In article ,
says...

On 2020-09-08 08:17, Jeff Findley wrote:

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.

At MaxQ for normal shaped rocket, what percentage of forces on structure
comes from beloow (acceleration) vs above (drag on nose pushing down)?

Are we talking 95% acceleration, 5% drag, or 50/50 ? or is drag even
higher than acceleration?

Don't know exactly as this is one of those "the devil is in the
details" sort of things and it's the end of my work day and I really
don't want to "math" anymore.

If a rocket is built to handle 5G acceleration, but only doing 3G at the
MaxQ altitude, then the structure is perfectly able to widthstand a bit
more pressure from above so continuing with normal acceleration would
be a no brainer.

Again, the devil is in the details. The stress is distributed entirely
differently during max-Q (due to aerodynamic forces) than they are
during other portions of the flight. For example, after max-Q the
rocket "throttles up" and continues to accelerate. In fact, since it's
burning fuel, its thrust to weight ratio keeps going up!

So, perhaps the stages themselves can take more acceleration during max-
Q, but the payload shroud can't handle the aerodynamic forces.

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.

Throttling down at MaxQ doesn't raise maxQ altitude since you've already
reached it. If the goal is to raise MaxQ altitude, then the flight
profile from launch to MaxQ would have slower acceleration. (which is
likely what happens with modern rockets without SRBs).

Some launch vehicles throttle down sooner than others before they reach
max-Q. It all depends on the details.

Jeff
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