Newest Learjet will be all composite

 - February 5, 2008, 11:34 AM
Bombardier’s Learjet division surprised the aviation world on January 22 when it announced that the airframe of the new Learjet 85 will be built entirely of composite materials. Launched as the Learjet NXT last October, the Learjet 85 is a midsize jet that will fill a niche between Bombardier’s Learjet 60XR and Challenger 300. Bombardier also announced that Grob Aerospace will design the jet’s structure and build the first three prototype Learjet 85s.

Before last month’s announcement, observers assumed that the Learjet NXT/85 would be built using aluminum, bearing in mind the distinctly Learjet configuration and Bombardier’s extensive experience building various Learjet models, including the in-production 40XR, 45XR and 60XR models. But for the past two years, Grob Aerospace CEO Niall Olver lobbied Bombardier Aerospace CEO Pierre Beaudoin to consider extensive use of composites in the new Learjet and to contract with Grob to design the jet’s structure, according to Olver.

Bombardier’s decision signals an increasing interest in composite construction for business jets and validates Grob’s efforts to develop the all-composite SPn utility jet and get recognition for its composites expertise. In addition, the Learjet 85 will be the first all-composite business jet to be certified under FAA Part 25 regulations. The Part 25 Hawker 4000 has a composite fuselage and metal wings.

Bombardier has already applied to the FAA for the Learjet 85’s type certificate, which will be an entirely new type certificate and not a derivative of earlier Learjet models. The manufacturer also plans to certify the Learjet 85 in parallel with the EASA, according to Mike Kanaley, Learjet vice president and general manager, which should help accelerate sales outside the U.S. Bombardier is also planning to complete all fatigue testing for determination of the Learjet 85’s full airframe fatigue life by the time it is certified. Many manufacturers certify to a short initial fatigue life, then expand that with additional post-certification testing.

Reducing the Parts Count
Grob’s contract with Bombardier is a strategic alliance, according to Olver, who told AIN that in addition to building the first three prototypes, Grob could also be involved in manufacturing Learjet 85 structure for an initial production run. “We’re in discussions around the final industrialization plan,” said Kanaley.

Grob will build the Learjet 85 using the same construction technique it does for the SPn. This method involves a just-in-time resin transfer to the carbon fiber weave before hand lay-up, Kanaley said. The advantage of this technique, he added, “is that it allows for a low-pressure cure.” An oven–not an autoclave (which controls pressure and temperature and is much more expensive)–is used for curing vacuum-bagged parts. Kanaley noted that a typical metal Learjet is made of 14,000 parts, while the composite Learjet 85 will consist of about 1,000 parts.

Bombardier already has composites experience at its Belfast, Northern Ireland plant, but in using a different technique to manufacture the horizontal stabilizer for the Global Express and parts for CRJs. The Grob method, Kanaley said, “would be a good technique to add to our arsenal.”

The next step for the Learjet 85 is finalizing the suppliers for the program, then starting the joint definition phase in April. Bombardier will continue revealing details about the program this year, likely at the EBACE show in May, followed by the unveiling of the Learjet 85 at the NBAA Convention in October.

So far, engineers have conducted low-speed wind tunnel testing of Learjet 85 models at the NIAR wind tunnel in Wichita and high-speed testing at Calspan’s wind tunnel in Buffalo, N.Y. The computational fluid dynamics analysis is “well in hand,” Kanaley said, “and our confidence is growing about exceeding our performance targets.” These include Mach 0.82 high-speed cruise, NBAA IFR range (100-nm alternate) of 3,000 nm and plenty of interior space to allow an eight-seat double-club configuration in the 71-inch-high, 675-cu-ft cabin.

Grob will build the three Learjet 85 prototypes at its facility in Tussenhausen-Mattsies, Germany, where it is also building the SPn. First flight will take place in Germany with Bombardier test pilots, who will then ferry the prototype Learjet 85 to Bombardier’s flight test center in Wichita. Final assembly, completion and delivery of Learjet 85s will be done in Wichita, according to Kanaley.

Bombardier decided on the Learjet 85 name as a result of a poll on the Learjet NXT Web site. “Learjet 85 emerged as the most representative of the real-life leap in terms of cabin volume and performance compared to the [midsize] fleet,” Kanaley said. Coincidentally, as of October 31, Bombardier held letters of intent with full deposits for 85 Learjet 85s.