Wing Tip Vortices

[Nacnac]

Are wing tip vortices greater when an aircraft is heavy, slow(high AoA) and clean or heavy, slow and in the landing configuration? After takeoff when the aircraft is heaviest or on the approach?

I have heard that a Boeing 757 has unusually strong wing tip vortices for the aircraft's weight?

:confused:

[Oktas8]

Wingtip vortices are a function of aircraft wing loading (or weight), AoA (or speed) and configuration. They are greatest at high weight, high AoA. Use of flaps tends to reduce the vortex strength.

So vortices will be a problem anywhere you have large, slow aircraft, but particularly when no flap is used. Thus after take-off is a case in point.

I guess whether approach or take-off is worse, depends on difference between LW & TOW, difference between landing & take-off configuration (how much flap in each case) and difference V2 and approach speed. I would have guessed after take-off is worse though.

I couldn't comment on the 757 in particular. But in general, wingtip vortices will be worst with aircraft wings designed with low washout, low taper and a high critical AoA.

amended to better answer the question...

[ 10 October 2001: Message edited by: Oktas8 ]

[Binary]

B757 is a special case and does appear to generate vortices that are stronger than would be expected for its weight. For this reason some states include it in the ICAO Heavy category. Other states have specified categories and separation minima that differ from ICAO standard.

[Cuban_8]

O8,

Be careful with the flap comment. Flaps tend to break up the tip vortices more rapidly when they are NOT full span in nature. Full span flaps, such as on the 146, result in intensified wingtip vortices.

Otherwise, it is generally accepted that vortices are at their strongest on initial climb subsequent to flap retraction.

Regards,

Cuban_8

[Binary]

This extract from a report of an NOAA trial gives more info:

"The vortex velocity of the 757 was approximately 50 percent higher than that of the 767 at similar vortex ages younger than 60 seconds. The most-intense 757 vortices were measured in the landing configuration with a flap setting of 25 to 30 degrees [tangential velocity of 326 fps]. The 767 vortices were longer lived than those of the 757, but were less intense than our baseline 727 aircraft [235 fps]. The highest 767 vortex was measured at 190 fps,"