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Pratt & Whitney is linking engine controls to other systems to lets the F-35B hover.

Electronics take charge

Electronic controls are slowly transforming aircraft engines of all types, bringing improved fuel consumption, improved efficiency, and more power. As the functionality of control units for jet engines increases, digital management is also adding more capabilities for helicopters and small piston engines.

Full authority digital engine controls (FADEC) continue to leverage the advances in semiconductors and software to improve engine management. As microcontroller capabilities soar, engine controllers can handle functions beyond the engines themselves. For example, the Lockheed Martin F-35B’s engine controller also manages the short takeoff/vertical landing system.

“Engine controls can be linked to other electronic systems on the aircraft when the engine control is expected to be the flight control,” said Louis Celiberti, Director of Control & Diagnostic Systems at Pratt & Whitney Engineering. “During STOVL operation, the F135 engine control is the heart of the integrated flight and propulsion control. The engine control software uses advanced methods to de-couple a highly coupled engine system comprised of the main engine and a lift fan with a driveshaft attached in between. The result is wings-level, rock solid hover and vertical landing performance.”

While the F135 represents the high end for engine controls, digital systems are also expanding their reach into the low end. Rockwell Collins is shipping what it says is the first dual-channel engine control unit for use in light sport aircraft. The controls for the Rotax 912 iS piston engine were developed in conjunction with the BRP-Powertrain affiliate of Bombardier Recreational Products. The ECU automates tasks like adjusting air/fuel mixture and controlling exhaust gas temperatures.

“Now operators can operate the engine with ease, without having to worry about completing manual tasks to optimize performance throughout all operating conditions,” said David Vos, Senior Director, Control Technologies for Rockwell Collins.

Design teams are also doing more with ECUs in helicopters. Rolls-Royce recently deployed a dual-channel FADEC system on the M250-C47E, the first new helicopter to be launched by the company since 2005. The advanced FADEC helps improve the fuel burn and cut engine operating costs.

Whether FADECs are employed on the simplest recreational plane or the most advanced jets, design teams face myriad challenges. Hardware and software must operate efficiently without glitches or failures, forcing engineers to work overtime to eliminate mistakes.

Software is a primary focus. Many aircraft routinely run several million lines of code. Increasingly, this software is generated by computer, not programmers.

“As controls get more complex, code generation tools are gaining attention,” said Mahendra Muli, New Business Development Director at dSPACE. “Advanced automatic code generation tools are being used to convert algorithm models into well-documented C-code used in production controllers with efficiency, repeatability, and high quality, while easing the process to comply with stringent standards such as DO178B/C."

Both hardware and software must continue to run even if other systems on the aircraft fail. Though many systems share information, they must also be segregated from each other so problems in one subsystem don’t cause errors in a related system.

“Engine controls should be isolated from other systems when a level of system redundancy is required to achieve flight safety requirements,” Celiberti said. “Systems require isolation to ensure cross contamination does not take place and allow secondary systems to be deployed when primary systems fail.”

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