The airplane is one of the great scientific achievements of the 20th century. The engineers were inspired by the study of nature flyers – the birds.
People have always dreamed of conquering the sky with the ability and grace of the birds. Even from Greek legends he flew with wax wings to the sky. But when it got too close to the sun, the wax melted and he collapsed into the void.
Leonardo da Vinci, the great Renaissance artist and inventor, was obsessed with the idea of flying. He left behind several projects of flying machines imagined by him. But 400 years passed until the secret of the flight was discovered.
The first flight attempts often had a tragic end. Some of the adventurous pilots tied their wings to their arms, giving them courageously to rise into the air. None of these attempts resulted, because the “pilots” did not realize that both the shape and the movement of the wing of a bird plays an important role in flight.
In 1738 a mathematician and Swiss physician, Daniel Bernoulli, took the first important step in conquering heaven. He realized that if a liquid or gas is leaking at high speed, it has lower pressure than a slow leak. Since air is a mixture of gases, the observation is also valid for air. If the air meets the wings of a moving bird, it will partially penetrate above, partly below them. Due to the fact that the upper surface of the wing is arched, so longer than the lower face, the air will travel a greater distance above the wing. This will increase the velocity of the airflow above the wing, thus the air will exert a lower pressure on the upper face of the wing than on the lower one. The pressure difference will push the wing up. This pressure difference is called the dynamic (aero) ascent force.
In the nineteenth century, many of the pioneers of flight used these principles to design primitive gliders. Sir George Gayley, named the father of the aviation, built the first glider in 1853, with which he flew. Later, through the 90’s of the last century, the Wright brothers built wings, with which the airplanes could be guided in certain directions.
The cross-section of the wing separated by the fuselage is reminiscent of the image of a drop of water flowing on a flat surface. In front, at the “attack board” the wing is thicker and rounded, but at the back, at the “drain board” it is completely thinned. This form is called a profile. The air currents oriented above and below the wing suggest the Bernoulli principle very well.
Besides the ascent force, the turbulence of the air contributes to the lifting of the wing. The air that passes over the wing when leaving the drain board turns and produces air turbulence, as in the case of water leaking into a hole. The phenomenon is called initial turbulence, which in turn produces another turbulence: the counter-turbulence.
This is as strong as the initial turbulence, but rotating in the opposite direction, so that when it passes under the wing, in the opposite direction, it will encounter the main air stream, which will slow it down.
The counter-turbulence will move further, and on the wing’s attack board it will move upward, joining the main current. For this reason, the lower air stream slows down, and the upper one, above the wing, accelerates. Thus, the pressure will decrease at the top and increase at the bottom, which follows the ascending force.
Later, the first airmen discovered how they can fly the aircraft heavier than the air. For this, it was necessary to realize how the necessary ascension force can be produced. In the case of floating in the air, things were simpler, leaving everything to the air, but in order to get up, a way had to be found to reach the speed necessary to obtain the ascending force.
Wilbur and Orville Wright solved the problem by using a smaller and easier engine. On the engine they mounted a propeller made of wing profile parts: it rotated vertically in front of the engine. The movement of the air caused by the rotation, or rather the force determined by this movement, is called the tensile force. The air will be pushed back, and the flight apparatus will move forward. On December 27, 1903 in Kitty Harok, North Carolina, the Wright brothers made the first flight on their motor plane. The aircraft could only travel 36 meters in 22 seconds, but it succeeded in putting into practice the principle used by the aircraft designers who followed it.
In the 1940s, flight researchers developed jet-powered aircraft. The traction force is obtained in this case by compressing the air in a combustion chamber, where it is mixed with a special fuel – kerosene, after which the mixture will be ignited. The explosion produces a strong jet of air that will propel the airplane when it leaves the combustion chamber behind the engine.
The jet planes fly at higher speeds than those with propellers, but they use a very large amount of fuel, especially at low speeds. For this reason, they have developed another type of jet engine powered propeller. Nowadays, double jet jet aircraft are used most often. They have a propeller made up of a multitude of blades, which pushes the air into the blast chamber, but produces currents of air around the engine, just like a normal propeller, increasing traction force. The gas jet can be directed in such a way as to reduce the propulsion force, slowing down the flight apparatus.
When the airplane has an adequate speed, so that the dynamic ascent force is sufficiently high, it will have to be guided accordingly. The flight has 6 main stages: take-off, ascension, horizontal flight, return, descent and landing. These movements will be obtained with the help of the guide plates located on the wings and on the so-called empennage. And these have the shape of the wing profile on the cross section, thus producing a dynamic ascending force.
When taking off, the flaps on the wing drain board rise, which increase the surface and in this way the intensity of the ascent force. The horizontal stabilizers (depths) on the horizontal gear are raised. During this time the muzzle of the plane is oriented upwards, the tail is lowered, and the plane rises in the air. It is very important that before the start of this maneuver the aircraft has the proper speed. The flaps and depths must be lifted exactly when the dynamic lift force equals the weight of the aircraft, otherwise the machine loses speed and fails to take off.
The issue of air resistance must also be considered. Moving the aircraft produces resistance from the air, which provides the aircraft. This force acts on anything in motion, but we can only talk about the force of resistance induced in the case of airplanes. It is about the fact that some of the energy flow from the air passing over the wing will turn in the opposite direction, preventing the airplane from moving. The phenomenon is caused on the one hand by the position of the wings, on the other hand by the air turbulence.
Upon take-off, the pilot counteracts the opposite resistance of the air by lowering the flaps. The plane will fly at a certain level, its speed being high enough for the propulsion force to exceed the air resistance force. The horizontal stabilizers will be raised again, the device rising to the final level. The plane can make a horizontal flight if its own weight is equal to the lifting force.
The airplane may fly to its destination, but the pilot will have to turn to move in the right direction. The trips can be performed with the help of other stabilizers, namely: with the wings on the wings and with the drift (or rudder), the component of the vertical gear.
The ailerons are on the wing drain board. If the pilot wants to turn the plane to the left, then he will lower the aileron on the right wing, increasing on that side the ascent force. At the same time it will raise the left aileron, on that side reducing the ascent force. When the plane is inclined to the left, with the ailerons it will pull the rudder to the left, thus maneuvering being complete.
Then, if the plane is oriented in the desired direction, the pilot withdraws the ailerons and drifts to the normal position.
As the airplane approaches its destination, the pilot must prepare for safe landing. It is a complex process and must be performed with extraordinary precision, so that the machine does not suddenly lose height. Under ideal conditions the pilot will fly in the opposite direction of the wind, the air currents facilitating the steering. The lateral wind can cause problems, as it can unbalance the aircraft and make landing maneuvers difficult.
For landing the pilot reduces the speed and descends the flaps and depths so that the muzzle is oriented downwards; the dynamic force of ascent will decrease, the force of resistance of the air will increase, the airplane will begin to descend. When it comes close to the landing strip, the horizontal stabilizers are lifted, and the front adjunct wings, located on the attacking wing of the wings, come into operation. These increase the surface of the wings and accentuate the ascent force. The result will be tilting the plane horizontally, the muzzle being oriented higher than the tail. This compensates for the decrease of the ascent force resulting from the reduction of speed. The speed of the airplane will be so low that for a few moments it seems to float above the runway.
To reduce the speed a few additional flaps are put into operation. They are on the wings’ attacking board and are called spoilers. These produce the air turbine, which in turn will increase the force of air resistance and exceed the ascent force.
At this stage the wheels will be lowered which further increases the frictional force. At first the airplane will hit the ground with the main landing gear wheels. The depths will be lowered, for the muzzle to descend and the front train wheels to touch the ground. The machine landed completely. The flaps are fully lowered to increase the frictional force as much as possible. The wheel brakes are actuated and the machine finally stops.
In takeoffs in general, a long runway is needed, in order for the aircraft to accelerate at an appropriate speed and to be lifted by the dynamic ascent force. Sometimes the space is insufficient for this maneuver.
One of the methods used to take off on the runways of islands or airports in the center of big cities has become known as STOL (Short Take Off and Landing). The principle of this realization is to obtain a surplus of the ascension force at the reduced speed.
The BOEING C14 aircraft have flaps so designed that they can be oriented beyond the wing drain board. The gases in the jet engine will extend over the wings, following the curvature of the flaps. This surplus of airflow then being directed downwards, will produce a strong ascending force. This is called the Coanda effect.
Another variant of the STOL model is that of the folding propellers, as in the case of the American Bell V-22 Osprey. On both wings of the airplane is mounted a propeller motor. The engines can be folded over the wing, at takeoff producing a vertical lift force, then they will return to their normal position, producing a propulsion force large enough for horizontal flight.