Max q

For other uses, see Max q (disambiguation).

A condensation cloud forms around an interstage as the Apollo 11 Saturn V encounters max Q, at about 1 minute 20 seconds into the flight (altitude 12.5 km, 4 km downrange, velocity 440 m/s).

In aerospace engineering, max Q is the point of maximum dynamic pressure, the point at which aerodynamic stress on a spacecraft in atmospheric flight is maximized.

Considering the definition of dynamic pressure: $q=\rho v^{2}/2$, we have that such quantity:

• is zero at lift-off, when the vehicle's speed $v=0$
• is zero outside the atmosphere, where the air density $\rho =0$
• is always positive (or zero, as above) given the quantities involved

Therefore, there will necessarily be a point where the dynamic pressure is maximum: that point is precisely max Q.

In other words, below the max Q point, the effect of the spacecraft acceleration overcomes the decrease in density. Above the max Q point, the opposite is true.

During a normal Space Shuttle launch, for example, max Q is at an altitude of around 11 km (35,000 ft). During a typical Apollo mission, max Q occurred approximately between 13 km and 14 km of altitude (43,000–46,000 ft).

See also

• Dynamic pressure
• Pressure
• Prandtl-Glauert singularity