Aexi - Electric powere aerobatic model for 3 function RC and 10-15 size electric motors.
Quote: "ELECTRIC powered flight is becoming a popular branch of our hobby and we have seen many recent improvements in the purpose designed motors and power packs offered by various manufacturers. The established modeller will find that electric powered models are very different from IC powered models. The power available from a '15' size electric motor is far less than a .15 cu in internal combustion engine. A 1.8cc (.10 cu in) motor would approximate the power (remembering of course that 14 ozs. of permanent ballast in the form of a flight battery has to be carried).
or best performance, the airframe of an electric powered model has to be of larger area and lighter weight than the norm for IC power. My approach to electric flight was to accept the weight/power of the 15 size unit, and develop an airframe to suit. Anyone who has built and flown thermal soarers will appreciate the strength of an apparently light/weak structure. Soft wood is not the complete answer, careful design and careful selection of building materials can lead to both lightweight and rigidity. A look at free-flight open-powered model construction will give a good indication of the type of airframe needed.
The AEX I has a wing area of 450 sq in, the weight of the completed airframe is 17.5oz. The flight pack and radio equipment bring the total weight to 48.5oz which includes 20oz of flight pack plus 11oz of radio equipment. This results in a wing loading of 15.5 ozs/sq. ft. By removing the propeller and flight battery, and adding 2-3oz of ballast in the nose, the model can be flown as a slope soarer of 35oz weight with a loading of 11oz/sq ft. In the pure slope mode using two servos and with the R/C equipment relocated forward, the model weighs 27oz. with a wing loading of 8.6oz/sq ft.
Construction is not complicated. I have taken the full size axiom of 'simplify and add lightness'. Wood selection is important, using straight quarter grain balsa throughout, apart from the wing tip blocks, which can be as soft as can be obtained..."
Aexi, RCM&E, November 1977.
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Article pages, thanks to RFJ.
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