Hi Ludo,
Great question! I'm no expert, but here is my take on things:
Imagine that you are travelling in a boat (at 3-4 kts) and trailing your hand in the water (like a wing). You will see a vortex appear behind your hand which will change in intensity as the angle of your hand changes. The speed of the boat is the same. The greater the angle of your hand, the stronger the vortex. I would contend that the strength of the vortex is proportional to the angle
and not a lot else.
Your explanations need to be looked at again, bearing this in mind:
-SLOW: when flying at slow velocities, angle of attack needs to be increased producing more lift thus producing stronger vorices.
A given aircraft will be at a constant weight so the lift required will be the same at any speed or angle of attack. But a slower speed will need a higher angle of attack to produce the same lift, hence stronger vortices.
-HEAVY: a heavy aircraft needs more lift thus producing stronger vortices.
A heavy aircraft needs to fly at a higher angle of attack than a light one (assuming they fly at the same speed), hence stronger vortices.
-CLEAN: ok here is where I got confused. Aren't we creating more lift when with full flaps? What exactly does flaps has to do with vortices? is it that flaps interfere with whem and don't let them develop? is it because of the drag produced by flaps?
Again, we are not creating 'more lift' with flaps, (constant weight, constant speed), rather we are increasing the coefficient of lift. This means that with flaps we can fly at a reduced angle of attack. So the vortices reduce in strength due to the lower angle of attack. So a clean aircraft has a higher angle of attack than one with flaps, hence stronger vortices. Cyclone733 makes a good point about flaps creating their own vortices. Just watch a 737 or 757 landing on a misty morning. They produce great white vortices from the outboard edge of the flaps.
Not sure an aerodynamisist would agree with my reasoning, but it makes sense to me!
