Understanding Lift Force and the Bernoulli Equation in Small Aircraft

[Donna14]

Homework Statement

See attachment

Homework Equations

Maybe lift force = C_lρAv²

A=area
C_l= 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...

 

[paisiello2]

V=air speed but don't know which one it represents... Under or below wing or average?
...

I think the diagram shows that explicitly.

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

Yes, can you try and apply it here?

 

[Donna14]

But I am stuck on how to continue... Can you please help me a bit?

 

[paisiello2]

Why don't you start by stating Bernoulli's equation and maybe try and substitute some values into it?

 

[Donna14]

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...

 

[SammyS]

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?

 

[rcgldr]

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.

 

[Donna14]

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...

 

[paisiello2]

Maybe show your work explicitly but the difference in air pressure is what generates lift.