Sou-Wester (oz14878)

About this Plan

Sou-Wester. Radio control electric-powered duration model. For geared Speed 400 motor.

Direct submission to Outerzone.

Update 21/10/2023: Added article, thanks to RFJ.

Quote: "Many model fliers are still sceptical of the practicality of electric power in spite of the ever increasing improvements in both electric motors and batteries. The number of converts in both free flight and RC is, however, increasing steadily across the whole spectrum of model types. Most of my own RC models since 1988 have been electric and include a ducted fan flying wing and a twin motor flying boat! The model which gets flown the most these days, though, is the one presented here.

The main reason is that I am lucky enough to be able to fly some quiet models from my garden and land in an adjacent. field. This model is one! Being relatively light and manoeuvrable ensures there is minimum risk, although I should point out that we live in a fairly remote spot.

Fast Preparation: Since the power/control system used employs BEC, the model can be safely in the air within about fifteen minutes of spotting the first thermalling Buzzard! I have used this system for several years and feel happier with it than with separate Rx batteries when I want to fly at short notice. Provided the Tx meter indicates a safe power level, the BEC cut off in the model will have a generous margin of at least half an hour before landing is prudent. This is the case even with the low voltage cut off circuit of the Hitec 1003 switch I use. Most other makes use a higher cut off voltage and will be even safer.

While on the subject of radio, The Rx is a Micron mini six channel and the three servos are Hitec 580s. If you want to economise, save a bit of weight and simplify the model, the flaps can be omitted. The flight performance will not be quite as flexible but the landings, the main reason for fitting the, will still be fairly docile.

Power: The power is supplied by a 6-cell pack of Sony 600AE or 500ARs and the motor is a 2.3:1 geared Graupner Speed 400 driving a 10.5 x 6 folding propeller. The set up is quite efficient and gives around ten minutes or so flying without much thermal help. If there is any of the latter about I usually manage two or three times that.

Construction Materials: As you will note from the plan, the construction and materials used are quite conventional. The only bit of 'modern' material on the original is a piece of 6mm diameter carbon fibre tube used as a wing joiner. It's good stuff but my suggested 5mm alloy knitting needle alternative should be safe. Note the dihedral is achieved by angling the guide tube through the three root ribs as shown. As a general guide to selection of wood, try a use light, firm balsa, except where noted. It is surprising how weight builds up if rock hard, heavy stuff is used indiscriminately.

Wing, Tail and Fin: The only place to use hard balsa is for the wing main spars. I used spruce on the original but will use balsa as a useful and safe weight saver on future versions. However; do not forget the shear webs between the ribs. The swept wing tips are not only aesthetically appealing (to me anyway!) but do help rudder turns even with moderate dihedral. However, a bit more complexity results as regards dihedral braces.

If you decide to fit flaps note they are simply bottom and front-edge hinged as they only move down. The wire flap stirrups are slid over the operating lever as the wings are brought together.

The all-moving tailplane is both light and strong. It is mounted fairly high but operated via a simple curved snake. To achieve a smooth curve, it is routed through a channel in the central 1/8 fin structure which is sheeted with 1/32. Note the tailplane joining rod (knitting needle again suggested), is reinforced by 1/32 ply discs cemented to the fin sheet. Also it is very important to ensure a sound fixing of the tailplane operating cross wire to the snake. Drill through both the outer brass support tube and the snake inner if it is plastic to lock the two together. Fix with a bit of Cyano but do not rely on that alone for the security. If the inner of the snake is metal, the joints can be soldered.

Fuselage: Turning now to the fuselage a few points are worth noting. The basic structure consists of 3/32 sides with 1/8 square longerons glued along the inside edge and joined with 1/8 square spacers and sheet formers. I used 1/8 square spruce on the original but again feel the hard balsa shown is adequate and again a bit of weight is saved. Both top and bottom of the fuselage is sheeted except for a small section forward of F4..."

Supplementary file notes

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