REFLECTOR: Nose Cooler Pressure Study

aminetech at bluefrog.com aminetech at bluefrog.com
Sun Oct 11 10:06:44 CDT 2009


My experience with my SERG seems to suggest that my exit is not limiting.  Three years ago I had high oil temps while flying on a hot dry Texas day.  I had installed a 3" bilge blower in the exit section to pull air thru the cooler when on the ground.  The blower occupies a lot of space in the duct and I suspected it was impeding air flow at cruise where it was turned off.  So I landed and removed the blower.  Back in the air, my oil temp was still high and unchanged from before.
I have also installed an extension on the exit which was flush with the fuselage before.  This improved cooling significantly during climb, but made no difference at cruise.  My cruise speed did not change as best as I can tell.
Sometime I will try the pressure measurments and see what I get.

John

--- scott at tnstaafl.net wrote:

From: Scott Derrick <scott at tnstaafl.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: Nose Cooler Pressure Study
Date: Sun, 11 Oct 2009 07:31:19 -0600

Brent,

Great info!  What your testing suggests is the forward scoop is maxed
out and best way to increase the efficiency of the nose oil cooler is to
lower the pressure on the exit side by building up a lip or dam on the
exit hole? 

Scott

Brent Bourgeois wrote:
> Scott,
> I have spent a lot of time getting my oil cooler working properly.
> Before cutting anything, please do a basic pressure study to
> understand what is going on. All you need is a plastic tube about 1
> inch in front of the cooler and one in the exit duct. Route them
> inside and use a airspeed indicator to get an inlet press and an
> outlet press. The key is to maximize the differential. 
> I have pages of data that prove (at least on my plane ) that the
> problem is positively not getting the air in, but getting it out.
> One example is : 155mph on the pitot, 88mph on the cooler face and 10
> mph in the exit duct. I was eventually able to get the exit duct to 0.
> This 88mph proved to be the max oil cooler inlet speed all the way
> past 220 pitot speed.
> I think that once the inlet pressures up, the air stops entering and
> flows on by. Once I got max vacuum possible behind the cooler I was
> able to block off some of the (weird NACA type)  inlet and not raise
> the oil temp.
> I believe the trick is to find a reverse scoop or lip arrangement that
> maximizes the air extraction
> I had thermocouples on the cooler inlet and outlet lines. The front
> cooler is worth 15 to 20 degrees in oil temp.
> I also found this method very useful at maximizing engine cooling
> while making the air inlets smaller.
> Let me know if I can help.
>  
> Brent
> N61VB
> Std RG
>  
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>
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