Original URL: http://www.theregister.co.uk/2009/11/16/f35b_starts_hover_tests/

First ever supersonic stealth jumpjet starts hover tests at last

Will Harrier heir survive Byzantine aero politics?

By Lewis Page

Posted in Science, 16th November 2009 13:43 GMT

The world's first supersonic stealth jumpjet, intended to replace the famous Harrier in British, US and other forces worldwide, has arrived at the American airbase where it will finally begin to flight-test its vertical-lift and hover capabilities.

F-35B doors open from below. Credit: JSF Program

Doors open - but nothing coming out until now.

The F-35 "Lightning II" B model will, like other versions of the same aircraft, offer supersonic performance and stealth technology - a combo so far offered in only one aircraft in the world, the famous F-22 Raptor ultrasuperfighter. But the F-35B, unlike its tailhook and normal-runway counterparts, is also equipped with a central lift fan mounted in a shaft through the fuselage and can swivel its jet exhaust downwards too.

This means that an armed and fuelled F-35B should be able to make a very short takeoff run to get airborne and then, having burned fuel and perhaps released weapons, make a vertical landing supported entrirely by engine thrust. This Short Takeoff and Vertical Landing (STOVL) capability has so far been offered in the Western-aligned world only by the famous Harrier, originally developed in Britain and now in service with the RAF, the Royal Navy and the US Marines.

STOVL means that an aircraft can operate from a cheaply-built carrier at sea, one without catapults or arrester wires, of the type used by and planned for the Royal Navy and US Marines. It also permits such a jet to operate from a quickly-improvised airstrip ashore, or in some cases from ordinary runways which are too damaged or run-down for conventional aeroplanes to use.

The first F-35B took to the air for the first time last year, with a British test pilot at the controls in recognition of the UK's involvement in the project (Rolls Royce make the lift machinery which attaches to the engine and may get to make some actual engines in future, and BAE make a fuselage section and other parts). This aircraft, "BF-1", should long ago have started trying out its vertical-thrust features in the air, but it has so far flown only as a normal runway aircraft. (Doors and lids have been opened in flight, and a successful ground hover-pit test was announced in April, but actual vertical thrust has not been used significantly in the air.)

The F-35 might be no good - but aerospace people would still hate it even if was brilliant

The F-35B doors open from the side. Credit: JSF Program

The fliptop lid covers the lift-fan shaft. The dorsal doors let more air into the engine for hover ops.

This is in part because the engine originally fitted had to be replaced with a modified one following bench-testing failures. There have been other delays, perhaps not surprising when one reflects that this is not just the world's first supersonic jumpjet but the first supersonic stealth jumpjet to boot. Now, however, the Forth Worth Star-Telegram reports that BF-1 has finally arrived at the US Navy's Patuxent River test field in Maryland, where the next month or so should see it flying slower and slower until it is actually hovering in mid-air.

These will be tense days for both F-35 engineers and for many observers. The whole F-35 programme - A, B and C models - has faced a barrage of criticism in the aerospace world, generally on the ostensible grounds that the jet isn't going to be good enough to tackle possible future Chinese and/or Russian planes. This school of thought holds that the Obama administration should have bought more expensive Raptor superbirds and fewer "affordably stealthy" F-35s.

It's possible to note, however, that such a plan would have been excellent news for the Western aerospace sector for business reasons. A smaller US buy of F-35s would drive up its price and so undermine the plane's likely dominance of the world fighter export market in coming years. This would be excellent news for the makers of the Super Hornet, the Eurofighter, the Gripen and the Rafale - thus for just about all the first-rank Western aerospace companies and anyone who makes their living from them - and still pretty good news for Lockheed, as they make the Raptor too.

The fact that the F-35 seems likely to put a lot of its rivals out of business in coming years, then, might account for as much of the criticism it gets as any genuine fear of Chinese or Russian air dominance in future.

Royal Navy will be hoping no repeat of the Sea Harrier's problems

The F-35B in flight doors open from the top. Credit: JSF Program

Sometimes it sucks to be a jumpjet.

That debate would seem to be largely over for now - the President and his defence secretary have made it quite clear that they are having no more Raptors and lots of F-35s - but nonetheless any problems in the F-35B's hover test programme will be pounced on instantly by the plane's many vocal detractors.

And there are other reasons, especially for British observers, to watch the upcoming vertical-lift trials closely. The Royal Navy wants to use the F-35B specifically as a carrier fighter, to protect the British fleet from air attacks at sea - and there are grave concerns that it may have trouble setting down vertically with missiles still aboard in some conditions, even with fuel at a safe minimum.

The RN has plans to get around this using a so-called Shipborne Rolling Vertical Landing (SRVL) method in which the F-35B would come down still moving forward fast enough to get useful lift from wings as well as engine. Indeed senior naval aviators have told the Reg that they expect this to become the standard RN deck-landing technique.

But if the F-35B's hover performance should turn out to be poorer than thought, even SRVL might become marginal in hot climates (jet engines lose power in hotter air - this is the problem which did for the Sea Harrier in the end, meaning that it couldn't fly routine armed patrols anywhere very warm). This would invalidate the whole present plan for the navy's new carriers, the more so as the RAF is known to be reluctant to replace its own Harrier force - the light-blue airmen would rather spend that money on other things.

It might make more sense for the UK to equip its carriers with arrester wires and catapults for use by simpler tailhook planes. This isn't cheap or simple, as it would involve either serious engine-room changes or development of new technology, but it would save in the long run on the cost of buying and operating the highly complex F-35B, and by allowing cheaper radar aircraft.

There are indications that the UK government is considering such a plan - which might see the Royal Navy equipped with some other plane altogether such as the Rafale or Super Hornet. The F-35B would still go ahead with the US Marines, but loss of its second-biggest customer early on would be a serious blow for the jumpjet.

Or, as many would argue, the UK could scrap the carriers altogether, or use one of them as an amphibious helicopter ship or something.

For all these reasons, then, the next month's hover tests at Patuxent River will be watched keenly from various places around the globe. ®