Valkyrie Redux: Supercruising Bombers Could Viably Replace B-52s

The U.S. Air Force just revealed that it was launching a study of a new heavy bomber that might replace the Boeing B-52. The analysis of alternatives in the FY27 budget will look at ‘future B-52 requirements and costs and/or a new heavy bomber aircraft configuration and costs.’

Let’s go.

It’s early days. The B-52 is undergoing its biggest renovation in 40-plus years: new engine, radar, communications gear and training systems. The engine replacement is expected to cost $15 billion and reach initial operational capability in 2033, after the first contract was awarded in 2021. Consider that the original B-52 took only 14 years from a balsa-wood model in a Dayton hotel to delivery of the last production aircraft, a B-52H, which was a very different aeroplane.

The results of the upgrade program, 76 B-52Js, will continue to carry nuclear-armed cruise missiles – the new Raytheon AGM-181 – as part of the U.S. deterrent triad. They will also be the launch platforms for hypersonic missiles.

Donald Trump’s Defense Department is excited about hypersonic weapons, and the U.S. Air Force, Navy and Army are all pursuing them, because nobody wants to be left behind. Air-launched standoff weapons are desirable because the bombers can be based thousands of kilometres from the enemy.

The smaller RTX and Northrop Grumman Hypersonic Attack Cruise Missile (HACM) is being developed for the USAF and Australia, and the Pentagon hopes that more and cheaper hypersonic weapons will emerge from new market entrants. But this may create a problem for the USAF: dual-hatted for the nuclear deterrence mission, the B-52 fleet is at a capacity limit. The Defense Innovation Unit issued a request for information in 2020 for a high-capacity bomber with four B-2-type rotary launchers, and something like this will be part of the bomber analysis of alternatives.

There’s a lobby for more Northrop Grumman B-21s: Mark Gunzinger, a retired USAF colonel working for the Air Force Association’s Mitchell Institute and one of the key figures in getting the B-21 started, has proposed a 225-aircraft B-21 force acquired at a rate of 20 per year. B-2 and B-21 advocates have argued that stand-off missiles on cheap platforms (arsenal aircraft) cost more than stealthy penetrators with short-range weapons when target sets are large and campaigns are long.

Both the arsenal plane’s advocates and the B-21 community are missing the fourth dimension.

The U.S. Air Force’s first and only supersonic-cruise bomber, the awesome North American XB-70 Valkyrie, resides in the service’s museum in Dayton. Since the Valkyrie was cancelled in 1961 the supercruising-bomber concept has barely been looked at.

But if you want to deliver hypersonic standoff weapons in large numbers, subsonic cruise imposes a hard limit. If the adversary’s anti-access capabilities can push your B-52s 2,500 nautical miles back, sortie cycle times will be more than 12 hours.

Hypersonic dreams are not needed. A bomber burning ordinary jet fuel and built from familiar materials can cruise at Mach 2.4, three times faster than a B-52. There’s more.

In a 1976 paper, Ben Rich, the then director of the Lockheed Skunk Works, used a notional strike version of the SR-71 Blackbird reconnaissance aircraft to illustrate the advantages of supercruise. The AGM-69 SRAM – a rocket-boosted nuclear bomb – launched at SR-71 heights and speed, would fly more than 500 nautical miles (930 km), five times its range when released from a B-1 at Mach 1.6. Alternatively, stand-off weapons launched from supersonic platforms can be smaller and less costly than missiles launched at subsonic speed with equal range.

Ramjet weapons are even more interesting. A ramjet or dual-mode ramjet or scramjet missile needs a heavy rocket booster to accelerate it to a speed where the ramjet can operate: Mach 2.5 for a reasonably efficient engine. A ramjet weapon from a supersonic bomber may not need a booster.

If the supersonic bomber’s weapons are two-thirds the size of a subsonic-launch equivalent, an F-15EX-like 6-tonne weapon load would be as good as 9 tonnes on a subsonic aircraft. But the supersonic airplane, getting to and from the target so much faster, is generating more than twice as many sorties, so its 6 tonnes is as good as 20 tonnes delivered subsonically – a payload like the B-52’s or B-2’s.

The first hit arrives sooner. A long-lost advocacy paper for the B-70 shows the bomber intercepting a Chinese fleet headed for Taiwan.

Do I have your attention? We’re not done.

Robert McNamara, defense secretary to presidents John Kennedy and Lyndon Johnson, planted the pervasive notion that faster aircraft would be shot down by bigger missiles. The laws of physics have other ideas. Once you detect a bogey heading in at Mach 2.4 and 70,000 feet (21,000 metres), getting an interceptor missile up there fast enough, and with enough energy to defeat even a mild, 2.5 g weaving manoeuvre isn’t a trivial challenge.

The Soviets’ anti-Blackbird surface-to-air system, the S-200, used (and uses) a monster interceptor missile of seven tonnes at launch with a troublesome liquid-fuel core. Rich judged that it could guarantee a kill only if it used the optional instant-sunshine warhead.

Throw two more elements into the mix: front-aspect radar-cross-section reduction and a panoply of electromagnetic warfare measures (decoys, Cross-Eye, brute-force high-power microwave – I have a big airplane and megawatts to play with). This is no sitting duck, and it doesn’t bring the full cost of extreme low observables.

Supersonic cruise is not the most difficult objective in aircraft design. Obstacles that have stalled new designs for supersonic transports – a ban on overland sonic booms, airfield noise rules – do not apply in the same way.

The high-pressure cores of commercial jet engines run for tens of thousands of hours at temperatures that would suit sustained-supersonic engines that had tailored low-pressure sections. At least one of the three big engine prime contractors has carried out studies in that area.

The fact that the supercruising bomber is seriously doable could be important. For computer-age designers to create the B-52J by making drastic changes to the B-52H, a very efficient structure designed in the 1950s on drafting vellum, should not be considered low-risk.  As home remodellers know, there’s never a nice surprise behind the panelling. A new bomber might be needed sooner than the planners think.

Is there a hotel suite available in Dayton?

Bill Sweetman is a veteran, award-winning journalist and aerospace industry executive. He is the author of Trillion Dollar Trainwreck: How the F-35 hollowed out the U.S. Air Force.

Images of XB-70s, prototypes for the cancelled B-70 Valkyrie program: U.S. Air Force.

AI contributed no ideas to this article – Bill Sweetman.

This article appeared originally at The Strategist (ASPI).