17.5 De icing equipment Flashcards
(24 cards)
what can happen as a result of ice build up?
distortion to the aerofoil section, vibrations and lower propeller efficiency.
what regions are most at risk for ice build up?
blades
spinner
engine air intake
what are the two most common anti ice protections for propellors?
fluid anti ice
electrical de ice
where is fluid anti ice typically used and why?
piston engine as the fluid can damage compressor blades
what is the most common and problem free fluid anti ice used?
iso-propyl alcohol
where is anti ice fluid stored?
reservoir in the airframe
how is anti ice fluid speed of distribution controlled?
with a rheostat
what does the pump for anti ice fluid do?
it injects filtered fluid through a fixed nozzle on each engine into a U shaped slinger ring on each propellor
fluid centrifugally enters grooved rubber de icing boots
what are the disadvantages of fluid anti icing?
-The weight of the fluid to be carried.
-The amount of fluid must be constantly monitored.
-The system must be operated before icing occurs.
-It is not able to remove impacted ice once it has formed.
what makes up electrical de icing systems?
-electrical energy
-resistance heating element
-system controls
-wiring
where are electrical heating elements mounted?
internally or externally on the propeller spinner and blades
where are Heating boots/mats containing electrical elements bonded?
inner third of each propellor blade
how is electrical power transferred from the aircraft system to the rotating propellor hubs?
by spring loaded carbon brushes rubbing against copper slip rings
how can the heater element be attached to the de icing boot/mat?
single, or segmented into two parts. A single element boot/mat has two electrical leads while a twin element has three leads (2 live and 1 earth).
when is the propellor de icing system only operated to reduce the risk of overheat?
when moving or shortly for testing
what is run back?
more than that required for melting just the inner ice face, but insufficient to evaporate all the water formed, water will run back over the unheated surface and freeze
what is done to limit the risk of run back and to limit the load on electrical systems?
cyclic heating
what is secondary effect of cyclic heating?
allowing a small amount of ice to form on the heater mat which when temperature rapidly rises causes ice to disperse centrifugally
what is done on propellors with an equal number of blades to prevent imbalance?
opposite blades are heated together
what controls the cyclic heating function?
cyclic timer
what is the timing cycle for a heating system?
15-30 seconds a complete cycle being 2-6 mins
what is usually used to accommodate propellor and spinner requirements in terms of cyclic heating?
a two speed cycling system
how long and what temperatures are a fast cycle used for?
2 mins
10 degrees to -6 degrees
what are the temperatures and timings of a slow cycle?
6 mins
below -6 degrees
