floating cube, The

Model Airplane News, Aug 2001 by Liotta, Lance

My highly maneuverable RC slow-flight model lacks most conventional aircraft elements. Aerodynamic lift, stability, turning and flight control are accomplished without any formal wings, rudder, tail, ailerons, or control surfaces. I borrowed elements from kites and helicopters to produce a new design that is simple and rugged. Over several years, I have conducted hundreds of flights with a series of experimental prototypes. It's an unusual aircraft in that it lacks a streamlined appearance, but the Floating Cube is remarkably agile in flight. It ascends at a steep angle and can virtually turn on its own axis to rapidly reverse direction.

The RC aircraft consists of a lifting body comprised of a series of lightweight planar or thin airfoil surfaces arranged in symmetrical configuration (diagonal cube or rhomboid) around a central cavity. Suspended within the cavity are a motor and propeller that can be rotated by a servo to change the angle of the thrust vector. The aircraft is essentially a diagonal box kite with a motor and a single prop suspended inside. With four lifting surfaces surrounding the propeller, a very high surface area to weight is achieved, yet the aircraft is very compact and crash resistant. Using only one propeller, with no blade pitch control and no control surfaces, controlled turning of the aircraft in a small radius at low speed can be achieved without significant induced banking or loss of altitude. The thrust direction is regulated by rotating the motor/prop thrust angle within the cavity of the lifting body.

The angle of the rotation plane for the prop is at an upward pitch to the horizontal, providing an upward thrust vector and a balancing force. This maintains longitudinal stability because the center of gravity (CG) is forward of the aerodynamic center or neutral point of lift. The upward-angle thrust vector counterbalances the nosedown imbalance of the CG being forward of the aerodynamic center. Increasing the power causes elevation of the flight path.

The model's compact size, light weight and resiliency are achieved by using internal tension and compression bracing and construction materials similar to those used for box kites. The lifting surfaces are all angled from the horizontal to achieve a large dihedral effect. Combined with a low CG (the battery is mounted in the lower apex), a high degree of lateral stability is achieved-even in mild, gusty winds. This design also generates a flat thin or thin symmetrical airfoil necessary for a tailless aircraft.

I experimented with a wide variety of shapes, power units and construction materials. Compared to a cylindrical design, I found that angled surfaces held under tension (the diagonal cube) were superior in strength, lift and lateral stability, and they weighed the least. Carbon-fiber wing spars and a pine central-mounting rod provided a light, strong structure, and Icarus ripstop polyester cloth used in the kites made by Daniel Prentice's Shanti Kite Co. was an ideal covering. In fact, one of the cube-shape kites sold by Shanti could be adapted nicely into the RC aircraft design. I've taken my patent-pending aircraft design to Prentice to commercialize a series of model aircraft products that apply kite technology to the world of RC slow flight.

Editor's note: a runner-up in the 4th Great RC Airplane Contest held by Model Airplane News, this unique model is the brainchild of Lance Liotta of Bethesda, MD. A video clip of the Floating Cube in flight is available at www.modelairplanenews.com. The Floating Cube will also be featured as the "Plan of the Month" in an upcoming issue of RC MicroFlight (www .rcmicroflight.com).