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Old 06-11-2008, 11:00 PM   #43
DGthe3
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Originally Posted by wild_weasel View Post
Your math is good. Great explanation, but its not the time to circle that we are calling into question. It's the 6089.656 mile/hour (Mach 8) number. The SR-71 was fast, but not that fast. Let's say it can get pretty close to Mach 4...then its like 8 hours to circle the earth if we just double the time for half the speed according to the math where you already took into account altitude.
That assumes that the SR-71 doesn't need to refuel. It needs to refuel every 3000 miles or so. So it would need to refuel 8 times to go around the world. I don't know how quick that can happen, but it would add a couple hours to the time for sure.

Also, when I found the range from wiki I read this little tidbit: "The SR-71's Pratt & Whitney J58 engines never exceeded test bench values above Mach 3.6 in unclassified tests." They didn't exceed 3.6 in unclassified tests. Wonder what they got them up to in the classified ones . . .

Also, the stealthyness was compromised by its exhaust which had its own radar signature. Can't win 'em all.
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My sister's dentist's brother's cousin's housekeeper's dog-breeder's nephew sells coffee filters to the company that provides coffee to General Motors......
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Old 06-11-2008, 11:17 PM   #44
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Originally Posted by DGthe3 View Post
That assumes that the SR-71 doesn't need to refuel. It needs to refuel every 3000 miles or so. So it would need to refuel 8 times to go around the world. I don't know how quick that can happen, but it would add a couple hours to the time for sure.

Also, when I found the range from wiki I read this little tidbit: "The SR-71's Pratt & Whitney J58 engines never exceeded test bench values above Mach 3.6 in unclassified tests." They didn't exceed 3.6 in unclassified tests. Wonder what they got them up to in the classified ones . . .

Also, the stealthyness was compromised by its exhaust which had its own radar signature. Can't win 'em all.
All excellent points DG. I forgot about the range issue. Gotta burn a ton of fuel to haul that much ass. About 8000 gal/hr at cruise in fact.

Those test bench values...I'm not sure how to take those. I'm guessing they took the effective exhaust velocity value and thats the 3.6M they are quoting. In an ideal ramjet engine, in laymans terms, the speed the air goes in is the same speed that its coming out, so that IS how fast you are going. All you are doing is dumping fuel into the ramjet to ignite it and keep yourself going. However the J58 is a ramjet/turbojet hybrid (I think I said turbofan before which is WAY off, my bad, stupid mistake I know) so actual speed will vary a lot from an ideal ramjet and with also vary some from bench values at ideal conditions.

When they tested those engines, they had to leave the hangar doors open to let more air in. It was so powerful that it started slowly sucking things like tool chests full of tools towards the intake.

Hahaha, I like the exhaust comment. Yeah, those contrails were kind of unavoidable. 50+ inch diameter columns of boiling air coming out of those engines are pretty hard to hide.
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Old 06-11-2008, 11:38 PM   #45
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so where's this magnetic propulsion system at that we were suppose to have by now? how about the colony on the moon. . .or lost in space. . .hmmmm weren't they all suppose to happen by now? what happened? lol.
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We do not want to use the Z28 moniker on a car that does not deserve this hallowed name.
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Old 06-11-2008, 11:41 PM   #46
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I'm with boxmonkey...where's my flying car?
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Old 06-12-2008, 12:40 AM   #47
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Yea I was just using that as a reference for speed (later argument was going to be a comparison to actual flight times).

ERAU Prescott campus was the one. This was WAY back in '99 and funnily enough it was aeronautical engineering I was going to major in. Now almost 10 years later I have a decent career (27 yo with 9 years in IT engineering) and I'm doing night school, grad this fall with an AAS in Microsoft Certified Applications Development, then on to BS in Software Technology Applications from ASU.






WOW talk about a full day! I think I just found my new role model....Heck I feel like there arent enough hours in a day now!!!
sorry bout the hijack but im impressed...my meds make me feel like the day is only 8 hours long as is!
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Old 06-12-2008, 09:32 AM   #48
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so where's this magnetic propulsion system at that we were suppose to have by now?
at groom lake . . .
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My sister's dentist's brother's cousin's housekeeper's dog-breeder's nephew sells coffee filters to the company that provides coffee to General Motors......
........and HE WOULD KNOW!!!!
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