the B-2 Stealth Bomber

Now this is funny ... or sad?

In 1990, the U.S. AirForce unveiled its newest long range bomber:
The B-2 "Stealth" bomber had cost billions to develop.
It was characterized by its all-wing design:

The aerodynamic analysis included a ritual for finding the volume distribution that maximized the range.
The ritual involved taking a derivative and setting it equal to zero.

In general, to find the maximum of f(V), one sets the derivative equal to 0: f '(V) = 0
... then solve for the value of V. It'll be a "candidate" for the maximizing value.
To guarantee that it IS a maximum, one checks to see if the second derivative is negative: f ''(V) < 0

Conclusion? The volume should be "almost all in the wing".
Hence the B-2.

Alas, the engineers who recommended the all-wing design neglected to test the second derivative ... to see if'n it was a maximum or a minimum.

It turned out (as discovered subsequently), that the all-wing design MINIMIZED the range of the aircraft.
Indeed, the flying wing was the aerodynamically worst possible choice of configuration.

Now, if'n I only had that story at my finger tips when I taught introductory calculus!