Organic Marble's answer to a previous question about Apollo abort limits clarified that the figure of concern was the product of dynamic pressure (Q) and angle of attack (alpha), with the 100% level apparently being the expected structural-breakup limit of the launcher.

What is the actual limit value for Qɑ for the Saturn V/Apollo stack?

What was the maximum Qɑ reached in nominal launches?

I'm looking for a value in psi•degrees or kPa•radians or some dimensionally equivalent pressure-times-angle units, not a normalized percentage-of-abort-limit value. Answers for other launchers are of interest as well.

I'm curious because the guidance equations in my launch simulator do produce some significant angle-of-attack, and I want to know if the trajectories I'm flying would be likely to wreck a Saturn V.


I have not yet found the abort limit figure.

According to Saturn V AS-507 "G" Mission Launch Vehicle Operational Flight Trajectory - September Launch Month (a trajectory planning document for Apollo 12), the peak Qɑ for a nominal flight would be between 18 and 22 kNº/m^2 (= kPaº):

Graph of Q-alpha product versus mission time for pre-launch simulation of Apollo 12. Three tracks are shown corresponding to three different launch azimuths (presumably for three different launch dates). The tracks peak sharply around T = 72 seconds at approximately 18.5, 20.0, and 21.5 thousand newton degrees per meter squared.

  • 4
    $\begingroup$ I'm kinda stunned that it's in metric units! $\endgroup$ – Organic Marble Nov 15 '19 at 12:17

Partial answer to help bound the values:

The SA-507 Flight Manual page 3-9 says the nominal meter indications shouldn't exceed 25% to 50% of the limit. With the max nominal numbers in the other answer of 20 kNº/m^2 that puts the limit somewhere between 40 - 80 kNº/m^2.

  • 1
    $\begingroup$ Good find! That helps me a lot. Unfortunately my max payload Saturn INT-21 sim run is hitting 44 kPaº, which is neither definitely over-limit nor definitely under-limit. XD $\endgroup$ – Russell Borogove Nov 18 '19 at 1:36
  • $\begingroup$ @RussellBorogove You don't simulate any winds, do you? If not, then your alphas / betas are probably too big by a {handwaving} amount. Cause a good wind would push you over the limit. $\endgroup$ – Organic Marble Nov 18 '19 at 2:16
  • 3
    $\begingroup$ "just add wind to your sim", he said breezily $\endgroup$ – Russell Borogove Nov 18 '19 at 3:10
  • 1
    $\begingroup$ You could have a lookup table of the wind speed vs altitude - it looks like they only applied it to head/tail, no side wind - then modify alpha by the wind velocity component. The wind is basically just going to change alpha a little and therefore change q*alpha. $\endgroup$ – Organic Marble Nov 18 '19 at 3:28
  • 1
    $\begingroup$ Huh, weird. If I add wind at all I'm doing it in all directions, heh. $\endgroup$ – Russell Borogove Nov 18 '19 at 4:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.