Skyranger 500 (oz15769)

About this Plan

Skyranger 500. Radio control sport model, for electric power.

Direct submission to Outerzone.

Update 17/1/2025: Added article, thanks to RFJ.

Quote: "Skyranger 500. Looking for a docile, high performace, elecro-soarer? Chris Ward offers this elegant solution.

I was attracted to electric thermal soaring models because they could be flown single handed, are relatively simple to operate and I always enjoyed soaring with gliders. Each day's flying, weatherwise, is usually different and poses various challenges for the model to stay airborne. No two days seem the same. Wind strength, direction and air temperature etc, relative to ones flying site nearly always cause variations in flying conditions.

The model: Skyranger was designed primarily to achieve a good performance without recourse to expensive motors and equipment. My local club, the St Albans MAC, run an electric flight competition each summer for ferrite motors only, with a one minute maximum motor run. The best total of any five consecutive flights is required to score, with a 10 minute maximum on any one flight.

An earlier basic model I had built for standard 540 type motors had shown limited climb performance with direct drive. It needed most of two minutes motor run to get to useful soaring height and was therefore at a disadvantage for the club competition, indicating that geared drive would be required, with perhaps a more carefully designed model.

The new model was planned and built through the autumn of 1994, ready for the forthcoming season's flying, the object being to produce a machine suitable for the club competition and for general fun flying. The emphasis would be on the ability to hold and use thermals, but also to have an improved climb. To achieve this, the following criteria were determined:-

Geared drive was a must and the Graupner Speed 500 7.2v race, with 2.8:1 concentric gearbox was chosen. A suitable 12"x10" folding prop, hub and spinner was available from Graupner to match.

Provision for either 6 or 7 sub 'c' cells for motor power.

The gearbox dictates a 'soft start' switch, or speed controller with brake, capable of handling at least 30 amps. I proposed to use a Gordon Tarling Softy IIIB soft start switch, as this had proved to be reliable for me.

Provision for a receiver pack of 4 x AA cells (I don't feel comfortable with BEC on thermal soarers) and a 'Micron' mini RX.

Mini servos, with control on rudder and elevator only. This type of model does not necessarily need ailerons and the extra weight of this could be saved.

I had decided on a target wing loading of 10oz sq ft, needed to handle and penetrate the usual winds of a typical summer day of up to 15mph, yet be light enough for calmer evening conditions. With an estimated all-up weight of approx 48-50 oz, this dictated a wing area of about 5 sq ft. With a practical aspect ratio of 10:1, I would need a model of approx 90" span.

Conventional structures of balsa and ply would be used (no hi-tech materials), as I just love building.

Efforts would be made to achieve a low drag model as this would enhance its performance. A clean nose entry and no protrusions at wing or tail fixings would be required. Flat plate sections on the tail surfaces, although simple to build, I hoped could be improved dragwise by using good airfoil sections.

The wing section would have to be a bit of a compromise between climb and glide performance, and at a wing loading of 10 oz/sq ft, would need to be about 10% thick. The old favourite E193 looked like a good choice, adjusted in thickness from 10.22% to 9.5% and reduced in camber from 3.57% to 3.2%..."

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