How aeroplanes fly
The names aeroplane, plane, airplane and aircraft are one and same, normally referred to as fixed-wing.
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Aeroplane wings are direct replicas of the wings of birds (Fig.1).
In 1738, a Swiss mathematician called Daniel Bernoulli published the formula that led to greater understanding of flight.
Bernoulli wrote that the total pressure PT, of air is made up of the pressures of the air at rest – ps – and of the air in motion – pd; PT = ps + pd. When ps changes, pd must change in the opposite direction to restore the balance.
When the air flow meets the wing, the air on top of the wing speeds up.
It has a longer distance to cover before meeting the air below the wing.
In line with Bernoulli's theory, the speeding air at the top will have a reduction in pressure, compared to the air below.
Scientists failed to show unanimity in explaining the reason for the speeding up. In the research for the article, I hit a blank in seeking for the explanation.
Bernoulli's formula can, however, be illustrated at home.
Hold a spoon by its handle and turn the back side of the spoon towards a flowing tap water. (See. Fig. 2.)
The water will pull on the spoon.
The wings of birds were copied by aeroplane & helicopter manufacturers
The faster the flow of water, the stronger the pull.
Also, the steeper the angle (angle of attack) the spoon meets the water, the stronger the pull.
The wings of the aeroplane moving through air produces the similar pull, upwards. This is called lift. (Fig.3).
Duplication
The entire body of the plane is a duplication of this aerofoil (wing) shape at various places in order to help control the plane at specific stages of flight.
The elevator, for example, is attached to immovable horizontal part of the tail called horizontal stabilizer. (Fig. 4)
This controls movement in the vertical plane (pitch).
Also attached to the immovable vertical part of the tail is the rudder.
The rudder and the vertical stabilizer control stability in the horizontal plane.
When the elevator moves down, the angle of attack increases, so the lift raising the tail.
The situation during descent.
The opposite is true for an elevator moving up.
As the elevator moves up, lowering the angle of attack producing less lift, the tail moves down.
This is the take off. (Fig. 5).
Climb
In the climb, the plane may turn, right, for example.
We introduce another control devices, called ailerons.
The right airelon moves up, decreasing the lift on the right wing, while the left aileron moves down increasing the lift on the left wing. (Fig. 6).
The height of the plane is measured by the altimeter.
Altimeter is a pressure instrument that measures pressure as height in feet.
These actions are reversed when the plane descends from the assigned level (cruise ) for landing.
When close to the ground over the runway, the pilot raises the nose to allow the main landing gears to touch the ground first, this is referred to as the flare. (Fig.7).
When the main landing gears touch the ground, the nose gear is then lowered to the ground.
There are devices on the plane which help to reduce the lift produced by the wings so that the plane can touch the ground firmly.
Controls
All the controls we have discussed so far are called primary controls which are germain to all planes.
These are elevator, aileron and rudder.
The entire gamut of flying revolves around the control of speed. Every stage of flight for a particular plane has its own speed limit.
When the airflow over the wings starts to slow down due to say, engine failure, for example, the lift will reduce to equal the weight of the aircraft and below.
The aircraft would fall from the sky and crash.
This condition is called the stall.
When the writer was a student pilot, his instructor, Wg. Cdr. Andy Mensah queried him for consistently flying at 78 knots, (nautical miles per hour), instead of 80 knots.
Speed control is a very serious exercise in pilot training.
This will keep the plane far from the dreaded stall.
The two devices for measuring the airspeed are pitot tube and static pressure measuring systems. (Fig 8).
The modern airplane also has pressurisation and temperature control.
As the plane climbs, air pressure and temperature both decrease.
It has been determined that humans can breath normally up to 8,000 ft.
However, the writer got to 16,000ft, without any breathing aid so it turned into a weather emergency at night.
My instructor then, Sqn. Ldr. Dan Larkai, saved the situation.
Wg. Cdr Francis W. Quayson was the overall hero.
Airplane designers have, therefore, included cabin pressurisation in all planes flying above 8,000ft.
This maintains a comfortable level of both oxygen and temperature.
It is very difficult to avoid the use of certain technical jargons in an article like this.
I, therefore, acknowledge the encouragement of my former instructor, Wg Cdr. Daniel Gomez.
The writer is a pilot, formerly with the Ghana Armed forces (GAF).
E-mail: [email protected]
