Experimenter

March 2013

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/113663

Contents of this Issue

Navigation

Page 45 of 53

Lift and Drag Coefficient F li g h t Te s t in g Te c hn i q u e s Max CL /CD occurs at only this AOA Figure 3 Angle of Attack There is some condition between minimum drag and maximum lift where the trade-off between less power and more speed gives you the best deal. This occurs at the maximum L/D, which occurs at only one AOA— the same AOA as your airplane's maximum range glide AOA. If AOA is so wonderful, why doesn't the FAA require AOA indicators in airplanes? Good question. Pilots can be just as safe and efficient with proper flight planning, solid piloting, understanding their airplane, and good judgment without an AOA gauge. Having AOA at their disposal makes it easier. Why does weight affect speed and not AOA? As your airplane burns fuel during a trip, it becomes lighter. If you fly a constant airspeed, you'd fly at a progressively lower AOA as fuel burned and your cruise range would be less. If you continue to fly at your maximum range AOA, you'd have to fly progressively slower as fuel burned, but you would get the most mileage from your fuel. For some small airplanes whose weight doesn't vary much, a few airspeed references for maximum cruise and glide range and 1g stall may be sufficient. For many amateur-built airplanes, however, where fuel and payload weight can vary by a substantial percentage of the airplane's overall weight, there can be a considerable consequence in range penalties and stall margins. Whether maximum efficiency is important depends on your needs. Most pilots cruise at a faster speed, and lower AOA, than maximum range AOA. These pilots trade money (for the extra fuel speed costs) for a shorter flight (the result of speed). Someday, however, you may face a diversion because of weather or an unexpectedly closed airport, and you may not have enough fuel to reach your new destination using your normal cruise speed. Having the ability to reference your "Max L/D" mark on your AOA gauge could just give you those needed extra miles. 46 Vol.2 No.3 / March 201 3 Next month's topic will be flight path stability. It's called stability, but it's really about how changing your airspeed during final approach affects your glide path— and it's different for different airplanes. Ed Kolano, EAA 336809, is a former Marine who's been flying since 1975 and testing airplanes since 1985. He considers himself extremely fortunate to have performed flight tests in a variety of airplanes ranging from ultralights to 787s.

Articles in this issue

Archives of this issue

view archives of Experimenter - March 2013