GB750714A - Control of ice elimination systems - Google Patents

Abstract

750,714. Electric control systems. CLEMINSON, J. A. C. C., HAKE, G., and ROE CANADA, Ltd., A. V. Feb. 9, 1954, No. 3751/54. Class 40(1) [Also in Groups XXXIII and XXXV] An aircraft ice elimination system comprises a plurality of de-icing elements switched into operation successively by a cyclically operated stepping switch which has further dummy positions variable in number under the control of selecting means responsive to the rate of ice formation to vary the cycling time and hence the frequency of energization of the deicing elements As shown, when ice forms on a detector 26 a differential pressure actuated diaphragm 28 closes a contact 23 over which a timer 17 is energized from a source 15. The timer comprises a constant speed motor 34 driving cams 31-33 which interrupt the supply over line 24 at different frequencies any of which may be manually selected by a switch 42. The pulses so selected are fed to the drive magnet (not shown) of a step-by-step switch 18. In successive positions 44a of the stepper 18, relays 45 are energized to connect their respective de-icing heater elements 11 into circuit from a generator 10, each element being energized for substantially the duration of dwell of the switch arm 18 on the corresponding contact 44a. The switch arm 18 is then stepped over dummy contacts 44b until it reaches a selected one of three contacts 44c when a relay 48 is energized to reset the stepper to zero during which time a further relay 50 is energized to prevent pulses from the timer reaching the stepper. The cycling time of the stepper and hence the frequency of energization of the de-icing elements depends upon the selection of the operative contact 44c. This is effected by a known capacitor type detector 53 responsive to the rate of ice formation between probes 54. The device yields a maximum voltage on line 55 for a minimum rate of ice formation which energizes relays marginal 56, 57 to select, i.e. energize the last contact 44c in which case the stepper cycling time is a maximum. As the rate of ice formation increases, the voltage on line 55 decreases to release, first relay 57, and then relay 56, whereby the operative contact 44c is switched first to the intermediate contact, and then to the first contact 44c. A heater 30 is energized over the detector operated contact 23 to remove the ice from this detector at substantialy the same rate as the de-icing elements remove ice from their respective portions of the aircraft. The cycling system may be applied to a hot air or pneumatic de-icing system.