MAX Q

For other uses, see Max q (disambiguation).

The max q condition is the point when an aerospace vehicle's atmospheric flight reaches maximum dynamic pressure. This is a significant factor in the design of such vehicles because the aerodynamic structural load on them is proportional to dynamic pressure. This may impose limits on the vehicle's flight envelope.

Dynamic pressure, q, is defined mathematically as

q = 1 2 ρ v 2 , {\displaystyle q={\tfrac {1}{2}}\,\rho \,v^{2},} q = \tfrac12\, \rho\, v^{2},

where ρ is the local air density, and v is the vehicle's velocity; the dynamic pressure can be thought of as the kinetic energy density of the air with respect to the vehicle. For a launch of a rocket from the ground into space, dynamic pressure is

zero at lift-off, when the air density ρ is high but the vehicle's speed v = 0

zero outside the atmosphere, where the speed v is high, but the air density ρ = 0

always non-negative, given the quantities involved

Therefore, (by Rolle's theorem) there will always be a point where the dynamic pressure is maximum.

In other words, before reaching max q, the dynamic pressure change due to increasing velocity is greater than that due to decreasing air density so that the dynamic pressure (opposing kinetic energy) acting on the craft continues to increase. After passing max q, the opposite is true. The dynamic pressure acting against the craft decreases as the air density decreases, ultimately reaching 0 when the air density becomes zero.

https://en.wikipedia.org/wiki/Max_q