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

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    Airplane Physics
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Discussion Overview

The discussion revolves around calculating the weight of a plane in level flight using Bernoulli's principle, given specific air speeds above and below the wing and the wing's surface area. Participants explore the relationship between pressure differences and lift, while addressing the complexities of real-world flight dynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about calculating the weight of a plane in level flight using given air speeds and wing area.
  • Another suggests using Bernoulli's principle to relate pressure differences to the weight of the plane, noting that this approach may not fully capture the complexities of flight.
  • A participant points out the need to consider the mass of the affected air and the variability of air speed around the wing, questioning the simplification of the problem.
  • There is a request for the specific equation to use with Bernoulli's principle to facilitate further calculations.
  • A participant presents a calculation attempt involving pressure differences and concludes with a weight estimate for the plane, though this is met with a suggestion to check units for accuracy.

Areas of Agreement / Disagreement

Participants express varying levels of agreement on the use of Bernoulli's principle, with some acknowledging its limitations in accurately representing flight dynamics. There is no consensus on the correctness of the calculations presented.

Contextual Notes

Limitations include assumptions about constant air speeds and the simplification of complex aerodynamic principles. The discussion does not resolve the complexities involved in calculating lift accurately.

ryanbe
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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
 
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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.)
 
Last edited:
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.
 
rcgldr said:
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 ?
 
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
 
Looks good to me, though I didn't check the units. Best to include them to make sure.
 

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