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For thousands of years, people have wanted to fly. Our legends and fairy tales are full of humans and animals that can fly – effortlessly gliding through the air. In real life, of course, no one can just fly into the air. We don’t have wings and a power source strong enough to keep the wings moving through the air to sustain the lift necessary for flight.

Our attempts to fly have taken us from flimsy paper hot-air balloons and strange-looking gliders to supersonic jet planes. We have learned about the forces of flight, and we know what it takes to keep birds and planes in the air.

Force can be defined as a push or pull. Unbalanced forces produce an acceleration of an object in the direction of the resultant force. Four main forces affect the flight abilities of birds and planes – weight, lift, thrust and drag

We all know that gravity is a force that pulls everything towards the Earth’s surface. This pull is called the weight force.

Planes and birds have to be able to provide enough lift force to oppose the weight force. Lift is a force that acts upwards against weight and is caused by the air moving over and under the wings.

The power source of a bird or plane provides the thrust. Thrust is the force that moves the object forward. Thrust is provided by:

For thousands of years, people have wanted to fly. Our legends and fairy tales are full of humans and animals that can fly – effortlessly gliding through the air. In real life, of course, no one can just fly into the air. We don’t have wings and a power source strong enough to keep the wings moving through the air to sustain the lift necessary for flight.

Our attempts to fly have taken us from flimsy paper hot-air balloons and strange-looking gliders to supersonic jet planes. We have learned about the forces of flight, and we know what it takes to keep birds and planes in the air.

Force can be defined as a push or pull. Unbalanced forces produce an acceleration of an object in the direction of the resultant force. Four main forces affect the flight abilities of birds and planes – weight, lift, thrust and drag

We all know that gravity is a force that pulls everything towards the Earth’s surface. This pull is called the weight force.

Planes and birds have to be able to provide enough lift force to oppose the weight force. Lift is a force that acts upwards against weight and is caused by the air moving over and under the wings.

The power source of a bird or plane provides the thrust. Thrust is the force that moves the object forward. Thrust is provided by:

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One of the most significant gas laws - Marriott and Gay-Lussac law states:

P x V = a x T with:
P : absolute pressure (Pa)
V : volume (ft3 m3)
T: absolute temperature (K)
a : constant

This relation is used within the compressor : constant air volume is pumped from the compressor chamber, and the volume decreases. This decrease causes an increase in both the pressure and the temperature of the air.

Flow is equivalent to the quantity of compressed air conveyed in a given section per unit of time.

Q = A1 x V1 = A2 x V2
Q: flow (cfm)
A: flow section (ft²)
V: speed (ft/min)

The international system of flow is cubic meters / second (m3/s), but we generally use l/s, m3/h or cfm. This varies according to several factors, and, in particular, to the air pressure and the length/ID of the pipe, which conveys the compressed air.

When compressed air flows in a straight pipe, the flow can depend on two factors: the laminar rate or the rate of turbulence, according to the value of the Reynolds Number " R ".
The Reynolds number is a dimensionless ratio between inertia and friction in a flowing medium.

Values for one metre air pipe system.

To convert Nm3/h to CFM, please use the coefficient of 0.588
To convert CFM to Nm3/h, please use the coefficient of 1.699




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