as the frequency of its use on the helicopter and the engine, is a subject that can and will be an article on its own in an upcoming issue of Helicopter Maintenance magazine. Right now suffi ce it to say a clean helicopter is a happy helicopter
EROSION
Running with the same crowd as the corrosive ele- ments in the air are tough little pieces of dirt and sand that work in tandem with the corrosive guys to exact as much damage as they can upon our helicopter and its components. The problem with the erosive ingre- dients is they remove any corrosive-resistant protective coatings. This gives their corrosive buddies an easier target for them to create mischief. Our defense against this destructive group is a good fi ltration system in the engine inlet. As a collective group, the OEMs have at- tempted to make the engine components out of more resilient materials with marginal success. Our job is to keep the fi ltration system clean and keep a vigilant watch on the wear limits spelled out in the Ops & Maint manual.
VIBRATIONS Unlike the song made famous by the Beach Boys, there are no “Good Vibrations” for a turbine engine. With turbine engine rpms running the gamut from 50,000 to 6,000 and several ranges in-between, rota- tional balance is critical. Unless we work for a repair station that overhauls
engines, we don’t have control over the rotational balance of the engine components. Our job is to recognize when it begins to exhibit an unbalanced behavior. As a former purveyor of turbine engine overhauls, I have always suggested to the operator that after installation of an overhauled engine or engine module, they should do a vibration survey prior to releasing the helicopter back to service. Be sure to keep the information obtained from the vibration analysis equipment for comparison when you suspect an engine vibration event. Without equipment, how do we recognize a vibration prior to installing equipment? A quick way to learn about the vibes without equipment is by touching the hard lines on the engine and other components during a ground run, as well as by feeling the sheet metal on the helicopter while it is running. A “high freq” feels like an electric shock to the tips of our fi ngers. Make note if there is a sudden and frequent requirement for external navigation light bulbs, or a rash of sheet metal cracks, or we are suddenly replacing hard line support clamps. Verifying our touch
information via vibration reporting equipment is best. Remember that vibration survey we did when things were working right? Now we have a baseline from before for a comparison which will help us identify the off ending component sooner rather than later.
METAL DEGENERATION: Ok, what about metal degeneration? Well, with all of those spinning gears and compressor and turbine wheels, the engine has a bunch of bearings that need the loving care of a good lubrication system. The compressor wheel and turbine wheel assemblies should be checked for balance also. Now is a good time for a quick review of the use of oil: 1.) Provide lubrication 2.) Remove heat 3.) Carry away dirt and debris. Bearing life is jeopardized if our lubrication system is not providing these services. All engine OEMs provide fi ltration and cooling systems to help the oil in its job. The other neat thing the OEMs have done is manufacture the gears and bearings out of ferrous material. If a bearing or a gear begins to fail and shed metal, it will be attracted to a magnetic capture and reporting system in the engine. These devices are known as chip plugs. The plugs are basically an open electrical circuit that sits strategically within the oil fl ow system. When a piece of ferrous material fl ows by the chip plug, it is attracted to the center section of the chip plug. It completes the electrical circuit once the metal debris bridges the gap between the center of the plug and the external grounding portion. It doesn’t take much metal to complete the open circuit which illuminates a bulb on the fl ight panel in the cockpit. The light projects through a translucent face with the word “CHIPS.” Trust me, the light is bright enough to get any pilot’s attention. Pilots are instructed to “land the helicopter as soon as practical” and investigate the cause for the light. Our job as the maintenance folks is to make sure they don’t have to experience an illuminated chip light. We make sure there is the correct level of oil in the
externally-mounted oil tank. There are markings on the tank sight glass to help with this inspection. We need to follow the OEM instructions on the frequency of oil changes. We monitor the fi lters for debris and make sure that the fi lters and oil cooler are kept clean. Along with correct oil temperature, proper oil pressure is also a must. In most turbine oil pressure systems, we should not have to constantly adjust oil pressure. Once it is set we should not have to change it. A decrease in oil pressure is an indicator of compromised system seals. An
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HelicopterMaintenanceMagazine.com August | September 2019
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