From: jfindley@cinci.nospam.rr.com   
      
   In article ,   
   jfmezei.spamnot@vaxination.ca 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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