As NBAA 2005 dawns, much of the attention is focused on flight tests of the first generation very light jets. But are they living up to expectations?

After years of hype and expectation over very light jets (VLJ), and their potential impact on general aviation, the first four major US-based projects are in flight test and first results are coming in. But as the Adam Aircraft A700, Aviation Technology Group (ATG) Javelin, Cessna Citation Mustang and Eclipse Aviation Eclipse 500 move towards certification, how close are they to meeting the ambitious targets set for them?

Leading the way in terms of hours is the Eclipse 500 effort, which is expected to have reached or exceeded 600h by the time the aircraft goes on display at this year’s NBAA show in Orlando, Florida. This tally, although still lagging behind the 750h target the company originally identified to have exceeded by this time, is still considered commendable given the 4 September wheels-up landing of one of the “beta” test aircraft and the resulting strain on the already delayed certification schedule.

“We should have all five test aircraft back in the air and continuing to work on various parts of the test programme by the start of November,” said Eclipse late last month. US certification is still targeted for March 2006 despite the remaining hurdles, the latest of which is flight tests of drag reduction features brought in to cure an apparent performance shortfall, details of which are still emerging. The chief focus of the work is a smaller wing to body fairing, various shapes having been evaluated during a series of tests on the third conforming aircraft, N504EA, at the company’s Albuquerque, New Mexico base.

The boundary line between the wing de-icing boot and the wing surface is also being reworked to reduce flow separation and improve both speed and range performance. Eclipse confirms the work is required to bring the aircraft “up to spec” which calls for a guaranteed cruise speed of 375kt (695km/h), ±2.5%, and a range of 2,370km (1,280nm), ±5%.

Until now the highest quoted speed achieved in flight testing is 285kt, while no firm figures for range have been issued to-date. Performance tests were originally due to have been completed by the start of August, but are now not likely to be finished until the final configuration is flight tested and decided upon. Test accomplishments so far include a maximum altitude of 41,000ft (12,500m), and the completion of lightweight foreign object damage (FOD) testing at various throttle settings up to take-off thrust and at a variety of speeds ranging from standstill to 70kt.

Other milestones include water ingestion tests, culminating with an aircraft taxiing through a 40mm (1.5in) trough of water at speeds up to 100kt to simulate heavy rain conditions. The aircraft also appears to be demonstrating its ruggedness during the most recent tests, highlights of which include 20 landings in one day on one aircraft to test tyre wear; achieving more than 100 test points on a single aircraft in one day; and endurance testing with single flight durations of more than 3h.

The aircraft has also been cleared by the FAA for an initial 10,000h structural life limit following the completion of static tests at the South West Research Institute in San Antonio, Texas. “The goal is 20,000h, but to have got this clearance without the fatigue test demonstration is virtually unprecedented,” says the company, which expects to extend the life limit further on completion of a second phase of ongoing tests.

Stable platform

The Eclipse handles well and is a forgiving, stable platform, says flight-test engineering director Terry Tomeny. “We’re flying finals at 85kt, and it is very comfortable in the pattern. If you are in the pattern with an airliner you can keep up, and if you get behind one you can slow right down,” he adds. At higher speeds “the flight control system provides very good control so far”, although Tomeny says work is under way to adjust for higher roll forces encountered at greater speeds.

Other issues addressed as a result of discoveries made during flight tests include an out-of-tolerance thrust lever angle that would cause the engine to default to either maximum or idle thrust, “and that’s not a good thing on take-off”, he says. The issue has now been corrected, as has a propulsion anomaly encountered with the Pratt & Whitney Canada PW610 turbofan. The problem was an airframe vibration encountered during flutter testing. This was traced to an engine overspeed, which in turn resulted from the full-authority digital engine control attempting to recover from an uncommanded rpm roll-back. The issue, which was “small and didn’t cause any damage to the engine”, has been addressed with FADEC and other minor modifications.

Further flutter tests are being carried out using the second conforming aircraft, N502EA, which first flew on 14 April. This aircraft was also scheduled to perform stalls at full aft centre of gravity, and expected to be used for flying-qualities work with the FAA. N503EA, which was the first conforming aircraft to fly, on 31 December 2004, has been used for unusable fuel tests, airstarts, powerplant tests, landing gear and tyre and brake evaluation and pressurisation tests.

The third conforming Eclipse 500 (N504EA), which made its maiden flight on 21 April, is the hardest working in the test fleet to date with around 120 sorties and more than 160 flight hours. Used primarily for avionics and electrical systems evaluation, it is scheduled to perform early autopilot tests as well as be used for the on-going drag reduction work.

The first of the two “beta” test aircraft, N505EA is due to fly to the US Navy test site at Patuxent River, Maryland after it rejoins the test programme. There the aircraft will undergo high-intensity radiated field (HIRF) tests, before resuming other certification work back at Albuquerque. N506EA, the next aircraft in the programme, will now serve as the hard-working “beta” test aircraft, proving the basic reliability of the systems in simulated day-to-day operations. Both betas are the fifth and seventh Eclipses off the line respectively, the sixth being the static test airframe. Fatigue tests, using the eighth airframe, are set to start at the end of November.

Mustang picks up pace

Flight testing of Cessna’s Citation Mustang in Wichita, Kansas, has accelerated following weather-related delays after the maiden flight of the prototype on 23 April. “It’s going really well,” says Mustang programme manager Russ Meyer III, who says “the flight-test pilots are very positive on its flying characteristics”.

At the end of August the Mustang proto­type was joined in the test programme by the first of two production-standard aircraft, P1 (serial number 001). P1 is being used mainly for avionics development and certification, while P2 is scheduled to undertake function and reliability (F&R) tests, and post-certification “service” tests. “The second aircraft will be used for a clean-up of the systems,” adds Meyer.

P2 is currently expected to fly some time in the first quarter of 2006. The fast-paced test schedule calls for up to three flights a day with US certification expected in the second half of next year, with first deliveries starting in December. Total test hours on the two aircraft at the end of October were approaching 320h over 200 flights, of which more than 60h had been amassed by P1 on some 30 flights.

The Mustang is capable of 340kt, Mach 0.63 and a maximum operating altitude of 41,000ft, and had proved these capabilities during envelope expansion work by mid-October. The Mustang is the second application for the new P&WC turbofan, using the 1,350lb-thrust (6.7kN) PW615F variant, and early flight-test experience led to the need for “some changes to the engine”, says Meyer, who adds the modifications were “more tweaks to do with the hardware and systems and how they were manufactured rather than performance related”.

The Mustang also features a Garmin G1000 integrated flightdeck incorporating three large-format liquid crystal displays – two 250mm primary flight displays and a 380mm multifunction display. Although this is Garmin’s first jet application of the G1000, Meyer says the avionics manufacturer is “doing pretty good, and is basically keeping to schedule to date”. Together with Garmin, Cessna and Flight Safety International are developing a “focused avionics” module for the training syllabus in recognition that “some of the Mustang pilots will be new to jets”.

On track

Although the initial Mustang airframes have been assembled at Cessna’s Wichita site, full production will take place at the Independence, Kansas facility where its piston singles are currently made. Production tooling was transferred in mid-2005, with full production starting in the fourth quarter, marking the first time any of the Citations will be built away from the Wichita area. Current firm orders for the Mustang jet are believed to stand at 232.

In Englewood, Colorado, flight tests of the Williams FJ33-powered Adam Aircraft A700 have now reached more than 310h on the proof-of-concept aircraft, says marketing director Marc Blakely. The all-composite, twin-boom VLJ is “on track for certification by the end of 2006”, he adds, saying the process is being streamlined thanks to pending certification of the structurally virtually identical piston-powered A500 variant, now at an advanced stage. “We think 2006 is achievable because a lot of the basic [certification] work will have been done with the A500,” he says. Around 70% of the parts and structure of the two aircraft designs are considered common for certification purposes.

Recent items checked off the test list include clearance of the aircraft’s autopilot and pressurisation systems, plus operation of the undercarriage doors. “The belly pod we added has also been successfully tested, and we’ve gone up to 30,000ft,” says Blakely. “Between now and NBAA the test programme includes altitude expansion, and we should be taking it up to 41,000ft next week.” Top speed achieved to date is 315kt, close to the 340kt expected to be achieved at a cruising altitude of 38,000ft. Range with NBAA reserves is anticipated to be around 2,035km.

The aircraft is powered by upgraded engines with dual-channel FADEC and other changes made earlier this year to ensure full conformance with the FJ33-4A-15 standard certificated in September last year. The A500, meanwhile, received restricted type approval from the FAA in May. “There were some outstanding issues, but those are being checked off as we speak,” says Blakely. Certification of the A700 has, however, been slowed because of “the intense resource allocation to push the certification and button up the outstanding items on the A500”.

The first FAA-conforming A700 aircraft, serial number two, is coming together, however. “We’ve done the dry mating on the wing, so the fuselage, wing and tail are coming together and it is due to fly this quarter,” Blakely says.

The firm orderbook for the A700 “is in the 60s, exclusive of fleet deals”, he says, adding the $150 million, 75-jet order from start-up air taxi operator Pogo is still “on the books”.

Operating from an adjacent hangar to Adam Aircraft at Centennial airport in Englewood, Aviation Technology Group’s Javelin prototype has just embarked on its test effort, having completed its maiden flight on 30 September.

Power play

The fighter-like two-seat VLJ, which is also aimed at the military training market as well as “sports jet” customers, reached a maximum speed of 180kt and an altitude of 12,000ft during the 30min sortie. The aircraft resumed test flights again in October. Piloted by ATG vice-president of operations and chief test pilot Robert Fuschino, the aircraft sustained an initial climb rate of 3,000ft/min (15.2m/s) on the first flight. “The pilot had to throttle back pretty quickly,” says chairman George Bye.

The prototype is powered by two Williams FJ33-4-15 turbofans that have been “tweaked” slightly to push thrust towards the 1,700lb level of the -17M engines intended for the conforming prototypes and production versions. The first conforming aircraft is due to join the test programme at the end of 2006. The certification effort will involve six airframes – four flying aircraft and two ground airframes for static and fatigue tests – not including the developmental prototype.


Source: Flight International