The SABRE air-cooler engine


The first fight of the prototype Lancaster bomber on the 9th Jan 1941 began the career of the most powerful offensive weapon of WWII.

The Mk 1 Lancaster had a max speed of 245kts and cruised at 200kts at 13,000 ft, with a service ceiling of 22,000 ft.  It weighed 64,000 lb. Eventually its four Merlin engines would enable it to carry Barnes Wallis’s massive 22,000lb Grand Slam earthquake bombs and the smaller Tallboys which together smashed the huge V3 fortress at Mimoyecques, sank the Tirpitz battleship and pierced 40 ft of reinforced concrete at le Havre to destroy Dönitz’s U boats. It was the ultimate bomber, but within eleven years of its first flight the Lanc was overshadowed by another Avro design, the mighty Vulcan.

On 30th August 1952 the prototype of the first Vulcan flew. In its operational incarnation the Vulcan B Mk 1 had a cruise speed of Mach .86 at 45,000 ft, with sustained max cruise capability of  Mach  .93 and a ceiling of 55,000 ft. It weighed 180,000lbs. That was how far things had changed in eleven years. Next to the oily, smoking, rattly old Lanc, the ‘Tin Triangle’ looked like something from outer space.

The Lanc had four Merlin engines, piston technology. The Vulcan had four twin spool Olympus turbojets. The transition between piston and jet made possible that huge leap in performance. Engine technology drives aerospace: build a better engine and you build better aircraft. The only other component that has such a dominating effect is wing design.

Back in the mid 1970s the UK ran a major project in the low speed wind tunnel at RAE Bedford, a concentrated push to design a wing that performed better during the phase of flight that all aircraft must enter eventually, approach and landing, but would still be economical during cruise at high transonic Mach numbers. Look out of your window when next you fly on an Airbus. During the cruise at height the wing is neat, slender, graceful. Then as you approach the ground the thing changes. Slats pop out at the leading edge, slots open at the rear as flaps curve down to bend the air in a dance of aerodynamic legerdemain. It’s as if the metal has acquired the ability to grow, to transmogrify, pure engineering alchemy. The wing built in the UK by Airbus (well, Hawker  Siddley really but let’s not be rude to the French) gave that company the ability to challenge Boeing for domination of the civil aviation market. Airbus wings performed their duralumin poetry for decades while Boeing wings clunkily opened a slot, put down flaps and lumbered onto the ground.

Applied research, funded during the extremity of war by governments, led to the move from piston to jet. Applied research into wing technology, funded by the UK government, created thousands of jobs, built an industry worth countless billions to various partners and remade the global aerospace market. In typical British fashion, aided and abetted by a civil service which values a classical education above anything achieved by simple engineers, successive governments handed that breathtaking advantage to foreign competitors.

We are in a position as a nation to do it again: targeted research, given enough impetus by the UK government, can move us forward to the next phase of engine development. Maybe.

The dream of space flight enthusiasts is SSTO, Single Stage To Orbit, a machine that takes off from a runway like a conventional aircraft, flies into space without discarding large chunks of its structure on the way, does its job and then returns to land on the same runway. Or, for the commercially minded, it takes off from a runway, travels to Australia in a couple of hours while carrying a load of wine-sipping, export-promoting businessmen and women. It may be that the dreams could become reality.

The physics and engineering challenges of getting into orbit are complicated. Because we don’t have the right technology we have to push conventional rocket engines to the limit – liquid hydrogen and oxygen are as good as it gets, and rockets with that combination got Armstrong and Aldrin to the moon, but only just. Elon Musk’s SpaceX rockets are wonders of conventional rocket technology while using cheaper fuel combinations, but to anyone who has seen the potential of the Reaction Engines Sabre air-breathing rocket they look like a better way of building airships, impressive but essentially a dead end.

If you can make your rocket start its mission by burning atmospheric oxygen like a jet engine then you save a lot of weight. Use on-board fuel and that oxygen to get to a very high Mach number, then convert your jet engine to a rocket using a small amount of on-board oxygen and you’re in space.  One problem: above about Mach 3 your engines will melt before it turns into a rocket – the air being rammed into your intake heats up as it enters, heats up as it is squeezed by the compressor and heats up when the fuel burns. All that hot gas then enters the turbine at the back of the engine and the rear of your spaceplane melts. That’s why the SR71 reaches only (only!) Mach 3 and NASA needed a rocket plane, the North American X15, to reach  Mach 6.7, 4000kts and 50 miles altitude in the 1960s. It looked as if multistage rockets were the only game in town if you wanted to get into orbit.

Enter Alan Bond and his team at Reaction Engines Ltd.

If you can cool the air entering the intake of a high Mach number engine you can avoid the melting problem. Bond has approached the problem like a proper engineer and his Sabre engine technology does just that. His pre-cooler takes the heat out of the airflow at astonishing rates –  SABRE dramatically cools the air from 1,000°C down to minus150°C in 0.01 sec.

So has our government been eagerly supporting this? Dream on. Remember Kid’s Company, that oddly run and badly monitored recipient of £60,000,000? While that was going on, Reaction Engines received £50,000,000. Rather than wait for the civil servants at the Department for Business, Energy & Industrial Strategy to read up on thermodynamics, aviation history and Sun Tzu’s Art of War, RE went out into the market and has attracted support from NASA and the European Space Agency. It’s going to be another case of invented here, developed profitably elsewhere.

I’m an old bomber pilot. I look at the potential of launching a military machine into orbit at short notice. I read of the potential lethality of simple kinetic weapons dropped from space, telegraph poles of tungsten steel which release huge amounts of energy when they connect, the 21st century equivalent of Wallis’s Grand Slam. We live in a turbulent world and it is as well to be prepared. An armed and powerful UK will be a land at peace. A weak UK and a weak West risk inviting war.

My first proper job was as a copilot on 617 Sqn at RAF Scampton, flying Vulcan B2s armed with Blue Steel stand-off missiles. Right through the Cold War we demonstrated the value of preparedness, of dominant technology, of cold determination. We validated the Scampton station motto. Armatus non lacessitur. An armed man is not attacked.

That’s Latin. Maybe that’ll grab the attention of the civil service. Maybe then they’ll give this technology the support it deserves.

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