# 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. 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.

• Got it - thanks! So this leads to a more differentiated question
– uhoh
Jul 10 '16 at 6:45
• @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
• Both q and the attach loads betwen the elements were predicted and checked for excedances when the STS trajectory was designed on launch day. As was the product of q x alpha and q x beta. Jul 10 '16 at 11:38
• @OrganicMarble I originally thought "Max Q" meant exactly maximum aerodynamic pressure. Since that maximum may occur at different times on the three very differently shaped objects due to aerodynamic details, I thought I had a "gotcha" moment. But it doesn't, so I don't. Instead, I'd like to know more about all of the major forces in this aerodynamically complicated superstructure. Thus the question Shear forces between Shuttle, tank, and boosters - what pushes what? However, now I'm wondering what alpha and beta and q mean also!
– uhoh
Jul 10 '16 at 11:53
• @Steve the value of q was just the dynamic pressure at any instant. Max q was the largest value. You seem to be asking "what is the q limit?" which is a different question. Although I agree that this "In this case, which was more critical - pressures on the objects and their internal structure, or drag-induced sheer forces between objects due to imballances of sums of drags and thrusts?" and the question in the title are really two different questions. The accepted answer, answers the question in the title, and not the question in the body. Jul 10 '16 at 17:23