Newsgroups: rec.aviation.military From: shafer@ferhino.dfrc.nasa.gov (Mary Shafer) Subject: Re: Blackbird fuel Date: Wed, 20 Mar 1996 21:11:36 GMT On Tue, 19 Mar 1996 22:24:45 GMT, wb8foz@netcom.com (David Lesher) said: D> I seem to recall reading that SR-71's used a thick gummy fuel that D> was in effect, preheated by cooling the skin. This is kind of an exaggeration. JP-7 is about the weight of 3-in-1 oil, which isn't exactly thick. It's not gummy, either; I've run my hand along the keel and collected some and it's just oily. It wipes right off. D> But a friend who observed them being prep'ed many times at D> {somewhere damn hot}, told me he recalled an exotic COOLING system D> on the fuel hoses connected to it; one that in itself was a D> constant hassle to keep working. He described a coaxial connector D> with JP-whatever in the middle & refrig. surrounding it. He's only a little confused. What he saw was, I think, TEB. Ask him if everyone was in fancy silver fire suits. If so, it was TEB. TEB is the "igniter" for JP-7. You can't get JP-7 to burn without it in the SR-71, as the ignition of JP-7 takes a higher temperature than is conveniently produced otherwise. You drop in a shot of TEB, which bursts into very hot flames the minute it has any oxygen, and this ignites the JP-7. Once ignited, the JP-7 keeps burning. The plane has twelve shots of TEB (either total or per engine, I forget), using one shot for each engine start and one for each burner light. I watched them TEBbing the plane once, keeping well back and being careful to not stand between the big green firetruck and the crew. They had a very, very tiny leak between the TEB nozzle and the aircraft fitting and were getting a drop of TEB released about every 20 seconds. These drops would be on fire as they fell, but they (sort of like most meteorites) burned completely before they reached the ground. It was really pretty, but I was glad it wasn't me in the silver fire suit. D> So what is accurate? How much of it is light ends vs #6 bunker D> grade? Think 3-in-1 oil or sewing machine oil. Light, clear, but definitely more like oil than like gas. Then add a non-hydrocarbon that bursts into flame on contact with oxygen and lights off the oil. D> [He also expressed astonishment that Dryden could AFFORD to keep D> such going.. "Do you have ANY idea how much money those things D> sucked?" were his approx. words...] We only have two flying (right now we only have two, period) and it's a lot cheaper for us to operate them than it was for the Air Force. The Air Force had to include a lot more in the price of operating more planes from dedicated bases. The base and its management (including everything from the housing and roads onward), the medical facilities, flight surgeons, chase planes, the SPs, the crews and associated management, squadron administration, wing administration, base administration, command administration, stores, payroll, financial management, chaplains, MWR, barbers, open messes, clubs, and on and on. There's a tremendous infrastructure required to fly any airplane, from small single-engine general aviation aircraft on up to SR-71s. We didn't add more than one or two civil service staff, though we did add at least two contracts (for the engines, with P&W, and the airframe, with Lockheed) and the Air Force provides the pressure suit support. We already have all the other pieces here and adding another couple of aircraft didn't really increase our costs at all, although our workload did increase in some areas. The spares came with the planes, too. It's really two different sides of economy of scale. We already fly a lot of aircraft, so we had all that we need for that in place, which is the classic economy of scale. Then we only took on two more aircraft, which is sort of the reverse of economy of scale, if you see what I mean. -- Mary Shafer NASA Dryden Flight Research Center, Edwards, CA SR-71 Flying Qualities Lead Engineer Of course I don't speak for NASA shafer@ferhino.dfrc.nasa.gov DoD #362 KotFR URL http://www.dfrc.nasa.gov/People/Shafer/mary.html Newsgroups: rec.aviation.military From: shafer@ferhino.dfrc.nasa.gov (Mary Shafer) Subject: Re: Just how fast and high can the SR-71 go? Date: Wed, 20 Mar 1996 21:35:18 GMT On Wed, 20 Mar 96 00:31:05 GMT, keenan@inforamp.net (Martin/Jennifer Keenan) said: M> According to Mary, they (NASA) stick to Mach 3.2. This was the M> normal operating limit before - going to Mach 3.3 required the M> Squadron Commanders OK, according to the flight manual. Right, sort of. Those numbers are for a standard day. On a cold day, the Mach can be a little higher for the same inlet temperatures. We've flown a number of flights at 3.22 or 3.23, for example. On a hot day, of course, it goes the other way. I mentioned that the service ceiling is 85,000 ft, but I should also tell you that the plane has been to 90,000 ft. However, the current envelope is 85K, not 90K. I suspect that the plane wasn't very satisfactory at 90K; pilots do like some response to their control inputs, after all. -- Mary Shafer NASA Dryden Flight Research Center, Edwards, CA SR-71 Flying Qualities Lead Engineer Of course I don't speak for NASA shafer@ferhino.dfrc.nasa.gov DoD #362 KotFR URL http://www.dfrc.nasa.gov/People/Shafer/mary.html From: Mary Shafer <shafer@reseng.dfrc.nasa.gov> Newsgroups: rec.aviation.military Subject: Re: Question for Mary Shafer about SR-71. Date: 15 Apr 1998 12:32:43 -0700 sferrin@xmission.com (D. Scott Ferrin) writes: > I have a some questions. The *maximum* altitude and airspeed for the > SR-71 is generally given as "Mach 3.2 and 85,000 ft". How is it that > the SR-71 was designed to operate for extended periods of time at > those figures but not the *slightest* bit more could be gotten out of > it? I think part of the reason everybody has a problem believing that > those figures are absolutes is that because it does it so routinely. > Most equipment, whatever it may be, does not operate in the "redline". > By stating these figures are both the maximum and operational figures > it's saying that they redline these valuable aircraft routinely. Most > mechanical devices have a "comfort zone" where they can be operated > at for extended periods of time with fairly predictable behavior. For > the SR-71 this happens to be 3.2 and 85k. There is generally some > room between "comfort" and "disaster". THAT'S what we'd all like to > know- how much is there? I know that on the SR-71s "last" flight > where it set records it hit 2,242 mph for several minutes which is > about Mach 3.4. Of course they could fly a bit higher and a bit faster, but not much and not for long. There is a difference between cruise and dash, not to mention the variablity of the atmosphere, that makes this possible. After all, I've repeated mentioned that we cruise at about 3.23 Mach and go somewhat above 85,000'. I was not involved in any way in the specification, design, construction, acceptance, or USAF operation of the SR-71. Everything I know about it comes from reading books available openly, from our operation of the aircraft, and from general knowledge gleaned throughout about 30 years of working in flight test and flight research. Because of this, much of what I have to say is speculation and shouldn't be regarded as inside knowledge. The SR-71 is what's known as a point design aircraft. Everything about it was designed to work perfectly for the length of a flight at the design flight condition. No more, no less. The aircraft was built and the hardware specified so that the redline was just beyond the design point. The only compromises were those necessary to get the plane from the end of the runway to the design point. Kelly Johnson and Ben Rich both said this repeatedly. I've heard them both do it in person. When you're building a special-purpose airplane, to be operated under very controlled conditions by very skilled pilots, it's possible to make the pad between "OK" and "oh-oh" pretty small. The U-2 is, according to numerous publications, operated much closer to its limits than the SR-71 is. I've read articles that claim that the airspeed envelope is less than 5 KIAS wide up at cruise altitude for this airplane. Too slow and you stall, too fast and you rip the plane apart. Again, I don't have any more information about this than what I've read in the open literature, but this seems to be pretty widely accepted. This is in marked distinction to "regular" aircraft. Airplanes like the F-15 and F-18 have more generous envelopes and can be flown by pilots with a wider range of skills. They're designed that way on purpose. It would be foolish to make such aircraft as finicky as the special-purpose aircraft like the SR-71 and U-2. If you read Richard Graham's book about being an SR-71 pilot and compare it to the accounts of pilots like Duke Cunningham, you'll see a real difference in the entire approach to the operation of the different types of aircraft. The SR-71 operation was very driven by the flight characteristics of the airplane, whereas combat operations are very driven by weapons and ordnance characteristics and combat tactics. That's exactly as it should be--the last thing a fighter pilot should be doing in combat is fretting about a couple of degrees difference in something like compressor inlet temperature. There's one last point I should mention. Several of the books I've read about the SR-71 imply that the original design point was Mach 3.0 at 80,000'. If this is true, then I would speculate that operation at a higher Mach and altitude would just indicate that the USAF and Lockheed discovered that the airplane performed better than they thought it would, so that they were further below the redline than they intended to be. Rather than keep this excess capability as a reserve, they would have decided, if this is true, to use as much of the extra capability as they safely could in normal operation. If that's the case, it's not surprising that there's very little pad. Considering the importance of the data the SR-71 brought back, and the risks inherent in sending it out to get this data, it's not exactly surprising to think that they'd use every bit of capability the airplane has. I certainly would in their place. -- Mary Shafer NASA Dryden Flight Research Center, Edwards, CA SR-71 Flying Qualities Lead Engineer Of course I don't speak for NASA shafer@reseng.dfrc.nasa.gov DoD #362 KotFR URL http://www.dfrc.nasa.gov/People/Shafer/mary.html For personal messages, please use shafer@ursa-major.spdcc.com From: Al Bowers <bowers@orville.dfrc.nasa.gov> Newsgroups: rec.aviation.military Subject: Re: SR-71 / YF-12 Date: 21 Dec 1999 10:59:37 -0800 [apologies, lost attributions] >>> it would encounter at Mach 3, so they left it out and left the >>> expanding of the Blackbird's titanium skin when it encountered >>> those Mach 3 speeds to seal the leak. >> Titanium gets smaller when it gets hot. The charectoristic that >> makes titanium desireable for high temperature use is its crystal >> structure shrinking at temperature. > Sigh. Then please explain why the aircraft grows in length at speed. Titanium has a coefficient of thermal expansion of 5.2 x 10^-6 (a positive number, so it expands with increasing temp). The SR-71 lengthens by about 12 inches at it's design cruise Mach number of 3.0. The only aircraft that grows more in length due to aerodynamic heating is the Concorde (aluminum structure, coefficient of thermal expansion is 22 x 10^-6), which at the end of it's Mach 2.0 heat cycle, is about 18 inches longer than when it took-off. Al Bowers -- Al Bowers Aerodynamics NASA Dryden Flight Research Center "...tactics always degrade strategy..." -Frank Bethwaite |
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