Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/134623
Un d e r t h e C o w l project as it can mean potential new business from wordof-mouth advertising if you're successful. But even though this has the prospect of being a symbiotic relationship between you and the engine builder, don't expect any favors or preferential treatment. There are countless projects out there that got off to a good start and have yet to fly. An engine supplier can't bank on your enthusiasm while waiting for you to finish, so be prepared to pay a reasonable fee for your engine mount if you go this route. Cooling Now the real fun begins. How does your proposed engine get cooled? If it's air-cooled, you are 90 percent there. (With 90 percent still to go!) Considerations are updraft or downdraft, inlet size, shape, and spacing (same for the outlet), baffles (size, shape, construction materials, pressure plenum, seals, cylinder movement, cable and wire routing), and delta P—ensuring a good pressure drop from the inlet to the outlet across the engine. If it's water-cooled, you have several issues ahead of you; the most obvious is where will the radiator be located. A few of the most common locations are: 1. Up front; either side of the spinner. 2. In back; up high, against the firewall but with enough space between to move the air through with minimal restriction. 3. On the side, or both sides of the cowl, supplied with air by additional scoops on the outside of the cowl to bring air in, or from the traditional inlets and vented by louvers to the outside of the cowl. 4. Under the engine; laid nearly flat against the inside of the cowl. 5. And then there are the belly scoops, some are mounted under the passenger compartment with the radiator at a slight angle or toward the rear with the radiator mounted vertical inside the fuselage in a more traditional P-51 orientation. With the scoop, the inlet has to be far enough below the belly of the plane to ensure uninterrupted airflow. There may be an airflow separation along the curved surface of the belly that's not evident without some tuft-testing. So I'm a plumber now? Once you've considered all the possible locations of the radiator and how to pass air through it efficiently, the next consideration is routing water to and from it. But before that you really have to consider CG again, as the radiator full of coolant will have a fairly significant weight contribution, as will the full coolant lines. The farther away from the water pump that the radiator is located, the more issues can arise. If the radiator is inside the cowl, traditional-length radiator hoses might be used. The longer the run, however, the heavier the installation becomes, and that's why so many builders have opted to use (properly sized) aluminum tubing wherever they can. This can be a double-edged sword, though, as the lightness of the aluminum and its ability to wick away heat Although not the fnal version, one would hope that your cowl would be a better match for the airframe and powerplant than this one is. 30 Vol.2 N o.6 / June 2013