Sender: <marv@lancaironline.net> (Marvin Kaye)
To: flyrotary
Date: Fri, 21 Mar 2003 01:19:00 -0500
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From: Ernest Christley <echristley@nc.rr.com>
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Subject: Re: [FlyRotary] Thick or Thin? The debate continues
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Tracy Crook wrote:
> OK, here's my take on the thick vs thin rad argument.
> 
> I agree that the thinner radiator is 'more efficient' in terms of
> dissipating a given number of BTUs with the fewest square inches of fin area
> *IF* the volume of air used to do the job is ignored.  This whole argument
> hinges on that 'if'.  Every thing I have read on the subject of drag
> reduction (related to cooling) points to using the *minimum number of cubic
> feet* of airflow to do the job, so, my premis is that the name of the game
> is using the *least* amount of air to do the job.
> 
> So, I see the choice as:  Do you want an 'efficient' radiator or an
> efficient airplane?
> 

There goes Tracy with all that facts and logic stuff again. 8*)

Interestingly enough, it may be that the Delta's rather unique 
properties may make it simpler to use the large thin radiator with a 
much slower airflow than it would be most other.  The most insiduous 
problem with the Delta, as I understand it, is that it has a tendency to 
be nose heavy.  Moving the radiators aft of the passenger seat will 
relieve the nose of that weight, and put it just behind the center of 
lift. The peripheral advantage, is that I now have a large volume of 
otherwise empty space to play with.

Now that I have it back there, the problem becomes one of delivering and 
venting air.  Scoops built into the wheel wells (with NACA scoops built 
into well doors if I ever incorporate them) will be near the center of 
the chord line, and one of the areas of highest pressure.  The air will 
continue on and vent through the top rear of the turtle back, near the 
rudder and elevon control linkages, one of the lowest pressure points. I 
hope to have an extremely high pressure differential, but I have no way 
of actually testing right now.  The radiator study report that I have 
read, (http://naca.larc.nasa.gov/  ...do a search on radiator)

A high pressure differential will allow me to have a smaller than 
expected scoop.  If I do a good job of designing and building a duct 
that will allow the air to expand and slow before it gets to the 
radiator, it will pass through slow enough to exchange heat efficiently.

Here's a question for the number crunchers.  Which will be more efficient:

A)A thick radiator with a high cooling air flow rate?
or
B)A thin radiator with a low cooling air flow rate?

Personally, it's starting to make my head hurt.


-- 
----Because I can----
http://home.nc.rr.com/deltabuilder
------------------------