thymekiller wrote on Oct 26
th, 2008 at 8:21am:
Curious about how far away from the tube is best. I was careful to align where the rubber will attach so that the rubber is parallel to the stick. Does that make any real differance? Does thrust setting cancel that notion out? Thrust setting will be easy with the wire holder.
I give it maybe 5/16"-3/8" clearance from side of tube to motor C/L, that's good enough for a bunchy 3/32" loop. I'll set the tube with the hook & bearing angled so the motor's running about that same distance from the model's frame and the thrust C/L running through the model C/L.
Careful lining up--maybe&maybenot. This may be one of those things we overworry while missing something big like getting the model set up straight. The important part is, keep what you can of the motor as low as possible; but don't make for extra bearing-bending to do it. Extreme thrust offsets in short bearings make friction and power loss, but we often forget that, and it's not real relevant in NoCals anyway. Three-four degrees can be handled by the nice Czech front end.
Quote:One more. What if a person put the rubber INSIDE the tube? Would the tube need to be so big that a stick/box frame would weigh less?
Well--that's what most of Duration has gone to, and it works there because you have no fuselage requirements to live up to.
Putting a motor tube inside a fuselage means one more structure to add weight. Okay, but you make the fuselage of lighter stuff to compensate? Well, but then how do you work up hardpoints to hang wings & tail on? And how to keep your thumb from going through the fragile structure?
It's been tried before. Try it, you may find the answer; but stick & tissue has evolved into a pretty good structure now called "traditional" that guys know and are used to building with, which makes building easy for them--they don't have to reinvent structure with every new model. You may find a new way, or learn something useful if you don't.
Stick & tissue structure uses balsa in its strongest mode--compressibility--held in position by tissue in tension mode, which traditionally means shrunk (for tension) and doped (to
set the tissue in a matrix, much like epoxy does with limp fiberglass). This is why guys who pre-shrink or don't dope (or Krylon or whatever) often end up with floppy, fragile models,
unless they modify their framework for more rigidity; which often means adding weight over the old good way. Notice, the magic film coverings are often springy, and the Duration guys who use them also are using CF torque tubes or D-tube wings to take up the flop. Then, there's the film/tissue sandwich, which just makes me wonder why?
We keep looking for some silver bullet to the win, and in the meantime these old geezers keep building their old models and winning, by the experience gained in doing the same thing over and over 'til they get it down GOOD.
It's all a trade-off. Y'find your own best way.
Michael