SparrowHawk all-carbon composite sailplane
The first-ever all-carbon composite sailplane yields unprecedented maneuverability and top performance.
By Karen Fisher Mason, Contributing Writer | July 2004
Sailplaning - unpowered flight - is an expensive pastime. There are several sailplane categories: Open, 15-meter, Standard and Ultralight. Large, high-performance Open-class sailplanes sport wingspans from 18m/59 ft to 30.5m/100 ft and a price of $100,000 to $200,000 (USD) or more. Smaller, more moderately priced sailplanes compete in the 15-meter class, limited to 15m/49-ft wingspans but with no other design restrictions. The Standard class, also limited to 15m wingspans, uses no performance-enhancing wing flaps. But the final category of sailplane, the Ultralight, is restricted not by wingspan, but by empty weight - to a maximum of 70 kg/155 lb. Ultralights are often dubbed "floaters" for their relatively slow speed and poor cross-country (i.e., straight-flight) performance. Standard-class sailplanes, by comparison, offer much better cross-country performance, but cost significantly more than Ultralight planes. They also may not maneuver as well in the air and are harder to manage on the ground because of both size and weight. Bridging these two classes, a new lightweight sailplane, the SparrowHawk from Windward Performance LLC (Bend, Ore., U.S.A.), is designed to meet Ultralight weight requirements and reduce sailplane cost into the bargain, while offering performance equivalent to or better than Standard-class sailplanes. The key to both performance and affordability, surprisingly, is carbon fiber.
Source: Windward Performance
The SparrowHawk's total empty weight of 70 kg/155 lb is slightly more than the weight of a single wing on comparably performing sailplanes.
For more than four decades, the vast majority of sailplanes (also called gliders) across all categories have been fabricated from a wet layup of fiberglass/epoxy. The SparrowHawk is the first sailplane with all-carbon composite wings and fuselage. It was created by general aviation veteran Greg Cole. Previously chief engineer of research and development at The Lancair Company Co., Cole helped design that company's Columbia 300 aircraft and the wing for the Legacy 2000. But his passion for soaring prompted Cole's formation, five years ago, of Windward Performance to design and build his own sailplane. He still maintains a business relationship with Lancair: all of the SparrowHawk's composite components are fabricated by Lancair employees in the company's Bend airport facility. Windward's team performs bonding, assembles the finished aircraft, and conducts testing operations in a nearby hangar.
The carbon structure's performance advantages over wet layup fiberglass were predictable, although achieving 15-meter performance with an Ultralight is notable no matter the material. But the real surprise was its affordability. With a base price of $33,950 (USD), the SparrowHawk is priced well under new 15-meter sailplanes, which cost from $50,000 to $70,000. Cole attributes both performance and affordability to the design freedom, design efficiency and fabrication streamlining that resulted from the use of carbon fiber.
"Smaller, lighter, smaller, lighter"
Looking first at conventional materials, including aluminum and fiberglass, Cole recognized that he could build a lighter sailplane with more advanced materials; and these more advanced materials afforded the craft aerodynamic advantages that allowed him to consider a shorter wingspan, a thinner wing profile and a significant overall weight reduction. "As the design went down this smaller/lighter spiral," he recalls, "it picked up all these benefits - handleability, fewer materials so less cost, the extra option of a parachute recovery system, and so on."
Source: Windward Performance
At 155 lb, the SparrowHawk (unpainted version at right) earned classification by the Federal Aviation Admin. (FAA) as an Ultralight aircraft, because its entire structure consists of carbon/epoxy composites.
The most visible result of the all-carbon design is the 11m/36-ft wingspan, which appears stunted since the SparrowHawk's length of 6.3 m/20.6 ft is comparable to sailplanes with 15m wingspans. Under conventional thinking, Cole points out, gliders are being designed with longer wings to decrease induced drag. But longer wings demand more material for strength and stiffness, so planform and airfoil design are restricted by material and structural requirements. In the SparrowHawk, however, wing airfoils could be aerodynamically customized rather than structurally determined because "I don't have to make the wings overly thick to make them stiff enough," Cole explains. The wing chord (width from leading to trailing edge) is 20 percent smaller than the typical 15m wing chord. "The wings utilize five airfoils tailored to the local span requirements, minimum drag or maximum lift with soft stall at the correct Reynolds number."
The SparrowHawk's flying weight loads the wings at only 10 lb/ft of wingspan compared to more than 16 lb/ft in a typical 15-meter craft, making possible a smaller wetted area (the surface area of the plane that directly meets the air mass), which in turn decreases drag. Thus, it achieves the cross-country performance of many standard 15-meter sailplanes. But it exceeds their performance in climbing because the short, tailored wingspan and light weight of the SparrowHawk can exploit even the weak "microlift" of small thermals (columns of warm, rising air that sailplanes most commonly use to climb). The SparrowHawk's tight turning radius and good maneuverability increase the sailplane's ability to exploit the thermal core, resulting in better lift and longer "runs" between thermals. Overall, the plane is more immediately responsive to the pilot, which, Cole points out, makes it more enjoyable to fly. "You fly sailplanes because it's challenging mentally and it's fun physically," he says. "If the plane is responsive, it tightens up the loop of your input and the plane's response."
"A light, responsive sailplane like the SparrowHawk can effectively use scraps of lift that often punctuate difficult soaring environments," comments Gary Osoba, who piloted this glider to three world records, including two speed records and a triangular distance record.
