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Module 17 > 17.5 Propeller Ice Protection > Flashcards

17.5 Propeller Ice Protection Flashcards

1
Q

What does ice formation cause during operation of the propeller?

A
  • Distortion of Aerofoil Section
  • Vibrations
  • Lower Propeller Efficiency
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2
Q

What regions are most affected from icing?

A

Propeller Blades
Spinner
Engine Intake

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3
Q

When visible moisture is present in the air, icing can occur at up to what temperature?

A

Up to 10 degrees Celsius.

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4
Q

What are the two main ice protection systems?

A

Fluid anti-icing

Electrical de-icing system

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5
Q

What de-icing System is usually found on piston aircraft?

A

Fluid anti-icing

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6
Q

What type of de-icing fluid is used?

A

Alcohol based fluid (Iso-Propyl-Alcohol)

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7
Q

Why is fluid anti-icing not used on a turboprop?

A

The fluid could contaminate the compressor blades.

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8
Q

What is the disadvantages of using the fluid anti-icing system?

A
  • Extra weight of carrying the fluid
  • The amount of fluid must be monitored constantly
  • System must be operated before icing occurs
  • It’s not able to remove impacted ice once it has formed
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9
Q

Why does the fluid system and components for the de-icing system need regular cleaning?

A

The fluid is thixotropic

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10
Q

What should you ensure that the fluid discharge nozzle is aligned with? (Fluid Anti-icing)

A

The Slinger Ring

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11
Q

When is a flow test required? (Fluid Anti-Icing)

A

-After reassembly of the System filter

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12
Q

When is a functional test not usually required?

A

When blades are fitted with overshoes (Depending on the manufacturer)

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13
Q

What is the percentage of mixing agents in the cleaning agent required to clean the blades?

A

95% methylated spirits - 5% distilled water

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14
Q

What should the blade overshoes be inspected for?

A

Cuts
Blisters
Signs of separation at edges

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15
Q

Can damage be cut back from blade overshoes?

A

Yes, only slightly if the AMM permits.

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16
Q

What are the heating boots/ mats bonded to?

A

Inner 1/3 of each propeller blade.

17
Q

How is the aircraft electrical power distributed to the heater booties?

A

Via spring loaded carbon brushes rubbing against a copper slip ring.

18
Q

How many leads does a single element boot/ mat have?

A

2

19
Q

How many leads does a twin element heater boot/ mat have?

A

3 (2 live, 1 earth)

20
Q

What is the main reason that continuous heating not used on the propellers.

A

It would cause water to be carried back and freeze on the trailing edge of the blade.

21
Q

What is used instead of continuous heating?

A

Cyclic heating.

22
Q

Why is cyclic heating advantageous?

A

It allows a thin layer of ice to form on the blade, when the mat is energised the temperature of the ice increases rapidly causing it to disperse via centrifugal force.

23
Q

How long is the heater element energised for in cyclic heating, and how long for complete cycles?

A

Energised for 15-30 seconds.

Cycled every 2-6 minutes.

24
Q

What is a fast cycle for the electrical de-ice system?

A

Approx 2 minutes , between temperatures of -6 to 10 degrees

25
Q

What is a slow cycle on the electrical de-ice system?

A

6 minutes below -6 degrees

26
Q

When are continuing and resistance checks required on the heating elements?

A

Prior to installation of the propeller.

27
Q

Why is an insulation resistance test carried out?

A

To ensure the heating elements are adequately insulated from the blades and spinner

28
Q

What type of conditions will wear away brushes in a brush gear the most?

A

Damp and dusty conditions

29
Q

What is the minimum permissible contact area allowed between the carbon brushes and copper plate?

A

80% minimum

30
Q

What is “run-back”?

A

It is the condition that would occur if the propeller blades were heated continuously. The ice would melt and run to the trailing edge, where it would freeze again.

31
Q

How are the brush blocks cleaned?

A

With a lint-free cloth or soft brush

Never use solvents

Module 17 (6 decks)

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