Nelson BB-1 Dragonfly

In 1945, William H. Bowlus and Ted Nelson formed the Nelson Aircraft Corporation to build a two-seat, motor glider version of the popular Bowlus BA-100 Baby Albatross. The designers nicknamed this design the Bumblebee but they sold the powered glider under the official moniker, Dragonfly. The men retained the basic Baby Albatross design but significantly widened the cockpit and added side-by-side seating and flight controls for each occupant. Other improvements included tricycle landing gear and a steerable nose landing gear, additional vertical fins mounted on the ends of the horizontal stabilizer, and a hinged canopy. A handle to pull-start the engine was also available inside the cockpit. The aft section of the fuselage pod on the Baby Albatross was an ideal place to install a pusher engine and propeller. Bowlus and Nelson first selected a Ryder four-cylinder, two-cycle power plant but this engine only managed to produce about 16 horsepower. This was not enough power for flight so Nelson decided to build a suitable engine from scratch. His new motor generated 25 horsepower, barely enough to takeoff and slowly climb.

This combination of power plant and propeller allowed the Dragonfly to climb 235 feet per minute at sea level. The extra weight of the engine, plus the drag from the widened fuselage, gave the Dragonfly a mediocre lift-to-drag ratio. The self-launch capability cost too much performance to appeal to most prospective motorglider owners and Bowlus and Nelson only sold seven Dragonflys. Nelson attempted to design another self-launching glider in 1949 but this time, he teamed with Harry Perl. Don Mitchell also helped on the new airplane. Nelson and Perl called this new design the Hummingbird (see NASM collection). Nelson mounted a more powerful Nelson engine on a retractable pylon behind a two-seat, tandem cockpit. This arrangement improved the soaring performance but the aircraft cost much more than a conventional, two-seat glider and Nelson and Perl built only six Hummingbirds.

Gift of Charles R. Rhoades.

Gliding and soaring gained popularity in the United States from the early 1930s through the postwar years but the difficulties of getting a glider airborne put off many potential enthusiasts. Glider pilots had a variety of options available but all were relatively cumbersome and sometimes dangerous, and required other pilots, drivers, or ground personnel. The most convenient method was to take off in tow behind either an automobile or a powered aircraft. When gliding and soaring began in Germany shortly after World War I, groups of healthy people ran down hills and towed the motor-less aircraft into the air attached to elastic 'bungee' chords. Bungee launches were very popular in Europe but the wider availability of auto and airplane tows, and the hot and humid weather in North America, prevented this labor-intensive alternative from migrating to the New World. Powered winches also pulled gliders aloft but this technique could be risky and required a certain degree of pilot skill. It also demanded a skilled winch operator.

Once aloft, a pilot might elect to boldly depart the vicinity of the airport and proceed cross-country. The result was usually an offsite landing in a meadow or farm field. To return the aircraft to the home base required another considerable expenditure of group labor. A ground crew first disassembled the glider into manageable sections, then loaded the pieces aboard a special glider trailer and hauled them back by road. Glider enthusiasts spent more time preparing to fly, rather than actually flying, than any other group in aviation. The solution to this imbalance between fun and work was to motorize the glider and allow the pilot to self-launch. This idea appeared simple in theory but it proved more complicated in practice.

A prospective designer of a practical motor glider had to overcome three obstacles. He first had to select a proper power plant. It must be strong enough to propel pilot and aircraft off the ground to altitudes high enough for safe soaring, yet not so powerful that the weight and size of the engine substantially subtracted from the glide-ratio. The second problem lay in streamlining the propeller and motor to reduce drag once the pilot silenced the engine and began to glide.

Glider enthusiasts in Germany first experimented with powered gliders during the early 1920s. Karl Plauth designed the two-seat D 8 "Karl der Grosse" in 1923. In the United States, William H. Bowlus and Ted Nelson built one of the first self-launching motorgliders in the United States. Bowlus had established himself as a master-craftsman in glider design and construction during the 1930s with two designs, the Bowlus BA-100 Baby Albatross and Senior Albatross (see NASM collection for both aircraft). Nelson had developed several of his own designs during the same period. In 1945, Bowlus and Nelson formed the Nelson Aircraft Corporation to build a two-seat, motor glider version of the popular Bowlus BA-100 Baby Albatross. The designers nicknamed this design the Bumblebee but they sold the powered glider under the official moniker, Dragonfly.

The men retained the basic Baby Albatross design but significantly widened the cockpit and added side-by-side seating and flight controls for each occupant. Other improvements included tricycle landing gear and a steerable nose landing gear, additional vertical fins mounted on the ends of the horizontal stabilizer, and a hinged canopy. A handle to pull-start the engine was also available inside the cockpit. The aft section of the fuselage pod on the Baby Albatross was an ideal place to install a pusher engine and propeller. Bowlus and Nelson first selected a Righter four-cylinder, two-cycle engine called the 4-0-34 but this engine only managed to produce about 16 horsepower. This was not enough power for flight so Nelson decided to build a suitable engine from scratch. His new motor generated 25 horsepower, barely enough to takeoff and slowly climb.

The low-horsepower engines could only turn small, lightweight propellers, but this was acceptable because larger propellers added weight and drag. On the downside, the smaller propellers had to rotate at very high revolutions-per-minute (rpm) to generate sufficient thrust. Nelson's engine had to turn 3,900 rpm to get the Dragonfly off the ground. The small diameter propeller that turned at a high rpm level was considerably less efficient than larger propellers turning at lower rpm.

This combination of power plant and propeller allowed the Dragonfly to climb 235 feet per minute at sea level. The extra weight of the engine, plus the drag from the widened fuselage, gave the Dragonfly a mediocre lift-to-drag ratio. The self-launch capability cost too much performance to appeal to most prospective motorglider owners and Bowlus and Nelson only sold seven Dragonflys. Nelson attempted to design another self-launching glider in 1949 but this time, he teamed with Harry Perl. Don Mitchell also helped on the new airplane. Nelson and Perl called this new design the Hummingbird (see NASM collection). Nelson mounted a more powerful Nelson engine on a retractable pylon behind a two-seat, tandem cockpit. This arrangement improved the soaring performance but the aircraft cost much more than a conventional, two-seat glider and Nelson and Perl built only six Hummingbirds.

Charles R. Rhoades donated his Dragonfly to the National Air and Space Museum in 1973. During the late 1990s, preservation specialists at the Paul E. Garber Facility discovered that the men that flew this airplane modified the induction system on the Nelson engine into at least three different configurations. They also discovered that the engine mounted on the motor glider was incomplete and missing several electrical system parts, suggesting that someone swapped the engine, or parts of it, for non-airworthy components before donation.