October 2012

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/84816

Contents of this Issue


Page 27 of 47

Under the Cowl Michael Goulian's 580-hp Lycoming-powered Red Bull racer does not let any air go wasted. Baffl ing… It needn't be By Tim Kern Aircraft engines, whether air cooled, air/oil cooled, or liquid cooled, are all ultimately cooled by transferring their heat to the air. This transfer is so important that we tolerate cool- ing being responsible for up to 20 percent of an airplane's total drag. Understanding the basics of cooling helps us to understand how much cooling we need and how best to achieve it. The principles are sim- ple; execution is not easy. (Mozart, it is often said, wrote simple music. You try it.) 28 NO. 2/OCTOBER 2012 The Basic Rule We're not cooling engine size, compression ratio, or numbers of cylinders. We're cooling horse- power. A tiny 600-cc (37-cubic- inch) motorcycle engine making 100 hp needs the same amount of cooling as a 200-inch Continental O-200 that's making 100 hp. A TSIO 540 throttled back to 100 hp needs that same cooling, as does a Rotax 912S at full tilt, or a 427-inch Cor- vette that's loafing along, cruising at 120 mph and using 100 hp to do it. Vastly different packaging and purpose make the cooling systems look different, but the amount of cooling needed at any given output is virtually identical. Two Important Generalities Although the air gets colder as we gain altitude, it also loses density. Less dense air carries off less heat. Less dense air also reduces the power potential for normally aspirated engines. Adding a turbo- charger to an existing design, even

Articles in this issue

Archives of this issue

view archives of Experimenter - October 2012