Understanding Lift Force and the Bernoulli Equation in Small Aircraft

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Homework Help Overview

The discussion revolves around understanding the lift force in small aircraft, particularly through the application of the Bernoulli equation. Participants are exploring the relationship between lift, airspeed, and pressure differences across the wing surfaces.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to relate the lift force to gravitational force and are questioning the specific airspeed variable in the lift equation. There are discussions about the application of Bernoulli's equation and how to incorporate pressure differences and drag into their reasoning.

Discussion Status

Several participants have provided guidance on applying Bernoulli's equation and interpreting pressure differences. There is an ongoing exploration of how to relate pressure, area, and lift force, with some participants expressing uncertainty about the information provided and its relevance to the problem.

Contextual Notes

Participants note that some information may be missing or extraneous, and there is a lack of clarity regarding the specific pressures involved and how they relate to the overall lift force needed for the aircraft.

Donna14
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Homework Statement


See attachment

Homework Equations



Maybe lift force = ClρAv2

A=area
Cl= lift coefficient= 0.3
ρ= air density
V=air speed but don't know which one it represents... Under or below wing or average?

And the bernoulli equation seems to be needed as well...

The Attempt at a Solution



To keep the plane just in the air the lift force must be equal to the gravitational force I guess. But I'm not sure how to continue from there...
 

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Donna14 said:
V=air speed but don't know which one it represents... Under or below wing or average?
...
I think the diagram shows that explicitly.

Donna14 said:
And the bernoulli equation seems to be needed as well...
...
Yes, can you try and apply it here?
 
But I am stuck on how to continue... Can you please help me a bit?
 
Why don't you start by stating Bernoulli's equation and maybe try and substitute some values into it?
 
Last edited:
P1-p2=1/2ρ(v22-v12)

But I don't know the pressure and I don't understand what to do with drag and lift force?
And do I have to use the given engine power?

Sorry this is completely new to me...
 
Last edited:
Donna14 said:
P1-P2=1/2ρ(v22-v12)

But I don't know the pressure and I don't understand what to do with drag and lift force?
And do I have to use the given engine power?

Sorry this is completely new to me...
Forget that equation for lift force. I assume there are more parts to this problem, which you didn't show us. Some of the given information may be needed for those -- or may just be extra information.


You have P1-P2=(1/2)ρ(v22-v12) .

Do the subscripts, 1 & 2 refer to the bottom surface of the wing and the top surface of the wing respectively?

How much lift force is needed?

What part of the plane generates the lift?

How are force, area, and pressure all related?
 
Going with the idealized assumptions about lift for this problem, you can assume the pressure below the wing is some ambient pressure P1 (for pressure below), and above the wing it's P2. The the difference in pressure (P1 - P2) times the wing area will equal the weight of the aircraft.
 
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But P x A= force isn't it? So you say (Pbelow-Pabove)xA=mass? Or mg? And I haven't got any other info about P...

I have substituted (Pbelow-Pabove) for mg/A and my result seems to be correct now. But I am not sure why I can say that the difference of P is this...
 
Last edited:
Maybe show your work explicitly but the difference in air pressure is what generates lift.
 

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