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Date: Sun, 27 Apr 2008 10:40:24 -0600
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Electric Water pumps - Interesting
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Hi Ed,

I did some testing on the EWP's.  The rating is the free flow rating,
but my measurements seemed to indicate that number was overly
optimistic.  I will have to dig around to see if I can find the stuff I
did on it.  With just a short hose on the inlet and outlet plus a flow
meter, I got substantially less flow.  The 3.8 hours I flew was with
the EWP exclusively.  As I recall, the in system flow rate was around
10 gpm.  Using calculations based on Bill Shertz' work I had wanted 15
GPM.

The 3.8 hours I flew was in 50F to 60F temps and cooling was adequate
but marginal.  I believe I had seen 220 on the oil temps once in
climb.  Water temps were a little lower.  When I leveled off and pulled
the power back, temps would drop below 200 pretty quickly.  I know the
air flow through my oil cooler was poor, and was on my short list to
modify.  Air flow through the radiators may not have been as good as
it could have been either.  

Now let me propose a theory as to why the simple argument that the EWP
wont work because it doesn't consume enough HP may be incorrect.  The
stock pump on the engine definitely uses 5 to 10 HP.  But does it
need to?  The stock pump has to provide adequate cooling sitting at a
stop light in 120F temps (Phoenix in the summer).  HP goes up as the
second or third power of RPM (one of the things I need to look up
again).  So to get adequate cooling flow at idle, the cooling flow at
cruise may well be more than adequate.  As mentioned earlier, I had
calculated that I needed 15 GPM.  The air flow needed to be sufficient
to give the delta T's I was using in the calculation.  The EWP has the
advantage of providing full flow at all speeds, so the use in a car
seems quite doable since there are very few times full power is
sustained for any length of time.

This is all just a theory, and it's not a theory like the "Theory of
Gravity".  It's the hypothesis kind of theory.

I will be using the exact same setup in the Alpine with the EWP.  I
will at least be able to report on how well it does in the car.

Bob W.


On Sun, 27 Apr 2008 10:31:47 -0400
"Ed Anderson" <eanderson@carolina.rr.com> wrote:

> I was just thumbing through a recent catalog from Summit Racing and came across a couple of pages on electric water pumps.  There has always been a degree of interest (and some debate {:>)) regarding the use of electric water pumps in aircraft.   It was interesting to read some of the descriptions, but basically the current consumed ranged from 4 - 9 amps and the quoted flow rate (presumably without back pressure) was from 16-35 gpm.
> 
> So if you take 9 amps at say 14 volts = 126 watts = 0.167 HP to get that flow.  However, some of them indicate you can save 15 - 20 engine HP at HIGH rpm.  So why the difference?
> 
>   Apparently (my best guess) is that they are advertising their product to best advantage (surprise?).  I would suspect that the flow rates shown are without back pressure and that when attached to a real engine coolant system that :
> 
> 1.  The flow rates would decrease 
> 2.  The current requirements would increase. 
> 
>  However, not to the point the electric pump would be required to make 10HP or more to provide the required flow.  I suspect there are considerable losses (such as pump cavitation and pressure drops through the cooling galleys)with mechanical pumps  at high pump rpm as driven by a high revving engine which accounts for the high power requirements.  Whereas the electric driven pumps may operate at lower and more efficient rpm without the majority of those losses.
> 
> That said, the pumps cost range from around $200 - $400 and while no weights were given, basic on the photographs showing the heavy electric motors and additional plumbing  would not appear to offer any significant weight savings over the proven, reliable mechanical pumps most of us are using. 
> 
>  So while certainly interesting and perhaps of value in some aircraft installations(how would you like to gain an additional 10 HP on takeoff?), I remain confident in my old 86 13B water pump housing and cartridge which is still going strong after 10 years.  I have moved it from my first 86 N/A engine to my current 91 turbo block, so it has performed for over 10 years in two different engines without any problem.
> 
> Interestingly, of  the  11 electrical water pumps advertised, only one was specified for drag race use only - and it had the lowest current drain - 3.5 amps.
> 
> Ed
> 
> Ed Anderson
> Rv-6A N494BW Rotary Powered
> Matthews, NC
> eanderson@carolina.rr.com
> http://www.andersonee.com
> http://members.cox.net/rogersda/rotary/configs.htm#N494BW
> http://www.dmack.net/mazda/index.html


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