getting to grips with aircraft performance 如何掌握飞机性能 1(36)

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5.5.2.4. Aquaplaning Phenomenon
The presence of water on the runway creates an intervening water film between the tire and the runway, leading to a reduction of the dry area (Figure C27). This phenomenon becomes more critical at higher speeds, where the water cannot be squeezed out from between the tire and the runway. Aquaplaning (or hydroplaning) is a situation where the tires of the aircraft are, to a large extent, separated from the runway surface by a thin fluid film. Under these conditions, tire traction drops to almost negligible values along with aircraft wheels’ braking; wheel steering for directional control is, therefore, virtually ineffective.

Aquaplaning speed depends on tire pressure, and on the specific gravity of the contaminant (i.e. how dense the contaminant is).

VAQUAPLANING  (kt) = 34 (PT/σ)0.5
With
PT = tire pressure (kg/cm2)
σ = specific gravity of the contaminant.

In other words, the aquaplaning speed is a threshold at which friction forces are severely diminished. Performance calculations on contaminated runways take into account the penalizing effect of hydroplaning.
5.5.3. Aircraft Manufacturer Data
The aircraft manufacturer has to provide relevant data for operations on runways contaminated by one of the above contaminants, as quoted below:

“JAR 25X1591 (a)(c) Supplementary performance information for runways contaminated with standing water, slush, loose snow, compacted snow or ice must be furnished by the manufacturer in an approved document, in the form of guidance material, to assist operators in developing suitable guidance, recommendations or instructions for use by their flight crews when operating on contaminated runway surface conditions.”
“JAR 25X1591
(d) The information [on contaminated runways] may be established by calculation or by testing.”
As far as performance determination is concerned, Airbus provides guidance material for the following runway contaminants and maximum depths (Table C10):

Table C10: Wet and Contaminated Runways
Note that takeoff is not recommended, when conditions are worse than the above-listed.

5.5.4. Takeoff Performance on Wet and Contaminated Runways
5.5.4.1. Acceleration Stop Distance

The ASD definition on a contaminated runway is the same as on a wet runway. Reversers’ effect may be taken into account in the ASD calculation, as soon as the surface is not dry. The distances can either be established by calculation or testing.
5.5.4.2. Takeoff Distance and Takeoff Run

The TOD and TOR definitions on a contaminated runway are similar to the ones on a  wet runway. They can either be established by calculation or testing.
5.5.4.3. Takeoff Flight Path

“JAR-OPS 1.495
(a)
The net flight path must clear all relevant obstacles by a vertical distance of 35 ft.”

“JAR 25.115

(a)
　
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