GB880530A - Detecting apparatus for icing conditions - Google Patents

Abstract

880,530. De-icing aircraft. NAPIER & SON Ltd., D. Sept. 7, 1959 [June 5, 1958], No. 18035/58. Class 4. [Also in Groups XX and XXXVIII] Icing conditions in the atmosphere are detected by a head 1, Fig. 1, mounted on an aircraft at a point where it will be subject to approximately the same icing conditions as parts of the aircraft on which ice may form. Heat is supplied to the head at a substantially constant rate, so that the temperature rises steadily with time, as on the left of Fig. 3, if no ice is present, whereas in icing conditions there is a period X during which no rise in temperature is observed, as on the right of Fig. 3, and this is used to operate indicating or de-icing equipment. As shown the head 1 comprises a thin platinum strip 2 connected by conductors 3, 4a in a bridge circuit, Fig. 2, which is normally balanced at -10‹C. The output from the bridge circuit is supplied through a differentiating circuit 9, 10 and rectifier 11 to a relay circuit 12 which only operates when two pulses are supplied thereto. A source 5 supplies current cyclically so that there is a heating period followed by an unheated period during which ice is allowed to form on the head 1, the source 5 also causing the relay circuit 12 to return to its initial position at the end of each heating period. If no ice is present only one pulse is supplied to circuit 12 during each heating period and this is insufficient to operate it but if there are two pulses relay circuit 12 is operated. This may control de-icing equipment of the type employing electrical heating elements which are heated cyclically and such heating periods and/or the intervals between such periods may be controlled in accordance with the thickness of ice formed on the strip 2 as represented by the length of the portion X of the temperature curve and/or the temperature at the beginning of each heating period. In a modification the sensing element on head 1 is indirectly heated.