First of all, wings allow the plane to fly: it is them who "carry" the plane. As any object, this one is "attracted" towards the ground by a strength which we call weight. Thus the plane, in a natural way, would tend in fallen. That is why, to counterbalance this "attraction", it is necessary to create an important surface which "will float" on the wing, as makes it a parachute. It is this role which play wings. From part their important surface, they are in contacts with a wide air mass, which is thus of use as "pillow" to the plane.
The wing allows the plane to be in equilibrium position because it creates a called portance strength.
It is important first of all to characterize geometrically (Face(Figure) 13) a wing (or buckle) by defining certain number of terms.
§ Extraback: superior surface of the wing.
§ Intrados: lower Surface of the wing.
§ Leading edge: the previous edge of the wing.
§ Trailing edge: later(posterior) edge of the wing.
§ Cord: right joining(contacting) the leading edge at the edge of flight(leak). The depth l is the length of this rope
§ average Rope: line passing by all the points equidistant between the extraback and between the intrados.
§ Thickness: distance e maximum between the intrados and the extraback measured perpendicularly in the rope. The thickness, for the classic profiles, is generally situated at a maximum distance about 30 % of the depth, from the leading edge.
§ Scale: the scale of the wing is the distance between both extremities of the wing.
B. The profiles of wing
A profile of wing is defined by several measures. The main clauses(head teachers) are presented on the plan above.
The air(sight) returns in touch with the wing by the leading edge and the quits by the trailing edge. The segment which joins these two edges is called the rope and the right which is the same managed is named(appointed) reference line.
The bottom of the profile is called intrados, while the top names extraback. The thickness of the wing confronts between the intrados and the extraback (it is the maximal distance which separates them).
The average rope indicates(appoints) the line connecting(binding) the leading edge at the edge of flight(leak) and situated at equal distance of the intrados and the extraback.
We call arrow of the profile, the maximal distance between the rope and the average rope. The report(relationship) between the arrow and the rope is when to him named curvature or relative curve. It allows to determine if the profile of wing is more or less hollow.
Ø convex Plan: he allows to obtain a rather high(high enough) portance with low(weak) incidence but in for inconvenience to be slightly unstable. He(it) generates an average trail. Used in general aviation.
Ø Biconvex symmetric: not carrying(wearing) in the low(weak) incidences, he(it) is used for the acrobatics.
Ø Biconvex asymmetrical: he(it) also gives a rather high(high enough) portance to no incidence while being very stable. Used for the aviation of leisure.
Ø bent Profile (or hollow): rather unstable profile, allowing a very high portance. When the incidence increases he(it) tries to rear. This profile creates a strong trail due to its curve.
Ø Double curve (or stable automobile): he allows to have a big stability, in depends on a rather strong trail and on an average portance.
The profile of the wing is modelled to obtain a most raised(most brought up) portance possible and a minimal trainée.
The diverse characteristics of an aircraft wing allow to modify at best the portance and the trainée, according to the popular purpose; speed or portance. We shall hold(retain) in particular the factor(mailman) of curvature of a wing.
So if we refer to the mechanics of the flight(theft), we notice that the more the curvature is important, the more the portance is important but the thickness also increases what also makes increase the trainée. In fact, a wing with strong curve will drop out in a stronger angle of incidence, it will thus have a better coefficient of portance. A wing with low(weak) curve will suit better in the low(weak) incidences and thus in the high speeds. On the other hand the very thin profiles lead(infer) a rough unhooking, which could show itself dangerous.
In a general way, the slow planes will have a thickness bigger than airliners, or supersonic aircrafts (fighters): the thick profiles have a portance big, but also a big trail. For a very fast plane, a coefficient of portance means can be compensated with a high speed, but a too strong trail would be too expensive in energy.
Airliners, considering their mass (300 tons for a Boeing 747) will thus have to reach(affect) a strong speed the takeoff, what is made on a long distance (approximately 3 km). For fighters, their mass is much lower(weaker) (16 tons for a mirage F1) and their power of high propulsion; the takeoff will be made on a shorter distance (about 300m)
If we express the report(relationship) of the thickness on the rope e/l, we have:
1. E/l < 6 %: thin profile of the fighter
2. 6 % < e/l < 12 %: semi-thick profile of the airliner
3. E/l = 12 %: light passenger aircraft with low speed
----------> wings of slow planes have rather an asymmetric profile, with the convex extraback and the intrados rather flat, to assure(insure) a sufficient(self-important) portance, but the price(prize) of a rather strong trail. The faster planes can use symmetric wings.
It is necessary to note that a profile of wing is conceived for the cruising speed of the plane, in flight(theft) landing. In strong speed, the coefficient of portance can be "low". But it is necessary to be also able to maintain the plane in flight(theft) in the phases of takeoff and landing, which are made in lower speed. That is why, in practice, in most of the planes and even the light passenger aircraft, there are called hypersustentateurs systems. They are mobile shutters(sectors) placed in the edge r beaks placed at the edge of attack. They are activated(sued) by the pilot(driver) and allow to play on the profile of the wing and its surface, and so on the portance and the trail.