What Is NASA Doing With Its Old Blackbird? [27:01]

Transcript

Chapter 1: The Mystery of NASA’s SR-71

Hello, it’s Scott Manley here. A few weeks ago, I posted a short video about something that NASA Administrator Jared Eisenman said at a conference. He basically had given a speech talking about, you know, the golden future that NASA is pushing forward towards and how they were going to rebuild their fleet of X-planes and go higher and faster. He included a cryptic picture of a black aircraft with, you know, familiar curves, caned inwards, tail planes, and of course, somebody afterwards commented, “You showed a picture of the blackbird up there?” And, uh, you sure that’s a blackbird? Well, okay. Uh, what was that picture that you showed up there? Like I said, NASA’s getting back in the business, flying high and fast again.

At that point, the internet started going on their, you know, putting on their detective shoes or whatever. They started investigating, uh, wondering what NASA was possibly doing in terms of X-planes, and some smart person noticed that an SR-71 Blackbird, which had been on display at NASA Armstrong, was no longer on display. People started asking questions, and, uh, people began to speculate: is NASA trying to get one of these flying again, and why would they be trying to get this flying again, and what would be the problems, and what actual original interesting research justification would exist for this? So yeah, look, NASA has a long history of building and flying X-planes and doing, you know, cool stuff at the edge of the envelope and before, but to be fair, the SR-71 at this point is pretty familiar. It’s 50 plus years old. Flying at Mach III isn’t the big deal that it used to be. Uh, but NASA actually started flying these kinds of airframes back in the 1970s before the SR-71 was available to NASA to do research.

There was a program in the 1970s, late ‘60s actually, which used the YF-12 prototypes. Now, this was originally built for the CIA, that was a single-seat version. Then they built the two-seater version for the Air Force, the reconnaissance version, SR-71. But the Air Force was also interested in an interceptor, and that would be the YF-12. So, this was an experimental F-12. It would fly Mach 3, and it would deploy missiles from the internal bay, which could shoot things down. This program ran for a while, and then Robert McNamara shut it down to save money, and they destroyed all the tooling, and no more of these things were built.

But that meant that by the end of the ‘60s, there were a couple of these airframes that were no longer needed. They were sitting around, and NASA and the Air Force actually had this program in the 1970s where they did high-speed research using the YF-12s which were left over, and that ran for about 10 years. Um, you know, they made maybe something like 300 flights, 450 flight hours, and of course, you know, it was performing like sustained Mach 3 flight, learning about inlet performance and how the inlets would become unstarted, thermal loading, that kind of stuff. But, uh, you know, that was sort of NASA’s state-of-the-art for quite a while.

Then, in the 1990s, the SR-71, which had been a military aircraft for such a long time, was sort of reaching the end of its life because, you know, surface-to-air missiles were getting higher and faster and were no longer felt to be as untouchable as it once was. Uh, it was also, you know, they couldn’t build new ones. So yeah, the military SR-71s got retired, and NASA had a few of them, and they did in the ‘90s a bunch of research flights at Dryden, which is now, of course, Armstrong. One of these flights would include, uh, tail number 844, which was the one that was on display.

One of the ones that keeps on getting highlighted, by the way, is the laser system, right? And that is not a weapon system. No, that is the linear aerospike SR-71 experiment, which essentially had a small model of like the, uh, was it the X-35, which was going to be this wedge-shaped vehicle with a linear aerospike engine down the back. They had half of it sitting on what was called the sled on top of the fuselage, and they would fire this linear aerospike rocket engine at Mach 3 plus to see if it generated thrust correctly. Right.

Uh, I mean, so that would — that’s an interesting data point because it shows that NASA wasn’t just taking these things and bolting small things on to test. They were making significant structural changes so they could deploy this kind of thing. They knew a lot about the environment in which they were operating. They were very familiar with the SR-71 Blackbird airframe. So anyway, yeah, these flights continued. The last time this airframe flew was in 1999, and that was the last time any Blackbird flew.

So there’s been some, uh, journalists doing some research, and one guy they talked to was Tim Connors, who at NASA was actually in charge of this program, or he was a propulsion engineer at NASA, and so he was in charge of this. He also worked on the F-15. So he had a lot of ideas about what might be going on, and he personally says he thinks that maybe they’re trying to get it flying again, and there’s probably a 25% chance that it might actually work in this form. But, uh, again, to be clear, NASA has not announced anything publicly at this time, and I am not privy to any special internal details. I’m merely guessing based on other people’s information.

Chapter 2: Sponsorship Break

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And now back to the video. So with all this in mind, what would be the state of the current hardware they have?

Transcript

Chapter 3: Engineering Challenges

Well, most of the things have been displayed in various locations. Some of them have been indoors. This particular one has been outdoors, albeit in the California desert for a long time. It’s a 1960s titanium structure. Uh, but honestly, the biggest thing I would be concerned about would be things like the hydraulics, things that are designed to move, things like the wiring, which, uh, you might age over time, although it is designed for high temperatures. But most importantly, those engines, the J58 engines, which are basically unique in this world, and those things haven’t been run since 1999.

Uh, there are obviously turbo machinery. They will have things like, uh, you know, fuel lines, oil lines. Well, actually, the fuel and the lubricant are the same thing, but they’ll have lines that run through it which will have fuel that has pooled in them, and that has probably broken down and turned into gunk over this time. Those big, uh, turbines, they sit on bearings. They haven’t spun. So one side of those bearings, they are going to have gotten slightly flattened out. And it’ll be an imperceptibly small change, but when you start this thing spinning at 7,000 RPM, you can bet that would be a big deal. So, these engines are very likely non-serviceable if they haven’t run for this amount of time.

Having said that, it’s not impossible to bring these things back. Uh, they are very likely missing a lot of the ground support equipment. Now, many of you might know the story about how when the Blackbirds first came out, there wasn’t like a — they needed a specialist start cart. He took a couple of like massive Buick V12 engines, put them side by side through a single clutch, and had a shaft that would connect to the gearbox, uh, the auxiliary gearbox or the, yeah, on the engine, and that would spin this thing up to 3,000 RPM so that the engine could finally actually accelerate on its own. And these things made a glorious sound as they were running.

Um, but of course, they would sometimes destroy these engines, and they were literally pulling these engines from junkyards, and they ran out at one point, and they had to switch to a different V12. These days, however, apparently there are air start systems which are more than capable of spinning up these massive J58 engines to the speeds needed. So that’s unlikely to be such a big issue. But there are other things. Uh, the simulator, there is a simulator which is on display in Dallas, and it runs on old hardware that uses like drum memory and things like that. I don’t know how you would train anyone to actually fly it.

So yes, uh, the spare parts. They can pull spare parts possibly from other museum pieces around the country if they were going to do something with this. Uh, documentation. Apparently, a bunch of documentation has been transferred from the Edwards Museum to NASA to look into this. So, again, we don’t know what they’re doing, but they’re certainly collecting materials that might indicate they’re trying to do something.

Another factor is the JP7 fuel, which is a very special ultra-low volatility fuel because this fuel would be the heat sink. You know, as it was flying at Mach 3 plus, the structure would be heating up, and they would run all the heating or they would run the fuel through the skin to keep the skin cool and structurally, you know, sound, and then that fuel would go into the engine. So, they needed a very low volatility fuel which wouldn’t, you know, flash instantly. Uh, so that special type of propellant or fuel hasn’t been made for a long time. Uh, the last time it was used was in an X-plane, a scramjet that flew about 16 years ago. Again, I have a video on scramjets if you want to watch that. Since then, apparently the stocks they have may have, uh, been disposed of. So, anyway, yeah, if you could get an SR-71 flying again, you could do some Mach 3 flying and stuff if you had all the stuff. If you didn’t have the special fuel, apparently it still works at Mach 1.5 because you can’t manage the level of heat rejection.

Transcript

Chapter 4: How the J58 Engine Works

Um, but why? I one of the things I’ve always wanted to talk about is how did the SR71 and the A12, all these aircraft with these magnificent J58 engines, how did they actually get to that speed? And you know, the engine is not a complicated engine in many ways. It is actually just a single spool turbo jet at its core. But around it, there’s a whole lot of other stuff that actually makes it capable of going at these speeds. So when they wanted to build when they started thinking about trying to go like Mach 3, they began looking at the engines they had and they realized that they would very quickly hit temperature limits inside these engines, right? They would end up with too much heat at the front of the engine for the compressors, too much heat at the back for the turbines. And so they needed a way to work around this.

And the way they work around this is that they have a series of doors throughout the engine which will reroute air. Sometimes they will dump air overboard. Sometimes they will suck extra air inboard. Sometimes they will take high pressure air from one part of the system and route it around the outside and then re-inject it at the afterburner. Once this thing is flying at about Mach 3.2 at, you know, designed cruise speed, the majority of the air is actually running around the outside of the engine and straight to the afterburner. And only about it’s less than 10% of the thrust is coming from that little core turbine running. They put just enough air into this so it can spin up so it can keep the fuel pumps running. So they can, you know, obviously run the cooling, run the auxiliary hardware, right? The accessory gearbox, that’s what they call it. All that stuff. But most of the thrust is actually coming from the engine behaving like a ramjet.

That intake at the front, that big spike that comes out is hugely important to how this thing generates thrust at design speeds. So they have like what’s called a spike intake. There’s a conical spike that comes out the front and then there’s a circular annular intake behind that. So this spike as it’s going through the air at high Mach numbers generates a conical shock wave and as the air crosses that shock wave it slows down, right? The next step is this air which is slowed down a little. It hits the lip of the annular lip of the intake and that will generate another oblique shock wave that angles across going in the other direction. And inside here you then have a few other shock waves and eventually end up with like what’s called the normal shock which is basically finally the air goes from supersonic to subsonic and it’s pretty much at 90° to the longitudinal of the engine. Right?

So it’s just going flat through the air has to go from supersonic to subsonic before it hits these compressors. And it has to be non-turbulent, you know, simple, you know, laminar as calm and boring as possible because if you have any ripples in this air, then the compressor blades will see slightly different air. That means that they can have a hard time. They could see momentarily air which is coming at the wrong speed, the wrong angle, and they could stall. And that’s of course called a compressor stall. And then that’s bad. The engine doesn’t work, you can end up with the gas surging back through the front of the engine, which is not good.

But yeah, on the SR71 intake, they basically have this cone, and the cone is actually angled slightly down, if you notice. It’s also angled slightly, there’s also a lateral component. And apparently if you swap the cones from one engine to the other, then you get a slightly reduced performance. Interesting fact I once heard.

But yeah, the cone in the center actually moves. It moves backwards over time. And what this does is opens up the intake and adjusts where those shock waves happen inside the intake. And they need all these shock waves to happen in exactly the right place because if they don’t, you can end up with too much pressure behind here. And what will happen is the shock waves move further and further forwards and there’s a catastrophic problem they have with the inlet which can happen with the engine when it’s running which is called an inlet unstart. Basically, they end up with too much pressure here. The normal shock gets pushed further and further and gets basically pushed out the front of the engine and suddenly your engine performance drops by 90%. And that can be really bad when you’ve got two engines thrusting and one of them suddenly loses 90% of its thrust. That has actually destroyed aircraft. There’s a famous story about a guy basically the aircraft breaks up around him and he, you know, falls to the ground and he’s fine and his buddy unfortunately isn’t.

So anyway, yeah, this intake at the front of the engine is designed to get as much air in as possible, slow it down. They then have a set of doors which can dump air overboard or they can bring extra air in before they get to the compressor depending upon the speed regime. And then inside the compressor, there’s like eight or nine stages, I forget, but around the fourth stage, they can then tap off some of this air, send it around the outside to the afterburner. And the J58 is the only engine that I know of which is designed for continuous afterburner operation. That’s where it gets most of its thrust from at operating speeds. Again, the core is doing very little. We’ve got this intake compressing at the front, a lot of air routed around the outside, and then the fuel is being injected, and you’ve got this massive afterburner out the back. And that’s basically how you fly this.

The throttle on SR71, like the first half of it is adjusting basically core engine speed. Once you get through that. Um, so and to switch on the afterburner, by the way, you need to use the ignition fluid. And I said that the JP7 is highly nonvolatile. To get it started, they use T, uh, TB, right? So they use tetraylin, which is this, you know, it’s a boron with four ethyl groups on it. And as soon as that touches oxygen, it just breaks down, creates a green flash, and you light stuff. It’s how SpaceX lights their engines. It’s actually pretty common for this situation.

Lesser well known, by the way, is that if they run out of that stuff, they do still have a way to light the afterburners. These catalyst masks, so you can fly the thing and heat these things up to get to the point where you can then try to light it and these will in theory light it. But, you know, it’s basically if you get in serious trouble, you still have the ability to light these things.

So anyway, these engines, they run through various different speed regimes, but ultimately they’re designed to operate at Mach 3.2.

Transcript

Chapter 5: Performance Limits

What then are the limits on it? Why is 3.2 like the design limit on this? Well, the design limit that the pilot is dealing with is the compressor inlet temperature, which I think is 800 Fahrenheit or 427 Celsius. That means that the air is coming in at, you know, mark 3.2 relative to the aircraft and then it gets slowed down to about, you know, subsonic speed. By slowing it down, basically you’re converting that kinetic energy in the gas into thermal energy. So the temperature rises, and that means it reaches the front of the compressor at, you know, 427 Celsius at the maximum, and they’re not allowed to go any higher than that because if they did, then the turbine inlet temperature would get too high and you would start to damage the turbines. I believe there’s also weaknesses at the front that can cause trouble.

Um, but, uh, yeah, the turbine inlet temperature is basically the limit. You also have problems with, like, the afterburner liner and stuff like that. If you’ve ever seen, there’s a famous image showing, like, the SR71, you know, the J58 engine firing on a test stand, and most people look at it and say, “Wow, look at all those mark diamonds.” And then the mechanical engineers are looking at the tube. The fact that it is almost, it’s really bright. It is, you know, yellow. It’s like putting out a lot of light ‘cause it is so darn hot. This is made from a lot of very special alloys. Things like waspaloy and hastoy, highly refractory, um, you know, steels which can handle these conditions. And it’s not that they’re strong; it’s that they are strong at these really elevated temperatures. So anyway, it’s a temperature limit. It’s not really a speed limit. And that means that under the right conditions, if you’re flying through very, very cold air, then you can get a bit more speed. And apparently, this has happened in the, you know, history where they were flying over cold parts of the planet. The air intake was getting lower temperature air, so they were able to run the engines at slightly higher temperatures.

But, uh, there’s also other things that affect the speed limit of the engine. That intake, right? Remember I said that spike? It moves backwards to adjust the positions of the shock waves and keep the shock waves inside the throat. Uh, basically that works down to about Mach 3.2, and then the spike has no place to go. It’s not designed to go any further back. Uh, and around Mach 3.55, I think the conical shock wave will start to get too close to the lip, and you have a chance of ingesting that shock wave, which, of course, then messes up all that carefully planned sequence of shock waves, which, uh, can lead to too much air going in, which can then lead to an airlet unstart, which is a bad situation. So you basically run out of unstart margin as you get faster and faster. Um, so that’s another problem that you have to deal with.

Uh, you also, yeah, once you start going faster and faster, the JP7, you start to reach limits on how much heat you can dump into that. Uh, you start to hit, um, like airframe temperature limits where the, you know, you’re basically heating up this titanium, and it will start to get weaker at certain temperatures. Control surface hinge points, those need to be able to actuate, and they will start to reach temperature limits as well. Normally, the airspeed is something like 400 knots effective airspeed. They fly at a constant angle of attack most of the time. If you start to go to higher mark numbers, it will require changes to the angle of attack, which can lead to, uh, interesting changes in your stability of your aircraft, and apparently, you lose stability margin as you go faster and faster. So look, this thing was built with, like, Mach 3.5 as being way out there. Or they were like, mark 3.2 is where it’s at. Definitely, they could go a little faster than that, and apparently, they have gone. Uh, they’ve done dashes at up to 3.5, but yeah, you know, you’re hitting a hard stop out there, uh, because of various parts of the engines.

Transcript

Chapter 6: Why Bring It Back?

So all that is to say is that we pretty much understand the SR71, uh, in a lot of detail, and we does mean that we definitely understand that sort of speed range that it operates over. Obviously, these things flew for hours at a time. The operations were somewhat, um, you know, routine at that point. So, you know, experiments in that range, uh, we’ve done a lot, and a lot of that stuff we can model with CFD. If you want to go faster, hypersonics is all the rage. You can just go and buy, like, a test launch from a Strat Launch and fly your payload on the Talon, or you can buy a launch from Rocket Lab and fly on Haste.

Uh, why would something around the more pedestrian Mach III be interesting? I mean, after all, you can actually also just get, like, missiles, hang them off a B-52, and fire those, and have your payload fly at that speed. That’s how they were, you know, starting these scramjets. Uh, well, maybe they need something that is really big. Maybe they want to actually test something that’s really big, like an engine, because, as I said, those J58 engines are probably unserviceable. Maybe there’s a new jet engine out there that’s designed for continuous operation at, uh, Mark III plus speeds. And I will point out there is a private company called Hermes who want to build a Mach 5, you know, jet of some sort which is going to use, like, a combination turbine and then ramjet. So it actually has some similarity to the J58. Their engine, I believe, is based on the F100. Um, I’m not saying that’s the engine. It’s probably the wrong size. It may be the wrong shape. It might be the wrong geometry. But if there were a need to test an engine on an aircraft in that speed regime, then having an SR71 do it might actually be the best option.

And having NASA be part of it would definitely, they would definitely be interested in that. After all, the guy running NASA is also very interested in, say, resurrecting the F-14. So resurrecting the SR71 is absolutely in line with personal goals of [laughter] of Jared Isaacman, and I fully support that because, boy, that’s, uh, the sci-fi future I grew up with, and it is now definitely the sci-fi past. But yeah, maybe there is some new engine out there that they want to stick on this and actually test it. Does that mean it will be able to go faster? Uh, well, you know, they might be able to make the engine work a bit faster, but they’re still going to start to run into limits with airframe, attitude, center of gravity, stability, and stuff like that.

So, they might need extra, uh, modifications to aerodynamics and stuff like that. And NASA, as we said, they’ve had that capability in the past. They made significant modifications to the SR71 for the laser test. And so, it’s entirely possible if they needed to do that that they could do that for this one. Uh, I’m not saying that’s what it is, but it would be pretty cool if that’s ultimately what it was, sort of, you know, in terms of, like, of what would be interesting, right? If they just powered up an SR71 and they got it to taxi, that would be actually pretty cool because it would show that you’ve been able to take this thing and take it out of a museum and get it running again at some level. If they got it airborne, that would be okay. It doesn’t need to fly. Maybe that’s only flying on regular jet fuel and it’s not flying at high mark numbers. It could still fly supersonic. That would be okay if they could fly it at mark 3. Well, that would be a return to the glory days. That would be very special.

But yes, if they say could put a new engine in it and bring it back and make it operational again, yeah, that would definitely be, uh, something, something that that would be, that would be some S tier stuff there. But honestly, it would be an S tier sidestep on the way to a more modern aircraft with modern understanding of the aerodynamics and performance that could actually push through that and perform perhaps even better. I don’t know what is going on here. I’m just watching it all play out. Uh, and don’t worry, when I do find out more, I will be letting you know because, uh, this is an interesting story for me. I’m Scott Manley. Fly safe.

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