Lift Experiments



Here are some simple experiments to demonstrate Newton and Bernoulli Lift:

Newton Lift

Next time when you will ride a car on a highway pull your hand out of the window (watch for the traffic!). You will notice that if you will tilt your hand upward, your hand will get pushed up. That is Reaction lift, and it is exactly the same as this second source of aerodynamic lift for aircraft.For this effect to exist, the wing or your hand must be tilted upward, at an angle that is called the "angle of attack".

Because of the high speed of the car or the airplane, a lot of air constantly hits the bottom surface of the wing or the palm (bottom) of your hand. After that air has hit that angled surface, it gets deflected downward, pretty much at the angle of the angle of attack. Therefore, the air now has a new VERTICAL movement downward due to the collision, which occurs due to a downward FORCE being applied to it. Newton said that there must therefore be an equal and opposite UPWARD force on the wing / hand.The same forces occur when you fly a kite.

When the kite’s angle of attack is zero, it will fall. Like an airplane, a kite is heavier than air and relies on the motion of the wind past the kite to generate the aerodynamic lift necessary to overcome the weight of the kite. The movement of the air past the kite also generates aerodynamic drag that is overcome by constraining the kite with a control line. The interaction of these forces determines the overall performance that varies with the design of the kite.

Bernoulli Lift

Experiment 1:

Take two pieces of paper, one in each hand; hold them close to your face and blow between them. You will notice that the pieces of paper will get closer one to each other, contrary to your expectations.Next, take the end of one of the pieces of paper in your hand so that the length of the paper falls over your hand. Now blow over the sheet of paper. It will rise!Can you explain why?

Experiment 2:

I this experiment we will use water instead of air.Both of them can be treated as fluids.

A mass of water flowing uniformly from a faucet shows neckdown; it is wide and thick at the top, and it tapers to become narrow and thin at the bottom. As the water falls from the faucet it accelerates, and as the velocity of the fluid flow increases the area of the fluid flow decreases; the stronger atmospheric pressure overwhelms the weaker static pressure in the quickly flowing water and compresses the water stream.Note:Think about other experiments that can use water instead of air to demonstrate the lift force.

Experiment 3.

When a boomerang is thrown, it is held nearly vertically. The cross-sectional shape is asymmetric, that of an airfoil. As it is thrown, it spins and creates a “Bernoulli Lift” which acted toward the left and makes the boomerang to fly in a circle, back to you.

Note:The boomerang is not actually held exactly vertical when throwing, but slightly tilted to the right. The rotational spin therefore creates the Bernoulli force vector that is slightly upward of being straight horizontal to the left. This small vertical component of the force vector overcomes the vertical weight vector of the boomerang, which keeps it from crashing down. Eventually, as aerodynamic drag slows down the boomerang's spin, the Bernoulli force vector also reduces. Once the vertical component of it drops to less than the weight of the boomerang, it falls and crashes.

From these experiments we can see that both "Bernoulli" and "Newton" are correct. Integrating the effects of either the pressure or the velocity determines the aerodynamic force on an object.

Newton and Bernoulli do not contradict each other. Explanations which are based on Newton's and on Bernoulli's principles are completely compatible. Air-deflection and Newton's Laws explain 100% of the lifting force. Air velocity and Bernoulli's equation also explains 100% of the lift

You will understand this better if you will consider the spectacular "Up Side Down" flight of an airplane.

People who understand the logic behind Bernoulli lift immediately realize that an upside down wing cannot really produce any Bernoulli lift. They are correct! Watch carefully the next time you see such an upside down aircraft flying. They must depend entirely on Reaction Lift, and therefore they must keep the nose of the airplane noticeably higher than usual, to get the greater angle-of-attack they need. Their situation is actually rather dangerous, because of the natural instability of relying entirely on Reaction Lift.

This sort of demonstration confirms everything we have described here. If ONLY Bernoulli Lift existed, no upside down flight would be possible. If ONLY Reaction Lift existed, then an aircraft could use the same angle-of-attack either shiny side up or upside down. The fact that maybe 1/3 greater angle-of-attack is necessary suggests that around 1/3 of the normal lift is probably provided by Bernoulli Lift (for that speed and altitude) while the other 2/3 is normally provided by Reaction Lift.

Now you can better understand why the takeoff and landing are the most potentially dangerous parts of a flight. The relatively slow speeds involved in both takeoffs and landings mean that very little Bernoulli Lift then occurs, and therefore you have situations that are nearly completely Reaction Lift.

The pure Reaction Lift flight is extremely unstable (and therefore potentially dangerous). The fact that Reaction Lift is also far less efficient regarding usage of power (due to truly massive turbulence created), the engines must be operated at very great power, but of course part of that is necessary anyway to accelerate such a large and heavy object up to flying speed! Once an airliner gets up near cruising speed, there is enough Bernoulli lift to provide a good deal of stability, as well as then using up far less fuel with the engines running far easier.

Because modern airliners are operated by companies that intend to make money, they try to have the heaviest payload that is safe. This is why purely Bernoulli Lift aircraft are commercially impractical. It has been found by practice that a combination of Bernoulli Lift and Reaction Lift, where the Reaction Lift predominates, especially at low speeds, represents the most cost-effective and safe choice.

In a sense, Bernoulli Lift might be thought of as representing stability and consistency, while Reaction Lift might be thought of as more brute force lift that is less easily managed.




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