# Physics Help

#### anksta

Soldato
Sorry Dons for posting another homework thread but I have been at this question for around 7 or 8 hours now and I am no nearer to gettin started than when I started.

The question is:

An Aeroplane weighing 250000N has a wing loading of 3125Nm^-2 and its Drag equation is given by

CD = 0.016 + 0.04CL^2

Calculate the minium thrust required for straight and level flight.

That is just the first part of a very long question, I think I can do the rest of it if I can get this first part done, so far all I have is the area of the wing is 80m^2.

Any help would be great. Not looking for a specific answer, just someone to suggest a forumla or something I might have missed. Used everything I can find in my books and on the internet, but obviously, I've missed something otherwise I would have done it.

Thanks

An Aeroplane weighing 250000N has a wing loading of 3125Nm^-2 and its Drag equation is given by

CD = 0.016 + 0.04CL^2

Calculate the minium thrust required to keep the aeroplane still on the treadmill.

Edited for hell of it.

thanks mate.

Does no one know?

anksta said:
Sorry Dons for posting another homework thread but I have been at this question for around 7 or 8 hours now and I am no nearer to gettin started than when I started.

The question is:

That is just the first part of a very long question, I think I can do the rest of it if I can get this first part done, so far all I have is the area of the wing is 80m^2.

Any help would be great. Not looking for a specific answer, just someone to suggest a forumla or something I might have missed. Used everything I can find in my books and on the internet, but obviously, I've missed something otherwise I would have done it.

Thanks

Well, i would imagine that coefficient of lift relates forward velocity to upward force generated. In level flight this will equal the planes weight, so you can work out how fast the plane needs to go.

Once you know how fast the plane is going you can calculate the power required, since power = velocity x drag.....

Visage said:
Well, i would imagine that coefficient of lift relates forward velocity to upward force generated. In level flight this will equal the planes weight, so you can work out how fast the plane needs to go.

Once you know how fast the plane is going you can calculate the power required, since power = velocity x drag.....
Erm, not sure why power is being discussed.
Thrust is a force, and the force must be equal to the drag. So work out the velocity for level flight by lift generated = weight of craft, then see how much drag is induced given said velocity, and the thrust required is equal to that.

Pickers said:
Erm, not sure why power is being discussed.
Thrust is a force, and the force must be equal to the drag. So work out the velocity for level flight by lift generated = weight of craft, then see how much drag is induced given said velocity, and the thrust required is equal to that.

how

anksta said:
Lift force = 250000N = CL * V^2 /2 * area * density of medium

Hmm though I'm sure you need more information as you have two unknowns - CL and V.

DO you have a value for CL?

no, thats the point

anksta said:
no, thats the point
Cant think at the moment - not sure what course/module/setting this is for so cant gauge how much work is expected of you. It sounds like it should be a simple substitue, rearrange substitute job. Google lift/drag/thrust equations and see if it can be solved using simultaneous equations.
I should really get on with my own revision now

ok fair enough, thanks for tryin, its degree level engineering by the way.

Anyone else have any ideas, would be appreciated.

I think for this one you need to plot a cD/CL curve such that you get minimum drag value then use that to determine a CL value to determine V.

Lift = 1/2(roe)V^2(Area)(CL)

Then Drag is same as above just swap CL for Cd. Min thrust = drag at that TAS.

Cant really remember without looking at my notes from 2 years ago