Joined: 11 Dec 2005
|Posted: Sun Apr 22, 2012 1:35 pm Post subject: Questions on Wet and Contaminated Runways
| How does the slush thickness affect the V1 reduction required?
a) Smaller reduction if thicker <-- Correct
b) Greater reduction if thicker
c) No affect if mass is reduced
d) No affect at all
Thick Contamination - More reduction in mass and smaller V1 reduction
Thin Contamination - Less reduction in mass and more V1 reduction
Water equivalent depth is:
a) the contaminant depth x specific gravity <-- Correct
b) the depth of water in the contaminant
c) the contaminant depth x 0.5
d) the measured depth of the contaminant
The equivalent water depth can be found either by melting the snow or by multiplying the contaminant depth by the specific gravity of the contaminant.
E.g. Runway covered in snow with a specific gravity of 0.6 to a depth of 2cm.
Equivalent water depth in millimetres = 20 x 0.6 = 12mm
2cm = 20mm
The effect of a runway contaminated with 0.5 cm of slush on take off calculations would be to decrease the TOM: "decrease V1 and decrease VR"
For a take off from a contaminated runway: "The performance data for take of must be determined in general by means of calculation, only a few values are verified by flight tests"
Which statement related to a take off from a wet runway is correct?
a) A reduction of screen height is allowed in order to reduce weight penalties <-- Correct
b) The use of a reduced VR is sufficient to maintain the same safety margins as for a dry runway
c) In case of a reverser inoperative the wet runway performance information can still be used
d) Screen height reduction cannot be applied because of reduction in obstacle clearance
During a take off from a runway contaminated by slush the drag caused by the slush will:
a) increase then decrease <-- Correct
b) increase then remain constant
c) increase with increasing speed
d) increase up to VP then increase at a greater rate
In the early stages of the take-off run, slush and water builds up as a bow wave in front of the wheel adding to the drag. Once a certain speed is reached the bow wave disappears. Wheel rotation slows or stops and the tyre slithers or starts to plane on the contaminant layer. From this point on, the resistance to acceleration is minimal. This is called dynamic hydroplaning. It can happen in water depths of less than a tenth of an inch (2.5 mm). The point at which the aircraft starts to plane is called the hydroplaning speed (VP or Vp).