Flight's mechanics is The mechanics of the flight is appropriate for planes, and consists in studying all the strengths being applied on an aircraft.
These strengths can be grouped together according to their origin :
All these strengths apply in the center of gravity G of the plane, now in uniform rectilinear flight its trajectory is a right and its speed is constant, thus sum of the strengths applying to the G-spot is inevitably invalid: SF=O
As any object, planes are subjected to various strengths. But in what has the wing a link with these strengths ?
By studying a plane, of mass "m" some in a Galilean reference table, we notice that it is subjected to four strengths:
The drive, applied at the level of propeller or reactors, horizontal (parallel to the ground), of even direction as that of the plane.The resultant of the aerodynamic strengths decomposed there portance and in trail :
- The portance, created by the movement (in geometry, a movement is a resemblance which preserves the distances and the directed angles) in the ascending profiled, vertical air(sight) of a wing
- The trail, the sum of the aerodynamic resistances, horizontal (parallel to the ground) and set against the movement.
These strengths are represented by 4 vectors:
§ the drive forwards opposes to the trail towards the back,
§ the portance upward opposes to the weight downward.
The portance is characterized by the wing. She so allows the plane to be in equilibrium position, because she compensates for the weight. Without the wing, the plane could not fly. The wing is thus one of key points of the plane's flight !
If the plane moves horizontally, in a rectilinear uniform way, we can assert, according to the principle of slowness (sum of the strengths applying to the plane S=0), that the value of the portance is equal to that of the weight and if the value of the trail is equal to that of the push
B. Studies of the strengths
1. The portance
The main reason of the portance explains with the Newton's third law
It says that: " in any strength exercised in a direction, there is an associated strength being applied in the opposite direction and having the same intensity ".
It is the principle of action-reaction.
An aircraft wing is tilted. In this way, it "prints" informed of air a change of direction : the airflow is going to follow the shape of the wing and in the end(final) the air(sight) will have a downward movement.
Now, if direction of the movement exchange there is production of a strength (it is the Newton's Second law), and this strength pushes the air downward.
This effect takes place above and below the wing:
Thus according to the Newton's 3rd law: if the air is pushed below, the wing is pushed upward and the whole plane with.
The portance is a strength, so called lift, managed by the bottom(stocking) upward, and which has its center in a point of the wing: the centre of pressure. It is set against the weight of the plane and must be equal to it at least so that the plane rises. It results from the penetration in the air, of the wing.
The flow of the air on the top of the wing (Extraback) is faster than that of the bottom ( Intrados). It is due to the profile of the wing, spray-painted on the top. It results from it a lower pressure on the extraback and thus an aspiration upward. The lift is mainly generated by the extraback.
The angle which forms the wing with the air layer which it crosses (conscript angle of incidence) acts on the portance of the wing. The more that this increases, the more the portance increases. But it to a certain extent. Beyond, the wing stalls brutally and loses its portance
2. The trail
The trail is the strength opposite to the movement of the plane and which results from its resistance in the air. It is the resistance in the progress(promotion), we thus try to reduce it at most.
Examples of influence of the shape of the body on the resistance:
§ The slender body is the best adapted to decrease the resistance in the air. Indeed, the trough of low pressure is filled, whirlwinds are invalid, and the nets of air join. The coefficient of resistance is very low.
§ The shape of aircrafts requires a meticulous study to have the minimum of resistance in the air.
To sum up, we shall say that the strength which are applied on the wing is resultant aerodynamic. It decomposes into two strengths: Portance and trail.
3. The Weight
It is the strength which acts on the total mass of the plane. It applies in a point: the centre of gravity. It is managed towards the center of the Earth and expresses itself in Newton.
It is against this strength that the aircraft has to fight to rise in the airs. So that the height is constant, the value of the portance has to be equal to that of the weight. The weight also plays a role in the choice of materials and in the structure of the plane because the buckle and the fuselage undergo important efforts.
It results from engines through the propeller. If the plane has reactors, it is the push of those this that balances the trail. A propeller prints in an air mass an acceleration towards the back and it receives in his turn a strength managed forwards: it is the drive and the plane is propelled forwards. During the takeoff, the wing meets the air chased away by the propeller, and it begins to have a portance there.