Turbine engines provide the propulsive force for a significant percentage of modern transportation systems and are especially important as the engine for a wide variety of aircraft. Although often viewed as a mature technology, a substantial amount of resources are expended to improve these Systems because of the large impact they have on society. The NASA program in Fundamental Aeronautics describes one such research effort and is aimed at reducing emissions, fuel burn, and noise. Separately, the Department of Defense’s Versatile Affordable Advanced Turbine Engines (VAATE) Program describes similar goals regarding fuel burn reduction with perhaps more emphasis on overall performance and reducing cost. A multitude of fundamental technologies are involved in realizing these improvements, however, many of them are only enabled or reach full potential through the use of supporting controls technology.
The control system is not generally considered to be the limiting factor in the performance of an engine. Controls do have a direct impact on performance by how well they enable the engine system to operate within its design envelope. Yet the control system negatively affects performance indirectly because it has physical mass and volume. It also uses electric power and dissipates heat which ultimately impacts weight and volume. More control capability through sensing and actuation could feasibly enable better engine performance; however this is constrained because the impact outweighs the gain. The control architecture can be a tool to reduce the negative impact of an existing control capability or provide additional performance capability with the same impact.
Changing the engine control system architecture towards a more “distributed” format has the potential to reduce overall life cycle costs, reduce control system weight, and provide an enabling path for new technologies which do not currently fit in the existing cost structure of small air vehicle systems.
FADEC – Full Authority Digital Engine Control
The newest version of a jet engine fuel control is called a FADEC – Full Authority Digital Electronic Control. The original fuel controls on early jet engines of the late 1940’s and early 1950’s were simply constructed and resembled a common gate valve connected to a throttle lever, Engines and controls became more sophisticated through the 1950’s and 1960’s, Better performance, more reliability, and increased safety became driving forces, the new electronic fuel controls will be even smarter, more precise, more accurate and more reliable than present day fuel controls and they will be with us for many years.
Full Authority Digital Engine Control (FADEC) is a system consisting of a digital computer, called an electronic engine controller (EEC) or engine control unit (EEU), and its related accessories that control all aspects of aircraft engine performance. FADECs have been produced for both piston engines and jet engines.
FADEC is a system consisting of a digital computer and ancillary components that control an aircraft’s engine and propeller. First used in turbine-powered aircraft, and referred to as full authority digital electronic control, these sophisticated control systems are increasingly being used in piston powered aircraft.
In a spark ignition reciprocating engine the FADEC uses speed, temperature, and pressure sensors to monitor the status of each cylinder. A digital computer calculates the ideal pulse for each injector and adjusts ignition timing as necessary to achieve optimal performance. In a compression ignition engine the FADEC operates similarly and performs all of the same functions, excluding those specifically related to the spark ignition process.
Full Authority Digital Engine (or Electronics) Control (FADEC) is a system consisting of a digital computer, called an electronic engine controller (EEC) or engine control unit (ECU), and its related accessories that control all aspects of aircraft engine performance. FADECs have been produced for both piston engines and jet engines.
ENGINE CONTROL UNIT
An engine control unit (ECU) is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure the optimum running. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps (called Look-up tables), and adjusting the engine actuators accordingly.
|Full Authority Digital Electronic Control (FADEC)|
Before ECU’s, air/fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical and pneumatic means. One of the earliest attempts to use such a unitized and automated device to manage multiple engine control functions simultaneously was the “Kommandogerät” created by BMW in 1939, for their 801 14-cylinder aviation radial engine.
- Better fuel efficiency
- Automatic engine protection against out-of-tolerance operations
- Safer as the multiple channel FADEC computer provides redundancy in case of failure
- Care-free engine handling, with guaranteed thrust settings
- Ability to use single engine type for wide thrust requirements by just reprogramming the FADECs
- Provides semi-automatic engine starting
- Better systems integration with engine and aircraft systems
- Can provide engine long-term health monitoring and diagnostics
- Number of external and internal parameters used in the control processes increases by one order of magnitude
Full authority digital engine controls have no form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. In the event of a total FADEC failure, pilots have no way of manually controlling the engines for a restart, or to otherwise control the engine. As with any single point of failure, the risk can be mitigated with redundant FADECs.
1. Porter, L., “NASA’s New Aeronautics Research Program,” presentation to the 45th AIAA Aerospace
Sciences Meeting & Exhibit, January 2007, Reno, NV.
2. The Versatile Affordable Advanced Turbine Engines (VAATE) Initiative, AIAA Position Paper, January 2006.