The 1-26 was a nimble, responsive and forgiving sailplane, but with a best L/D of 21.5, its performance was limited. While Hank Thor had completed successful badge and Diamond flights in the 1-26, he realized how challenging such flights were - most soaring days are less than ideal, and pilots don't want to be limited to a 10-mile radius around the field. A simple, compact sailplane with a best L/D in the high twenties would have obvious appeal.

Soaring Society of America membership had been growing steadily and Hank correctly assumed that he was not alone in his desire to build and fly his own machine. As an aeronautical engineer and former airframe designer, Hank Thor knew it would be easy to get the modest cross-country performance he wanted. Keeping it buildable, practical and affordable were going to be the real challenges. In the early 1960’s, Hank met Ben Jansson, an aerodynamicist with Saab, Ben shared Hank’s enthusiasm for the small sailplane concept, and they quickly sorted out the essential characteristics for a new glider, Over a period of 2 years, they designed and built the BJ-1 "Dyna Mite" in Hank's garage. Flying for the first time from El Mirage in August 1966, the BJ-1 delivered - it performed well, was fun to fly and easy to rig. And, at a total out-of-pocket cost of $800, it was affordable.

Although the BJ-1 was a success in the eyes of its builders, it was not ready to market. Four years of flying had shown the need for refinements, Ben Jansson had returned to Sweden, leaving Hank Thor to carry out the development of the Duster.

It was like starting from scratch. The Dyna Mite had been built from rough sketches. Thor invested 1,400 hours doing air load and structural calculations and preparing detailed design drawings. The basic plywood structure was simplified and lightened to permit the substantial payload increase many potential pilots would need. The Jansson-developed airfoil, a "Wortmannized" NACA 4415 non-laminar section was retained, but span was increased to 42ft 8in. The cockpit profile was lowered significantly, reducing drag.

The result was a new glider with a best L/D of 28, a two-point increase over the Dyna Mite. Although Ben Jansson was no longer involved, Thor retained the original "BJ' designation as a reminder of the role he had played. No doubt this helped initial marketing efforts (photos of the Dyna Mite were used in early Duster ads), but it has caused many, even Jane’s All the World’s Aircraft, to overlook Hank Thor’s primary role.

Hank Thor selected the name “Duster" for his new design. Plymouth's muscle car of that name had become popular, and Hank enjoyed the car's cartoon logo - a caricatured dust devil with eyes. In August 1971 the first ad for the Duster plans and kit appeared in Soaring magazine, and the first "real” Duster, built by Jim Maupin and Norm Barnhart took to the air. The ad emphasized the key features: amateur construction from wood, medium performance, low cost, and garage storage.

Every feature reflected Hank Thor's' desire to make the best possible cost /performance /utility tradeoffs. No component was over 18 feet, mindful that it would probably be built and stored at home, most likely in a garage. The wooden structure matched the tools and skills of many amateur builders. (Jim Maupin once claimed that it could be built with only a saber saw, disc sander and 3/8" drill.) The plywood kit made fast assembly possible, and gave a smooth exterior. The canopy was a plexiglas flat wrap, eliminating the need for molding.

The fixed center section of the wing kept the outer panels light, and made the Duster easier to rig. The wing had a high aspect ratio (17.4) for a wooden home built glider, which gave it the look of a "real" sailplane, especially in the air. Everything was optimized to make the Duster appealing to the motivated enthusiast home-builder.

In 1973 the Duster Sailplane Association was formed, and the Dust Rag newsletter provided a sense of identity for builders. By 1974 over 150 sets of plans had been sold (in the US and 10 other countries), and a handful of Dusters had flown. As completed Dusters began to log time in the air they demonstrated the performance that was Hank Thor’s initial objective. The time required to complete a Duster varied greatly. Hank Thor’s initial estimate was 800-900 hours. Two editors of the Dust Rag reported different experiences: Bob Walters spent 950 hours spread over 13 months, and doug Bell took 1600 hours over 8 years. One exceptionally meticulous builder reported 3,400 hours! The record for longest elapsed time is held by Terry Whitford and Peter Raphael from Australia, who reported completing their Duster in March of 2000.

Many were indeed built at home in the garage, and stored there when not flying. The 7-foot wing stub permanently mounted to the fuselage made it a bit of a challenge to enclose a Duster trailer. An open trailer for a design intended to fit into a garage in the first place is a fair trade. even today.

The Duster proved easy to handle on the ground and fast to rig. The most common comment is that it took half the time of the familiar 1-26, from trailer to flight line. Every builder seemed pleased with the performance and handling. First light accounts trace a predictable sequence of emotions, beginning with uncertainty at takeoff, guarded relief on tow, elation during the flight, and a deep sense of accomplishment at day's end.

Duster instrument panel (left) and Aussie Duster (right)

This layout (above) was used to design the main version of the Duster Glider.

Designer Hank Thor is kneeling next to the fuselage- left of the the Duster instruction sheet

Hank Thor's BJ-1B Duster is truly a piece of sculpture in black and white

Here's a couple views of the Duster's structure. Tons of thanks to Kancho and Cam for all the help and support with this Duster model !!

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Some interesting gliding stuff..

L/D (lift over drag) is a very handy way to express the efficiency of a particular glider, and its potential for cross-country flight.

Actually, many of the other important qualities can be, and are, described numerically. These include things like wing loading, sink rate, roll rate, etc.

Glider airspeeds have a big effect on how efficiently a glider is being flown. Best L/D is the optimum cruising airspeed for maximizing the distance covered from a given altitude.

Minimum sink airspeed is the airspeed used to loiter, and maximize time airborne, but not distance covered. It is the best airspeed for climbing.

The faster you can fly, the longer your range, because the length of a soaring day is tied directly to the amount of daylight available, and to solar heating. So experienced glider pilots strike a compromise, and generally fly faster than best L/D, and slow down when they find themselves flying through lift. Glider pilots stop to thermal only when they must. Cars don't stop at every gas station along the way, and glider pilots don't stop for every thermal they find.

Glider performance numbers are used to develop the "Handicap" which allows gliders of different wing spans and aerodynamic "eras" to compete against each other in "Sports Class Contests".

By comparison, a Piper J-3 has an L/D of about 10 and a Boeing 747 has an L/D of about 17. Glider L/D averages about 20 for utility class trainers, 40 for racers, and as high as 60 for super-refined open class long span sailplanes.

As an interesting and totally unrelated aside, glider L/D numbers are almost directly comparable to automobile gas mileage in MPG.Two seat training gliders have L/D ratios in the High Teens (18), refined racers have L/D of about 40, and really expensive high end machines have an L/D of 60. A car that gets 60 mpg would be thought of as very efficient, and a glider with an L/D of 60 is just about the maximum you'll see in actual practice.

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Specifications for the DSK BJ-1B 'Duster' Sailplane

Length: 20 ft 6 in Wingspan: 42 ft 8 in Wing area: 103 ft² Aspect ratio: 17.7 Empty weight: 620 lb Gross weight: 580 lb Performance Maximum speed: 128 mph Maximum glide ratio: 29 Rate of sink: 148 ft/min

 

Important links:
South West Soaring Museum, Moriarty, NM
The Duster Prototype BJ-1b, N11BJ, is now in the collection of the Southwest Soaring Museum. The current nose art "Eagle Dreams" is some of the more elaborate paintwork applied to a Duster.