-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Dube
Sent: Wednesday,
October 20, 2004 12:00 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: EWP
Looking at the relationship between speed, flow and power
dissipation, I come to a different conclusion. The pump output curve goes
up relatively linearly with speed and bends over toward flat as the back
pressure builds. The power dissipation required (with a prop) goes up
roughly as the cube of the speed (parabolically), so it goes up slowly at first
and then heads up pretty steep as you get past 3-4000 rpm.
Because the heat
transfer behavior of the radiator and the engine block are NOT simple functions
of water flow, you really gain no insight by doing simple flow calculations.
You have to do the experiment, or do the computer model of the whole system. In
reality, you would end up doing both.
The
heat transfer formulas are very complicated and VERY non-linear.
Bill;
You’re
right, of course. I was just looking at first principals; ability of the
coolant to carry heat from engine to radiator. That is linear and is a
function only of heat capacity, assumed delta T , and flow rate. That’s
the first thing to consider for the design point you chose, and a condition that
has to be met. From there it is very complex on what the delta T actually
is. Yes, I suppose that inferring from this what the margin is at
conditions off the design point is stretching it.
Al