REFLECTOR: Cooling

[Velocity Aircraft Owners and Builders list]

Hi again...

Larry says:
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"Dave,
 
My CHT's run about the same as yours which would indicate that both can be 
made to work.  The article also mentions that on ram type inlets that they 
need a proper lip at the entrance to work properly.  The kit supplied 
scoop has the same lips as found on a chicken.  That is why I modified my 
scoops which I believe improved pressure recovery and reduced drag.  I can 
top out at 180 kt TAS so the drag can't be too bad."

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Very interesting... my STD-RG tops out around 186-188 kts TAS flat out and 
all in.  Now, those numbers are subject to all kinds of errors and 
variations between our two planes, but it'd sure be interesting if they 
were truly apples to apples...! 

Thanks - fun conversation.
 
Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering


To:
<reflector at tvbf.org>
Subject:
Re: REFLECTOR: Fw: Cooling
Dave,
 
My CHT's run about the same as yours which would indicate that both can be 
made to work.  The article also mentions that on ram type inlets that they 
need a proper lip at the entrance to work properly.  The kit supplied 
scoop has the same lips as found on a chicken.  That is why I modified my 
scoops which I believe improved pressure recovery and reduced drag.  I can 
top out at 180 kt TAS so the drag can't be too bad.
 
Larry

From: Velocity Aircraft Owners and Builders list 
Sent: Wednesday, June 25, 2014 9:36 AM
To: reflector at tvbf.org 
Subject: REFLECTOR: Fw: Cooling

Hi again - 

Larry, a couple of thoughts (after reading the article).  It's a good 
article, but it's really focused on maintaining the energy of the incoming 
airstream for a jet engine.  What we are focused on here isn't that energy 
- we're focused on pressure recovery at minimum drag.  The article states 
that ." Submerged inlets were unsuitable for "oil coolers, radiators, or 
carburetors of ... reciprocating engines," the report continued, because 
"the required diffusion of the air and the range of inlet-velocity ratios 
is too great to give desirable characteristics at all flight conditions.", 
and I have no doubt that that is true. 

What it's not saying, however, is that a system including the NACAs, 
flowing into a diffuser created by ducting that is smooth, straight, and 
expanding, and then flowing into a plenum, has more or less drag than an 
exposed scoop.  Remember, it's the system we've got to look at, not just 
the scoop itself.  And that we're focused on both overall cooling capacity 
and drag minimization. 

Secondly, the author states "North American's bad experience-and those of 
others, such as Long-EZ builders who tried to use them for engine cooling 
air-did not put paid to the NACA scoop".  That's just plain wrong.  Go try 
to find a Long-ez or a Cozy that has a male scoop.  There are a few out 
there, but the NACA cooling has been standard since my Long-ez was built 
in the early 80's.  They work great, and have much better performance 
because the drag is inherently less and you're not disturbing the airflow 
to the prop to the same degree.  The key, again, with those airplanes is 
that the NACA dumps into an expansion duct that does pressure recovery. 

Terry Schubert has done some really great work on cooling and cooling drag 
- take a look at the Central States catalog to find good articles. 

At the end of the day, what we are all looking for is sufficient cooling 
capacity at the lowest possible drag, over all flight regimes.  NACAs and 
scoops can both do that (as I've seen with my Velocity - they both can 
work).  A properly installed NACA, however, creates less drag. 

My two cents...  Great discussion - Thanks! 
 
Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering 
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