I'm currently attempting to assign handling qualities to the A-4D, and I would like to know how to find the term:

$ n / \alpha = \overline{q} \times C_{L\alpha} / (W / S) $

where $C_{L\alpha}$ is the lift-curve slope. I think I could solve for the lift-curve slope by using the value $1/T_{\theta2}$ or $1/T_{P2}$, the phugoid frequency, somehow, but I cannot find that equation.

I'm not given a chart of the change in lift-curve slope per Mach number.

  • $\begingroup$ Who or what is A-4D? Is this homework? $\endgroup$
    – bogl
    Oct 25, 2018 at 7:31
  • $\begingroup$ A-4D is the airplane assigned-- a military fighter pilot that could reach transonic speeds. It's a project I am doing for a class. I can find the lift-curve slope before before M=.6 using a certain equation I got from a NASA document, but the A-4D achieves up to M=.9, so the compressibility of the gas affects the lift-curve slope. A plot of lift-curve slope (lcs) for a plane shows that the lcs is constant until about M=.4, then you get an exponential growth as M approaches 1. I am either trying to find a plot of this for the A-4D or an equation for lcs that works until M=.9. $\endgroup$ Oct 25, 2018 at 15:00
  • $\begingroup$ I would prefer the equation that I asked for above because that equation was developed from empirical relations, so it is usually close to the actual lcs(lift-curve slope), but if you have a graph of Mach number vs lcs, that would work better since those are the actual, tested values. $\endgroup$ Oct 25, 2018 at 15:06

1 Answer 1


The solution that I needed is the following image:

enter image description here

  • 1
    $\begingroup$ It would be helpful for others to explain how your determined the equation $\endgroup$
    – fooot
    Oct 25, 2018 at 17:29
  • $\begingroup$ The equation posted was incorrect; it didn't work well for different values of w_sp. This here is the empirical data for just this one plane. $\endgroup$ Oct 25, 2018 at 17:50

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