Consider a Boeing 777 flying at a standard altitude of 11 km with a cruising velocity of 935 km/h. At a point on the wing, the velocity is 280 m/s. Calculate the temperature and pressure at this point.

Respuesta :

Answer:

 ΔP = 97.93 Pa ,     T₂-T₁ = 71.5° C

Explanation:

For this problem let's use Bernoulli's relationship, as point 1 we will take the plane and as point 2 the air

            P₁ + ½ ρ g v₁² + ρ g y₁ = P2 + ½ ρ v₂² + ρ g y₂

As the whole process occurs at the same height y₁ = y₂ = 11 km. We will consider that the air goes in the opposite direction to the plane

            P₂ –P₁ = ½ ρ (v₁² - v₂²)

             

Let's reduce the magnitudes to the SI system

           v₁ = 935 km / h (1000 m / 1 km) (1h / 3600s) = 259.72 m / s

           v₂ = 280 m / s

The density of air at 11000 m is

           Rho = 0.3629 kg / m

           P₂-P₁ = ½ 0.3629 (259.72 + 280)

           ΔP = 97.93 Pa

The variation of the temperature with the altitude is 0.65 per 100 m

            T₂ –T₁ = (0.65 / 100) 1000

             T₂-T₁ = 71.5° C

The temperature has decreased this value