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 other light aircraft.
Issue link: http://experimenter.epubxp.com/i/81495
A conical mount in a tension application. Note that nut is not yet secured on this display piece seen on a Zenair/Lycoming combination. By: Tim Kern Engine mounts are simple enough in theory. They are the interface between the stiff, lightweight airframe and the solid engine. Engine mounts—the elastic parts—are placed between those two big pieces to isolate the vibrations of the one from the vibrations of the other, and they also keep the natural frequencies of the system from coinciding with the operational frequencies, which could create extremely severe effects. Because engines are powerful and heavy, these isolators need to be large enough to carry the weight, while being small enough to fi t under the cowl. They must be stiff enough to prevent large motions of the engine and be soft enough to provide a pleasant ride. When properly matched to the components and mission, that's the happy result. Selecting the Mount In the certifi cated world, there is no question about which engine mounts to use. The proper mount is listed on the engine's type certifi cate or a supplemental type certifi cate. Equivalent parts must meet stringent requirements to ensure they perform exactly as the originally specifi ed parts. The repairman has no choice. In our experimental world, it's good practice to look at similar confi gurations (engine, prop, airframe) and use those as the basis for our selection of a mount. While most "close" matches provide good starting points, a radical departure from existing practice should be approached with caution and some solid engineering. As a rule, if you know enough to specify your own radically unusual engine mounts, this article won't stop you; if you don't… then don't do it. EAA EXPERIMENTER 29