Faultygoods quote:
Bookworm wrong...........wrong ..........wrong
carb heat CAN cause icing in the venturi of the carb and starve the engine of fuel. air below 0 degrees still has a moisture content. However its frozen and will not adhere to the carb venturi, fuel jet etc but bounce straight through, but..... heat that air to just above freezing and the moisture will then freeze as it goes through the venturi.
Agree that air at temps below 0 degrees celcius does still support moisture, however this moisture can present itself as ice crystals or as super cooled water droplets - therefore suggesting that it will 'bounce straight through' is wrong. Super cooled water droplets would more likely cause impact icing e.g. around air intake, wing leading edges etc. ie you'd be in cloud below 0 degrees.
Foyl
Agree ref use of carb heat - should be all or nothing!
Incidently if I remember correctly from my PPL days risk of carb icing is at its greatest in air temps of -15 to +25 degrees celcius.