Patent GB-574947-A (GB)
Title: Improvements in and connected with safety or protective means for aircraft
IPC: A62C3/08
Filed: 1943-11-04
Abstract: 574,947. Fire extinguishing. CORFIELD, A. H., CHAPMAN, E. E., and STONE & CO., Ltd., J. Nov. 4, 1943, No. 18287. [Class 47 (ii)] [Also in Group XXXVII] In a fire-extinguishing and preventing system for aircraft of the kind in which extinguishing medium is released automatically by electrical means in the event of a crash, the crash detectors comprise a pair of contacts concentrically arranged and adapted to be brought into contact positively by breakage or distortion. of a protecting cover. Detectors are fixed at the nose of the fuselage, on the wings, and at the engine stations. In addition, hand, gravity, and inertia-operable switches are provided in the system. As shown in Fig. 1, a detector comprises a straight contact wire g and a coiled contact h, connected respectively to terminal blocks d, e and enclosed in a thin or frangible cover k formed with a cup j to position the contact h. The base a of the .detector is secured to the surface of an aircraft part c. In the event of a crash or pancake landing, the cover k will be broken or distorted, bringing the contacts g, h into engagement. In a modification, the contacts are additionally enclosed in a frangible thimble. In another modification, Fig. 3, the contacts g, h are mounted in a bulb t adapted to screw into a socket after the manner of a flash lamp bulb. The cover k is streamlined and secured to the base by spring clips m<1>, n<1>. A modification of this form is provided with manual means for shorting the contacts for test purposes without opening up the detector which, as in the other forms, has sealing,means for rendering it watertight. In the form shown in Fig. 8, the contacts are mounted in an elongated tube o adapted to project from the wing tip, the tube screwing into the base a and the contacts g, h being in electrical connection with contacts m, connected in the electric control circuit. A press button may be provided at the outer end of the tube for test purposes or, as shown, the base may have openings k<3> for the insertion of test pins. In modifications of this form, the tube is adapted to be bent to curved form, e.g., around a wing tip, and the contacts are normally separated by a frangible insulator adapted to be broken by teeth on the straight contact, or by glass or like beads which pulverise in the event of a crash. In another modification, Fig. 13, the straight contact g<10> is resilient and carries a weight g<11> adapted to make contact with the coil contact h, due to its inertia, in the event of a crash, even before the cover o is broken or distorted. The various detectors of the system are connected to terminals 13 in a relay, Fig. 14, comprising an hermetically sealed box 14 enclosing an electromagnet comprising a coil 1 and armature 3. The box may contain hygroscopic material. The armature has a stem 2 mounted on springs 6, and carries contacts 8 adapted to make contact with fixed contacts 9 in the extinguisher control circuit when the armature is attracted to the annular polepiece 4 upon closure of the contacts of a detector. The stem 2 is weighted at 10 and biassed by a spring 11, so that it is adapted to act as an inertia switch in the event of a severe crash. One pair of contacts 8, 9 is arranged in a holding circuit for the electromagnet, to prevent re-opening of the extinguisher control circuit in case contact at a detector should be only momentary. In order to provide for the aircraft turning over gently, a mercury switch, Fig. 15, mounted in the relay casing, comprises a tube 15 of the shape shown, with a mercury reservoir 16 at its lower end and contacts 17 at the upper end. The latter are in series with switches operated by the retractable undercarriage of the aircraft, so that operation of the mercury switch will not be effective if the aircraft is flown upside down. Also in the casing of the relay, manual means are provided for breaking the holding circuit of the electromagnet after it has been closed for test purposes. Instead of the holding circuit, a mechanical latch may be provided for locking the relay switch after it has closed. In the complete circuit for an extinguisher control system, the various crash detectors are arranged in parallel in the conductor connecting the electromagnet across the mains. The gravity switch and undercarriage switches are in parallel with the crash detectors. Leads from the positive main include control means for the extinguishers and manual switches operable by the pilot, and are connected to the relay armature contacts, the fixed contacts being connected to the negative main. A pair of relay contacts are connected in the relay holding circuit and others may be connected in a battery cut-out circuit. Separate extinguishers may be provided for each engine and for the petrol tanks. In addition, the relay may be arranged to fire explosive charges for destroying secret apparatus. The Provisional Specification describes an arrangement in which the contacts of the crash detector normally are closed, and open when the cover breaks.