Aviation technology reuse is an essential R & D
strategy for AWE. One of the best concepts in this regard is the
glider-kiteplane based on conventional high-performance composite-built
gliders. There is no flygen or conductive cable to haul around the sky.
Towing aloft & operation on a tether is a standard glider method,
boosting confidence. A range of surface work can be done, from reelgen
pumping to electric vehicles. Unpowered kiteplanes can be flown at will
by towing/winching about, so motor/gen kiteplanes have no particular
Early AWE glider & motor/gen kiteplane take-off & landing methods copy
classic gliding at the same scales. Common practice is to release tether
& land conventionally. A hot glider requires a fairly long airstrip, not
because its roll-out is long, but especially to prevent undershoot. If a
long runway is not a satisfying solution, some proposed ideas are less
promising. Landing a fast glider kiteplane in a cradle is like hanging
up a phone by throwing it across the room. Landing nets are a grotesque
large-scale solution, but these are desperate times.
Glider accidents mostly happen during short periods of take-off, towing
(tether-mode), & especially landing. These are complex flight states. A
recurring glider failure-mode is to foul the landing wheel with the
tether when both crowd near CG. Many safety rules read like this-
"If you lose sight of your tow-plane, RELEASE IMMEDIATELY!"
Low altitude aerobatic flight is the most dangerous flight regime of
all, powered or unpowered. High stall speed & tethered flight compound
risk. The AWE kite-loop pattern is especially dicey. As a hot aircraft
surges against its tether at the bottom of the low-altitude loop, the
load-factor spike can easily fold the wings. Loaded up by gravity,
centrifugal-force, & tether force, the margin of safety against stall
can suddenly disappear, especially in wind shear; the airplane, with no
altitude to recover, falls out of the sky.
High performance gliding is a dangerous branch of aviation even without
AWE capability. Accident studies suggest that glidertech-based AWE is a
risky proposition for the fancy airframe/avionics capital-asset (the
flying part, by itself, will cost about 3$ per watt of rated capacity).
Composite airframes in mishaps crack like eggs, where all the Kings men
can't easily put it right.
If autonomous glider kite-planes merely rival current human glider-pilot
reliability, they will tend to experience a major mishap within a few
months of intense (24-7) operation. High-end autonomous UAVs are
historically about ten percent as reliable as human piloting, esp. in
demanding maneuvers, but slowly getting better. Its currently
respectable, but poorly acceptable, if a hot glider-kiteplane
engineering prototype can currently survive a week or two of intense
operation. The half-time of a state-of-the-art flygen-kiteplane may be
considerably less, given far greater weight & complexity.
The crude state of high-performance aerobatic flight-automation is a
persistent problem. Low-complexity expedients are in order. A
glider-kiteplane can be reliably raised & lowered by "skycrane". The
cheapest most general method is to first launch a pilot-lifter kite or
array, then the kiteplane is raised up by a pulley (& can use its
halyard as the reelgen tether). The kiteplane held above the crash-zone
can go nuts, especially as the pilot-lifter absorbs destructive surge
energy. Flying from a "short" tether well aloft may also prevent
exceeding Vne, Vra, VA, & VFC ("V speeds" are aircraft operating
The fully autonomous AWE glider-kiteplane concept is exciting & will
succeed. Initially it will be an expensive techno-fashionista way to
make electricity. Small (3mWS/5kw) cheap models could become popular
soonest, as they are within the aero-modeler's scale. Eventual
utility-scale glider-kiteplanes could someday dominate AWE.
A great glider-god thread, esp. read the middle pages...
Devices for avoiding VNE? - Page 3 - AviationBanter
Another method to reduce fight automation "program risk"-
The Raptor is a high-altitude, long endurance UAV by Scaled Composites.
The prototype was flown in a manned configuration to allow testing of
changes to the flight control system with minimal risk to the airframe.
The safety pilot was provided manual controls which can override control
system commands. This somewhat novel approach allowed rapid development
of the vehicle handling qualities and evaluation of the flight controls
at low cost and program risk.
This will not do for aerobatics on a tether at low altitude.
DZ Note (see detailed prior post)
Parachuting Drop-Zones (DZ) offer potential airspace synergy with early
AWE R & D.
The airspace is already integrated as a no-fly zone for general air
The sport is limited to part-time mainly weekend activity.
Skydiving ram-air parafoils are close relatives to kites most used for
AWE, so an operational overlap of key people & skills is possible
(rigging & piloting).
AWE Arrays can support base jumping as an adjunct application.
Look for a DZ with low or declining use, hampered by high winds, with
good grid access. This might be the research haven the industry needs.
~Dave Santos August
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