Marabu III (oz15345)

About this Plan

Marabu III. Radio control pattern plane. World Championship winner design.

Note this is not a fullsize plan. This is a scan of the drawings as they were printed in the pages of MAN, July 1972. This planfile is really just here for now as a marker, in the hope that someone can send in a clearer scan at fullsize.

Direct submission to Outerzone.

Quote: "Two-time World Champion shares with us his FAI Pattern plane. The MK III version flown by both himself and his brother Emil at '71 World Champs in Doylestown incorporates all of the mods and represents best in FAI! Marabu Mk III, by Bruno Giezendanner.

Top flyers are always accused of holding back secrets about their designs. Modelers are very unhappy when their new model doesn't fly the way they thought it would - they think there is some kind of trick or information that the expert didn't include on the plans for his design. Normally, the problem is with building the model - it simply wasn't built according to the specifications on the drawing.

We know that model information is very freely given out by the experts. At the recent World Championships we noted that the so-called 'tricks' were being freely given out to anyone who asked. Problems of expert-to-novice communication do exist because most modelers do not find the time to write about their experiences or make drawings. The drawing of our Marabu MK III is our attempt to pass on to those interested the result of many thousands of hours of development that produced what we feel is the ultimate competition Stunt model.

Interest in our 1971 version of the Marabu that we flew at the 1971 World Championships was so great that we decided to update our drawing for the Marabu G. The latest version is now the Marabu MK III, shown with this article.

The design considerations that follow are only in reference to the Marabu type of aircraft. Perhaps our comments can apply to other designs as well. The modifications are minor in nature when taken individually, but when combined, result in a major improvement over last year's Marabu G.

We have observed many Marabus flying that were built from our plans. Major differences have been observed from model to model even though each was built from the same plans. The builders made minor changes, some on purpose, others in error. We have been completely amazed how some minor change drastically alters the model's flying. The point to be made here is: don't change the design. Build it according to the plan. We have flown the Marabu MK III design for hundreds of hours - believe us, everything is done for a purpose. There are no unnecessary frills offered here; we feel that no significant performance increase with the model can be obtained with today's rules and equipment.

Marabu can be built with a fixed landing gear. Performance is satisfactory; however, the acrobatic ability is certainly held back with the fixed gear. Our experience with retractable landing gears has shown that the rolling maneuvers are very accurate about the longitudinal axis -fewer pilot corrections are required, therefore the model is easier to fly, and is also easier to fly under strong wind conditions. The reduction of landing gear drag is very noticeable under these conditions.

Today's flying standards are very precise. The model is usually flown parallel to the takeoff and runway direction, regardless of wind direction. Proof of Marabu's crosswind ability was shown by its victory at the 1969 Internats in crosswind conditions. We found that the model's crosswind performance could be further improved by shortening the nose; the shorter nose increased stability about the lateral and vertical axis. Engine torque now became less of a consideration and rudder response was now much more positive. Hands-off stability improved and noticeable reduction of transmitter trim corrections were observed. The neutral position of the elevators was less critical. Net result was the model 'grooved' much better.

Because of reduced size of R/C equipment we were able to thin down the fuselage somewhat, thus cutting down drag. The airfoil of the vertical fin was changed to a flat airfoil.

The wing was not changed - the Marabu wing still features a semi-symmetrical airfoil at the root, going progressively to a full symmetrical section at the tip. There is also a slight amount of wash-out in the tips. Purpose of the washout is to improve low airspeed performance and stability. We generally fly off rough grass fields, and landings and takeoffs are normally done at the lowest possible speed so as to keep the stresses on the retractable landing gear and airframe to a minimum. Marabu at low airspeed will keep its wing level until the very last moment before the model stalls.

Construction: Construction of the Marabu is not difficult. Standard construction materials are used, with the exception of the fuselage sides. We used Graupner laminated 1/ 8 balsa plywood, a material not readily available in the USA. Medium soft 1/4 balsa sheet can be used as a substitute. The width of the bulkheads and other minor modifications will have to be made to obtain the correct outside fuselage width.

Fuselage: First the triangular gussets are glued on the sides. Note the slight curve necessary on the forward half of the top gusset. The motor mount is made up as a separate unit. Two pieces of filler blocks are glued to the left side of the maple mount. The inside filler block has a cutaway for the engine crankcase. The other piece does not, and is slightly smaller, as shown by the dotted lines. Drill the engine mount holes; #6 sheet metal screws will be used to bolt the engine in place. Mounting holes for the retractable nose gear should be made at this time (Giezendanner gear used in the original). The bulkheads can now be attached to the sides. The top and bottom are now attached..."

Supplementary file notes

Article.

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