Towards Tomorrow: Transforming the General Aviation Aircraft

In the mid-1970s, coincident with the beginning of the fuel and litiga­tion crises that would nearly destroy GA, production of homebuilt and kit-built aircraft greatly accelerated, reflecting the maturity of light air­craft design technology, the widespread availability of quality engineer­ing and technical education, and the frustration of would-be aircraft owners with rising aircraft prices. Indeed, by the early 1990s, kit sales would outnumber sales of production GA aircraft by more than four to one.[869] Today, in a far-different post-GARA era, kit sales remain strong. As well, new manufacturers appeared, some wedded to particular ideas or concepts, but many also showing a broader (and thus generally more successful) approach to light aircraft design.

Exemplifying this resurgence of individual creativity and insight was Burt Rutan of Mojave, CA. An accomplished engineer and flight – tester, Rutan designed a small two-seat canard light aircraft, the VariEze, powered by a 100-hp Continental engine. Futuristic in look, the VariEze embodied very advanced thinking, including a GA(W)-1 wing section and Whitcomb winglets. The implications of applying the configuration to other civil and military aircraft of far greater performance were obvious, and NASA studied his work both in the tunnel and via flight tests of the VariEze itself.[870] Rutan’s influence upon advanced general aviation air­craft thinking was immediate. Beech adopted a canard configuration for a proposed King Air replacement, the Starship, and Rutan built a subscale demonstrator of the aircraft.[871] Rutan subsequently expanded his range of work, becoming a noted designer of remarkable flying machines capable of performance—such as flying nonstop around the world or rocketing into the upper atmosphere—many would have held impossible to attain.

NASA followed Rutan’s work with interest, for the canard config­uration was one that had great applicability across the range of air­craft design, from light aircraft to supersonic military and civil designs. Langley tunnel tests in 1984 confirmed that with a forward center of gravity location, the canard configuration was extremely stall-resistant. Conversely, at an aft center of gravity location, and with high power, the canard had reduced longitudinal stability and a tendency to enter a high – angle-attack, deep-stall trim condition.[872] NASA researchers undertook a second series of tests, comparing the canard with other wing planforms including closely coupled dual wings, swept forward-swept rearward wings, joined wings, and conventional wing-tail configurations, evaluat­ing their application to a hypothetical 350-mph, 1,500-mile-range 6- or 12-passenger aircraft operating at 30,000 to 40,000 feet. In these tests, the dual wing configuration prevailed, due to greater structural weight efficiencies than other approaches.[873]

Seeking optimal structural efficiency has always been an important aspect of aircraft design, and the balance between configuration choice and structural design is a fine one. The advent of composite structures enabled a revolution in structural and aerodynamic design fully as sig­nificant as that at the time of the transformation of the airplane from wood to metal. As designers then had initially simply replaced wooden components with metal ones, so, too, in the earliest stage of the com­posite revolution, designers had initially simply replaced metal com­ponents with composite ones. In many of their own GA proposals and studies, NASA researchers repeatedly stressed the importance of getting away from such a "metal replacement” approach and, instead, adopt­ing composite structures for their own inherent merit.[874]

The blend of research strains coming from NASA’s diverse work in structures, propulsion, controls, and aerodynamics, joined to the cre­ative impact of outside sources in industry and academia—not least of which were student study projects, many reflecting an insight and expertise belying the relative inexperience of their creators—informed NASA’s next steps beyond AGATE. Student design competitions offered a valuable means of both "growing” a knowledgeable future aerospace workforce and seeking fresh approaches and insight. Beginning in 1994, NASA joined with the FAA and the Air Force Research Laboratory to sponsor a yearly National General Aviation Design Competition estab­lishing design baselines for single-pilot, 2- to 6-passenger vehicles, tur­bine or piston-powered, capable of 150 to 400 knots airspeed, and with a range of 800 to 1,000 miles. The Virginia Space Grant Consortium at Old Dominion University Peninsula Center, near Langley Research Center, coordinated the competition. Competing teams had to address "design challenges” in such technical areas as integrated cockpit sys­tems; propulsion, noise, and emissions; integrated design and manu­facturing; aerodynamics; operating infrastructure; and unconventional designs (such as roadable aircraft).[875] In cascading fashion, other oppor­tunities existed for teams to take their designs to ever-more-advanced levels, even, ultimately, to building and test-flying them. Through these competitions, study teams explored integrating such diverse technical elements as advanced fiber optic flight control systems, laminar flow design, swept-forward wings, HITS cockpit technology, coupled with advanced Heads-up Displays (HUD) and sidestick flight control, and advanced composite materials to achieve increased efficiencies in per­formance and economic advantage over existing designs.[876]

Succeeding AGATE was SATS—the NASA Small Aircraft Transportation System Project. SATS (another Holmes initiative) sought to take the integrated products of this diverse research and form from it a distributed public airport network, with small aircraft flying on demand as users saw fit, thereby taking advantage of the ramp space capacity at over 5,000 public airports located around the country.[877] SATS would benefit as well by a Glenn Research Center initiative, the GAP (General Aviation Propulsion) program, seeking new propulsive effi­ciencies beyond those already obtained by previous NASA research.[878] In 2005, SATS concluded with a 3-day "Transformation of Air Travel” held at Danville Airport, VA, showcasing new aviation technologies with six air­craft equipped with advanced cockpit displays enabling them to operate from airports lacking radar or air traffic control services. Complementing SATS and GAP was PAV—a Langley initiative for Personal Air Vehicles, a reincarnation of an old dream of flight dating to the small ultralight aircraft and airships found at the dawn of flight, such as Alberto Santos – Dumont’s little one-person dirigibles and his Demoiselle light aircraft. Like many such studies through the years, PAV studies in the 2002-2005 period generated many innovative and imaginative concepts, but the

Agency did not support such studies afterwards, turning instead towards good stewardship and environmental responsibility, seeking to reduce emissions, noise, and improve economic efficiencies by reducing air­port delays and fuel consumption. These are not innocuous challenges: in 2005, airspace system capacity limitations generated fully $5.9 bil­lion in economic impact through airline delays, and the next year, fuel consumption constituted a full 26 percent of airline operating costs.[879]

The history of the NACA-NASA support of General Aviation is one of mutual endeavor and benefit. Examining that history reveals a surpris­ing interdependency between the technologies of air transport, military, and general aviation. Developments such as the supercritical wing, elec­tronic flight controls, turbofan propulsion, composite structures, syn­thetic vision systems, and heads-up displays that were first exploited for one have migrated and diffused more broadly across the entire aeronau­tical field. Once again, the lesson is clear: the many streams of NASA research form a rich and broad confluence that nourishes and invigorates the entire American aeronautical enterprise, ever renewing our nature as an aerospace nation.