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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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