Really great read, thanks for posting. No need for any deletions! That their range was so limited was something I really wasn't aware of - Take off, refuel. Go a little way, refuel. Rinse & repeat.... Fantastic engineering & logistical support. As Florian noted, definitely a bucket list "must see". Cheers, Ian
The range isn't that bad, it only seems bad because it doesn't take very long to go that far at 2200 miles per hour....... They went from over Labrador to the north sea in one leg.. That's not bad at all.. When you're up at 80k feet, the air is so thin that the efficiency of the airfame is pretty good. That said, propulsion at high Mach is a thirsty thing, no matter how you cut it. The SR-71 is pretty much a big fuel tank with a couple of engines hung on the wings, a mission bay up front and two guys up ahead of that, the rest of all you see is pretty much all fuel tankage except for the wings outboard of the engines....... Here's a link to a diagram of the fuel tank system.. SR-71 Online - SR-71 Flight Manual: Section 1, Page 1-48
To someone who was involved with the propulsion system in the mid-seventies, what was truly amazing is that the entire engine and propulsion system was conceived and designed when all they had to use for analysis tools was mechanical calculators and slide rules. There was no such thing as a computer and they had to grind through the calculations for engine performance basically by hand. Now we have computer programs that simulate the performance of each component of the engine and quickly allow us to converge on a solution as to what the bypass ratio and the pressure ratio of compressors need to be to get an efficient system. In those days they had none of that. I'm sure that there were people locked in a room with mechanical calculators running full bore for hours to try to figure out how much air needed to be bypassed around the core and how much air the ejectors needed to make an efficient propulsion system. The fact that it wasn't changed during the life of the aircraft, even though computers came along in the mid 70's shows how good a job the folks doing that analysis were in the first place.
Wonder if any of the stud drivers are Ferrari guys on fchat? That would be a hoot to listen to some new stories. MDS
As a measure of engine efficiency, the combat range (Mach 3 flight) of the SR-71 was 2900nm while the ferry range (flying for max range regardless of speed) was only 300nm greater. That is, the aircraft was pretty close to its max efficiency at Mach 3+. In comparison, most aircraft would cruise subsonically to obtain max range, and their supersonic range would be a small fraction of their subsonic range. I guess only Concorde come close in that respect.
Fan engines lose performance the faster you go. As you go up to speeds above Mach 1.5 or so you want a turbojet, and as you go faster than Mach 3.2 or so, you want to start to go towards a ramjet by starting to bypass some air around the engine as is done on the J58. The J58 is best described as a "leaky" turbojet. The bypass ratio is low and the air bypassed is used primarily to feed the afterburner. The air leaving the core of the engine has already been burned, so there isn't much air left for the afterburner unless you pump in some fresh air to burn. Early in the SST competition Boeing was pushing a fan engine with a "duct burner" that burned bypass air and (it was thought) would provide the capability to make it to land if it lost an engine somewhere over the ocean and had to proceed subsonic to an alternate landing site . The better fuel consumption of the fan made it possible to cruise subsonic where a pure turbojet could have an engine problem somewhere over the ocean, and it would run out of fuel before it could make landfall since it was so inefficient at lower speed. So there are times that you could want a fan engine, but not when you're going fast. Lockheed's competitor (which they couldn't really talk much about at the time) used turbojet. By the time Boeing got around to the final design they had gone to a turbojet and dumped the duct burning turbofan. The YF120 was an attempt to provide a "variable" bypass ratio. That would allow a fighter to have a longer subsonic cruise range and then cut the bypass ratio for "supercruise" above Mach 1. It didn't work all that well.. When the YF-23 was flying with that engine one of my friends was watching the approach (we made the "troughs" after the engine and had a rep on site for the flight test program)... On approach the engines were very unstable, with speed and engine control obviously all over the place.. My friend was horrified and he looked over at the GE rep who saw his concern and said... "Oh, that's nothing now, you should have seen it when we first started flying it,compared to that this is really good!!!"... Variable cycle sounds good, but the real range you can get out of it isn't as big as you would want. The internal turbine rotor inlet temperatures have gone up since the J58 was designed. That is, most of the air in the core of fan engines nowadays is burned so there isn't much air available to burn in the afterburner. At this point you only have the cooling air from the turbines (about 12 to 15% of the airflow in the core) to burn since the air leaving the combustor is close to stoichiometric. For that reason you could want some kind of fan or some more bypass and a burner in the fan duct to make the engine into a lightly boosted ramjet. The J58 was a very specialized engine and much like the SR-71 it is very much a "design point" design that is in a corner of the envelope of what you can do. While today we could make it shorter, lighter, and more efficient, the basic cycle for that speed point probably wouldn't change that much because of how the cycle works at those speeds. The things like the engine inlet temperature (900F) really drive the design. While we have much better analysis tools the actual material properties of the cold section components really hasn't improved since the 50's. Only the first stage of the engine is titanium, from there back the rest of the engine is all high temp alloys (high temp steels and nickel base alloys). At Mach 3 cruising speeds the inlet provides 54 percent of the thrust and the exhaust ejector 29 percent. At this point the turbojet continues to operate but provides only 17 percent of the total motive force. When I was first introduced to the engine it was explained to me that the most of the thrust was generated by the inlet and the ejector/nozzle, and the engine was just a pump in the middle, that's a pretty good way to describe it. The inlets and ejectors aren't going to change in performance, they are very good already, so the chance to improve the performance isn't going to change a lot with better engine design. Even if you improved the efficiency of the engine by 10% (maybe doable) then the overall efficiency of the propulsion system would only increase by about 2%. This is why nobody ever built anything better, and why they never replaced the engine (although they did add a "zero" stage ahead of the fan to increase the airflow of the engine). Even if you made big and expensive changes to the engine it wouldn't have made a big improvement in overall system performance. Kelly Johnson was very good at finding the "corners" of the envelope and putting his design out on the edge, and then was able to develop the technology and get it to work. That they got it to work as well as it did was a testament to the folks a Lockheed and P&W at the time who solved countless problems that they faced to get it all to work. The design is placed about where titanium starts to lose it's advantage over steel as a structural material. Go much faster and you're starting to look at making a lot of the airplane out of stainless steel and it gets bigger and looks more like a B-70. Like I said, inside the envelope but not by much. The SR-71 propulsion system is a very good system for speeds up to Mach 3.5 or thereabouts. TBCC is aimed at higher speeds. Most high Mach systems use booster rockets to get them up to speed. The TBCC uses turbomachinery to allow horizontal takeoffs and landings and a scramjet for high speed part of the mission. I haven't looked at a cycle for higher mach than 3.5 but as you go faster the temperatures go up and the less you want the engine to do and the more you want a ram jet or a scram jet.
K..you just melted my brian. The people on this site continue to astound me. I enjoyed reading your post.
Low bypass, afterburning turbofans work fine way above mach 1.5. The F-111, F-14 and F-15 had no trouble reaching mach 2.5 with TF-30s and F100s. You needed some tricks with the bleeds at around mach 1.6-1.7 or you would get a compressor stall. The aluminum airframe was usually the limiting factor for all three on how fast they could go. Somewhere in the mach 2.5-2.8 range, the afterburning turbofans started running into problems, depending on inlet design, but by that time the airframe was ready to burn off or melt at any rate. Have been to 2.55 with TF-30s myself and they were running fine with relatively low fuel consumption (~25,000 lbs/hr each), much better than at low altitude (~60,000 lbs/hr each). We did get total temp warnings (slow down within 300 seconds or risk structural damage). Concorde cruised at mach 1.7 because of airframe limitations, not because of engine limitations. Ramjets work fine up until somewhere around mach 5 and then you want to go to a scramjet (supersonic combustion ramjet). AFRL's X-51 recently demonstrated scramjet propulsion on an expendable test vehicle. Incidentally, a compressor stall at mach 1.7 (bleeds not opening), was spectacular with flames coming forward past the cockpit and the aircraft yawing pretty violently. Nothing compared to a compressor stall at mach 3, though, like the SRs sometimes saw.
I, too, am amazed at the dearth of interesting and informative posts on this site. I doubt that there is another like it. Now, can somebody tell me why some of the videos have to have the garish sounds of somebody beating a drum to death while another is flailing the strings off a guitar? I would like to hear the airplanes just once without the overwhelming blinga-blanging sounds of rock "music" drowning everything out.
Sort of thread creep, but it is unfortunate that the F-22 will never see its originally projected production numbers. Might have seen a future where the YF120 was further developed/refined and been competitively sourced against the F119 for later production, similar to the F100/F110.
If we have to use the F22 in anger against a serious foe we will, most likely learn that we built way too few of them... I can only pray that we don't ever find ourselves in that situation. The F110/F100 "Great Engine War" was responsible for the improvement of both engines. I think that because the 110 was a derivative engine that the cost was not as great as building an engine from scratch so it made sense. The government paid for both the 120 and 119 and they were already to flight test status so it wouldn't have cost a lot more to do a competition. OTOH I worked on the F136 and didn't think that it was near worth what was put into it. I was surprised that it lasted as long as it did. The 135/136 competition was taken to the point where the prices for the 135 were locked in for a long time and there are costs to bring along two engines with two logistics trails and that is expensive far into the future. Killing it was the right thing to do, despite what GE and RR wanted. The idea of an engine competition sounds good, but when you look at the costs to develop two engines and the the cost to maintain two logistics tails, you're kidding yourself if you think that it's going to save anything in the long run. Remember that the F100 was the winner of the original competition and then GE came back later and wanted to compete against the F100 with the 110.. It makes sense to compete in the early stages, but at some point you need to cut your losses and go with the best engine and get on with it.
Awesome, great shot, the brain required to fly that thing, mind boggling, remarkable. As a kid I remember it flying to a UK air show and it was travelling so fast from the US to the UK it turned over Paris to begin its decent
For a real insight into flying the SR-71, the "SR-71 Revealed: The Inside Story" by Richard Graham, who flew it for several years and eventually became the wing commander, is hard to beat. I think I read it in one sitting! It's objective yet engrossing reading, without the bluster of the works from another well known SR-71 pilot on the same subject. From brake release to Mach 3 cruise in under 15 minutes....in 1964. Gives Ferrari something to aim for. Watching it in flight as a kid was one of those truly indelible memories.
Thanks! My interest is so piqued, I just ordered it from Amazon. And while there, also ordered a copy of another I've been meaning to get for a while; "The Puzzle Palace". Supposedly a good "insight" into the NSA. Then, they offer me free 2 day delivery. Cool. Then I remember I've got a few "miles" on my Amazon card - Redeem a few of those, and the entire mess is gonna be here by Thursday, for free! Cheers, Ian
Gotta disagree there Brian. For example, my last order (coffee pods) was free 2 day shipping. It arrived the following day. No charge. I've never had a problem with Amazon TBH. I'll report back once received. Cheers, Ian
I have had things take so long I recently had my CC company reverse the charge only to have it arrive 2 days later after plan B was already in my hands. Have had near zero luck. Just received 2 more late after paying extra for the fast shipping.
Brian- Amazon Prime for $99 actually turns out to be a pretty good deal. I have a signed copy of Byrnes' and Hurley's book "Blackbird Rising". Pretty good with limited photos. One was an engineer on the program and the other an RSO. Cheap from abebooks.com used at ~$7-10 and new from $15. Used copies less than $1 on Amazon.
+1 May very well be the best $99 I've spent in a long time..... The printer recently ran out of ink & the replacement was available via Prime the same day!.... I paid a minimal surcharge at around 10am and the ink was with me by 3:00pm that afternoon! In general, "free shipping" gets me my stuff within two days at the most. Very, very, impressed with Prime. Cheers, Ian
