GB772188A - A new or improved icing indicator for aircraft - Google Patents

Abstract

772,188. Indicating information on aircraft. MINNEAPOLIS-HONEYWELL REGULAT- OR CO. Sept. 9, 1954 [Sept. 11, 1953]. No. 26170/54. Class 4. [Also in Group XXXV] To detect impending icing conditions on an aircraft, perforated tubes 12 and 25, Fig. 1, are positioned in the aircraft airstream e.g. in the air inlet of a gas turbine engine. Temperature variable resistances 15 and 27 responsive to the temperature of tubes 12 and 25, respectively, are connected to a bridge-operated relay circuit 100 controlling the direction of rotation of a reversible A.C. motor 114 adjusting a valve 49 to maintain a constant difference in temperature between tubes 12 and 25 by ensuring an appropriate supply of cooled air or volatile fluid, e.g. alcohol, from a reservoir 45 to an evaporator 38 of porous sintered material associated with tube 25. Tube 25 is thus maintained at a lower temperature than tube 12 so that impending icing conditions on the aircraft result in actual icing of tube 25 to block its perforations. This unbalances air pressures applied from tubes 12 and 25 to opposite sides of a diaphragm 82 so that a switch 85 is closed to switch on a heater 30 for tube 25, and a switch 135 is changed over to run motor 114 in a direction to close a valve 49 and stop the supply of cooling fluid. Heater 30 de-ices tube 25 and the cycle repeats as long as impending icing conditions obtain so that a lamp 95 is illuminated as a warning to the pilot. When actual icing conditions obtain, the perforations of tube 12 become blocked to reduce the pressure applied to the underside of a diaphragm 56. A switch 65 is closed to energise a, heater 18 for tube 12. A lamp 76 is then illuminated intermittently in a similar manner to lamp 95 to indicate actual icing conditions. An arrangement in which ice formation reduces the gap and hence air flow between concentric cylindrical members is described. Diaphragm 56 may also operate a potentiometer to control the energization of heater 18 the current through which is displayed as an indication of the icing rate. U.S.A. Specification 2,423,534 is referred to.