Max Q

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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 = ρv² / 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 ρ = 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).^[1] During a typical Apollo mission, max Q occurred approximately between 13 km and 14 km of altitude (43,000–46,000 ft).^[2][3]

See also

• Dynamic pressure
• Pressure
• Prandtl-Glauert singularity

References