EAA Sport Aviation - April 2012

want to maximize the grip of the attaching No. 4 by 1/2-inch sheet metal screws that go into the foam case wall filler. Drill two pilot holes through the case wall for the water ports, and enlarge these two holes with a 1/2-inch-diam- eter spade bit. Also drill a 1/4-inch hole for the water pump cable.

PLUMBING

Install the nylon right angle hose bibs on the radiator and orient the barb ends parallel to the radiator frame. Cut a 5-inch length of the 1/4-inch ID Tygon tubing and attach it to the lower hose barb. The remaining length is attached to the upper hose barb. Remove the paper drill template and install the black ABS plastic mount on the left side of the cooler case using four No. 4 by 1/2-inch sheet metal screws. Note its orientation; there is a front and top side. The bottom surface plane has a 1-degree tilt to compensate for the 1-degree draft angle of the blow-molded cooler case.

The deep cutout in the back side of the mount is for clearance of the pipe fittings. In addition to the sheet metal screws, use ABS/PVC pipe dope between the mount and the case wall just prior to tightening the screws. Guide the Tygon tubing through the holes in the case and align the radiator in its mount. Use two 4-40 by 1/4-inch pan head screws to secure the mount to the front face of the radiator. The back face of the ABS mounts seats just inside of the rear flange of the fan frame. It is secured to the mount by two No. 4 sheet metal screws.

PUMP MOUNT

Fit the lower Tygon hose on to the water
pump output stub, apply RTV to the bottom
of the suction cup feet on the water pump,
and position it on the floor of the cooler near
the back wall. Use some weight to hold the
pump in position until the glue cures. Route
the pump power cord through the case side-
wall. Apply RTV generously around the
tubing/wall and pump power cord/wall
interface to make it watertight. Position and
glue the ABS 2-inch by 4-inch sheet on top of
the radiator.

ELECTRONIC INVERTER DRIVE WATER PUMP The purpose of the circuit board is to convert the aircraft DC power to 60Hz AC for the water pump. It uses an LM555 timer, and the MTS2916A is a single chip stepper motor controller and a dual H-bridge stepper motor drive. These devices are typically used to run printer motors and are suitable for running the circulation pump motor.

BOARD ASSEMBLY

Mount the PC board to the ABS floor plate glued to the top surface of the radiator. Use two 4-40 screws. Wire up the pump, fan, and power cord as shown in the above illustration. The location of the bulkhead female power connector is left up to you. I encourage you to