Posted by Rick Denney on November 07, 2001 at 16:15:58:
In Reply to: Re: Re: More travel protection??? posted by Jim Andrada on November 07, 2001 at 14:32:14:
Well, if Yamaha has done it, then their cases seem singularly lacking in benefitting from that testing. I suspect that cost control had a bigger influence on the design of Yamaha cases.
The whole point is the same as Charlie Krause's inflated soccer ball. It transfers the loading from the bell rim, which is weak along the axis of the bell stack, to the throat, which is strong. It also preloads the inside of the bell, which is strong as a hoop, so that any force on the outside of it would not only have to overcome the strength of the brass but also the preload. This is a common concept in engineering and leads to things like pre-stressed concrete.
Your notion of chamfering the corners is a good one, especially for the corners at the rim of the bell.
Suspending the tuba in a steel box with elastic straps would be the best, if the straps were strong enough so that the tuba never touches the box, if the attachment points to the tuba were strong enough when that limit was reached, and if you have something to damp the motion so that the box doesn't go dancing down the loading dock.
The foam of a case tries to do the latter, by allowing the tuba to move with respect to the case, lowering the G force of the impact such that it stays below the strength of the instrument, and damping the motion. The problem is that the foam used in cases like those made by Yamaha is too stiff, compared to the air inside the bell. The soft foam used, say, in Anvil or Walt Johnson cases provides much more movement and damping, but requires much more distance between the tuba and the walls of the case. Plus, the stiff foam in a Yamaha case, once crushed, does not spring back. This helps reduce G forces by absorbing shock, but also ruins the effectiveness of the case if it is banged up.
The other problem with Yamaha cases is that the shell is not stiff, and some case shapes can be bent and crushed easily.
Walt Johnson cases, for example, provide a much stiffer and stronger shell, and also softer foam and more space. But the bell rim fits tightly, and is therefore vulnerable to the movement of the tuba within the case, even if it fits tightly. Steve's insert, if it pushed the bell rim away from the case foam a little bit, would solve that problem.
The ideal tuba case would incase the body of the tuba in form-fitting foam, except for the bell which would be suspended in free air within a hard shell. Steve's approach (and also Charlie's soccer ball) gets you most of the way there.
Rick "thinking that a structural engineer hasn't yet been hired to solve this problem" Denney