EFFECTIVE, INEXPENSIVE PREHEAT
2013/01/22
This unit is based on a 1500
watt ceramic electric room heater but it is re-packaged to include a higher
volume air flow, a safety thermostat and recirculation of the air to and from
the engine compartment. Ceramic heaters are frequently on sale for about $20,
the thermostat is about 15, and the pipes another 20.
I happened to have my blower so not sure what one would cost.
Instead of the blade style
fan that the heater comes with, a much higher volume squirrel cage centrifugal
blower is used. Typical blade style fans may draw 1/3 amp but this blower is
about 1.35 amps which is an indication of it moving a lot more air.
Rather than let the heater pull
in cold outside air, the inlet to the heater is fed from hoses going to both
cowl air inlets while the heated air is routed into the cowl lower down. On
this Rans (unlike stock S7S) the oil cooler is much larger and is mounted under
the engine. It is fed from a duct below the prop spinner. It is to this duct
that the heated air is routed. From there it goes through the oil cooler and
upwards around the crankcase before exiting top front to the hoses.
Looking at the picture above,
the blower is on the left. It is mated to an aluminum box which houses a
standard single pole baseboard heater thermostat. That is the silver box with
the round knob. Also on the box is a red light which is on when there is power
to the heater core.
The next black chunk before
the propeller is the plastic housing from the original heater to which the
ceramic core is attached. One side of it is a rectangle which fits the ceramic
core and the aluminum box; the other is round which fits a 5” furnace duct
pipe. Next is a 3 x 9” furnace duct boot which mates to my oil cooler input.
The final addition is some insulation over all the metal pipes. All this sits
on a sturdy camera tri-pod.
Power comes into the blower
housing and is connected to the blower motor which is always on when the unit
is plugged in. From there it goes through the thermostat, then through a fuse
that is included with most room heaters mounted after the heater core and only
then to the ceramic element. The red LED is wired in parallel with the heater
core.
For monitoring, there is a
thermometer probe in the air stream entering the blower as well as another
remote sensor I put on top of the engine before installing the return hoses.
After startup, you will see temperature
readings rise inside the cowl but how quickly they climb depends on how cold
out it is. At -15C you will need about
an hour to get the engine up to room temp. When the
temp gets to about 60C, the thermostat sensing the air from the cowl shuts off
the heater core but the blower continues to circulate. As the temp drops the
thermostat will turn on the heater core to maintain that temperature. The
baseboard heater thermostats do have an adjustment nut that allows them to shut
off at higher temps so you can set the temp as you want.
The tri-pod makes positioning
the heater assembly quite easy and allows mating it to different aircraft.
