Understanding Turbomeca DEECU Systems
By Greg Napert
Question — What do the Arriel, Arrius, have in common? Answer — More than you think!
For starters, they are two major geographical features in the Pyrenees Mountain Range in the South of France.
But this isn't a geography lesson, so for our purposes, they are Arriel 2 and Arrius 2 turboshaft engines produced by Turbomeca in France.
Also, both of these engine models were introduced into service with digital engine controls.
(Incidentally, Turbomeca names all of its engine models after major geographic features in the Pyrenees).
Turbomeca now considers the latest models of digitally controlled turboshaft engines it manufactures "third generation" turbine engines. According to Bill Mizell, Training Manager for Turbomeca Engine Corporation in Grand Prairie, TX, "The Makila, was the first turboshaft engine that Turbomeca designed which used an automatic electronic control. This is an electronic control box using analog type technology. This system works very well, but the natural evolution was to move to digital electronic controls."
He explains, "Many people today use the term FADEC, which stands for Full Authority Digital Engine Control. The Arrius 1A, was the first of Turbomeca's new generation digitally controlled engine to come on the scene. It doesn't have Full Authority, however, it utilizes a manual backup.
Turbomeca doesn't refer to its digital technology as FADEC, however, as the controls are not technically "Full Authority."
"Turbomeca is very adamant about this," explains Mizell. None of the controls on its engines are referred to as FADECs. FADECs technically require two or more channels so that there is redundancy in the system. Instead, Turbomeca uses the acronym DEECU, which stands for Digital Engine Electronic Control Unit. Turbomeca's DEECUs have only one channel and have a mechanical backup — an actual mechanical linkage between the cockpit and the engine. All Turbomeca engine electronic control designs are currently DEECUs so that in the event of an electronic failure, the pilot can revert to manual control."
Mizell continues, "This term FADEC has become one of these buzz words people use to talk about any kind of electronic engine control. But it's important to realize that the DEECU is not full authority, it's single channel and uses a mechanical linkage for backup.
"Having said that, some of the Helicopter manufacturers continue to use the term FADEC when referring to our equipment as installed on their helicopters."
The two Turbomeca products in the medium helicopter, medium engine power class which have new generation DEECU controls are the Arriel 2 and the Arrius 2 which can be grouped together in terms of their technology.
The Arrius 2 engine is an improvement over the Arrius 1 which uses a digital control unit somewhat larger in size than the Arrius 2 units. In both cases, they are using Digital Engine Electronic Control Units. They may be lighter now, but they all work in essentially the same way.
Mizell says the Arriel and the Arrius are very different in terms of horsepower and design, but they still use very similar control units.
Electronic controls have not only made the engine easier to operate, it has allowed the engine manufacturer to increase horsepower output. It does this by enhancing the ability to control the engine during power changes and acceleration and prevent surge.
Mizell explains, "The nice thing about the digital electronic control system is that by using the various assorted sensors on the engine, the control system knows more about what's going on with the engine than a mechanical system does.