Vibration Management Enhancement Program

Vibration Management Enhancement Program

The saying goes that helicopters don't fly they beat the air into submission. If you have ever put up a ceiling fan then you can relate to the tracking and balance problems associated with rotating blades. Just imagine what would happen if that fan was not connected to the ceiling and was traveling thru free air in various configurations and weather. This is what helicopters go through consistently. "The helicopter system derives its vertical lift from continuous conflagration upon the mass of air in proximity to its location. In response, the helicopter is rewarded with levels of vibration that would be unacceptable of more pedestrian vehicles" (Grabill, 2002, p1).

Helicopters made their first debut during Vietnam and were a vital part of the day-to-day combat operations. With the helicopters being relatively new to the military the maintenance practices had tremendous learning curves that had to be overcome. One of the main obstacles in helicopter maintenance is the management of the vibrations to eliminate possible catastrophic failures. The helicopter has a numerous amount of rotating parts that are necessary for flight from hydraulic pumps to engines to rotor blades.

The rotor blades have to be tracked and balanced in order for any rotorcraft to achieve flight and stay together. The earliest technique for rotor tracking was the flag method, where the tip of the blades was marked with colored chalk and a white flag or strip of cloth attached to a pole would be pushed toward the leading edge of the rotating blades. The marks on the cloth would give you an indication of the flight path of each blade. Another method of achieving this task were to have the helicopter do a ground run and tape a grease pencil to a long stick and slowly approach the rotating blades until you could feel it strike the blade and quickly pull back, Shut down the helicopter and look for marks on the blade. The heaviest and longest marks meant that that blade was flying lower than the others and you would adjust to all blades had similar markings. This was a primitive but effective method of tracking the blades and it worked for decades.

In the early 1970's new technology arrived. The new system called the Vibrex was a vast improvement over the old grease pencil and flag system. The Vibrex system adopted the use of the strobe light and reflective tip targets. This allowed the technician the capability of track and lead-lag to be measured in flight. However, the system still seemed to focus primarily on the rotor blades. The Vibrex also relied on highly skilled individuals to accurately remember the position and location of all blades and to transfer the data based in their interpretation. This system had a wide range of error due to the fact that everyone saw a different picture. The Vibrex saved many man hours and was the system of choice until another system the Rotor Analysis and Diagnostic System (RADS) was introduced in the early 1980's.

The RADS system was a tremendous improvement over the Vibrex and had additional features that allowed it to monitor the vibrations of gearboxes and engines also. The RADS system was a very portable and universal system that eliminated the human error when calculating adjustments. The RADS would monitor, interpret and recommend appropriate adjustments necessary during a single flight. However, it still had numerous items such as accelerometers, tachometers, sensors and cable that had to be installed and removed each time it was used. The RADS system also focused primarily on the rotor system with limited use on engines and gearboxes.

The most widely used system in todays Army is the Aviation Vibration Analyzer (AVA). The AVA was the beginning of a new era of vibration analyses and was a quantum leap over its predecessors. The AVA was designed to handle rotor smoothing and component vibrations however, all the accelerometers and sensors had to be installed on the aircraft and the AVA was only authorized for maintenance test flights. Maintenance personnel continue to use the system and for what it is designed for it basically does a great job. The major draw back is each time you want to test a component or system you must install the complete AVA system and restrict the aircraft for test flight purposes only until the AVA is removed.

The helicopter industry and related contractors have mastered the rotor smoothing and balancing using all the above type systems. However, what's missing is the capability to monitor the health of all components necessary to keep those blades turning. A majority of the components will give vibration indications prior to failure and if a system can track this, those parts can be replaced prior to failure. The benefits of such a system is critical to the ability to accurately diagnose the health of key components that must work collectively to ensure dependable flight.

The US Army is currently working with the South Carolina National Guard with the latest technology called Vibration Management Enhancement Program (VMEP). The VMEP system has taken years of data and experience from a variety of other systems and created one capable of not just rotor smoothing but also component life tracking and forecasting. The VMEP system provides a single source for collection, detection, and identification of mechanical faults throughout the airframe.

"The VMEP technology is enabling a paradigm shift from the current time-based maintenance system to a condition-based maintenance system. In other words, only perform maintenance when the machine requires it" (Orincon, p1). The military currently operates based primarily on the time-based maintenance system and countless components are removed daily simply based on time instead of condition. When a component is replaced based on time alone it will never be known if it was in need of replacement or if it still had hundreds or thousands of hours left. When a component can be tracked every time it flies the replacement and overhaul life can be either extended or done away with. The VMEP technology will save the military millions of dollars on maintenance and parts annually. It will also save aircraft and lives by being able to monitor the key components that might fail and cause catastrophic failure during flight.

The major advantage VMEP has over all of its predecessors is its capability to monitor all components on the airframe simultaneously for the duration of all flights. The VMEP can also be programmed at any time to single out a component and collect data. A network of sensors, tachometers and accelerometers are mounted and gearboxes, engines, pumps, transmissions, oil coolers, drive shafts bearings, rotor blades and even the airframe to pick up any indication of an abnormal