jsharkey
Well Known Member
The Whitman Strut legs are damped laterally due to tyre scrub just like on a Cessna but they can vibrate fore and aft. Do the wood molding and fiberglass stiffener/dampers work - and if so how do they work? Do they add significantly to the fore/aft bending stiffness of the legs and/or do they add some type of "material damping" to the system.
Simple wood moldings and hoop wrapped fiberglass won't add much bending stiffness - especially when compared to the forged steel leg. A significant proportion of axially aligned glass or carbon fiber rovings might add more stiffness, especially if concenrated on the "nose" and "tail" of the leg but the drawings don't mention this.
A damping mechanism might be the wood rubbing on the metal leg as the fiberglass encapsulated assembly shears fore and aft, however the wood is generally adhesively bonded to the leg so the bond would have to break for this to work - unless the internal flexing of the wood acts as a damper - which may be the most likely answer.
Has enyone tried bonding the wood to the leg with a thick layer of RTV before encapsulating it in fiberglass. The "rubber" would then be working hard in shear as the leg tried to vibrate fore and aft and may soak up more energy than if the wood was "hard" bonded.
What about just wrapping the leg with a tube of rubber - say 1/8" thick - and then wrapping that with a layer of say 2/3 axial, 1/3 hoop glass (or carbon) with the axial fibers concentrated on the nose and tail. Leave one end of the rubber exposed, say the lower end, and only bond the composite sleeve at the other end to keep it fixed on the leg. This would form a concentric beam around the steel strut and spaced from it by the layer of rubber. As the two beams bent, one inside the other, the rubber would be forced to shear between them and absorb energy.
It would be easier to build than the wood molding version to boot! Too whacky?
Anyone have any experience of different options?
Tuned mass/spring dampers (like the little dumb bells on power lines) inside the wheel pants?
???
(I need to get out more!)
Jim Sharkey
Simple wood moldings and hoop wrapped fiberglass won't add much bending stiffness - especially when compared to the forged steel leg. A significant proportion of axially aligned glass or carbon fiber rovings might add more stiffness, especially if concenrated on the "nose" and "tail" of the leg but the drawings don't mention this.
A damping mechanism might be the wood rubbing on the metal leg as the fiberglass encapsulated assembly shears fore and aft, however the wood is generally adhesively bonded to the leg so the bond would have to break for this to work - unless the internal flexing of the wood acts as a damper - which may be the most likely answer.
Has enyone tried bonding the wood to the leg with a thick layer of RTV before encapsulating it in fiberglass. The "rubber" would then be working hard in shear as the leg tried to vibrate fore and aft and may soak up more energy than if the wood was "hard" bonded.
What about just wrapping the leg with a tube of rubber - say 1/8" thick - and then wrapping that with a layer of say 2/3 axial, 1/3 hoop glass (or carbon) with the axial fibers concentrated on the nose and tail. Leave one end of the rubber exposed, say the lower end, and only bond the composite sleeve at the other end to keep it fixed on the leg. This would form a concentric beam around the steel strut and spaced from it by the layer of rubber. As the two beams bent, one inside the other, the rubber would be forced to shear between them and absorb energy.
It would be easier to build than the wood molding version to boot! Too whacky?
Anyone have any experience of different options?
Tuned mass/spring dampers (like the little dumb bells on power lines) inside the wheel pants?
???
(I need to get out more!)
Jim Sharkey
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