Path: utzoo!attcan!uunet!cs.utexas.edu!usc!snorkelwacker!apple!uokmax!jabishop
From: jabishop@uokmax.ecn.uoknor.edu (Jonathan A Bishop)
Newsgroups: sci.space.shuttle
Subject: Re: center engine out
Keywords: Apollo
Message-ID: <1990Sep21.003525.20264@uokmax.ecn.uoknor.edu>
Date: 21 Sep 90 00:35:25 GMT
References: <7285@eos.UUCP> <5556@mace.cc.purdue.edu> <1133@larry.sal.wisc.edu>
Distribution: sci.
Organization: Engineering Computer Network, University of Oklahoma, Norman, OK
Lines: 19

roberts@larry.sal.wisc.edu (Tim Roberts) writes:

>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.

     Seems reasonable, but apparently shutting off the engine wasn't always
enough to prevent pogo, since Apollo 10's ascent was quite rough.
-- 
jabishop@uokmax.ecn.uoknor.edu

"Ground Control to Major Tom: Your circuit's dead; there's something wrong.
Can you hear me, Major Tom?" -- David Bowie