SCHAPEL SA-882

(The following was extracted from the April 1985 issue of Ultralight Aircraft, pp. 22-25.  It provides a history of what the aircraft was originally destined to be, although many perceived it to be something for the general aviation market.  Someday perhaps, Rod Schapel will tell us the rest of the story behind this aircraft.)      “Rod Schapel doesn’t have much confidence in the structural integrity of most of the ultralight aircraft on the market today (1985).  As a maverick mechanical and aerodynamic engineer with year of practical experience in designing an building everything from planes to sailboats (he designed the original concept for the revolutionary LearFan business aircraft and worked alongside the late William Lear on several other projects), Schapel wanted to build an ultralight of unquestionable structural integrity.  With a market already overcrowded and undersold, why bother?  ‘I’m always interested in a new challenge,’ he says.      “The biggest challenge was how to fit into that constricting aerodynamic ‘box’ defined by FAR Part 103.  Building a wing big enough to afford stall speed below 27 mph has traditionally meant cable bracing or other backdoor methods to lend proper structural credentials, since the added restriction of a 254-pound maximum weight put the double whammy on a more conventional approach to ultralight design.  Some designers, Schapel definitely among them, don’t believe that you can build a strong enough airplane at that weight.  Many have tried, and achieved their goals.  But one man’s max is another’s mini.  Schapel felt that the terms ‘ultralight’ and ‘safe’ were still mutually exclusive.      “’It’s a simple problem, given the requirements to build a strong ultralight in that performance box, ‘ says Rod.  ‘A flying wing is a logical solution.’      “A properly designed flying wing is inherently more stable than any aircraft with a fuselage and tail.  The immediate benefit is in inherent resistance to stalls and spins, two perennial killers in conventional aircraft.  Hang gliders, which still bear a  media-bestowed, undeserved reputation as death machines, demonstrate daily from mountain tops around the world irrefutable proof of flying wing stability.      “Add to the stability factor an enduring affection for flying wing mystique, plus the potential for impressive structural integrity without fudging on the ultralight weight limits, and Schapel’s decision to built UltraWing is not hard to understand.      “Because production tooling to build a composite material aircraft is incredibly expensive, a proof of concept ship was the first order of business.  The proof of concept was to be a dramatically  nonultralight aircraft that would be constructed of hand layed up fiberglass in sufficient number of laminations and reinforcement to guarantee no structural problems whatsoever during the flight test program.  This naturally led to a larger powerplant; in test flying, altitude is king, and the altitude in Reno begins at 5000 feet.  The proof of concept aircraft was deliberately overbuilt and weighs 875 pounds.  To move around that much hard plastic, you need something like a thirsty 180 hp Mazda rotary engine and s St. Croix custom built ground adjustable three-blade Kevlar propeller.      “Once the flying parameters are tested, modified and understood, then recalculated to phase in with the ultralight ‘box’, Rod will return to the drawing board, retaining only the proven aerodynamic outer shell of the aircraft and completely design an ultralight production building technique, including spars, ribs, landing gear attach hard points, motor mounts, female molds, etc.  Literally, it is working from the outside in, almost like propping up a roof, then deciding how to most efficiently support and apportion the interior.      “The aircraft was constructed of PVC foam and unidirectional fiberglass supported by an epoxy matrix.  The fibers were oriented in different directions in different locations to optimize required strength and flexural qualities.  A .005 inch think layer of cloth was applied overall for abrasion resistance.      “The roomy, high-profile Plexiglas cockpit adds to the sensuous reptilian curve of the aircraft.  Rod’s approach to the control problems encountered when there is a tail with which to separate axis control is innovative; everything is in the trailing edge.      “Starting inboard, a clamshell like device is used to provide yawing action.  In effect, the trailing edge splits into two pieces that stick up and down into the airflow, producing drag on the left or right side of the vehicle.  Conceptually, the clamshell is a horizontal instead of a vertical rudder, identical in effect on the yaw axis as the ‘tip draggers’  on ultralights like the Falcon or Eagle.      “Pitch is controlled, just as in a tailed ship, with an elevator.  Just outboard of the ‘rudders,’ the left and right elevators move in unison up or down, essentially to deflect airflow and provide a moment arm working against the centers of pressure and lift.  Farthest from the pilot are the ailerons, which work just as they ought to.  ‘It really is a three-axis ship,’ says Rod, ‘and it works.’      “A primary appeal of the flying wing is the previously mentioned stability.  This is designed into the wing by a complex combination of such factors as sweep angle to elongate the pitching moments and center of gravity envelope front to back as much as possible; 9 ½ degrees per side of variable wingtip washout to provide stall resistance, dive recovery and enhance longitudinal stability; and properly calculated depth of wing section and airfoil shape; and trailing edge reflex.”      The article went on to talk about the problems of having a flying wing this efficient and keeping inside the speed ranges of Part 103 without seriously affecting the overall performance of the aircraft.  It is obvious that the project never made it to the point of producing an ultralight prototype.

...1/17/01......................................................