EFFECTIVE, INEXPENSIVE PREHEAT
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.