I refuse to buy a bunch of the expensive metal flanges for the attachment of SCAT/SCEET hose for heating and cooling. So I bought one each of the two most probable sizes if hose I will be using, and used them as a template to make a mold so that I could replicate them in fiberglass. Mold release wax was used liberally on the metal, and then a liberal layer of cabo on the surface (poor mans gel-coat) followed by 4x bid was laid up on the outside of the metal template to make the mold. I added graphite to the epoxy to make the mold black. After smoothing and filling and waxing, I could punch out replicas of the SCAT hose flanges. I will use these on the various air boxes and ducts for the cabin heating and cooling system.
I purchased a squirrel-cage blower to use to recirculate air in the cabin, and as a side experiment, I wanted to measure the airflow characteristics of the fan. I tend to geek out on the physics aspects of things, so I set out to measure the zero-flow pressure and the no-back-pressure flow rate, and several intermediate points in-between. In analogy, its like measuring the source characteristics of a power source, where one would measure the open circuit (zero current) voltage, and the no voltage (short circuit) current, and points in between to get the source impedance.
So I rigged up a flow tube with several fixed-sized circular orifices, with dynamic pressure measured on both sides of the orifice to obtain (via the equations for compressible orifice flow) the air flow rate, and then an independent pressure measurement (re: atmosphere) at the fan output.
Measurements indicate (see graph below), that at a fan voltage of 13.5V, the measured airflow vs. back pressure (dots) agrees in shape, and is consistently above the manufacturer’s data (solid curve), which was taken with a fan voltage of 12.0V.
I think if I keep the resistance to flow low enough, this fan will deliver an adequate air flow. Further experiments will include measurement of flow resistance of SCAT and SCEET tubing.
I have decided to depart from the plans regarding oil cooler location and cabin heat. I plan to put the oil cooler in the rear of the aircraft, and use the nose NACA inlet for cabin fresh air only. Details, calculations, and full plans to follow later. To control the amount of fresh air entering the aircraft, I am building an electrically actuated door that will fit flush in the NACA inlet when closed, sealing it completely against incoming air, and also retaining the fuselage contour. When open, outside air will be routed to cabin ducts for cooling in the hot Texas summer. In the winter, and at altitude, the nose NACA duct will be closed, and hot air from exhaust muffs will be mixed with outside air and routed from the engine compartment into the same ventilation ducts.