RE: Terry - "Improved" propeller gap design

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

At 08:00 AM 1/29/2003 -0700, you wrote:
>Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><Gary.Lau-at-hp-dot-com>
>
> >>Seriously, I had come up with a design improvement similar to your
> >>suggestion of using a split shaft-collar to secure the tungsten rod.
> >>Instead of using a shaft collar captured in a slot in the hub, why not
> >>just make the hub itself have the split-collar clamp built in?
>
> >I like the idea of silver soldering a collar on the rod.  Now you've got a
> >physical bump or lip to rest against a retention device that's loaded in
> >shear(safety wire, set screw, whathaveyou) rather than relying on friction.
>
>Trouble is, the motor hub is typically made of a plastic that would melt 
>as such a collar is soldered.

I was thinking that you'd solder a single ring/collar/short piece of brass 
tubing/something in the middle of the rod.  For that matter, the blob of 
silver solder might be enough to get some mechanical "tooth" to engage.

Epoxy is good too, assuming it sticks to tungsten. Or Silicone?  I think 
the forces are pretty low, in a good design, so what you're really looking 
for is a way to prevent it from creeping and loosening to the point of 
disaster...

>  As Terry originally suggested, if it turns out that imbalances do tend 
> to pull the rod through the hub (which has NOT yet been demonstrated), 
> why not just apply a small blob of epoxy to the rod to constrain it on 
> each side of the hub?  The temperature of the rod is not elevated at that 
> point, and if you were really concerned about the epoxy slipping, you 
> could file a small notch in the rod where the epoxy was 
> applied.  Remember, the whole point of this design is to K.I.S.S.


At some point, aren't windage losses going to start to be a signficant 
factor?  Anybody have any actual measurements on typical windage loss on a 
conventional disk type RSG? (i.e. actual power going to the motor... see.. 
we all need those RS Kill-a-watt meters) not that it makes much difference, 
but, for someone designing a new gap, it would be nice to know for 
approximately sizing the motor.