Monday, May 16, 2011

UK’s Retirement of the Harrier Jump Jet: End of an Era?

Even though the 20th Century’s best “jump-jet” or VTOL was inevitably retired, does the decision mark an end of an era in vertical take-off aircraft technology?

By: Ringo Bones

The British Royal Air Force’s decision to retire the Harrier Jump Jet back in December 14, 2010 was probably seen as an end of an era to anyone who knew full well the capabilities of the 20th Century’s finest vertical / short take-off and landing capable jet fighter. And anyone with the good fortune of flying the Harrier Jump jet side-by-side with its Soviet-era counterpart – the YAK-36/38 better known to the West and NATO as FORGER – will attest that the Harrier is magnitudes better. The Harrier is now slated to be replaced by the 60-million US dollar STOVL variant of the F-35 Lightning JSF deemed by maker Lockheed Martin as the logical replacement for the F-16 Fighting Falcon. As the most widely exported wonder of British aerospace engineering, will retirement of the Harrier Jump Jet prove rather premature?

As one of the icons of the Cold-War era Western/NATO bulwark against the Soviet threat, the Harrier Jump Jet first started life as the Hawker P-1127 resulting from the late 1950s design of the British Hawker Siddeley Aircraft Corporation. Although there were plans for a supersonic capable version of the Harrier, this dream was inevitably scrapped by the realities of the fiscal austerity of late 1960s Britain.

The Rolls Royce Pegasus jet engine used in the Harrier Jump Jet is probably the only one of its kind that uses cascade-vane-nozzle technology – analog of the deflected-slipstream turbojet engine. This type of jet engine is basically a turbojet engine – or in the case of the Rolls Royce Pegasus jet engine a high-bypass turbofan jet engine specially designed with a special nozzle that has been fitted so that the propelling jet can be deflected vertically to permit vertical take-off and hovering, although the Harrier only carries enough cooling water to allow it to hover in a virtual standstill for only 90 seconds. The special nozzle is provided with adjustable vanes. Control in hovering flight is obtained with auxiliary jet reaction nozzles, and control in high-speed flight is obtained by conventional fixed-wing control surfaces.

Since entering service with the British Royal Air Force (RAF) and the Fleet Air Arm in 1969, the US Department of Defense was very impressed by the Harrier Jump Jet’s performance that it eventually bought “several” for service in the US Marines back in 1971. Despite of its vertical and short take-off capability, the Harrier Jump Jet can never go supersonic – its top speed is only a little over 700-mph. And it is a rather “thirsty bird” with a combat radius of only 300 to 700 miles. Nonetheless, the Harrier Jump Jet prove its worth during the Falklands War of 1982 by being able to shootadown supersonic-capable French built Super Etendards (comparable in performance to the McDonnell-Douglas A-4 Skyhawk) by piloting skill alone.

And by the mid 1980s, The British Hawker Siddeley Aircraft Corporation eventually allowed US plane-maker McDonnell-Douglas to manufacture its own version of the Harrier – the AV-8B with advanced composite materials used in fabricating its wings that eventually allowed the American version of the Harrier to carry more fuel and weapons than its British counterpart.

Even though the Harrier Jump Jet has proved its worth for much of the 20th Century, it is still plagued by two main problems that most Air Forces of the world are reluctant to buy it. The first one is the hot-gas ingestion problem where the Rolls Royce Pegasus engines “accidentally” ingests the hot gas from its exhaust leading to temporary compressor stall that makes the Harrier drop like a rock when taking off vertically and its range restrictions because the rolls Royce Pegasus jet engine is rather thirsty. The STOVL-capable version of the F-35 Lightning solves the hot-gas ingestion problem by using a dedicated lifting fan with a gear system that allows it to be coupled to the main jet engine. And since the F-35 is largely made of lightweight composites, it resulted in increased fuel efficiency. The added bonus of the F-35’s lightweight design is supercruise – i.e. it can go supersonic without using afterburners – the afterburners are only necessary when the F-35 wants to go faster than Mach 1.5; and there’s the added bonus of stealth capability. Sadly, the F-35 still has to prove itself in combat if it is really a worthy successor to the Harrier Jump Jet.

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