Lessons learned from flight testing the Learjet 45 are beneÌting the Global Express

Graham Warwick/MONTREAL

Bombardier's Wichita, Kansas, flight-test centre is busy, with certification testing of the Global Express gathering pace as that for the Learjet 45 light business-jet winds down.

Testing of the Learjet 45 should have been wrapped up months ago, but has made significant progress only since being restructured in late 1996. Lessons learned have been applied to the Global Express flight-test programme which, although marginally behind schedule, is "going well", says John Holding, Bombardier Aerospace executive vice-president for engineering and product development.

Provisional US certification of the Learjet 45 was granted on 3 September, nine months later than planned, but approval of the ultra-long-range Global Express is still on track for May 1998, the company says. By that time, Bombardier's de Havilland Dash 8-400 regional turboprop will be in flight test at Wichita. Plans call for the company's Canadair Regional JetSeries 700 to enter flight testing in 1999, followed after the turn of the century by a proposed new mid-sized business jet. Experience gained with the Learjet 45, and refined on the Global Express, will prove central to achieving this aggressive product-development schedule.


Underestimated effort

Bombardier admits that it underestimated the effort involved in developing and certificating the all-new Learjet 45 - its first programme to involve risk-sharing partners. Holding says that the company did not realise fully the level of sophistication needed in the management tools used to control the partners, which include Bombardier sister companies de Havilland and Shorts. "During the programme, Bombardier has evolved from four separate companies into Bombardier Aerospace. The latter stages have involved all of the organisation," he says.

"We are late, but not because of any redesign [of the Learjet 45]. The problems were to do with the way we structured the programme," Holding says. Flight testing began in October 1995, but was effectively halted in late 1996 while Bombardier conducted a major review. This concluded that most of the early flight tests had been "wasted", he says, because aircraft had not been configured correctly for certification testing. "We had difficulty getting the aircraft configured to do flight tests."

As a result, after more than a year of flight testing, Bombardier found itself with 75% of the certification-test programme still to do. So flight testing was restructured and aircraft were configured to gather valid certification data. One change was the introduction of an "earned-value" flight-test concept, which Holding describes as "-deciding what has to be done to get real data, not just burn holes in the sky".

The outstanding flight tests required for certification have been completed in about nine months. Initial certification will be provisional, with some follow-on testing required to remove any restrictions, but Holding says that the Learjet 45 programme has been "pretty successful" since being restructured.

"We're late, but we've not got a lemon," he maintains, using the derogatory term for a bad product. "If we were late and we had a lemon, then there would be a problem." Bombardier is pleased with the end product, which meets its performance guarantees - some only by small margins. "It is overweight, but the customer buys performance, not weight. Range, speed and altitude are all there," Holding says. "Field performance is not there, but we will have a post-certification recovery programme."

An increase in empty weight has necessitated raising the maximum take-off weight by 225kg, to 9,070kg, to maintain the 2,720kg fuel load. Visual-flight-rules range meets the guarantee of 3,970km (2,150nm) with four passengers, while the maximum cruise speed of 458kt (850km/h) is close to the guaranteed figure. Take-off field length and landing distance are near the upper limits of the guarantees, at 1,425m (4,670ft) and 955m, respectively. Holding says that further analysis work and anti-skid optimisation should improve field performance by 10%.


Competitive aircraft

"Relative to what's out there, the Learjet 45 is still a very competitive aircraft," Holding maintains, citing a better combination of payload, range, speed and cabin volume than those of the rival Cessna Citation Excel and Raytheon Beechjet 400A light business-jets. He says that the aircraft "-is very stable, feels very safe and solid, has a nice cabin and has the right performance. We can live with the extra weight and we can do something about the field performance."

A modification line has been set up at Learjet's Wichita plant to bring 20 aircraft already produced up to certification standard. The changes are "mostly minor", says Holding, and involve items such as re-routing wiring and hydraulic lines. Deliveries are expected to begin in October or November and Bombardier plans to hand over 24 aircraft by the end of January 1998. A further 60 will be delivered in 1998-9.

Holding says that Bombardier has held on to its Learjet 45 customers "-by being honest with them". The company has orders for some 130 Learjet 45s, including 25 for the FlexJet fractional-ownership programme operated by Bombardier Business JetSolutions. Shares in "four or five" aircraft have already been sold, and the Learjet 45 promises to be a "good product" for the FlexJet scheme, he believes.


Breaking new ground

Assessing the Learjet 45 programme, Holding says: "At the end of the day, the concept was right, the basic design was right. Bringing it together and certificating it was difficult." He believes that the programme "-has broken new ground" by being the first to involve concurrent US Federal Aviation Administration and European Joint Aviation Authorities (JAA) certification of a business jet - JAA approval is expected soon after that of the FAA. Concurrent FAA and JAA certification is also a key goal of the Global Express programme.

Holding seems relaxed about progress with Global Express flight testing, despite the third aircraft having been grounded for six weeks for repairs following an inadvertent wheels-up landing. "We're about four to six weeks behind where I'd like to be, but there are no real concerns overall," he says. One reason for his confidence is the progress made using the first two aircraft; another is the imminent first flight of a fourth Global Express, which will join the Wichita-based test fleet in late September.

Aircraft 9001, assigned to performance and handling flight-tests, has been used for stall, stability and flutter evaluation - all of particular concern, Holding admits, because of the Global Express' highly swept, high-speed, wing with its complex high-lift devices. "There was some concern about our high-speed wing, but we designed it to have very good low-speed characteristics. It's very pilot-friendly," he says.

"The aircraft has demonstrated good natural stall," Holding says, adding that handling qualities during stalls are "superb". Stall speeds equal the company's best estimates and stall characteristics meet or exceed predictions; there has been "excellent" correlation between computational fluid-dynamics analysis, windtunnel testing and flight, he says. Low approach speeds have been confirmed - reference speed (Vref) is 125kt at maximum landing weight - and preliminary flight testing has shown that take-off performance meets predictions. Brake testing to determine the landing performance will begin in September.

In-flight handling characteristics are "excellent". Dutch roll is controllable throughout the flight envelope with yaw dampers off, Holding says. Flutter testing has been completed out to 398kt and Mach 0.95. Buffet onset during manoeuvres at high speed and altitude has shown good correlation with predictions, "-confirming the superior manoeuvre margin". A bank angle of 53í can be attained before buffet onset at M0.8 and 51,000ft, he says.

Aircraft 9002 is assigned to systems evaluation, and early tests have involved the brakes, landing gear, auxiliary power-unit (APU), engines and avionics. Overall brake performance is "exceptional", says Holding, and assessment of the brake-by-wire system has been completed. Landing-gear testing has included successful in-flight extension and retraction after a prolonged high-altitude cold soak. The APU has been operated up to 45,000ft and started up to 37,000ft, meeting the specification.

Holding says that all results to date from the BMW Rolls-Royce BR710 turbofans "-have met or exceeded expectations". The engines will be overweight when the Global Express enters service, but a plan has been proposed to achieve the guaranteed weight. The aircraft weight guarantee will be met and, even with overweight engines, there will be "no problem" meeting the performance guarantees, he says. Bombardier may certificate the Global Express with a 225kg higher maximum take-off weight, he reveals, to give the operator more flexibility.


Testing the range

Tests to confirm the Global Express' quoted 12,400km range have still to be conducted. Aircraft 9003 and 9004 will be used, because 9001 and 9002 have instrumentation which increases drag. "We have enough data already to know that we will meet our commitments," Holding says. He hopes to have completed a good range test before the National Business Aviation Association show at Dallas, Texas, on 23-25 September, where 9004 will be displayed.

Aircraft 9004 has been outfitted with an interior at the Global Express final-assembly plant at de Havilland in Toronto. Holding says that the aim has been to demonstrate what can be achieved within the aircraft's 2,700kg completion allowance. Beginning with GlobalExpress 9005, now in final assembly, aircraft will be outfitted and painted at Bombardier's new completion centre, now under construction in Montreal. Aircraft 9005 is to arrive there in November, and the centre will be able to accommodate up to 14 GlobalExpresses at a time and complete 30 business jets a year.

The Global Express is due to enter service in June 1998, but much testing remains to be done. Holding is confident that the certification date will be met, and that there is flexibility in the programme. Aircraft 9004, for example, is assigned to function and reliability testing in early 1998, but will be available from September for other flight testing, he says.

Source: Flight International