EC145 VARTOMS Control Panel
only provides that optimum effi ciency, it also allows the manufacturer to program engine limitations and receive engine health and maintenance reports. The engines must still work together to share the work load and inputs from demand still aff ect engine perfor- mance, the diff erence is that they are controlled by a computer instead of a pilot. This computer, however can maintain vigilance over many more parameters during starting and operation than the pilot ever could. The computer monitors air density, throttle lever posi- tion, engine temperature, engine pressures and many other parameters, 70 times a second. If necessary, the pilot is able to adjust the torque with the engine trim switch. Moving the collective lever upward or the left pedal forward will increase the power demand. To prevent a momentary decrease of Nr, the FADEC “anticipates” this situation using signals from the linear transducers connected to the fl ight controls. The linear transducer is a position sensor which transforms a mechanical defl ection into an electrical signal. This electrical signal is sent to the computer to be processed with the other information it receives. Instead of the defl ection of a mechanical lever on an engine control unit controlling the fuel fl ow to an engine, the HMU (Hydro-mechanical unit) receives its inputs from the FADEC control box and internally governs the per- formance of the engines and adjusts the performance characteristic of both engines to each other. Each of these designs have their advantages and
their fl aws. Fine tuning during the initial installation of these systems is critical. Trouble-shooting issues during operation must be more than throwing parts at them. Critical information must be received from pilots to do eff ective trouble-shooting. In the case of the VARTOMS, pilot knowledge of the operation
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HelicopterMaintenanceMagazine.com August | September 2019
EC145 VARTOMS Controlled HMU
EC145 Collective Trim Switch
and technic are very important factors determining its reliability. Again, the goal is always to get multi-engines to work together to share the load. I guess if you could hook up a sensor on the
mules’ yoke and give the mule a little electrical “Zap” whenever he let up, you would have a primitive FADEC system and your team would run a little more effi ciently and a little smoother.
Terry L. Peed has been working in the aviation industry for more than 46 years. He is a Vietnam-era Navy veteran and is a graduate of Embry-Riddle Aeronautical University with an associate of science degree in aviation maintenance. Peed holds an
A&P certifi cate with IA. He is employed by Air Methods Corporation as a fi eld/base mechanic at the University of Wisconsin in Madison, WI. You can contact him at
terrypeed@yahoo.com.
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