Articles

Jump Jets

In Uncategorized on June 4, 2010 by hillermuseum

Past, Present, Future

Twenty-three years after the invention of the jet engine, Bell Aircraft Corporation in 1953 produced and flew a jet powered, vertical take-off aircraft designated the Bell Model 65. This Air Test Vehicle was lashed together in just eight months using a Cessna wing, the fuselage from a Schweizer glider, and landing skids from a Bell helicopter. Power was provided by Fairchild turbojets mounted under the wing on either side of the fuselage. The engines were supposed to swivel from vertical to horizontal for flying horizontal. However, engine thrust was insufficient so it never flew horizontally. Though the Model 65 did not achieve all goals, it did provide enough data to justify going on to the next design in 1957, the Bell X-14.

As with the Bell 65, the X-14 was constructed from other aircraft parts – the wing and landing gear from a Beech Bonanza and the tail from a Beech Mentor.  Unlike the Model 65, the X-14 had two fixed jet engines with movable exhaust ducts capable of deflecting the engine exhaust straight down from a position at the airplane’s center of gravity.  This provided a means of attaining vertical takeoff completely different from helicopter-like hybrid aircraft such as Bell’s own XV-3 tiltrotor.  At altitude, the ducts moved to a rearward-facing direction to provide traditional forward thrust.  The X-14 made its first flight at the Bell plant near Buffalo, New York, but soon moved to the NASA Ames Research Center at Moffett Field for more extensive tests.

The X-14 was a rather ugly appearing machine, but its vectored-thrust technology provided the pattern for several other “jump jets”. No less than a dozen variations were built in ten or so countries. Only two went into full production and operation:  Hawker-Siddeley Harrier and the Yakovlev Yak-38.

By the early 1960s, the British took the lead in research and development of vectored-thrust VTOL aircraft.  A French engine concept utilizing swiveling nozzles to redirect thrust was considered especially promising. The British Government was not interested, resulting in a joint development arrangement between the Bristol Engine Company and the United States government. Hawker Aircraft began designing an aircraft based on the thrust-vectored engine design. The design effort focused on an “attack-reconnaissance” V/STOL (Vertical/Short Take Off and Landing) vehicle. The first aircraft, designated P.1127 was rolled out mid 1960. Eventually the United Kingdom, United States and Federal Republic of Germany concluded an agreement to purchase the aircraft and seven upgraded units were delivered. The aircraft was initially called the Kestrel, after a small falcon capable of hovering in flight.  . Six of the seven aircraft were shipped to the US for evaluation. The test program attracted the interest of the Royal Air Force, which placed an order for 60 further-improved aircraft in 1966.  This was the first production order for any VTOL airplane, and the newly redesigned jet was designated the GR.1 Harrier, with the name taken from a larger raptor capable of hovering in flight while searching for its prey.  The Royal Navy also found the design useful and subsequently ordered the Sea Harrier, a naval version of GR.1.

By the mid ‘60s, the US Marine Corps determined it needed an aircraft capable of supporting amphibious landings and set out to buy Harriers for this purpose. Though the other US military units and Congress were opposed, the Marines were determined and successfully received approval. An order for 113 AV-8 Harriers was placed, introducing the Marines to VTOL operations.  It was replaced in service during the 1980s by the more powerful and more AV-8B Harrier II, manufactured in the United States by McDonnell Douglas.  The RAF’s Harrier force upgraded to a British Aerospace-manufactured Harrier II with similar capabilities during the same period. 

In 1971, the Yakovlev design bureau in the Soviet Union introduced its own VTOL aircraft with thrust-vector technology, the Yak-38.  Developed to operate off of the Soviet Navy’s small-decked aircraft carriers, the Yak-38 differed from the Harrier in having two small auxiliary jet engines that were used together with vectored thrust from the main engine to achieve vertical take-off.  The design worked and over 200 Yak-38s were built, but limitations to the aircraft’s engine power prevented it from flying with any appreciable payload in hot or high-altitude conditions.  All Yak-38s have been retired, leaving the Harrier as the only operational VTOL fighter.

With the basic Harrier design approaching forty years of age, the US military began a comprehensive analysis of its future aircraft requirements. The result was a decision to develop a “common” aircraft with several variations that would serve the needs for all branches, replacing not only the Harrier aircraft operated by the Marines but also US Air Force F-16 Falcons and US Navy F-18 Hornets. The result is the Lockheed Martin Joint Strike Fighter (JSF) F-35 Lighting II. Three variants are currently in flight test:

> F-35A  For the US Air Force, the A model is a conventional takeoff and landing (CTOL) variant as a replacement for the F-16.

> F-35B For the US Marine Corps, the model B is a short takeoff and vertical landing (STOVL) replacement for the Harrier and F/A-18. The Marine Corps plans to purchase 340 of this model. The British Royal Air Force and Royal Navy plan to use the model B to replace their Harriers.

> F-3C For the US Navy to replace early-model F/A-18s based aboard aircraft carriers.

Total US procurement is planned to be over 2,000 aircraft, although development delays and cost increases are likely to reduce near-term production.  In addition to the US and UK, several other nations are interested and/or plan to use it. Among those are The Netherlands, Italy, Canada, Turkey, Australia, Norway, Denmark, Israel, and Singapore.

As a replacement aircraft, the F-35 incorporates a control system that is highly improved over the Harrier.  The F-35B introduces an innovative new means of achieving VTOL capability.  A large lift fan in embedded in the center of the airplane’s fuselage.  During VTOL operations, the lift fan is powered by the main engine, with supplemental lift provided by vectoring the main engine’s exhaust downwards.  The lift fan, included only in the F-35B version, greatly enhances VTOL performance compared to the Harrier’s vectored engine thrust while reducing the impact of hot jet exhaust on the ground or aboard ships.   

After extensive ground testing, the F-35 completed its first flight on December 15, 2006.  The conventional take-off F-35A is expected to enter service with the US Air Force in 2011, with the F-35B VTOL version arriving for the Marines the following year.  Countries around the world are participating in development of this new airplane and expect to order it in quantity to replace aging 1980s-vintage aircraft.  Many observers expect that the F-35 will ultimately become the most-produced fighter design of the first half of the 21st century.

Harriers from VMA 513 “Nightmares” will perform at Vertical Challenge June 19, 2010 at the Hiller Aviation Museum. For more info visit http://www.hiller.org/vertical-challenge.shtml

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