Durex V (oz5855)

About this Plan

Durex V. Radio control sailplane.

Quote: "DUREX V. Designed by Bob Hansing. Article by David P. Andersen Photos By Michael Kuller

Built from all balsa, the Durex is an unlimited class competition sailplane. It was overall champion of the 1979 Suds City Soar-in, placed 4th in 1979 AMA Nats and 5th in 1980 AMA Nats. It has acquired the name of 'The Minnesota Floatah.'

Winner of the 1979 Suds City Soar-In and fifth place in the 1980 AMA Nationals, Bob Hansing's Durex is an unlimited class sailplane that was designed for competition. It combines a light wing loading with a strong wing. The sink rate is extremely low, which makes it a floater in the Duration events, but when ballasted with up to 34 ounces of lead it can be very competitive in the speed and distance events as well. But light wing loading and a strong wing are important for another reason, too. In sailplane competition, it is necessary to first get a high launch; and the height of the launch is simply a function of the sailplane's lift to weight ratio. This also requires a strong wing and light weight.

The attractively streamlined fuselage has a round cross section with wing fillets. In turbulence or circling flight in a thermal, a glider is always yawing to some extent and the wing fillets smooth the wing to fuselage airflow during flight. In addition, the wing fillets reinforce the fuselage sides in the wing root area, and increase the support of the wing rods. Adding this reinforcement to the outside of the fuselage, where it helps aerodynamically, leaves more room inside for ballast.

The thick symmetric stabilizer airfoil gives exceptionally smooth handling at all airspeeds.

Five Durex prototypes have been built and tested during the last two years. Early versions had a shorter wingspan and a longer tail moment, and their outer wing sections used turbulator spars. Later versions improved the speed range by a change to a faster airfoil. Strength was improved based upon experience. The wingspan was lengthened, and the fuselage shortened when it was decided that the predecessor had more stability than required. An all-moving rudder was changed to a hinged design with a slight amount of sweepback. This change traded off excess rudder control for drag reduction, and no buffeting in speed runs. Wing incidence was reduced based upon appearance in the air. Much experimentation was also performed to determine the best towhook and CG location. Many of these changes were evaluated by using the poor man's wind tunnel - the new version was flown side-by-side with the old version. Differences in speed, sink rate and control response were observed this way.

The design presented here is a well proven competition sailplane that is a joy to build and a thrill to fly, If your joy is to build, and your thrill is to fly, then you'll be pleased with this design.

Construction. Fuselage: The fuselage has a round cross section with large wing fillets. Impossible to build? Look again! The fuselage is the traditional box and former construction. The important difference is that the sides are thick, and the corners have triangular stock gussets. Extreme rounding of the corners with a razor plane and sanding block reduces the box to an almost round cross section. The wing fillet is a sheet of 1/2 in balsa carved to shape with a wood carver's gouge or an X-Acto ring blade. The fuselage shape is similar to the Borne Free (oz6757) sailplane from RCM Nov 1977 - but Durex's fuselage is easier to build.

Start by cutting the fuselage sides from 1/4 in medium balsa. Because these sides arc more than 48 in long it will be necessary to splice two pieces of balsa sheet..."

Supplementary file notes

Article pages, text and pics.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction