Kobra (oz16104)

About this Plan

Kobra. Radio control sport model. Wingspan 730 mm, for Cox .049 Tee Dee engine.

Quote (google-translated): "Drawing of the month. Cobra with 0.8. A long-nosed creation with a bit of Corsair and Helicat on top, for two servos and a sharp 08. And all for 20 kr balsa!

How many times have you had an extra hour on a beautiful afternoon with excellent model flying weather, only to remember that it takes half an hour to the airfield and half an hour back. At the same time, you have wished for a model that you only need to walk around the corner from your house to fly!

With this as a driving force, I sat down and started sketching out a model that would be simple, fast and cheap to build. It would be hand-thrown at take-off and therefore would not need a landing gear. It would only need ailerons and elevators to be as light as possible, but still be capable of some 'multi' flying. The wing would be firmly mounted so that you wouldn't have to 'screw away' a lot of time.

After a few weeks, the Kobra was finished with a 0.8 cc engine and 50 grams/dm2 of wing loading. Once it was finished, it took me 3-1/2 hours to build and turned out to be a successful construction that didn't need to be redrawn anywhere!

Since then, about 25 models have been built around Skåne and one example was flown on a beach in Italy last summer. If you have a couple of 3 mm and a couple of 1.5 mm sheets at home, just get started!

THE BODY: Start by cutting out the bottom of the body onto which the frames 2-5 are glued. Don't forget that no.3 should be made of pine and epoxy glued. Otherwise, regular white glue can be used. Be careful with the fit of this piece, as it is the only thing that prevents the wings from falling off.

Don't be tempted to make the wing beam in one piece. The intention is to make a deliberate break-in indication here in the event of a crash. Do not reinforce here either, the attachment of the wings is just as large as needed to handle all the stresses during 'bus flying'.

Then cut out the fin and stabilizer and glue these to a complete unit. The elevator should be cut out before gluing. Be careful with the angles, which must be exactly 90°. Use a square! When the glue has dried completely, it is time to glue the entire stabilizer unit to the bottom. Here it is important to make sure that the fin is really straight, since we do not have a rudder to trim with. Then fit the lower body sides in and remember that they must be cracked slightly at frame 5 to handle the bend. The edges must be chamfered slightly towards each other along the body's joint line where the body side angles upwards, to get a strong joint. Then fit the upper sides of the rear fuselage and glue them in place after filing the top edge where the fin will stick through. Then do the same with the front of the fuselage and glue the upper side of the nose, which will later also form the hatch for the radio installation. Finally, use epoxy glue to glue the engine frame no.1, which is made of 3 mm plywood.

The fuselage is now finished with wood and should be lightly sanded with sandpaper. Round off all sharp corners with the exception of the part of the underside of the fuselage that forms a joint with the wings (should be left sharp).

Now you can mark out the hatch on the front of the fuselage and make it as large as shown in the drawing. If you have a very large and bulky radio, you can let the hatch continue backwards to frame no. 4/5, but remember that a large hatch makes the body less rigid. When you have decided on the size of the hatch, cut it out of the fuselage with a very sharp knife. You should not get any "balsa fringes" here, but think about getting as tight a joint as possible when the model is dressed. Glue in 10 mm wide strips of about 1 mm thick plywood along the bottom edges of the hatch and let these protrude 5 mm below the edge. These strips serve two purposes. First, to lock (clamp) the hatch in place, and secondly to seal against the oil from the engine.

THE WINGS: Start by joining the balsa together to complete the upper and lower sides of the wing. Two 1.5 mm sheets are enough for the entire wing. Draw out the parts directly on the balsa, which should be of hard quality. Put the pieces to be joined together, tape along the joint, turn everything over and glue the joint, which is easy to fold apart when taped. Place the pieces on a flat surface with the tape facing down and remove any excess glue that has squeezed out of the joint. You should put some weights on top of the joint to prevent the glue from being crooked. You now have four identical 'wings'.

When the glue has dried, take and glue the leading edge (10 X10 mm balsa strip) at the front of the panels that are the undersides of the wings. Then cut out and glue the sprigs 1-4, making sure that sprig no.1 is glued slightly inclined for the sake of the V-shape..."

Direct submission to Outerzone.

Quote: "Hello Mary, Hi Steve, Hope all is well with you. Here is another contribution for the archive. This one is from Sweden, is called Kobra and is drawn to scale 1. Not everything is translated. A Swedish model giving a headache; who would have thought. Maybe a Swedish customer can fill in the blanks. The motors are artist expression.
Greetings from the Netherlands, HJ van Tol."

Note the main planfile here is a vectorPDF format. See article supplement file for bitmap greyscale scan of the drawing as published in the magazine pages. The CAD download is in SVG format.

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