IMPROVED AERIAL DELIVERY PLATFORM Aerial delivery platforms are used in the air transportation and delivery of payloads such as military vehicles. They are contained within aircraft and discharged whereupon they descend under parachute to the ground. In order to provide some measure of protection to the payload and/or platform it is known to provide shock absorbing measures and typically airbags are used which open upon descent by gravity. The inflated airbags provide a measure of deceleration when the platform lands, and by means of controlled overpressure in the airbags, an upwardly directed reaction slows final descent of the payload-bearing platform before it reaches the ground. Overpressure in the inflated airbags can be controlled by a small orifice, initially sealed with a latex burst patch, otherwise the airbag is essentially airtight upon landing. For an illustrated example of a known construction, the reader is referred to US-A- 2,774, 560.

The known system described above does however suffer from a number of disadvantages.

For instance, the conventional airbags deployed have unsatisfactory overall performance. At and above substantial platform weights from e. g. heavy payloads, the conventional airbags have insufficient shock absorbing capacity to absorb all the descent energy. The airbags incorporate non-reusable sacrificial components so the airbags are not readily reusable without additional work and materials. Inflation of the bags takes place through ram air effects at slow descent speed, and in consequence initial overpressure is small. Significant stroke of the bags is used to develop satisfactory overpressure, representing inefficient use of the material. Moreover, the conventially fitted airbags only provide vertical deceleration generally limited to approximately two thirds of the available underside area of the platform, and no lateral pressure gradient exists. This limits any rollover protection in side wind landing conditions. Any resulting rollover causes serious damage to the payload and platform.

Accordingly we have now devised a modified and improved aerial delivery platform which seeks to avoid or reduce the aforementioned disadvantages.

According to one aspect of the present invention there is provided an aerial delivery platform comprising a generally flat base for supporting a payload, at least one pair of inflatable airbags mounted underneath the base and capable of inflation during aerial descent, the

airbags having a main body part extending downwardly of the base, and an extension part adjacent the main body part extending outwardly thereof and having a sidewall which, upon airbag inflation, extends to the region of at least one base member edge, the extension part also forming an extension to the base of the main body part.

It is preferred for the main body part to be integrally formed with the extension part. Upon inflation of the airbags, it is preferred for the underside of the extension part and the underside of the main body part to become generally coplanar. It is preferred that the underside of the main body part and the underside of the extension part provide protective coverage to the underneath surface and edges of the platform base upon impact with the ground.

The main body part may constitute a primary internal chamber whilst the extension part may comprise a secondary internal chamber wherein the chambers are separated by a membrane located internally of the airbags.

In order that the invention including further preferred features of it may be illustrated, more easily appreciated and readily carried into effect by those skilled in the art, exemplary embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings also showing a conventional construction and wherein: Figure 1 is a side elevation of a known construction in a form suitable for loading into an aircraft; Figure 2 is an elevation similar to Figure 1 in which the airbags are released to commence inflation; Figure 3 shows inflation of the airbags in the Figure 1 and 2 arrangements; Figure 4 shows the airbags fully deployed; Figure 5 shows landing of the known aerial platform; Figure 6 shows the known platform wherein the airbags deflate following landing;

Figure 7 is a side elevation of an embodiment of the present aerial delivery platform; Figure 8 is a side view similar to Figure 7, wherein the airbags are released for deployment; Figure 9 shows the platform wherein the airbags are fully inflated before a landing, Figure 10 shows the platform wherein the airbags impact upon a ground surface, Figure 11 shows a conventional construction of skid door timer release mechanism, Figure lla shows an enlarged detail of the release mechanism present in Figure 11 in the fired position, and Figure lib shows an enlarged detail of the release channel and hook present in Figure 11.

Referring to the drawings and initially to Figures 1 to 6 and 11 showing a known construction, an aerial delivery platform 1 has a generally flat base which is essentially a rectangular framework array. On the underside of the base, at least two airbags 18 are fitted.

The airbags are suspended from a medium stressed platform by top boards which locate in grooves. At rest and before deployment, the airbags are retained uninflated by a pair of hinged skid doors 17. As shown in Figure 2, following discharge from an aircraft, the skid doors 17 are arranged to open by a timer release mechanism, and spring open through 180 degrees. Both airbags 18 start to deploy during further descent by virtue of the weight of the bottom boards 20 securely affixed to the lowermost, ground engaging, surface of each airbag.

Referring to Figure 3, internal sleeves 19 (integrally formed in each airbag) open and allow air to enter to inflate the airbags. In Figure 4, showing a subsequent stage of descent towards the ground, both airbags 18 fully deploy and achieve slight overpressure as a result of the continuing descent. In this configuration, the sidewalls 21 of both airbags become fully extended as depicted in Figure 4. The airbags 18 have a generally cylindrical form and bear only upon the central part of the underside of the platform 2. Rollover performance is poor and the burst patch system is not adjustable for varying mass. The current design is insufficient for use with current mass.

As shown in Figure 5, the platform lands whereby the bottom boards 20 impact upon the ground surface. The internal sleeves 19 seal and collapse, whereupon the airbags begin to pressurise and the latex seals 23 start to stretch. The airbag sidewalls rapidly compress to the form identified at 22. In the final stages of ground impact, the arrangement is as shown in Figure 6. The latex seals 23 have burst to become air exits 24 whereby the pressurised air in each airbag exits the airbag through the burst seals as depicted generally by arrows.

Accordingly the air vents but at a controlled rate which leaves high pressure in the bags. The platform decelerates because of this pressure.

The timer release mechanism of Figure 11 is described subsequently, being essentially of known construction but suitable for use in the context of the present invention.

Referring to the illustrated embodiment of the present invention in Figures 7 to 10 inclusive, the platform in Figure 7 is similar to that shown in Figure 1 to the extent that the platform 1 has a generally flat base 2 consisting of a rectangular framework array, and a skid door 17 is provided to retain the modified airbags 3 in closed position, and for hinging through 180 degrees as in the above described known platform. The modified airbags 3 are suspended from medium stressed platform by top boards which locate in grooves.

Referring to Figure 8, the skid doors 17 are arranged to open by timer release mechanism, described subsequently with reference to Figure 11 and spring through 180 degrees. The airbags 3 start to deploy through means of a different pressurisation system than the conventional flaps just described. The pressurisation system can be aspirator driven, from a gas generator, by gravity or by some other means, or by a combination of one or more of the aforesaid means. As will be seen from Figure 9, the modified airbags deploy over the full bottom surface of the platform.

Here, the modified airbags 3 fully deploy and achieve optimum overpressure from the pressurisation medium selected. The optimum overpressure is that which allows minimum deceleration over the stroke of the airbag with zero residual velocity. With particular reference to the arrangement in Figure 9, the modified airbag has sidewalls 14 and a base 15 which together with a neck part 13 and a separating wall 11 define a main body part of the modified airbag. The airbags also have an extension part 5, defined by a sidewall 8, the same separating wall 11, a base 16 and an uppermost part 25 such as an upper wall. The base 2 of

the delivery platform has an edge 7 at the far side of the rectangular framework array. The sidewall 8 of the extension part 5, in its fully inflated condition extends to the region 6 of the base member edge 7 in the sense that the sidewall edge 8 and the base member edge 7 become generally coplanar with the region 6 of the base member edge. As will be appreciated, this substantially extends the impact area of the airbag base whilst simultaneously providing much greater protection to the platform base and to the payload thereon. In particular, such an arrangement provides enhanced rollover protection, and avoidance of a bursting patch deflation mechanism (the absence of which is preferred), permits a degree of adjustment to deflation characteristics depending upon the mass of the payload.

Referring to Figure 10, the delivery platform impacts upon the ground whereby the base of the modified airbags makes first contact with the ground. The modified airbags are internally zoned or provided with a plurality of chambers to allow differential pressure between the main body part 4 and the extension part 5. By suitable choice of material with appropriate air permeability, for the separating wall 11, the main body part 4 can form an internal low pressure zone (or chamber) 10 whilst the extension part 5 can form an internal high pressure zone (or chamber) 9. High pressure zones at the outermost side walls 8 of the extension part 5 tend to resist rollover when the aerial descent platform lands in prevailing side wind conditions.

Venting of pressurised air from the airbags 3 is directed though a venting control device, preferably maintenance reduced or free for the life of the airbag and flow rate adjustable for payload and/or platform mass variance. As shown, the venting may take place at aperture or region 12 in the sidewall 8 of an extension part 5.

Suitable venting control devices, which can be incorporated into the material of the sidewall 8 of extension parts 5, include for example valves, restrained vents, porous fabric material, other means or a combination of one or more of the aforesaid devices.

It will be appreciated from the Figure 10 arrangement that upon ground impact, the separating wall 11 and the extension part sidewall 8 distend to a greater extent than the sidewall 14 of the main body part. This helps contribute to the extension part forming an internal region 9 at higher compression pressure, than the main body part region 10.

Referring to Figure 11, the known platform release mechanism can be used in the present invention, with little if any modification. With the skid doors in the closed position (not shown) and drop bars (not shown) supporting the doors (not shown), the time delay release mechanism 26 has an arming bolt pushed to the rear and locked in position by rotating the spring biased 33 static line bracket 32. The arming block abuts the channel roller pushing the release"U"channel 28 back against the spring 30 pressure, keeping the hooks 27 pivoted under drop bar rollers. The arming bolt is prevented from moving forward by the time delay release lever. The aerial platform is provided with a centre longitudinal channel 31 and spring attachment bracket 29 from which a spring 30 extends in the region of a release channel 28, to the hook bracket 34.

As the platform starts to move forward, the static line connected between the static line bracket and cargo floor tie down position, becomes taut and rotates the static line brackets to actuate the clockwork timing mechanism. After a seven second delay, the platform is clear of the aircraft and goes into the inversion phase of the extraction. The time delay mechanism 26 trips, the release lever pivots and releases the arming bolt. The arming bolt and release channel 28 move forward under spring 30 pressure and rotate the hooks 27 into the hook bracket 34 away from the drop bars (not shown). The drop bars fall away and skid doors open allowing the airbags to extend.

Embodiments of the present aerial descent platform have or are capable of providing a number of distinct advantages over and above the conventional descent platform described above with reference to Figures 1 to 6 of the accompanying drawings. In particular such embodiments can provide an increased stroke length to absorb more or even all of the descent energy. Embodiments need not incorporate sacrificial components. In such cases, the airbags become immediately re-usable. The exterior of the bag can remain non-porous, but the venting medium could be a sleeve (sealed by elastic band to allow initial pressure build up) or a piece of porous fabric together with the sleeve.

There can be a wide spread of available impact area over most of or the entire damage- vulnerable area of the platform. Internal membranes and vents can be provided in a manner which so distributes the released air on a sideways landing that a restoring moment is created to right the platform. It is possible to use inflation methods other than the conventional ram air effect, to improve upon ram air inflation. For instance, aspirators an used on aircraft escape slides or cold gas systems as used in motor vehicle airbags could be deployed for positive airbag inflation after the skid doors have swung open.