PPRuNe Forums - View Single Post - Theory on lift
Thread: Theory on lift
View Single Post
Old 20th Oct 2012, 00:52
  #175 (permalink)  
italia458
 
Join Date: Jun 2010
Location: Canada
Age: 37
Posts: 382
Likes: 0
Received 0 Likes on 0 Posts
Lyman...

What you're saying makes sense.. but not to create lift - it makes sense to accelerate the airflow and deflect it downwards. It's the downwards velocity that creates an upward force on the wing that lifts it. The pressure isn't the direct cause to the lift.

In the article he describes how an airplane flying over a big scale would indicate the weight of the airplane - the earth does not get lighter when the plane takes off. It seems like you believe that the 'suction' created by that void on top of the wing is responsible for sucking the wing upwards. If you're sucking in air, you need to displace it somewhere - where are you displacing this air that you're 'sucking' up?

Bookworm and Peter...

It's not that Bernoulli is wrong with regard to pressures and velocities - it is correct that as the flow over the wing is accelerated, the static pressure will drop. The author seems to have a big deal with saying Bernoulli is involved for a wing in real life when it's clear that Bernoulli is for a closed system and it's also clear that lift in real life is an open system with energy added.

The measurements of the static pressure and velocity is important to plane makers because they can calculate lift/circulation around an airfoil and determine how the airfoil will perform in real life, with adjustments for accounting for viscosity (Computational Fluid Dynamics). I don't think the authors mean to say that, what the aerodynamicists that work on designing planes do is, ignore Bernoulli because it's not applicable - it sounds like the author wants to argue that a better 'overall' description of lift should focus on Newtonian laws, as it once did.

That's my take on it.
italia458 is offline