Probably one of the most photographed aircraft of all time. For a 50-year-old design it still looks futuristic.
Few airplanes in history have the mystique of the SR-71 Blackbird. Capable of flying to the edge of space, it looks like it could go into orbit if it wanted to. Designed before I was born, retired in the 1990s, we're still talking about this thing. It set so many speed and altitude records I don't have room to list them.
I have seen an SR-71 fly exactly once in my life. Way back in 1983 I was still an ROTC cadet on my summer training camp at Eglin AFB. An SR-71 made an emergency landing there with an engine problem.
We got to venture into the maintenance hanger while the engine was being worked on and get fairly close to the sleek, black beast. We even got to meet the crew superheroes who flew it! Quite an experience for a kid still in college.
When it was finally fixed we got a break from our daily routine to watch it take off. It thundered into the air, circled around the field, and made a low pass down the runway while rocking its wings before heading off. I'll never forget that sight.
Time spent in reconnaissance is seldom wasted. - Sun Tzu
The earliest use of military aviation was for reconnaissance. Before the invention of the aircraft, balloons were often used to get a look behind enemy lines. During WWI, airplanes acted as artillery observers long before anyone thought to stick a gun on one.
During the Cold War our need for reconnaissance was critical. Had to keep an eye on what those sneaky commies were up to.
The origins of this most amazing aircraft go back to 1957. We were conducting regular overflights of the Soviet Union with our U-2 spy planes. The Soviets were less than pleased with the situation. Seeing as we have a hissy-fit whenever a Russian military aircraft flies into this hemisphere, I can actually understand their displeasure. Even in 1957 the CIA was starting to worry about the continued ability of the U-2 to operate in Soviet airspace. Their worries were confirmed in 1960 when Francis Gary Powers was shot down by an SA-2 missile. In a less well known incident, a second U-2 was shot down during the Cuban Missile Crisis, also by an SA-2.
The U-2 flew very high but very slow and was easy to spot on radar.
The U-2 could fly quite high but it was rather slow. More importantly, it had a large radar cross section. Even in 1957 people were already talking about "stealth" technology. The new aircraft would need to fly as high as the U-2, but much faster, and it would need to have a much smaller radar cross section. The idea was that by the time enemy radar actually spotted it, they wouldn't have time to shoot it with anything.
What most amazes me about the SR-71 is that it was designed in an age of slide-rules and drafting tables.
I suspect at this point everybody knows about Clarence "Kelly" Johnson and his famous Lockheed "Skunk Works" that came up with everything from the F-80 to the F-22, and of course the SR-71. Not much I can say about Kelly Johnson that hasn't been said already.
One of the greatest aircraft designers of all time. Clarence "Kelly" Johnson.
What you perhaps didn't know is that the CIA went to both Lockheed
and Convair with proposals for their "black" project. They actually liked Convair's
design better, but they weren't real pleased with how Convair had delivered on the
B-58 bomber. Oh the plane itself was OK, just that they had gone way over budget and past deadline. Lockheed had a better track record of delivering the goods on time, so they picked Lockheed's A-12 prototype. In this case the "A" stood not for "Attack" but for "Archangel". The project code name was randomly chosen as "Oxcart" and the pilots of the A-12 would actually call it "the Oxcart".
Convair's spy plane design. Lockheed actually adopted the canted twin vertical stabilizers.
Wait a minute! I thought we were talking about the SR-71. What the heck's an A-12?
It's fairly easy to mistake an A-12 for an SR-71. The main difference is it only has one seat.
The A-12 was basically the SR-71 before the SR-71. It looks an awful lot like an SR-71 except it only has one seat. Performance wise they flew about the same. The A-12 could fly a bit higher because it was lighter. Functionally they carried different sensor packages but did roughly the same job. The main difference was the A-12 belonged to the CIA while the SR-71 belonged to the Air Force.
Early A-12 test flight. The A-12s were based out of Groom Lake Nevada.
SR-71 crews called their plane "the sled" but it was also referred to as a "Habu". What's a Habu? It's a poisonous snake found on Okinawa, where the SR-71s frequently operated from.
I like this Big Daddy Roth inspired SR-71 cartoon from Kadena AFB in Okinawa.
OK let's get to the good stuff. Starting sometime around 1960, a bunch of guys with crew cuts and pocket protectors sat down with their slide rules and produced the fastest aircraft to this day. Probably puffing on cigarettes the whole time. This was 1960 after all.
I have to add a few caveats to "fastest". To call the A-12/SR-71 the fastest I have to limit the categories to "manned" and "air breathing". Rocket planes like the X-15 have gone faster and unmanned aircraft have gone faster.
To get a plane to go Mach 2 isn't all that hard. Mach 2 capable fighters have been pretty common since the late 1950s. To go Mach 3 is another level of difficulty altogether.
Guys like this designed the SR-71 with slide rules.
Building engines that can do it is a big problem. They need to be powerful of course but that's just part it. Turbojets don't like to inhale supersonic air. Most supersonic aircraft have used some system of moveable inlet doors, ramps or shock cones to slow the airflow down to a speed that keeps the moving parts happy.
You can do it with rockets, but the CIA wanted a range of 2000 nautical miles and no rocket plane was going to come close. You can do it with a ramjet, but ramjets won't even run until they're already going supersonic. So now you're looking at a very complex arrangement of rocket boosters and ramjets or turbojets and ramjets. What they really needed was an engine that could function as a turbojet at low speeds and transition to a (mostly) ramjet at supersonic speeds.
Fortunately Pratt & Whitney had their own set of guys with white shirts and crew cuts. They produced the incredible J-58 engine. Oddly enough this engine had been originally designed for a Navy seaplane bomber that was never produced. That's an interesting story in and of itself. With more than a bit of redesign they were able to produce an engine that could sustain speeds in excess of Mach 3.
The amazing J-58 engine.
So how's it work? At low speeds it works like a normal turbojet engine. At supersonic speeds most of the air gets shunted around the compressor section and goes straight back to the afterburner. Those big "spikes" at the front were designed to trap the shock wave in the inlet before it got to any of the moving parts. Behind the inlet was a "diffuser" which slowed the air down to subsonic speeds. At high Mach numbers roughly 80% of the air was going straight back to the afterburner, with the engine functioning
almost like a ramjet. I say "almost" because air was always going through the core, which was always running. Early on all this was driven by an analog computer. It would move the spikes to keep the supersonic shock wave downstream of the inlet but upstream of the compressor.
J-58 afterburner and its signature "diamond" pattern.
Fun fact for my fellow gear-heads. The J-58 engines were started by an external cart that used two 425 cubic inch Buick "nailhead" engines. I had one of these in my old 64 Riviera. They would be connected via a driveshaft directly to the J-58 and spin it up to 4,500 RPM. That's unusual because most jet engines are started pneumatically.
Airflow isn't the only problem with going Mach 3. At those speeds things start to get hot. Really hot. The skin of the aircraft, the fuel and even things you don't think about like the tires.
To keep the fuel happy at high temperatures they formulated a special jet fuel called JP-7. It was developed for thermal stability (won't break down) and a high flash point (won't go kablooey). To get it to light off they had to use a chemical called triethylborane or TEB. Yeah, I don't know what that means either. Chemistry was never my best subject. What's important is that each engine only carried enough of this stuff for 16 starts, restarts or afterburner lights. This limited how far they could go. They could only air refuel so many times before they ran out of TEB to relight their afterburners with.
Heat is a big problem for the skin of any aircraft traveling at high speeds. The top speed of the F-104, for example, was limited by skin temperature. If they went too fast things started to melt (bad). No problem. We'll just build our new spy plane out of titanium. Never mind that it's never been done and oh by the way most of the world's titanium is in..........Russia.
So how did we get the titanium? Send James Bond in to steal it? Actually the Russians sold it to us. More correctly they sold it to several fake companies that the CIA had set up. Capitalism for the win!
I can see it now.
"Hello, Sergei? This is Mister um......Smith from Central Imports and Associates. We'd like to buy several tons of titanium."
"Da. Is good. What do you want it for?" (in thick Hollywood Russian accent)
"Well certainly not to build a Mach 3.2 spy plane with!"
Titanium was pretty exotic stuff at the time and required special tools and welding techniques to work with. Today we make high-end bicycle frames out of the stuff but in the early 1960s we were still learning how to work with titanium.
According to Kelly Johnson:
“We produced 6,000 parts, and of them fewer than ten percent were any good. The material [Titanium] was so brittle that if you dropped a piece on the floor it would shatter”.
What wasn't made of titanium was made from advanced (for the time) composites. I didn't realize composites were a thing back then but they were.
Even the tires, since they're coming along for the ride, contained aluminum compounds to handle the high heat. If you've ever been up close to an SR-71 you likely noticed that the tires are grey. They were filled with nitrogen to a whopping 450 psi.
When metal heats up it expands. The skin of the SR-71 heats up a lot so they had to make all the parts fit together loosely on the ground. Once everything got heated up it all fit together the way it was supposed to. That's also why the skin of the wings looks to be corrugated like a tin roof - it was.
Iconic head on shot of an SR-71. Note the corrugated skin on top of the wing.
The SR-71 leaked fuel, especially when it was sitting on the ground. The reason usually given for this is that the fuel tanks wouldn't seal until they heated up and expanded.
I have seen other sources, however, that claim this was because they just couldn't find a sealant that would work properly with 300 degree fuel. That source claims the plane always leaked, even in flight, just that the leakage was considered acceptable.
The fuel leakage is usually given as the reason the SR-71 always had to hit a tanker right after takeoff. Once again other sources claim that they routinely took off with a reduced fuel load to improve their single engine capability.
A special fleet of KC-135s were configured to refuel the SR-71. These were originally "Q" models but were changed to "KC-135T" when they got re-engined. I've flown a "T" but never refueled an SR-71. The Q had an improved "high speed" boom, although today all 135s have the high-speed boom. The other difference was a couple of extra valves to keep the tanker's JP-4 out of the forward and aft body (refueling) tanks. The tanker could burn the JP-7 just fine but the SR-71 couldn't take "regular" jet fuel.
A-12 refueling behind a KC-135. That's a very early paint scheme on the tanker.
One of the most challenging parts of an SR-71 mission was finding the tanker. They burned fuel very quickly down in the lower altitudes so they couldn't afford to be wandering around looking for the tanker for very long. Fortunately they had a very good inertial navigation system with an automated astral tracker (wow). This thing could automatically track several stars and keep the INS accurate to 3000 feet. How does an astral tracker work? I don't know, it's FM (freakin' magic).
I never realized that KC-10s refueled the SR-71 but I guess they did.
The air refueling rendezvous had to be timed perfectly. Once the SR-71 started down from high altitude they had to fly a specific descent profile and there wasn't much they could do to change it. They were dependent on the tanker crews to position the refueling track away from the weather because the SR had no weather radar of its own.
Air refueling was reportedly a difficult maneuver for the SR-71 pilot. The refueling receptacle was well behind him and he had limited visibility due to his space helmet and the SR-71's small windows. If they couldn't get hooked up for some reason they would have to abort the mission and land at their alternate airfield.
SR-71 on what looks like a KC-10 boom. Note the poor visibility and then remember that he's also looking through a space helmet.
Why go to all this trouble to have spy planes in an age of satellites? Because we know when the satellites will be overhead,
they know when the satellites will be overhead, everyone knows when the satellites will be overhead. An aircraft can be where you need it, when you need it. If it sees something interesting, it can go back and take another look. Even today we still operate spy planes, both manned and unmanned.
For such an exotic airplane the cockpit is standard 1960s fighter.
While it was a super plane, the SR-71 was not a super-plane. It had no magical powers. It didn't have warp drive. The airframe was limited to 2.5 G's. Aerobatics were strictly prohibited. It was generally flown like a airliner, with the autopilot engaged most of the time. Fun fact - it had the exact same top speed as a P-51 Mustang. Both were limited to 450 knots indicated airspeed. Except up at 80,000 feet where the SR-71 flew that 450 indicated works out to Mach 3.2 or so. It had incredible performance but it had to be flown within very specific parameters.
I want the version that the X-Men had in the one movie. It had room for a bunch of people in the back and could even takeoff and land vertically. Only Hollywood could make something this cool even cooler.
The SR-71 also wasn't invincible. True, none were ever shot down, but we took great care to keep them out of places where they could get shot down.
By the time the A-12 entered service in 1967, overflight of the Soviet Union was considered to be too risky except for reasons of "emergency". Plus Kennedy had publicly said that we wouldn't do it any more. Spy satellites had reduced the necessity for manned overflights by that time. Had tensions escalated I suspect we would have flown these over the Soviet Union but fortunately things never got that hairy.
That didn't stop us from overflying "secondary" countries like North Vietnam and North Korea with them however. They did come under fire from SA-2s on occasion but their speed and electronic countermeasures kept them from getting hit. One A-12 did have a North Vietnamese missile explode close enough to take a piece of shrapnel. The design was "stealthy" but not as much as they had hoped for.
The A-12 had a rather short life. First flown in 1962 it was only operational from 1967 to 1968. Only twelve were built and six were lost due to accidents.
The SR-71 lagged the A-12 by about two years. First flown in 1964 it entered service in 1966. In 1967 the SR-71 was chosen over the A-12 as the superior reconnaissance platform, partly due to its side-looking radar. The A-12 was the hotter airframe but the SR-71 carried more sensors - which was the reason for this whole exercise. We weren't trying to see how fast we could go, we were trying to see what the other guys were up to.
The normal mission profile of the SR-71 was to fly just outside Soviet airspace and use its long range cameras and powerful side-looking radar to look as far in as they could.
These were dangerous aircraft and the loss rate confirms it. A total of 32 SR-71s were built and a dozen were lost over the years. Most were lost prior to 1972, which makes me think there was a bit of a "learning curve" to the program. A big problem was a engine "unstarts". An unstart occurred when the airflow into the engine got out of whack (very technical I realize) and the engine starting surging violently. This was accompanied by loud banging and the aircraft violently yawing. Then the other engine would likely get disturbed and start a "sympathetic unstart". The pilot knew which one went first by which side of the canopy his head smacked. Once they replaced the analog computer with a digital processor this problem was greatly reduced.
SR-71 with afterburners lit. At speed the afterburner produced roughly 80 percent of the total thrust.
Approach speeds were around 175 knots. Single engine landings were reportedly pretty hairy, taking full rudder plus 5-10 degrees of bank to control it.
If you want to read an actual SR-71 flight manual, it has been declassified and is available on line. SR-71 Online has a copy plus a ton of pictures.
As impressive as these aircraft were they were not immune to being intercepted. I know, I didn't believe it at first but it's true. F-15s used to run intercepts on SR-71s. How can a Mach 2 Eagle-jet catch a Mach 3 Blackbird? Well it can't, of course, but it doesn't have to. It just has to know that the SR-71 is coming and get into position in front of it. I was told by an F-15 driver that it had to be a "perfect intercept" but it could be done.
I asked our own resident Eagle-driver pwoodford about this and he related a briefing by a couple of F-15 "patch wearers" (Fighter Weapons School graduates) who had done it.
This was back in the AIM-7 days, before AMRAAM, early 1980s.
The setup was a 180-degree head-to-head pass. The SR was at Mach 3, very high of course. The Eagles were in the high 40s or right at 50K, around Mach 1.5. They got radar locks and took a single AIM-7 shot each. There was no turning, because they'd never have been able to catch the thing anyway.
Your only shot opportunity against an SR or a Foxbat was an AIM-7 face shot taken in the very short window between max and min missile range. At the speed the SR was going, that window was only a couple of seconds long, if that. They took their shots, which were electronically scored somehow, and it was over in the blink of an eye. I don't think either shot scored.
Ranges are probably still classified, but I'd guess max range for the shot would have been around 50NM, with min range about 45NM, if that gives you an idea how tiny the window was. The ranges could have been farther out ... I can't remember all the details. In any case, if you shot when the SR was on your nose at 50NM, by the time the missile got close enough to fuze the SR would have been about 10NM away.
I don't remember the range at which these guys were able to lock up the SR, but I think it was pretty far out, in spite of the SR's stealthy design: it was still a big fast target, and that's what the Eagle's pulse doppler radar was designed to see.
I remember one of them saying he got a visual on the SR at around 15NM. He said it looked gray, not black, as it whizzed past.
Of course the Soviets didn't have F-15s but they do have MiG-31s. The "Foxhound" was developed from the earlier MiG-25. It has a much better radar and a much better missile in the R-33 (AA-9). The MiG-31 has a huge radar, making it a "mini AWACS". It can reportedly see targets out to 120 nautical miles. The R-33 missile it carries is similar to the US Navy's Phoenix missile that the F-14 carried and has a range of close to 100 miles. More importantly it was designed to take out very fast, high-flying cruise missiles. On at least two occasions, MiG-31s were reportedly able to lock on to SR-71s
and do it within the engagement envelope of the R-33 missile.
The MiG-31 may have been able to engage the SR-71. We'll never know for sure.
Could they have actually shot one down? I'd guess it all depends on how good the missile was. According to
MiG-25 pilot Victor Belenko, the R-31 (AA-6) missile couldn't do it because its electronics couldn't react quickly enough to make the required course corrections at those speeds. The AA-9 is a much better missile so who knows? As the Mythbusters would say, it's plausible. Keep in mind that by the time of its final retirement the SR-71 had been operational for 30 years. Radar, computer and missile technology had come a long way over three decades.
Foxhound with its very large AA-9 missiles. The plane/missile combination is roughly equivalent to our F-14 Tomcat.
The retirement of the SR-71 was, like many aircraft, based on politics and budgets. Robert MacNamara ordered the tooling for the A-12 and SR-71 destroyed back in 1968. The Air Force initially retired the SR-71 fleet in late 1989. In 1993 Congress pressured the Air Force into bringing the aircraft back into service. They made three of them operational again and kept them going until 1998. NASA kept two of them flying until 1999.
So how fast did it really go? The Air Force always just claimed "Mach 3.2+" because the official top speed was classified. The actual limiting factor was compressor inlet temperature, which was limited to 801 °F. This worked out to around Mach 3.3, although SR-71 pilot Brian Shul claimed to have hit Mach 3.5 once while outrunning a Libyan missile. Top speed of the lighter and higher flying A-12 was listed as Mach 3.35.
How high did it really go? Once again the Air Force cryptically said "80,000+". It once set an absolute altitude record of 85,000 feet so we know it could go at least that high. The A-12 could go to at least 90,000 and I've seen numbers as high as 95,000!
Note that operationally both aircraft flew at roughly identical speed and altitude. Everything was optimized for Mach 3.2 so that's about how fast it flew on any normal day. And why quibble over the difference between Mach 3.2 or Mach 3.5? Either way it's freakin' fast!
So with that much performance why not build an armed version? We did look into it. There was talk of a B-71 but that's as far as it went. I'm not sure anyone ever figured out how to drop a bomb while going Mach 3. Plus the SR-71 didn't have anything close to intercontinental range.
An interceptor version of the A-12, called a YF-12A actually made it to the prototype stage. It had impressive capabilities. One successfully shot down a drone that was flying at 500 feet from an altitude of 75,000 feet. It carried the AIM-47 Falcon missile which had a range of around 100 miles. What's amazing is that it actually worked. Previous Falcons generally didn't.
YF-12 interceptor prototype. The idea worked but we weren't sure we really needed a Mach 3 interceptor.
I had a plastic model of a YF-12 sometime back in the 1960s. I used to pretend it was a space ship, because I was six or eight and it looked like it ought to fly in space. George Lucas apparently had the same idea.
I think I know where George Lucas got the idea for this thing.
The YF-12 project was cancelled by, who else, Robert MacNamara. By the late 1960s Soviet bombers weren't considered to be enough of a threat to justify the expense of a Mach 3 interceptor. Money was a bit tight then since his other "project" in Vietnam was using up all available funds. It wasn't a total loss. The AIM-47 became the parent of the Navy's highly successful Phoenix missile.
A-12 with a D-21 drone on its back. The drone carriers were actually designated M-21 (Mother Ship). If this looks like a bad place to launch a drone from, it was.
What's even cooler than a Mach 3 spy plane? How about a Mach 3 spy plane that launches drones? Specifically a Mach 3.3 drone called a D-21 that flew at 90,000 feet. It looked like a baby A-12 with only one engine. The D-21 used a pure ramjet engine since it had the A-12 to get it up to speed. Then it would fly a one way mission, eject its camera module and then self destruct. That was the idea anyways. They had a couple successful test launches and then things got ugly.
D-21 drone looks like a baby SR-71.
During one of the test launches the drone malfunctioned and hit the mother ship, causing the loss of both. They gave up on using the A-12 as a launcher but stuck with the drone. A modified B-52H (I had to get a B-52 in here somewhere) carried one under each wing. Since B-52s are most definitely not supersonic, a big honking rocket booster would get the D-21 up to speed where its ramjet could take over.
These flew operationally four times to spy on Chinese nuclear tests in 1971. None of the flights was a complete success. One of them crashed in China and now sits in their aviation museum. Another flew into Soviet territory where it self destructed. The Russians found enough of the wreckage to reverse engineer it. Oops. The program was scrapped shortly after.
B-52H with a pair of D-21 drones. The drone required a rocket booster when launched from the B-52.
The D-21's rocket booster was larger than the drone.
So what followed the SR-71? My guess is a drone of some sort. As far as I know, there was never a "Project Aurora" to create a manned successor to the SR-71. Today our strategic reconnaissance is a combination of satellites, manned aircraft like the U-2 and drones like the RQ-170. The RQ-170 looks like a baby B-2 bomber.
RQ-170 Stealth Drone
Supposedly the Lockheed Skunk Works is still hard at work. They are working on an "SR-72" drone that will be capable of going Mach 6.
What the proposed SR-72 might look like.
Whatever we come up with, the need for strategic reconnaissance will likely never go away. There will always be somebody we want to snoop on and they most likely will try to keep us from doing it. Hence the "need for speed".
Something was photographed making sonic booms over Texas. An SR-72 prototype perhaps?