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AERODYNAMICS
Simply Complex

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Aerodynamics is about how air moves; the dynamic behavior of air. Goal in aviation is to create a "thrust" force (including lift) in an energy efficient way. The behavior of one atom/molecule may be predictable, but how billions of atoms act together, that is a more complex story.

The power of atmospheric pressure
The atmospheric pressure is high: about 1.033 kg/cm2 (normal air at sea level), and is created by the earth's gravity. On a steel plate of 1 x 1 meter is 10330 kg of pressure! On both sides!! Now if you can reduce the air pressure on top to for example: half, you will have 5165 kg of atmospheric lift!
Or take 8 m2, and reduce the pressure only 10%, this will give 8264 kg thrust!

How to create low and high pressure
When if you stand somewhere and then move to somewhere else, you leave a "void" (an emptiness) at your first position. Also did you push away all the air away from the second position. The ambient air, being a fluid under high pressure, moves away from where you are going and into the void you leave behind, at high speed. Every solid object does this to the ambient air when moving through it.



This solid cube does so to. When it moves from position A to position B, air is pushed away from position B and air rushes into the void of position A. When moving the cube really fast; the air from position B explodes away, and the ambient air implodes into position A.

This cube is only two steps away from a wing's airfoil, it does two things wrong: 1) It creates high pressure in front and low pressure behind, while the goal is; high under and low on top. It is not a good option to move the object downwards because you want the object to move upwards & forward really. Better is to move forward and leave a void behind on top (an airfoil does so).
2) The other thing that is going wrong here, are the sharp corners. Air does "not like" to make sharp turns, the inertia of its mass will resist and a lot of friction & turbulance will occur, thus a loss of energy and lift. A wing's airfoil should have a shape that makes the air flow gently to were you want it to go.

Communication speed of air
The speed of "communication" between air atoms/molecules is very high: about 340 m/s (normal conditions at sea level). This is equal to the speed of sound, so when a pressure difference is created, the air "knows" where to accelerate to in "no" time (very little time). The weight of air is not very much: about 1,225 kg/m3, but the pressure is very high: about 1,033 kg/cm2, thus it is not hard to make air move away and a void is filled very fast. But the faster the speed difference between a solid object and the ambient air gets; the harder it becomes to fill the void, and the lower the air pressure becomes. When the relative speed becomes supersonic (faster than sound), the ambient air can't fill the void immediately, so a hole in the air appeares, for a little while, until it is imploded. In the opposite situation, the air pressure will rise more and more, up to the point where it can no longer flow, where its behavior becomes like a solid, solid gas.

Maintaining low pressure.
- As ambient air flows into an area of less pressure, this low pressure area disappears, therefore a void has to be created continuesly.
- The more downward motion air has (relative to the aircraft), the harder it gets to create a void mechanically (electrostatic propulsion might not have that problem so much). One solution is to move to an other area with calm air, or even better: an area with rising air (thermic). A helicopter can crash when it is caught in the downdraft of its self created vortex-donut wind.

Pressure wall
If in a huge wall a duckted-fan is mounted that accelerates air from zero ambient air speed to say 200 m/s, it is removing air from one side of the wall and adds this air to the other side. A huge amount of air on both sides is set in motion by this action. Not just the moved air, also all the surrounding air; tons of air.
The difference between these areas is:
- the suction side has less air and thus less pressure.
- the blow-in side has more air and thus more pressure, and the air it has more has a great speed relative to the ambient air.
The pressure difference on the wall is small, but the wall is big, so there is thrust. The shape of the pressure areas is important for efficiency, and can be used for large slow aircraft.
Note that this great difference of speed created by the duckted-fan is a great loss of energy, only creating tons of turbulent air. (The rocket is the best-worst example of creating tons of turbulent & hot gasses).

How to treat air.
If your goal is to move air in an energy efficient way, you better respect what air wants. If you don't treat air gently; it will resist. Air does not want to accelerate; it wants to maintain its motion constant (for it is mass).
Thus:
- Air does not want to make sharp turns, it does not want to turn anyhow.
- Air will become turbulent as it gets in contact with mass that has a different speed, because friction will accure, causing a change of motion.
- Air does not want to flow from a low pressure area to a high pressure area.
And:
- Air likes to vibrate. Every air volume has its own resonance frequency.
- Air likes to flow from a high pressure area to a low pressure area.
- Air likes the way of least resistance.

In case you want resistance from air, you should be hard on air.

PROPERTIES OF AIR
Air is like a pressurised soup of vibrating bouncing-balls.

This is how I imagine air to be in a 2 dimensional world. It is of course not equal to reality for it is a symbolic image of air and not air it self. All images we have in our mind are not equal to reality, but that is an other story. These airballs make it easier to distinguish pressure from weight; only the center dot has mass:


One cubic meter of air weighs a little but is of high pressure. Standard air weighs only 1,225 kg/m3, but the pressure is high: 1,033 kg/cm2. On just 1 m2 there is 10330 kg of pressure. To get that many kg from the weight of mass one would need 8433 m3 of air! Note the the weight of mass is towards the earth,
It is clear that the goal is to reduce the pressure on top of an aircraft, and not to repel on mass. Reducing the pressure on top of an 8 m2 surface to just 3/4 will give 20660 kg atmospheric lift.

How can the pressure be reduced?
The pressure on top of a wing can be reduced by simply; removing the air and it's pressure (VTOL wing), or inverted; by removing the wing (classic wing). The mass of the air is atracted by the earth's gravity, but it can also have an additional force in any direction. One of the directions the force can point to is upwards, wich is opposite to the air that is pressing down on the aircraft. This sound useful because we try to fly, but there is a down side: accelerating mass upwards gives an equal and opposite force downwards. Accelerating mass downwards gives a positive force upwards, but is not opposite to the air pressing down on the aircraft. Rests one more possible action-direction, which is: horizontal, with a horizontal reaction force (in the opposite direction). A relative fast airstream flowing attached to a curved VTOL-wing surface, is able to create less pressure. When an atom moves away from one location, it leaves a "void" behind, an "emptiness" which is an area of no pressure. Other atoms rush in to that void when possible and with great speed, destroying the no-pressure area. Thus the low pressure area has to be continuesly maintained, and this costs lots of energy.

Mass
- Air has mass. Standard air weights about 1,225 kg/m3 at sea level.
- Air wants to maintain its motion constant, for air is mass

Pressure
- Air pressure is created by the earth's gravity. Gravity is pulling the air towards the earth. Many kilometers of air are stacked on the earth, resulting in compressed air. The highest pressure is near the earth's surface and the lowest pressures is near space.
- Air pressure is about 1,033 kg/cm2 at sea level (relative to an absolute vacuum).
- Air wants to accelerate from a high to a low pressure area.
- Air pressure drops WHILE it is accelerating towards a low pressure area.
- Air pressure rises WHILE it is de-accelerating towards a high pressure area.
- Because speed is relative; speed has no influence upon pressure.

Low pressure
When on top of a wing there is low pressure; this does not mean the air is pulling the wing up. The right interpretation is: there is more pressure under the wing than there is on top, thus the force is up. The atmospheric pressure (about 1.033 kg/cm2 at sea level) is pushing the wing up, pressure created by the earth's gravity. Low pressure is still pressure.


Temperature
- Standard air has a temperature of 20°C.

- While air is being compressed; it gets warmer.
(same vibrations in less space)
- While air is being decompressed; it gets colder.
(same vibrations in more space)

- While air is heated; the pressure rises.
(same volume and mass, but more vibrations).
- While air is cooled; the pressure drops.
(same volume and mass, but less vibrations).

- Hot air weighs less than cold air
(same pressure and volume, but less mass).
- Cold air weighs more than hot air
(same pressure and volume, but more mass).


Electrical charge
- Air can be electrical charged, positively (+) or negativily (-). An "ion" is a charged atom or molecule.
- A neutral atom has a same number of protons and electrons.
- A negatively charged atom has less protons than electrons = an anion.
- A positively charged atom has more protons than electrons = an ion.
- An +ion repels an +ion.
- An -anion repels an -anion.
- An +ion attracts an -anion.
- An -anion attracts an +ion.
- Air is, up to a certain point, an "isolator"; it does not conduct electricity.

Other air facts
- Air flows, it is a fluid.
- The speed of sound in standard air is about 340 m/s.
- The speed of sound increases when air density increases.
- A shockwave can travel at about Mach 5 (5 times the speed of sound)
- When spinning air is moving towards the center, the rpm increases (rounds per minute).
- Air volumes vibrate (with the speed of sound).
- An airstream can push and suck on surrounding air or other mass/objects.


Acceleration, friction and the "springiness" of air.
- While an airstream accelerates from a higher than ambient pressure to ambient pressure; the pressure in the airstream drops from high to ambient, and the temperature drops also.
- While an airstream accelerates from ambient pressure to a lower than ambient pressure area; the pressure in the airstream drops from ambient pressure to the lower pressure, and the temperature drops also.
- The area inbetween the ambient air or solid object and the gasstream, are of difference speed and thus produce collisions of atoms: friction. This area is called the "boundary layer".
The friction produces:
* turbulance,
* heat, and
* both speeds (air/air, air/solid, solid/solid) are accelerated to less difference.
- Air is not a solid object but a fluid, obvious. Air is like a pressurised soup of vibrating bouncing-balls. This "soup" can be compressed to a smaller volume with more pressure and higher temperature. And and vice versa can it be decompressed to a larger volume with less pressure and lower temperature.
- Air can easily behave like a 3D spring: vibrating between high and low pressure, and when the pressure is kept constant; potential energy is stored.

Explosion versus Implosion.
If an air volume has a very high pressure compared to the ambient air, it will explode. If an air volume has a very low pressure compared to the ambient air, it will implode. In both cases there is a great pressure difference and the explosion/implosion motion goes from the relative high pressure area towards the relative low pressure area. The difference is, and here it becomes interesting; the difference is that in case of an explosion the energy spreads away in all directions and in case of an implosion the energy moves towards the center of implosion. I case of explosion; the energy is lost, but in case of implosion; the energy is preserved, concentrated in the center of implosion.
Exploding air tents to become turbulent as it gets in contact with air of different speed. Imploding air does not get in conflict with air of different speed. The pressure difference accelerates the air towards the center of implosion with great speed. This speed is not lost but is likely to transform into circular motion around a low pressure area. Some notes about imploding & fast spinning air:
- While air accelerates from high to low pressure, the temperature becomes less.
- Different molecules get separated because of the difference in weight.
- Molecules may split because of the difference in weight of its atoms, resulting in highly charged atoms.
- Atoms may get bent, also because of the huge centrifical forces, resulting in...

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THE SPEED OF SOUND
The speed of sound in air varies with air-temperature, air-pressure, and air composition (like humidity).
On a standard day:
Mach 1 at sea level is about 340 meters per second.
Mach 1 at 45,000 feet is about 295 meters per second.

The speed of propagation of sound in dry air at a temperature of 0° C (32° F) is 331.6 m/sec. If the temperature is increased, the speed of sound increases; thus, at 20° C (68° F), the velocity of sound is 344 m/sec. Changes in pressure at controlled density have virtually no effect on the speed of sound. The velocity of sound in many other gases depends only on their density. If the molecules are heavy, they move less readily, and sound progresses through such a medium more slowly. Thus, sound travels slightly faster in moist air than in dry air, because moist air contains a greater number of lighter molecules. The velocity of sound in most gases depends also on one other factor, the specific heat, which affects the propagation of sound waves.

MACH NUMBERS
Mach 1 = 1x the speed of sound
Mach 2 = 2x the speed of sound
Mach numbers are named after Ernst Mach (1838-1916), an Austrian philosopher and physicist. The term Mach number came into use in 1929.

THE SOUND BARRIER
The transonic band extends from around Mach 0.8 —when the first supersonic shock waves form in front of the aircraft— to Mach 1.2, when the entire aircraft has gone supersonic.

An airplane or any vehicle is said to be crossing the sound barrier when its speed exceeds the speed of sound. Many attempts were made by normal aircraft in the 1940s to break the sound barrier, but they caused the planes to disintegrate because the transition from subsonic to supersonic speeds causes strong nose-heavy changes of trim and sets up structural vibrations that can tear a plane apart. The sound barrier was finally breached on Oct. 14, 1947, by U.S. Air Force captain Charles E. Yaeger in a Bell X-1 research plane. Proper airplane design has since made supersonic flight routine.

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SPINNING AIR

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Spinning air is a logical process but hard to understand because it is very complex, as are most things in life. I'll try to make it more understandable for you and myself!

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Spinning air
Air does not want to spin; it wants to maintain it's speed and direction of motion constant for it is mass. There has to be a force acting upon it continuously, forcing the fast air towards the center of spin: centripetal force. The centripetal force can come from a pressure difference: The ambient air pressure is high (about 1.033 kg/cm2) and low air pressure is in the center of spinning air.

How can the low pressure in the center remain low? A circle is two dimensional, and we live in a 3D world, thus air will be sucked in from sideways... To prevent air from moving in the low pressure area there are some options:
- make a tunnel (of spinning air) between two surfaces.
- make a very long tunnel: from on top of an IFO to space.
- make an endless long tunnel: a donut shaped tunnel.

a tunnel (of spinning air) between an IFO and space.

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