Yoicks Junior (oz11774)

About this Plan

Yoicks Junior. Control line biplane stunt model.

The 33 inch span CL Yoicks (oz1581) design first appeared in Aeromodeller, October 1949. This here is a reduced scale, later version at 20-1/2 in.

Quote: "Hello Steve, here is a plan which I received as a free pull-out, this is printed on the reverse of the Cessna O-1E Bird Dog (oz3418) plan. This is a U-Control stunt biplane for 1.5 to 2.5cc motors called 'Yoicks Junior', designed by Stuart Fletcher after an original from 1949, 'Yoicks' by John W. Coasby (oz1581). Span is 20 1/2 inches. Regards,"

Direct submission to Outerzone.

Update 5/4/2026: Added article, thanks to RobinLewis.

Quote: "Build from our full size plans. Yoicks Junior. Stuart Fletcher turns back the clock with a junior version of this popular classic.

Grace with efficiency: this phrase was aptly used to summarise the key characteristics of the late John W Coasby's Yoicks (oz1581) when his design was first published in October 1949 Aeromodeller. Apparently, the model materialised out of his interest in an ongoing controversy concerning the relative merits of monoplane and biplane control line stunters. Naturally, it was designed for extreme manoeuvrability and intended to be flown fast. lightweight construction, l0ccs of raw power and those distinctive laminar flow section wings combined effectively to fulfil these exciting performance criteria. Nevertheless, this potent flying machine could also be operated in more sedate fashion as a general sports model with a smaller engine.

45 years on, Yoicks Junior is a five-eighths scale version of John Coasby's design. Construction adheres closely to the original, with just a few minor detail changes, and wood sizes are reduced in proportion as far as practical. The result is a compact, lightweight airframe which produces a lively performance with a powerful motor in the 1.5 to 2.0 cc range. The rearward position of the fuel tank would be ideal for a rear induction motor, as indeed was used to power the original Yoicks. However, motors of this configuration are not so common these days and you may have to opt for a front induction type, as shown on the plan. Installed in the prototype, my trusty OS Max 10FSR runs perfectly consistently, but other motors may not be quite so tolerant. If you do experience problems, then silencer pressure to the tank would be worth trying.

Readers may be familiar with the name of John W Coasby as a pioneering control line flyer, prolific model designer and former Aeromodeller chief draughtsman. Although he did not enjoy the best of health in his final years, it is a measure of the man and his love for our hobby that, in spite of his illness, he could still raise sufficient enthusiasm to encourage the publication of this plan from his home in South Africa. We should all be very grateful for his many contributions over the years.

Construction: Begin by building the two wings. These are basically identical, except for the installation of a tip weight in the lower wing and the surface location of the rib segments which are provided to support the covering material each side of the interplane struts. You will need to make two plywood templates conforming to the wing rib profile. These are used to produce 30 ribs by the sandwich method, six of these being subsequently undercut in depth to allow for the centre section sheeting. The templates are also utilised to produce the four tip blocks, which are recessed between the leading and trailing edge sheeting and are, in effect, like very thick angled ribs. Clamp each block in turn between two triangular balsa wedges cut to the correct tip angle and with the templates on the outside of the wedges. The tips can then be planed to profile - just as you would shape an ordinary set of rib blanks. Note that two tips of each hand are required. Hollow out three of the tips as shown and install around 1/2 oz of lead in the fourth, outboard block. The weighted tip should be reserved for the lower wing.

Begin each wing by pinning the lower leading edge sheeting over the plan. Then pin down a continuous balsa strip of appropriate depth to pack up the ribs at the trailing edge. Next, glue the ribs and tip blocks into position on the leading edge sheeting and pin to the trailing edge packing strip. Make sure the ribs are truly vertical, particularly each side of the interplane slots. Add the upper leading edge sheeting, followed by the leading edge strip, which will need to be chamfered slightly on the underside to fit properly into position. Cut the upper trailing edge sheeting oversize in width to allow for subsequent trimming and dampen its outer surface to induce a slight curvature. Remove the pins holding the ribs to the trailing edge packing, then glue the trailing edge sheeting into position. Re-pin through the sheeting and ribs into the packing strip to hold everything truly in place. Add the upper centre section sheeting and rib segments at the interplane slots, then leave to dry thoroughly.

Lift the partially completed wing from the board and trim the trailing edge sheeting to the required angle. Prepare the lower trailing edge sheeting initially oversize as before, and glue into place, followed by the lower centre section sheeting. When dry, trim off the surplus trailing edge sheet, plane the leading edge to a rounded profile and carve the tip blocks..."

Supplementary file notes

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