What was the actual Q-alpha limit for Saturn/Apollo launches, and what was the typical max Q-alpha?

Question

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.

Russell Borogove · Answer 1 · 2019-11-15T05:32:52.143

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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):

edited Nov 15 '19 at 05:32

answered Nov 15 '19 at 05:23

Russell Borogove

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I'm kinda stunned that it's in metric units! – Organic Marble Nov 15 '19 at 12:17

Organic Marble · Answer 2 · 2022-03-17T21:01:24.497

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Edit: I stumbled upon the limit.

The maximum angle-of-attack dynamic pressure sensed by a redundant Q-ball mounted atop the escape tower was 0.28 N/cm2 (0.4 psid) between 89 and 91 seconds. This pressure was only 12.5 percent of the EDS abort limit of 2.2 N/cm2 (3.2 psid).

Source: Saturn V Launch Vehicle Flight Evaluation AS-506 page 15-1

edited Mar 17 '22 at 21:01

answered Nov 17 '19 at 22:03

Organic Marble

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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 – Russell Borogove Nov 18 '19 at 01:36
@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. – Organic Marble Nov 18 '19 at 02:16
That document you linked in your answer has the mean winds in it. Try adding them into your sim and see what happens. Figure 3-81 and subs. – Organic Marble Nov 18 '19 at 02:23
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"just add wind to your sim", he said breezily – Russell Borogove Nov 18 '19 at 03:10
I mean, I'm sure you're right, it's just a pretty major factor that I don't have a good handle on how to implement. – Russell Borogove Nov 18 '19 at 03:12
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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. – Organic Marble Nov 18 '19 at 03:28
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Huh, weird. If I add wind at all I'm doing it in all directions, heh. – Russell Borogove Nov 18 '19 at 04:53
@RussellBorogove I came across the actual answer. – Organic Marble Mar 17 '22 at 21:01
Thats a pressure (Q) figure, not a pressure•angle, isn't it? – Russell Borogove Mar 20 '22 at 03:29
I think they screwed up on the metric units. First sentence of the quote says 'angle of attack dynamic pressure' and the English units have a 'd' in them. – Organic Marble Mar 20 '22 at 12:36

What was the actual Q-alpha limit for Saturn/Apollo launches, and what was the typical max Q-alpha?

2 Answers2