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Airship 'Sky Tugs' ordered from Lockheed for Canadian oilfields

P-791 military hover suck-blimp gets civil application

By Lewis Page, 28 Mar 2011

The famous P-791 prototype airship - built last decade for a military transport programme which eventually came to nothing - is to give birth to new, mighty commercial versions of itself with Canadian financial backing.

Alberta-based private company Aviation Capital Enterprises says it has inked a deal with US aerospace colossus Lockheed, builder of the P-791, to "design, develop, build, flight test and Federal Aviation Administration certify a family of hybrid aircraft". The first ship, dubbed "SkyTug" and able to lift 20 tons, is to be delivered in 2012. Further versions are to scale up to "several hundred tons", apparently.

A hybrid air vehicle isn't a conventional lighter-than-air dirigible, whose weight is entirely supported by the buoyancy of its lifting gas. A hybrid's gas only counteracts part of its weight: in order to get airborne, the SkyTug will swivel its propellors downwards for vertical thrust. Once it starts flying forward its hull will generate dynamic lift just as an aeroplane's wing does, allowing the props to be swivelled horizontal for greater cruising speed.

According to Aviation Capital, the fully vertical-takeoff-and-landing (VTOL) capable SkyTug will provide "greater payload and range at a fraction of the cost of a helicopter". The larger ships that will follow apparently won't be fully VTOL - they'll require something of a run-up on the ground to generate dynamic lift and get airborne, rather as an aeroplane does.

However the big ships aren't expected to need massive runways: they'll be able to land and take off from "unimproved surfaces and water". This will be achieved by the cunning air-cushion undercarriage which is such a novel feature of the P-791: rather than wheels or skids, the airships will move about on the ground supported on air blown down through big skirt assemblies, just like a hovercraft.

The fact that a hybrid ship is heavy helps to avoid one of the main headaches of unloading an airship at a place where there's no way of taking on water ballast. A traditional airship struggles to manage such operations, as once the payload is gone the ship becomes uncontrollably buoyant and is likely to soar up through its "pressure height" - the point at which the lifting gas has expanded to fill the entire envelope - and lose most of its helium via the automatic safety valves (or burst). Helium being expensive, this is not ideal.

P-791 style ships have another ace up their sleeve for unloading, in that the hover undercarriage can be switched from blow to suck, thus sticking the ship firmly down on the ground (or sea) even if it might have become a bit flighty during unloading. This is also handy for preventing the vessel being blown around by the wind.

The P-791 itself was originally built by Lockheed in 2006 as a contender for the US military's proposed "Walrus" project, intended to deliver a brobdingnagian airship capable of hauling an entire US army combat battalion of 500+ troops - plus all their vehicles, heavy weapons and other kit - in one lift. But a heavy-lift airship needs a lot of gas, and this in turn means that "pressure height" can't be too high or the envelope will have to be unfeasibly huger still.

Thus the Walrus was specced for 10,000 feet maximum altitude, which was realistically a show-stopper for the military - even shoulder-launched missiles can reach that high, and the ship would have been a very easy target.

This is the environmentally friendly way of exploiting the wilderness for oil

Thus the Walrus project never went ahead. There are multihundred-million-dollar US military airships being built even now - the LEMV and the ISIS - but they are meant for use as unmanned, long-endurance surveillance platforms. As their payloads are thus relatively small they don't need as much gas and their pressure height limits can be high enough to survive above the battlefield.

Concept of the 'Skytug' hybrid airship. Credit: Lockheed Martin

Technology that really blows. Or sucks

Lockheed evidently hasn't given up on a military role for the P-791 despite having been beaten to the LEMV deal by a British design. Under the new arrangement with Aviation Capital, Lockheed keeps the military rights to its technology, but has sold civil applications to its Canadian partner.

These civil applications are quite likely to start off with the oil and gas industries, or other groups needing to move heavy loads into and out of places without access roads. It's no surprise to find that Aviation Capital is based in Alberta, thought to have vast reserves of black gold lying unexploited in its oil sands. Getting this oil out of the ground involves more machinery than a normal oil-well requires, and moving this kit about would normally require a lot of new roads - which would be expensive and heavily criticised for further despoiling the wilderness.

Various crafty solutions have been proposed to deal with this situation, including riverine hover barges. It was announced in 2008 that Lockheed's great rival Boeing would build an ambitious heli-stat - a combination blimp and helicopter - again in partnership with a Canadian company: but it appears that this project has now folded, with its backers unable to secure Canadian government funding. It would appear that the oilsands field is now clear for Lockheed's P-791 technology - and that this is what the initial application of the SkyTug will be.

Aviation Capital, in common with most airship companies, likes to suggest that its craft will be "environmentally sound", and this is true as far as it goes - they should be fuel-sippers compared to normal cargo aircraft. But not many greens will approve of the uses to which the SkyTug seems likely to be put, at least to begin with.

The company tells the Leading Edge blog that the initial experimental craft of 2012 will be followed by another in 2013 which will achieve FAA certification. Work will begin on the first production craft that year, if all goes according to plan. ®

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