PAUL LEWIS / SÃO JOS‚ DOS CAMPOS
Embraer made bold decisions on the 170's fuselage design, wing size and engine. With the huge changes in the regional market, have these choices proved wise?
When Embraer began considering a new 70-seat aircraft to follow its successful ERJ-145 in 1998, it faced three immediate and fundamental questions that would shape the programme's future. The Brazilian manufacturer had to decide on a fuselage cross-section, wing size and powerplant at a time when the regional airline industry looked a lot different than it does now. Through foresight and good fortune, its choices have proved flexible and adaptable enough to evolve into today's Embraer 170/175 and 190/195 family of four aircraft.
Among the first pre-design concepts explored was a derivative of the ERJ-145's low wing and rear engine mount configuration, but going from a three- to a four-abreast cabin. This was ruled out on the grounds that it was too marginal a design in terms of performance and capacity. A more efficient solution from an engineering and operational standpoint was an all-new design incorporating underwing-mounted engines built around either a four-abreast fuselage or, like the rival Fairchild Dornier 728JET, a five-abreast cross-section.
"We took the two aircraft to the airlines and the result was the adoption of the four-abreast," says Luis Carlos Affonso, Embraer 170/190 programme director. "I think it was the right decision and confirmation came at last year's Farnborough air show, when we showed not a normal four-abreast but a new double-bubble four-abreast fuselage. It has the same comfort level as a larger jet, but no middle seat. The response from the mainline carriers was very positive."
Robust family
The response reflects the shift in emphasis since 1998 away from a product geared solely to the regional airline market to a more robust family design with equal appeal to traditional mainline carriers. At the urging of launch customer Crossair - now Swiss International Air Lines - the 195 version was added, stretching the maximum design capacity to 110 seats. By the end of the joint definition phase in March 2000, overall cabin volume had increased and greater flexibility was incorporated into the design to offer a wider range of seat, galley and toilet layouts.
The double bubble was chosen rather than a cylindrical shape. This has enabled Embraer to design a four-abreast cross-section, offering up to 2m (6.5ft) interior headroom, plus a 0.94m-high underfloor baggage hold, and lay claim to greater cabin volume per seat than the rival Bombardier CRJ700/900 or even the Airbus A320 series. The drawback is a more complex pressure vessel that has required structural strengthening and added some weight. To mitigate risk, a fuselage barrel has already completed 320,000h of fatigue testing - four times the 170's design life.
Today, Embraer is offering operators four pre-designed configurations, with the baseline 170 accommodating from 70 seats at 32in (81cm) pitch up to 78 seats at 30in pitch, and either a 42+28-seat, 33/31in pitch mixed-class or 6+60-seat, 36/31in pitch dual-class layout with a three-abreast business section. The 190 with the same pitch options will seat between 98 and 108 in a single class, 58+40 in mixed or 8+86 in a two-class plan. The 195, again based on a similar pitch, is designed to hold between 108 and 118 seats in single, 58+40 in mixed and 8+86 in dual class.
The 175 was the fourth member to join the family in 2001 which, thanks to the addition of 83.8cm forward and 93.9cm aft plugs, will accommodate two more rows of seats. The aircraft was added to better counter the now-stillborn 728JET and new CRJ900 stretch. The 175 will accommodate 78 seats at 32in pitch, or can match the 86-seat CRJ900 in a 31in-pitch layout. The aircraft could have been stretched further to close the gap with the larger winged 190/195, but this would have further eroded payload/range performance.
"There is no perceived demand to fill that gap currently," says Satoshi Yokota, Embraer executive vice-president industrial. "Technically it can be done if someone comes up with a scope clause limit of 85 seats one day and says he'll order 100 if we make an 85-seater." Embraer's other option is to remove about the same amount of fuselage from the basic 170 as was added to the 175 and produce a 60-seater version, but again the company says there are no plans on the table to do so.
Embraer's two other major design decisions centred on the choice of engine and the sizing of the wing. Prospective operators had been pressing the company for a choice of powerplant, but the need to enlist risk-sharing partners drove Embraer to enter into a sole-source business agreement with General Electric for the CF34. The company has elected to go with two different baseline versions of the engine, the CF34-8E for the 170/175 with a range of different take-off thrust ratings up to a maximum of 14,200lb (63kN), and the CF34-10E for the 190/195 rated at up to 18,500lb thrust.
The latter is essentially a new engine, incorporating a larger 53in diameter wide chord fan and new nacelle from Goodrich in place of Aermacchi/Hurel Hispano design on the -8E. The -10E draws heavily on GE's existing powerplant technology, including CF6 composite swept and leaned outer guide vanes and fan blade retention, the CFM56's high-pressure compressor aerodynamics, single-stage high-pressure turbine, single annular combustor and the CF34-8's four-stage low-pressure turbine and full authority digital engine control.
To preserve the 170's 3,430km (1,850nm) range and accommodate the 195's heavier operating empty weight (OEW) of 28,970kg (63,860lb), versus the baseline aircraft's 20,940kg OEW, Embraer has developed a larger wing for both the 98- and 108-seat versions. "We still see the Russians and Chinese talking about a single wing and engine, which we looked at and said no, it doesn't make sense," says Yokota. "You end up either sacrificing performance at the low or high end of the family. What we did has paid off with the different customer focus of the 170/175 and 190/195."
Shortened take-offs
The 170/175 wing incorporates movable, double-slotted flaps and the option of a ventral airbrake for shortened runway take-offs at less than 1,200m in length and steep angle approaches up to 7.5° into airports such as London City and Switzerland's Lugano, which Crossair/Swiss made a requirement. Improved field performance brings with it weight and payload/range penalties, but in the case of the 190/195, where this is required, designers have reverted to a fixed single-slotted flap configuration.
The CF34-10E's wider fan has, in turn, driven the need for a taller nose and main landing gear, as well as bigger wheels and brakes, for better nacelle ground clearance. Overall responsibility for both the 170/175 and 190/195 landing gear rests with Liebherr and its local partnership with Embraer Divisio Equipamentos. The main gear on the 70- to 78-seat jet is a telescopic design retracting inwards. On the 170 it features three-rotor carbon brakes and full electrically signalled braking, while the nose gear features a straight leg with steering integrated into the main avionics system.
While the 170 and 175, like the 190 and 195, enjoy about 95% system commonality, differences in the two subtypes' wing, engine and main landing gear reduces this figure to about 85%.
Cockpit commonality
Where Embraer has succeeded in achieving complete commonality is in the cockpit and aircraft handling qualities, thanks to its decision to go with a fly-by-wire (FBW) flight control system developed by Honeywell in partnership with actuator supplier Hamilton Sundstrand and hydraulic supplier Parker.
The three-axis FBW system controls the rudder, roll spoilers and elevators, with two electric hydraulic actuators per control surface and two separate channels to each actuator. For further redundancy, the horizontal stabiliser is independently electrically powered, while the ailerons are cable-controlled and hydromechanically actuated. Rather than choosing between the Airbus and Boeing control law philosophies, the company has "gone the Embraer route, which is somewhere in the middle", says Affonso. "For most aspects, the pilot has authority and we don't have envelope protection, apart from a variable limitation on the angle of attack to prevent the aircraft being stalled."
The aircraft's avionics are based on the same Honeywell Primus Epic architecture that Fairchild Dornier chose for the 728/928JET, and include its enhanced ground proximity warning system. Embraer, however, has opted for a cleaner design than its former German rival, based around five 255 x 205mm liquid crystal smart multifunctional displays (MFD) and slightly less integration. As well as displaying primary flight, navigation/weather, engine indication and crew alerting system information, the MFD can host colour-coded synoptic page displays for the aircraft's auxiliary power unit, electrical, fuel, hydraulic, air management, ice and auxiliary power unit (APU) systems.
Avionics software maturity has proved a challenge and contributed to slippage of eight months in first deliveries from the end of 2002 to August this year. Version 9 is being flown and will be followed shortly by 10, which promises to address any remaining nuisance messages. Finally, the aircraft will deliver with Version 11 loaded. Thales is supplying the aircraft's back-up integrated electronic standby instrument housed in a separately powered, small liquid-crystal display. The aircraft will be cleared for Category 3A landings, with head-up display and enhanced vision a planned future option, along with datalink.
Triple redundant
The aircraft employs a triple-redundant electrical system comprising three 40kVA generators - two engine-mounted integrated drive units permitting unlimited flight time with one inoperative, and the third with the APU. There is also a drop-down 0.6m ram air turbine beneath the right-hand side of the nose and two nickel carbide batteries as a final back-up. Honeywell, in addition to supplying the generators and overall APU package, including a Goodrich-built tail cone, is also responsible for the air management.
Embraer has designed the aircraft around two wing fuel tanks holding up to 9,470kg (20,860lb) for the 170/175 and 13,000kg for the 190/195. There is room for extra tanks in the belly if a longer range version or the proposed ECJ-170 executive transport are pursued, which would demand a range of 7,400km. The fuel management system employs a motive flow system with ejector-type primary boost pumps backed up by AC motor-driven auxiliary pumps and a DC motor-driven pump for APU and engine start.
Redundancy has also been designed into the hydraulics, with three independent systems operating at 3,000lb/in2 (207bar). Installed in the wing-to-fuselage fairing are systems one and two, both employing engine-driven AC electrical pumps, while system three is in the aft fuselage behind the rear pressure bulkhead and uses two AC pumps. "We did look at going to 5,000lb/in2 to reduce weight, but it could have created extra cost for operators," says Affonso. "We wanted more mature technology and not a risk in terms of maintenance and support."
Key to selling the 170 is cost, of which maintenance accounts for 8% of the estimated $2,748 direct operating cost of flying a 170 over a 925km sector in the USA. Airlines are looking to decrease aircraft turnaround time and lengthen the interval between maintenance visits. One powerful new tool will be the central maintenance computer (CMC), to which data can be downloaded on the ground or in the air using the ACARS datalink system. The CMC, in turn, will instruct a maintainer's laptop on the problem and even provide a link to a relevant electronic manual.
Embraer has invested about $50 million in new infrastructure to support the 170 programme. This ranges from $3 million spent on a three-dimensional virtual prototyping centre to simulate man-machine interface processes and conduct semi-immersive design analysis, and up to $15 million to buy seven production docks. Additional funds have gone into shared facilities, such the opening of the Gaviao Peixoto test centre 300km north-west of Sao Paulo, complete with a 5km runway, and a $12 million paint shop at Embraer's main Sao Jose dos Campos plant.
The assembly docks are housed back-to-back in a new 16,000m2 (172,000ft2) hangar that will be capable of turning out up to seven aircraft a month. Embraer looked at a number of options, such as a flow and moving line, but its experience with the Legacy corporate jet having to be pulled off the ERJ-135/145 production line for rework and customisation, pointed to a dock solution. "If you have different products on the same line, it doesn't work well," says Yokota. "We have four aircraft with different-sized fuselages and wing, and we can't expect a 170 to take the same time as a 195, so for that reason we have gone for a dock system."
Work is divided between Embraer and 16 partners around the world. France's Latecoere ships to Brazil a common forward and aft fuselage barrel for all four versions, while Embraer has responsibility for the nose section, centre fuselage, wing-to-fuselage fairing and the different-sized fuselage plugs for the 175, 190 and 195 versions. Spain's Gamesa supplies the empennage for the 170/175, and the wing is assembled by Embraer using leading and trailing edge components supplied by Kawasaki Heavy Industries (KHI) of Japan.
Embraer has been encouraging its partners to establish a local presence to bolster local content on the new aircraft, with the goal of having at least 50% of the jet by value produced in Brazil. Wing panel and slats supplier Sonaca already has a local entity in the form of its Sobraer partnership with Embraer, and GE already does some engine dressing work at its local GE Celma operation and is thinking of moving to Sao Jose dos Campos. KHI last month became the latest supplier to invest in local plant at Gaviao Peixoto and, in return, has been given complete responsibility for the larger 190/195 wing (Flight International, 6-12 May).
Test programme
To date, six development test aircraft and the first production-standard 170 have flown, and by early May the programme had completed 94% of the planned 1,800h test programme. Structural load testing is complete, and full-scale fatigue testing is on track to reach the 5,000h mark, which is required for certification, this month. On the assembly line currently is the first of two 175 test aircraft due to fly in June and the first production jet for delivery to Alitalia in late August. The first of two 195s is scheduled to fly by the end of the year, followed by two 190s in 2004.
The company is planning an initial build cycle of six months per aircraft, with the final month spent in the final assembly dock, where the fuselage is mated to the wing, empennage and cone, and the landing gear and engines are installed. More critical is the supply of long lead components, which cannot be ramped up or down as quickly as final assembly. The company plans to deliver 12 aircraft this year, starting with the six ordered by Alitalia and two for General Electric Capital (Gecas), leaving four unspoken for.
Embraer plans to increase this to as many as 45 aircraft next year, including the first four 170s for Swiss, deferred from this year, and 10 aircraft ordered by LOT, six of which will come from Gecas's earlier order for 50. This leaves a good number of aircraft unsold, which must placed in the coming months to give suppliers enough notice. Much is riding on an expected US Airways order for up to 100 170/175s, with early deliveries the key. "If we did not have the capacity next year, then we would be well out of the race," says Fred Curado, Embraer executive vice-president airline market.
Source: Flight International
