Wake vortex
 

Probably should go in the tech. section, but possible relevance to exam questions.
What generates most wake vortex;
A 300 ton Jumbo climbing out after take off with climb flap or
a 150 ton Jumbo in ldg. config. on approach.

Both are presumably in steady flight around 1.3Vs - so generating the same proportion of induced drag.

The 300 tonner as lift =weight, and induced drag is proportional to the square of lift.

G

...or a B757 on the approach at 90 tonnes but with full flap deployed? The vortices off the outboard edges of the flaps are VISCOUS! and required the a/c to be re-designated 'Heavy' in that phase of flight.

TOO

And because 'landing' flap, as opposed to 'takeoff' flap, will reduce the AoA of the outer wing sections, and thereby also, the intensity of the wingtip vortices.

At the same time, new vortices are created at the edges of the flaps, thus spreading the total energy of the trailing vortices across the wingspan, rather than having it concentrated at the wingtips.

I suspect that, If it were possible to add up the energy of all the trailing vortices in the landing configuration, it would be greater than the the 'clean', or 'takeoff' case.

Perhaps the question should read:

What generates most hazardous wake vortex;



MJ:ok:

The strongest vortices ...
 

… as I remember it from ATPL theory revision classes in BGS many years ago.

Matches Mach Jumb´s reasoning.

jr

Well I assumed a heavy with clean wing at low speed would produce the highest wake vortex.
But landing config. probably produces most wake turbulence due all the draggy bits out, but is that balanced out by reduced thrust?

All vortices are driven by viscous fluid effects.


In terms of total vortex strength, I'd intuitively expect the clean(er) wing to be worst as flaps move the lift distribution inboard, and reduce the pressure differential at the tips - which creates the large tip generated vortices which tend to be the major component of wake vortex power.

G

I have a feeling he meant vicious......

Heavy slow clean wing giving the largest value lift and pressure differential and hence strongest vortices.

Probably, but I don't suppose that he has any meaningful data about localised vorticity behind the flaps either.

G

No, you're quite right, if you mean data derived from instrumentation using either sound tomography or Doppler lidar, I don't. I only have empirical evidence.

Yes, I meant vicious. My bad.

TOO

Out of interest, what's the evidence that you do have ? - it's an interesting issue that must have given Boeing a hell of a headache - not unlike the one that the "Superheavy" issue gave Airbus over the A380.

G

I was behind a B788 last week, descending through FL70 - that was fairly interesting as well (A319).