Sporty Forty (oz1248)

About this Plan

Sporty Forty- RC Sport Bipe for RC. Wingspan 40in, length 40in, engine .40 power.

Quote: "Spoty Forty - it's forty inches long, has a forty inch wingspan, and sports a K & B .40 up in the nose.

Let's talk about the practical features of the Sporty Forty. Note that there's no dihedral, and the wing section is flat bottomed. That means that the wing can be built in one piece, on a flat work bench, using standard 36 in lengths of wood. No dihedral braces, no splicing, just put it all together.

The engine is upright, and the tank is just about level with the carburetor intake. Reason? Upright engines are the easiest to adjust and, if you nose up on landing, you don't scrape the muffler. With the tank just about level with the intake, you don't need a fuel pump.

The wide tread of the landing gear is almost one-third of the wing spread. This not only makes for good tracking, but also helps to reduce the incidence of wingtip scraping with the resultant 'wing rash'.

Note the relatively high tail wheel setting. It's done on purpose. Remember all those learned discussions we had about P factor and gyroscopic action? Well, it seems that the problem with most tail draggers comes on take-off, when the plane tends to veer to the left as you raise the tail for take-off. With the Sporty Forty, this is seduced to the minimum. Don't bother to raise the tail on take-off. Just give it the gun gradually, and it'll pick up speed and take off at the same angle that it sets on the ground, with absolutely no tendency for a wingtip stall.

How about that low aspect ratio? You don't see many biplanes like that, do you? All I can say is - try it, you'll like it! The Sporty Forty has one of the most amazing speed ranges you'll ever see. You can throttle back and float along at about 20 miles an hour, or pour the coal to it and zip along about 70. Caution - don't put too much throw in the elevators or the ailerons. The short coupling, both longitudinal and lateral, makes it very responsive to control surface actions. Its not intended to be a competition biplane — just a Sporty Forty.

So there's the design philosophy behind the model. Let's get on with the construction features. Actually, it's so simple to build that you probably can put it together just by following the plans, but there are a couple of hints and kinks that may help. Let's start with the fuselage.

Fuselage: Building the fuselage is straightforward. But I'm not going to say it's straightforward, because a lot of you have written in to complain that the designer says, "It's straightforward," and what you want to know is howinell to build it - not how straight it goes forward. So here are the easy steps:

(1) Study the plans.
(2) Look at the construction photos.
(3) Build the fuselage in accordance with the plans and photos.

That's all there is to it. Hm-m-m. Maybe that's not the whole story, so let's talk about some of the details, such as, after you have cut out the fuselage sides and glued the doublers, wing saddles, and longerons to them, join them together with the three fuselage bulkheads (some modelers call them formers) as shown..."

Update 25/01/2015: Have rescaled this plan to correct full size at 40 in span, thanks to Rob.

Update 01/02/2015: Replaced this plan with a clearer copy, thanks to theshadow.

Update 18/03/2015: Replaced this plan with a clearer copy thanks to Balsaworkbench. Scanning by Don at EAC, cleanup by theshadow.

Supplementary file notes

Article pages, text and pics, thanks to hlsat. Also, previous scan.

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