I don't want to sound out to lunch.... but...... Am I wrong by thinking the aircraft stays in the air through the pressure difference between the top and bottom of the wing.... I don't think it has anything to do with pushing air downwards?????? Hence Bernoulli’s (sp) principle. Please correct me if I'm wrong.......
Bill, you are certainly right. But just as the aircraft reacts on that pressure difference - by flying in the air instead of sitting on the ground - then the air masses reacts the same way (or more precisely the opposite way).
There is no way that the air masses can stay unaffected by for instance a 700,000 lbs 747, which tells the air to carry it.
In layman's terms: The air masses are pressed downwards.
To every action there is a corresponding reaction.
It is not so that there is a constant pressure difference which keeps the plane in the air. Instead thousand of tonnes of air per minute is accellerated downwards by the pressure difference. The force needed for that accelleration is the "reaction".
Fortunately air is not weightless - it would make flight impossible.
If you take a cube of air at sea level with sides of the same length as the wing span of a 747-400, then the weight of the air inside that cube is some 300 or 350 tonnes, or roughly the same as a fully loaded 747-400. It takes a lot of power to "push" such air masses downwards in only a fraction of a second. It takes exactly the same power as pushing a 300-350 tonnes boulder the same distance in the same time. That's - again in layman's terms - what makes flight possible.
Best regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs