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You have heard of the pumped
laser and maser. Here is a new type of pumped energy system: the vaser. 'Laser'
is an acronym for 'light amplification by
stimulated emission of radiation,'
and 'maser' is an acronym for 'microwave amplification
by stimulated emission of radiation.'
I coined the term 'vaser' after reading an article in the June 2014 edition of
Model Aviation about
a relatively new form of radio controlled (R/C) model sailplane sport - dynamic
soaring - that, using a specially developed technique to exploit geography and prevailing
winds, produces aircraft speeds of more than 400 miles per hour. Per my definition,
'vaser' is an acronym for 'velocity amplification
by stimulated enhancement of energy'
(OK, it's a lame attempt at being clever).
It occurred to me that the mechanism used
to add energy to electrons in atoms is fundamentally the same as that used to add
energy to the sailplane in dynamic soaring. In pumped laser and maser systems, an
external power source (stimulus) is used to cyclically add energy to the electrons
of certain elemental atoms by forcing them into higher level orbitals. Since the
electrons naturally want to reside in their ground state, they return there once
the stimulus is removed. The difference in energy is emitted as electromagnetic
radiation at a wavelength concordant with the Planck equation,
λ = (c ·
h) / (E2 - E1), where c is the speed of light,
Planck's constant, and
E2 - E1
is the energy level difference. A diagram of the laser pumping mechanism is provided
With dynamic soaring, the sailplane is analogous to the electron, altitude is
analogous to orbital energy levels, and orographic lift is analogous to the external
pumping energy. Orographic lift is generated when the horizontal component of an
air current (wind) is forced to vertical in the presence of an upward sloping surface
such as the windward face of a slope (see diagram below). To begin the dynamic soaring
cycle, the model sailplane is launched at the top of the ridge and it is lifted
by the high speed upward moving air, thereby increasing its potential energy by
virtue of an altitude gain. At some point on the leeward (downwind) side of the
slope, lift is significantly reduced and the model is placed in a dive, exchanging
potential energy for kinetic energy (speed). According to a location determined
by the experienced pilot, a sharp is executed at the bottom of the loop and the
sailplane zooms back up, loosing kinetic energy (and therefore speed) in the process,
but regaining some potential energy. Aerodynamic drag and heating losses expend
some of the total system energy, so without an external energy source to replenish
the lost energy, the model would not be able to reach its beginning altitude; this
is analogous to the emitted radiation. However, the orographic lift impinges upon
the sailplane when it breaches the top of the ridge and pumps energy back into the
system (the model). Since the sailplane, if piloted skillfully, was traveling faster
at the breach point during this cycle than during the previous cycle, it reaches
a higher altitude this time, resulting in an even greater potential energy. The
dive/climb cycle is repeated until the model reaches its maximum speed. Nifty, n'est-ce
the albatross figured out dynamic soaring a long time ago. IEEE's Spectrum
magazine published a story, "The
Nearly Effortless Flight of the Albatross," and a video (see below) last year,
but they did not point out the pumped energy analogy.
What ultimately limits the speed the sailplane can achieve? The airframe is a
major factor since its aerodynamic drag saps energy from the pumping system. Assume
for the sake of argument that the pilot is perfect, never making a mistake and flying
the course flawlessly. Frontal cross-sectional area as well as presented cross-sectional
area during turns slows the model down via resistance to the wind. At such high
speeds and G-forces, flexing of all components occurs, thereby increasing cross-sectional
area. Another factor is the robustness of the airframe regarding stress loading
from all three axes. Finally, the geography of the landscape and wind characteristics
limit the maximum height and thereby maximum potential energy for a given location.
The vertical component of orographic lift diminishes with height above the ridge,
and at some point cannot lift the sailplane any higher.
The speed of sound at sea level is 761 miles
per hour (mph), so Spencer Lisenby's record speed (as of this writing) of 468 mph
is Mach 0.61! A video of his record flight is posted below. The airframe must be
incredibly strong to endure such dynamic forces. In fact, the
Kinetic 100 DP used is a hand-made
sailplane made for speed. Carbon fiber construction comprises most of the airframe
components in order to achieve the highest strength-to-weight ratio possible. It
has a 100" wingspan and weighs about 250 ounces ready to fly, including the airborne
radio control system. Ultra high speed /high torque servos as used on all control
surfaces, and cost around $60-$80 each. You must get placed on a waiting list to
own a Kinetic 100 DP, and expect
to shell out close to $2,000 for it.
Spencer Lisenby's World Record 468 mph Kinetic
100 DP Flight Video
Albatross Dynamic Soaring Video from IEEE
Posted October 14, 2014
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