Klaus,

Dependent on what you call light winds.

Stalling of the sail in light winds can also because by having too much draft in the sail; as in contrast to having a too large angle of attack. I think this could be the case here as the bottom part of the sail is widest and therefor the flow needs to have relatively alot of "internal energy" to overcome the "long" negative pressure gradient at the back of the sail.

In really light winds you'll want a flat sail with a considerable amount of twist. The flatness assures the sail won't stall due to negative pressure gradients that are too large and the (relatively) large twist on the leech compensates for the windshear.

However at some point in windspeed the wind itself transitions abruptly from laminair flow (with a significant windshear gradient) to a turbulant flow (with much less windshear) and then you'll need to bring the leech back in. When the wind increases more then the increase the draft; as the airflow is becoming more energized. You are now in medium wind conditions typically 6- 12 knots.

And only in high winds due to increase twist and decrease draft again.

In simple terms ; very light wind sailing has an almost identical sail profile as high wind sailing where the sail trim in the medium conditions is with a relatively full draft and tight leech.

Flat and rough water are influence factors as well. In flat water you can typically sail with a leech that is a little bit more tight and with a relatively unform draft profile. In rought water you sail with more twist and a draft that is located more in the lower part of the sail.

You use mainsheet, downhaul, diamond wire tension, spreader rake simultaniously to adjust the mainsail to these different conditions. Sadly it is not like one control only affects one adjustment. For example when you sheet the mainsheet tighter then you reduce twist and reduce draft in the top of the sail. Only be also using the downhaul at the same time can you increase twist again while flattening out the top even more. So if you only want to reduce draft in the top of the sail but keep the same twist profile then you have to adjust both settings simultaniously. This is sadly one of the more easy ones. Setting the draft profile properly also requires resetting the spreader rake and or the diamond wire tension together with the mainsheet, downhaul AND mast rotation.

As an aerodynamists you have more then enough learning and experimenting to do on your F16 !

But that is all part of the fun right.

Wouter