REFLECTOR: updraft cooling

John Dibble aminetech at bluefrog.com
Sat Feb 17 15:04:56 CST 2007


I assume that updraft simply refers to the intake air coming from below
as opposed to downdraft where the air comes from the NACAs above.  I
think the way it passes the engine is the same.  It would be inefficient
to pass the air past the exhaust pipes first.

John

Chuck Jensen wrote:

>  I've not seen the layout of an updraft cooling system, but does the
> air get preheated from passing by the exhaust pipes before it every
> gets to the cylinder heads?  If it does, that would greatly increase
> the volume of air required because of the reduced delta T across the
> heads.  By comparison the top NACAs provide clean, cool air directly
> to the CHs.  Too simple--I must be missing something?
> Chuck Jensen
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
> On Behalf Of John Dibble
> Sent: Saturday, February 17, 2007 2:41 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: updraft cooling
>
> I think the amount of air going past the cylinders will determine the
> degree of cooling, so it's a matter of making the NACA or armpit scoop
> and ducts big enough for sufficient air.
>
> John
>
> Ron Brown wrote:
>
>> And, the downdraft NACA cooling for some unexplainable reason, runs
>> about 40 degrees cooler than the updraft cooling.  Mark Machado
>> converted what is now the factory trainer from updraft to downdraft
>> and says the heads ran 30-40 degrees cooler.  My 173 Elite RG runs
>> 360-370 max on a long climb out and 320-340 degrees during a 2600
>> rpm/155 kt cruise.  I highly recommend the NACA cooling system.
>
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