Why does an airplane need gas to fly?

Answer 1

In order to provide the thrust needed to maintain flight, the engine must have some sort of fuel.

Ans2:As the mixture of gas called air flows over the wings and control surfaces, by Bernoulli's principle, it produces lift. Since the pressure above the wing is less than below, the pressure of the atmospheric gases pushes the airplane upwards.

The Bernoulli's principle or theorem,even though valid when considered as a separate entity, as being the main force that causes lift for an airplane's wing had been taught as being the main force providing the lift, however it has been recognised as being a relatively small part of the total lift force which was also debunked in the venerable book Stick and Rudder, first published in 1944 and still sold today, which explained how it is Newton's law of action and reaction of the air upon the wing that is the main force which results in causing lift for the wing. Basically it is the same thing that occurs when you put your hand outside the window of a car traveling at about 30+mph with your palm tilted upward and you feel the wind pushing your hand upward. You can also see this effect taking place when observing airplanes taking off off at any airport when they tilt backward(rotate) during the takeoff portion of becoming airborne and while climbing, then when level the flat bottom of the wing is not parallel too the ground but is tilted back about 1-3 degrees from horizontal to continue providing the main part of the lift.