In article , lid
says...

On 04-Sep-20 3:12 pm, Sylvia Else wrote:
How does this actually help?

The aerodynamic forces on the craft are a function of its speed and air
density. There's not much one can do about the speed, given that the
craft is accelerating.

If the craft accelerates more slowly overall, for each speed it will be
traversing less dense air than it would do otherwise. But in that case,
is there a benefit from high initial acceleration and then reducing
acceleration on the approach to max-q?

Is it really about reducing vibration loads during max-q?

Sylvia.

The thing is, it's not as if the rocket thrust and aerodynamic forces
are adding together to squeeze the vehicle from both ends.

Actually it is. If I clamp a board in a vice, at the center of the wood
the forces from each side of the vice do cancel out to precisely zero
(i.e. it's not accelerating due to the forces). But, the wood is under
stress due to the compression caused by the vice. Tighten the vice
enough and the wood will be crushed (permanently deformed).

That's exactly what's happening during max-Q. Thrust and drag are
acting opposite each other and are placing the vehicle under more stress
than it would be if it were operating under the same thrust in vacuum.

I'm not suggesting that the throttle down is not required, but the
rationale for it doesn't appear as straight forward as it might seem at
first sight.

This bit is true. Throttling down early decreases acceleration so that
max-Q happens at a higher altitude, where density is lower and therefore
aerodynamic forces are lower.

As was posted earlier in this thread, Apollo/Saturn V experienced max-Q
at a much higher altitude than the space shuttle due to its slower
acceleration.

Jeff
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