High-speed dynamic soaring
High-speed dynamic soaring
Date
2012-04
Authors
Richardson, Philip L.
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Abstract
Dynamic soaring uses the gradient of wind velocity (wind shear)
to gain energy for energy-neutral flight. Recently, pilots of radiocontrolled
gliders have exploited the wind shear associated
with fast winds blowing over mountain ridges to achieve very
fast speeds, reaching a record of 487 mph in January 2012.
A relatively simple two-layer model of dynamic soaring was
developed to investigate factors that enable such fast speeds.
The optimum period and diameter of a glider circling across a
thin wind-shear layer predict maximum glider airspeed to be
around 10 times the wind speed of the upper layer (assuming a
maximum lift/drag of around 30). The optimum circling period
can be small ~1.2 seconds in fast dynamic soaring at 500
mph, which is difficult to fly in practice and results in very large
load factors ~100 times gravity. Adding ballast increases the
optimum circling period toward flyable circling periods of 2-3
seconds. However, adding ballast increases stall speed and the
difficulty of landing without damage. The compressibility of air
and the decreasing optimum circling period with fast speeds
suggest that record glider speeds will probably not increase
as fast as they have during the last few years and will probably
level out below a speed of 600 mph.
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Author Posting. © B2Streamlines.com, 2012. This article is posted here by permission of B2Streamlines.com for personal use, not for redistribution. The definitive version was published in R/C Soaring Digest 29, no. 4 (2012): 36-49.
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R/C Soaring Digest 29, no. 4 (2012): 36-49