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sgean dubh


Utilising the same type of construction as in the Iolaire the Sgian Dubh is desinged to be an affordable, safe and comfortable aircraft which can be constructed without the use of specialist skills or equipment


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*NEW* A gallery of photos showing construction is now available

Once I had more or less finalised the layout, I built a 1/4 scale radio controlled model and put it through a fairly rigorous program. The results were very encouraging indeed. The stall was a non-event, no adverse yaw could be seen and, flying slow at tick-over RPM then applying full power produced no negative pitching (the thrust line of the engine is aligned with the wing C.of G. position). The landing flare was perfect. I tried different strakes, but the results were inconclusive.

The lack of downward vision always seemed to be a problem with wings so the pilot had to be out in front, therefore the engine was put in the correct place as a pusher. I had a spare Rotax engine (a 447) so that was the one I used.

The NACA 23012 section was chosen for its nearly neutral pitching moment, and more importantly, I already had the co-ordinates and some of the figures for such a section. The extended centre section has a reflex from about 80% chord with the T/E level with the section height. The ramp effect between the extended fins should help with aero effect. The ailerons are large with small movements and are differentialled 1:1.5. For the first flights they will be set at about +3°. The rudders act "out only" and have tip plates to help with rudder authority at low speeds since they are outwith the propwash.

As you can see from the photo in the field (above, right), we were taxiing without the outer wing panels to check out the undercarriage. After this test I molded a new, stiffer undercarriage and a new nosewheel steering system.

As mentioned, the Sgian Dubh is constructed from extruded polystyrene foam with 290t glass cloth and West System epoxy. All awkward contours, leading edge D's etc. were hot wired. The main spar is built up plywood to take the mortice and tennon wing joints. The strakes round the lower edge of the cockpit extend the "pitch platform" and are set at +1.5° covered with carbon fibre whilst also adding structural rigidity without sacrificing cockpit space.

The tank is situated on the C.of G. Home designed and made prop and undercarriage. The all-up-weight so far, with 86 kg pilot is around 266 kg. The side stick is a slider type and the same push rod operates both elevators and ailerons.


© Hugh Lorimer 2008