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
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