FADEC - Full Authority Digital Engine Control
A FADEC (Full Authority Digital Engine Control) is a system consisting of a digital computer, called an Electronic Engine Control (EEC) or Electronic Control Unit (ECU), and its related accessories that control all aspects of aircraft engine performance. The term FADEC is an acronym for either Full Authority Digital Engine Control or Full Authority Digital Electronics Control. FADECs have been produced for both piston engines and jet engines, their primary difference due to the different ways of controlling the engines.It is a system continuously monitors and controls ignition timing, fuel injection timing and fuel to air ratio mixture. Therefore a FADEC equipped engine doesn’t require magnetos and eliminates the need for manual fuel/air mixture control.
FADEC utilize a set of redundant sensors linked to the ECU. ECU then uses data to analyze and control the ignition timing,fuel injection timing and fuel to air ratio for each cylinder. FADEC is powered by 3 sources: alternator, primary battery , emergency battery. FADEC needs only 1 power source to operate. Reduces a pilot’s “busy work”. 15% more fuel efficiency than correct and accurate conventional mixture control.
The goal of any engine control system is to allow the engine to perform at maximum efficiency for a given condition. The complexity of this task is proportional to the complexity of the engine. Originally, engine control systems comprised simple mechanical linkages controlled by the pilot. By moving throttle levers directly connected to the engine, the pilot could control fuel flow, power output, and many other engine parameters.
Following mechanical means of engine control came the introduction of analog electronic engine control. Analog electronic control varies an electrical signal to communicate the desired engine settings. The system was an evident improvement over mechanical control but had its drawbacks including common electronic noise interference. This system was pioneered in the 1960s and first introduced as a component of the Rolls Royce Olympus 593 engine. The 593 was the engine of the supersonic transport aircraft Concorde.
Following analog electronic control, the clear path was digital electronic control. Later in the 1970s NASA and Pratt and Whitney experimented with the first experimental FADEC, first flown on an F-111 fitted with a highly modified Pratt & Whitney TF30 left engine. The experiments led to Pratt & Whitney F100 and Pratt & Whitney PW2000 being the first military and civil engines respectively fitted with FADEC and later the Pratt & Whitney PW4000 as the first commercial "dual FADEC" engine.
True 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. If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an Electronic Engine Control or Electronic Control Unit. An EEC, though a component of a FADEC, is not by itself FADEC. When standing alone, the EEC makes all of the decisions until the pilot wishes to intervene.
FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many others. The inputs are received by the EEC and analyzed up to 70 times per second. Engine operating parameters such as fuel flow, stator vane position, bleed valve position, and others are computed from this data and applied as appropriate. FADEC also controls engine starting and restarting. The FADEC's basic purpose is to provide optimum engine efficiency for a given flight condition.
FADEC not only provides for efficient engine operation, it also allows the manufacturer to program engine limitations and receive engine health and maintenance reports. For example, to avoid exceeding a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.
The aircraft magneto is a cursed thing. Its technology seemingly dates to the discovery of fire, every engine needs at least two and on a dark and stormy night over the Appalachians, the last thing you want to think about is how many fragile moving parts are whirling around inside a mag at the speed of heat.
But just try to come up with something better. Or even something that's almost as good that doesn't cost three times as much. That's precisely the challenge the engine and airframe industry faces as it marches smartly up to the toll gates on Al Gore's bridge to the 21st century.
Some segments of the industry are positively euphoric with talk about electronic controls that will re-invent the way pilots operate engines, with improved fuel economy, easier starting and-gasp-better longevity. We're seeing the word "revolutionary" appearing in every other line of more than a press release or two.
While there's a certain inevitability to electronics in the engine compartment, it's also true that bringing these things successfully to market has thus far been a snake-bit proposition. The problem is not making systems that work or certifying them, but convincing buyers that the benefits of electronic controls are worth the asking price and generating enough sales volume to keep bean counters from pulling the plug.
As of summer 1998, the push for FADECs-full-authority digital engine controls-screeched to fever pitch, with both Lycoming and Continental developing clean-sheet electronic control systems and a couple of other companies proposing FADECs or related systems of their own.
We have to give these guys a tip of the hat for persistence. Over the last decade, electronic engine controls haven't exactly sparked a buyer stampede. Much as we hate to dredge up ancient history, the ill-fated Porsche Mooney PFM comes first to mind.
Introduced in 1988, the PFM was a giant boulder tossed into the ripple-free, technological calm of GA. And it sank just about as fast. The PFM was powered by a six-cylinder, air-cooled engine with automotive-style electronic ignition, fuel injection, autoleaning, automatic cooling control and-what was supposed to be the irresistible marketing lure-a single power lever.
It worked; push the throttle forward to go fast, pull it back to slow down. No prop, no mixture and no worries about shock cooling. Even though it was a bit slower than the 201, owners loved the airplane. Unfortunately, there weren't many of them. Only 41 PFMs were sold, a poor sales history due in part to the $60,000 price premium over the 201 and a flat GA market. Thanks to slow sales and money squabbles with Mooney, Porsche grew disenchanted and bailed out of the project. To its credit, it has continued to support the engine.
More recently, another European company, Rotax, developed an 81 HP engine used in the popular Diamond Katana trainer. Again, electronic ignition, autoleaning and worry-free cooling thanks to partial watercooling. Although it has no mixture knob, the Rotax has a conventional prop control and throttle.
This progressive powerplant was well received and despite glitches with the electronics and maintenance difficulties due to lack of familiarity with the systems, owners like the Rotax/Katana combination. Yet once again, the engine manufacturer became disinterested in promoting its engine in the aviation market, leaving Diamond to fend for itself. Diamond has since abandoned Rotax in favor of Continental's IO-240B, a fuel-injected conventional aircraft engine with none of this new-age digital gimcrackery that allows any fool to start a heat-soaked motor.
More recently yet is Unison's LASAR ignition system, the world's first limited authority electronic magneto, with bulletproof conventional reversion and automatic variable timing. LASAR drew intense interest when it appeared at Oshkosh three years ago but the system's performance gains have proved elusive and sales anemic. With no discernible benefit to offset the added cost of installing it, the airframe makers have thus far passed on LASAR.
Against this backdrop, how do the developers of the next generation of electronic controls hope to succeed? What will they do differently?
It's the Money, Stupid
Setting aside the technobabble for a moment, one immediate distinction over previous systems is that the two major players here-Continental and Lycoming-intend to offer their FADECs on new engines to be installed in new airplanes at a cost comparable to current new engines.
That means that a new Cessna 182 costing $225,000 with the current iteration of the Lycoming IO-540 would cost about the same with a new FADEC-driven engine.
"If we have learned anything about the GA market," says Lycoming's head engineer, Rick Moffett, "it's that it's extremely price sensitive. People just aren't going to spend $20,000 for an engine control system." Anyone who doubts that merely needs to recall Mooney's PFM experience.
Second-and ignoring the retrofit market-these systems will capitalize on the flexibility and capability of state-of-the-art digital electronics to produce an integrated system that includes sexy cockpit displays and, no doubt, onboard diagnostics of some kind.
Even at that, Moffett says meeting the price point will be a tall order. Ridding a current engine of its conventional mags and harnesses, injector servo, flow dividers, waste gates plus such cockpit instrumentation as manifold pressure, tachs and engine gauges will have to save enough money to pay for -or at least almost pay for-the new electronics.
"If we hit it within five percent, we'll consider ourselves successful," says Moffett. Add up the cost of all that conventional hardware and you you'll arrive at some idea of what a retrofit FADEC for an older airplane would cost: Our guess is between $6000 and $10,000.
The rest is pure sales. Fuel economy gains of 10 to 15 percent seem likely; engines with electronic ignition are demonstrably easier to start and, in theory, without the pilot whipsawing the power or trashing the valves by mis-leaning, an engine might actually stand a better chance of reaching TBO. The single-power lever concept may or may not be a market draw. Frankly, we doubt that it is.
At Oshkosh, both Lycoming and Continental announced FADEC systems and a third company, Aurora Flight Sciences is already flying a single-lever system developed under a NASA small business technology grant. We suspect the two major players will produce market-ready systems within a year or two.
Lycoming has joined with Unison to develop the so-called EPiC FADEC, for electronic propulsion integrated control. Continental will likely use a system being developed by Aerosance, Inc., (formerly Aerotronics) a Connecticut company bought earlier this year by TCM's parent, Allegheny Teledyne, specifically to engineer electronic controls for piston engines. But the Aerosance-TCM marriage isn't meant to be monogamous; Aerosance is free to sell its technology to all comers, presumably including Lycoming. Both systems will incorporate the single-power lever concept to one degree or another, although at this point, it appears as though Aerosance is more committed to a fully automated engine control which entirely eliminates pilot input, save for a single power control lever.
We recently toured Aerosance's research and production facility in Farmington, Connecticut and were shown a Continental IO-240B running on a prototype FADEC. By current standards, the Aerosance system is a radical departure and although it shares common ground with the Porsche Mooney engine in principle, it will also pioneer some intriguing new components.
Gone, of course, are traditional engine-driven magnetos, replaced by a high-energy spark coil for each cylinder. Variable timing will be controlled by a microprocessor for each cylinder. Fuel will be direct port injection through a new electronic pulsed injector Aerosance has developed to replace the continuous flow injectors that are standard equipment in aircraft engines.
Aerosance's design is a closed loop system, meaning that it uses a series of sensors-manifold pressure, fuel pressure, cylinder head and exhaust gas temps, engine speed, knock detection, turbo boost pressure-to operate the engine to a set of fixed control laws burned into the FADEC's brain. Virtually all of the hardware for this system is clean-sheet stuff, including the coils, electronics, a master speed sensor that will occupy one of the magneto pads, electronic monitoring and annunciation. Still under development are an electronic prop governor and a waste-gate controller for turbocharged engines.
Like the Porsche Mooney system, the Aerosance FADEC is all-electric, with no mechanical reversion. For redundancy, each microprocessor controls two cylinders and each coil generates spark for two cylinders. Aerosance envisions dual electrical power sources, with back-up provided by an optional engine-driven, self-exciting generator, another component under development.
Being fully automatic, the Aerosance system relies on the FADEC's fixed operating parameters, with the only pilot controlled variable being throttle position. We were told that these parameters are still being tweaked but basically, each microprocessor would control the combustion in each cylinder as an independent event, with timing and fuel flow electronically manipulated to deliver either best power or best economy.
The optimum operating mode would be based on throttle position and power output calculated not by direct measurement but surmised from a "look-up" table developed from the dyno-derived power charts.
Like the LASAR system, the Aerosance FADEC would probably apply very little spark advance for takeoff power but would advance timing and lean aggressively in cruise. Would that include lean-of-peak EGT operation? Probably, says Aerosance CEO Steve Smith.
Standard equipment with the Aerosance system will be something called a health status annunciator, a small panel-mounted box that watches over each cylinder and combines CHT, oil pressure and other sensors and signals out-of-limit conditions.
An optional accessory is the Engine Performance Data Display, which is a graphic monitor device that displays power level, fuel level and consumption, EGTs, oil temps and other useful engine info. The EPDD could store engine operating history from zero-time to TBO.
Easing Into It
Compared to the Aerosance system, the Lycoming-Unison EPiC represents a more conservative approach to FADEC. On injected engines, it would do away with the Bendix/RSA servo system but would retain a simpler throttle body assembly and conventional constant flow injectors.
As currently being tested on an IO-540, EPiC uses the next generation of LASAR mags with electronic spark advance controlled by a single-channel FADEC computer. Reversion is purely mechanical, with an engine-driven fuel pump and the LASAR's conventional magneto back-up mode. Current versions of the LASAR system advance timing based on fixed look-up tables burned into the system's chips, using manifold pressure, RPM and CHT input.
EPiC will do the same, by reference to a fixed look-up table, with power output indirectly calculated from sensor input. Lycoming's Moffett told us that these power tables are being revisited during FADEC trials and lean-of-peak EGT operation will be considered. Like Aerosance , EPiC will have a cockpit display; details on that haven't been settled yet.
Interestingly, EPiC may not be a strict single-lever system that would limit pilot input to throttle position only. Moffett and Unison's Norman MacLeod told us the system may very well have a pilot-selectable switch for best power versus best economy. Presumably, switching to best economy would engage a more aggressive leaning map. Lycoming is currently polling the airframe makers about this option. (We think it's a good idea in that some efficiency is reclaimed in not surrendering engine operation to a one-size-fits-all-dumb-as-rock mode.
What'll They Do?
What are FADEC's claimed benefits? Easier starting and improved fuel economy, to name two. We think these have been convincingly proven by the LASAR system, even if economy gains have been minuscule in the field. There's no doubt that if they work as claimed, single-lever power controls will simplify pilot workload. Whether that will yield much market stimulation is an open question, however. We shopped the idea to Michael Slingluff, CEO of Diamond, whose IO-240-powered Katana may be the first production airplane to use the Aerosance system.
"There's no weight savings and no cost savings. If these systems take out some of the operational variability and you get an upgraded warranty, then yes, it has market appeal," says Slingluff, adding that sooner or later, electronic engine controls will be an expectation, especially in high performance airplanes. He believes sophisticated cockpit displays are essential to add curb appeal and salability to FADECs.
Besides simplicity of operation, a FADEC's chief claimed benefit is improved thermal management of the engine, reducing shock cooling, spikey CHTs and other temperature excursions thought to be bad for engine longevity. In other words, greater likelihood of reaching TBO. Lycoming's Moffett says maybe, but he's fearful of overpromising a benefit that may take years to materialize, if it ever does.
From what we've seen thus far, both Aerosance and Lycoming-Unison are on the right track and we're excited about the prospects. That said, we would still like to see more fundamental research into improved induction and exhaust systems-that appears to be happening at Lycoming-and development of control laws based on direct measurement of power output, rather than the necessarily compromised fixed power tables.
Still, the rather large nut to crack is to produce FADECs that are as reliable as the venerable magneto at a competitive cost. We suspect that all of the players in this game will find that far more difficult than pesky problems with computers and circuit boards.
With the operation of the engines so heavily relying on automation, safety is a great concern. Redundancy is provided in the form of two or more, separate identical digital channels. Each channel may provide all engine functions without restriction. FADEC also monitors a variety of analog, digital and discrete data coming from the engine subsystems and related aircraft systems, providing for fault tolerant engine control.
To perhaps more clearly illustrate the function of a FADEC, explore a typical civilian transport aircraft flight. The flight crew first enters the data appropriate to the day’s flight in the flight management system or FMS. The FMS takes environmental data such as temperature, wind, runway length, runway condition, cruise altitude etc. and calculates power settings for different phases of flight. For takeoff, the flight crew advances the throttle (which contains no mechanical linkage to the engine) to a takeoff detent or opts for an auto-throttle takeoff if available. The FADECs know the calculated takeoff thrust setting and apply it. The flight crew notes that they have merely sent an electronic signal to the engines, no direct linkage has been moved to open fuel flow. This procedure is the same for climb, cruise, and all phases of flight. The FADECs compute the appropriate thrust settings and apply them. During flight, small changes in operation are constantly being made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but remember, limitations can’t be exceeded. The flight crew has no means of manually overriding the FADECs, so if they make a decision the crew doesn’t like, it must be accepted.
FADECs today are employed by almost all current generation jet engines and increasingly in newer piston engines, on fixed-wing aircraft and helicopters.
In piston-engine powered aircraft, the system replaces both magnetos, making obsolete repetitive and costly magneto maintenance, and eliminates carburetor heat, mixture controls and engine priming. By controlling each cylinder of the engine independently for optimum fuel injection and spark timing, the need for the pilot to monitor and control mixture is eliminated. Because imprecise mixture operation can affect engine life, the FADEC has the potential to reduce operating costs and increase engine life for the average General Aviation pilot. Tests have also shown significant fuel savings potential. FADEC paid for itself in reduced operating costs.
• 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
• Reduces the number of parameters to be monitored by flight crews
• Due to the high number of parameters monitored, the FADEC makes possible "Fault Tolerant Systems" (where a system can operate within required reliability and safety limitation with certain fault configurations)
• Can support automatic aircraft and engine emergency responses (e.g. in case of aircraft stall, engines increase thrust automatically).