Does this type of equation for an airfoil exist? In a common airfoil, such as a plane's wing, diminished pressure over the top of the wing and increased pressure under the wing, generally speaking, will cause the wing to lift. Now, a man standing under a speeding aircraft should feel the wing's bottom pressure as the wing passes over his head. Conversely, if he is above the wing as it passes, he should sense the diminished pressure of the top of the wing. But in both cases, only up to a certain distance. If the distance between the man and the wing is too great, he will no longer feel the effects of the passing wing.  My question: Is there an equation that, when fed all the variables, will give the theoretical distance above and below the wing where the man, or a sensor, will no longer detect the effects of the wing's increased and decreased pressures? Thanks!
 A: I can't answer the question as posed - but I can point you to something related. If you have an (infinite) cylinder perpendicular to a flow, you can calculate the flow around it (see for example this interesting page where these images and equations come from).
The velocity profile would look like this:

and the pressure profile is similar:

They give the following expression for pressure as a function of distance $r$ and angle $\theta$ (polar coordinates relative to the center of the cylinder):
$$p(r,\theta)=\rho ^2[U^2−(u^2+v^2)]=\frac{\rho U^2}{2}\frac{a^2\left[2r^2\cos(2\theta)−a^2\right]}{r^4}$$
The main takeaway is that large distances, the pressure component drops off with the inverse square of the distance - and with a cosine dependence on angle. So even when you are quite far away you can still feel it.
Now when a wing is finite size, you can imagine that these equations will get an additional factor $r$ in the denominator when the distance is large compared to the wing span - from far away the flow around the wing will look more like flow around a sphere.
Obviously because of the actual shape of the wing you should expect some scaling factors to change, but I expect that in the limit of long distances the above is not too far off. As I said - you need to define your limits of "can't detect".
