Hi there. Can you please assist me with a query on Impact Ice and Throttle Ice. I Have had 15 lessons mainly in a Fuel Injected C172 and have not read or heard of the terms IMPACT ICE OR THROTTLE ICE. However, the term Carburettor Icing has been spoken about. I am going over some old question papers and came across these questions and just wanted to clarify them.
Q.Ice that forms on the engine air filter IS;
A. Impact Ice.
Q. What common action should be taken if Impact Ice or throttle icing occurs?
A. Apply Carburettor Heat.
I understand the application of Carby Heat to the Carburettor but does it assist in the de-icing of the air filter.
Thanks in advance
Claw.

Impact ice is really just an example of normal airframe ice that has formed over the air intake to the induction system. It requires sub-zero temperatures and the presence of supercooled water droplets. The application of carburettor heat will do nothing to remedy impact ice. If the aircraft is not equipped with alternate induction system air, the only other option is to descend below the freezing level. Impact ice is not at all likely for a VFR aircraft in Australian latitudes.

Throttle ice refers to the additional adiabatic cooling caused when the throttle is partly or completely closed. For example, in a glide passing through 5000 feet, the pressure upstream of the throttle is about 25" while the pressure immediately downstream of the closed throttle is about 10". This sudden pressure drop is accompanied by a significant drop in temperature in accordance with the gas laws.

The evaporation of fuel in the vicinity of the throttle adds an additional cooling effect due to the absorption of latent heat during the process of evaporation. This is sometimes called refrigeration ice - not a very appropriate name actually.

By the way, I once had a complete engine failure just after lift off in a Cessna Cardinal. In this case the problem wasn't ice, it was a collapse of the scat hose that carried induction air to the carburettor. When I applied carburettor heat, power was restored simply because the carburettor heat was an alternate source of air to the carburettor. Just goes to show that the application of carburettor heat after a power loss is always a good option - even if the problem is not ice.

Bob

Thanks for the quick reply Bob. I am still unsure as to what they are asking. The choice of answers are;
Q.What common action should be taken of Impact ice or throttle icing occurs.
a. Reduce power
b. Increase power
c. Apply Carburettor heat
d. Warm the engine
Regards
Claw

Out of those choices you would have to pick [c]. But I don't see how carby heat would remedy impact ice.

The answers to some of these exam questions are not really definitive. I try my best to source the answers before taking the easy option of annoying you, but I do appreciate your assistance and expertise.
Thanks again Bob.
Regards
Claw(Gary)