Saab J21A (oz12209)

About this Plan

Saab J21A. Radio control PSS model.

Quote: "Inspiration for the SAAB 321A came while searching for a more stable PSS model which might handle lighter wind conditions and still be fun to fly, With a smoothish fuselage, flat bottom wing and dihedral the SAAB seemed perfect, plus at 1/12 scale all the panels and planks would divide economically into 36 inch lengths of balsa.

Let's start: The wing is built-up construction and the fuselage is planked. If you haven't tried planking, give it a go, with a little practice it is quick, cheap, strong and light. For compound curves it can't be beat.

Start by building the wing centre section flat on the board. Basic enough but be sure to incorporate and box in the elevator snake and torque rods before fitting the top skin. Now begin the fuselage by building a former and spine skeleton onto the wing, where the formers meet and top skin these can be psseted with 1/2 inch triangular balsa. The fuselage is planked in 1/8 medium balsa strips maybe 1/4 inch wide. Work evenly from the sides to top and bottom to prevent warping. A bit of Lilliputian carpentry may be involved in places, but 'stick' with it?

The cockpit forward of E3 is blue foam or similar, and the fillets between the fuselage and wing nailing edge are best sanded from soft balsa as these help consolidate the join. The fuselage is best sanded smooth at this stage; I used blue foam for the rear spinner to reduce rear weight and firm balsa for the nose.

The wing outer panels can now be made up - remember the dihedral. I cut the ailerons out and faced them off to keep them light, but solid balsa may be used if you don't mind sanding washout into them. Now butt join the wing panels together with dihedral, You may choose to reinforce the joins; I didn't bother since the boom formers and soft block infills tend to take care of this. The booms are soft 1/2 in and are built upside down on the board since the top surfaces are flat.

With the top, bottom and formers glued together, the side skins (firm 1/bin) can be attached, but leave a run for the elevator snake in the left hand boom. Sand the booms to a nice profile, but leave the tail 4in square until later. Trim the booms to mate to the wings with the required upsweep. When happy with the snake route and operation, the booms can be glued to the wings and the soft block fillets added. If you now sand the top 4 in of the booms to the correct incidence you can add the elevator made from light 1/8 sheet.

Sand the fins from soft 1/2 in balsa before you glue them in place, whole thing should feel really rigid now. With a fine saw cut out the hatch: the pinholes remaining in the fuselage can be used as a guide to former positions. Although installing the linkages at the start of the build is fiddly you should now reap the rewards, since they now only need connecting up. When facing off the hatch I installed false 1/8 floors in the cabin to support the radio gear.

Finishing and flying I had to add a little weight to get the balance correct but the nicads could have gone forwards to F1 (hadn't a long enough lead). The kids insisted on the colours of the prototvpe J21A, green top surface, pale blue undersides and tiger's mouth and eyes. Given some exhausts at the rear and a cannon in front and the Swedish insignia, the looks great on the kitchen table.

The cockpit was painted out with matt emulsion, windscreen pillars cut from thin card painted gloss black and the rest in humbrol enamel. When flying, be warned, the SAAB is small and those colours don't help with orientation. Inverted flight is limited but it doesn't look right upside down anyway. The low inertia of an aircraft this size gives it a very snappy performance, but with a forward CG and a little up trim it will virtually fly itself, and looks most realistic this way. Loops are fine and rolls across wind show off the twin booms beautifully. In light lift when the symmetrical wing hotships are grounded, try a high banking turn followed by a low pass and straffe them all into the grass. Great fun!"

Alan Harkness' 1/12 scale SAAB J21A for PSS, from August '91 Radio Modeller.

Direct submission to Outerzone.

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