[NSRCA-discussion] Cooling/spinners

[Thomas D. Simes]

On Mon, 20 Feb 2006 17:26:27 EST
Rcmaster199 at aol.com wrote:

> It's "elementary" Thermo 101 kind of stuff with a little fluid
> dynamics   thrown in for good measure. Keep the air in the turbulent
> regime around the   engine to maximize cooling effectivess. To some
> degree, we did that in our  earlier  designs by maintaining a slender
> fuse and cowling in tighter by  necessisity.
>  
> With the advent of the Pachyderm fuses, we copied full scale size-wise
> but   with little forethought about cooling. Having a large bucket of
> dead air up   front in our fatso fuses does nothing for the
> engine/motor. Slows the plane down 
>  tho.
>  
> And BTW, the exit really doesn't need to have 3X the entry area to be 
> effective if properly designed to draw the air out. Remember
> Bernoulli?? 

In a round about way, that was my point.  The bucket of air is the
problem.  We use the 3X rule because it is easy to apply, and it fits
a wide variety of configurations without modification.  Crafting proper
ducting/baffling is more work, but the material costs are quite low -
the primary cost is time involved in experimentation.

> On the other hand, with so many of us having stopped building, where's
> the   creativity and innovation going to come from? It saddens me to
> see a whole new   generation of "modelers" who only want to fly, using
> ready made everything.  It  does produce wonderful piloting skill tho.

One benefit of the ready-made "Pachyderm fuses" is that there is plenty
of room up front for experimentation.  Since the thread originally
started with someone asking about a better way to cool an electric, I've
been pondering that problem.  With the outrunner designs external
cooling fins would be tricky to implement and would also rob thrust with
the drag they create.  What about using cheek/chin cowls to feed air
into an annular duct surrounding the motor - perhaps with a few strakes
to help straighten the flow and keep it moving towards the exhaust.  For
first cut evaluations an appropriately sized plastic beverage bottle
could be easily cut and deformed to fit inside the cowl.  Aft of the
bottle a simple angled balsa plate to deflect the flow towards the
exit...

Just thinking out loud - I should probably stop that though.  In the
interest of full disclosure I have a grand total of 4 lipo packs and
the biggest is 450 mAh so you should probably consider the source
carefully before taking any of the above too seriously.

Tom
 
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   "Z-80 system stack overflow.  Shut 'er down Scotty, the system's
         sucking mud" - Error message on TRS 80 Model-16B

Thomas D. Simes                                 simestd at netexpress.com 
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