Sao Jose dos Campos, Brazil – Four years ago, the only offering in Embraer’s business jet stable was the Legacy 600 which had to prove to operators that Embraer was offering a quality business jet that was a step up from the competition. With its first business jet program having successfully proved its mettle in a new market, the company launched into the big iron biz jet market with the Lineage which was certificated earlier this year. Related Story

Since then, true to the company’s ambitious roots, Embraer launched four new clean sheet designs, the latest being the Legacy 450 and 500 which, like its Phenom 100 and 300, benefit from a significant competitive advantage – Embraer’s successful experience in the commercial market. Raising the Bar – Embraer’s Business Jet Advantage – Part I

All this, from a company only 40 years old which has become the number three commercial jet manufacturer in the market. Given the fact that it has managed to capture 50% of the market for what it calls entry level and light jets – the Phenom 100 and 300 – its progress seems to promise the same for the biz jet side.

Legacy 450, 500
Formerly known as the MLJ and MSJ, these two versatile jets are aimed at the markets that are either transcon or just under transcon. And as Vice President Market Intelligence-Executive Aviation Claudio Camelier told Aviation Today’s Daily Brief promise value for dollar. “Our aircraft are not the least expensive ones in their categories, but they deliver more value to the customer,” he said, recently, as he briefed reporters on the progress of the newly renamed Legacy 500 and 450 programs, due for service entry in 2012 and 2013, respectively. He spoke of the innovation in these jets, with the $18.4 million 500 “a real U.S. coast-to-coast-capable aircraft with eight passengers and headwinds and a range of 3,000 nm). The $15.25 million 450 range is 2,300 nm.

Launched in 2008 and designed with the largest and quietest cabins in their classes, the Legacy 450 and 500 are medium-sized executive jets with interiors designed in partnership with BMW Group DesignworksUSA. That relationship resulted from a customer tip. Faced with the usual executive jet interior, the customer noted that his car was more comfortable than a multi-million-dollar jet. The Legacy 450 includes a complete refreshment center and the Legacy 500 includes a fully-equipped wet galley. Both have what Embraer calls “unmatched baggage compartment volume.”
The jets promise to be the fastest in their categories, according to Sales Engineer Executive Jets Maurelio Novaes Jr., Legacy 450 and Legacy 500 projects strategist, who added they will also be the only ones with cutting-edge, full fly-by-wire electronic flight controls.

“The redundant high-speed computers and side-stick control will enable a smoother flight and offer to passengers and pilots the advantage of optimized performance, increased comfort, greater control, reduced workload and flight envelope protection,” he said. “Both aircraft will also provide a reduced time to climb to high altitudes and excellent field performance.”

The Legacy 450 is being designed for a range of 2,300 nautical miles (4,260 km) with four passengers, or 2,200 nautical miles (4,070 km) with eight passengers, including NBAA IFR reserves, affording such nonstop missions as Atlanta to Seattle, New York to Mexico City, Moscow to Madrid or Riyadh, and from Rio de Janeiro to Bariloche (Argentina).
The Legacy 500 is being designed for a range of 3,000 nautical miles (5,560 km) with four passengers, or 2,800 nautical miles (5,190 km) with eight passengers and Mach 0.80, including NBAA IFR reserves which affords nonstop coast-to-coast from Miami to Seattle, New York to Los Angeles, or Los Angeles to Honolulu, in the United States, as well as from Gander (Canada) to Paris, Paris to Riyadh, Moscow to New Delhi, and Rio de Janeiro to Chicago, with a stop in Caracas. For performance charts on the two aircraft and how they compare with the competition see below.

These programs, too, reflect Embraer’s airliner philosophy being the only aircraft in the category with a full, six-foot stand up, flat floor cabin which “provides a huge difference in the cross section from its competition and, like the Phenom, it is designed for high dispatch reliability and low operating costs learned in producing the regional jets,” said Camelier.

Camelier, who emphasized that the clean sheet design of the two new aircraft, said they provided a competitive advantage since they offered new-generation technology which incorporated vast customer input.

“This is a new paradigm for the segment,” he said, adding the company completed the joint definition phase in April. “They offer extensive situational awareness and intuitive user interface.” He also reported that the detail design and certification phase has started, with more than 500 Embraer engineers engaged in the program. The company completely a second man-machine interface meeting in August.

This new paradigm includes state of the art technology, Rockwell-Collins Pro Line Fusion Avionics, full fly-by-wire flight controls, VNAV, auto-throttle, paperless cockpit capability, an optional head-up guidance system.

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Still ongoing are the structural layout definition, systems architecture and interfaces definition, integration of systems and structures, fly-by-wire control validation, interior mock up performance evaluations and the virtual reality manufacturing process evaluations. The next steps, he said, included critical design reviews expected to be completed by the end of the year and the start of drawings release.

Unique in Class
“It is the only aircraft below $40 million that offers fly-by-wire (FBW) technology application for the elevator, aileron, rudder and spoiler,” Camelier said. “This offers advantages in weight savings, improved performance, reduced workload, smoother flight and increased pilot control. It replaces conventional mechanical links between flight deck controls and flight control surfaces and reads the pilot’s desire and decides which surfaces should move, in which direction and by how much.” See full interview here. www.aviationtoday.com/videos/

Embraer has a lot of experience with FBW. In the 1980s, it was put on its AMX military jet, co-developed with Aeritalia, and more recently on its ERJ 170/190 regional jets which join the Boeing 777, 787 and Airbus A340-600 and A380 in using FBW technology. The ERJs include FBW flight control in pitch and yaw axis and a Hybrid FBW/hydro-mechanics roll axis with FBW spoiler married to a conventional aileron. Embraer is the owner of some of the patents related to FBW, such as steep approach and angle-of-attack limiter systems now on the regional jets.

In the business jet market, FBW is usually reserved for the highest end, ultra-long-range products such as Dassault’s Falcon x and the developing Gulfstream G650, both of which use full FBW controls.

“The Legacy 450 and 500 are breaking a paradigm by bringing a technology that is now available only on larger and more expensive airplanes into the midsize and midlight business jet categories,” said Fabrício Reis Caldeira, Flight Control Laws manager. “The experience accumulated during the development of these programs has allowed Embraer to move one step further, in order to take full advantage of the technology.”

FBW Technical Briefing Transcript –– Chief Test Pilot Mozart Louzada Jr.

FBW Flight Control System Advantages
A demonstration of the FBW capability by Chief Test Pilot Mozart Louzada Jr. was impressive for its inability to allow the aircraft to fly outside its envelope.

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All of the Legacy 450 and 500 competitors have a conventional mechanical flight control system, which means the aircraft has a direct mechanical link from the cockpit inceptors to the actuators of each primary flight control surface.

“The strategic decision to go to FBW was made because Embraer is committed to design and produce the best airplanes in their respective categories, combining the unparalleled handling, increased performance levels, passenger comfort, and safety characteristics afforded by FBW flight control technology, with unmatched cockpit and cabin design,” said Louzada. “The Legacy 450 and 500 FBW flight control system is tailored to optimize the airplane’s performance (speed, range and climb), provide weight savings and fuel economy, reduce crew workload, increase passenger comfort, and enhance flight safety.

“With the FBW high-speed protection system, the aircraft can achieve higher maximum cruise speeds, getting closer to the structural limits of the aircraft without compromising its safety,” he continued. “The range/climb improvement is possible because of the weight savings and drag reduction.”

He added the company imposed control laws that provide automatic compensation for thrust variations, landing gear, and different flap configurations, and that provide the same flight characteristics for different weights, center of gravity (CG) positions, and speeds. All of which make for reduced crew workload.

“With the longitudinal flight path rate control law that will be used in the Legacy 450 and 500, the pilot does not have to trim to change speeds,” he said. “The FBW system provides low workload, predictability and excellent flying qualities. The passenger experiences greater comfort because FBW provides increased stability and a damped response, reducing aircraft oscillations during turbulence. Also, with FBW the aircraft has precise pilot control and reduced transience with configuration change such as flaps or landing gear changes.

“From a safety point of view, FBW can reduce transience in the case of a system failure such as an engine shut-down or surface hard-over, in such a way that the aircraft is easier to control,” he continued. “For some flight conditions, like wind shear escape and Controlled Flight into Terrain (CFIT) avoidance, FBW can achieve the best climb rate through a simple pilot procedure – a commanding full aft stick. Moreover, the Legacy 450/500 have three hydraulic systems and an extra power source (the Ram Air Turbine - RAT), whereas the competitors have only one or two hydraulic systems and no RAT. The increased systems redundancy implies greater safety, as well.”

FBW Architecture
The main components of the FBW flight control architecture are cockpit inceptors (pilot and copilot side sticks, rudder pedals, speed brake, and flap handle), Inceptor Interface Modules (IIM), Remote Electronic Units (REU) and the Primary Flight Control Computer (FCC). Embraer tapped Parker Aerospace, teamed with BAE Systems and SKF, for the FBW flight control system.

The IIMs are responsible for reading cockpit inceptor sensors and sending the data to the FCC through the digital data bus. The FCCs are the main computer. There are two redundant FCCs, each of which has dual dissimilar lanes, in a command/monitor scheme. The two FCC channels operate in an active/standby configuration.

The REU is the electronic unit that operates the airplane’s flight control surface actuators. The REUs operate the primary control surfaces, and also the spoilers, flaps, and horizontal stabilizer.

Cockpit/Side sticks and Pedals
Embraer is using side-stick controls for the Legacy 450/500, instead of the conventional control wheel and yoke system. This offers a better view of the displays, a cleaner cockpit, and more precise control of the airplane, as well as reduced weight, maintenance and spare parts, he said.

The side stick is passive, where force feedback is provided by dual fixed springs, each tuned to the longitudinal and lateral axis, respectively. If dual pilot input is computed, aural and visual warnings and stick vibration alert that both pilots are making inputs. The rudder pedals are mechanically linked with dual fixed springs, also providing a feel of the force of the airplane’s movement.

Flight Control Laws
For the Legacy 450 and 500, the flight control computers (FCC) compute the commands to move the flight control surfaces based on input from the pilots via the side stick and the rudder pedals. In normal operations (that is, without significant system failures), the pilot commands are interpreted by the FCCs as demands for aircraft response rather than surface deflection, as in a conventional aircraft. The FCCs move the surface, in order to achieve the desired response.

Also in normal operations, the longitudinal control law maintains the aircraft flight path and stick deflection command flight path rate. This means that the Legacy 450 and 500 do not behave like a conventional aircraft; they are flight path stable, rather than speed stable.

A conventional aircraft will maintain its trimmed speed. If velocity is lost, the aircraft pitches down to maintain the trimmed airspeed and, likewise, if airspeed increases, the aircraft will pitch up to maintain velocity. Thus the conventional airplane is speed stable, rather than flight path stable.

The Legacy 500 control law for most of the flight phases is flight path stable. When the aircraft begins to change speed the control law maintains the flight path. The control law automatically trims the aircraft to the new speed. This significantly reduces pilot workload and is totally compatible with a side-stick operation, because the stick can stay in the neutral position, while the control law trims automatically.

The control law provides conventional speed stability during the landing flare flight phase. When the aircraft begins to lose speed, the pilot has to pull back on the stick, in order to prevent a pitch down movement, like with a conventional aircraft.

During turns, the control law will automatically compensate for the pitch command required to maintain the flight path to a bank angle of up to 33 degrees. There is no side-stick back pressure required to maintain the flight path for bank angles up to 33 degrees.

The lateral flight control law for the Legacy 500 maintains the given bank angle rate based on side-stick deflection and provides neutral spiral stability for bank angles of up to 33 degrees, and strong positive spiral stability beyond 33 degrees. Thus, the control law will indirectly maintain the given bank angle at 33 degrees, with the side stick at neutral, and roll the aircraft back to 33 degrees, if the side stick is in the neutral position and the bank angle is greater than 33 degrees. Combined with automatic pitch compensation of a bank angle up to 33 degrees, this allows safe recovery from roll upset by returning the stick to the neutral position.

The lateral control law also significantly reduces pilot workload. The Legacy 500 can automatically keep a steady rate of turn with the side stick in the neutral position. During situations when it is necessary to maintain a sideslip angle (like one engine being inoperative), the control law significantly reduces workload, because it provides most of the compensation automatically, leaving only a residual for the pilot to recognize engine failure.

When it is not possible to maintain the normal mode operation, due to multiple system failures, the flight controls revert to direct mode operation. In this case, the normal mode control laws are replaced by direct mode control laws. The inceptor commands go directly to the REUs that have a gain schedule based only on air data or, in the case of loss of air data, flap position information. During this operation, the aircraft behaves like a conventional aircraft, and the side-stick and rudder pedal deflection are directly related to the surface positions.

Flight Envelope and Protection
One of the key aspects of the Legacy 450 and 500 Fly-by-Wire controls is flight envelope protection. That is, the control laws prevent the aircraft from exceeding the limitation of the flight envelope, such as structural load, high- and low-speed limits, and stall.

The flight envelope protections for the Legacy 450 and 500 are used for structural load factor (G protection), angle of attack (stall / buffeting protection), dive speed (high-speed protection), and sideslip (lateral structural load protection). The control laws calculate the appropriate surface commands to keep the aircraft inside the limits. Hard flight envelope protection is not applied to bank and pitch angle limits. If necessary, the pilot can make aggressive maneuvers to exceed these limits.

A concept applied to the project in the design of the flight control laws is the definition of two envelopes for the aircraft. One is the normal flight envelope; inside this envelope, the control of the aircraft requires less pilot workload, and provides significant passenger comfort. The control law will keep the aircraft trimmed to any condition inside this envelope, with the stick in the neutral position. The limits of the normal flight envelope are a bank angle of 33 degrees, maximum operational speed, 1.1 stall speed, +30 or -15 degrees of pitch angle.

Beside the normal flight envelope, there is the flight envelope limit. This envelope is when the aircraft is close to the extreme envelope limits, and a greater pilot workload is needed to maintain the aircraft in this condition. The pilot cannot override the extreme limits and, if the stick is released, the aircraft is automatically brought back to the normal flight envelope. The hard limits of this envelope are the aircraft structural limits, maximum angle of attack, dive speed, and sideslip.

Tomorrow – Embraer Adjusts Forecast – Part III

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