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From: Dale Rogers <dale.r@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Belt rumnations; 
Date: Sun, 27 Feb 2005 9:41:54 -0500
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Al Gietzen <ALVentures@cox.net> wrote:

>> The case for EWP for example is performance.  PL insisted that an EDWP
>> absorbs over 10 hp at 6000 rpm.  He is probably damned close.  He then made
>> the unfortunate leap that therefore an EWP must absorb the same power.  Not
>> true.  EWP conservatively absorbs 14V x 5 A = 70 W =~ 0.1 hp.  He was off by
>> about two orders of magnitude or about 9.9 hp.  Don't know about you  but I
>> can always use an extra 9.9 hp.
>  
> PL may have been considerably off; but at .1hp with the EWP you will be
> getting only a fraction of the flow of the belt driven pump; even if it were
> 100% efficient.  Keep in mind that converting power into electricity is
> about 85% efficient, as is converting electricity back into power. 0.85 x
> 0.85 = 0.72; so you have lost 28% of the power in the process.  Pumping
> coolant against even a small pressure head takes power.  Any 'performance
> improvement' you may see with EWP vs belt driven pump comes from lower flow
> rate.  
> Al

   But, Al, that's the whole point.  The stock pump is designed 
to provide adequate cooling in stop-and-go traffic; it wastes 
a lot of energy at cruise RPM.  If the losses due to conversion 
are 25%, that still a *net* 7.4 HP gain - nothing to sneeze at.  Add 
to that, that the coolant flow is tailored to the actual requirements 
of the engine, and that the thermostat can be eliminated, and 
the EWP has a lot to like.

Dale R.
COZY MkIV #1254