Patent GB-787851-A (GB)
Title: Airplane instruments
IPC: B64D45/00
Filed: 1955-01-25
Abstract: 787,851. Indicators and control devices for aircraft. SAFE FLIGHT INSTRUMENT CORPORATION. Jan. 25, 1955 [Feb. 5, 1954], No. 2239/55. Class 4. [Also in Group XXXVIII] Signals and indicators. An indicating device on aircraft which provides an indication of flying speed or warns of an impending stall or which may be used to operate elevator controls comprises a pivoted vane 14 responsive to variation in pressure in the zone of the shifting stagnation point at the leading edge of a wing and having an armature 28 that co-operates with an exciting coil 40 and secondary coils 34, 36 having electrical outputs, varied by movement of the armature. Coils 34 and 36 each have one terminal connected through a choke 48 to the arm 66 of a null potentiometer 54, the rectifier 52 being connected to one end of the potentiometer and the rectifier 50 to the other end through one resistance 56 which is manually pre-set and another 60, which is adjusted by movement of the wing flaps. A preferred nominal setting for the null potentiometer 54 is maximum lift in calm air during landing approach with flap resistance 60 set in its " flap up " position. A lead 83 from potentiometer 54 connects with a thrust transducer 68 comprising a free pedulum which operates the arm of a thrust transducer potentiometer 76 supplied with voltage from a battery 78 through an adjustable potentiometer 80. In parallel with the potentiometer 76 is a null potentiometer 82 set to attain zero potential during landing approach of the aircraft. Consequently a combined signal which is a function of lift and thrust is fed to wires 84, 86 which are connected to two mechanisms 88 and 90 in series. The mechanism 88 is wired as a bridge B<SP>1</SP> and comprises actuating coils 146, 148 for a relay 142 and actuating coils 150, 152 for a relay 144, both relays being polarised and respectively operating normally open contacts 166, 168 which are in series circuit with a battery 170 and further relays 174, 178. The relays control three signal lamps 192, 194 and 196 which when illuminated indicate respectively if the aircraft is flying slowly close to a stall, at a correct speed or at a high speed. When at high speed, the vane 14 moves upwardly, neither relay 142, 144 is actuated and hence arm 186 of relay 178 remains on contact 188 and " fast " lamp 196 is illuminated. When, at low speed, vane 14 moves downwardly, both relays 142, 144 are energised and arms 180, 186 of relays 174, 178 will be moved to contacts 184, 190 which illuminates " slow " lamp 192. In circuit with contact 184 is a vibrating warning device 212 of the type described in Specification No. 668, 805 and an under-carriage pressureoperated switch 220 which ensures that device 212 operates only when the aircraft is airborne. A battery 208 and an adjustable potentiometer 210 is placed across the contacts.158, 160 of bridge B<SP>1</SP> so that when vane 14 is in neutral position, i.e. with the aircraft at correct flying speed, the relay 144 only is energised. This places arm 186 on contact 190, and, with relay 174 de-energised, completes a circuit to illuminate lamp 194. The potentiometer 210 may be adjusted to select the speed ranges at which the lamps will operate. Correspondence control of surfaces The mechanism 90 is adapted to control an engine throttle 232 (See Group XXXVIII). When the aircraft is on an approach landing under ILS control, means are provided to prevent excessive elevator movement in response to an ILS signal which cannot be matched by increased throttle opening. To this end relay 172 operates two arms 242, 244 which move between fixed contacts 246, 248 and 250, 252. Normally the arms are as shown to complete a circuit between an ILS input 240 and an input 262 to elevator control mechanism. When vane 14 is moved downwardly by excessive elevator movement the " slow " or " stall warning " relay 142 is operated and the arms 242, 244 are moved to place input 262 in circuit with bridge B and so place the elevators under the same control as the throttle. Specifications 668,805 and 787,852 are referred to. Reference has been directed by the Comptroller to Specification 660,854.