Rearwin Speedster (oz16875)

About this Plan

Rearwin Speedster. Radio control scale model. Wingspan 46 in, for electric power with geared 400 motor

Quote: "Full size plans for a delightful electric powered RC scale model. Rearwin Speedster, by Philip Rawson.

When I first saw a photograph of the Rearwin Speedster, I was immediately attracted to its purposeful shape. Despite being slightly 'chubby' in appearance, it is sleek and clean - an ideal subject for an electric scale model with little power to spare. I had only just finished a successful electric model of the Eastbourne Monoplane which proved that the diminutive Speed 400 could power a light-weight scale aircraft of around 50 inch span. My aim was to design the new model to be as light as possible in order to achieve long flight times and slow, realistic flight. I started drawing up a plan!

For the motor/gearbox I settled on the popular and inexpensive Graupner Speed 400 with the 2.33:1 unit. I already had the battery, a pack of seven Panasonic 1200mAh cells which although less suited for high current delivery than the popular Sanyo 500ARs, offer twice the capacity for only a small increase in weight. I hoped this combination would allow me to use a scale-sized prop, my best guess was a 9x6. After feeling the rather pathetic draught from this combination, however, I made a 9x7 prop. I didn't want to increase the diameter as 9in looked about right and the clean nose of the Speedster offers little resistance to the airflow; going higher in pitch seemed the best solution.

As a speed controller is essential to get the most from the model, I ordered the reasonably priced Jeti JES 10 (10 amp) from Brian Anderson (0191 3887649). This has BEC (battery elimination circuit) so no separate receiver pack is used. Two 110 micro servos move the elevator and coupled rudder/ailerons, controlled by a standard mini receiver.

The wing section chosen (Seelig 3021) is a popular soaring section and a favourite of mine, being easy to build and having a good all-round, low drag but lifty performance. With such a tiny motor up front, and a desire for a prolonged flight with scale speed, there is little room for wasting energy.

The decision to couple the rudder and ailerons was made as I suspected a problem with adverse yaw if I used ailerons alone. Besides, a rudder is needed for taking off. I didn't opt for rudder-only as I wanted to keep a scale dihedral and prefer the authority offered by aileron control.

I decided from the outset that my Speedster would have to be stand-off scale. There are some features, such as the compound curvature of the windscreen that I have simplified, and others, like the wheel spats and fairings that are impractical. I don't have the luxury of a mown strip; sheep grazed moorland is the best I've got. The most elegant landings are those made in the occasional areas of grass long enough that the plane doesn't have to touch the hard earth. The screw-on undercarriage is easily removed to straighten it.

The plug-on wings are held lightly to the fuselage, the clever wing joiner (although I can't take credit for the idea) is flexible to allow for movement in an accident. It is made from 6 leaves of 1/64in. ply with only the middle 1/3rd glued together. This makes it flexible fore and aft but quite rigid vertically, where it takes the load from the wing- shared with the wing struts. This arrangement has proved to be very successful as I've experienced a couple of landings where the model has nosed-over. The wing/fuselage joint has been flexible enough to handle the shock and no damage has been sustained.

The decision that gave me most concern was what to do with the battery pack. Conventional wisdom is to allow the pack to eject in a crash, so that it causes minimum damage to the airframe. Well, I thought about it, and then I thought some more, building the fuselage in the meantime. Reluctantly I opted for a strong box to house the pack, and hoped for the best. The battery pack hasn't demolished the front of the aircraft yet. One of the problems was the round belly of the fuselage making it difficult to design an 'escape' hatch. Also the undercarriage is immediately below the pack, right in the way. The other major consideration was that I wanted the pack as central as possible in the fuselage to minimise the pendulum effect.

Building: It was easier to build the Speedster than to draw the plan for publication! Although not terribly difficult to build, it is fiddly and some experience of lightweight building would be useful. I normally start building long before I have a full plan to follow. Dimensions for this plan were taken directly from my prototype: in general, the curve of the fuselage and shape of the formers either just happened' or were made to fit as I went along. I suggest you build your Speedster in the same spirit. I can't give a detailed account of the building as it would fill a magazine, the photos should clarify the minor details that are difficult to see on the plan.

Before I start building a lightweight built-up structure, I prepare stripwood to the various sizes needed, selecting and cutting, testing for flexibility and weight. Longerons and spars are selected in pairs, one for each fuselage side, then labelled. Stringers are all cut from the same sheet to ensure that they match. Wood is graded so that the heavier is used at the front of the plane, the lighter for the rear and tail..."

Rearwin Speedster from Aviation Modeller International April 1999.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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