User:
Wing in the flow
Concept
If we assume that the flow around a wing is laminar, we can observe multiple layers surrounding the wing. Those on the upper side tend to be slightly longer due to the upward curvature, while the lower layers tend to be shorter and, therefore, closer to the wing.
Supposing that the flow is such that these layers converge in a way that points close together on either side of the wing return to the same relative position once the flow separates, the speed of the upper layers will necessarily be higher than that of the lower layers. It's important to keep in mind that this is just an assumption, and there is no real necessity for them to converge; in fact, they could end up being out of phase without any issues.
ID:(7016, 0)
Force on the wing
Concept
Since the velocity in the upper layers of the wing is greater than in the lower layers, this implies that the pressure on the upper surface of the wing is lower than on the lower surface.
This effectively means that there is a greater force from below the wing compared to above the wing, which leads to the generation of lift force.
ID:(7018, 0)
Flight, balance of forces
Concept
The forces that influence an aircraft or bird can be categorized into two fundamental groups:
Forces that impact the control of the center of mass's movement:
• the lift force ($F_L$), which counteracts the gravitational force ($F_g$).
• the propulsion force ($F_p$), which opposes the resistance force ($F_W$).
Forces aimed at achieving the rotation of the aircraft or bird around the center of mass, achieved through the ailerons on the wings and the rudder:
• Ailerons allow the generation of a turning moment by asymmetrically altering lift on each wing.
• The rudder controls the direction of the aircraft or bird by redirecting the airflow.
Boeing Images - 777-300ER Illustration in Boeing Livery
Key parameters for controlling the center of mass's movement are:
• the surface that generates lift ($S_w$) and the total object profile ($S_p$).
• the coefficient of lift ($C_L$) and the coefficient of resistance ($C_W$), the latter being dependent on the angle of attack of a wing ($\alpha$).
ID:(11080, 0)
Gravitational Force
Equation
The gravitational Force ($F_g$) is based on the gravitational mass ($m_g$) of the object and on a constant reflecting the intensity of gravity at the planet's surface. The latter is identified by the gravitational Acceleration ($g$), which is equal to $9.8 m/s^2$.
Consequently, it is concluded that:
 $ F_g = m_g g $ |
ID:(3241, 0)
Lift force
Equation
To generate higher pressure below than above the wing and generate lift, Bernoulli's principle is employed, correcting for the lack of energy density conservation using ($$). The pressure over the wing, the lift force ($F_L$), can be estimated using the density ($\rho$), the surface that generates lift ($S_w$), the coefficient of lift ($C_L$), and the speed with respect to the medium ($v$) through the following formula:
| $ F_L =\displaystyle\frac{1}{2} \rho S_w C_L v ^2$ |
The lift force ($F_L$), along with the wing span ($L$), the density ($\rho$), the wing top speed factor ($c_t$), the wing bottom speed factor ($c_b$), the upper wing length ($l_t$), the bottom wing length ($l_b$), and the speed with respect to the medium ($v$), is found in
| $ F_L = \rho L ( c_b l_b - c_t l_t ) v ^2$ |
If we consider the surface that generates lift ($S_w$), given by the wing span ($L$), the upper wing length ($l_t$), and the bottom wing length ($l_b$),
| $ S_w = \displaystyle\frac{1}{2} L ( l_t + l_b )$ |
and for the coefficient of lift ($C_L$), defined as
| $ C_L = 4\displaystyle\frac{ c_t l_t - c_b l_b }{ l_t + l_b }$ |
we obtain
| $ F_L =\displaystyle\frac{1}{2} \rho S_w C_L v ^2$ |
ID:(4417, 0)
Total force of resistance
Equation
With the relationships of the lift force ($F_L$), the resistance force ($F_W$), and the angle of attack of a wing ($\alpha$), we can calculate the total resistance force ($F_R$) as follows:
| $ F_R = F_w \cos \alpha + F_L \sin \alpha $ |
If we apply these relationships to each force, assume small angles, and consider a situation in which the angle is such that the mass of Object ($m$) can be maintained, we obtain the following expression using the coefficient of lift ($C_L$), the coefficient of resistance ($C_W$), the surface that generates lift ($S_w$), the total object profile ($S_p$), the gravitational Acceleration ($g$), the proportionality constant coefficient sustainability ($c$), the density ($\rho$), and the speed with respect to the medium ($v$):
| $ F_R = \displaystyle\frac{1}{2} \rho S_p C_w v ^2 + \displaystyle\frac{2 m ^2 g ^2}{ c ^2 S_w \rho }\displaystyle\frac{1}{ v ^2}$ |
Using the relationships of the total resistance force ($F_R$) with the lift force ($F_L$), the resistance force ($F_W$), and the angle of attack of a wing ($\alpha$):
| $ F_R = F_w \cos \alpha + F_L \sin \alpha $ |
we can calculate using the resistance force with the density ($\rho$), the coefficient of resistance ($C_W$), the total object profile ($S_p$), and the speed with respect to the medium ($v$):
| $ F_W =\displaystyle\frac{1}{2} \rho S_p C_W v ^2$ |
and the lift force with the surface that generates lift ($S_w$) and the coefficient of lift ($C_L$):
| $ F_L =\displaystyle\frac{1}{2} \rho S_w C_L v ^2$ |
using the relationship for the coefficient of lift ($C_L$) with the proportionality constant coefficient sustainability ($c$):
| $ C_L = c \alpha $ |
using the relationship for the sine of the small angle of attack $\alpha$:
| $\sin\alpha\sim\alpha$ |
and the cosine:
| $\cos\alpha\sim 1$ |
with the condition to balance the weight of the bird or aircraft for the mass of Object ($m$) and the gravitational Acceleration ($g$):
| $ \alpha =\displaystyle\frac{2 m g }{ c \rho S_w }\displaystyle\frac{1}{ v ^2}$ |
we obtain:
| $ F_R = \displaystyle\frac{1}{2} \rho S_p C_w v ^2 + \displaystyle\frac{2 m ^2 g ^2}{ c ^2 S_w \rho }\displaystyle\frac{1}{ v ^2}$ |
ID:(4546, 0)
0
Video
Video: Flight