30 ice and rain protection Flashcards
what are the types of surfaces which require ice and rain protection
ICE protection:
- nontransparent surfaces (LE, inlets…)
- external surfaces (sensors, antennae..)
- internal surfaces (water lines
- windshield
FOG protection:
-windsheild
Rain removal:
-wind removal
what are the two main ice protection principles?
antiicing (not allowing ice to form or allowing ice to form on less critical surfaces) and deicing (allowing ice to build up and periodically removing it
what are four technical solutions for antiicing and deicing and which are they used for (a / d)
- pneumatic boot system (only d)
- hot are system (a and d)
- electrical resistance system (d rarely a)
- fluid systems (d rarely a )
at what temperature will all the water in the air be frozen?
(-40 deg C) ! not 0!
what is the condition for supercooled water to exist
nothing has disturbed the water during cooling
what is supercooled water?
water below 0 deg C
why is supercooled water a problem
supercooled water wil turn instantly to ice upon contact with the aircraft.
The contact force will provide the necessary input for the phase change
what are the four conditions for aircraft icing to occur ( due to supercooled water -> common one during flight)
- the air contains water (clouds)
- air temp is below 0de C
- air temp above -40 deg C
- airplane sureface temp is below 0 deg C
what are other icing mechanisms beside standard supercooled water during flight
- during descent -> the aircraft surface especially by the feul tank, is still below 0 deg C and the humid air (even above 0 deg C can freeze on the surface
- carburator icing
- ice buildiup from snow etc before take off
- pick up slush / water picked up during takeoff can freeze during flight
describe the three types of ice, draw them, and at what temperatures do they form?
clear ice:
- 0 to -10 deg C
- large water droplets
- clear
- can spread over surface -> change shape of LE
- bulky shape
rime ice:
- -15 to -20 deg C
- from smaller, fine droplets of water
- freeze immediately
mixed ice:
- -10 to -15 deg C
- bad combinations of both (change shape, build up quickly)
what ATA chapter is Icing?
ATA 30
what is the total water catch of the wing?
The amount of ice that will build up on the a given section of the wing per unit time (expressed as a mass flow rate)
what is the equation for total water catch?
mdot = v * t * dy * rhoLWC * Em
v == velocity t == thickness (of wing) dy == portion of span rhoLWC == the mass of supercooled water per volume (ie the liquid water content) Em is the water catch efficiency
what does the water catch efficiency depend on?
- air parameters (density)
- airfoil shape, thickness
- droplet shape
what type of aircraft will have high water catch efficiency (Em)
- high aircraft speeds (although this does heat up wing)
- thin airfoils (divert molecules less)
- large droplet size
where can detailed information about the water catch efficiency be found?
AIR 1168/4
why is it bad if ice changes the airfoil shape of an aircraft
-increase stall speed
-decrease amount of lift produced
-really increase drag
-
what detrimental effects can ice have on the aircraft?
- change shape of airfoil (change aoa stall angle, change stall speed, decrease lift, increase drag)
- increase weight (cant maintain altitude)
- block or limit range of control surfaces
- block sensors (aoa sensors, pitot tube..)
- antennaes break off
- ice can fly off propellors
- tailplane stall (ice on horizontal stab cause pitch down (can be uncontrollable)
what determines the design of the ice protection system
certification requirements
FAR 25
what is the most common use for pneumatic boot system deicing?
propellors
what is the basic principles of the pneumatic boot deinc system?
tubes alternately inflate and deflate to break chunks of ice and then aerodynamic and centrifugal forces propel the ice off of the surface. The tubes (boots) are inflated via pneumatic pressure in 5 -6 seconds and deflated via a vaccuum.
what is the typical orientation of pneumatic boots?
spanwise (but can also be chordwise)
what are advantages of teh pneumatic boot deicing system?
- light weight
- light power usage
- relatively low cost
- maintenence well known, established
what are components of the pneumatic boot deicing system?
boots
pressure source
vacuum source
air distribution system
describe the drag penalties of the pneumatic boot deicing system? in multiple stages of flying
during icing conditions there issome penalty but not so major
boots are vacum sucked for smoth edges and no penalty in nonicing conditions
which two technical solutions are thermal ice protection systems
hot air systems
electrical resistance systems
what are the three types of thermal ice protections systems
evaporative antiicing-> provides enough heat to evaporate the water upon impact. Most energy
running wet antiicing -> provides enough heat to keep teh water as water until it runs back to non critical surfaces. Ex: engine inlet bc water can flow into engine
cyclic deicing -> allows ice to build up and periodically goes through to (quickly) heat up surface to zero adhesion and ice is aerodynamically forced off. uses least energy
which technical method is most commonly applied on large transport aircraft? why? where?
hot air antiicing and deicing
there is a lot of hot air available from engines. pneumatic systems of these aircraft are efficient and reliable.
LE , high lift devices, engine inlet
what are the relative energy uses of the three thermal ice protection systems
most:
evaporative antiicing
running-wet antiicing
cyclic deicing
least
what are common applications of the electrical resistance thermal ice protection systems? how does each work?
- external components via evaporative method
- internal components (heated above 0deg C to prevent freezing)
- non transparent surfaces
- nontransparent surfaces with cyclic deicing (to reduce electrical loads)
what is the main principle of electrical resistance deicing?
electrical resistors provide heat. Its in the name.
what is a parting strip
used to break chord into regions for cycling deiicing via electrical resistance
what is the biggest disadvantage of the electrical resistance thermal ice protection system?
large power demand
what is the basic principle of a fluid ice protection system
a freezing point depressant is alpplied to the surface to be anit/deiced. This fluid causes the supercooled droplets to mix with the fluid and not freeze when they come in contact with the wing. Can be anti or deicing (if wait for fluid to be introduced and tehn use it to melt the bottom layer)
what is the main disadvantage of the fluid anit/deice system?
- The fluid is heavily
- once fluid id gone there is nothing to do.
what technical solution is typically used for windshield ice and fog protection?
thermal resistance (film or wires in the laminate)
what is the purpose of thermal resistanace in the windsheild?
antiicing
defogging
correct temp against bird strikes
what is an alternatice for rain removal on the windshield
external hot air blasts
what are three forms of rain protection for the windows (used during takeoff and landing)
windshield wipers (high drag) external hot air blast rain repellent (addition to one of the two)
when is rain protection used on the wiper?
rain conditions during take off and landing (not common during altitude cruise)
what are the two methods for determining when the ice protection systems will be used?
- visual detection (look at wing and engine leading edges and their lights)
- electronic detection (oscillating probe)
how does electronic ice detection take place?
There is a probe which oscillates at a known frequency. if ice buids up oon it the freequency decreases.
