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High-Performance Glider Kiteplanes

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 operational advantage.

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 limitations).

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.

SEE PHOTO: http://www.scaled.com/images/uploads/projects/raptor.jpg

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 traffic.
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.

FairIP/CoopIP                       ~Dave Santos             August 9, 2010        M1952

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