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What I take from the points below leads me to focus on the main gear more than the nose. As Fred so well described, resonance occurs when the modal frequency of a system coincides with the frequency of a vibration source. If there is little damping, then the source can be very small but still result in potentially catastrophic motion/damage. Perhaps I'm misunderstanding, but it seems that:
1. Vibration has been observed with various nose strut designs
2. Braking (on the mains) has an influence on the vibration
Though I'm not arguing that the nose strut does not have exhibit resonance itself, I wonder if the mains act as an amplifier, that if removed would relegate a nose strut vibration mode to an infrequent or non-existent issue.
I proffer that a small imbalance (due to the wheel or rotor CG not being precisely on the rotational axis), or uneven brake application (due to a slightly warped brake rotor) may excite a
longitudinal mode of the strut/wheel/pant. The energy of one or both wheels/struts/pants moving longitudinally may cause a yawing motion of the fuselage that either simply loads the nose strut laterally, or also causes the nose strut to shimmy (energetic nose wheel yaw to strut roll interaction). A modal impact (rap) test could be used to determine the natural frequency of the strut and damping of the structure (which I'm guessing is very low), and a simple calculation would show at what wheel speed an imbalance would coincide with this. Removal of the wheel pants will reduce the mass, thus driving the natural frequency up, and potentially out of range of normal landing speeds.
I have no personal experience with this, and offer the above solely as conjecture. If someone is willing to provide the bird, I may be able to assist with said rap test. It would have to be in south FL, after October.
Cheers,
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Kyrilian
Skip Slater <skipslater@verizon.net> wrote: <snip>
I don't have a taxi speed that I avoid, though I can get a shaking if I try to brake lightly at low taxi speeds. I don't get any shimmy at all when taxiing with the brakes off.
<snip>
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