To: Spaced
Not all helicopters incorporate vibration dampers and those that do utilize as many designs as there are helicopters that employ them.
The bell 412s use pendulum dampers while some two blade Bell rotors incorporate a tuned weight inside the blade at the nodal point. Remembering the example of the moving rope and the traveling wave this included weight keeps the vibration from passing to the root of the blade by absorbing the energy of the wave.
The Bristol Sycamore has three weights suspended on flexible shafts, which are attached to the transmission. These weights vibrate on the flexible shafts in tune with the vibration generated by the blades. The vibrating weights absorb the energy of the vibration keeping it from passing into the fuselage.
The MIL Mi-17 uses a Bifiler system similar to that used on Sikorsky helicopters. I am not too clear on how the weights move in relation to the attaching arms in that they move to absorb loads generated by lead and lag or if they move up and down to absorb the traveling wave or, if they do both.
Many Eurocopter helicopters have a weight mounted on a coil spring which is mounted under the coollie hat on the rotorhead. The incoming vibrations excite the weight and in doing so the vibrations are cancelled out.
Bell helicopter devised an electronic system on the Huey that sensed the incoming vibration and the device generated a signal (vibration) that canceled out the incoming vibration. The unit was installed in the nose compartment.
Boeing has a mechanical system that mounts under the pilots’ seats on the CH-47 and this device absorbs vibrations. If it ever goes unserviceable the vibrations would be so great that the helicopter could not be flown. The poor guys in the back don’t have this convenience.
The most unique way of absorbing vibration induced by rotor movement is the NodaMatic system designed by Bell. This system allowed the transmission to move up and down in relation to the fuselage. The suspension system had a tunable weight that would be displaced by the linkage on the suspension. The displacement of the weight absorbed the incoming vibration that caused the transmission to move up and down keeping any vibration from passing through the fuselage. The system worked great but it caused a lot of problems.
The Hiller UH-12 had flexible arms attached to the flight controls below the rotor. Attached to the flexible arms were metal weights. Any vibration that would feed-back from the flight controls would cause the weight to deflect thus absorbing the feed-back forces.
