That is a facinating report Pam.
From that BBC report Pam provided:
Quote:
The sudden current of air was powerful enough to blow tiles and masonry from the home of Patricia Hills in Old Windsor, Berkshire.
BAA, which operates Heathrow Airport, says only one in 10,000 flights results in a vortex.
If this BBC report is correct, then somebody at the BAA is talking a lot rubbish when they say only one in 10,000 flights results in a vortex.
All aerofoils that produce lift will produce vortices. Vortices can be reduced by wing design and flying conditions, but not abolished.
This article helps to explain:
http://www.skybrary.aero/index.php/Wake ... TurbulenceQuote:
Potentially hazardous turbulence in the wake of an aircraft in flight is principally caused by wing tip vortices. This type of turbulence is significant because wing tip vortices decay quite slowly and can produce a significant rotational influence on an aircraft encountering them for several minutes after they have been generated. Jet Efflux and Prop Wash can also hazard the control of an aircraft both on the ground and in the air but, whilst these effects are often extreme, their effects are more short-lived.
The origin of counter-rotating wing tip vortices is a direct and automatic consequence of the generation of lift by a wing. Lift is generated by the creation of a pressure differential over the wing surface. The lowest pressure occurs over the upper wing surface and the highest pressure under the wing. This pressure differential triggers the roll up of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wing tips. After the roll up is completed, the wake consists of two counter-rotating cylindrical vortices.
The strength of the vortex is governed by the weight, speed, and shape of the wing of the generating aircraft. The vortex characteristics of any given aircraft can also be changed by extension of flaps or other wing configuring devices as well as by change in speed. However, as the basic factor is weight, the vortex strength increases proportionately.
Vortices usually persist for between one and three minutes, with survival often greatest at low level in calm or very light wind conditions and at higher altitudes in thinner air. Once formed, vortices descend until they decay (or reach the ground). Decay is usually rapid and occurs more quickly in windy conditions over land because of the greater variation in both components of wind velocity which are induced by frictional effects of terrain. Cross-winds can carry a vortex away from the flight path which the aircraft generating them has followed.
It is because of these vortices produced by flying aircraft, especially large aircraft, that flying aircraft aren't allowed to fly to close behind one another on a given flight-path, such as when landing and taking-off. A small aircraft following a large aircraft too closely can come to grief if the disturbed air from violent vortices of the leading larger aircraft take over the following aircraft.
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