open end

of the bore 16. The first lever 24 is thus pivotable in a plane generally parallel to the

back plate 11 and the front plate. The first lever 24 is formed with a notch 26, which,

in the position of the first lever 24 shown in Figure 1, has its entrance in register with

the slot 23 and subtends an angle of about 45° to the length of the slot 23. The end of

the first lever 24 remote from the pivot axis 25 carries a pin 27. Its purpose will be

described below.

A stop 28 provided on the retention plates 53,54 and limits pivotal movement of the

first lever in an anti-clockwise direction as viewed in Figure 1.

A second lever 29 is pivoted about a pivot axis 30 parallel to the pivot axis 25 of the

first lever 24. The pivot axis 30 of the second lever 29 is, however, located adjacent

the blind end of the bore 16. A V-shaped notch 31 is formed adjacent this pivot axis

30 and, when the first and second levers 24,29 are positioned as shown in Figure 1, the pin 27 of the first lever is located adjacent the notch 31. The end of the second

lever 29 remote from the pivot axis 30 is formed with a peg 32.

The casing 10 also contains a spring catch 33 formed by a flexible strip of metal

having one end attached to a mounting 34 adjacent the bore 16 and having the other

end attached to a drive rod 35 of an electro-magnetic device in the form of a solenoid

36 mounted within the casing 10. The drive rod 35 is surrounded by a spring 37 that

tends to urge the drive rod 35 into the position shown in Figure 1.

The spring catch 33 is for co-operation with the peg 32 on the end of the second lever

29. This co-operation will be described in detail below.

The casing further includes a battery compartment 38 closed by a screw plug 39. The

casing also includes an electrical connector port 40 mounted on the front section 14

of the wall 12.

Referring next to Figure 4, the casing also includes a printed circuit board. Figure 4

is a block function diagram of the printed circuit board.

A microcontroller 41 is connected to a pressure transducer 42 via an analogue/digital

converter 43. A clock 44 provides timing signals to the microcontroller 41 and

software 45 within the microcontroller 41 runs programmes that will be described below. The microcontroller 41 is connected to an indicator 46 which gives a visual

indication of the status of the device and also visual messages. The solenoid 36 and

the connector 40 are connected to the microcontroller 41 by a power switch 47. A

self-checking programme 48 is also provided for the microcontroller 41. A battery 49

in the battery compartment 48 provides power to the pressure transducer 42, the

analogue/digital converter 43 and the microcontroller 41.

The microcontroller 41 is also provided with a data output socket 50 which is located

in the connector part 40 of the casing. The casing also includes a hole 51 which

locates a data exchange socket 55 (see Figure 4).

The pressure transducer 42 is located in the casing adjacent a hole (not shown) in the

front plate. The hole is covered by a microporous material patch. The microporous

material patch is protected by a sintered metal filter (both not shown). This thus

allows ambient air to the pressure transducer 42 but protects the interior of the casing

from moisture and dust.

T e pressure transducer 42 outputs an analogue signal representative of the ambient

barometric pressure. This is converted by the analogue/digital converter 43 into a

digital signal representative of the ambient barometric pressure which is fed to the

microcontroller 41. The device described above with reference to Figures 1 to 4 is used with a pack

including a main parachute 56 in a main parachute container 57 and a reserve

parachute 58 in a reserve parachute container 59. These containers 57,59 are of

conventional type and are not shown in the enclosed drawings. The main container

is held closed by locking pins 60. These locking pins are connected to the rod 20.

The reserve container for the reserve parachute is held closed by cords 61 which pass

through an electrically operated explosive guillotine 62. This guillotine 62 is of

conventional kind and includes a blade which can be driven through the cords by

electrical detonation of an explosive charge, in order to cut the cords 61 and open the

reserve container 59. The guillotine has an electrical input lead 63 for connection to

the output socket 50 within the connector port 40.

The purpose of the device described above with reference to the drawings is to open

the main container and deploy the main canopy if the rate of descent of the load is

above a predetermined level at a predetermined height above the ground. In the event

that the main parachute does not deploy, its purpose is also to open the reserve

container and deploy the reserve canopy if the rate of descent of the load is above a

predetermined level at a second height above the ground which is lower than the first.

The device performs these functions in the following way.

Barometric pressure varies with the height of a load above ground level. Accordingly,

changes in barometric pressure can be used to measure changes in height and, when combined with a time signal, changes in barometric pressure can also be used to

determine rates of change of height (i.e. rates of descent). However, barometric

pressure is not constant at ground level everywhere; it varies. Accordingly, in order

for the device to operate, the device requires a measurement of barometric pressure

at ground level at the location where the load is to be dropped by parachute.

In many cases, particularly in training drops, the ground level which is to form the

dropping zone is accessible. In this case, the device is taken to the dropping zone with

the guillotine unconnected to the output socket 50. At the dropping zone, the

guillotine lead is connected to the output socket 50 and this actuates the power

switches 47 to pass power from the battery 49. The microcontroller 41 is then tested

by the self-checking system 48 and, if the check is positive, an indication is provided

on the indicator 46. A different indication is also given if the device is found to be

malfunctioning.

The supply of power to the pressure transducer 42 causes the transducer to produce

an analogue signal corresponding to the barometric pressure at the dropping zone.

This is converted by the analogue/digital converter 43 into a digital signal fed to the

microcontroller 41. The software 45 programmes the microcontroller 41 to accept this

signal as representing zero height. The microcontroller 41 then calculates five

heights. The first height is an activation lock-out height below which, in ascent, the

microcontroller 41 will not output any activation signal. The second is a reserve

"wake-up" height below which, in ascent, the microcontroller 41 will not output any

signal to activate the reserve parachute. The third is a main "wake-up" height below

which, in ascent, the microcontroller will not output any signal to activate the main

parachute. The lock-out height is lower than the reserve "wake-up" height which, in

turn, is lower than the main "wake-up" height.

The fourth is a reserve activation height at which the microcontroller 41 is enabled to

output a signal to activate the release system for the reserve parachute. The fifth is a

main activation height at which the microcontroller 41 is enabled to output a signal

to activate the release system for the main parachute. The reserve activation height

is lower than the main activation height.

At the same time, the spring 18 is cocked. Referring to Figures 2 and 3, this is

achieved by pulling the piston and rod assembly 20 out of the tube 17 to compress the

spring 18 against the end cap 52 as described above. This motion causes the spring

pin 21 to pass along the slot 23 and thus engage the notch 29 in the first lever 24.

Continued compression of the spring 18 causes the pin 21 to slide along the edge of

the notch 26 and pivot the first lever 24 in a clockwise direction, as viewed in Figure

1 , about the pivot axis 25. The effect of this is to move the pin 27 at the end of the

first lever 24 into the notch 31 on the second lever 29 and to engage the edge of that notch. This causes the second lever 29 to pivot in a clockwise direction, as viewed in

Figure 1 , about the pivot axis 30. This moves the peg 32 at the end of the second lever

29 from the position shown in Figure 1 to the position shown in Figure 2. This

rotation continues until the peg 32 engages the spring catch 33. At this point, the pin

21 has reached the end of the notch 26 on the first lever 24 and further compression

of the spring 18 is not possible. The rod 20 is then released and moves back slightly

but the spring 18 remains compressed because the pin 21 is held against movement

as it bears against an edge of the notch 26 in the first lever 24. Reverse rotation of the

first and second levers 24,29 is not possible because of the engagement of the peg 32

in the spring catch 33. This fully cocked position is shown in Figure 3.

The software 45 provides three modes of operation of the device. These will now be

described.

In the first mode, the microcontroller 41 uses stored values to determine the heights

above ground level at which the device will be actuated if the main canopy or reserve

canopy have not been deployed. For example, the predetermined height for the main

canopy release may be about 750 metres and the predetermined height for the reserve

canopy operation may be about 300 metres. These are not, of course, held in the

microcontroller as heights but as digital values of barometric pressures at those

heights derived from the ground level barometric pressure sensed on startup. The second mode of operation allows adjustment of the dropping zone barometric

signal to take account of the fact that the dropping zone may be remote from the

position at which the guillotine is connected to the output socket 50 to activate the

device. In this case, the microcontroller 41 includes the stored values of the first mode

but a programming unit allows a height to be entered into the microprocessor via the

exchange socket 55, which adjusts the barometric pressure signal used by the

microprocessor 41 as a reference. The entry may be expressed as a number of metres

above or below the position at which the reference barometric pressure transducer

signal is generated. Thus, provided the height of the dropping zone above or below

this point is known, a reference signal correct for the dropping zone can be generated.

The required lock-out and reserve and main wake-up and activation values are then

calculated using software in the microcontroller 41.

This mode of operation can also allow adjustment of the height at which the main

canopy is opened and the height at which the reserve canopy is opened using the

programming unit via the exchange socket 55. The microcontroller 41 is

programmed, however, so that the reserve operation height cannot be set below 300

metres and the main operation height cannot be set lower than the reserve height plus

450 metres.

In the third mode, which can allow the connection to the guillotine lead to the output

socket 50 to power-up the system to be performed in an aircraft at altitude, the dropping zone reference from the pressure transducer 42 at startup is overwritten by

the microcontroller 41 with a default barometric pressure (e.g. 1013 mb). This default

barometric pressure can then be further adjusted for the required drop zone. The main

canopy operation height and the reserve canopy operation height can be adjusted if

required using the programming unit. This is subject to the constraints referred to

above. The microcontroller 41 then calculates values for the wake-up height and the

main and reserve wake-up and activation heights.

The programming unit is self-powered by, for example, a battery pack which may

include primary and back-up secondary batteries. The battery levels are checked

when the unit is switched on using an on/off switch. The unit also includes a display

such as an LCD. When the battery level is low, an indication is produced on the LCD.

The unit has two push-buttons that allow an operator ID and sortie number to be input

to the unit. This activates the unit. The unit then asks if the second or the third mode

of operation is to be used and a choice is made using the push buttons. The heights

required by the chosen mode are then entered using the "+" and "-" buttons to adjust

a displayed height for the height being adjusted. For example, the LCD might, in the

second mode, display the message "The DZ is ##,###Ft above/below here" with the

displayed height being adjusted until it reaches a desired value. This is then accepted. All data transferred from the programming unit to the microprocessor 41 is checked

and returned. If any differences are detected then the reprogramming of the

microprocessor 41 is aborted. The programming unit and/or the microprocessor must

then be removed from use and replaced.

All information is stored by the programming unit and is retrievable by "sortie

number" and "operator ID". The information may be retrievable into a PC.

In use, the pack with the containers and the parachutes is carried by a person to the

position at which the referenced barometric pressure is to be taken. One of the three

modes of operation is chosen, as appropriate, and the associated steps described above

are taken to render the microprocessor 41 fully operational for that mode.

The person then ascends in an aircraft or balloon. During ascent, the pressure

transducer 42 provides a succession of signals to the microcontroller 41 that are used

by the microcontroller 41 to derive the instantaneous height of the person above

ground level. Until the wake-up height is detected, this sampling rate is slower. When

the wake-up height is detected, the microprocessor is enabled. The sampling rate then

increases to a faster rate as the reserve wake-up and main wake-up heights are

detected and the reserve and main activations take place. Once the main wake-up

height is detected, the sampling rate drops from the faster rate to a moderate rate

between the faster and slower rates. The person is then dropped from an aircraft or a balloon. In normal operation, the

person will open the main container and deploy the main parachute using a rip cord

and, if that does not work, will deploy the reserve parachute from the reserve

container by actuating the guillotine. If, however, the person does not operate either

of these parachutes, the device operates as follows.

As the person jumps from an aircraft or a balloon, the pressure transducer 42 provides

a succession of signals to the microcontroller 41 at a rapid rate which is greater than

the faster rate (for example, about 0.5 second intervals) that are used by the

microcontroller 41 to derive an instantaneous height of the person above ground level

using the ground level reference signal. From successive stored values of this signal,

and utilizing the signals from the clock 34, the microcontroller 41 can derive a rate of

descent. If the rate of descent exceeds a predetermined value (indicative of the main

parachute not having opened), then, when the barometric pressure signal indicates a

height equal to the stored main activation height, then the microcontroller 41 outputs

an electrical signal to the solenoid 36. The effect of this is to withdraw the drive rod

35 against the spring 37 and release the spring catch 33. This in turn allows reverse

pivotal movement of the second lever 29 and thus reverse pivotal movement of the

first lever 24. This releases the spring pin 21 thus allowing the spring 18 to

decompress. This pulls the piston and rod assembly 20 into the casing 10 and causes

the pins to be pulled from the main container 57 so deploying the main parachute 56. If this deployment is successful, the person will be decelerated and the device will

perform no further functions. If, however, the main parachute 56 does not deploy

properly so that the speed of the person does not decrease, then detection of a rate of

descent above the predetermined rate of descent at the reserve parachute operation

height will cause the microcontroller 41 to pass an electrical signal to the data output

socket 50, at the stored reserve activation height, and thus, through the guillotine lead

63, to the guillotine 62. This detonates the explosive in the guillotine 62 and so cuts

the cords 61 holding the reserve container 59 closed. This container 59 thus opens

and the reserve parachute 58 deploys.

Referring next to Figures 5 to 7, these Figures show a second form of automatic

parachute opening device. This second device has parts that are common with the first

form of the device described above with reference to Figures 1 to 4. Those common

parts have the same reference numerals in Figures 5 to 7 as in Figures 1 to 4 and will

not be described in detail.

The second form of the device has the tube 17 provided with an internal shoulder 70

and the coil spring 18 extending between this shoulder 70 and a piston 71 of the piston

and rod assembly 20. The pin 21 is carried on the piston 71 and extends through the

slot 23 on the casing 10. A shock pad 72 is carried on the end of the piston 71

opposite the tube 17. A primary lever 73 is mounted on the plate 22 for rotation about an axis normal to the

length of the piston and rod assembly 20. The primary lever 73 has a first arm 74

provided with hooked end forming a recess 75 and an opposed second arm 76 formed

towards one end with a step 76a. A secondary lever 77 is also mounted on the plate

22 for rotation about an axis normal to the length of the piston and rod assembly 20

but spaced from the pivot axis of the primary lever 73. The secondary lever 77 has

a first arm 78 formed with a step 79 and a narrow elongate second arm 80.

The secondary lever 77 extends in a direction generally normal to the length of the

primary lever 73. The end of the second arm 76 of the primary lever 73 is adjacent

the end of the first arm 77 of the secondary lever 76. A coil spring 81 is mounted on

a post 82 and has one limb 81a acting against the second arm 80 of the secondary

lever 77 and a second limb 81b acting against a face 82 of the step 76 in the second

arm 76.

In the device of Figures 5 to 7, the solenoid 36 of Figures 1 to 4 is replaced with an

electromagnetic device in the form of a stepper motor 83. The motor 83 has an output

shaft 84 which carries a block 85. The output shaft 84 extends out of or retracts into

the stepper motor 83 depending on the direction of rotation of the stepper motor 83.

The block 85 carries a pin 86 that engages in a slot 87 at one end of a lever arm 88

mounted on a rotatable boss 92 including a face 93 that bears against the second arm

80 of the secondary lever 77. The second device of Figures 5 to 7 also includes a battery compartment and an

electrical connector port, as in the device of Figures 1 to 4, but these parts are omitted

for clarity in Figures 5 to 7. The second device of Figures 5 to 7 also includes a

printed circuit board as described above with reference to Figure 4 except that the

actuator 36 of Figure 4 is replaced by the stepper motor 83 as described above.

In use, the device of Figures 5 to 7 is used with a pack as described above. The device

operates as described above with reference to Figures 1 to 4 except in the operation

of the piston and rod assembly 20. This will now be described.

Figure 5 shows the second form of the device prior to cocking. In this position, the

output shaft 84 is retracted into the stepper motor 83 by the maximum amount. This

causes the lever arm 88 to rotate clockwise as viewed in Figure 5 against the action

of the spring 81 so allowing the primary lever 73 to move clockwise as viewed in

Figure 5 so that an end of the second arm 76 of the primary lever 73 engages a face

89 of the step 79 of the first arm 78 of the secondary lever 77.

In this position, the shock pad 72 is forced against the casing 10 by the spring 18. The

associated rod 90 is retracted within the tube 17.

The device in the configuration of Figure 5 is cocked by pulling the rod 90 out of the

tube 17. This compresses the spring 18 and moves the pin 21 along the slot 23 until the pin 21 engages a wall 91 that forms part of the recess 75 at the hooked end of the primary lever 73. As a result of the location of the wall 91 relative to the pivot axis

of the primary lever 73, continued movement of the pin 21 pivots the primary lever 73 anti-clockwise as viewed in Figures 5 and 6 against the action of the spring 81.

Once the end of the second arm 76 of the primary lever 73 passes the end of the first

arm 78 of the secondary lever 77, the secondary lever 77 is pivoted in an anti¬

clockwise direction as viewed in Figures 5 and 6 under the action of the spring 81.

This engages the end of the first arm 78 of the secondary lever 77 with the step 76a in the second arm 76 of the primary lever 73. This prevents the primary lever 73 rotating clockwise under the action of the spring 81. It also engages the second arm 80 of the secondary lever with the face 93 of the boss 92. The output shaft 84 of the

stepper motor 83 is retracted.

This is the cocked position shown in Figure 6.

When, in any of the modes described above with reference to Figures 1 to 4, the

microcontroller 41 passes a signal to the stepper motor 83, the motor 83 operates to

extend the output shaft 84. This causes anti-clockwise rotation of the lever arm 88 about the boss 92 via the block 85 and pin 86. This, in turn, rotates the secondary

lever 77 clockwise via the face 93 as viewed in Figure 6 so moving the end of the first

arm 78 of the secondary lever 77 out of engagement with the second arm 76 of the primary lever 73. This allows the primary lever 73 to rotate clockwise under the action of the spring 81 so releasing the pin 21 from the recess 75. This in turn allows the piston and rod assembly 20 to retract under the action of the spring 18. As described above, this causes the pins to be pulled from the main container, so

deploying the main parachute. The device is then in the after firing position shown in Figure 7.

The output shaft 84 of the stepper motor 83 is then retracted to allow the device to be

cocked again. The device is then in the prior to cocking position of Figure 5.

It will be appreciated that there are a number of changes that could be made to the device described above with reference to the drawings. The device need not operate a pin pulling system and a guillotine; it could operate any form of container opening

mechanism. The mechanisms need not be different; they could be the same.

The use of the lever system is optional; the necessary motion could, for example, be provided solely by a linear movement of an actuator of a solenoid or an output shaft

of a stepper motor.

The load need not be a person; it could be an inanimate load. In this case, the device is not used as an emergency device, it is used as the principal means for opening the

main and reserve parachutes. Of course, the two parachutes need not be main and

reserve parachutes, they could be two main parachutes. The device could simply act on the second (or reserve) parachute. The circuits need not be exactly as described above. The pressure transducer 42

could, for example, provide digital signals directly to the microcontroller 41. The

indicator 46 could be any suitable form of indicator such as an LED or an LCD screen.

The device described above with reference to the drawings is compact and reliable in

operation. The casing can be made water and dust-tight giving reliable long-term

operation. By allowing automatic opening of both canopies, there is improved safety.

In addition, the microcontroller 41 need not operate to release the spring catch 33 by

determining the rate of descent at a predetermined height above ground.

Alternatively, the microcontroller could monitor height above ground directly and

release the spring catch 33 at the predetermined height.

Claims

1. An automatic parachute opening device for use with a pack containing a

first parachute and a second parachute and carried by a load, the device comprising

a first actuator for connection to a first release mechanism for the first parachute, a

second actuator for connection to a second release mechanism for the second

parachute and a control system, the control system detecting when the load has a rate

of descent at a predetermined height above ground level above a predetermined rate

of descent and operating the second actuator mechanism on said detection.

2. A device according to claim 1 wherein the control system detects when the

load has a rate of descent at a height, which is above said predetermined height for the

second parachute, is above a predetermined rate of descent and operates the first

actuator mechanism on said detection.

3. A device according to claim 2 wherein the control system is an electrical

control system, the control system outputting a first electrical signal when the load has

a rate of descent at the first predetermined height above ground level above the

predetermined rate of descent, the first electrical signal operating the first release

mechanism, and outputting a second electrical signal when the load has a rate of

descent at the second predetermined height above ground level, the second electrical

signal operating the second release mechanism.

4. A device according to claim 3 and including a barometric pressure

transducer connected to the control system, the transducer feeding said signals to the

control system and the control system deriving therefrom said rate of descent and a

height signal, the control system comparing said height signal with said first and

second predetermined heights until said first and second predetermined heights are

detected.

5. A device according to claim 4 wherein a switch is provided for actuating

the device, the control system, on actuation of said switch, taking the transducer signal

present an actuation of the switch as a reference signal for use in determining

barometric pressure signals corresponding to said first and second predetermined

heights.

6. A device according to claim 5 wherein the switch is actuatable at ground

level at a dropping zone for the load, the control signal deriving from the reference

signal a signal defining the barometric pressure at ground level at the dropping zone.

7. A device according to claim 5 or claim 6 wherein the first and second

predetermined heights are fixed.

8. A device according to claim 5 or claim 6 wherein the first and second

predetermined heights are variable by use of an input device connected to the control

system.

9. A device according to claim 8 wherein the control system is programmed

to require a predetermined minimum distance between said first and second

predetermined heights.

10. A device according to any one of claims 5 to 9 wherein the switch is

actuatable at heights above ground level remote from said dropping zone, an input

device being provided by which the signal defining barometric pressure at the height

above ground level remote from the dropping zone is adjusted to provide a signal

defining the barometric pressure at the height above ground level at the dropping

zone.

11. A device according to any one of claims 4 to 10 wherein the control system

stores a signal defining a barometric pressure at a height below which neither actuator

mechanism is to be operated, the receipt by the control system of a signal from said

barometric transducer corresponding to said height disabling the production of said

first and second electrical signals.

12. A device according to any one of claims 3 to 11 wherein the first actuator

comprises a compressible spring and an electromagnetic operating device, the first

electrical signal operating said operating device to actuate said device to release the

spring when compressed, said release operating the first release mechanism.

13. A device according to claim 12 wherein the operating device includes a

lever system, compression of the spring moving a lever of the system into

engagement with a catch to hold the spring compressed, operation of the operating

device releasing the catch.

14. A device according to any one of claims 1 to 13 wherein the first release

mechanism is a pin pulling system associated with a main parachute.

15. A device according to any one of claims 3 to 14 wherein the second release

mechanism is an electrically detonated explosive charge for operating a guillotine for

cutting a cord or cords which retain a reserve parachute within a container, the second

electrical signal detonating said explosive charge to operate said guillotine.

16. A device according to claim 15 when dependent on claim 5 and including

an electrical connector for co-operation with an electrical connector of the second

release mechanism, connection of said connections operating said switch.

17. A device according to any one of claims 1 to 16 and including a wate╧åroof

external casing.

18. A device according to claim 17 when dependent on claim 4 wherein the

barometric pressure transducer receives ambient air through a microporous material

and a sintered metal filter.

19. An automatic parachute opening device substantially as hereinbefore

described with reference to Figures 1 to 4 or to Figures 1 to 4 as modified by Figures

5 to 7 of the accompanying drawings.