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#91
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In article ,
Morgans wrote: I had always heard that the fuselage tank was the source of the instability, with it being so far behind the CG, to give it a dangerously aft CG. Today, in peacetime, I don't suppose they would ever dream of putting that much weight that far back, but it was war. Yep, lots of compromises in some of those wartime designs... Some of the photo-recon versions of the Spitfire had a tail tank that compromised stability even more drastically: the aircraft was outright aerodynamically unstable with that tank full or nearly full. (Naturally, you emptied that tank *first*... and didn't have much attention to spare for anything else until it was empty.) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#92
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![]() "Mxsmanic" wrote in message ... One wonders what sort of emergency would justify running the engine a bit faster for just ten minutes, and then replacing the entire aircraft. Getting away from a bunch of someones shooting at me, for one. If I can't get away within ten minutes, it's pretty obvious I'm not going to get away. |
#93
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![]() "Dudley Henriques" wrote in message ... At 40 gals in the tank, anything involving maneuvering flight was a toss up for pitch control. "This is your wingman. You appear to be leaking oil." "Negative, wingman. The CG just shifted and I **** my pants." |
#94
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In article ,
Kyle Boatright wrote: That said, the SSMEs are cranky, marginal engines, and taking *them* up to 120% (as was once intended) is much more iffy than doing the same for robust engines like the H-1 or F-1. What makes the SS engines "cranky and marginal" vs the H-1 and/or F-1? Mostly, they were too much of a leap into the technological unknown at the time: NASA tried to pioneer bold new technology on what was supposed to be a long-lived reusable engine, and unsurprisingly, this didn't work too well. The H-1 and F-1 were much more conservative designs -- notably, although the F-1 was a lot bigger than anything previously built, the project tried hard to *avoid* pioneering in any other way -- and although they did hit surprises and ended up breaking some new ground, they had much more continuity with previous experience. (For a while there was some feeling that the SSME's staged-combustion cycle was just *inherently* troublesome, but that idea sort of collapsed when it became clear that every major Russian rocket engine since about 1960 had been a staged-combustion design, typically including features like oxidizer-rich preburners, which even NASA had deemed impractically difficult...) Three specific snags also aggravated this problem on the SSME: (a) Most of the technology development on staged combustion had been done by Pratt & Whitney, but oddly, the contract for the staged-combustion SSME went to Rocketdyne instead. So the experienced people were shut out, and the guys who were actually doing the work were having to come up to speed on a technology that was new to them. (b) The SSME program, like the shuttle in general, was starved for money and opted to cut corners on subsystem testing in particular. The result was an unusually long and painful development process, with subsystem problems often not surfacing until whole-engine testing. (c) Partly as a result of (a) and (b), it didn't become clear until too late that the main LOX (I think it was) turbopump really needed one more pump stage. Since a major redesign was politically and financially impossible at that point, the result was a pump in which each stage was pushed to the ragged edge of engineering practicality to meet a very ambitious spec. The combination of (b) and (c) was particularly nasty, because all too often, a LOX-pump failure becomes a LOX-pump fire, which destroys the evidence of what went wrong. Having this happen repeatedly to whole test engines was just what an already-stressed development program didn't need. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#95
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![]() "Mxsmanic" wrote in message ... John writes: Ummm . . . a FW-190 (option: replace FW-190 with opponent on your six . . . really close . . . perhaps still there and shooting after after what you have just finished what you used to think was your very best move . . . in my book that rises to the level of an emergency. At that point getting the pilot home was goal one. OK, but if you can only fly at emergency war power for five minutes, and if it only offers a moderate advantage over normal maximum power, it seems that there would be relatively few situations in which it would make a difference. Either you'd be out of luck to begin with and EWP wouldn't get you out of it, or you wouldn't be in danger and so you wouldn't need EWP. If EWP can give you an extra 50 kts, for example, at best you'd have an advantage of five nautical miles when the engine disintegrates. If the bad guys are only 30 knots slower, your advantage shrinks further. And with a blown engine, you'll need to be completely out of danger after five minutes, or all that effort wouldn't help. Yes, but that 5 nm may be enough to get out of their range, or get back to friendly air-cover, etc. The piont of it being emergency power is you can't always predict when or how it'll be used. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#96
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![]() "Morgans" wrote in message ... "Brian Gaff" wrote Yes, and it is also why the shedding foam can only do serious damage within the lower atmosphere, as the drag cannot decelerate the chunks enough to strike with enough force to do harm at that altitude. Sorry, but you got that one wrong. The foam does the damage because of the high speed that it has when it hits the shuttle. If there was no drag, the foam would not hit with any force; it would be going the same speed as the shuttle. When a chunk of foam falls off, it is the drag of the stationary atmosphere slowing the foam so effectively and rapidly, that causes the relative closing speeds of the now nearly stationary foam hitting the speeding shuttle. -- Jim in NC OK, now I'm trying to figure out how to insert a magical, imaginary conveyor belt into this scenario. :-) TP in FL (Go Gators!) |
#97
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![]() "Tim Rogers" wrote in message ... : : "Blueskies" wrote in message : . net... : : "Danny Deger" wrote in message : ... : : : : "Danny Deger" wrote in message : : ... : : : : Why does the shuttle throttle to 3 Gs on ascent? : : : : : : The 3 G throttling is done late in the flight (about 7:30)and has : nothing to : : do with dynamic pressure. It was designed in to allow "regular" people : fly : : the shuttle. : : : : : : Yes, the aerodynamic loads are highest early in the flight so the engines : are throttled then back up. The shuttle rolls : over on its back to fake the occupants into feeling 3 gs when in fact the : vehicle is pushing 4 gs.... : : No. : The 3 Gs is at the backs of the occupants (and along that same axis for the : vehicle.) This is the same if they are heads up or heads down. : If you lie with your back on the floor, you feel the same 1 G if your head : is facing north or south. : : Tim : : Not talking about facing north or south, they're talking about hanging from your feet or standing upright... |
#98
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![]() Glad you liked the report. The Mustang is really very easy to fly. It does require constant attention and doesn't suffer fools gladly however. Like any high performance airplane, it has to be flown by the book and fooling around on the left side of the envelope can get you killed in a hurry. Other than that....a piece of cake. Dudley Henriques "Pat Flannery" wrote in message ... I tried to reply to you personally, but the e-mail address doesn't work. I flew a D, as well as various other prop fighters as a civilian operator. Never flew ours with external tanks. The airplane is stable on takeoff if flown correctly and I wouldn't anticipate any specific issues with the external tanks except the extended run. I believe the only caution on the external tanks was for high speed buffet above 400 mph. We had the fuselage tank removed and only flew the Mustang using the 2 mains at 92 gallons each.(90 usable) If you are interested in a pilot report on what it was like to fly the D, I did one for the Warbirdalley site some years ago at the following ; http://www.warbirdalley.com/articles/p51pr.htm#pirep1 Hope you find the report interesting. Dudley Henriques Thanks for putting me on to that pilot report, that was very interesting to read. The overall feeling I got from it was of an aircraft that takes a lot of effort to get fully attuned to and in sync with, but is capable of doing outstanding things once you get enough hours in on it and understand how it behaves. I particularly liked your description of starting the Merlin up. :-D You mentioned you had flown several types of prop driven fighters, what other ones did you fly? I once talked to a Navy pilot of a Grumman Bearcat who was very taken by that aircraft. About the most fascinating conversation I ever had with a pilot was years ago after the Soviet Union had just fallen who flew a two-seater TA-4J Skyhawk to the Minot N.D. airshow. He worked for Navy R&D and had done three tours in Vietnam with the A-4. His backseater was in awe of him, and like most really competent combat pilots, he was one of the easiest-going down-to-earth guys you ever ran into... no attitude, no mirrored sunglasses, no waxed mustache. The reason he was there was that the Ukrainian Air Force had sent a pair of MiG-29's on a U.S. tour, and the Navy wanted to see what they could do aerobatically and try to get some insight into what they'd do if they came up against a FA-18, so they had him and his inconspicuous Skyhawk following them around the airshow circuit and observing them in action. One thing we both noticed was the effortless way the Fulcrum could ignite its afterburner stages; this is apparently nearly fully automatic- the pilot merely advances the throttle, and the aircraft senses airspeed, g forces, air density, and what type of maneuver is going on and gives the amount of afterburner required. The MiG was going in and out of various degrees of afterburner at several points during even fairly simple aerobatic maneuvers. He had been in on the abortive A-12 program, and his take on it was that the Navy screwed over General Dynamics because it wanted to spend money elsewhere after the end of the cold war; he described flying the simulator and stated that he thought it was an excellent aircraft, particularly complementing the pilot's view out of the cockpit, which he said was truly outstanding. Pat |
#99
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![]() "Blueskies" wrote in message et... "Tim Rogers" wrote in message ... : : "Blueskies" wrote in message : . net... : : "Danny Deger" wrote in message : ... : : : : "Danny Deger" wrote in message : : ... : : : : Why does the shuttle throttle to 3 Gs on ascent? : : : : : : The 3 G throttling is done late in the flight (about 7:30)and has : nothing to : : do with dynamic pressure. It was designed in to allow "regular" people : fly : : the shuttle. : : : : : : Yes, the aerodynamic loads are highest early in the flight so the engines : are throttled then back up. The shuttle rolls : over on its back to fake the occupants into feeling 3 gs when in fact the : vehicle is pushing 4 gs.... : : No. : The 3 Gs is at the backs of the occupants (and along that same axis for the : vehicle.) This is the same if they are heads up or heads down. : If you lie with your back on the floor, you feel the same 1 G if your head : is facing north or south. : : Tim : : Not talking about facing north or south, they're talking about hanging from your feet or standing upright... Considering the velocity vector is forward, it still doesn't really matter which way they are. |
#100
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![]() "Henry Spencer" wrote in message ... Three specific snags also aggravated this problem on the SSME: (a) Most of the technology development on staged combustion had been done by Pratt & Whitney, but oddly, the contract for the staged-combustion SSME went to Rocketdyne instead. So the experienced people were shut out, and the guys who were actually doing the work were having to come up to speed on a technology that was new to them. (b) The SSME program, like the shuttle in general, was starved for money and opted to cut corners on subsystem testing in particular. The result was an unusually long and painful development process, with subsystem problems often not surfacing until whole-engine testing. (c) Partly as a result of (a) and (b), it didn't become clear until too late that the main LOX (I think it was) turbopump really needed one more pump stage. Since a major redesign was politically and financially impossible at that point, the result was a pump in which each stage was pushed to the ragged edge of engineering practicality to meet a very ambitious spec. The combination of (b) and (c) was particularly nasty, because all too often, a LOX-pump failure becomes a LOX-pump fire, which destroys the evidence of what went wrong. Having this happen repeatedly to whole test engines was just what an already-stressed development program didn't need. To be fair, the engine has improved greatly since the first ones were built. The current Block IIs appear to have incorporated several major changes improving them, prolonging their cycles between tear-downs and over-all making them far better than the originals. (and much of the work was done by Pratt & Whitney.) (of course I still think some people continue to hold old biases against the SSME :-) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
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