Shoestring. Radio control electric glider, for MFA Hummingbird 380 motor or similar.
Quote: "Shoestring is an easy to build, traditionally constructed electric powered glider, with viceless flying characteristics that can form an ideal low cost introduction to electric flight or be an interesting diversion for the conventional power enthusiast.
The lightly loaded model flies relatively slowly and has a small turning circle, enabling it to be flown from a surprisingly tiny area of grass as well as wider open spaces. Light weight equates with safer flying, especially in well populated places; because of this and its quiet performance the model may be operated within the confines of the works' sports field at lunchtime with little fear of complaint.
Shoestring occupies only a small part of the car boot when on holiday and is a simple fly for fun electric powered model that can be built on a shoestring budget, hence the name. Why not have a go?
Why electric? I began to use electric power some four years ago as an alterna-tive to towline, bungee and slope soaring radio controlled gliders and was at first apprehensive about a wrongly perceived power/weight ratio problem. Experience has shown that the power produced by a small electric motor is amazing and is able to propel a lightly loaded model swiftly skywards. A short motor run gives sufficient height to search for a thermal or to move well away from the turbulence of a rough slope into smooth rising air in marginal soaring conditions. With several successive applications of power available, quite long flights can be achieved, even without thermal or slope assistance.
It is possible for me to make use of slope lift from a hill near my home and once initial height has been gained, with only a light wind in almost any direction, I rarely use all of the three inexpensive packs of cells that I take for an afternoons flying. If the day is completely calm and without thermal activity, one pack can be charged from the car whilst flying continues.
A separate radio control battery pack has been dispensed with in the interests of saving weight and to reduce the power required. No radio problems due to low voltage will be experienced using five 500 or 600 mAh cells if the model is landed when a reduced rate of climb under power is noticed.
The 'hardware' required for the model consists of a two channel transmitter, a BEC (common supply regulator) receiver, two mini or micro servos, an MFA Hummingbird 380 motor (or similar), a propeller and adapter, and a sub-miniature 5 amp rated spot lever (micro) switch (Tandy catalogue number 275-017). A 0.1 micro farad ceramic disc capacitor (Tandy 2720135) is soldered across the motor tags and a wire is attached from one tag to the motor casing.
Keep it light. It is important to use light to medium density balsa wood to keep the flying weight as low as possible, consistent with adequate strength. Carefully trace the wing rib shape from the plan and produce a thin plywood or stout cardboard template. When 32 ribs have been cut, reduce the template by 1/16 in along the top and bottom edges so that it matches the centre section shown on the plan and cut the remaining four ribs. Protect the plan and avoid parts sticking to it by covering with cling film or similar. PVA wood glue is used throughout, except for the alloy wing joining tubes and plastic parts, when a contact adhesive can be used.
Pins may be pushed through the trailing edge into the building board, but should be at the sides of the spar and lead-ing edge. Whilst building, the leading edge is packed up to the correct height with scrap pieces of balsa. Construct the inner and outer panel of one wing half over the plan, angling the double ribs at the dihedral joint using the template. Add the triangular gussets at this stage..."
Shoestring, RCME, February 1995.
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This model plan (like all plans on Outerzone) is supposedly scaled correctly and supposedly will print out nicely at the right size. But that doesn't always happen. If you are about to start building a model plane using this free plan, you are strongly advised to check the scaling very, very carefully before cutting any balsa wood.
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