REFLECTOR: High Oil Temps

Scott Derrick scott at tnstaafl.net
Sun Jun 23 19:22:12 CDT 2013


Oh, I also run the oil up the pilot side duct, and down the co-pilot 
side duct. This improves cooling.

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: High Oil Temps
From: Brian Michalk <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Date: 06/23/2013 06:02 PM

> After looking up some racing forums, it appears as though the parallel
> configuration is more efficient, all things being equal.
>
> On 06/23/2013 05:42 PM, Brian Michalk wrote:
>> Today I had a very good test flight.
>>
>> I've been battling high CHT and oil temps, and made the decision to
>> increase my prop pitch for todays flight to bring down RPM's. That
>> made a marked difference in CHT temps, and I could fly without
>> redlining the CHT's.
>>
>> Now, I still have high oil temps.  My oil cooler arrangement is two
>> oil coolers in the nose in parallel.  The secondary cooler has a
>> radiator fan attached with a flapper valve that doubles for ground
>> operations and cabin heat.  Needless to say, the fan doesn't do a very
>> good job, and I think is the source of my high oil temps.
>> For this thought game, assume two identical oil coolers with equal oil
>> flow in parallel.  This means that each cooler gets 50% of the oil.
>> Now, assume no cooling air flows through one of the coolers. The
>> result is that half the oil is cooled, and the other half gets
>> returned at the same temperature it began.  The result is that I get
>> 50% of the cooling that's available.
>>
>> What I've done in the meantime is I've capped off my second cooler. I
>> have not flown with this configuration, and will do so this coming
>> weekend.  I really do think this will get me within the temperature
>> ranges to get around to some serious flight testing.
>>
>> Now, the real question:
>> Given two identical coolers that flow equal parts oil, and also have
>> equal amounts of airflow, is it better to plumb them in series or in
>> parallel for maximum heat rejection?  It seems to me that parallel is
>> like having more frontal cooler area, while in series would be like
>> having a thicker cooler, with the larger frontal area being the more
>> efficient design.
>>
>> Does anyone have any info on this?
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