Bill Lear created a market when he designed the first Learjet. Now Learjet is seeking to revitalise that market with the all-new Model 45.
Graham Warwick/WICHITA Cutaway poster/David Hatchard
LEARJET HAS A tough mission for its first all-new aircraft since the original Learjet 23 was introduced three decades ago: to recapture the leadership of the light business-jet market which Learjet created. Its expectations for the Learjet 45 are great. In 1976, Learjet delivered 93 light jets; but in 1994, it delivered just 14, against Cessna's 97.
Initial signs are encouraging. The first two years' deliveries are sold, despite Learjet having increased planned production rates. The Learjet 45 line is now sold out into 1999 and the company is considering a further production hike to make more aircraft available earlier.
At the same time, sales of the Learjet 31A light jet are recovering and the mid-size Learjet 60 continues to be a strong seller. The Learjet 45 will fit between these two aircraft and, with it the Wichita, Kansas-based company hopes at least to double business-jet production.
Learjet believes that its 45 offers exceptional value: a $6 million aircraft offering traditional Learjet light-jet performance (and style), combined with a cabin comparable to those of mid-sized business jets costing $9-14 million. Fuel efficiency, maintainability and attractive warranties - five years on the airframe, engines and avionics - are also part of the value equation.
COMPANY FIRST
The company claims several firsts for its 45, including the first business-jet designed entirely from scratch on computer, and the first developed jointly with other Bombardier companies (Flight International, 7-13 December, 1994). Significantly, these two factors have conspired to delay the programme by six months, but Learjet remains convinced of the long-term benefits of electronic product-definition and shared company-resources.
Overall design has been Learjet's responsibility, from the initial market research, through advanced design and wind tunnel testing, to definition of the external lines, aerodynamic loads and design rules. Detailed design has been the responsibility of Bombardier companies de Havilland (for the wing) and Shorts (for the fuselage and empennage).
De Havilland and Shorts deliver the major airframe sections to Wichita for final assembly, interior completion and painting by Learjet, which is responsible for flight-testing and certification, and for marketing and support. "The aircraft is clearly a Learjet design," says Learjet president Brian Barents.
Learjet took advantage of Bombardier's "centre-of-excellence" approach to draw on the manpower and machinery available at its sister companies. Learjet would not have been able to tackle the programme alone, without adding significantly, to its engineering workforce and investing heavily in the machines needed to automate manufacture.
Vice-president for engineering Bill Greer estimates that fewer than 250 people have been added by the companies to handle the programme, while Barents says that "very little" capital investment in new machinery has been required. Manufacture of the wing and fuselage is highly automated, to achieve the man-hour-content reduction necessary to meet the design-to-cost target.
Learjet was only slightly behind Boeing in pioneering the use of electronic product-definition, Barents notes. Initially, this used the computer-aided-design systems already in place at the three companies - Unigraphics at Learjet, CATIA at de Havilland and Computervision at Shorts - but interfacing these systems "...did not go as smoothly as anticipated".
The result was a three-month delay. The solution was for Learjet to acquire CATIA and Computervision workstations so that it could access design data produced by de Havilland and Shorts. Bombardier is standardising on CATIA.
The 45 programme marks Learjet's first formal use of design-build teams, to reduce risk and cost, and of design for assembly, to reduce parts count and assembly man-hours. The 45 is a machine-built aircraft, where previous Learjets have been "bent-metal" designs. Numerically controlled machining is used to improve manufacturing quality and reduce parts count. The 45 has some 45% fewer parts than the 31 Greer says.
"Concurrent-engineering design takes longer, but pays off in lower parts-count, less scrap and reduced manufacturing time," he says. Parts-quality has been high, with low rejection and discrepancy rates compared to those achieved in Learjet 31 and 60 production. The rejection/rework rate for the first fuselage was 1.3%, compared with 20% for a typical first article, the company says.
Aircraft are being built from the outset on production tooling, produced using the same three-dimensional design database. Building four flight-test aircraft on production tooling at the same time as drawings were being released brought problems with configuration management and, Barents admits, Learjet lost control of the documentation, leading to another three-month delay while conformity was restored.
He says that initial deliveries will still be made, as scheduled, by January 1997 - the end of Bombardier's financial year - although they will be fewer than had been planned. Learjet believes that the schedule margin built in for the incorporation of design changes resulting from flight tests will not be needed, and production has already started, on schedule. "The goal...is to have no changes during flight test, to be as close to the final aircraft as possible," Greer says.
CABIN COMES FIRST
Learjet says, that the 45 was designed "inside-out". According to Greer, the company began wanting a state-of-the-art performance increase - "the Learjet mindset", he admits - but the market wanted more comfort. The design had started out with the Learjet 31 fuselage-diameter. This was increased, but the design-to-cost target was not, he says.
The Learjet 45 cabin has a non-circular cross-section - curvature starts at shoulder level, rather than at the hip - with 16 large windows and a flat floor, the latter made possible by a wing carry-through structure which curves under the pressure vessel, rather than passing through it. The cabin is 1.55m wide, 1.49m high and, at 6.02m from cabin divider to pressure bulkhead, is longer (but narrower) than that of the mid-sized Learjet 60.
This length allows the cabin to accommodate eight swiveling, reclining, Erda seats in a "double-club" layout, with a galley and closet forward and a lavatory, with 0.5m3 of carry-on baggage accommodation, aft. A belted toilet-seat certificated for a ninth passenger is optional. Entry to the cabin is through a forward clamshell door, the upper part of which serves as an emergency exit. A 0.65bar (9.4lb/in2) pressure-differential provides an 8,000ft (2,400m) cabin altitude at the 45's 51,000ft service ceiling.
The aft fuselage houses a heated, 3.45m3-capacity, baggage compartment long enough to house an optional rack for eight sets of skis. Manufacture of the fuselage is highly automated. Shorts uses a numerical-control router to cut out door and window apertures and drill holes for frames and stringers, which are attached using an automatic riveter.
Enlarging the fuselage without relaxing any performance goals required an efficient wing. The section and planform are new, and are designed to give the benefits of a supercritical wing without the high sweep and aft loading which would require powered flight-controls, which Learjet wanted to avoid in a $6 million aircraft, Greer says.
The Learjet-designed aerofoil is optimised for Mach 0.81. The top is flattened and the wing twisted to keep the outboard sections flying at low speed - the leading edges forward of the ailerons are drooped to enhance flow over the control surfaces at high angles of attack.
Fully supercritical winglets, to reduce cruise drag, and outward-angled "delta fins" under the rear fuselage, to improve low-speed stability, reinforce the 45's familial resemblance to the Learjet 31A and 60. The T-tail is also another Learjet hallmark.
Compared with earlier Learjets, the wing structural design is simplified, with three spars instead of the eight in the 30-series wing. About 80% of the wing components are machined, including the skins, which are auto-riveted after milling. The parts-count, at around 2,300, is about half that of the 30-series wing.
Structurally, the Learjet 45 is a conventional all-metal design. Composite materials are used only for fairings. "It is hard to justify composites in a design-to-cost aircraft," says Greer. Aerodynamically, the aircraft is the product of extensive computational fluid-dynamics analysis, using NASA's TranAir program, and wind tunnel testing. This contrasts with Bill Lear's concept of a "wind tunnel in the sky".
A big contributor to performance and efficiency is the engine. Compared to the TFE731-2 powering 30-series Learjets, the AlliedSignal TFE731-20 has a 20% higher bypass-ratio, 33% higher pressure ratio, 15% higher cruise thrust and 11% lower specific fuel consumption. Thermodynamically capable of 20kN (4,435lb) thrust, the engine is flat-rated at 15.6kN to 34¡C, with a single-engine rating of 16.2kN. Dee Howard cold-flow (using bypass air) target-type thrust reversers are standard.
A TFE731-20 has been flown on a Learjet 35 testbed to check operation to 51,000ft and refine the full-authority digital engine-control (FADEC) software. The single-channel FADEC, with hydro-mechanical back up, provides features such as automatic starting and relighting, and also increases maintainability. Compared to the -2, the hot-section inspection interval is increased by 75%, to 2,500h, and the compressor-zone interval to 5,000h.
Honeywell's Primus 1000 integrated-avionics suite includes four large (200 x 180mm) cathode-ray-tube displays - two primary-flight displays, one multi-function display and an engine-indication and crew-alerting system (EICAS) display. The suite is built around dual integrated-avionics computers providing display-processor and flight-director redundancy. The autopilot is single-channel, but sensors, such as the fibre-optic-gyro attitude- and heading-reference systems, are duplicated.
Two liquid-crystal-display radio-management units are used to control the Primus II integrated radios, and serve as back-up navigation and engine displays. Honeywell used a MacIntosh Quadra 900 computer running Aldus Supercard graphics software and driving three large-screen monitors for rapid prototyping on the Learjet 45 controls and displays, incorporating suggestions from advisory-council pilots who "flew" the system.
Learjet's systems-design philosophy was to provide capability without complexity. The primary flight-controls - ailerons, elevators and rudder - are mechanically operated. The spoilerons and single-slotted flaps are hydraulically actuated, while the horizontal stabiliser is moved electrically for trim. A Dowty Aerospace spoileron-control system allows these surfaces to be used as fully variable speed brakes, lift dumpers, or for aileron augmentation or back-up roll control.
A trailing-link, twin-wheel, main landing gear was selected for ride quality and ground handling. Heroux supplies the gear; BF Goodrich provides the wheels and carbon brakes; Crane Hydro-Aire furnishes the brake-by-wire system; and Dowty Aerospace contributes the steer-by-wire nosewheel-steering system.
The electrical system includes two engine-driven starter/generators, two main batteries and an emergency battery. The 280bar hydraulic system includes two engine-driven pumps, plus one electrically driven auxiliary pump. AlliedSignal supplies the digital cabin-pressure control and air-cycle environmental-control systems.
Fuel is contained in one fuselage and two wing tanks, fuel being moved from the fuselage tank to the wing tanks, which supply the respective engines. Single-point pressure refueling is standard. Bleed-air anti-icing is provided for the wing and horizontal-stabiliser leading edges and nacelle inlet-lips. The Sierracin windshields are electrically anti-iced.
SUCCESSFUL COMBINATION
Design objectives for the 45 were set in October 1990, just months after Learjet had been taken over by Bombardier. These called for an aircraft combining the performance of the Learjet 35 and the handling of the 31 with increased passenger comfort and a good ratio of price to value, says vice-president, programme management, Andre Brais. Launch approval came in January 1993, and only after the company had completed a structured definition programme, new to Learjet, but familiar to Bombardier, which was designed to reduce risk.
"This is not a derivative," says Greer, "there is no part of any other aircraft in the Learjet 45." As a result of Bombardier's structured approach, "...the aircraft was much more defined before launch...the planning reduced the overall programme cost and risk", he says. A "very vocal" new-product advisory group, consisting of 16 flight-department and maintenance managers, helped guide the design process.
Learjet aircraft typically have good payload/range performance, "...and the 45 will be a good Learjet", Greer says. The design range is 4,075km (2,200nm) with four passengers and two crew: range with two passengers will be 4,300km; with eight passengers, 3,840km - "the best we have come up with yet", he says. Maximum Mach number is 0.81 and maximum altitude 51,000ft - typical Learjet figures.
The company believes that the Learjet 45 will give corporate flight-departments the flexibility to serve different markets with the same aircraft - to fly eight passengers from New York to Washington DC, one day, then fly a key executive two-thirds of the way across the USA the next. The 45 is not seen as a company's first aircraft, but as a step up from a light jet or large turboprop.
This analysis appears to be borne out by initial sales. About 60% of the customers are existing Learjet operators, Barents says, but the rest are moving up from heavy turboprops and other manufacturers' light jets. A handful is moving from older mid-size business jets, he says.
Barents is encouraged by the early penetration of the large-turboprop market. "Our concept was to price the aircraft against heavy turboprops, to make it a logical step up from a $4-4.5 million large turboprop and an alternative to late-model light jets, so that operators did not have to step up to a mid-sized jet."
Learjet believes that the 45's combination of mid-jet comfort and light-jet operating costs will allow flight departments to consolidate on a single aircraft type, rather than needing both a high-speed light jet and a large-cabin heavy turboprop to meet its transport requirements.
The second Learjet 45 was formally rolled out on 14 September as preparations continued to fly the first aircraft between 22 and 24 September, on the eve of the US National Business Aircraft Association convention in Las Vegas, Nevada.
Learjet has added a fifth aircraft to the flight test programme in a bid to recover some of the delay. The aircraft will be used for functional and reliability testing. Learjet, is planning simultaneous US and European certification, which is expected now in early December 1996.
Source: Flight International
