Message-ID: <004101c38921$6c58f080$1702a8c0@WorkGroup>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2620990@logan.com>
Subject: Electric Water Pumps and Heat Rejection
Date: Thu, 2 Oct 2003 16:11:53 -0400
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> In a message dated 10/1/2003 11:53:22 PM Eastern Daylight Time,
> canarder@frontiernet.net writes:
>
> > I was away for a few months late last year and the first half of
> >  this year.  What's the status of Leon's EWP these days?
> >  Inquiring minds need to know ... Jim S.
> >
 SNIP

> At the national championship races at Mid Ohio I saw a "C" sports racer
with
> a 12A and a remote electric pump. It must have been working, and at the
> highest possible stress levels. A race (For them) is about 35 minutes
above 8,000
> RPM.
>
> Lynn E. Hanover
>
I agree Lynn, I think some of the views on electric water pumps are based on
some faulty analysis.

While I do not desire an Electric Water Pump, I know that some of you do for
various reasons.  There is certainly a lot of opinions regarding them of
that there is no doubt.  One analysis was conducted that supposedly "Proved"
that an Electric water pump would not be suitable for aircraft use and would
probably be of benefit only to very short duration evens, such as drag
racers.  That analysis was based on the fact that the Mazda water pump
supposedly consumed 13-16 HP at 6000 rpm.  The analysis then continued to
show that a 16 HP 12 volt water pump would consume somewhere around 400 amps
and be impossibly large (about the size or bigger than the 13B)  - clearly
proving that electric water pumps were totally unfeasible for aircraft use.

Well, the only problem I found with the Analysis is the assumption that the
13-16 HP consumed by the mechanical water pump was all required to provide
the necessary coolant flow rate.  I strongly suspect that a lot (if not
most) of that power was consumed pumping against unnecessary head pressure
(at that rpm), turbulence, and other non-cooling losses.  If 16 HP is
required then clearly an EWP is hopeless, but at least one person has had at
least one flight and had no serious cooling problems although I believe the
pump failed shortly thereafter (apparently nothing to do with its use).  I
have also noted that on the other list, flow tests have been conducted with
a new water pump housing and a Mazda pump caltrage.  The flow figures are
impressive - over 20 GPM (can't remember the exact figure) which looks quite
good for engine use.  What I found VERY interesting is that the test rig
motor driving the pump is a 2-3HP electric motor... a long ways from 16
HP{:>).

Sometimes, you just have to try it to see.  Don't get me wrong, I am all for
using any mathamatical tools and engineering logic to assess the potential
of any component.  But, I have seen too many times when the "experts" have
been wrong.  Its generally not the theory that they base their
pronouncements on (or even in some cases experience), its the overly broad
conclusions they draw or the failure to understand the real-world factors
and the role they play.

I continue to have excellent cooling from two evaporator cores whose
thickeness supposedly relgate them to the "hopeless" category for cooling.
In realiity, when I did the BTU heat rejection calculations for my aircraft
crusing at 170 MPH TAS burning 7.5 GPH, I found the radiator (evaporator)
cores have a cooling capacity reserve of 58% above that being used at that
power setting. This is taking in to account that their extra thickenss does
adversley effect the thermal gradient (Delta T) as well as the additional
pressure required to force air through the thicker core. I also found that
the oil cooler was at its limit (due to air flow).  The latter was a
surprise as I can bump up the "go juice" to higher HP and while oil temps do
increase, it appears that the extra capacity of the evaporator cores provide
heat rejection after the oil cooler reaches its limit.  The 1" thick (or
thinner) large surface area automobile radiators are necessary because of
the low dynamic pressure at typical auto speeds in a urban area, dynamic
pressure of course is much higher at the speeds we fly at.  So again what
works fine designed for one environment is not necessary the "Cats Meaow" in
a different environment.

These calculations only address the airflow ability to carry away the needed
waste heat, not whether the water pump or oil pump is flowing the heat
carrying medium to the cooling fins fst enough - thats another issue.  If
the air flow is not sufficient to carry away the heat from the cooling fins,
then it doesn't matter how much coolant/oil flow you have carrying heat to
the fins.

Sorry, get to rambling on at times.

Ed Anderson