SIFT Army Aviation Information Practice Test

When generating lift, how should the pressure below the airfoil compare to the pressure above it?

1. Less than it

2. Equal to it

3. Greater than it

4. Unrelated to it

The correct answer is: Greater than it

To generate lift, the pressure below the airfoil must be greater than the pressure above it. This principle is rooted in Bernoulli's equation, which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. As air flows over the curved upper surface of an airfoil, it travels faster compared to the air beneath the flat bottom surface. This increased velocity leads to lower pressure above the airfoil and a relative higher pressure beneath it. The resulting pressure differential creates the lift force that allows the aircraft to rise and maintain flight. The greater the difference in pressure between the lower and upper surfaces, the greater the lift generated. The other options do not accurately represent this relationship: if the pressure above the airfoil is equal to or greater than the pressure below, or if they are unrelated, lift would not be effectively generated, and the aircraft would not be able to rise or sustain flight as needed.