When it comes to the future of Tail 844, the SR-71 Blackbird that mysteriously disappeared from NASA’s Armstrong Flight Research Center, few people have more insights than Tim Conners. When he worked at NASA in the 1990s, Conners was the lead propulsion engineer for the agency’s Blackbird program. He worked extensively on 844 and has an intimate knowledge of what made the iconic aircraft tick. Now, he brings an insider perspective on NASA’s secretive work to get the Blackbird back in the air and speculates on what it would take to do so, as well as the famed jet’s possible flight test role for the agency after 27 years of dormancy.
Late last month, we wrote about how satellite imagery taken over Armstrong showed that Tail 844 had been missing since at least May. The revelation was first made by Steve Trimble, Aviation Week‘s defense editor and friend of TWZ. It came after NASA Administrator Jared Isaacman cryptically teased plans for a new high- and fast-flying X-plane with a silhouette of an aircraft that immediately drew comparisons to the Blackbird. Trimble reported just this week that NASA had been talking to ex-SR-71 program personnel about coming back to work on the aircraft. This confluence of events has led to rampant speculation about whether NASA was planning to resurrect the Blackbird and for what purpose?
In an exclusive interview with TWZ, Conners, now technical director for advanced weapons systems at Tiberius Aerospace, gave us his take on NASA’s Blackbird revelations and insights into what NASA is working on and how far along they are in the process.
Some of the questions and answers have been slightly edited for clarity.
Q: Tell me about your background with the SR-71 program. How did it begin? How long did it last? And what did you do?
A: So that basically fell in my lap when I was an engineer at NASA’s Dryden [Flight Research Center] back in the early ’90s when NASA took delivery of three of the airframes when the Air Force was retiring the fleet. So NASA got two A models and a trainer. Obviously, tail number 844, which is NASA’s designation, is the one that’s getting all of the attention right now. But those came to Dryden in the early ’90s.
By luck of the draw, I was in the propulsion group. We were short-staffed for a number of reasons, and they needed an engineer on Blackbird. And I had been with NASA for about three or four years at that point, and I got tapped to prepare the NASA side of the mission for the upcoming research flights. So I had a few years to get familiar. That was a part-time job, by the way. I also owned the F-15 fleet at NASA as a propulsion engineer, and that was occupying a lot of my time, but it did give me an adequate amount of time to get familiar with the way that the airplane operated, at least from the propulsion standpoint. And then we began doing research missions in ’96. I left NASA in ’98, but I was able to support the program through two years of flight testing and all the years of preparation for those two years.
Q: Tell me more about your role with the Blackbirds.
A: I was lead propulsion engineer on the NASA side. So what NASA would do is they would assign disciplinary leads across from their industry and government counterparts. So Dryden’s disciplinary leads, their job was basically to make sure that any experimental packages were integrated safely with the airframe, and that we could execute the proposed test missions safely and successfully. I owned propulsion and I also owned performance. So if you recall the Lockheed Linear Aerospike rocket engine activity, that package weighed 20,000 to 25,000 pounds and was mounted externally on the back of the SR-71. That was a drag issue, obviously. So part of my role was to make sure that we could actually accelerate through the transonic drag rise with that package and get out to the target test conditions.
Q: There is a tremendous amount of interest in seeing the Blackbird fly again. The biggest question seems to be why? What kinds of experiments or research would an SR-71 provide that couldn’t be done more effectively with a modern aircraft, rocket or unmanned vehicle? Can you walk us through some of the reasons NASA would like to see it in the skies again?
A: Yeah, that’s a question that everybody’s been asking. Why? I’m speculating, although I do have a good feel for where this is going. So bear with me.
They probably are not going to do this for — or trying to do this — for aerodynamic reasons. You can do CFD [computational fluid dynamics]-based modeling in this speed regime all day long and very accurately in this day and age. It does not take a lot of time or money to do that. What you cannot do is an accurate representation of a new type of engine integrated into a high-speed airframe. You can do the conceptual modeling of it. Of course, it’s difficult to get the final installed answer, especially if it involves an engine that operates at long duration. That is where I think they’re going with this. I believe that they’re developing basically a high-speed engine test bed. That would make the most sense to me.
Q: That’s something you couldn’t do with a more modern aircraft or rocket or unmanned vehicle?
A: That’s a good question. But you know, probably two-thirds of that battle is just developing the airframe. It does depend on the size of the engine that you’re after.
Obviously, if this were a Williams engine or that size class, you could get by with probably a bespoke drone to do your testing. That wouldn’t be that expensive. If your goal is to test something that’s man-rated or very large, like a J58-size engine, what better way to do it than use an airframe that’s already proven to fly at that speed?
Q: Were you asked to join a team at NASA tasked with getting a jet back in the air? Who else was asked, and what kind of team were they building?
A: I did not receive an offer. There was a tongue-in-cheek text that I got earlier in the year that said, ‘Hey, Conners, how would you like to help get the Blackbirds flying again?’ And that was from somebody who was positioned with inside information. That is where I first heard of this. This was back in spring, but nobody formally reached out to me.
I believe that the only one that’s been tagged so far, as far as a retiree, was Mike Relja. Mike was a crew chief on the Blackbird, and that makes sense that they would potentially want to pull on him. But there was no formal offer, and I tell you what: If somebody approached me to work it, I don’t think I could turn them down.
Q: Do you know where the idea for this project came from and who is in charge?
A: I don’t have an answer. I’d love to know as well.
Q: What can you tell me about this effort? What are the latest developments in this project that you know of?
A: So what I’m hearing is that they’re looking at doing power-on testing fairly soon. That’s pretty big. So of course that’s not engine power on. That’s external power applied to the airframe, seeing which systems still live, which ones don’t, and then moving from there. So that would be an expected first step.
It’s an encouraging step. That means NASA would have gotten beyond cracking open all the bays, inspecting the interior, making sure that the thing at least passes visual inspection for airworthiness from that standpoint.
Q: Have they actually gotten any systems working?
A: No, they’ve done the visual inspection, actually, putting electrons on the airframe. [To get systems working] would be the next step, but it is forthcoming, from what I understand.
Q: What is the timeline?
A: That’s supposed to happen within the next couple weeks.
Q: Really? Where is this work taking place?
A: That I do not know for sure. Although I assume it’s happening at [NASA’s] Armstrong [Flight Research Center].
Q: So what is going to happen?
A: That’s a good question. Let me tell you about what I heard more recently, and then you can begin to connect the dots. JP-7. People ask about the fuel. I think it’s pretty well known that NASA had a huge amount of JP-7 stockpiled that they received from the Air Force back in the early ’90s. So much that it was in a dedicated tank, like one of the giant jet fuel tanks at Edwards Air Force Base. You know, the tanks up on the ridge.
From what I understand, that supply unfortunately was discarded about 20 years ago, and JP-7 is a unique fuel. Obviously, low volatility. When I poked at what might be the way forward there, it didn’t sound like that was a showstopper. I got the impression that there’s been dialogue underway with refineries for a replacement or a surrogate that would work. So I went from being deflated, hearing that the fuel was gone, to being encouraged that potentially there was a surrogate workaround.
But that led to the question regarding the engines themselves, so the feedback there was more discouraging in that it looks like the engines are indeed unserviceable. I don’t believe that is based on an actual attempt to run them. It is based on inspection. Probably no surprise. They’ve sat idle, you know, for 27 years. That is what led to questions going back and forth regarding how the airframe would be powered. And that’s what led into where, if you connect the dots, that’s where the airframe would be used as an engine test bed.
So different engines, they would have to be high-Mach bypass systems. We can speculate on which engine company might be developing those systems, but yeah, I don’t want to give it too much away because I don’t want us to lose the inside information that we got.
Q: Are they working on a completely different engine to power Blackbird?
A: I don’t know that for sure. I think if the J58s are not an option for powering the Blackbird, you either button it back up and walk away from it, or you go bring in engines that are already under development that we’re not privy to at this point in time. But there’s no other option. So what are we going to use? It’s not like we can slap in F100s or F110s. They’re not going to cut it.
Q: Obviously, restoring an aircraft sitting out in the elements for years into one able to withstand the rigors of Mach 3 flight is one hell of an undertaking. In your mind, what are the biggest hurdles to this endeavor?
A: Number one would be the engines for sure. Number two would be anything that’s made of elastomerics. Plastics, Wiring. Covering connectors. All that stuff degrades and oxidizes with time. You can imagine what frayed wiring and broken wiring insulation – what kind of havoc that would create. What Blackbird has going for it is that all those casings and connectors were built for the rigor of sustained Mach 3.2 flight for an hour, an hour plus, so they are not going to deteriorate quickly. The question is: Have they deteriorated in 27 years? So, if the answer is not a significant amount, then we’ve probably addressed one of the biggest questions – other than the engines – regarding reviving the airplane.
Q: Do you think NASA is going to attempt to just fly tail 844 largely in its original configuration, or will they deeply modify it or build something new based on it?
A: Completely unknown. They definitely have the ability to modify the airframe, right? They did it before in the ’90s to carry the Linear Aerospike package. That was a huge undertaking on the airframe itself. They did it successfully. Armstrong still has a pretty deep bench in that area, so if they wanted to take on modifying the titanium structure, I think they could do it.
But it’s a good question. Again, that would probably point to aerodynamic studies, and if it were me and my dollar as a taxpayer, I would lean on computational studies to get those answers. That’s what I tend to do in my day job is forego testing in lieu of computational when it involves external aero, but it’s when you do the integrated propulsion in this speed regime, that’s really when you need test data from the actual operating conditions.
Q: As opposed to digital modeling?
A: Yes. For instance, say the aerodynamic databases for Blackbird are gone, which they might be. I know there are simple aerodynamic models that still exist, but like a true high-fidelity model that would go into a piloted simulator, that could probably be regenerated fairly quickly. Probably on the order of months computationally in this day and age. So I think simulation capability could be stood up in fairly short order. That of course will be foundational for the pilot training task.
Q: We’ll talk more about pilot training later, but first I want to ask about modernization. If NASA were to inject modernized features into the SR-71, what would you like to see? And what makes the most sense in terms of material science, avionics, propulsion and so on?
A: I’m not a materials expert. I think it would be really interesting to see how the airframe could be optimized using adaptive flight control capabilities. So, if the flight control system could be digitized, I think that would lead to some very interesting in-flight experiments. I doubt that that would be. I could be wrong, but if the goal is to get the airframe back up as a propulsion test bed, you don’t need to cut out the hydromechanical flight control system and replace it with a digital one.
That all said, what I would like to see is what we talked about a few minutes ago, and that’s basically modern high-speed engine technology. So what could be done? The J58s were low operating pressure ratio systems. What could be done with a modern, digitally controlled, multistream, high-Mach engine, I think, would be truly trailblazing.
One of the reasons why there’s interest in this speed regime, it was neglected for a number of years. The focus was on hypersonics. If you proposed anything going back, say, 15 years in the Mach 3.5 speed regime, it was ignored. The glitz and glamor was on hypersonics. Hypersonics is great tactically for certain scenarios, but the weaknesses of hypersonics are now becoming apparent.
And as far as countermeasures, hypersonics still has a place. Don’t get me wrong, but every system cannot be hypersonic from an affordability standpoint. So, now you’ve seen it over the last, say, five years. A lot of systems are coming back on the scene that operate in the Mach 2 to Mach 4 regime, and there’s a reason they’re all fitting in there, right? You stay below the speed limit that requires more exotic metallics. You stay in the titanium regime. You can fly, of course, up to [Mach] 3.5 with brief excursions up to about [Mach] 4, so that is tactically relevant against a lot of military targets and defensive systems. So here it is. You know we now have a potential flying test bed that can carry engines in the J58 size class.
Q: How much could a project like this cost, and is it really economically feasible? How long do you think it could take?
A: I’ve been thinking that over, and I think it depends on who does it. I don’t want to disparage my former government brethren. I had great respect for the folks at NASA when I worked with them, but one of the reasons why I left the agency is because it was becoming so risk-averse. That was adding bloat to everything. And what we used to do quickly, we no longer could do quickly or cheaply at what was Dryden Flight Research Center, so that is what concerns me.
If NASA could operate with the agility that it had, if Dryden/Armstrong could operate with the agility it had 30 years ago, they could do this work in probably a few years. I would say again, it would depend on what exactly they need to do to the airframe. If it’s to resurrect the airframe and bolt in new engines using existing interface hardpoints, that would go much, much more quickly than doing extensive airframe modifications.
Q: Given that 844 has been sitting idle since 1999, what would be the very first thing you would want to inspect or test before even considering putting it back in the air?
A: Exactly what I’m hearing the rumor is that they’re doing this. What is the condition of all the components in the airplane that are flowing electrons? Because if the entire airframe is shorted out, you know how it is.
If you have a car where you’ve hooked up the battery cables backwards – I had a car once where somebody jumped in and did that. It ruined the car because I was chasing shorts constantly, constantly breaking down in the months that followed because the wiring was compromised, melted, bubbled all over the vehicle. And then it would get wet. You get shorts. That, I believe, is what one of the objectives of power-on testing is. To make sure continuity still exists, reliable continuity throughout the airframe. So that’s exactly the first step.
I would say the second would be hydraulics. That vehicle is hydromechanical. So what is the state of the actuators and whatnot?
Q: And you said that work is taking place now?
A: It’s certainly being inspected. That was one of the reasons why they pulled it off of the display pad at Armstrong. But that work has been going on for a couple of months, and it certainly seems that there was at least reason to be encouraged and to go forward with this next step. Otherwise, they would have just towed it back to the parking spot.
Q: And the next step is testing the systems?
A: That is correct.
Q: We touched on this a little before, but how realistic is it to get an SR-71’s J58 engines operational again after nearly three decades of inactivity? What would worry you most about those engines? How many are left?
A: Well, that’s a good point. As far as [engines] that are readily available, there are several that are at the [Air Force Flight Test (AFFT) Museum at Edwards AFB]. I believe they’ve been stored outside. But if you consider all the museums around the world with Blackbirds on display, almost all of them have installed J58s, and there’s usually one sitting alongside the airframe on display, so there are plenty of engines. Whether or not they’re serviceable, that of course is the question.
But probably the biggest problem with an engine – well, there are several with a gas turbine that sits unmoved for decades – it’s going to be that you’re going to flatten the bearings. Probably not visible to the eye, but rotating turbo machinery doesn’t like flats on the bearings. So for obvious vibration reasons, you got that. And you’ve got the seals. Seals are going to crack. Trapped fuel is going to turn to gunk and clog up lines. That engine was all hydromechanical, of course, or no digital controls on that because of the heat involved. So fuel hydraulics played a big role in that engine.
There is likely a lot of goo in those lines. I believe that’s why they’ve essentially been written off as unserviceable. I was discouraged because one of the questions I asked that I didn’t get an answer to was: Did anybody try to run the engines or pull them apart? But I don’t even know if the instructions exist to unstack a J58 at this point. I’m sure it could be figured out with the right people, but you know how it is. Pulling something apart is a lot easier than putting it back together.
Q: So there’s no manual for that anymore?
A: I don’t know if there’s a manual specific to that. Like I told Steve [Trimble] at Aviation Week, there certainly are operating manuals. You’ve probably seen the pilot’s manual for the SR-71A. It’s a beauty. There are a lot of copies online. You can get PDFs of those. They are very well-written, huge manuals. I know prints exist for the airplane. Those were in the keeping of the Edwards Museum. I believe those have been handed back over to NASA. So, it’s not like there’s a complete dearth of information.
When I was at NASA, I was the person who received everything that Pratt & Whitney had left on the J58s when the Air Force decommissioned the program, and that information was in two or three smallish boxes and consisted of hard copy code printout or printout of numerical data, along with some magnetic reels of code. It was not much. And I was told at the time the only reason I received that information was somebody missed it when the Air Force gave the destruct notice. It was under somebody’s desk, so it was not much in the way of knowledge transfer, unfortunately.
Q: What did you do with all that?
A: I left it behind in 1998 when I left NASA.
Q: What happened to it?
A: I have no idea. Hopefully, somebody scanned it. But again, that was J58 info, right? So if they’re going with a new engine, they’ll have the full digital models for those new systems. And I do believe that recreating the aerodynamic database, including inlet performance, that kind of data can all be regenerated fairly quickly with computational tools.
Q: We touched on this a little bit before, but how difficult would it be to reproduce the JP-7 fuel that powered the Blackbird? It would need designated tankers too, correct?
A: So that was one of the questions I asked is whether or not that formulation exists still. The answer I got back was that essentially a refinery should be able to recreate a suitable surrogate. If you think about it, JP-7 was unique in that it had a very low volatility characteristic.
What I’ve learned about Jet A from some of the ramjet work that I’ve been doing is that it has a ridiculously low volatility too, of course, by design. So I don’t know that JP-7 is that far apart from the chemical characteristics of a Jet A-class fuel, JP-8-type fuel. JP-8 was a significant change from JP-4, so the Air Force was using JP-4 in their fleet, and then moved to JP-8 to be consistent in the ’90s with the Navy with their formulations. That’s a lower volatility fuel, and at NASA we had to recharacterize the flight performance of all of our jets with JP-8, but it worked fine.
We were concerned about operability – that we were going to have flameouts and engine relight and flight relay problems. Those did not materialize, so I don’t want to oversimplify it, but I am thinking that you might be able to take an existing Jet A and with the right additives knock down the volatility to a level that’s safe for flying in the Blackbird.
Q: What would need to happen to have aerial refueling jets be able to handle fuel for the Blackbird?
A: There were dedicated JP-7 tankers for the Blackbird. I don’t know if they can take an existing system and flush it. It would depend on the formulation, right? JP-7 was notorious for its unseemly characteristics. It was toxic.
I had a shirt that got dripped on when I was standing under the wing of the Blackbird once, and I had to throw it out. I could not get the stink out of that shirt from the JP-7. It was a weird fuel. So if you can get one that’s more aligned with the fuels used in the service, then I don’t believe that’s going to be a showstopper as far as tanker support, but you do know tanker support is going to be required for that airplane.
Q: You said the JP-7 fuel stank. What did it smell like?
A: I just remember it turning my stomach. Like I kept smelling something as the day went on, and I reached over and saw a stain on my shoulder. I don’t recall what happened the rest of the day, but I just remember being repulsed by the odor and then not being able to get it out when I washed the shirt.
Q: Beyond the fuel, the SR-71 depended on a huge ecosystem of specialized equipment, fluids, personnel and procedures. Which parts of that infrastructure would be hardest to recreate today?
A: That was something that Mike Relja pointed out when he talked to Steve Trimble. That’s a good one. You probably heard that the J58s were started with a start cart that was basically a bank of Buick 12-cylinder engines, all next to each other. It’s a beautiful-sounding system, but very unique. But what is starting, you know, other than you’re either doing a power takeoff via shaft, or you’re using compressed air. It depends on what the engine demands. So I think the start cart development would be fairly straightforward.
But there is a lot of specialized equipment, like Mike pointed out, the wings when they’re split up, they are held in place by a specific scaffolding. The way the engines were craned out of the wing required special equipment. Pulling the inlet spike off that required a special cradle. Those are not insurmountable, but you don’t want to wait till the last minute to realize you need unique equipment. So it’s all got to be taken into consideration.
Q: Could existing SR-71s in museums realistically be used as sources of spare parts for 844, or would cannibalizing those aircraft create more problems than it solves? Were those airframes left structurally intact?
A: I believe that was the agreement with the Blackbirds. If a museum were to put one on display, there was a certain expectation regarding care and maintenance. Not so much maintenance, but care and preservation. If you think about it, many of them are under roof in climate-controlled facilities. I know several of them that are preserved like that, including one here in Tucson. That, of course, is the best place for preserving anything with elastomerics and plastic. So I think it’s encouraging that so many of them have been so well cared for. Again, it’s going to come down to which components, regardless of whether or not they’re indoor or outdoor, which components are going to fail first, and I believe that’s the exercise NASA is looking at.
Then you’ve got to start beating down, chasing supply chain sources for some of this, and you know the nightmare that’s out there with supply chain and aerospace. So it’s not going to be an easy task. I don’t want to act like it is. I don’t think it’s insurmountable though.
Q: So these aircraft can be used as sources of spare parts?
A: Sure, absolutely.
Q: Is anyone with a Blackbird already contributing parts?
A: I know that the Edwards Air Museum is contributing what they can as far as spares and prints. I don’t know who else, although I believe the second NASA SR-71A went to the Evergreen Aviation & Space Museum in Oregon. I would expect them to be in the loop.
(TWZ reached out to the Evergreen to find out what, if anything, it is contributing to this effort.)
Q: How difficult will it be for modern test pilots to fly tail 844, or whatever aircraft is created from this project? What would actually be the hardest part of training a pilot to fly the aircraft today? Do you think they will convert it into an unmanned configuration?
A: Well, that would be a difficult airplane to convert to unmanned, unless it went with a digital backbone, and like I said, I think that would be an enormous undertaking. It’s not unheard of. NASA, along with McDonnell Douglas, converted a couple of F-15s to all-digital backbones before the F-15E program began. It can be done. It’s just expensive. It’s not easy.
But the piloting task starts with a good simulator, right? The piloting task is absolutely a big deal. I saw it firsthand at Dryden. That said, it took a couple years, probably two. I would say that’s about right for the Dryden pilots, who are pretty good at what they do, to learn to fly the Blackbird safely, and that was with the use of the two-seat trainer, which we’re not going to have this time.
So I think the key to this happening is getting a digital sim together very quickly, and it wouldn’t surprise me if NASA has begun this process already. Getting that together, plus getting the former pilots who are still with us in the seat to make sure that it aligns with what they recall as far as the unique features of the airplane.
I have 100 hours of stick time on the Air Force Blackbird simulator. I’m not a pilot, but I used to pre-fly the maneuvers for the pilots and NASA on the high-drag missions, so I’m familiar with the way the airplane flies up and away, and it is a bear to fly. It is not easy. So training is not insurmountable. Like I said, it takes a good, high-fidelity sim. NASA is expert at building those kinds of simulators, modular simulators quickly. In this day and age, we should be able to put a high-fidelity sim together fairly quickly for training.
If you recall, the cockpit is an analog nightmare on a Blackbird. Breakers everywhere. Dials everywhere. I doubt that somebody suggested that we go with an all-digital cockpit. That would be so much work to do. But if we go for it with just a pure analog cockpit that we used previously, that’s going to require a lot of familiarity. I do believe that the training systems might still exist for that. It would just be for that airplane. It would just be getting them all cobbled back together.