Paul Czysz on Hypersonic Aircraft & Suborbital Spaceplanes

It’s a name that evokes awe in the aerospace industry — Aurora, a Mach-6 hypersonic aircraft that nobody’s sure exists. We interview hypersonic pioneer Paul Czsyz for the inside scoop on Aurora and a next-generation Mach-15 successor that may be capable of even reaching space…

Paul, an Air Force officer recently told me that a colleague of his paid a visit to one of the big R&D test-bases in the early 90’s and saw a high-dollar budget item for “Aurora” on a financial report. He thinks that this Mach-6 hypersonic aircraft exists, but he isn’t sure — what do you think?

It could exist. There’s no magic required to build it. I was convinced that the group I was with at McDonnell-Douglas in the mid-60’s could have built it back then.

Paul Czysz, presenting at the 2006 STAIF Conference

We built two hypersonic aircraft models for Mel Buck over at Wright-Patterson that we tested for pressure measurements, force measurements, and thermal mapping to get the heat-transfer rates. Those models went in every tunnel we could find — from the low-speed tunnels all the way up to the Mach-6 and 8 tunnels. We had over 1,300 hours of wind-tunnel test-time on those models…

So at least technically, Aurora could be part of our military arsenal, then. Have you ever seen any evidence that aircraft like this might really be in service today?

If they were built, and that’s the big question. I’ve had strange calls in the evening by people who were telling me, “I used to work with you, and I’m standing next to the aircraft that you’d recognize”, and then they hung up. I think the rumor mill is probably right about Aurora.

Those strange calls make sense, though, in the context of your remarkable background in hypersonic aerospace engineering, culminating in your role as the chief scientist for the National Aerospace Plane project, touted by Reagan as the successor to the Space-Shuttle after the Challenger tragedy in 1986.

Well, I started out at Wright-Patterson in 1958, but when Sputnik went up we were all re-assigned: in my case, to a high-temperature hypersonic wind-tunnel, working with the people from the Flight Dynamics Lab. Mel Buck was one of the fellows in charge of the aircraft side of things, and Dick Newman and Al Draper were on the hypersonic-glider side, working on the type of vehicles we call spacecraft today.

Artist’s rendering of the Mach 6 Aurora spyplane (PopSci)

When I left in ’63 and went to work for McDonnell Aircraft Company, one of the first things that I got involved with was their hypersonic impulse tunnel, and we were doing some Mach 12 testing of one of the vehicles I was working on at Wright-Field.

In ’66 I joined the advanced design group over at McDonnell, and one of the projects that I was working on was a Mach 6 hypersonic vehicle that would fly unrefueled in a combat situation about 1,500 nautical miles, with about a 4,000 nautical mile overall range.

There were a couple of different versions of it — one was to shoot down submarine launched ballistic missiles launched off the coast of the United States, and the other one was essentially to interdict soviet ships that were coming through the GIUK gap.

“In ’66 I joined the advanced design group over at McDonnell, and one of the projects that I was working on was a Mach 6 hypersonic vehicle…”

If you launch a Mach 6 interceptor out of something like the New York area, by the time it gets to the GIUK gap, even the fastest soviet ships could not have moved more than about 10 miles. So using the last known position of the ship provided by even simple radar contact, the aircraft can pull a 3.5 gee turn, it can fly a circle around the last known contact point to find the ship that it’s looking for.

That’s not a difficult maneuver for this aircraft — in fact, a Mach 6 interceptor burns less fuel in a 3.5 gee turn than the F-15 does at full-afterburner. So you’ve an aircraft that can rapidly reach the ship’s last known location and fly a circle around the last known contact point — whether or not ship has changed direction, it’s still going to be inside that search radius, making this a highly effectively quick-response weapon.

Well in terms of the hypersonic concept, I’m wondering if this originated out of the need to outrun enemy missiles. Apparently the strategy of the U-2 was simply to fly higher, and I’m wondering if Aurora is attempting to fly faster as another solution to the problem?

It’s not about outrunning missiles — it’s about response time. In other words, at flank speed, a cruiser like the Kirov can run at about 32 knots, which is 32 nautical miles per hour. The horizon for a ship is about 6 miles away, so you have to be up in an aircraft to see it — so if you’re going to detect it, you have to get there before the ship travels too far.

In other words, you have an increasing radius for the ship’s probable location, and if you have a response time that might be 4 to 6 hours to reach the last known contact point, it becomes that much harder to find it.

Yes, with a slow response time, you’ll never find it — the ship will be completely out of your search range. However, if you can get there in 45 minutes or an hour and a half, then the ship will still be inside the circle that you fly around its last known position.

Now the other application for this Mach 6 aircraft is intercepting ballistic missiles. If a submarine pops up just off the coast and launches a ballistic missile, if you have a the right kind of Mach 6 aircraft with a good hypersonic kill missile, then you can still hit that ballistic missile while it’s climbing, so you can use it to help protect the United States from nuclear attack.

There were a whole bunch of applications — these were powered by air-turbo ramjets, both Pratt & GE designs — we had vehicles that went all the way from a Mach 4 deck-launched interceptor for the Navy to vehicles that went all the way up to Mach 12. These ended up in a study for NASA called the “Hypersonic Research Facilities Study”, which essentially was a comparison between ground-test facilities and flight-test facilities to see which ones give you the most information to build an operational high-speed aircraft. The flight-test vehicle won hands-down, because the ground-test facilities were so expensive, and they could only work on a fraction of the problem.

Out of curiousity, in terms of actual, tested aircraft, what’s the fastest speed that they’ve ever gotten a hypersonic aircraft up to?

We don’t know, because at least publicly we never completed the hypersonic facilities study — but there were programs in existence inside the classified community that may have taken the research farther than we did. The X-7, which was a Lockheed scramjet research vehicle that recovered itself with a long spike sticking in the sand over in the desert supposedly exceeded Mach 7 or 8.

My group actually tested engines in aircraft past Mach 12 — we had data on some of our hypersonic glide vehicles when the tunnels were still operating all the way to Mach 20 or 22 down in Tullahoma.

Now you’ve talked about losing test-pilots during this process also, right? I remember you saying something about the aerodynamics being very counterintuitive at hypersonic speeds…

No, no — we didn’t actually lose test-pilots — I was referring to the aerodynamics during training in a hypersonic flight simulator. The bottom of the aircraft in a Mach 8 to 12 scramjet is the engine. Now the way you get an engine to put out more thrust is to increase the capture area of the engine — that’s how you get the variable capture inlet area on the F-15 — you can control the thrust level potential by controlling the airflow to the engine.

Example scramjet engine (NASA)

So if you have a scramjet vehicle, and you want to increase the thrust of it, you have to increase it’s angle of attack — not by much, only by about 2 or 3 degrees. Nevertheless, as you advance the throttle, the nose comes up, and that’s very counterintuitive to a pilot, who will think that the nose coming up when you advance the throttle means that there’s something wrong.

So in the simulator, these pilots were not pulling up, but they were advancing the throttle. Again, in order to get more thrust out of a ram-compression engine you have to increase the capture area, and the way that you increase the capture area is to pull the nose up — and since the whole bottom of the aircraft is the engine, it increases its capture area.

Most people probably weren’t really aware of the rumors about Aurora until Bill Sweetman’s Popular Science article about it in 1993. Now in that article, they discussed a “string of pearls” UFO reported traveling westerly over northern California, followed moments later by the same traveling back over SoCal –which enthusiasts took to be evidence of an external-burn engine they thought proved Aurora’s existence.

“Donuts on a chain” is actually the common term — but this stuff goes back a lot further than those UFO’s reports that Sweetman was talking about — the aircraft that we were involved with go back at least to ’64 or ’65, and I was convinced while I was with the Advanced Design Group over at McDonnell in the mid 60’s that we could have built one of these.. It wouldn’t have even been a challenge.

All of this “donuts on a chain stuff” is pretty basic — if you’ve ever watched when Fred Billick used to run his scramjets up a John’s Hopkins you’d get a really good visual of what’s going on here. There’s no such thing as an absolutely steady shock-compression engine. Little changes in the atmosphere and other variables cause the shockwave to move back and forth inside the engine, which changes the compression slightly. This causes the exhaust-glow to pulsate — what that means to me is that it’s an engine like Fred used to build. There’s no magic to it.

Now would a hypersonic aircraft like this be much larger or heavier than a conventional fighter interceptor?

Our Mach 6 interceptors weren’t built like the X-15 prototype, which used a steel-alloy hot-structure that served as a heat-sink for aerodynamic heat-loads. Ours were built with metal thermal protection-systems over a lightweight aluminum structure, so most of the thermal energy was radiated away into space, and for those vehicles we were running somewhere around the weight of a DC-9. These were neither exceptionally large nor heavy vehicles — they were somewhere on the order of 60 to 70 feet long. That was for a single person combat vehicle — now for a multi-crewed, very long-range vehicle, you might start looking at something with a size and weight comparable to a 747.

Well, wasn’t the larger vehicle design closer to the goals of the National Aerospace Plane (NASP) project that you worked on later in the 1980’s, for hypersonic passenger & cargo transport?

Well, it’s hard to say what NASP was aimed at. Between about ’76 and ’83, I was involved with some special programs at McDonnell. On the last day in July in 1983, I was out there on Thursday and I was supposed to leave the next morning to be home for the weekend.

Artist’s rendering of the National Aerospace Plane (Going Faster)

Anyhow, I got a call from one of the Directors who said, “I happen to be out here for something — you’re not going home yet, you’re going to meet me at the Air Force station tomorrow for lunch over by the Aerospace Corporation on Sepulveda. Maybe you’ll make it home by Monday — we’ll see.”

So I show up for lunch over at the Air Force station, and Harold Ostroff was sitting down at this table with a big group of military & civilian guys in business suits, and as I walked up to the table, he turns to the other guys sitting there and says, “I’d like to introduce you all to the new head of McDonnell’s Advanced Aerospace Program.” Anyhow, I didn’t know anything about this beforehand, and when he said it I looked around a bit for the person he was talking about — and after a second I guess that it finally sunk in that he was talking about me.

So that was how I found out about it — I had a deputy program manager from Huntington Beach, and there was a group there from Aerojet — Don Kissinger, Mike Hamel, and Ron Samborski — that were there to talk about the air-turbo ramjet work that they’d patented back in 1946.

I went out to Aerojet the next couple of days for briefings on their engine designs, and when I came back home, we did a proposal for the Air Force TAV program, but the main thrust was a proposal that we put together with the people from Huntington Beach on a 2-stage to orbit vehicle. The first stage would fly with air-turbo ramjets to about Mach 6 or 7, and then it would stage with a scramjet vehicle a rocket that would deploy up into orbit.

We had several different concepts for this, depending on how soon we wanted we wanted the thing to fly. One of the people out at Huntington Beach named Joe Shergi had a concept for what he called a “toss-back booster”, that looked like an Apollo capsule with engines mounted in what looked like the heat-shield. After you separated the upper-stage, this thing would turn around and retrofire to toss back to the launch site, making everything recoverable.

We had 2 or 3 concepts that we were briefing as 2-stage to orbit vehicles. The first one that we could build quickly, based on all the hardware that was available, was a hypersonic FDL-7C glider on top of a toss-back booster. Then we went to an air-turbo ramjet first stage which went to about Mach 7 to 8, and later we went to a scramjet first stage that went to about Mach 12.

We hired a guy named Larry Fogel from the Titan Corporation, and he actually toured all of the SAC bases that had operational B-52 squadrons and asked them what they would do if they had one of these NASP vehicles — how they use it, maintain it, and stuff like that. We built an entire database on what the Strategic Air Command estimated these vehicles would cost to operate. We’d given them all the numbers that we had at the outset — how much thrust we had, how much propellant we needed, how many times the engines could be re-used, etc — and they gave us back operational cost estimates compared to a traditional B-52 squadron. It was quite interesting…

We took this information and used it for briefings in Washington DC, which is where I met Scotty Crossfield, who was working with Dan Glickman — and what we ended up with was the first stage vehicle, which was a large, Mach-6 vehicle. This led to the development of a prototype that we created as a demonstrator to validate the technology.

So the prototype was built to show how the NASP vehicle could fulfill 3 primary mission roles. The first was simply as a Mach-6 transport for passengers, the second was a Mach-8 strategic strike-aircraft for the Air Force, and the third involved combining the vehicle with an upper-stage rocket to go into Low-Earth Orbit.

It sounds like this technology really blurs the line between an aircraft and the Space-Shuttle or maybe even a true spacecraft…

Well the shuttle’s not an aircraft — it’s an abortion trying to figure out how to fly. You never want to build a vehicle that looks like that. The best vehicles ever designed came out of the Air Force Flight-Dynamics Lab, and Draper made one huge effort to try and get NASA to listen, and they absolutely refused to take his advice.

From the beginning, NASA had their own ideas about bluntness and all sorts of crazy design ideas that ended up in the Shuttle. The real hypersonic vehicles that were inherently stable — from Mach 22 all the way down to zero, and had thermal protection systems already worked out — were simply discarded.

These weren’t new ideas, even when the Shuttle was being designed. The Department of Defense was involved with this between ’58 and ’68, and they were discarded because the President at that time decided that no military systems would enter orbit. The administration was deathly afraid back then of militarizing space, which meant that everything going into space had to be civilian, so NASA took over everything.

XLR-129 Rocket Engine (Wikipedia)

The Air Force has something called the XLR-129 — it’s in a book that one of the Pratt & Whitney guys wrote that you can buy from the Society of Automotive Engineers library. The XLR-129 had about 580,000 pounds of thrust from a LOX-hydrogen engine and 3,500 psi chamber pressure.

It was fired 40 times without any overhaul, and it was brought up to full-power in about 3.5 months — whereas the Space Shuttle Main Engine (SSME) took about 38 months to come up to full-power.

This very same XLR-129 engine was donated to NASA when the Air Force got out of the space-race. The plans, the engine, and everything related to it were destroyed, and the last sentence in that chapter in Pratt’s book says, “NASA destroyed all of this because they didn’t want to embarrass their present engine contractor.”

Given the issues that NASA’s having with the Shuttle Program at the moment, do you think that they may someday return to this type of hardware for a next-generation Shuttle design?

One of Reagan’s assistant secretaries of commerce — for innovation, technology, and productivity — was named D. Bruce Merrifield, and he was very Russian in his thinking. The Russians have prototype factories that take laboratory ideas, and translate them into something that can be used in a functional, operational piece of hardware.

Merrifield’s concept was that the deficiency in the United States is that it uses projects to prepare technologies for application, which doesn’t give the new technologies adequate time to properly mature. He always advocated that just like with baseball players, technology needs a “farm team” to develop it so that it can later be used functionally. The Japanese do this, the Russians used to do this, and they do it because it produces great results.

What we were doing when I was at McDonnell-Douglas — because “Old-Man Mac” was a hardware guy — was looking at how you could take these big ideas and build samples & prototypes out of them, to see if we could come out of this with an operational concept.

When we designed a Mach-6 aircraft, we didn’t follow NASA’s strategy of building a research and develop vehicle that could only be flown 3 times a year. What we developed were vehicles that were operationally functional as much as a B-52 is.

Our resupply vehicle in 1964 for the manned orbiting laboratory had 11 operational vehicles and 3 spares — and those 11 vehicles flew 100 times a year for 15 years. That’s 1964 industrial capability — no magic at all. I don’t need magic. Now compare that to the Shuttle.

Well again, the NASP design is a really beautiful design — it’s really remarkable as being an evolution of the lifting body. It’s what the Shuttle could have, and probably should have been, right?

The baseline vehicle that was used as the reference vehicle for NASP was the original 1963 Mach-12 scramjet powered vehicle by McDonnell. I’m putting together some of our older materials that you can post on the website — including stuff back to ’58. When you at the old Mach-6 aircraft, you’ll look at it and immediately say it’s Aurora, but it’s not — it was called our Mach 6 manned hypersonic fighter.

One thing I’d wondered about from some of the NASP schematics I’ve seen is the blunt nose — why is that?

Not blunt — 2 dimensional. It’s got a sharp wedge at the nose. Now the original hypersonic vehicle for McDonnell-Douglas had a pointed nose — it was based on a conical body. It was a lifting body, but it had a pointed nose. Back in those days the low-drag vehicles were all pointed cones.

However, if you go into any reference book and you look up the wave drag of a pointed cone versus a sharp-wedge, the wedge has the square root of 3 over 3 of the pointed cone. The 2-dimensional wedge at the same angle has less drag than the cone does.

So Dick Newman over at flight dynamics lab at about ’59 and 60 with Will Hankey, Jack Pike over in England, and Bob Kreger who’s a VP over at Boeing now came up with a 2-dimensional nose. You look at it from the side and it looks like a point, and you look at it from the top and it looks blunt. It’s not a blunt nose, though — it’s a 2-dimensional nose. It’s a wedge.

The whole idea here is having less drag. You want the least drag you can get — especially for an air-breather. You can argue whether it’s a straight across the top or it’s a power-law — we’ve had all different kinds depending on whose theory we were operating on. But it’s still a 2-dimensional nose.

Now in terms of hypersonic aircraft, do you think we’ll ever see something like this become a recognized part of our arsenal and a larger component of future air-power? It seems like there’s always a need for faster aircraft, and but today’s state of the art seems to be going in a different direction…

Well when Scott Crossfield, Gus Wyss, and myself were sitting over at the aerospace club in Washington DC, we put together a chart for Sandy McDonnell that talked about the demonstator that we were proposing for the Air Force — this came well before Copper Canyon ever started. Now at Mach 6, it could carry about 40 people, a Mach 7 capability to carry military goods, and it could be used as a demonstrator to show that with the right equipment — a rocket boost inside of it plus the air-breathing engine — we could get it to orbital speed.

Now we weren’t going to take it into orbit — we were going to take it up to nearly orbital speed and then glide around back on the other side. So a full-sized version of this would fly at Mach 4.5 across the Pacific. So we were sitting there talking about what this concept, and that’s when Scotty came up with the name “Orient Express”….so that’s where that name originally came from.

Artist’s rendering of NASP in flight (High Frontiers)

If you go back and look at the original B-70 proposals, one of concepts was proposed was to take the fuel out of the fuselage as a demonstrator to show that a Mach-3 transport could carry commercial passengers without killing them. If you take the hydrogen tank and block it off so you can fly with methane instead as an aerodynamic vehicle, then you have enough space in the tank for about 40 or 50 people. Since the tank was built to keep liquid hydrogen cold, keeping the people warm to 72 degrees wasn’t even an issue. You see, the critics kept telling us, “the people are going to burn up”, but that’s not true — why would they burn up? They’re sitting inside of a tank designed to hold -450 degree hydrogen.

So you’re talking about Mach 3 commercial transportation in your vehicle, then? What kind of coast to coast flight-times are you going to get with something like that?

No — the B-70 project was Mach 3.2, and ours was Mach 4.5. Same idea, though. The Coast to Coast times you’re talking about are too short — it takes you a certain length of time to climb and a certain length of time to descend.

Let’s use an extreme example: let’s say that you’re going to fly at Mach 12. The shortest possible distance that makes it possible is about 5,000 miles. For something like Mach 2.5, then something like 2,500 miles might be practical. I don’t have the graph any longer, but the idea is that for each distance there is a speed that gives you the least time — if you fly faster or slower than that, it’s going to take longer.

That basically involves climbing, accelerating, and getting to the right altitude, right?

The hard part is slowing down — because if you have air-shocks in the inlet from slowing down too fast, you’ll unstart the engine. So it takes you twice as long to slow down as it does for you to accelerate.

Now in terms of maneuverability for a hypersonic aircraft, is it pretty maneuverable, or is the aircraft just flying too fast to maneuver well?

It’s maneuverable — you can pull load-factor with that. With our Mach-6 strike reconnaissance craft flying over the GIUK gap, we could pull a 3.5 gee turn with no difficulty. It gets harder the faster you go, because the angle of attack increases the temperature, so you have to be very careful — but at Mach 6 it’s no problem.

The reason I asked is because there was speculation in the Popular Science article on Aurora that the vehicle was taking the length of the entire state of California to turn around. That’s why the “UFO” was supposedly heading westerly over San Francisco and seen returning over San Diego, if I remember correctly…

At Mach 12 maybe, but not Mach 6. If you were flying over a spot in the GIUK gap at Mach 6, you could do a 150 or 200 mile diameter turn — which is perfect for interdiction, because you wanted the ship or whatever you were tracking to be inside the turn. So as you banked up to do the turn, your sensors would be pointing right straight down at the ground.

Did you guys ever look at deploying weapons out of a hypersonic aircraft? Would there be any problems with that?

Naw…they used to bet Kelly Johnson that he could never deploy all kinds of stuff out of the YF-12, but he designed his own system and deployed 6-missiles out of the YF-12 with no problems at all. I have never met a group of aerospace engineers or aeronautical engineers like that group of people. The mold for them is gone — people don’t think like that anymore. They were problem solvers.

Lockheed YF-12 overflying a mountain (Wikipedia)

They did a lot of pioneering work with beta-titanium, and it’s very hard stuff to work with. When Kelly first started making structural components out of this material, out of the first hundred forgings that he performed, he had 1 component that worked — the rest were garbage. Three months later, out of the 100 parts that he tried, he got 94 out that worked. He didn’t bring in outside specialists or contractors to solve the problem — it was his own team that came up with the solution. When you actually tell people some of the experiences they had on the SR-71 Project, in today’s environment it would be cancelled.

Those are impressive colleagues — it’s no wonder you were getting late-night calls from people standing next to “an aircraft you’d recognize”. Did you ever follow up later with any of them to see if they’d be more open to discussing it now that they’re retired?

No, the ones that I knew who were involved are no longer alive, and the ones who are involved today don’t talk.

Do you think that’s because these projects are still ongoing, and anybody who knows about them is bound by a secrecy agreements?

Well, remember, there’s a whole new young generation of engineers designing today’s aircraft. If these aircraft exist, it’s like the how the B-52 pilots of today are the grandsons of the ones who started flying B-52’s when they were first introduced — so whatever kind of secret aircraft are out there now are being designed & flown by an entirely new group of people, with new mission roles.

I don’t know what’s out there, but it could be. To say that Aurora is a technical impossibility is an incorrect statement — it has been technically feasible for the last 35 or 40 years.

Our Guest

Paul Czysz was a Professor Emeritus of Aerospace Engineering (retired) at Saint Louis University, the former Chief Scientist for the National Aerospace Place (NASP) project, and the CEO of his hypersonic research & consulting company, Hypertech Concepts, LLC. He passed in Aug 2013, and his obituary is available here.

Futurist, marketing executive and sometime writer with 25+ years of industry experience and a passion for the future.

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