Centurion (oz11401)

About this Plan

Centurion. Radio control sailplane. This design used a prefabricated fibreglass fuselage, so no formers are shown for the fuse.

Quote: "A 75 in Span Maximum Performance Sailplane Designed for All-Out Competition in the Standard Class. Centurion, by Don Dewey.

Several years ago, our good friend Willie Richards, came up to the shop with a prototype of an original sailplane design he had just completed. On the initial test flights he had experienced difficulty in achieving satisfactory flight performance and asked for some assistance in correcting the problems he had encountered. After making a few suggestions as to incidence changes, modifying the stab area etc, the Gus (oz6017) was born. Within a few months after the publication of the Gus, this design became one of the most popular sailplane plans ever to be published.

My own experience with the Gus consisted of three prototypes built from the finalized plans and well in excess of a thousand flights with these prototypes over a two year period. Although designed primarily as a sport sailplane, the 75 in span Gus had placed high in numerous sailplane contests around the country and I even managed to miss a first place win by one point flying this amazing little ship.

Yet, during the two years in which we flew the Gus against many different sailplane designs, the experience gained indicated a need for a higher performance machine that would be capable of the tasks required by present sailplane contests. Thus, I kept notes on the modifications I felt would be necessary to take this design to a higher plateau of competitive performance while retaining many of the desirable characteristics of the original design.

The Centurion is the result of these two years 'research' on the original design by Willie Richards. First of all, one of the greatest areas of maximum drag on a sailplane is at the junction of the wing to the fuselage, accounting on some sailplanes for as much as 30% of the total drag. Thus it was decided to have a custom fiberglass fuselage made for Centurion by one of the master craftsmen in the field of fiberglass lay-up. The criterion I established for the construction or the fuselage seemed to me impossible accomplish in fiberglass, but it was decided to give it a try.

The first requirement was that the fuselage should weigh no more than 6 oz complete - a 2 oz weight reduction from the original built-up balsa fuselage. The second requirement was to add an additional inch to the tail moment, a factor that we felt would be a definite improvement over the original design. A third criteria was to eliminate, as much as possible, the amount of drag created by the wing-fuselage junction. Thus, it was decided to fair the fuselage in smoothly over the top of the wing and to use no method of hold-down except a friction fit between the leading edge and the top of the wing and the fiberglass fuselage and two 4-40 nylon hold-down bolts at the trailing edge. This, I felt, combined with a very streamlined fuselage, would reduce the overall drag factor to an absolute minimum.

Another factor we wanted incorporated into the fuselage was one whereby absolutely no bulkheads of any kind had to be used in the fuselage for, as is characteristic of any fiberglass fuselage, the normal breaking point in the event of a crash is directly adjacent to the union of a bulkhead with the fiberglass fuselage. Thus the fuselage had to be light, strong, and completely free of any bulkheads or internal wood bracing.

In addition, we wanted to allow enough room in the cockpit area to take any of the currently available proportional systems, instead of limiting the design by a confined equipment area to the microminiature proportional sets, as seems to be the practice with many designs currently available.

The job of manufacturing the fuselage was given to P&M Fiberglass, PO Box 1020, Nipomo, California 93444. Several months later, several prototype fuselages were given to us, the heaviest of which weighed 5.95 oz, complete with canopy! All of the design criteria were incorporated in these prototype fuselages including a sturdy molded-in skid, a 'rolled' wing seat and cockpit area, all double filled in areas where maximum strength was needed. This fuselage is one of the prime factors for the outstanding flight performance of the Centurion and thus, if you want to build this high performance Standard Class sail-plane, you will have to purchase a fuselage for $19.95 from P&M Fiberglass.

No built-up fuselage is shown on the plans since we have proven to our own satisfaction that any attempt to duplicate this fuselage in balsa detracts immeasurably from the performance of the aircraft.

The wing has the same basic configuration as the original Gus insofar as the planform and overall area is concerned. However, here the similarity ends. The wing structure of the Gus was quite weak and suffered the most damage over long periods of flying. in addition, the excessive polyhedral that was employed on the Gus overshadowed the tight turning characteristics that can be gained from polyhedral by causing a severe rocking motion in normal flight attitudes.

What we wanted to accomplish on the Centurion was the advantages to be offered by polyhedral without its disadvantages. This, coupled with an all flying stabilizer of generous area, would achieve the extremely tight turning radius we desired while the overall reduction in drag and the streamlined characteristics of the Centurion would give us the necessary penetration when moving from one thermal to another. One of the problems with the original Gus was that, while it had excellent ability to thermal its even the lightest air, it did not have a wide speed range..."

This is the 'Centurion' RCM-513 by Don Dewey, published in the December 1972 RCM.

It complements the Centurion 2 (oz10952) RCM-567, also by Don Dewey and published in the August 1974 RCM.

Direct submission to Outerzone.

Supplementary file notes

Article.

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