AIRFRAME CONTAMINATION Flashcards
(11 cards)
Types of contamination
> > Frost. Frost can form on the surface of the aircraft either when it is standing on the ground when the temperature falls below 0°C, or in flight, if the aircraft, after flying in a region where the temperature is below 0°C, moves into a warmer layer of air. It consists of a fairly thin coating of crystalline ice.
> > Ice. The main forms of icing are clear ice, rime ice and rain ice.
–Clear ice (glaze ice) is a translucent layer of ice with a smooth surface, caused by large super cooled water droplets, striking the leading edges of the airframe. As there is some delay in freezing, there is some flow back along the surface behind the leading edge.
–Rime ice forms when small supercooled water droplets strike the leading edges and freeze almost immediately so that there is no flow back. It is a white opaque formation.
–Rain ice is caused by rain which becomes supercooled by falling from an inversion into air which is below 0°C. It does not freeze immediately and forms considerable flow back, and builds up very quickly.
EFFECT OF FROST AND ICE ON THE AIRCRAFT
The formation of ice and frost on the airframe will:
– modify the profile of the aerofoil. Ice will normally form on and behind the leading edges of wings and tailplane and can result in severe distortion of the leading edge profile. This will give a large increase in drag and a substantial decrease in C L MAX.
– increase the roughness of the aircraft surface.The main effect of frost will be to increase the surface roughness and this will increase the energy loss in the boundary layer. The skin friction drag will increase and the boundary layer will have an earlier separation, giving a reduced C L MAX
– increase the weight of the aircraft
–The reduced CL MAX of the wing will give a higher stalling speed and the decreased CL MAX of the
tailplane could cause it to stall when the aircraft is flying at low speed, particularly if the wing
downwash is increased as a result of flap extension.
–Tailplane stall will result in loss of longitudinal control. Clear ice and rain ice especially can
add considerable weight to the airframe, and this will in turn give a higher stalling speed, as
well as increased induced drag. The margin of thrust to drag will be decreased, reducing the
ability to climb. Increased power will be required to maintain height, resulting in increased fuel
consumption.
–Ice formation on propeller blades can upset the balance of the propeller and cause severe
vibration, particularly if pieces of ice break off from one blade. Pieces of ice shed from propellers
can also cause damage to the fuselage.
–EFFECT ON INSTRUMENTS. Formation of ice on static vents and pitot heads could cause errors in the readings of pressure instruments, and eventually, failure to show any reading.
–EFFECT ON CONTROLS. Any moveable surface could become jammed by ice forming in the gaps around the control,or by pieces of ice breaking off and becoming jammed in the control gaps. The controls could
become difficult to operate or immovable.
–AIRFRAME AGING.Over a period of years the condition of the airframe will deteriorate due to small scratches,
minor damage, repairs, and general accumulation of dirt and grease. The overall effect of this will be to increase the drag of the aircraft (mainly skin friction drag) with a consequent increase in fuel consumption
After an aircraft has been exposed to severe weather:
a. snow should be removed but smooth ice may be left.
b. all snow and ice should be removed.
c. loose snow may be left but ice must be removed.
d. providing the contamination is not too thick, it may be left in place.
B
Icing conditions may be encountered in the atmosphere when:
a. relative humidity is low and temperature rises.
b. pressure is high and humidity falls.
c. relative humidity is high and temperature is low.
d. relative pressure is high and temperature is high.
C
Which is an effect of ice, snow, or frost formation on an aeroplane?
a. Increased angle of attack for stalls.
b. Increased stall speed.
c. Increased pitch down tendencies.
d. Decreased speed for stalling
B
Frost covering the upper surface of an aircraft wing will usually cause:
a. the aircraft to stall at an angle of attack that is lower than normal
b. no problems to pilots
c. drag factors so large that sufficient speed cannot be obtained for take-off
d. the aircraft to stall at an angle of attack that is higher than normal
A
If it is suspected that ice may have formed on the tailplane and longitudinal control difficulties
are experienced following flap selection, the prudent action to take would be:
a. immediately decrease the flap setting
b. allow the speed to increase
c. select a greater flap deflection because this will increase CL max
d. reduce the angle of attack
A
When considering in-flight airframe contamination with frost or ice, which of the following
statements is correct?
a. Build-up can be identified by the ice detection equipment fitted to the aircraft.
b. The pilot can visually identify build-up on the wings, tailplane or flight controls by
looking through the flight deck windows; at night by using the ice detection lights.
c. Visual evidence of the accumulation of airframe icing may not exist.
d. Due to the high speed of modern aircraft, significant airframe contamination with frost,
ice or snow will not occur.
C
In the event of an icing-induced wing stall, which of the following indications will reliably be
available to the flight crew?
1 - Activation of the stall warning device (horn or stick shaker).
2 - The aircraft pitching nose down.
3 - Loss of elevator effectiveness.
4 - Airframe buffet.
5 - A roll control problem (increasing roll oscillation or violent wing drop).
6 - A high rate of descent.
a. 1, 2, 3, 4, 5 and 6
b. 1, 3 and 4
c. 1, 4 and 6
d. 4, 5 and 6
D
