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/254584
28 Vol.3 No.2 / Februar y 2014 GLIDERS AND SAILPL ANES 101 GLIDERS AND SAILPLANES are potentially the lowest cost way to fly. In this review, we will address rigid-wing, aerodynami- cally controlled, wheeled landing gear gliders, not the floppy wing and/or weight-shift-controlled gliders. EAAers are uniquely positioned to make lower cost flying and flight training possible with homebuilt gliders and launching methods. AN INTRODUCTION TO THE L ANGUAGE AND TERMS OF SOARING Gliders are normally thought of as unpowered aircraft, but that would make one type of glider, the motorglider, a bit problematic. Gliders are powered by a force that never sleeps— gravity. In normal fl ight, they are always going downhill relative to the air. Just like most sailboats, many gliders and sailplanes have auxiliary engines. The terms glider and sailplane are often used interchangeably, but there is some distinction. A sailplane is a glider that is ef cient enough to sustain fl ight by the use of natural-lift phenomenon. The space shuttle is an extreme example of a rocket-powered motorglider. With the engines of , there is no question it is gliding down for a landing. A sailplane, on the other hand, comes down slowly enough that a skilled pilot can fi nd air that is going up faster than the sinking speed of the sailplane so that altitude can be gained without an operating powerplant. The dif erence between a glider and a sailplane is their ef- fi ciency. The measures of ef ciency for gliders and sailplanes are minimum sink and maximum lift-to-drag ratio. A mini- mum sink speed of less than 3 feet per second (fps) is desir- able for a sailplane; less than 2 fps is much better, and less than 1 fps is the Holy Grail. A max lift-over-drag (L/D) ratio at least in the mid 20s is desirable in a sailplane. L/D is the equivalent of the glide ratio: 40-to-1 or better is not uncom- mon in competition sailplanes. The current record is about 70-to-1. That is more than a mile of still air glide for each 100 feet of altitude. As areas of natural lift can be quite small, the ability to circle tightly is important, which means being able to fl y at quite low airspeeds. Sailplane stall speeds are often well under 40 knots. The range of wing loadings for gliders runs from 2 to 4 pounds per square foot for ultralight-like gliders to 5 to 7 pounds per square foot for medium performance and training gliders to more than 10 pounds per square foot for ballasted competition gliders. One of the obvious characteristics of glid- ers and sailplanes are their long wings. When an aircraft has suf cient power to fl y fast when one of the drag components, induced drag, is low, short wings work fi ne. It is obvious that fl ying fast takes more power. It may not be obvious why fl ying slowly also takes more power. As the angle of attack increases, to produce more lift at lower speeds, more of the air from underneath the wing leaks around the tips, increasing the tip vortices. That is the source of induced drag that increases rapidly as the aircraft slows down. The most direct way to decrease induced drag is to increase span. It is rare to fi nd a sailplane with less than a 40-foot span. Fifteen-meter (49 A Piuma Project glider get-together. Piuma's are light, plans-built, mostly wood, one- and two- place motorgliders. This is a ULF-1 glider; it is a foot-launchable, plans-built, wood ultralight sailplane from Germany. The ULF 2 is a very light, plans-built, wood motorglider from the same designer. Photography courtesy of Murry Rozansky E A A E X P _ F e b 1 4 . i n d d 2 8 EAAEXP_Feb14.indd 28 2 / 3 / 1 4 3 : 1 7 P M 2/3/14 3:17 PM