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At the double
Embraer has passed through the 25% point in its 2,000-hour E2 trials campaign – its nine-prototype effort should see the next-generation airliner variants enter service in 2018, 2019 and 2020
Responding to airline demands for dramatic improvements in fuel efficiency, reduced emissions and advances in passenger comfort, Bombardier created the clean-sheet C Series, while Embraer turned to its game-changing E-Jet for inspiration. Visitors to July’s Farnborough International Airshow were treated to the initial overseas appearance of the E190-E2 first prototype, and could easily have been forgiven for walking away with the impression that little had changed compared with the in-production E190.
In this instance, appearances really are deceptive. Alexandre Figueiredo, Embraer vice president, ground and flight test, reports, “The E-Jets E2 is far from a simple derivative. The driver for our engineering developments since the beginning of the program has been to create the most efficient aircraft family in the segment. To reach that goal, every opportunity to increase efficiency and performance was considered. The family has new engines, new, aerodynamically optimized wings, a new empennage, different landing gear, full fly-by-wire and generally improved systems. From a test campaign standpoint it is a new aircraft.”
E190-E2 aircraft 20.001 completed the new model’s maiden flight on May 23, 2016. The culmination of many thousands of hours of ground testing, modeling and simulation, it was entirely successful and might be considered more validation exercise than flight test.
Figueiredo explains that the aircraft’s configuration owes much to the wind tunnel: “Wind tunnel testing was Embraer’s primary source of aerodynamic data, helping us understand and optimize aircraft configuration. The E2 aerodynamic database, for example, derives its information from high-end wind tunnel testing with several scale models, each dedicated to understanding a specific phase of flight.
“Besides typical high-speed cruise configuration testing [in the transonic regime] and low-speed characteristics [the subsonic regime], the E2 was also wind tunnel tested for ground effect [in take-off and landing configurations], loads and aero-elasticity, airframe noise and flight in icing conditions.”
Simulation is being used extensively in the development program and was relevant from the beginning. “In the initial and joint definition phases, modeling and simulation using the concepts and tools embodied in Embraer’s own Virtual Airplane system were heavily used. As development advanced, enhanced modeling and simulation tools were employed, and we began incorporating hardware-in-the-loop systems, including our Mid-EDS and E-SIM engineering development simulators.”
Later in the process, an Iron Bird and several rigs came into play, gradually introducing configurations similar to those on the aircraft and eventually featuring fully representative systems. The latter have become integral to the development and certification process. Embraer credits much of its E2 first flight success to this complex validation and verification process which, it says, validated system integration security; the manufacturer had completed over 20,000 hours of E2 testing before May 23.
Little on that first flight was likely to surprise the flight crew either, since they were involved in the development process early on and had ‘flown’ the E190-E2’s maiden hop many times on the Iron Bird; flight operation was therefore entirely normal and safety scenarios well rehearsed. According to Figueiredo at Embraer, “The involvement of flight crew in the development process, using engineering simulators and rigs, enabled a deep knowledge of aircraft characteristics before first flight. The process enhanced the confidence of our engineers and crew and was largely responsible for such a successful first flight, during which many flight envelope limits were reached.”
With so much of the aircraft new, Embraer has employed a mix of its own system testing with supplier trials. “Avionics system development, including interface systems, began with early integration tests at supplier facilities,” says Figueiredo. “After this, we began using System Integration Test Station (SITS) and Avionic Integration Rig (AIR) testbenches at our own and supplier facilities, assessing avionics software and components for system integration, maturity, endurance/robustness, pilot-in-the-loop and requirements validation,” he continues. “The same process was applied to the flight controls, hydraulics, landing gear, electrical system, environmental control, engine control, APU, anti-icing system and fuel system, always beginning at the suppliers’ facilities and continuing at Embraer and supplier sites.
“Thanks to this continuous integration testing process, on the E190-E2 first flight all aircraft systems worked as expected, including the flaps, landing gear and FBW, which operated in normal mode. This enabled us to expand the aircraft envelope to maximum altitude and operational speeds.”
Even with the flight test program at an advanced stage, ground testing plays an important supporting role in integrated product development. It makes an essential contribution to the assessment and certification through system failure propagation trials and structural testing. The latter addresses ultimate loads and fatigue issues, ground vibration work for flutter test clearance and other factors.
There could have been no greater demonstration of the E2’s systems maturity than the transatlantic Farnborough trip, which came just 45 days after first flight. Flown at less than optimum altitude given the phase of flight test, the aircraft nonetheless performed more efficiently than Embraer’s extensive modeling had suggested.
Invited guests aboard the aircraft explored a cabin packed with equipment racks, operator stations and, most obviously, ballast tanks. Very far from the E2’s operational configuration, 20.001’s interior is furnished for three flight test engineers, and the aircraft features extensive embedded instrumentation for data acquisition. The primary operator station provides an overview of all test parameters and control over the aircraft’s cameras and flight test systems, including ballast and telemetry. Engineers at the other stations are able to follow the data being collected, but unable to interact with the test systems.The entire aircraft is instrumented, with in excess of 10,000 sensors and around 30 cameras. Combined with the data generated by the aircraft’s digital buses, this equipment array generates around 100,000 parameters used in the aircraft development and certification process.
Yet most of the cabin is given over to the large ballast tanks. The system enables engineers to change the aircraft’s center of gravity in flight by pumping water between tanks, or dumping it overboard.The cockpit is equipped with cameras and equipment that record the aircraft’s flight deck display screens.
The test pilots have access to a summary of primary flight test data, similar to that displayed on the cabin workstations, through an in-cockpit tablet.Flight test crews typically comprise two pilots and an engineer, but the engineer cadre is increased for more complex trials. The aircraft accommodates a maximum of two pilots and four flight test engineers. Although the prototypes are extensively instrumented, Embraer is also using chase aircraft and high-speed photography during the E2 flight test campaign. Chase aircraft are especially useful during the initial phases, cross-checking air data readings (before the prototype’s system has been fully calibrated), and for the more prosaic task of enabling visual checks for issues with prototype integrity – open doors, loose panels, fluid leaks, smoke and so on.
Although the company has a veteran Hawker Hunter on its chase aircraft fleet, it is particularly proud of its E2 chase aircraft, says Figueiredo: “We employ two state-of-the-art machines from our business jet family, a Phenom 300 light jet and a Legacy 500 fly-by-wire aircraft.”
Flight test anatomy
Embraer aims to complete one flight test of approximately two hours’ duration every day. It targets 50 to 60 hours per month, per aircraft, as it works toward the 2,000 hours required to complete the test campaign. Preflight planning begins a week before the test flight, with the crew and engineers defining the work and completing their risk assessment. Two days prior, the test card is generated, containing all the information related to the planned trial. The crew and engineers meet again for a one-hour preflight briefing on the day of the test and again for a 60-minute debrief afterward.
During the flight, the engineers at the cabin workstations analyze aircraft data points for validation. If a data point is not validated, procedures might be repeated during the flight to achieve a valid result. Data may also be telemetered in real time to ground stations, but the flight test parameters are always downloaded for analysis after landing. The flight test report is released some days after the trial.
By August, three E190-E2 prototypes were flying and had accumulated 240 hours between them. Trials are primarily out of Embraer’s Gavião Peixoto flight test center in Brazil, but adverse weather work will require deployments abroad. Early in 2017, for example, the third prototype will fly maturity and adverse weather trials, including cold weather operations, in the USA.
The full flight test campaign requires four E190-E2 prototypes, two for the longer E195-E2 and three more prototypes for the smaller E175-E2. First flight of the final E190-E2 prototype is imminent. Of the E190-E2s, 20.001’s primary tasking involves system, loads, aero elasticity, external noise and crosswind testing; 20.002 is also flying system tests, and is engaging in performance flights; 20.003 is taking responsibility for flying qualities trials, including icing evaluations; 20.004 will have representative cabin furnishings, required for cabin evacuation, comfort and internal noise assessment.
By early October, the E2 campaign had performed envelope expansion, ground loads calibration and in-flight thrust determination (IFTD) trials. Ongoing work included stall, climb performance and brake system evaluation. Embraer was also working to freeze the E190-E2’s aerodynamic configuration and control laws, an important milestone for the flight test campaign. “The E-Jets E2 program is on schedule and on target. The first aircraft to come to market will be the E190-E2, in the first semester of 2018,” concludes Figueiredo.
Paul E Eden is a UK-based freelance writer and editor specializing in the aviation industry.
This article was also published in the December 2016 issue of Aerospace Testing International magazine.