Condensation and pressure distribution
I had a nice approach into MUC last week on an A340 with great condensation on the wing right up to touchdown. However, what I was able to see was confusing me a little bit. Condensation only happened aft of the mid chord of the wing, mainly on top of the flaps.
According to the pressure distributions I have seen so far, a modern supercritical airfoil with flaps and slats should have a suction peak in the area of the fixed leading edge at high lift coefficients, and most of the wing upper surface should see less pressure than the upper surface of the flap.
So what I would expect is to see lots of condensation on the forward half of the wing, exactly the opposite of what happened. How can this be explained ?
Does condensation take some time to occur, so does it take a certain time after air pressure has dropped and temperature therefore as well (ideal gas), before tiny droplets do form around seeds (dust particles) in the air, hence visible condensation is produced? Did the air travel along half of the wing before it finally condensates? Does condensation show the pressure which was present a few milliseconds ago?
Or do modern aircraft keep that much margin to Cl max during approach and even during the flare, that indeed the lowest pressure is located on the flap upper surface (where calculation / wind tunnel tests do show the lowest pressure for moderate lift coefficients)? Do we "waste" that much high lift capability to have a safe margin?
Is condensation on a wing visualizing the chordwise pressure distribution? Or just the spanwise lift distribution?