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The eccentric engineer: an aviation ostrich destined never to fly

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How big could an aeroplane get? The US Air Force decided to find out, with a result that was enormous, sometimes verging on the ridiculous – and riddled with problems.

Not all engineering is about novelty. A great deal of time and energy goes into improving things that already exist – making them lighter, faster, stronger and, in a world where economies of scale matter, bigger.

Just how big can you make something? That was exactly the question the US Air Force posed to Lockheed. How big could an aeroplane actually get?

What they got back from Lockheed’s Skunkworks in 1969 was the plans for the CL-1201 – the largest aeroplane never built. Everything about it was enormous, verging sometimes on the ridiculous. The CL-1201 had a crescent wingspan of over 341 metres (15 metres taller than the Eiffel Tower) and was nearly 170 metres long (two and half times as long as a 747), 11 storeys high and weighed in at 5,265 tonnes.

The inside was spacious to say the least, with over 56,600 cubic metres of volume. Obviously, such a large plane would require a considerable crew. In this case, that was envisaged as somewhere between 475 and 800 people, housed over six decks containing sleeping areas, recreation rooms, mess halls, a strategic command centre, and a hold 22 times larger than in an Antonov 225.

Of course, powering such a behemoth would require a very special type of engine, and for this Lockheed proposed four nuclear fission-powered turbojets, sited on the top side of the back of the blended wing, producing half a million pounds of thrust. Fuelled by an onboard liquid-sodium-cooled 1.83GW closed-cycle nuclear engine, this would have the advantage of being able to keep the plane aloft at 30,000 feet at Mach 0.8 for up to 1,000 hours before needing downtime. After 41 days in the air, it would be necessary to land the aircraft if only to replenish the food supplies for the crew.

To protect the crew – and anyone near the crash site of one of these monsters – from the reactor, the nine-metre-wide core was surrounded with six metres of shielding. The reactor could be shut down in 20 seconds and was designed to survive a 950km/h impact.
Nor was the CL-1201 designed to be a lone giant. The plans were produced for two versions: one was the Aircraft Attack Carrier (AAC), which would hold 22 fighter jets on pylons under the wings, with another two in hangars in the main fuselage. These were originally to be F4 Phantoms, with some modification. The aircraft would also carry ten long-range attack missiles and was designed to be able to make a first strike anywhere in the world.

After the AAC had gone in, it would be the turn of the other variant, the Logistical Support Aircraft (LSA). These would bring troops and equipment into the strike area after the AAC had softened it up. There would be seven of these in each fleet group, each carrying 400 troops and 1,150 tonnes of cargo. Both would be delivered to the theatre using five ‘Medium Intra-theatre Planes’ – converted 707s, which could physically dock with the LSA in flight to transfer materiel. Each of these would already have an additional 150 troops on board, so the total fleet strength would be 3,896 ground troops, 24 Phantom F4s, 6,207 tonnes of equipment, 30 days food and water, artillery, light aircraft, and attack helicopters.

There were problems. Most importantly: how would these giants ever get airborne? Lockheed made several studies for this, concluding that the nuclear turbofans could run on conventional JP-5 fuel for take-off, provided a large enough runway could be built. This would have to be at least 200 metres wide and kilometres in length. Needless to say, none existed. An alternative, yet more extraordinary, plan was posited, whereby the plane could use vertical take-off. This would be achieved using clusters of 24 747 engines running on conventional fuel. For the LST version, they calculated that this would require 54 such engines. For the AAC version, it would need 182 engines producing 15 million pounds of thrust.

Then there was the vulnerability of such a huge machine to attack. Lockheed dodged these concerns by suggesting that missile cover would be provided by point defence laser cannons – a technology very much in its infancy in 1969 and, frankly, today.

Weighed down by these concerns, the CL-1201 never made it off the drawing board.

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