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Wake / Turbulance Watch out.


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Interesting article about Wake / Turbulence for you.

All aircraft produce wake turbulence, which consists of wake vortices formed any time an aerofoil is producing lift.

Lift is generated by the creation of a pressure differential over the wing surfaces. The lowest pressure occurs over the upper surface and the highest pressure under the wing. Air will want to move towards the area of lower pressure. This causes the air to move outwards under the wing and curl up and over the upper surface of the wing. This starts the wake vortex.

The pressure differential also causes the air to move inwards over the wing. Small trailing edge vortices, formed by outward and inward moving streams of air meeting at the trailing edge, move outwards to the wingtip and join the large wingtip vortex. Swirling air masses trail downstream of the wingtips. Viewed from behind the left vortex rotates clockwise and the right vortex rotates counter- clockwise. They spread laterally away from the aircraft and descend 500 to 900 feet at distances of up to five miles behind it. These vortices tend to descend 300 to 500 feet per minute during the first 30 seconds. Light crosswinds may cause the vortices to drift, and crosswinds in excess of five knots tend to cause them to break up behind the aircraft. Atmospheric turbulence generally causes them to break up more rapidly.

The intensity or strength of the vortex is primarily a function of aircraft weight, wingspan and configuration (flap setting, etc). The strongest vortices are produced by heavy aircraft flying slowly in a clean configuration. For example, a large or heavy aircraft, which must reduce its speed to 250 knots below 10,000 feet, while flying in a clean configuration is producing very strong wake vortices while it descends.

Viewed from behind the generating aircraft, the left vortex rotates clockwise and the right vortex rotates counter-clockwise. They spread laterally away from the aircraft and descend 500 to 900 feet at distances of up to five miles behind it. Vortices tend to descend 300 to 500 feet per minute in the first 30 seconds.

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Helicopters also produce wake turbulence. Helicopter wakes may be of significantly greater strength than those from fixed-wing aircraft of the same weight. The strongest wake turbulence can occur when the helicopter is operating at lower speeds (20 to 50 knots). Some mid-size or executive class helicopters produce wake turbulence as strong as that of heavier helicopters. Two- blade main rotor systems produce stronger wake turbulence than rotor systems with more blades.

Thanks to http://www.pilotfriend.com for this little gem.

SW :D

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Simon,

Very good point to note there, people often overlook this- even fixed wing pilots.

One other point to note that PPG's themselves also generate significant wake turbulence- due to the slow moving nature. Be particuarly careful if flying in formation, especially behind other PPGs. Most turbulence will be felt at the 7-8 o'clock position, or 4-5 o'clock position (relative to the lead pilot), and several meters below (depending on distance).

I'd suggest if flying in formation, the rearward pilot should stay above the lead, maintain lots of separation and ensure that both pilots can have visual contact at all times.

For added safety pilots should have air/air radio contact so that the rear pilot can be pre-warned of any directional/height changes.

GD

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Curiously Advance paragliders with their little wing tip fins seem to produce more than most, but beware tandems most of all!!!!!

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