Patent GB-506843-A (GB)
Title: Means for indicating ice formation
IPC: B64D15/20
Filed: 1938-01-12
Abstract: 506,843. Means for indicating the formation and preventing the accumulation of ice on aircraft surfaces. GOLDSCHMIDT, R. Jan. 12, 1938, No. 1087. [Class 4] Apparatus for indicating ice-formation on aircraft, comprises a movable member exposed to the atmosphere, means for normally maintaining the member in motion, and indicatng means responsive to an impediment to the motion of the member produced by ice forming thereon. In one form, Figs. 1 and 2, a diaphragm 1 is pulsated by an electromagnetic system comprising a U-shaped armature 4 carried by a plunger 3 fixed to the diaphragm, a yoke ring 7 mounted in a casing 2 and carrying pole pieces 6, and coils 8 surrounding the air gap between the pole pieces and the armature and maintained in position by springs 9 which also urge the armature away from the pole pieces. The coils 8 are periodically energized through a commutator unit 20, secured to the underside of a strap 11 secured to the casing and enclosed in a shield 22. The armature carries an insulated contact 12 co-operating with an insulated contact 13 carried by the strap 11, and its movement'is limited by studs 10 slidable in the strap. A second electromagnetic system comprises a U-shaped armature 14, Fig. 1, located at right-angles to the armature 4 and slidable on a reduced portion of the plunger 3 against a spring 15, a yoke 16 fixed to the plunger, and coils 17 maintained in position by a plate 25 and the springs 9. When the coils 17 are energized the armature is moved upwards and impacts a shoulder 18 on the plunger 3, which impact is transmitted to the diaphragm 1. As shown in Fig. 5, the commutator comprises an arm 23 which is moved over six fixed contacts 24 by a motors, 32 through reduction gearing. Five, of the contacts are connected together and through the coils 17 and a time switch 27 to one terminal of an electrical source 28, the other contact being connected through the coils 8 to the same terminal. The contacts 12, 13, an indicating lamp 31, a resistance 30 and the motor 32 are connected across the source 28 and a main switch 29. To set the indicator in operation, the switch 29 is closed and the arm rotates, thus closing the circuit of the coils 8 once per revolution and causing pulsation of the diaphragm. Short interruptions of the short circuit through the contacts 12, 13 do not cause the lamp to be noticeably illuminated. If ice accumulates on the diaphragm the contacts 12, 13 remain open and the lamp 31 lights up. The lamp may be arranged behind a frosted glass screen bearing the word " Ice " in clear glass. Instead of or in addition to the lamp, a relay, adapted to set de-icing apparatus in action, may be provided, the time constant of the relay being made of suitable length by the use of a condenser. The circuit may be arranged so that the lamp is lighted when the contacts remain closed. In order to de-ice the indicator, the switch 27 is closed and the coils 17 thus excited five times per revolution of the arm 23 to cause impacts to be delivered to the diaphragm which serve to break up and detach the ice. If de-icing apparatus is fitted to the aircraft, this may be used to device the indicator and the self-de-icer omitted. In another form, Fig. 6, the diaphragm 1 carries an armature 34 cooperating with an electromagnet 35 having an exciting coil 36. The terminals of the coil 36 are connected to a casing 37, one terminal being directly connected, and the other through a source of current 38, the energizing winding of a relay 39 for setting de-icing apparatus in action, an indicator lamp 40 and contacts 41, 42. The contact 41 is fixed to the casing and insulated therefrom and the contact 42 is fixed to the armature and electrically connected to the casing. The contacts 41, 42 are normally in engagement so that when the battery 38 is connected in circuit the diaphragm will be set in vibration, the contacts 41, 42 acting as a make and break switch. Under these conditions the current flowing is insufficient to light the lamp, but, when ice accumulates on the diaphragm, its amplitude of movement decreases, the current in the coil increases, the lamp lights and the relay is energized, the diaphragm being finally brought to rest with the contacts closed. Tode-ice the diaphragm, the contacts &c. are shorted by a switch 43 so that the armature is strongly attracted towards and impacts the electromagnet 35. The pulsatory movement of the movable member may be imparted by hydraulic, pneumatic or mechanical means, and the indicating means made responsive to an increase in the pressure or torque required. The moving member may be a rotating member. For example, the load on the shaft of an electric motor may be arranged to be increased by ice-formation, the increased current through the motor winding being utilized for indicating purposes. Instead of a lamp, aural indicating means may be used. According to the Provisional Specification, the diaphragm may be arranged to vibrate at an audible frequency so that ice-formation is indicated by a change in the note or cessation of sound. Also, the current through the indicator may he passed through the primary winding of a transformer so that an alternating voltage is developed in the secondary winding when the diaphragm is vibrating but falls to zero when the diaphragm ceases to vibrate. A plurality of indicators may be provided to indicate different thicknesses of ice.