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Aviation History
1961
1961 - 1881.PDF
FLIGHT, 28 December 1961 995 locked in such a way that the starboard parachute cannot be selected unless the port lever is fully in the "release" position. Another possible hazard is the chance that, perhaps through enemy action, an extractor parachute might carry away of its own accord. The extractor-parachute cable is therefore broken, and joined by a safety link attached to the cargo-floor sill by a shear wire which will fail at the load imposed by a deployed parachute. The cable from the parachute is attached to this safety link by means of a spool normally held in place only by shear wires not even able to carry the load imposed by the falling away of an unopened parachute pack. The accidental release of an extractor parachute will not, therefore, initiate the dropping sequence. When the dropping officer makes a selection, however, the first movement of his selector lever inserts a strong pin through the safety link and the spool carrying the extractor-parachute cable. This pin, which will bear the load of a deployed parachute, remains as part of the safety link when the latter breaks its main shear wire and leaves the cargo-floor sill. If the dropping officer should decided to cancel the drop, he can return his selector lever to "safe," which will withdraw the spool pin and again protect the load from accidental release. During an air drop, the automatic sequence begins when the officer operates the correct selector lever (he cannot operate the wrong one). The spool in the extractor-parachute cable safety link is "armed" with its load-carrying pin, and the parachute is released from its sill stowage. (The parachute deploys, and its pull withdraws the safety link from its stowage on the sill. The link now becomes an integral part of the extractor-parachute cable, which is attached to the automatic release mechanism on the load platform. The point of attachment is the upper end of a vertical pivoted TO MAIN PARACHUTES TO EXTRACTOR PARACHUTE PLATFORM RETAINED IN AIRCRAFT PLATFORM RELEASED- EXTRACTOR PARACHUTE DEPLOYED MAIN PARACHUTES RELEASED BT EXTRACTOR PULL Operation of the automatic release mechanism, described on this page, is clarified by this diagram. An actual example—one of many used in trials—is illustrated on the facing page arm, normally held in position by a shear wire. The lower end of this arm is trunnion-mounted in a pair of jaws (part of the release unit) which are locked in the closed position until after the load platform has departed. The pull of the extractor cable breaks the shear wire and moves the arm down towards the horizontal. The lower part of the arm forms part of the housing which attaches the release unit to the ball-ended rod securing the release unit (and hence the platform) to the cargo floor. When the extractor cable rotates the arm to the bottom of its travel, the ball-ended rod is released and drops into the channel-section beam to which it is attached. The platform is now free to move aft under the pull of the extractor parachute, because the guidance-rail hooks impose no restraint in this direction. The complete platform and main-parachute pack now travels along the roller track and leaves the aircraft cleanly. At this stage the pivoted arm to which the extractor parachute is attached is still firmly held in the jaws of the automatic release unit. But these jaws are controlled by a trigger within the unit itself. When the platform is secured in the aircraft, the looped end of a cable is passed over this trigger, the other end of the cable being attached to a strong-point on the floor, near the centre-line. The length of cable is such that it will operate the trigger only when the platform A complete section of roller system, guide rails, air-drop load and plat- form, parachute packs and automatic release unit connecting the extractor-parachute pack prominent in the left foreground is well clear of the aircraft. When the platform tightens the cable, the trigger is pulled and the looped end of the cable falls away from the unit. Pulling the trigger allows the jaws in the release unit to open, and the released pivoted arm is pulled away from the unit by the ex- tractor parachute. There is now no connection between the load and the aircraft. The extractor parachute and freed pivoted arm have one more task. A cable runs from the pivoted arm to the top of the main parachute pack surmounting the load, and, now that the arm has been released from the platform, the pull of the ex- tractor cable is transferred to it from the release unit. The cable releases the parachute pack from the harness which holds it in place, and pulls the pack away from the load. When the pack is as far away as the shroud-lines allow, the continuing pull of the extractor parachute removes the bag from the main canopy, which is thus free to deploy and support the loaded platform. The ex- tractor parachute, cable and pivoted arm now float away free; if recovered, they may be used again. Put in a nutshell, the automatic release sequence is:— (1) Dropping officer selects "drop." (2) Extractor-parachute safety link armed, extractor parachutereleased. (3) Extractor-parachute drag unlocks load platform fromrestraint. (4) Load platform is withdrawn from aircraft.(5) Extractor-parachute pull is transferred to main pack. (6) Main pack is released from load.(7) Main parachute deploys, extractor parachute and cable float away free. The procedure for dropping the second load is exactly similar, except that the starboard-mounted extractor parachute is used. Safety Devices Two main safety features have already been described—the ex- tractor-cable safety link, and the load-selector interlock. A third is inherent in the automatic sequence of operations. Few things are less welcome in a supply-drop than an accidentally released main canopy foaming all over the cargo, and the Blackburn system makes such an event as impossible as could be wished. The main parachute cannot begin to deploy until its bag is removed; the bag cannot be removed until the harness holding it to the load is released; the harness cannot be released until the relevant cable is pulled; and the far end of the cable is locked to the load platform until the platform is well clear of the aircraft. Only then can the pivoted arm (to which the cable is attached) be released from the automatic release unit. Once the system has been installed in the aircraft, the loading process is straightforward. Loaded platforms are brought up to the aft door on ramps or on vehicles equipped with roller tracks similar to those on the cargo floor. The load platforms arc then moved into the cargo hold. Four platforms, together carrying
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