Paul,
here is an html version.
much smaller
Bill Schertz
Bill can you send me those charts you made as well? I lost them in the
hard disk crash.
Paul Lamar
Opps I don't think that worked. The graphs and photos where not included.
I am not sure but I think you have to send them along with the html file.
Paul Lamar
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Measuring the flow of a 13-B Water Pump
The cooling of an engine used in an aircraft application is critical to the safety of the
operation of the aircraft. If overheating occurs during flight, the operator may have
insufficient time to get to a safe landing area.
During many discussions on e-mail newsletters, one factor became apparent, namely that the actual
flow that the water pumps that were being installed in aircraft could generate was not known.
Because of this lack of data, much speculation has reigned on what was the best pump, and how it
should be configured.
Background
I am installing a normally aspirated Mazda 13-B in my KIS Cruiser, a four place, low wing
composite aircraft that had a Lycoming 0-360 in the prototype. From data that I have been able to
obtain, it appears that the normally aspirated engine will generate equivalent horsepower to the
Lycoming. The difference is that the Mazda is water cooled, as opposed to the air-cooled
Lycoming. Therefore I need to have an adequate cooling system, and also need to have background
information that will let me diagnose any cooling problems correctly. Knowing the flow
characteristics of the water pump on my engine is part of the information that I need in order to
properly interpret any cooling problems that might arise during engine and flight tests.
Test setup
I am interested in the performance of the pump in a configuration that is as representative of my
installation as possible. Therefore the pump was tested installed on the engine, with the
waterpump modified to give clearance for the cowling and interface to the planned plumbing on the
engine.
[Image]
These modifications consisted of removing the thermostat, cutting off the jportion of the
water-pump housing that projected above the cowling, and having a horizontal outlet tubing welded
into place. The inlet to the pump had a ?Y? section welded into place to interface with the
return plumbing.
[Image]
The water source for the pump tests was a 55 gallon barrel set on a work bench. It was necessary
to have the water level in the barrel be above the pump in order to keep the pump properly primed
between runs. Water was pulled out of the barrel by the pump, flowed through the block of the
13-B, and then back to the barrel. A valve was installed on the pump outlet, in order to vary the
flow rate. A pressure guage was installed at the inlet and the exit of the water pump so that I
could measure the pressure during operation.
[Image]
I used an electric motor from my table saw and a long V belt to drive the pump. By varying the
pully size on the motor, I could take data at several different RPM, simulating the fact that the
pump speed would vary with engine RPM.
The data was taken by the old-fashioned bucket and stopwatch method. The flow was stabilized, and
then the flow was diverted to a bucket and the stopwatch was started. To eliminate as much as
possible any effects due to head changes as the pump transferred water from the barrel to the
bucket, the bucket was floated on the water in the barrel, and allowed to sink as it filled.
Therefore there was no effective change in the head that the pump faced. The raw data, after
being converted to PSI vs flow in GPM are shown in the next chart.
[Image]
You can see some variation from a smooth curve due to the vagaries of taking data by this
technique. You can see that the pump inlet pressure goes negative, due to the pressure drop in
the hoses leading from the barrel to the pump. In an aircraft installation, that hose will be
much shorter, and therefore the pressure available to drive fluid through the radiator cores is
the difference between the pump curve data and the inlet pressure data. To make the data more
useful, I did a curve fit of the data and replotted it as shown below.
I plotted the data from above on a pressure as a function of (flow-rate)^2, since the pressure
drop in general is linear with the square of the flow rate. This allowed me to make a ?best fit?
of the data, and to generate an equation for the pump curves. I also could combine the equations
to allow for the negative pressure in the inlet line due to the long (and corrugated!) hose. The
data analysis chart is shown below.
[Image]
This then allowed me to make a chart showing the pump curves as a function of flow rate, as a
smooth curve as shown below.
[Image]
The next piece of missing information is how much pressure drop is experience across the radiator
core(s). My current plan is to follow in the path of Tracy Crook and Ed Anderson who used
evaporator cores to cool their engines. Others are using a single large radiator located under the
engine, this is a concept that has much merit, but I have not done any pressure drop testing on
this combination.
My initial tests of the evaporator cores was done using tap water from the sink, measuring the
pressure drop as a function of the flow rate. This gave me some data that allowed me to put it on
the same chart as the pump curves. The pressure drop across the core(s) must be supplied by the
pump, to the operational point will be where the two curves cross.
[Image]
The water source I had could not effectively supply enough water for two cores in parallel, which
is what I had designed for my system. So the data is shown for a single core (multiple runs), and
the curve fit data shows the operational curve for a single core. To get the expected performance
for two cores in parallel, I could calculate the curve, since the flow would be twice as much at
any given pressure. This is shown on the figure above.
Calculated curves are fine, but I also desired to see if I could measure the flow through the
cores with the pump doing the water supply.
My configuration of the evaporator cores is to have them in parallel as shown in the photo below.
[Image]
[Image]
The heavy point labeled ?Real Rad Test? is the result of testing done with the evaporator cores in
the system. The fact that it lies close to the calculated curve leads me to feel that I can trust
these curves in the analysis of my system as I proceed.
I recently obtained a little bit of manufacturers data for the performance of an Electric Water
Pump. This unit is made by Meziere, and is stated to deliver 55 gallons per minute maximum flow.
A further data point from the company rep indicated that at zero flow, the maximum pressure would
be 10 psi. Using the fact that pressure drop is a quadratic function of the flow rate, I have
superimposed the EWP curve on the data that I measured. One important difference must be observed
in viewing that curve. The EWP is not pumping through the engine block, whereas the measured
curves for the 13-B do have that pressure drop. Based on that data, I do not believe that it
generates enough pressure to operate the system that I am installing.