Plane & Pilot
Tuesday, May 7, 2013

Prius With Wings

Two-fisted thermal grabber, fuel-sipping cruiser and trainer—in one airplane!

The Glories Of Soaring Flight
Soaring pilots quickly learn to discern and make use of the distinction between glide ratio and sink rate. Both come at specific speeds.

Minimum sink rate means the actual loss of altitude per second at the optimum speed, which in the Sinus is 48.6 knots.

Maximum glide ratio indicates how far the aircraft will glide forward for every foot of altitude lost. A glide ratio of 20:1 means in optimal conditions and at best glide speed, 20 feet across the ground will be covered for every foot of altitude lost. For the Sinus, a one-mile altitude would ideally yield a 30-mile glide. Soaring pilots all learn to use these numbers to maximize time aloft and distance traveled.

Several types of lift exist. Some are terrain-dependent, such as ridge lift, (or orographic lift), where air rises on the windward side of a hill or mountain ridge. In the early 1970s, I hovered stationary in a hang glider for two hours 100 feet above a sand dune in 25 knot winds. Talk about pole sitting!

Wave lift comes from the harmonic, wave-like undulations of higher-altitude winds moving across tall mountains. These standing waves in the lee are predictable, often marked by lenticular (lens-shaped) clouds, and have glass-smooth lift. Severe turbulence often is endured getting up into a wave.

The current altitude record, set in a wave, is 50,699 feet! In South America, waves in the Andes helped a German pilot, Klaus Ohlmann, fly 1,869 statute miles. Both records were set in unpowered sailplanes.

Thermal lift derives from columns of rising air (think: dust devils) that break loose from ground areas heated by the sun. When that hot air rises high enough, colder air aloft makes the thermals' moisture condense into clouds. Pilots often find thermals marked by these cumulus clouds. Birds use thermals (think: vultures, hawks, eagles) to circle up.

Soaring pilots learn to circle to stay within the typically small lift "core" of a thermal. The tighter a glider can turn without losing too much sink rate performance, the better it will climb.

Thus, best sink speed is used to maximize lift, especially when thermalling or ridge soaring. Best glide speed is used to glide the greatest distance between thermals or to hop gaps with high sink rates enroute to the next ridge. Glider pilots have soared more than 1,000 miles on ridge lift alone.

There are few flying joys comparable to hooking a thermal and flying downwind for miles and miles without burning an ounce of gas.

Labels: LSAsPiston Singles


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