Icing

Question 1

Engine icing can effect -

Impact icing can effect -

Answer 1

Carburettors

Engines(air intakes, cowlings etc) and airframe icing.

Question 2

The main difference(in relation to temperature) between carburettor icing and impact icing?

Answer 2

Carb icing is more probable in temperatures above freezing while impact icing will only occur below freezing.

Question 3

The two type of carb ice:

Answer 3

1. Throttle ice

2. Fuel evaporation ice

Question 4

Throttle ice:

Principle -

Important factor(atmosphere related) -

The affected areas within the engine -

Fuel evaporation ice:

Principle -

The affected areas within the engine -

The temperature range for carburettor ice(both throttle and evaporation ice)?

Answer 4

Ice forms as a result of pressure decrease in the venturi. The pressure decrease leads to a decrease in temperature.

Humidity is the most important factor. Explains why this can occur in +20 temperatures

Sides of the manifold, on the venturi and the butterfly valve.

As a fluid changes from a liquid to a gas it required latent heat, this results in a temperature drop.

Anywhere after the fuel nozzle, but most severe wherever the pressure is lowest.

between +5 and +27 but most critical is +15.

Question 5

Factors to remember when applying crab heat(3):

Answer 5

1. If carb is to be used(unfiltered hot air type), use it fully and never partially. Partially will only serve to raise the temperature into ice zone.
2. RPM will initially decrease due to the hot air
3. Full power may not be regained with carb heat on

Question 6

Impact icing:

Principle -

Conditions in which this will occur -

Prevention(3) -

Answer 6

ice which forms on the air intake restricting or disturbing airflow to the engine. Supercooled water droplets freeze upon impact.

Super-cooled water droplets occur between 0 to -10 degrees in layer cloud, and up to -18 in heap cloud. Will not occur in clear air.

1. Carb heat(serves as an alternate heat source)
2. Alternate air for fuel injected engines
3. Bleed air for turbines engines or heated pads. Both should be selected before ice forms, otherwise it may be thrown off into the engine.

Question 7

The 4 types of airframe ice:

the 4 affected areas(in order of importance):

Answer 7

1. Hoare frost
2. Rime ice
3. Glazed/clear ice
4. rain ice
5. Wings, tail planes and fins
6. Propellers
7. Windscreens
8. Radio antennae

Question 8

Hoar frost:

The two types and how each are caused -

The dangers of each -

Answer 8

1. Ground

Occurs during winter months when aircraft is parked outside overnight. Temperatures must be below 0.

2. Air

When an aircraft rapidly descends from high altitude to a lower warm more moist air below.

Ground frost increases the stall speed slightly, air frost can reduce visibility.

Question 9

Rime Ice:

Principle -

Temperature conditions -

Dangers -

Answer 9

When small super-cooled droplets/cloud particles(-20) of water freeze on impact.

0 to -40

It will form on leading edges, windscreens, aerials and pitot. The weight increase is not substantial, it main dangers is that it alters the aerofoil and chokes intakes.

Question 10

Glazed/Clear ice:

Principle -

Temperature conditions -

Dangers -

Answer 10

Super-cooled water droplets/cloud particles(larger than those of rime ice) freeze on impact but after impact latent heat is releases causing it to melt. It will flow down the aerofoil until it freezes again. This will form a sheet of clear ice.

0 to -20.

Causes vibration on propellers.

Question 11

Rain Ice:

Principle -

Dangers -

Conditions where it is found -

Answer 11

This is caused by super-cooled rain rather than super-cooled water droplets/cloud particles.

Because of the longer freezing time, the back flow is extensive and a larger area is covered. It is regarded as the most dangerous type of airframe icing.

Usually below a warm front. On occasions a cold front

Question 12

Between a thin, low drag high speed aerofoil and a high lift slow airspeed, which is more susceptible to airframe ice?

Answer 12

The former

Question 13

The kinetic heating formula for velocity in knots:

Answer 13

Temperature rise = (TAS / 100) squared