fiddler%concertina@Sun.COM (Steve Hix) (04/21/89)
In article <1039@calvin.EE.CORNELL.EDU>, johns@calvin.EE.CORNELL.EDU (John Sahr) writes: > In article <883@sactoh0.UUCP> bncox@sactoh0.UUCP (Brian N. Cox) writes: > >This is little bit old, but during the last shuttle launch I heard > >one of the radio messages say "...engines at 104%..." This seems > >like a contradiction to me. If someone has succeeded in making the > >perpetual motion machine let me know, an engine running at 104% > >sounds great though. Please excuse my cynicism, but I truly don't > >understand. Someone please explain?! OK. 104% of the original design spec thrust.
howeird@hpwrce.HP.COM (Howard Stateman) (04/22/89)
>This is little bit old, but during the last shuttle launch I heard >one of the radio messages say "...engines at 104%..." This seems >like a contradiction to me. If someone has succeeded in making the >perpetual motion machine let me know, an engine running at 104% >sounds great though. Please excuse my cynicism, but I truly don't >understand. Someone please explain?! > >Brian Cox >pyramid!amdahl!pacbell!sactoh0!bncox >---------- Well, the idea is that there is an optimum number of RPMs at which the engine can run. If you rev it any faster, you're at over 100% of the number of optimal RPMs. The FCC has a similar measurement for modulation of a radio signal. When you are at 100% modulation, the signal is as strong as it can get without being distorted. At 101%, your signal is stronger than at 100%, but it is distorted. At 99% it is still undistorted, but not at full strength. So to carry this over to your engine running at 104%, it is running harder than at 100%, but it is past its point of peak efficientcy, and may do something non-user-friendly, like blow everyone all to Hell. -------------------------------------------------------------------- |Howard Stateman, Hewlett-Packard Response Center, Mountain View, CA | |howeird@hpwrce.HP.COM or hplabs!hpwrce!howeird | |Disclaimer: I couldn't possibly speak for HP. I know too much. | |--------------------------------------------------------------------| |Sysop of the Anatomically Correct BBS (415) 364-3739 | --------------------------------------------------------------------
donegan@stanton.UUCP (Steve Donegan) (04/22/89)
In article <1039@calvin.EE.CORNELL.EDU>, johns@calvin.EE.CORNELL.EDU (John Sahr) writes: > In article <883@sactoh0.UUCP> bncox@sactoh0.UUCP (Brian N. Cox) writes: > >This is little bit old, but during the last shuttle launch I heard > >one of the radio messages say "...engines at 104%..." This seems > >like a contradiction to me. If someone has succeeded in making the > >perpetual motion machine let me know, an engine running at 104% > >sounds great though. Please excuse my cynicism, but I truly don't > >understand. Someone please explain?! The explanation is really rather simple. The 104% is relative to the ORIGINAL engine specifications. The newer engines are capable (so I've heard, second-hand) of roughly 111% maximum thrust relative to the original system. I'm really surprised that such 'new' hardware hasn't met with the same man-rating hassle that the mere suggestion of more modern computer systems on-board seem to meet. After all... isn't a modification of an explosive burning system just as dangerous as the modification of antique core-memory control computer systems? Large smiley intended... -- Steven P. Donegan These opinions are given on MY time, not Area Telecommunications Engineer Western Digital's Western Digital Corp. stanton!donegan || donegan@stanton.UUCP || donegan%stanton@UUCP
ajk@mentor.cc.purdue.edu (Jeff Boerio) (04/23/89)
In article <9130002@hpwrce.HP.COM>, howeird@hpwrce.HP.COM (Howard Stateman) writes: > So to carry this over to your engine running at 104%, it is running > harder than at 100%, but it is past its point of peak efficientcy, and > may do something non-user-friendly, like blow everyone all to Hell. Something tells me that this is incorrect. Why, in NASA's infinite wisdom would they knowingly send up all these space shuttles whose engines run inefficiently?? Why would they use an engine that would be prone to blow up? Sure, things may have gotten out of hand before the Challenger accident, but that's not quite what I meant. Getting something into space is a delicate maneuver and needs all the precision there is. Using something that is inefficient and succeptable to blow up seems quite unreasonable. My personal opinion, and something that I certainly don't know as fact, would be that the engines used were originally expected to operate at a level X, or 100%. But, the production engines actually operate at X+4%, or 104%. That's what seems a little better to me, but again, I could be absolutely wrong. - Jeff Boerio --- Jeff Boerio -- Tg Programming FidoNet: 1:201/100 Purdue University Computer Science Dept. E-Mail: mace.cc.purdue.edu!ajk
dave@viper.Lynx.MN.Org (David Messer) (04/24/89)
In article <1039@calvin.EE.CORNELL.EDU> johns@calvin.ee.cornell.edu.UUCP (PUT YOUR NAME HERE) writes: >In article <883@sactoh0.UUCP> bncox@sactoh0.UUCP (Brian N. Cox) writes: >>This is little bit old, but during the last shuttle launch I heard >>one of the radio messages say "...engines at 104%..." This seems >>like a contradiction to me. If someone has succeeded in making the >>perpetual motion machine let me know, an engine running at 104% >>sounds great though. Please excuse my cynicism, but I truly don't >>understand. Someone please explain?! > >Well, this is clearly explained in the Rob Reiner film "This is Spinal Tap." >In the movie one of the band members demonstrates that the amplifier can >be turned up to "11", one past "10". So it's just a little bit louder, >just right for those stressful times when you can't hear your own monitor. That's it exactly. The Russians only have engines that go up to 100% -- ours are better because they go to 104% I hear that the next design might go up to 110% or even 115%. -- Paranoia is just good thinking if | David Messer dave@Lynx.MN.Org -or- everybody IS out to get you. | Lynx Data Systems ...!bungia!viper!dave
petej@phred.UUCP (Pete Jarvis) (04/24/89)
In article <2516@mentor.cc.purdue.edu> ajk@mentor.cc.purdue.edu (Jeff Boerio) writes: > >My personal opinion, and something that I certainly don't know as fact, would >be that the engines used were originally expected to operate at a level X, >or 100%. But, the production engines actually operate at X+4%, or 104%. > The SSME's have a nominal thrust for their use on the Shuttle at 100%. The design limit is 109% of nominal thrust. The use limit is 104% of nominal thrust leaving a 5% safety factor. In order for there to be good guarantee of the engines working at the 100% point, they had to be designed to guarantee reliable operation at a higher thrust, in this case 109%. However, they don't use them beyond 104%. Peter Jarvis.............
nunelson@ndsuvax.UUCP (James Nelson) (04/24/89)
In article <2516@mentor.cc.purdue.edu> ajk@mentor.cc.purdue.edu (Jeff Boerio) writes: >In article <9130002@hpwrce.HP.COM>, howeird@hpwrce.HP.COM (Howard Stateman) writes: >> So to carry this over to your engine running at 104%, it is running >> harder than at 100%, but it is past its point of peak efficientcy, and >> may do something non-user-friendly, like blow everyone all to Hell. > >Something tells me that this is incorrect. Why, in NASA's infinite wisdom Some official type said (a few launches back, can't remember which one) after the shuttle commander said "throttling back to 100%" that the engine power is in relation to the original engines in Columbia. It was because that the current shuttle's engines are more powerful than the engines originally in Columbia. Upgrades, and all that. Jim Note: The opinions expressed here are entirely my own. Why should I copy someone else? #! rnews
raveling@venera.isi.edu (Paul Raveling) (04/24/89)
In article <9130002@hpwrce.HP.COM> howeird@hpwrce.HP.COM (Howard Stateman) writes: >>This is little bit old, but during the last shuttle launch I heard >>one of the radio messages say "...engines at 104%..." If my memory's not too foggy, the main engines were originally certified for a given power level. After enough testing they cleared them first to 104% of that level, then to 109% for limited burn periods. > >So to carry this over to your engine running at 104%, it is running >harder than at 100%, but it is past its point of peak efficientcy, and >may do something non-user-friendly, like blow everyone all to Hell. Last night I found a note in Feynman's Appendix F to the Challenger Commision's report, where he spoke briefly about blade cracking in the high pressure fuel turbopump. Info at that time suggested that running at 109% rather than 104% would reduce the blades' safe lifetime by a factor of 2. ---------------- Paul Raveling Raveling@isi.edu
howeird@hpwrce.HP.COM (Howard Stateman) (04/25/89)
>My personal opinion, and something that I certainly don't know as fact, would >be that the engines used were originally expected to operate at a level X, >or 100%. But, the production engines actually operate at X+4%, or 104%. > >That's what seems a little better to me, but again, I could be absolutely >wrong. > >- Jeff Boerio You're absolutely wrong, Jeff. :-) Seriously, when I read your response I thought you were joking, till I saw this last line. Every engine I have ever seen has had the ability to be pushed beyond its limits. It's why they have a red line on the tachometer in your average sports car (Camaro, Firebird, etc). I find it hard to believe that the folks at NASA have build an engine which only operates at peak efficiency. mostly because there is no such thing. -------------------------------------------------------------------- |Howard Stateman, Hewlett-Packard Response Center, Mountain View, CA | |howeird@hpwrce.HP.COM or hplabs!hpwrce!howeird | |Disclaimer: I couldn't possibly speak for HP. I know too much. | |--------------------------------------------------------------------| |Sysop of the Anatomically Correct BBS (415) 364-3739 | --------------------------------------------------------------------
willisa@cs.glasgow.ac.uk (Mark Willis) (04/26/89)
In article <2591@ndsuvax.UUCP> nunelson@ndsuvax.UUCP (James Nelson) writes: > >Some official type said (a few launches back, can't remember which one) >after the shuttle commander said "throttling back to 100%" that the engine >power is in relation to the original engines in Columbia. It was because >that the current shuttle's engines are more powerful than the engines >originally in Columbia. Upgrades, and all that. > No, because engines do not belong to a particular orbiter, but instead are just allocated according to whichever happens to have finished reprocessing. I always thought that the thrust level was measured at sea-level, so that as the orbiter ascended the engines were capable of higher thrust. Or does it work the other way round - thrust decreases with altitude? I am aware that the engines dont require an atmosphere to "push against", but it must have some effect. Mark ----
holroyd@dinl.uucp (kevin w. holroyd) (04/27/89)
>In article <9130002@hpwrce.HP.COM>, howeird@hpwrce.HP.COM (Howard Stateman) writes: > So to carry this over to your engine running at 104%, it is running > harder than at 100%, but it is past its point of peak efficientcy, and > may do something non-user-friendly, like blow everyone all to Hell. > I suspect that rocket engines work similar to some airplane reciprocating engines. (Specifically turbo-charged engines.) On certain models of planes there is a maximum continuous power setting of usually ~30" of manifold pressure. During certain power critical events (like takeoff) it is permissible to power up past this point for periods under 5 minutes. BTW the B737 that crashed on the 14th street bridge in Washington D.C. was not at full power. In their attempt to get off the ground (and stay off the ground) the pilots only used maximum take-off power, not FULL power. There was some speculation that if they had gone to full power it might have made a difference. In their attempt to save wear and tear on the engines, they totally destroyed the engines (and the rest of the airplane.) -- ******************************************************************************* Kevin W. Holroyd * CFI Aspen Flying Club * Got tired of last .signature file Denver CO. * *******************************************************************************
kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) (04/28/89)
In article <2859@crete.cs.glasgow.ac.uk>, willisa@cs.glasgow.ac.uk (Mark Willis) writes: > I always thought that the thrust level was measured at sea-level, so that > as the orbiter ascended the engines were capable of higher thrust. Or does > it work the other way round - thrust decreases with altitude? I am aware > that the engines dont require an atmosphere to "push against", but it > must have some effect. > At a given altitude, the thrust of a rocket engine is maximized when the pressure of the exhaust is exactly equal to the ambient air pressure. This is achieved by tailoring the configuration of the nozzle to the design altitude. If the altitude is lower than the design, or optimum, altitude, the ambient air pressure is higher than the exhaust, resulting in a net reduction in thrust. Shortening the nozzle will balance this condition. At altitudes greater than the design altitude, the exhaust pressure is greater than the ambient air pressure, and thrust is correspondingly less than its theoretical maximum. Lengthening the nozzle corrects this. Putting it briefly, you want a short nozzle at low altitudes, where the air pressure is higher, and a long nozzle at high altitudes. The design altitude for a rocket engine is usually a compromise between the two. (There also are double-geometry engines, which use a nozzle extension. This extension, at launch, is retracted. At a given altitude, the extension is put into place, lengthening the nozzle and increasing the performance of the rocket.) [Oates, 'Aerothermodynamics of Rocket and Gas Engines', or something like that--the reference isn't right in front of me. Two chapters in the book deal with rockets--the rest is boring jet engine stuff!] ********************************************************************** Norman Kluksdahl Arizona State University ..ncar!noao!asuvax!enuxha!kluksdah standard disclaimer implied Useful criticism always appreciated. Senseless flames always discarded.
larson@unix.SRI.COM (Alan Larson) (04/30/89)
Jeff Boerio wrote: >My personal opinion, and something that I certainly don't know as fact, would >be that the engines used were originally expected to operate at a level X, >or 100%. But, the production engines actually operate at X+4%, or 104%. > >That's what seems a little better to me, but again, I could be absolutely >wrong. In article <9130003@hpwrce.HP.COM> howeird@hpwrce.HP.COM (Howard Stateman) write s: >You're absolutely wrong, Jeff. :-) > >Seriously, when I read your response I thought you were joking, till I >saw this last line. > >Every engine I have ever seen has had the ability to be pushed beyond its >limits. It's why they have a red line on the tachometer in your average >sports car (Camaro, Firebird, etc). I find it hard to believe that the >folks at NASA have build an engine which only operates at peak efficiency. >mostly because there is no such thing. Howard, Jeff is right. By the way, peak efficiency is not normally the 100% power point on an engine. Peak power and peak efficiency are different. Alan