Turtle (oz379)

About this Plan

Turtle. Control line FAI team racer, from Aeromodeller
November 1973.

Quote: "The winningest FAI team racer of them all? Certainly the most thoroughly developed and race-proven by the many Dutch enthusiasts, in particular Eep Buys, Henry Helmich, Rob and Bert Metkemeyer, plus Hans Visser.

TURTLE dates back to the early part of 1970, when Rob Metkemeyer and Eep Buys drew-up the basic design and built two examples. These were our first lightweight models with a CG (rearward) wheel and this combination produced much faster pit-stops than previously achieved. Apart from the designers, one of the first Dutch flyers to get really enthusiastic for the model was Henry Helmich, who produced an inked drawing and ran off some dye-line prints of the plan. He also began producing the cast aluminium pans and cockpits for it — so what could be easier for the Dutch teams, especially the beginners, to build when the 'difficult parts' could be bought so easily.

Since then, some 50 Turtles have been built in Holland. Many, mostly small, modifications have been made since and so we can safely say that very few models have been so extensively tested, both by experts and beginners, under such varying conditions. As a model for newcomers to FAI racing it turned out to work extremely well: possibly because of its nice slow-flying characteristics when the engine is way off tune.

About the design. To provide a machine that is both stable in level flight and yet responsive, the Turtle has a rather short tail moment and a relatively large tailplane area. Another big advantage of a short tail moment is that with the fuselage being so short, its construction may be very light as you do not need much strength - just stiffness. That is why the fuselage aft of the wing has a small cross-section and monocoque construction. Also by having a very light tail end, a short nose is permissible, even necessary, to get the centre of gravity in the right place. The construction of the fuselage under the wing consists basically of two 'tubes', the cowling duct and the fuselage 'skin'. This guarantees a very stiff lightweight construction in which the undercarriage is fully integrated. It might be clear by now that the low weight of the model is one of its most important properties! Our experiences are that, especially when the motor is not really on song, light models keep on going much better - the advantage is relatively bigger the slower the motor performs. Normal advantages of light-weight racers are fast acceleration and deceleration, easier overtaking, better manoeuvrability etc - all points covered in Rob's article in the October issue.

The model is designed to weigh around 500 grammes (18 oz). Over 550 grammes (20 oz) and the CG will be too far back and noseweight will be necessary. Our own Turtles weigh (with Super Tigre G.15's) about 450 grammes (16 oz.) - the lightest ever was 15+ oz. Henry Helmich now produces the lower part of the fuselage in glassfibre, and this weighs about 40 grammes. Although I still believe (Rob M.) that it costs something in terms of constructional efficiency and stiffness, many Turtles have been built this way, and they were all as good as the original ones. For those experienced in using this material constructional time will be less..."

Update 25/07/2016: article pages, text & pics added, thanks to RFJ.

Supplementary file notes

Article pages, text & pics.

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