# How is max Q for the shuttle actually defined?

In this article about max Q https://en.m.wikipedia.org/wiki/Max_Q the shuttle launch is discussed. Since there are four distinct large objects - two boosters, one shuttle and one giant tank - there could be several ways to define an effective max-Q.

There are three different aerodynamic pressures on leading surfaces, and two distinct average shear forces on struts connecting the components. Since both the boosters and the shuttle produce thrust, and since each had a different mechanism for reducing thrust around the one-minute mark, this must have been quite an interesting problem compared to a single body cylindrical rocket.

In this case, which was more critical - pressures on the objects and their internal structure, or drag-induced shear forces between objects due to imbalances of sums of drags and thrusts?

• it's shear forces, not sheer. – Hobbes Jul 10 '16 at 8:17
• @Hobbes I had one right, fixed the other one. Thanks! – uhoh Jul 10 '16 at 8:20

Max Q is simply the maximum of the dynamic pressure of the external flow, ${1\over 2}\rho v^2$. It has nothing to do with the vehicle, except for the vehicle's speed relative to the undisturbed fluid.
• @Steve I think Mark may be saying that the term "Max Q" actually refers to the point where the term ${1\over 2}\rho v^2$ is maximum, period. Maximum aerodynamic pressure will probably occur nearby, but it depends on many real-world effects. But the term "Max Q" does not actually mean the same thing as "maximum aerodynamic pressure". – uhoh Jul 10 '16 at 11:24