aerofoil, lift, bernoulli's therom???
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Re: aerofoil, lift, bernoulli's therom???
Re: aerofoil, lift, bernoulli's therom??? -- sambha	Post Reply	Top of thread	Forum

Posted by: Schipperus ® 09/30/2005, 05:57:43 Author Profile Mail author Edit

Just a little experiment to show what air pressure can do... Maybe you've seen this one before, if so, imagine what a greater surface could do to an airplane. Take a glass, fill it to the top with water (all air must be out of the glass). Take a sheet of paper and put it on top. Turn the glass and paper up side down, don't do this to slowly. Let go of the paper, you'll see the water stay in the glass and the paper staying in place despite the weight of the water. Regards, IJsbrand

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Re: aerofoil, lift, bernoulli's therom???
Re: aerofoil, lift, bernoulli's therom??? -- sambha	Post Reply	Top of thread	Forum

Posted by: swearingen ® 09/27/2005, 10:00:27 Author Profile Mail author Edit

The key here is velocity. You'll notice in the equations that the velocity is squared. Lift (and drag) at subsonic speeds vary by the square of the velocity. With wings as large as theirs going as fast as they do, they can lift an amazing amount of weight. Consider the A380: it has a wing area of 845m^2 and a max. takeoff weight of 560 tonnes. That works out to an average differential pressure of less than 1 psi (0.94psi). My hand is about 20 square inches in area. At 0.94psi, that would equate to 18.8 lbs of lift to be comparable. I bet I could get that much lift sticking my hand out of a window at 70mph and holding it at the most favorable angle. Now imagine that monster wing on the A380 moving at 150mph! It truly is a version of Bernoulli's equation (in its differential form, taking into account compressibility) that governs the entire process. This is very simplistic, but it'll give you an idea of how it's done. I'd invest in a good basic aerodynamics book. I also recommend remote control aircraft - building and experimenting with them will teach you volumes.

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Re: Re: aerofoil, lift, bernoulli's therom???
Re: Re: aerofoil, lift, bernoulli's therom??? -- swearingen	Post Reply	Top of thread	Forum

Posted by: tooleng ® 09/30/2005, 16:11:42 Author Profile Mail author Edit

The amount of air diverted by the wing is proportional to the speed of the wing and the air density. The vertical velocity of the diverted air is proportional to the speed of the wing and the angle of attack. The lift is proportional to the amount of air diverted times the vertical velocity of the air. The power needed for lift is proportional to the lift times the vertical velocity of the air. Now let us look at some situations from the physical point of view and from the perspective of the popular explanation. The plane’s speed is reduced. The physical view says that the amount of air diverted is reduced so the angle of attack is increased to compensate. The power needed for lift is also increased. The popular explanation cannot address this. The load of the plane is increased. The physical view says that the amount of air diverted is the same but the angle of attack must be increased to give additional lift. The power needed for lift has also increased. Again, the popular explanation cannot address this. A plane flies upside down. The physical view has no problem with this. The plane adjusts the angle of attack of the inverted wing to give the desired lift. The popular explanation implies that inverted flight is impossible. As one can see, the popular explanation, which fixates on the shape of the wing, may satisfy many but it does not give one the tools to really understand flight. The physical description of lift is easy to understand and much more powerful. The preceding is an article by David Anderson, Fermi National Accelerator Laboratory, and Scott Eberhardt,

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