The V-Jet II, created by Sam Williams and Burt Rutan to boost interest in small turbofans, points to a new way forward.
Small-turbofan creator Dr Sam Williams and light-aircraft guru Burt Rutan have teamed up to produce a design which they hope will revolutionise general aviation. Williams' Rutan-built V-Jet II will be the testbed for a NASA-sponsored small turbofan designed to replace piston engines in the next century's single- and twin-engined aircraft.
The V-Jet II will be flown daily at the US Experimental Aircraft Association's OshKosh, Wisconsin, fly-in, beginning on 31 July, in a bid to spark interest in jet-powered light aircraft.
When powered by two of Williams International's 3kN (700lb) thrust FJX-2 high-bypass turbofans, the five- to six-seat all composite twinjet will fly higher, faster and further that piston twins, with a lower fuel consumption per kilometre, says Williams, company founder, chairman and chief executive. The aircraft is powered initially by two interim, 2.4kN FJX-1 low-bypass turbofans, but has already been flown to 30,000ft (9,100m) and 295kt (545km/h) "…with considerably more to come", he says.
Design in miniature
Williams is famed for designing miniature turbine engines, notably cruise-missile power-plants and the FJ44 turbofan powering small business jets such as the Cessna CitationJet. His company, based in Walled lake, Michigan, has always had a certain level of aircraft-design capability, reveals Williams. "To do a good job designing engines, we needed to understand aircraft characteristics. Engine parameters, such as pressure ratio and bypass ratio, are affected substantially by the flight characteristics you are shooting for," he says.
Williams also has a personal interest in aircraft design. "Many years ago, I started designing light aircraft with forward swept wings, fitting them to various engine parameters," he says. Over the years, the company has made about a dozen small-scale models and three full-scale ones. A full-scale mock-up of the V-Jet I, an FJ44-powered twinjet with forward swept wing and T-tail, was produced to stimulate interest in that engine. "It was not our intention to produce the aircraft, just to excite the business-jet arena, to show the performance that could be achieved," he says. The V-Jet I mock-up helped interest several companies in the FJ44, including Cessna, Raytheon and Swearingen. "It worked, so we decided to do it again," he says.
Williams conceived the V-Jet II, but turned to Burt Rutan's Scaled Composites to complete the design and build and test the aircraft. "I've known Burt forever. He built the Triumph, the first aircraft to fly with the FJ44. It did not go into production, but it was a good starting point for the engine," he recalls. Williams engaged Rutan to carry out the detailed design and structural analysis on the V-Jet II, and to manufacture and flight-test the prototype. "He did a fine job," he says. The aircraft is not intended for production, Williams says, but will be used to demonstrate the FJX-2's characteristics over the speed and altitude range of future turbofan-powered light aircraft.
There were various features which Williams wanted to achieve in the V-Jet II. First was the use of a forward-swept wing, to provide good low-speed handling. A forward-swept wing stalls at the roots first, which "…gives the pilot good warning of the stall, while providing strong aileron authority," he says. The 15 degree forward sweep also allows the wing structure to pass through the fuselage behind the cabin.
Birds go by
A second requirement was to protect the engines from birdstrike, while mounting them as close together as possible, to minimise engine-out yaw asymmetry. "That is good for non-professional pilots," says Williams. The V-Jet II's engines are mounted at the base of the V-tail. "The engine installation has worked out well. We have run the throttle all the way back on one engine, and the asymmetry is hardly noticeable," he says. The engine inlets, meanwhile, are "hidden" behind the fuselage. "ice and birds go on by," says Williams. To achieve uniform flow into the engines, boundary-layer build-up over the fuselage must be minimised. "We use a long, thin, pointed nose to get good flow down the tailcone into the inlets," he says.
The V-Jet II is a 1,700kg aircraft - "about the size of a (Raytheon Beech) Bonanza," says Williams. While the twinjet will be flown daily at OshKosh, a second, single-engined, version will be displayed in model form. This will have an FJX-2 mounted at the base of its single vertical tail. Williams says that two markets ar envisaged for the FJX-2: that for single-engined aircraft, flown at similar altitudes to today's piston singles "…but able to go further further, faster, and so fly around the weather2; and the other for twins, with 3,000km (1,600nm) range, and higher speeds and lower fuel consumption than for piston twins. The V-Jet II is designed to be pressurised, something Williams hopes to add later in the programme.
Williams would prefer the market to start with twins. "School is out on single-engined jets," he admits. Despite this reservation, the FJX-2 "…makes a good single," he believes. Turbofans are more reliable than piston engines. "We expect to surpass the reliability of pistons pretty quickly," he says.
The FJX-1 engine now powering the V-Jet II has a lower bypass ratio - and is therefore noisier - than the FJX-2, "…but it is a good engine to check out the aircraft with," Williams says. The aircraft will be flown at OshKosh in 2000 with the FJX-2. Williams declines to give details of the engine, except to say that it is an all-new turbofan, with a larger fan and higher bypass ratio, and which is lighter ("under 100lb") and "considerably quieter" than the FJX-1. The engine will be digitally controlled, he reveals.
The FJX-2 is being developed in a $100 million co-operative effort with NASA, under the General Aviation Propulsion (GAP) programme. Williams and its industry team-members, which include suppliers and aircraft manufacturers, are providing 60% of the funds, with NASA supplying 40% for the initial engine-demonstration phase. The GAP programme is intended to demonstrate piston- and turbine-engine technology for the next generation of light aircraft. Certification of the FJX-" would follow completion of the GAP demonstration and would take "a couple of weeks," says Williams. "We can start (certification) before GAP ends, if the market is there and people are getting pretty excited," he says.
The target price for the FJX-2 is "…in the cost category of a piston engine and its propeller, assuming a good production base," Williams says. "We have set cost targets, and are working every component with costs defined.
We will keep working at it until we get there - we have always been able to achieve our cost goals," he says. Component testing will begin this year, and Williams will run the full engine in 1998. "we will get a lot of running on the engine before it files in the aircraft," he says.
The FJX-2 uses technology from the FJ44 and small-engine manufacturing processes which the company has been evolving over the years. "We have built a lot of miniature engines. Our thinking fits this engine," Williams says, adding: "Some parts get pretty small." Much of the effort is in making the engine simpler and cheaper. "We are not going way out there in technology," he says, although the company has applied advances such as magnetic bearings and electric accessories to other small engines.
The FJX-2 will be only the second Williams commercial engine after the FJ44, which was developed jointly with Roll-Royce. Certification of the FJ44 went smoothly, Williams says, although there have been some "surprises" in service. "We have been able to correct the few problems quickly and keep the fleet going. We are not seeing any more problems," he says. Some 500 engines have been delivered for the CitationJet and re-engineing of Swedish Air Force Saab SK60 trainers. The FJ44 also powers the Sino-Swearingen SJ30 now in flight test, and will be on Raytheon's Premier I when it is flown later this year. Another application is the Lockheed Martin / Boeing DarkStar stealthy unmanned air-vehicle.
Williams' plans for the V-Jet II include expanding the flight envelope and learning more about the aircraft's characteristics. He would like to pressurise the aircraft and install new avionics. Williams is enthusiastic about the progress being made in avionics, particularly the ability to transmit weather images to the cockpit. After the OshKosh demonstration, he believes, suppliers "…might get interested in showing off their technology" in the V-Jet II.
Leopard spot
The real interest for which Williams is hoping is from manufacturers willing to design aircraft around the FJX-2. There is already one application - the UK Chichester-Miles Consultants plans to re-engine its Leopard small business jet with FJX-2s, when the engine becomes available. The long-gestating Leopard is now being flight tested with two FJX-1 interim engines.
Williams professes no plans to put the V-Jet II into production. "Our intent is to stimulate interest, not to go into production. We do see other aircraft being developed - some metal, some all-composite. I hope they are all as slick (as the V-Jet II)," he says.
Source: Flight International
