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Rubrik The “Fairey Rotodyne” is ready for its maiden flight. An extraordinary scale model is created with the “Basic 540” Phillipp Gardemin from Baden-Württember, Germany, reports about building this helicopter model with the aid of a Step-Four Basic 540. With a rotor diameter of almost three metres, this is a mighty big chopper. I dreamt for years about building a “Fairey Rotodyne” scale model. I flew this extraordinary helicopter in the late 50s, in England – but unfortunately this project didn’t get past the prototype status. This helicopter was extraordinary due to the fact that the almost 30 m main rotor was tip-driven. The tips were powered by a mixture of fuel and compressed air bled from two wing-mounted turboprops. The model was constructed at a scale of 1:10. In order to be able to bypass the mechanical complexity of the tip drive, the plan was to operate the model as an autogyro aircraft. This means that the rotor is driven by the airflow, thus, allowing the model to take off. The first drawings were created on the CAD. The dimensions were then taken over from a plastic model by the Airfix company. Realisation with Step-Four The fulfilment of the dream, however, could only take form with the acquisition of the “Basic 540” milling machine. The general layout drawings in the CAD gradually became a tangible plan. Thus, the individual parts separately drawn, exported to the milling software, and then be directly milled. Only poplar plywood in thicknesses of four and three millimetres was used. The sheeting was made from 1,5 mm balsa. Ten month construction period During a construction period of over ten months, the milling machine became a best friend. Even the smallest of parts were drawn, exported to the milling software, and subsequently milled. The large cockpit, for instance, was quasi drawn from nothing in the CAD, the parts exported and milled. After a total construction period of twelve months, the model stood on the meadow, ready for flight. Two Hyperion external rotors with 4 blade airscrews from Varioprop and a 6s LiPo 6500 mAh served for propulsion. The rotor blades – consisting of a Styrofoam cores with carbon reinforced plastic spars and plywood sheeting – rotated in a four-blade rotor hub from Varioprop and a self-built swivel mechanism. The entire model now weighed 10.5 kg. Test flights The “Fairey Rotodyne” was unfortunately unable to perform its maiden flight, which was due to the fact that the self-built autogyro mechanism wasn’t powerful enough for the enormous rotor diameter of almost three metres. The model is currently undergoing modifications, whereby mechanical details are being improved upon, as well as the mechanic of the swivelling vertical tail fins. New test flights are planned for spring 2010. The “Basic 540” will certainly provide me with many more good services until then. Philipp Gardemin 10 STEP-FOUR | March 2010
Model making The original „Fairey Rotodyne“ of the 50s unfortunately never quite past the prototype status. The frames and spar caps were milled from 4 mm poplar plywood. The rotor tower with the mounted mechanism. The tail with the swivelling vertical tail fins consist of a spar-ribbed construction made from milled 3 mm poplar plywood parts. Thanks to CAD and CNC, retrospectively constructed parts also fit perfectly, such as the servo holder above. Many parts of the cockpit construction were designed as a basis on the CAD and then milled. The wings are also rib constructions with standing crest spar. The engine nacelles consist of inner parts constructed and mounted as housings – all drawn and milled, of course. After a construction period of eight months, the body shell was practically complete. The rotor mechanism unfortunately proved to be insufficiently stable enough for flight. STEP-FOUR | March 2010 11
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