Halpin says, “Excess grease that slings out of fittings appears nasty, and when operating rentals and training helicopters appearance counts.” He goes on to explain a caution regarding the cleaning of excess grease after purge lubrication. “Be careful to not use excess force when cleaning excess grease from bearing retainers, rubber boots, and protective covers,” he says. “In some cases I like to use an acid brush just so I don’t apply excessive or uneven pressure around certain retainers.”
He went on to explain how a local helicopter owner/pilot learned an expensive lesson regarding cleaning excess grease from areas of the rotor head on his personal helicopter. While wiping excess grease from the area he unknowingly snagged a cotter pin with his cleaning rag and opened the legs of the cotter pin. The pin stayed in place; however, it now contacted the upper portion of the swash plate and eventually scored the component requiring a very costly replacement. Again, pay attention to detail.
Vibration, balance, and blades
Cooper says, “Vibration management is another issue that helicopter maintainers need to be very mindful of. Beginning at the tail of the helicopter, the tail rotor provides a lot of stress at the end of a long arm — the tailboom. We pay particular attention to the entire tail rotor area and tailboom for any unusual wear, cracking, or other signs that vibration is beginning to create a problem.”
Vibration resulting from both the tail rotor and main rotor blades can be linked to many mechanical failures from simple burnt-out light bulbs to fatigue cracks in the structure and the engine cooling baffles.
Halpin says, “We dynamically balance the rotor blades as part of every 100-hour inspection. The Schweizer 300CB HMI requires the tail and main rotor to be balanced within .2 inches per second (ips). With the modern equipment available today you can easily do a much better job of balancing the rotor blades. We regularly are able to balance within .02 ips which we feel is much better on the helicopter.”
Careful balancing of the internal components of an engine during overhaul is an important feature that can help with overall vibration management. The Lycoming engine in the 300CB operates constantly at a power setting of 2,600 rpm and dynamic balance under operating conditions enhances overall comfort.
Another vibration-related aspect is the ground resonance dampening system on the 300CB. It was explained that the dampening system for the fully articulating rotor system on this helicopter consists of three lead-lag dampeners, one associated with each main rotor blade, and four landing gear dampeners, one on the fore and aft points of the right and left skids. Together they make up the entire ground resonance dampening system which is necessary to dampen out possible vibration induced when landing. The main rotor blade lead-lag dampeners contain a series of potted-rubber “donuts.” The landing gear dampeners are a cylinder containing oil and charged with 700 psi of nitrogen.
Halpin explains, “The landing gear dampeners have a tight tolerance and should have no visible signs of weeping. We have special fixtures and tooling for overhauling the landing gear dampeners and provide this service to other Schweizer operators.”
Then there’s blade erosion, another area to pay particular attention to. Cooper says, “Each of the three main rotor blades costs approximately $18,000. Flying in the rain, sand, and dust can rapidly erode the leading edges.”
Cooper shares this final comment to other operators, “Regular inspection and preventative maintenance based on your specific type of operation is a key element in controlling maintenance and operating costs at a small operation like ours.”
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