On Sat, 17 Jan 2004 21:21:48 -0000, "karel adams"
wrote:

depending on where one flies, icing is a major concern
the risk of icing depends on outside air temperature and humidity

but this puzzles me:
it is quite normal for an aircraft to have an ourside air termometer
but i never heard of an outside air hygrometer gauge

there is no such thing as an outside air hygrometer. the instrument is
called a psychrometer and it basically is a fan forcing air over two
thermometers. one is surrounded by a wet wick, the other is just bare
dry glass. evaporation cools the wet thermometer. when you set it in
motion and the temperatures stabilise you read the two temperatures.
precalculated tables are used to derive the humidity.

on an aircraft icing is to be expected occasionally and that is what
the carby heat is for. it directs hot air from an exhaust muff into
the carby to melt away the ice. works well on my aircraft.
Stealth Pilot
Australia