BERNOULLI - OR PERHAPS MORE NEWTON? For the German version, click here
Flying without flow…?
For more than 100 years, the well-known theory of flow has been used to explain the flight of an airplane. But perhaps it will be determined that Newton's mass theory is the more correct explanation.
Please do not say at this point: "What kind of nonsense is this?". Please go on reading and maybe I can inspire you to think about, or even convince you, to think otherwise.
It is undisputed that the behavior of air flow, as Bernoulli has described in his fluid dynamics, can be observed on a profile of an aircraft when the air flows around it in a wind tunnel with an accelarated air mass.
But, in fact, in the wind tunnel, there are conditions on an aircraft wing, which moves in a stationary mass of air (atmosphere) that is comparable. Can these conditions actually be transferred one by one?
I don't think so!
Some observations on starting aircrafts, on insects, and on bird flights are the reason of my doubts about the flow theory for lift production:
Let's observe a starting or landing aircraft on a very wet day.
You can see a seemingly standing and relatively thick shapeless "fog" on top of the wing. That actually should not exist in the flow theory. The fog is formed by water dissolved in the air that condenses by expansion, and with it cooling down, of the air. There are enough images on which this fog can be seen if you, yourself, have not already observed this.
Also, in nature there are many examples which prove the theory of lift production by mass acceleration, such as probably everyone knows, the great nature video clips, one example would be when an Eagle lifts a large heavy fish out of the water. Following the fluid dynamics (after Bernoulli) the Eagle should move its wings rapidly forward to produce a corresponding negative pressure on the top of its wings. In fact, the Eagle moves its wings level, holding down with all its strength to accelerate a mass of air downwards at the same the air over its wings becomes rare (a vacuum arises - "Lee-effect"). Then it turns around its wings vertically, whitch minimizes the resistance as little as possible and rapidly to the top, to accelerate with the next wing beat the mass of the air down again and the "thinning" of the air over the wings to carry out again.
The same process can be observed on flying insects.
To explain the insect's flight, it is spoken about the "vortex theory", because the fluid mechanics do not work as insects' wings are flat and have no profile, an example beeing the butterflies.
Let's see what happens in a wind tunnel:
There are air masses strongly accelerated by a fan, leaded over a fixed wing profile. The air mass is loaded with kinetic energy! The wing itself has no kinetic energy, because it is firmly fixed in the wind tunnel.
If we have a look at the air particles that are streaming with the mass of air through the wind tunnel, we can see, that these air particles are streaming in an orderly manner and without a major change of direction in line (streamline) above and below the profile. We know that a mass that is in movement (kinetically charged), only "reluctantly" likes to change again the once chosen direction (mass inertia). This explains the optimal flow conditions, which you can make visible by trail of smoke or threads in the wind tunnel.
But what happens during a flight in free atmosphere?
There is a decisive difference!
In the free atmosphere, the wing (together with the aircraft powered by the engines) is moving through a resting air mass that is not loaded by kinetic energy. That means the air particles are still, or almost so, at the same place as before, after the wing has been moved away!
Certainly it seems to be, as often it is explained using the example that a passenger looking out of a window of a plane and seeing the air particles, believes that the air particles are flowing over the wing. From this observation it is concluded that the behaviour of an air particle is the same, whether in a wind tunnel or in flight. The crucial difference is, as already mentioned, that a particle of air in a wind tunnel is loaded with kinetic energy and is much more a subject to the mass inertia and thus behaves otherwise than does a resting particle that is diverted by an aircraft profile.
This "relative motion" (aircraft through standing air) may not be equated as "flow" (movement of a mass: liquid or gas) in my opinion!
How shall lift on a wing without flowing air be generated?
Lets have a look to a wing profile:
The wings' upper and lower surfaces have a more or less strong curve. When a wing profile is moving in an air mass, the wing profile (nose leading edge and the expanding profile behind) sends the air particles that it hits in different directions. As we know, an impact angle equals an angle of reflection, that means the air particles are accelerated from the resting position in different directions.
At the top of the leading edge the air particles, therefore, are accelerated in an upward direction and also accelerated against the direction of flight.
On the wing's upper surface caused by the fact that upwards accelerating air particles by the wing's leading edge (and the thicker growing area behind) are causing negative pressure (= lift component of the wing's upper surface), but no laminar flow! At the same time the above mentioned "Lee-effect" happens.
That the behaviour is, as desrcibed before, has been confirmed by flight tests and documented by video. In a test, with approximately two-inch long thin strips of paper that has been fixed transversely to the direction of flight and vertically standing on the top of a wing. Following the flow theory, the strips should completely fit tightly to the wing surface in flight! Actually the strips of paper remained, or nearly so standing up, caused by the nose's leading edge vertically-accelerated air particles, i.e. by the "Lee-effect"!
By a further test, the top of a wing has been fitted with a nose leading edge only. That means that behind the edge of the nose and down to the wing chord, the wing has been flat to the rear edge. Also this wing has generated lift, at the same speed, which would be impossible following the flow theory!
On the wing's lower surface the air particles "captured" from the leading edge of the wing are accelerated downwards and this happens despite the decreasing thickness of the profile over the entire wing, due to the so-called angle of attack. This effect can be reinforced by extended flaps at the wing's trailing edge for takeoff and landing.
This reaction force (action = reaction) under the wings is contrary to gravity. The kinetic energy which the airplane has transferred in the direction of flight by the wing to the air particles, is now converted into lift energy which reacts contrarily to the weight of the aircraft (= lift component under the wings).
Because the opposite is happening on the top of the wing, a power imbalance is induced and the wing is lifted upwards due to the lower ambient pressure on the top of the wing. This process continues only as long as the aircraft moves forward fast enough (!) in the mass of air.
Conclusion: Over the wing there is in fact a vacuum and below the wing there is an overpressure which is created in my opinion by vertical and not by horizontal accelerated air masses!
Actually there is remaining a decisive question:
Why have we been taught for more than 100 years that an airplane is flying by the flow theory...?
Interestingly, I found the follwing article in a physics textbook (source unknown):
Source?: If you know out of what physics textbook this section originate's, please notify me.
Translation: The wings of the aircraft are slightly inclined or curved down. Thereby air masses are deflected down in flight. This is enough by the high speeds to provide the necessary upward power. This keeps the balance of the gravity, when the aircraft maintains its level.
When we are swimming in the water, we push the masses of water first to the rear so this is driving us forward. We are pushing the masses of water down as well. Therefore, we can keep our heads out of the water as the hydrostatic lift alone makes it possible.