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To: flyrotary@lancaironline.net
Date: Sat, 2 Jun 2007 08:00:40 -0700
Subject: Re: [FlyRotary] Re: RV-7a cooling - continued!
Message-ID: <20070602.080053.2788.2.alwick@juno.com>
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From: al p wick <alwick@juno.com>

Have to admit Ernest, I'm really impressed with your approach on this.
Absolutely brilliant method of testing. Love the pressure measurement
tool.
If you didn't have that little tool, I wonder if you could just wet the
outside of radiator. Then watch for which areas blow dry off first?

-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing. 
Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html

On Fri, 01 Jun 2007 11:42:22 -0400 Ernest Christley
<echristley@nc.rr.com> writes:
> Bobby J. Hughes wrote:
> >
> > I can't find the post but maybe someone else has it or remembers 
> who
> > posted it. Could have been on PL's listed also. 
> >
> > If I remember correctly a one inch square grid was mapped and 
> measured
> > on the backside of a radiator. The top side was a wedge of some 
> sort. I
> > do not remember if the measurements were pressure or airspeed. The 
> data
> > indicated that more air was flowing through the core at the narrow 
> end
> > of the wedge and less air as the wedge opened up toward the 
> source. 
> >
> >
> >   
> For a naive wedge, this would be the case.  A barn door won't make 
> an 
> easily controllable wing, either.  However, it is not difficult to 
> build 
> a duct that will flow air evenly through a radiator core place at an 
> 
> acute angle.  It is no more difficult than building a naive wedge, 
> but 
> it does require some preparation to map out the correct 
> coordinates.
> 
> I attached a 3ft 'tube' constructed of cardboard to the front of my 
> oil 
> cooler, added a large box to the end, then inserted a leaf blower 
> into 
> the side.  I was trying to assure a even flow down the length of the 
> 
> tube.  I measured the exit air with a borrowed sensitive digital 
> barometer.  I attached a 2" diameter spray-can cap to the end of the 
> 
> static probe to capture the dynamic pressure exiting the cooler 
> core.  
> Higher velocity would have to translate directly to higher static 
> pressure.  I had less than a 10% differential across the face of the 
> core.
> 
> This "I tried one thing and it didn't work, therefore it must be 
> impossible" line of thinking belongs on MythBusters or the Discovery 
> 
> Channel, not in real development environments.  This experiment 
> provided 
> a single data point.  The conclusion should not have been that 
> wedges 
> don't work.  It should be that this configuration didn't work, which 
> 
> should lead to questioning what is the root cause of the failure 
> found 
> in simple laws of physics (Ooops!  I'm starting to sound like Bob 
> Knuckolls here.)
> 
> The root cause is the air's velocity is converted to pressure almost 
> 
> exclusively at the rear of the duct.  Can that be modified?  Sure.  
> Add 
> some diverting vanes that block the air at multiple points.  There 
> will 
> be multiple high pressure areas in front of the core, which 
> translates 
> directly to multiple high flow areas.  Are there other methods?  How 
> 
> about designing the duct so that the air is slowed in such a way 
> that 
> it's velocity will be converted to pressure evenly across the face 
> of 
> the core.  K&W, chapter 12, has a diagram of how to shape it.  I've 
> 
> verified to my satisfaction that it works (I could have made some 
> modifications to make the distribution more even, but <10% was 
> plenty 
> good enough).  It is simpler and lighter than any other method you 
> can 
> come up with, because it is just a duct that you will have to have 
> anyway.
> 
> http://www.ernest.isa-geek.org/Delta/Pictures/OilCoolerDuctIntake.jpg
> 
> http://www.ernest.isa-geek.org/Delta/Pictures/OilCoolerDuctTop.jpg
> 
>
http://www.ernest.isa-geek.org/Delta/Pictures/OilCoolerInletDuctTest1.jpg
> 
> --
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> 


-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing. 
Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html