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From: Dale Rogers <rogersda@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: EWP
Date: Tue, 19 Oct 2004 12:24:28 -0400
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> 
> From: "Al Gietzen" <ALVentures@cox.net>
> Date: 2004/10/19 Tue AM 10:29:24 EDT
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Re: EWP
> 
> I understand the EWP has higher efficiency than the stock pump - does
> someone know how much? (I may have missed it because I haven't followed this
> issue very closely).  But I'm sure it is less than 40% better.  And you can
> save some pumping power in some flight regimes where the belt driven pump is
> pumping more flow than needed.  But, overall, saving power is not a likely
> reason for going to an EWP.
> 
> Configuration - yes.  Redundancy - yes. Power saving - not.
> 
> Al

Al,

   I wonder if you misunderstood the nature of the question 
and of my reply.  I keep saying that I shouldn't reply to 
messages at 0-dark-30 when I can't sleep, but I keep doing 
it.  Still, the question wasn't whether to convert or not 
but whether or not to use the controller.

   The belt-driven water pump has to be able to provide 
cooling flow under worse-case conditions: low-speed city 
traffic.  Therefore, it is way over capacity at 6500 RPM.
This can be mitigated somewhat by changing pulley sizes, 
but at the risk of the cooling at idle and taxiing.  

   The electric pump allows demand-based flow, using only 
as much energy as necessary to provide adequate cooling at 
that moment.

   Not using the controller, leaves three basic options: 
(A) wire direct, pumping full flow all the time and using 
    a thermostat to maintain minimum heat.
(B) wire direct, with no thermostat, and run cold during 
    decents and other low-load conditions.
(C) Put in a manual speed control.

Rusty's concern - inadequate "minimum" flow speed - can 
be dealt with fairly easily.

It would seem to me that the only time the pump needs to  
be at maximum output is during climb-out. The rest of 
the time, the system needs significantly less flow and 
therefore considerably less input.  

How much? That *does* yet need to be evaluated, but the 
experience of the racers seems to indicate that it is 
not trivial.

Dale R.
COZY MkIV #1254