Icing Flashcards
Ice formation
Icing will occur when temps fall below 0 degrees
Low pressure can cause icing when temps are above 0 degrees
Types of icing and snow
- Rime ice, opaque white and granular ice.low temps in clouds of small water drops. brittle and easy to break off so not really an issue unless its prolonged flight
- Clear ice, transparrent dense and tough and adhesive. forms from mainly large super-cooled water. occur when rime happens but you can tell which is predominate
- Rain ice, Sub zero temps where rain occurs, rain is caught by a/c then freezes, occurs quickly because the airframe is below 0degrees c
- Packed snow, happens in wet snow or sleet because the airfram is not well streamlined, cover cover air intakes which is bad.
- Hoar frost, when a/c is below 0degreese c so thatr the air cooled below dew point, forms in early winter months, when a/c parked overnight on clear winter nights and quick descents.
- restricts view and increases stalling speed, which is critical in landing/take off.
Provision- sensitive to ice are as
- Aerofoil surface
- Engine intakes-
- Engine internal surfaces
- rotor blades and propellers
- Windscreens
- instrument probes and vanes
- control hinges and linkages
- weapons and weapon carriers
Aerodynamic Effects of ice formation
Aerofoil will not become aerodynamic increasing drag, decreasing lift and increase stalling speed. build up on moving parts can lead to serious control effect.
ice under the wing can cause change in performance of a/c
Weight and vibrations
Ice can cause weight issue which will lead to increase vibrations, especially on propellors. can also lead to fracturs within the airframe and changes in CoG
Effects on instruments
ice on external instruments (Pitot tubes) can cause a false reading inside cockpit.
effects on control surfaces
more risk on smaller a/c because the gap between the controls can build up ice jamming the controls and prevent them from being used properly., highly dependant on design rather than a/c size.
Misc effects
Ice on windscreens and canopys can cause decrease in vision, hoar frost causes this the most
communications and ice
ice can cause comm issues as the ice can reduce effectiveness, increase weight and vibrations
Undercarriage and ice
Undercarriage assemblies could be stopped by ice, landing gear etc,
Engines and ice
Engine intakes can be blocked by ice and snow hindering fuel and air flow
descending
Quick descent can cause fogging up of canopys and intruments inside, demisting devices should be used and at times the a/c should be allowed to heat up befire descent
icing on helicopters
Helicopter icing is critically bad, ice on rotor systems can interrupt laminar flow increasing drag nd reducing lift.
Ice on blades happens at tips because of water droplets, can change blade shape and blade imbalance
asymmetrical shed can be fatal as it will change the path of a blade causing violent vibrations and seriously effect a/c control. CoG of rotor disc changes moves away form the center of rotation.
icing on helicopters cont
ice can build rapidly in freezing fog conditions,
hovering causes build up of pack ice/snow over wet slushy surfaces
Rain ice is fatal, combination of loss of lift, increasing weight and engine icing forces it down
Groundcrew can be injured if shedding ice is flying around the joint
what to do in low temp environments
A/c should be positioned top ensure drift on wind driven snow dont form on the a/c where it shouldnt
monitor the effects of snow on upper services, effects on CoG
Fill fuel tanks in a heater hangar to allow for fuel expansion, reduces condensation in fuel tanks
fit protective covers where possible to stop the effects of ice and snow. use anti icing fluid where possible
Protective covers
if a/c parked in open area use appropriate covers on intake blanks, pitot heads and air condition bungs. covers should fit tight and conform to a/c shape preventing snow etc
dont fit when aircraft is water wet because the covers will adhere to the ac. dont fit over snow etc as the same thing will happen, use de icing etc before fitting
Ice detection
use weather data initially, however there a lights that show the vital parts of the a/c which are prone to icing. some will automatically trigger de icing systems, some have sensors that alert the cockpit if there is ice present by noticing different pressures..
frequency can also be used as ice will change the frequency so it can notify is ice is present
Ice protection systems
either active or passive.
active increase temperature on certain components while passive use the shape to minimise the formation of ice. many active systems will perform both roles mentioned above.
systems that use ice protection syst
most a/c use more than one type. de icing tends to be lighter and use less energy however not all areas cant use this. anti icing is used instead on some critical parts eg the engine air intake.
Icing- engine air intake
any ice will reduce the aerodynamic capability of the part. if ice is dislodged it would enter the air intake causing damage like engine flames and damage to compressor blades. both active and passive systems are used for air intak
Thermal (hot air) airframe
Most airframe use the compressor hot air to aid in anti/de-icing effort. A mix of pressure, selector and mixing valves change the pressure and temp to a useable rate.
thermal (electrical)
Copper-manganese alloy heating elements are used to heat up smaller and more concentrated areas or complex control arangements.
Heater mats
used for de-icing helicopters and fixed wing propellers . wide manufacturing and small cross section of the element makes them ideal. the electrical load is greater than what the a/c has to they are heated up intermittenly
Chemical (fluid) diffusion
Use anti icing fluid from reservoir and push it through the porous aerofoil. mixes with moisture lowering it melting point. require low power but need to be replenished and cant be tricky to maintain. effectiveness depends on how the chemical is spread across aerofoil.
Windscreen protection
A thing gold film is laminated into the windscreen that acts as a heating element and can be turned on with an electrical supply. the system server to de mist and de ice
Wiper system maintenance (functional test)
- Put clean water on windscreens (dry can damage the wipers and motor blades)
- Make sure drive end fittings and wiper heads are fitted and locks
- Examine wipers for damage, correct attachment
- do the same for steady brackets
- examine wiper rod and bearing bocks for damage
- examine wiper rods for damage, correct attachment
- examine wiper arms for attachment, damage
- Make sure wiper springs are attached and work
- Examing any rubber for wear
- run wipers to make sure they work
servicing de-icing/anti-acid systems
most passive systems are designed to not need maintenance, but double check for damage etc and that they work
fluid systems will need replenshing so make sure its got chemicals
inspections of the systems
Done it a set time, in accordance with the repair manual, aims to reduce the probability of failure/prevent deuteriation of components
Testing the system
tested on a routine basis, done to make sure they work. done when trying to find a defect, or to isolate specific system malfunctions
Rectification of defects
Can be easy tasks like replacing a known fault. can turn into combined defect investigation which can take days to complete. all rectifications are to be done following AMM
Servicing Thermal de-icing system
Routing service include:
- visual exam of ducting and system components
- look for cracks, damage, overheating and security of attachment
- check torque loading of adjustable duct clamps
- check joints of bellows
- examine rupture discs for signs of over pressure
- check all attachments
- connecting link of mechanical controls
- moving components should be inspected for damage often
- Pressure testing the system
- Functional test
- Fault finding
serviving de icing systems
Visual exam
functional exam
Fault finding
Visual inspection of de-icing systems
distributor panels for corrosion, damage,corrosion,deformation,malaignment with the surrounding aerofoil surface
pipelines for signs of leaks, kinks, chaffing, corrosion and clearance between pipes and airframe
servicing electrical anti-icing and de-icing systems
Elecccy tech job.
