17.5 Propeller Ice Protection Flashcards
What does ice formation cause during operation of the propeller?
- Distortion of Aerofoil Section
- Vibrations
- Lower Propeller Efficiency
What regions are most affected from icing?
Propeller Blades
Spinner
Engine Intake
When visible moisture is present in the air, icing can occur at up to what temperature?
Up to 10 degrees Celsius.
What are the two main ice protection systems?
Fluid anti-icing
Electrical de-icing system
What de-icing System is usually found on piston aircraft?
Fluid anti-icing
What type of de-icing fluid is used?
Alcohol based fluid (Iso-Propyl-Alcohol)
Why is fluid anti-icing not used on a turboprop?
The fluid could contaminate the compressor blades.
What is the disadvantages of using the fluid anti-icing system?
- 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
Why does the fluid system and components for the de-icing system need regular cleaning?
The fluid is thixotropic
What should you ensure that the fluid discharge nozzle is aligned with? (Fluid Anti-icing)
The Slinger Ring
When is a flow test required? (Fluid Anti-Icing)
-After reassembly of the System filter
When is a functional test not usually required?
When blades are fitted with overshoes (Depending on the manufacturer)
What is the percentage of mixing agents in the cleaning agent required to clean the blades?
95% methylated spirits - 5% distilled water
What should the blade overshoes be inspected for?
Cuts
Blisters
Signs of separation at edges
Can damage be cut back from blade overshoes?
Yes, only slightly if the AMM permits.
What are the heating boots/ mats bonded to?
Inner 1/3 of each propeller blade.
How is the aircraft electrical power distributed to the heater booties?
Via spring loaded carbon brushes rubbing against a copper slip ring.
How many leads does a single element boot/ mat have?
2
How many leads does a twin element heater boot/ mat have?
3 (2 live, 1 earth)
What is the main reason that continuous heating not used on the propellers.
It would cause water to be carried back and freeze on the trailing edge of the blade.
What is used instead of continuous heating?
Cyclic heating.
Why is cyclic heating advantageous?
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.
How long is the heater element energised for in cyclic heating, and how long for complete cycles?
Energised for 15-30 seconds.
Cycled every 2-6 minutes.
What is a fast cycle for the electrical de-ice system?
Approx 2 minutes , between temperatures of -6 to 10 degrees
What is a slow cycle on the electrical de-ice system?
6 minutes below -6 degrees
When are continuing and resistance checks required on the heating elements?
Prior to installation of the propeller.
Why is an insulation resistance test carried out?
To ensure the heating elements are adequately insulated from the blades and spinner
What type of conditions will wear away brushes in a brush gear the most?
Damp and dusty conditions
What is the minimum permissible contact area allowed between the carbon brushes and copper plate?
80% minimum
What is “run-back”?
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.
How are the brush blocks cleaned?
With a lint-free cloth or soft brush
Never use solvents
