Aerodynamic resultant

The flow of air around the fuselage creates a force called the Aerodynamic Resultant (Ra), which is broken down into its components parallel and perpendicular to the relative wind: drag and lift. The other forces acting on the aircraft are traction and weight.

In the following diagrams, the orders of magnitude between lift and drag are disproportionate, for ease of reading. The lift/drag ratio (glide ratio) is around 10 on light aircraft, i.e. lift is 10 times greater than drag.

Level flight

Lift balances weight, traction balances drag. The entire system is in equilibrium.

Expression of lift :
is the density, characterizing the medium in which displacement takes place.
is speed.
is the surface area of the object (known as the wing area for an aerodyne wing).
is the lift coefficient.

Drag coefficient :

is the drag force, which by definition is the component of the force in the direction of the velocity vector, is the density of the fluid, is the object’s velocity relative to the fluid, is the reference surface.

Lift coefficient :

F
_z
in newtons
= density of the fluid in ^kg/m3= travel speed in m/s. reference surface (projected surface in the x-y plane for a wing).

To sum up:

ρ: air density
Density depends on altitude, temperature and atmospheric humidity.

S: wing area
The wing area can vary depending on the flap and/or slat extension. We consider
however, is a constant value.

V: air speed of the aircraft

Fz: lift

Cz: lift coefficient
A dimensionless number that essentially represents the wing’s incidence.

Cx: drag coefficient
Dimensionless number representing everything that opposes forward motion (profile drag, induced drag, etc.).

Climbing flight

Lift remains perpendicular to the relative wind, while weight remains vertical. This creates a weight component parallel to the relative wind, which adds to the drag. To compensate for this increase in drag, power must be added. If you’re already at full throttle, you can’t go any higher, you’ve reached the propulsion ceiling.

Descending flight

In this case, the weight includes a component which is parallel to the relative wind, but which is added to traction, or which replaces traction in the case of gliding without an engine or with a reduced engine.

Load factor : This is a variable that expresses the force applied to the aircraft structure. The load factor is the ratio between the total load supported by the structure of a device and the actual weight of that device.
(calculation: load factor = lift/weight)

In straight flight (straight line at constant speed) in level flight (constant altitude), the vertical load factor is 1 (i.e. lift = weight and drag = drag).
When an aircraft makes a turn or exits a dive, the load factor increases.
For example, an aircraft in a symmetrical horizontal turn with a roll angle of 60° is subject to a load factor of 2. In this case, the aircraft’s structure has to support twice its weight, and the pilot has to increase the aircraft’s angle of incidence to produce more lift.

Finesse:
We talk about “finesse” for all flying “objects”: paragliders, hang gliders, helicopters, gliders and airplanes, of course. A plane’s “glide ratio” is its ability to glide with all engines off.
The glide ratio of a fixed-wing aerodyne is the ratio of its lift to its aerodynamic drag. Gliding (without traction/propulsion) at true speed (speed of the aircraft in relation to the mass of air in which it is moving), and therefore at constant slope, is equal to the ratio between the horizontal distance covered and the height of fall, or the ratio between the horizontal speed and the vertical speed (sink rate). Of course, this definition must be adapted to the object under study: boat sail, hull profile…