I need a good CL equation
I need a good CL equation
(OP)
Can some one tell me where to find a good CL equation???
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I need a good CL equation
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I need a good CL equationI need a good CL equation(OP)
Can some one tell me where to find a good CL equation???
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RE: I need a good CL equation
Generally, L=(1/2)* air density* (Speed)^2*wing area*CL
work out the CL = 2*L / air density*Speed^2*wing area
RE: I need a good CL equation
RE: I need a good CL equation
is just the slope of the Cl vs alpha plot..classical
2d linear potential flow theory give this as 2*pi for a 2d airfoil..for a 3d wing you have to modify it somewhat
to take into account Aspect ratio and sweep. R.T Jones
gave a formula which went like 2*pi/(p*AR+2) where p is the ratio of the wing semi-perimeter to wing span
and AR is the aspect ratio. This slightly overestimates
the lift curve slope for AR>2 .
RE: I need a good CL equation
it will b better if u specify what all variables u have the values with u. And what d u want to calculate ?? That will help in giving u the xact solution.
Sanab.
RE: I need a good CL equation
-2288
RE: I need a good CL equation
Excessive accuaracy is a sign of poor breeding. -Socrates.
RE: I need a good CL equation
i can not belive i did not see that i under stand now thank you very much knobhead... i would still like to get as much as i can on this subject...
-2288
RE: I need a good CL equation
I have further suggestions to our friend.
If the wing is already built and you know the profiles you used (that's the shape of the ribs of the wing), then with patient you could try to calculate the aerodynamic properties of the wing (Lift Coefficient slope, Roll Speeed Coefficient slope, etc.) using Multhopp's method.
Have you tried it before?
Regards,
Cristian
RE: I need a good CL equation
i have not heard of Multhopp's Method before but i will try to find more about it online or in my books... if you have any tips about where to find more i would appreciate them very much...
-2288
RE: I need a good CL equation
Try to find it in the NACA Technical Report Server.
Let me know if you can't get it.
Regards,
Cristian
RE: I need a good CL equation
-2288
RE: I need a good CL equation
-2288
RE: I need a good CL equation
L = (1/2) * rho * V^2 * S *CL
CL = dCL/dalpha * (alpha - alpha0)
alpha0 == Zero lift line for an aerofoil section (wings with varying sections or with twist will make this different. Look at the numbers and guess. It'll be closer than you think.)
dCl / dalpha == 2*pi *(AR/(AR+2))
accurate to within 5%.
More accuracy requires more sophistcation. Unfortunately, it isn't linear.
daccuracy / dcomplexity > 0
d^2accuracy / dcomplexity^2 > 0 ( allitle bit more accurate means a lot more complex.)
Alternate formula is =
dCl / dalpha == a2d / (1+(a2d/ (pi*AR)))
a2d is lift curve slope for 2d section. (If you let it equal the theoretical 2*pi value then
(AR/(AR+2)) appears.)
Not for swept wings.
Regards,
Timbo
RE: I need a good CL equation
RE: I need a good CL equation
(Ignore "daccuracy / dcomplexity > 0
d^2accuracy / dcomplexity^2 > 0 ( allitle bit more accurate means a lot more complex.)" It was my attempt at humour.)
Take out a sheet of paper and draw a set of axes on it. Label the horizontal axis x and the vertical y. Now draw an arbitary curve. The closer the curve is to being parrallel with the vertical axis the larger the value of dy/dx.
Note that the value of dy/dx can change along the curve.
The best way to think about dy/dx is the amount y (the vertical value) will change by changing x a little bit.
A steep line means there is a large change of y with respect to x. A shallow line means that there a small change of y with respect to x.
I suppose now might be a good time to ask about your background.
Timbo
RE: I need a good CL equation
you wanted to know my background so... i am not a true aeronautical i am going to become one (i hope you can tell that i am not out of college yet) i build things by myself right now and i needed some equations for lift CL and so on... because i want to know them in my head and not depend on a computer (if you recall i said i have several computer programs)... so i found this site and asked you guys, and as you can see i do have a lot of questions but i know a lot and wish to expand what i know...
RE: I need a good CL equation
RE: I need a good CL equation
Timbo
RE: I need a good CL equation
Dan100
RE: I need a good CL equation
Which is NASA's foil sim program. it gives all equations and even allows a simulated wind tunnel test of your wing. Hope it helps.