Theorie Basiskurs

When an object is moved through the air, it must displace the air.  

If you move your hand quickly through the air, you hardly feel any resistance.  If you hold your hand in the air while riding a bicycle or even a car, you will feel the air resistance much more clearly.  

This shows that air resistance increases with higher speed.  

But also the shape has a significant influence on the resistance.  If you hold the palm horizontally out of the window, the resistance is smaller than if you place it vertically.  

_{Picture: Bergdohle, License: Public Domain, Link}

Of course the shape of the aircraft has a big influence on the resistance.  It is logical that large transport aircraft have a much greater drag than a slim fighter aircraft.  

But also an extended landing gear, mounted weapons or extended airbrakes increase the drag.  This will reduce the airplane's speed / range.