FairIP index

Origins & Dynamics
of KitePlanes & Tethered Flying-Wings

High-performance AWE Kiteplanes of varied design are envisioned by TU Delft, Joby Energy, Makani Power, & others. A KitePlane is a fixed/rigid-wing aircraft of conventional configuration designed to operate on a tether. A flying wing is an airplane-as-pure-wing that trades control and stability for maximal lift over drag. A tethered flying-wing will likely be the ultimate kiteplane when avionic control is perfected.

The earliest known kiteplanes are a handful of drawings and surviving examples of large Maori kites with superb high-aspect ratio wings. These spectacular high-speed fliers' tendency-to-crash was used for divination. Legend relates that spears were affixed to giant versions at public ceremonies, and  it was divine judgment who got impaled.

The modern kiteplane dates to almost a century ago when airplanes and gliders began to be towed aloft to ferry or launch. The tethered flight modes attracted less attention being secondary to modes like soaring. Far from the Kiting Dark Age some commentators have painted, this early period fully explored kiteplane performance, from very hot flying wing gliders up to the jumbo scale of the Gigant cargo glider.

Kiteplanes where found workable but dangerous when control forces were overwhelmed, a condition called Lock-Out. The forces on a surging kiteplane easily pulled wings off or parted the tether in many accidents. Sport gliding still generally employs tethered launch. Great care is required to launch safely. Pilots depend on reliable quick-release to allow safe landing in glider mode. Banner towing is tether-intensive aviation. Similarly model aeronautics uses tethered launch by high-speed winch or bungee. A common glitch is to get stuck on the primitive launch hook. One soon learns the difficulties of safely landing a hot glider while still on a tether.

My direct experience with kiteplane dynamics began with being towed aloft in a glider at an early age. I was exposed to many aviation kiteplane niche applications, like the banner towing business. Later I developed dozens of small tethered hot flying-wings in the 80s & 90s to demonstrate aeronautic principles at schools and science centers. I met and began to work with the amazing Brooks Coleman (ZapKites) at this time. Since childhood he had made his own flying-wing control line fliers.

We worked together on many cool mini-airshows, which even included early quad-rotor electric VTOL. The culmination of our kiteplane-mode aircraft was the flight of two 3m WS radio controlled aircraft over downtown Austin, funded by the city's cultural arts program. Model aviation guru, George Parks, was a key mentor. He taught us many things, like mixed turns using elevons alone. Many of the tethered flying-wing variants we flew in the 80s are uncanny precursors to Makani's kiteplane.

In our current AWE circle the leading kiteplane guru is aeronautical engineer Dale Kramer, a soaring champ and record-holder who intends to demonstrate Free-Flight soon with a tethered high-performance glider/soft-kite combo. Countless aviators and designers have extensive experience with kiteplane dynamics. You just have to know where to look to find vast prior art. Kiteplane-based AWECS R & D can tap into this talent pool to progress more surely and rapidly.

A likely key to perfected kiteplanes will be a variable tow-point. Both "tow-high" and "tow-low" modes are desirable in some apps; and  side towing is possibly useful. Combinations of moving the tow point along tracks and dynamic bridles could serve. The ability to release or pickup a tether, with unencumbered take-off and landing, is desirable. A major failure mode to worry about is fouling a kiteplane-mounted flygen turbine with its tether. Shrouding may be required.

FairIP/CoopIP                                   ~Dave Santos                                      May 27, 2010        M1570

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