Eli5 what bernoulli’s principles is and how it works for aviation.

Question

Eli5 what bernoulli’s principles is and how it works for aviation. Been watching videos about it and still cant wrap my head around it, thanks heaps for any help.

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Answer 1

Am aerodynamicist.

Many people are missing the real principle behind Bernoulli’s principle, which is the conservation of energy : ie. energy cannot be created or destroyed.

Imagine a balloon filled with air; when you push it inwards, the pressure increases. In other words, you have added energy into the air.

When air moves, it has kinetic energy, just like anything else.

Bernoulli found a way of relating “pressure energy” to “kinetic energy”. As aerodynamics developed, Bernoulli’s equation was eventually superseded by more accurate models, but the fundamental point remains.

How does it relate to flight? This is where stuff gets really messy and not well explained. Bernoulli’s is best thought of as a way to calculate the pressure and velocity in an airflow of interest. The rest is more philosophy than science. No equation can really ever truly explain “why”. We just know that this equation can describe what you see.

To clear up the many misconceptions on this thread :

– The pressure integrals and Newton’s third law are different faces of the same coin. Pressure forces are the -only- forces acting on a wing (apart from shear forces ie drag). So the net force on a plane can be completely determined by the pressure distribution.

-Every aerodynamic effect you can think of essentially alters the surface pressure distribution. So, as far as an engineer is concerned, pressure distribution easy to measure, so we do that.

– As far as the momentum change in the air column is equal and opposite to the wing, that’s true too. Its more that there’s no clean way of measuring how much a given amount of air was deflected. So it’s perfect science, but pretty useless engineering. However, for drag (where the air simply slows down), momentum rakes have been used to some success. (momentum in – momentum out = drag force).

– To marry the two you could look as pressure distribution as the kinematics way of looking at it (resolve all forces in detail and get the resulting lift), and the conserved quantities approach as the big picture approach (this momentum change must be equal and opposite to the other one).