What is the formula for calculating the weight of a plane in level flight?

[ryanbe]

hi

how do i calc the weight of a plane if it stays in level flight with the air speed on top of the wing 62m/s and the bottom 54m/s. the surface area of the wing is 16m^2

 

[Ken G]

Google "Bernoulli's principle". You'll find that the excess pressure on the bottom of the wing (which you can relate to the weight of the plane, how?) is given by the difference in the kinetic energy densities above and below. The latter is the mass density times the velocity squared. You'll have to look up the density of air, so apparently the plane is not flying at high altitude.

(By the way, this is a cute problem, but it is not an accurate portrayal of the real reason that planes fly, as proven by the fact that this plane could fly upside down. But perhaps it is the maximally efficient flight, and maybe many planes are designed to get close to this limit. The other key design issue is stability.)

 

[rcgldr]

You'd need to know the mass of the affected air. Also the air speed over and under the wing won't be constant, it will vary depending on distance from the wing.

Maybe this is just a simplication of the real issue and just wanting you to use Bernoull as opposed to the actual and complex process of calculating lift.

Also air speed relative to what? It appears to be relative to the wing. Air speed relative to the ambient air would be less, or else this is a very large airplane.

 

[ryanbe]

Maybe this is just a simplication of the real issue and just wanting you to use Bernoull as opposed to the actual and complex process of calculating lift.

yes i must use bernoulli but not sure how ?

anybody got the equation in the form that i must use it, then i can take it from there ?

 

[ryanbe]

is this right : p1+1/2*1.29*62^2 = p2+1/2*1.29*54^2

p1 + 2479.38 = p2 + 1880.82
p1 - p2 = 1880.82 - 2479.38
= -598

p = f/a
598= f/16
9568n = f

plane = 975kg

 

[Ken G]

Looks good to me, though I didn't check the units. Best to include them to make sure.