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".
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?
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.
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.
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.