# What creates lift?

Hey

I have just started doing my ppl and just wanted to check if i have the concept of lift right. Is lift achieved by the venturi effect, where there is a low static pressure on top and a higher static pressure at the bottom of the wing. And it is the difference of pressure that creates lift?

Thanks

Jonathan (99jolegg) Chief Captain

There are various theories to lift but yes, the most commonly accepted theory is the camber of the wing increases the speed over the top of the wing surface creating low pressure (suction if you like) whilst the slower speed of the air under the wing is at a relatively high pressure. The difference between them creates lift.

As you rotate the aircraft, and therefore increase the angle of attack (the angle between the chord line [line linking the leading edge to the trailing edge of the wing] and the relative airflow over the wing) the upwash ahead of the wing increases, air is sped up even more over the top of the wing, the pressure is even lower and therefore the differential is even greater so higher angles of attack (effectively high pitch angles) give higher lift.

The components of lift are Lift = 1/2 air density x velocity squared x coefficient of lift x surface area

Probably a little above PPL level but a bit of background info never hurts.

Ian Stephens (ianstephens) Captain
Ian Stephens is an expert on this topic. Read his bio here.

Hello there!

You're on the right track in understanding lift, but there's a bit more to it than just the Venturi effect. Lift is generated by the interaction of a wing (or airfoil) with the airflow around it. There are two primary theories explaining this phenomenon: the Bernoulli's principle and Newton's third law of motion. I'll give you a brief overview of each:

• Bernoulli's Principle: This principle states that an increase in the velocity of a fluid (air, in our case) results in a decrease in pressure. Airflow over the top of the wing is faster due to the shape of the airfoil, which creates a lower pressure area on the top surface. On the bottom surface, the air moves slower, creating a higher pressure area. This difference in pressure generates lift. This principle is often associated with the Venturi effect you mentioned, but it's essential to understand that the Venturi effect is a specific application of Bernoulli's principle that deals with fluid flow through a constriction, while lift generation is a broader concept.
• Newton's Third Law of Motion: According to this law, for every action, there is an equal and opposite reaction. As the air flows over the wing, it is deflected downwards due to the airfoil's shape. This change in direction of airflow imparts a force on the air, and in return, the air exerts an equal and opposite force on the wing, generating lift.

Both theories are interconnected and contribute to lift generation. So, in summary, lift is created by a combination of pressure differences (Bernoulli's principle) and the deflection of airflow (Newton's third law). Keep in mind that other factors like wing shape, angle of attack, airspeed, and air density also play a crucial role in determining the amount of lift produced.

I hope this helps clarify your understanding of lift. Good luck with your PPL journey, and feel free to ask if you have any more questions!