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From: roberts@larry.sal.wisc.edu (Tim Roberts)
Newsgroups: sci.space.shuttle
Subject: Re: center engine out
Keywords: Apollo
Message-ID: <1133@larry.sal.wisc.edu>
Date: 20 Sep 90 17:36:00 GMT
References: <7285@eos.UUCP> <5556@mace.cc.purdue.edu>
Reply-To: roberts@larry.sal.wisc.edu.UUCP (Tim Roberts)
Distribution: sci.
Organization: Space Astronomy Lab, Madison, WI
Lines: 20

>In article <7285@eos.UUCP>, brody@eos.UUCP (Adam R. Brody) writes:
>> middle engine of the S-1C first stage goes out while the surrounding four
>> burn until completion.  The same thing occurs with the SII second stage at
>> 3:30.  Why is this?
>
>In article <5556@mace.cc.purdue.edu> dil@mace.cc.purdue.edu (Perry G Ramsey)
>writes:
>The inboard engines of the Saturn V shut down to reduce acceleration.

Sorry, but that is half the story.  The first Saturn flights had trouble
with oscillations of a compression wave, i.e. the rocket got longer and
shorter due to harmonic coupling of the acceleration vs. gravity.  To
reduce the effect (called the "Pogo effect") they either had to stiffen
the rocket longitudinally or break the harmonics.  The solution was to
maintain wave interference by shutting off the center engine.  Apollo
7 rode a Saturn 1b and they had the shorts scared off them by this Pogo
stick ride to orbit.  I believe the solution was found in time for Apollo
8, which was the first manned Saturn V.

						-Tim