Ch 30 - Airframe Contimination And Deformation Flashcards
Contaminations
Frost Snow Heavy Snow Rime Ice Clear Ice Heavy Rain Dirt Oil Other Fluids Sand
Frost
Contamination, if on the ground, just brush it off or de-ice depending on size of AC
Caused by moisture in the air, attaching to a freezing airframe only below a certain speed
When descending, it usually accumulates under the wings as the cool fuel rests on the bottom of the wing tanks
Snow and Heavy Snow
Knock it off if light AC, De-ice the wings and the fuselage area
Increases the mass and stalling speeds
Can damage airframe if falling off in large chunks of damaging the control surfaces (hinge points)
Rime Ice
Crystalline structure, easy to see because there is lots of air trapped in the freezing process
Not as heavy as clear ice due tom the air
Effects; Aerodynamics, forms at slower speed on the leading edges
Fixed by either de-icing boots (pneumatic) or thermal mat
Clear Ice
Far more dangerous as it is much heavier and changes the shape of the aerofoil drastically
Can restrict control surfaces and is difficult to spot
Occurs on speeds less than 250kts (both clear and rime) and at temperatures <5C
Aircrafts Prone to Icing
Usually slow and operate in the mid altitude ranges
Turbo props, propeller aircraft
Turbojets only really a problem for TO and for Approach/Landing
Stalling Due to Contamination
Stalling angle decreases with frost and severely with ice
Stalling speed increases
Tail plane stall possible due to icing of the tail
Ice on tail can lead to a CG moving aft slightly (if prone) to prepare for the stall
Contamination hazard for TO
More drag induced by the contaminant which leads to a decrease in excess thrust
Icing on Leading Edges
More icing on sharper leading edges - tail or Fin
Tail poses a real problem, especially if it is an all moving tail plane as you would lose elevator authority
Fin is not so much of a problem unless engine failure etc
Icing Impacts with Flaps deployed
Increased downwash leads to an increased AoA on the tail.
If the tail is iced, the stalling AoA is lower and due to the separation bubble, is likely to stall which could be a real problem during finals. Even just with small elevator inputs, you risk stalling the tail
If there is a possibility of tail icing, test authority with flaps deployed high up in the approach
Descend with anti-icing equipment on if possible especially if going into cold most air
Before TO
De-Ice first, removing the ice (anti-icing equipment will help with this)
Auto pilot will not help, will just trim out the effects until it is too late so engage at a higher alt on the climb and disengage at a higher alt on the approach so that you have feel and can see if anything is up.
Q-Feel isn’t as effective with icing as you potentially cant feel the change
De-Icing Truck
Uses hot water and anti-icing fluids to remove the ice on aircraft. There is then a time limit to which you can then take off before you have to be re de-iced
At a busy airfield, this will be just before the threshold
Heavy Rain
Increases the mass of the AC which increases the skin friction drag and leads to an increased Stalling Speed
Degradation
Paint over time will wear and be dirty so every ~3 years (depending on use and areas operating in) will need to respray.
You can only usually respray an aircraft 3 times before you then need to totally strip it to bare metal and completely redo the paint due to the increasing weight every time.
Deformation
Damage of the airframe increases the drag as well as decreasing the structural integrity of the AC
Repaired with patches if not to major
Baggage handlers are most likely to damage AC
