Leonard Niemi's Sisu is one of the most successful American competition sailplane ever flown. John Ryan in 1962, Dean Svec in 1965, and A. J. Smith in 1967, all won the United States National Soaring Championships flying a Sisu ('see-soo'). In 1967, Bill Ivans (his Schempp-Hirth Nimbus II in NASM collection) set a national speed record flying a Sisu 1A at El Mirage, California, by skimming across the desert at 135 kph (84 mph) over a 100-kilometer (62-mile) triangular course.

Alvin H. Parker took off from his hometown, Odessa, Texas, at the controls of the National Air and Space Museum's Sisu 1A and flew 1,042 km (647 miles) on July 31, 1964. This flight also shattered a symbolic and psychological barrier that had defeated sailplane pilots around the world for years. Joseph Lincoln called the 1,000-km milestone "for a good many years …the soaring pilot's four-minute mile on both sides of the Atlantic" in his soaring anthology, "On Quiet Wings," published in 1972.

Leonard Niemi's Sisu is one of the most successful American competition sailplane ever flown. John Ryan in 1962, Dean Svec in 1965, and A. J. Smith in 1967, all won the United States National Soaring Championships flying a Sisu (see-soo). In 1967, Bill Ivans (his Schempp-Hirth Nimbus II in NASM collection) set a national speed record flying a Sisu 1A at El Mirage, California, by skimming across the desert at 135 kph (84 mph) over a 100-kilometer (62-mile) triangular course.

Alvin H. Parker flew from his hometown, Odessa, Texas, at the controls of the National Air and Space Museum's Sisu 1A (serial number 102 registered N1100Z) and set three world records: a declared-goal distance record flight of 784 km (487 miles) set in 1963 that Parker himself smashed in 1969 when he again reached his declared goal 931 km (578 miles) from Odessa; and a free distance record of 1,042 km (647 miles) set July 31, 1964. This flight also shattered a symbolic and psychological barrier that had defeated pilots around the world for years. Danish pilot Harald Jensen said in 1959, "we already have a 1,000 kilometer [soaring distance] club. Now all we need is some members." Joseph Lincoln called this milestone "for a good many years …the soaring pilot's four-minute mile on both sides of the Atlantic" in his soaring anthology, "On Quiet Wings," published in 1972.

Inspiration to design and build the Sisu dates to 1951 when Richard Johnson flew the RJ-5 sailplane 881 km (547 miles). This world distance record generated publicity that broadcast the superiority of laminar-flow airfoils similar to those first employed on the World War II P-51 Mustang (see NASM collection) but with one crucial difference. Where the Mustang airfoil performed best at high speeds, the RJ-5 wing used a laminar-flow profile tailored specifically to operate most efficiently at low speeds. Harlan Ross had built this wing and Richard Johnson refined it, under guidance from Dr. August Raspet at the Mississippi State University. The success of the RJ-5 marked the beginning of a fundamental shift in the design philosophy of high-performance sailplanes.

A year after Johnson's flight in the RJ-5, Leonard A. Niemi started developing the Sisu 1. Neimi had spent four years learning the aircraft mechanics trade while attending a technical high school in Buffalo, New York, followed by another 6 years working for the Bell Aircraft Corporation and the Curtiss-Wright Corporation, Airplane Division. After a stint in the U. S. Army, Niemi attended the University of Michigan and earned a B. S. in Aeronautical Engineering. He also spent four years performing stress analysis at Bell Helicopter. It is not clear why Niemi chose to name his design the Sisu but it is a popular Finnish word with no precise English equivalent. The term describes a fundamental characteristic of native Finns, their strength, perseverance, and backbone. Aini Rajanen, wrote in "Of Finnish Ways" (Barnes & Noble Books: New York, 1984) that Sisu is "a word that can't be [directly] translated. … Sisu refers not to the courage of optimism, but to a concept of life that says, 'I may not win, but I will give up my life gladly for what I believe.' … Sisu is the only word for the Finns' strongest national characteristic."

Niemi's Sisu flew on laminar-flow wings and he designed it for private pilots to construct at home. The first flight in 1958 was so successful that Neimi decided not to sell plans or kits for the homebuilders but to modify the design for production as a finished, ready-to-fly sailplane. He changed the designation to Sisu 1A and lightened the wing structure, added vents to the dive brakes, and introduced slotted flaps to expand the low-speed performance envelope even further. Niemi also increased slightly the area of the vee-tail, elevator/rudder to compensate for increased pitch force from the new slotted flaps, and increased the deflection range of the rudder too. Niemi also introduced the 'plate-stringer' wing structure on the inboard wing sections to reduce weight without compromising the rigidity of the smooth, laminar-flow surface contours. The designer also increased the size of the dive brakes, and lengthened and widened the cockpit to hold bigger pilots.

To manufacture the Sisu, Nemi set up the Arlington Aircraft Company in the city of the same name located about halfway between Dallas and Ft. Worth, Texas. Construction began on the first four sailplanes in 1960. Pilots quickly snapped up these aircraft but production costs surpassed profits and Neimi had to sell the project to Philip J. Baugh, a retired Air Force pilot and soaring enthusiast from Charlotte, North Carolina. Baugh and Niemi moved the factory to Greenville, South Carolina, in 1963 and the firm became the Sisu Division of the Astro Corporation. Clifton McClure III managed Astro and he and Baugh wisely decided to keep Neimi on as project engineer. McClure was governor of the South Carolina division of the Soaring Society of America. He intended to carry through with Niemi's original plan for the Sisu and obtain Federal Aviation Administration type certification for the design but the daunting costs of such work forced him to abandon the effort. Baugh generously underwrote production of six more Sisus but profits never covered expenditures and metal smiths and technicians finished the tenth and last Sisu 1A in 1965.

Niemi paid careful attention to eliminating parasite drag when he conceived the Sisu. He opted for a vee-tail, retractable tow hook and main wheel, and swept-forward wings shaped to a 653418 laminar-flow airfoil. The wingtips leaned ahead of the inner wing sections to insure that the ailerons, hinged just inboard of each wingtip, continued to bite the air and provide the pilot control during a stall. Washout, twisting the wingtips to reduce slightly their angle of attack and lower their stall speed, is a much more common technique but Neimi eschewed it. Twisting the wings, however slightly, would have generated unacceptable drag. The wing surfaces had to be extremely smooth to maintain laminar-flow over a broad speed range and the designer took great care in this area. Neimi used an aluminum plate stringer technique covered with relatively thick, aluminum wing skins to prevent even the slightest buckle. Before applying finish paint, craftsmen checked the wing closely for minute imperfections, covered these depressions with filler paste, and sanded the patch smooth.

This obsession with a smooth finish enthralled one soaring pilot to remark that at "first glance one may wonder and doubt the claimed [Sisu] performance figures. The tiny wings, the delicate fuselage keeping doubt alive, till one moves close and runs fingers over the surfaces of wings and fuselage, realizing at once that a perfectionist was at work." Pilots also rated the cockpit roomy and comfortable, very important attributes in high-performance sailplanes that are easily capable of flying from early morning to dusk nonstop. They said that visibility was outstanding directly in front of the pilot.

Neimi took the second Sisu built (now at NASM) into the air for the first flight on May 1, 1963. Less than two weeks later, John J. Randall of Coral Gables, Florida, bought the sailplane on May 13. After several flights, Randall lent the airplane to Dr. Cornish at the Mississippi State University in Starkville. Cornish teamed with test pilot Sean Roberts and the two engineers conducted flight tests, and measured and analyzed the Sisu's flight performance at a gross weight of 329 kg (730 lb). The research yielded these numbers:

Minimum Sinking Speed .7 m (2.2 ft) per second at 88 kph (55 mph)

Maximum Glide Ratio 37:1 at 92 kph (57 mph)

Stall Speed, Flaps Up 79 kph (49 mph)

Stall Speed, Flaps 20 Degrees Down 60 kph (37 mph)

Maximum Airframe Load Factors + 6 G, - 4.6 G

Maximum Design Airspeeds:

Never-Exceed 277 kph (172 mph)

Rough-Air Cruise 192 kph (119 mph)

Maneuver 192 kph (119 mph)

Flaps-Down and Auto/Winch Tow 151 kph (94 mph)

Cornish and Roberts believed that additional work on the sailplane could boost performance. The men further refined the "surface contours" on this Sisu but specific details about this treatment remain hidden. On July 21, 1963, Alvin H. Parker bought Randall's Sisu for $9,700. Parker was 45 years old and a successful rancher and financier. The father of three sons, he was also active in the oil business and operated a soaring flight school and a Schweizer sailplane dealership in Odessa, Texas.

Parker had spent his entire life in West Texas, except for a stint in the U. S. Army during World War II when he saw combat as a tanker in the First Armored Division fighting in North Africa and Italy. Parker had flown about 5,000 hours in several different aircraft by the time he was ready to attempt the record flight. A year and ten days after he bought the Sisu 1A, Parker took off from Ector County Airport north of Odessa and released from the tow plane just before 10 am. He found weak lift over the airport and glided north. "I gradually worked north along the Andrews Highway. Then to the west of the town of Andrews and up to about 2,800 feet [851 m] northwest of the town. From there, I could look down on the family ranch land where I spent so many hours as a cow-puncher during my youth. If someone had told me that I would someday pilot a motorless aircraft across this area, I would have told him he was 'loco.'"

By 2 p.m., Parker had descended to a few hundred feet above ground over northeastern New Mexico, still spiraling in search of lift, but now eye-level with the canyon walls that clutch the banks of the Cimarron River. "The quiet, desperate scratching techniques of the recent National Contest at McCook [in Nebraka, site of the 1964 national soaring contest] enabled me to get up and away [from the canyon]. Placing thirty-eighth in a National Contest [McCook] has its advantages - sometimes." Parker was referring to his poor showing at that meet held just a few weeks before. He had finished nearly last out of forty pilots but the experience taught him much about the hard work required to fly the Sisu in the weakest lift. On several occasions, he put these lessons to good use during the record flight.

Upon touching down at Kimball, Nebraska, about twenty minutes past 8 pm, Parker "struggled out of the Sisu after those ten and one-half hours and looked around for landing witnesses. There was no one in sight - just the [airport] rotating beacon, the runway lights, and I." This quiet finish to a spectacular flight did not prepare Parker for the accolades that poured in from around the world. "Soaring" magazine called it the "Soaring Story of the Year - U. S. First to Break 1000 Kilometers." Parker claimed that "the performance of the Sisu 1A was astonishing, actually beyond imagination. It would gain back, in one 360 degree [sic] chandelle, the altitude lost [by flying] at 120 mph ind[icated, or 193 kph] between cu's [cumulus clouds] about 20 miles [32 km] apart."

On July 24, 1967, Parker's son Stephen, then 14 years old, qualified to fly the Sisu 1A. He made 32 flights in this aircraft including a 452-km (281-mile) flight from Odessa to Wheeler, Texas. On August 3, 1967, Stephen flew 555 kms (345 miles) from Odessa to Farley, New Mexico. This flight earned him the coveted Diamond C soaring badge for distance, altitude gain, and endurance flying. Stephen was the youngest American to earn the badge by more than two years. The Parker men finished 194 flights in their Sisu and ten are regarded as notable cross-country flights that spanned an average of 650 km (404 miles).

In August 1967, Parker sold the Sisu to Mr. Philip J. Baugh and then purchased another so that Baugh could donate the record 1000-km ship to the Smithsonian Institution. The men consummated this deal over the winter of 1966. On July 12, at a ceremony held atop Harris Hill close to Elmira, New York, the birthplace of American competitive soaring, Baugh formally presented the Sisu 1A, registered N1100Z, to the Smithsonian. The airplane was still equipped with the same instruments, radio, oxygen system, and other equipment that it carried during the 1000-km (622-mile) flight in 1964.

The end of the nineteen-sixties also marked an end to the Sisu's dominant position in world competition glider flying. "As one decade ends and another begins," quipped "Soaring," the all-metal Sisu finds itself fighting on against mounting odds-a tin soldier in an increasingly hostile world of fiberglass, where the prevailing language is German…" With sustained and ample support from the West German government, researchers and technicians at major universities had begun to design and build motorless aircraft from fiberglass. These sailplanes claimed the lead in competition soaring by 1970 and as the new millennium dawned, skilled pilots soaring these aircraft remain the best in the world.