by Merv Buckmaster
In the May-June 1984 issue of Airborne, Celestino Rossi presented the MiniDrake, an .049 powered motor soarer, to Australian modellers, having known about the design from contact with his home club in Bergamo in Italy. The MiniDrake had the engine mounted above the wing trailing edge as a pusher, and it needed only two function radio control. It was easy to build, flew very well and became one of the most popular models in the Airborne Plans Service. It also generated quite a trade in 6 x 4 pusher propellers, but only one was needed for each model because, being above and behind the wing, it could not get broken, as it might have done on a nose-mounted engine.
When the idea of building a larger version of the MiniDrake was considered I made no changes to the planform, and only a few adjustments were incorporated to make it even easier to build than the smaller original. The actual changes were:The nosewheel and skid were omitted.
The engine pylon was mounted on the fuselage and not on the wing centre section.
The wing panels were adjusted in length to match standard balsa sizes;.and
The wing was made as two separate halves. The name for the new version just had to be SuperDrake.
The MiniDrake was enlarged by one third to give a model of seven feet (2133 mm) wingspan. This size of motor soarer could be powered by engines in the 2.5 to 3.5 cc range. On the MiniDrake, only rudder and elevator controls were necessary, but, with the use of a larger engine, throttle control would be a natural option for a third RC function.
The first prototype of the SuperDrake was powered with one of Ivor F's Sesquis, which is a 1.5 cc. Schnuerle ported diesel.
When I proposed the project to the editor, he suggested the inclusion of a version with the engine mounted conventionally on the nose. This required only re-positioning of the engine and then the re-location of the wing to allow for the different weight distribution, resulting in a shorter nose. Thus the SuperDrake is available in two versions, as a tractor and as a pusher.
The lightweight wing structure of the MiniDrake was strengthened to cope with the larger size by using thicker wing ribs and a tapered I-beam spar. However, with the possibility of using a more powerful engine, I realized that an even stronger wing would be needed to avoid wing flutter. Therefore a wing with a D-box structure was designed for the second version. This gives four combinations of fuselages and wings to choose from, the choice being governed by the engine to be used. These are, firstly for a low powered engine, the light, open structure wing with the pusher or nose mounted engine; and secondly for a high powered engine, the D-box wing with either the pusher or nose mounted engine configuration.
Since the SuperDrake is a conventional balsa model, conventional methods are used to build it. The choice of material is left to the builder, remembering that hard, heavy wood will result in a strong, heavy model, and vice versa. Since the in-flight stresses on a motor soarer are small, light to medium wood can be used confidantly. There is sufficient strength in the design to cope with mild aerobatics. Any glue suitable for balsa may be used. The covering material may be a light iron-on film such as Oz Cover, or the traditional combination of a fabric and dope, with an enamel finish on the fuselage for fuel proofing.
Strip some 4 mm balsa sheet for longerons and cross pieces, and build two side frames directly over the plan. When the glue is dry, lift the frames and glue them, still attached to each other, to some 2 mm sheet and press them down on the building board until the glue is dry. Trim the sheet around the edge of the frames, glue on the other side sheeting and weight the assembly down flat as before.
Trim the second side, separate the sides, and glue in the formers, then glue the sides together at the tail and attach the noseblock.
Glue on the bottom sheeting and trim it to size.Cut the engine mount pylon from suitable plywood, build up the tank and engine fairing as required and glue it in position, pulling the rear of the wing mount together at the trailing edge of the pylon.
Glue the servo tray in place, and lay in place the elevator pushrod and the rudder cables. Put some masking tape on the ends of the rudder cables to prevent them from slipping back into the fuselage. Glue in pushrod supports to prevent it from bowing, and glue on the fuselage top sheeting.
Finish the fuselage with the usual sanding, doping and painting.
The tailplane and fin are flat plate structures, so strip the required pieces from some medium weight wood and assemble them over the plan.
Cut the elevator and rudder from some light quartergrain wood, shape them to a thin wedge section, and hinge them to the tailplane and fin, respectively.
Finish them in the same way as for the fuselage.
Strip the leading edge pieces, cut the trailing edge and shape to the wedge section, and cut the spars using a long straight edge to the specified taper. Since this operation cuts slightly across the grain of the wood, make the initial cuts with very light pressure so that the blade is not deflected from the straight edge. Make heavier cutting strokes as the cut gets deeper into the wood.
Cut out the ribs, pin them into blocks and sand each block to a uniform shape, two for the main panels plus one for the port and one for the starboard wing tip panels.
Drill the holes for the wing joiner in the main panel rib blocks. Pin down the LE, TE and bottom spar with packing as shown.
NOTE. The bottom spar for the lightweight wing is flat on the building board, but it requires packing to allow for the bottom sheeting on the D-box wing.
Notch each rib for the bottom spar, and glue the spar in position.
Cut and glue in place the spar webs.
Glue the wing joiner tubes in place, allowing for the thickness of the plywood root rib, and block around them with scrap wood to fill the space between the spar flanges.
Cut the notches for the top spar and glue it in place, fixing it firmly in position with weights while the glue dries. Add the wing tip blocks.
Remove the wing frame from the building board and shape the LE and tip block, and trim the spar ends to give a good fit at the dihedral joints and at the root ribs.
For the D-box wing, pin it down and add the top sheeting. When the glue is dry, lift the wing, shape the underside of the LE and add the bottom sheeting.
Check the fit of the tip panels to the main panels, insert the dihedral braces and glue the panels together at the specified dihedral angle, using props and packing to hold them in position. Cut the plywood root ribs slightly oversize, drill the holes for the wing joiner and glue the ribs in place with the stub of the tubing slotted into the hole, and allow to dry. Then trim the root ribs to exact size.
Prepare the wing for covering with the material of your choice.
Glue the tailplane and fin into their positions, checking them for correct alignment. Install the radio gear and connect the control surfaces to the servos.
Install the engine. Check the balance. No extra noseweight was needed on either of the SuperDrake prototypes.
The hand launched test glide of the pusher prototype showed that it needed no trim adjustment when rigged and balanced as shown on the plan. The only minor problem was to allow for the unusual position of the engine and propeller, but a safe technique for starting the engine and launching the SuperDrake was sorted out in two flights, and from then on the model was very easy to manage by the hand launch method. The climb with the Sesqui was gentle, the control responses were light and positive, and there was no trim change between power-on and power-off. The glide was very steady and the model could be set up for the landing approach and then needed no further input for touchdown, although a gentle flare could be given to take advantage of ground effect.
The SuperDrake was a very good soarer, and altogether a better aircraft than the 049 version, simply because of the larger, more efficient size. This also made it visible for a greater distance, enabling it to range a good way for thermals, and many long flights have been since been recorded.
The tractor version of the SuperDrake with the D-box wing was flown with an SY 15 which turned a Bolly 7 x 3 at about 20,000 rpm and hauled the model up at an angle of about 45 degrees. This required more attention to the control of the climb and some prompt control inputs to get a good transition into the glide. However, the SuperDrake responded quickly and easily to the controls, and the glide was just as steady as the pusher version but a little faster. The stronger wing allowed higher airspeed to be achieved for loops, wing overs and barrel rolls which used quite a bit of sky. The extended flight envelope of the tractor version of the SuperDrake also brought the challenge to find and use thermals to gain height for aerobatics, making this probably the most versatile motor soarer in the Airborne plans range.
Super-Drake plans are available from:
To order a plan via e-mail
Airborne Plans Service
P.O. Box 30 Tullamarine Vic., 3043
Cost: $40.00 (2 sheets) plus $5.00 postage
Plan No. 680
Credit Card Orders: Phone: (03) 9333 5100
Fax: (03) 9333 5099