Stubble Jumper (oz14497)

About this Plan

Stubble Jumper. Radio control sport parasol model.

Direct submission to Outerzone.

Update 14/4/2023: Added article, thanks to RFJ.

Quote: "A rough field, easy-flying R/C sports model for .15 motors, designed by Peter Miller and built by Dave Perryman.

This design started out as a doodle of a simple way to make cabane struts. I then added an aircraft to this sketch, then the drawing became ever more complicated with slots (and slotted ailerons), even flaps. I wore out two erasers playing with the design.

At about the same time that I got fed up with the complications, friend and fellow club member Dave Perryman expressed an interest in building from one of my designs: he really needed a model that was relatively easy to fly, with good low speed handling to practice approaches, and yet still be capable of mild aerobatics. He also wanted something fairly quick to build and which was capable of being operated from one of our rougher sites.

A quick re-draw of my doodles, and we had a nice little parasol wing model with plenty of wing area, simple construction, attractive looks and - hopefully - when powered with a .15cu.in. engine, the desired performance.

Now Dave is still learning to fly, but he has built a number of models, all from plans. He has only recently built his first kit. Not only that, but he builds well and his covering is excellent - rather better than mine, I have to admit. No worries about handing over the plans to him, then!

Construction has been kept as simple as possible because the model is designed for quick building and easy repair. There is only one area which might be considered slightly tricky, or complex: the cabane strut assembly. However, this has been designed to be as foolproof as possible and utilises motorcycle spokes in its construction. You should be able to buy these from a motorcycle dealer near you (especially one that specialises in motocross or trials machines) or look in the Yellow Pages under 'Motorcycle Engineers' for wheel builders.

Fuselage: This needs to be built first so that the cabanes can be constructed in the jig, using the ply plate that is built into the wing later.

Construction is very conventional. Start by gluing the doublers to the fuselage sides, then glue formers F1, 2 and 3 to one side, ensuring that they are at exactly 90 degrees to the side. When the glue is dry, add the other side. Leave to dry, then pull together at the rear and glue, making sure the fuselage is straight and true: use a jig if possible. Finally, fit the remaining formers.

I used 12 swg struts, but these are quite rare and you would be better off using 10 swg spokes. They are very strong, but not quite as hard as piano wire.

Cut the 1/2 in square strut mounts and make grooves for the tubes. As an alternative, you could use 1/2 x 3/8 and fit strips of plywood to build-up the groove. At the same time, cut the 1/2 x 3/4 undercarriage mount, you can make it in the same way as the strut mounts, or groove out to take the two wires.

Now glue the strut mounts in place. Also glue in the undercarriage mount and drill for the U/C uprights. Cut the slotted 'Ain. ply pieces which take the uprights of the U/C legs: note that the slots must be staggered to allow for the slight displacement of the Undercarriage wires.

Alternatively, you can glue the 1/4 ply in and drill together with the main U/C mount, just be careful not to drill out the side of the fuselage.

Cut the brass tubes for the cabane struts to length and epoxy into the slots so that the ends are flush with the fuselage sides: make sure that they are level with the top of the mounts and parallel to each other.

Mark out, cut out and drill the 1/16 ply plate that fits in the wing. Cut out the two strut jigging pieces, using scrap Liteply for these. Now tack-glue the jigging pieces to the fuselage: they should locate neatly between F2 and F3 and rest on the strut mounts. Bend the struts as shown, then slide into the tubes and wrap some thin copper wire round each... "

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