Last week, I listened to the first episode of a podcast miniseries talking about the development of the B-1 Lancer. Interestingly, that first episode was primarily focused on a different aircraft entirely: the B-70 Valkyrie, a proposed supersonic bomber design that was eventually canceled and turned into a pair of experimental aircraft.
I didn’t know much about the Valkyrie going into the podcast. But listening to it, the engineering problems encountered seemed pretty similar to another aircraft known for flying high and fast: the Lockheed SR-71 Blackbird. As you do when driving, I had the thought—why did the SR-71 endure while the B-70 never entered service, and in fact was outlasted by the aircraft it was meant to replace?
I recognize that these are two very different use cases: an intercontinental nuclear bomber versus a strategic reconnaissance aircraft. That would probably be enough of an answer to satisfy most people’s curiosities. But I wanted to know how that difference in purpose was reflected in the designs and led to the fate of each.
I’m going to step through some of the history, design choices, and circumstances surrounding both aircraft. And at the end, I’ll see if there are any lessons that we can take away from the comparison.
Fly Higher, Fly Faster, Fewer Fighters
Like I noted before, the B-70 was intended to be a nuclear bomber capable of flying from the United States to (and over) the USSR, carrying both its payload and enough fuel to cross the Atlantic twice.
The philosophy of the time encouraged bombers to fly higher and faster, using superior speed and altitude to evade enemy fighters. Its requirement to fly at Mach 3+ at 70,000 ft would make the B-70 safe from any interception. By the time radar controllers could identify the bomber and scramble their fighters, supersonic speeds would take the Valkyrie well out of range of any threat.
But prolonged high speed flight would generate a lot of heat, reaching absurdly high temperatures on some exterior surfaces—later testing would show an average temperature of 450° F, with certain sections hundreds of degrees hotter. Only a few materials can handle those kinds of temperatures, notably stainless steel and titanium.
North American Aviation, the aircraft’s designer and manufacturer, had no way of acquiring enough titanium to manufacture multiple aircraft. Instead they devised an alternative panel made of heavier but cheaper stainless steel, sandwiching a foil honeycomb core. Titanium was used only on the sections that would see the most heat, like leading edges.
The engineering decisions made for the B-70 were sound, given the intended mission, technologies, and limitations of the program. But then the USSR unveiled their first surface-to-air missiles in the late 1950s, and thoroughly rained on everyone’s parade.
The New Paradigm
In short, the existence of surface-to-air guided missiles obliterated the B-70’s intended mission. Fighters no longer had to scramble to intercept an enemy aircraft; instead a missile could be launched at an identified intruder, rocketing up to target altitude faster than any airplane and quickly “handling” the incursion.
The efficacy of this was soon illustrated when a U-2 flown by American pilot Francis Gary Powers was brought down over the Soviet Union in May 1960. Though the U-2 didn’t fly at supersonic speeds, it already cruised at 70,000+ ft; clearly, flying at high altitudes no longer guaranteed safety.
Immediately strategy began to shift towards a low-altitude style of operations. Radar relies on line of sight and can’t sense anything beneath it; an aircraft flying very close to the ground could hide behind terrain features and effectively sneak under the fence of missile radar and airborne fighters. And as designed, the B-70 just wasn’t any better at this job than the B-52 Stratofortress already in service. It was possibly even less suited due to its smaller load capacity and shorter range.
The justification for the B-70 to exist had evaporated. The program was canceled; only two representatives were fabricated as experimental aircraft for research into large supersonic transports.
The Blackbird – a Better Bird?
A lot of the history of the SR-71’s development is well-known lore for most aviation buffs, so I’m going to skip a full retelling. Instead, let’s look at the notable ways the SR-71 program distinguished itself from the B-70.
I’ll start with the obvious ones: the SR-71 came later, and had a very different purpose as an aircraft. B-70 development started in 1955, with the contract awarded to North American in 1958. The SR-71’s precursor program, Archangel, didn’t start until quarter 2 of 1958. It’s likely it even took advantage of the technological advances provided by the B-70 development.
Speaking of mission: the B-70 was designed as a bomber and as such is substantially larger than the SR-71. It has nearly twice the length, twice the wingspan, and is at least three times heavier! That’s a much bigger plane to notice on radar, and a bigger target for a missile.
The SR-71 was purely a surveillance aircraft and so could optimize entirely for speed and altitude. At least according to Wikipedia, its thrust-to-weight ratio is 0.44 while the B-70’s is 0.314: this means the Blackbird has proportionally more thrust available for a faster acceleration and top speed, assumedly making its missile evasion strategy of “just outrun it” much more feasible.
Though both aircraft were selected through a typical proposal → review → contract award process, they had different “customers.” The B-70 was a request from the US Air Force, and so relied on its contracting and funding mechanisms, as well as the resources and support it could provide. The A-12’s predecessor, and thus the SR-71, was instead requested by the US Central Intelligence Agency (CIA) and went through that organization’s processes.
In my view, this difference is a major contributor to the fates of these aircraft. North American received funding for development of the B-70 as a series of phased contracts, while Lockheed received a single contract for the design, manufacture, and testing of 12 aircraft. My interpretation of this is that the B-70 contracts set the tone of “go explore designing this airplane,” while the very specific, decisive A-12 contract was a strong signal of “just make this happen.”
Contracting with the CIA probably opened doors that were not an option for the Air Force. North American could not acquire enough titanium for an entire aircraft, and thus had to use the notably heavier stainless steel. Meanwhile, Lockheed could use titanium: the CIA was not above using dummy companies “based” out of third-world countries to purchase titanium from one of the world’s leading exporters, which just so happened to be the Soviet Union.
Using this material over the majority of the aircraft enabled Lockheed to take advantage of weight savings that just weren’t available to the B-70’s engineers. Guaranteed sales of their aircraft, Lockheed was also able to invest in the design and fabrication of new tooling to properly work with their plentiful titanium. I wonder, if North American could have taken advantage of titanium’s weight savings in the same way, would the B-70 have been able to adapt to the new missile-ruled environment it found itself in.
What we can learn – maybe
After digging into it, I’ll admit this isn’t exactly the most fair comparison. These are two different aircraft with their own unique use cases and historical context. The B-70 likely would have been a perfectly good airplane, but it was a casualty of the emergence of a game-changing new technology. The A-12 and SR-71 programs were actually triggered by that change, and could better adapt to it.
I think there is still something to be said for how both aircraft were contracted. Once the CIA selected a design, they were all-in on it: they wanted it optimized, they wanted it built, and they would do anything needed in order to make that happen, even clandestine operations. Lockheed had the security of knowing they would be supported for the full duration and so could throw their best resources at the project.
At least from what I read, the Air Force program was not nearly as purposeful. Somehow at least $800 million (of 1961 dollars) was spent on the entire program, released in contracts spanning multiple phases. This drip-feeding of funding might have contributed to the pace of development; North American received large awards, but when follow-on funding isn’t entirely guaranteed, it’s hard to work up the motivation to really lean forward on progress. And it’s much easier to lose momentum for the project as a whole.
The timelines illustrate my point: B-70 development started in 1955 and phase I awarded in 1958, but the first XB-70 didn’t fly until September of 1964. Meanwhile the A-12 was being discussed in early 1958, ordered by the CIA in early 1960, and first flew in April of 1962. That’s nine years for the bomber, four years for the sled. The numbers tell a story.
Having gone through all this, I’m still percolating on what decent lessons we can pull from this comparison. There are two that currently stand out to me.
One: being able to move fast and respond to what your market or customer wants can be a big factor into your success. I’m not judging the B-70 or its designers for its unfortunate timing, and even if it had entered service a few years earlier it may have retired early anyways due to the changing landscape. But having a healthy level of urgency and maintaining the project’s pace helped Lockheed get a real, metal-and-bolts A-12 out the door in just a few years (and Kelly Johnson’s focus on small, agile teams couldn’t have hurt).
Two: your customer and contracting vehicle can have a much bigger impact on the program than you might think. Whether it’s a private customer or a program office, having a “final authority” willing to champion you and work with you to be successful means it might be worth it to prioritize those opportunities, if and when you can.
The CIA was able (and willing) to acquire titanium for Lockheed when the Air Force couldn’t do the same for North American, pushing them to use a heavier material. Admittedly that’s a very extreme case, and you could probably say the CIA was giving an unfair advantage—but my point still stands. Even just the decision to pay for design and manufacture of 12 aircraft in one contract had to have played a part in how quickly and confidently the Lockheed team worked.
I’d be really curious to hear your thoughts on all this. Is comparing the B-70’s development to the A-12 and SR-71 a big ol’ nothingburger? Do you have thoughts on the two takeaways I’ve detailed here? Is there something I missed that stood out to you? I know there’s a number of you with extensive design or program management experience, and I’d genuinely appreciate getting feedback from a different perspective than mine.