Anti-icing/De-icing Flashcards
Ice can cause the following issues:
Reduced performance:
- increased drag
- decreased thrust
Increased stalling speed
- reduced lift
- additional weight
control surface hinges restricted
blocks pitot tubes and static vent giving earenous pressure indications
Ice protection are required in..
- Wing leading edges
- tailplane
- engine and intake inlets
- propellor
- windshield
- static and flight instruments
- sensors and probes
Countering effects of ice
De-icing:
Process of removing accumulated ice in flight or before
Anti-icing
process of preventing ice forming or building up in critical areas of aircraft
BOTH can be done onground using special fluids and hot air
This only lasts a short time..
measures for protection must take place in flight via the aircraft’s own systems
De-icing and anti-icing techniques
HOT BLEED AIR
for wing, fin, tailplane, engine nacelles
HOT ENGINE OIL & AIR
engine nacelles
ELECTRIC HEATED MATS
Propellers and heated edges
PNEUMATICALLY OPERATED INFLATING MATS (de-icing)
leading edge wings, find, tailplane that breaks off accumulations
DE-ICING FLUID
fluid weeping from pores along the leading edge of aerdynamic surfaces.
ICE DETECTION
Vibrating Rod System
ROSEMOUNT
Located on:
Outside of the fuselage
How it works:
** *In normal condition:** Electrically vibrates at 40 Khz
*With ice: the vibration is reduced, signaling ice warning and energises a heater element in the rode
*Returns to normal: Once ice melts, the heater element is switched off and rod vibrates at 40KHz, extinguishing ice detection warning.
ICE DETECTION
Pressure Operated Ice detector
Aneroid capsule connected tube
- protrudes into the airflow
if sensor holes become clogged, pressure in the aneroid drops, triggering ice warning.
Modern systems = electrical sensors
Fluid systems
DE-ICING
Use isopropyl alcohol
Used to de-ice aircraft
Used to de-ice windshield
How it works:
* fluid is pumped from a reservoir along a gallery pipe and into perforated strips on the leading edge
* Fluid flows back over the surfaces to melt the ice
TO KNOW:
1. sequence of deicing is time controlled
- a head compensation valve directs appropriate amounts of fluid to tail and wing
- There are indicators on ice protection panel showin how much fluid remains + warnings
Thermal ice protection
Heat source used to melt ice and prevent it from forming
1. Engine Bleed Air
* most common in jet transport
2. Electric powered matt
* turboprop
Bleed air system
ANTI-ICING/DE-ICING
Bleed air is exteracted from compressor
When de-icing system is on, the de-ice shut off valve opens to allow hot air to flow to perforated tubes (piccolo tube) along the leading edge
mainly sprayed onto inner face of the leading edge or inside the leading slats (inner most slats don’t have this system)
TO KNOW
-Bleed air affects performance - system MUST be OFF during take-off and performance critical phases
- A rise in temperature of air bleed will **warn if there is unacceptable temperature.
**
-Too hot to be used on ground. Only switched on in flight
Jet engine ANTI-ICING
2 Systems:
FOR THE ENGINE
- internal
- can’t be controlled by pilot
- may use either or both hot oil, or hot engine air
- to heats the nose cone and the fan
FOR ENGINE INTAKE
- Uses bleed air passing through ducts inside nacelle
Both reduce thrust and increase of temperature due to hot air entering the enging
Electric powered matt - turboprob
DE-ICING
Use in cases where there isn’t large amount of bleed air
used in leading wing (inner slats usually) and engine intake area
COmposed of:
Resistive metal stripes
how it works:
- switch off and on in sequence (to ease load on generator)
- but some are heated continuously
Intermittently heated areas allow ice to form but they melt again.
Dereflector/Bypass doors Turboprop
Dereflector door and bypass door both drop down to create airflow in the intake and allow ice particles to exit
Electric Protection system
series of electrial matts bonded to the wings leading edge
has **sophisticated control system **
- adjusts the sequence and heat applied to each matt depending on the sensed conditions
Propellors
Need electrical de-icing/anti-ciing system
ice forms near the roots
ice on tips falls off
Electrically heated boots cover 50% of the blade area
Power supplied through** slip rings and brushes**
**Power to heated mats is cycled between inner and outer **
heating sequence is symmetrical across multiple propellors and blades
for odd # of blades, the blades are heated simultaneosly.
Ice protection plate
fitted on fuselage abeam
to protect fuselage from ice flying off the blades
cockpit indication
Propeller and airframe ice protection normally operates 2 cycles
Light indicator = green = in operation
fast cycle = for light icing
slow cycle = slow icing (heavy condition)
weeping system
DE-ICING
old propellors use de-icing fluid weekeping from root of blades
Pneumatic boot system
DE-ICING
Composed of:
* Rubberized boots (with chord or span wide inflattable boots)
located:
* wing, fin, taiplane
* absolutely flush when deflated for aeerodynamic effect
how it works
* after a certail amount of ice has formed
* tubes inflate inside the boots by compressed air (engine bleed air18psi)
* compressed air is from compressor pump
* when they expand, they break off the ice
* then they deflate
Cycle of inflation:
* 6 second cycle in large aircraft
* simuleanously in small aircraft
- this is indicated in detecgtion panel
IMPORTANT
if little ice has formed,, the ice will be flexible enough to withstand the inflation
if too much as formed, there will be in little power to break the ice.
ideal thickness 0.5 to 1.5cm
Windshiled
Electrically heated - 3 phase AC
themostat set for 35 degrees
Operates on cycling system
Indicator:
Amber = overheating
Green = operational
Low setup= light icing conditions
high setup = heavy icing conditions
Rapid De-misting
hot air can be used to de-mist the windshied
Fluid de-icing
some aircraft have this
NOTE:
aircraft cannot fly if heater is not working
heat is good for hte structure of the glass and helps it withstand impact
Electrical de-icing - switched off and on by pilot - anticing - thermostatically controlled
Pitot probes
Engine air
propelor edges
windshield
Fluid de-icing
Wing leading edge
Large surfaces
Bleed air system
pneumatic boots
weeping wings
pitot tube and static port
Pitot tubes are in the nose and they detect air speed = needs to be always heated
static port are ahead of the wing and they detect altitude = may be heated
**Hot rod ice detector
Normalair - Garrett system or Teddington ice detector **
heated rod with built in floodlight
accumulates ice and is visible from the cockpit
can be seen from cockpit
pilot can then make necessry action
Sangamo weston ice detector
has a temperature sensor and moisture sensor
alarm is triggered
Smith ice detector
small heated pipe with holes
alarm is triggered
measures dynamic pressure
if ice is on the holes at the front of the tube, the holes in the back are clear = negative pressure = pressure decreasing
pilots then need to turn on the heating
Primary Automatic
Primary Manual
Advisory
Advisory:
crew activates ice protection system based on advise/info in the AFM about total temperature reading and presence of visible moisture
primary manual
flight crew activates ice protection systems based on ice detector signals
Primary automatic
ice detector automatically activates ice protection systems at optimal moments. can be manually overriden
