Push Moth

The Push Moth plan is available via the RCM&E plans service. This article and pull out plan was originally published in RCM&E, December 1965. It is reproduced in its original form, including references to R/C equipment of the time. But with minor modifications it could be easily fitted with modern micro servos, an inexpensive electric motor, speed controller and Li-Po battery. Extend the rudder trim tab to form a full length rudder. Boddo recommends adding small elevators to the rear of the tailplane, but we think it would look better if they were incorporated into the original tailplane outline during the build, installing the trailing edge inboard by ½" and adding a ½" elevator in place of the original T.E. Sewn hinges would give it an authentic look, but diamond tape hinges would be much easier to fit.

For anyone who fancies a change from the conventional single channel rudder only model this could be your answer. This pert little pusher looks different and includes an unusual form of escapement linkage but for all that is simple to build. The aileron control makes for a smoother style of flying and, once one has become used to this type of flying, is a pleasant change from rudder. There is no reason why ‘kick-up’ elevator should not be incorporated, providing the torque rod connection is on the bottom of the escapement, although the original was fitted with a sequential type. Remember that if elevators are used they should be in addition to the designed tail plane area.

‘Push Moth’ resulted from a long considered desire to design a model with a simple and functional aileron control from a standard rubber driven escapement. At the same time I had been sketching some ideas of a small pusher and it was soon obvious that the two thoughts of aircraft and form of control were going to marry together in an easy and efficient manner.

The original fuselage had a shorter nose than the present design and, although ample for storing the R/C equipment, the balancing of the model at the correct point was only achieved by adding Plasticine in front of the nose. With the present model, using a 225 Deac pack as far into the nose as possible, a small amount of lead weight was still required to obtain the correct balance point.
Possibly this additional weight could be avoided by increasing the sweep back on the wing. I’m sure there’s room for experiment in many ways with this form of design. ‘P.M.’ is no lightweight and tips the scales at just over 15 oz. but try to keep the weight down where possible otherwise flying is going to be a little too fast and furious.

You should find ample room for all modern small radio gear in the deep fuselage and, should you prefer it, a small motorised servo could be used for either aileron or rudder control. With the Cox Golden Bee mounted ‘up back’, turning a Keil Kraft three bladed prop in a clockwise direction, the power is just about right for normal sports flying. Any glow or diesel engines from 0.5 to 1.0 cc. (or even 1.5 cc. with an efficient silencer!) should cope according to the style of flying required. But any engine which will run in the opposite direction to normal has the advantage of allowing the use of a standard propeller and in this design it is essential to have a three blade to reduce the diameter.

Try to organise a building schedule before you start your project and keep to this programme. Don’t start on all the interesting parts and leave the dull items till last. Cut out all your sheet parts before commencing building and build the wings and tailplane first. I'm a keen ‘spare minute’ builder; I know that by finishing the evening by gluing one wing panel over the plan it will be ready for removal the next morning and, if I’ve managed to get up a few minutes earlier,
I can glue the opposite wing panel in position before setting off to work. You should find construction straightforward with no particularly difficult parts. Choose the balsa wood carefully for lightness and evenness, especially the fuselage sides.

1. Wings are constructed in two sections and joined together with dihedral braces. After soaping the drawing, pin down a piece of 3⁄4 x 1⁄32in. trailing edge. Cut 1⁄8in. square hard lower spars to length and pin in position.

2. Cut wing ribs by the blocking method, afterwards trimming the root ribs slightly due to the narrower spacing of this rib.

3. Glue 1⁄8 and 1⁄16in. wing ribs in the positions shown and check that all are vertical except for the root rib, which should be angled from the root rib template. Glue the top spar in position. Fix the top trailing edge in position and glue the leading edge in position.

4. When dry remove from the plan and sheet in the upper surface of the wing from the rear of the top spar to the leading edge, and from root rib to the tip.

5. Add 1⁄2in. soft balsa tips and sandpaper, together with the leading edge, to a smooth contour.

6. Construct the second panel in a similar manner.

7. When both panels are set, cut slots in the first three ribs to receive the dihedral braces. Check these for accurate fit and then glue into position on one wing panel. When dry add the second wing panel to the projecting dihedral braces. Glue thoroughly and pin down, then prop up the opposite wing tip to 23⁄4in. to obtain the correct dihedral angle. Hold firmly in position until dry, pinning the two root ribs together.

8. Sand and prepare for covering and glue on the trailing edge stock reinforcement.

9. Cut ailerons from hard 1⁄16in. quarter grain sheet and sand and prepare for painting. Ailerons should be sewn to the wings after all parts have been covered, doped and fuel proofed.

1. Construct the basic frame from 1⁄8in. sq. strips and 1⁄8 x 1⁄2in. T.E. stock as shown on the plan. Remember to prop up the T.E. to allow for the symmetrical section.

2. When dry remove from the plan and add 1⁄8in. square to rib positions and 1⁄8in. sheet to the centre section and aerofoil section.

Fin and Rudder
This is a straightforward construction of 3⁄32in. sheet sanded to a slightly tapering T.E. and a rounded L.E. A trim tab may be fitted if desired.

1. Mark on the handed fuselage sides the positions of the formers and strengthening longerons and uprights. Glue the 1⁄8in. sq. and 3⁄16in. sq. longerons and uprights and 1⁄2 x 1⁄8in. top and bottom doublers in position. When the sides are dry glue the formers F1, 2, 3 and 4 in position ensuring that they are square with the sides.

2. Add 3⁄8in. soft balsa sheet to the lower nose area. Glue internally to the battery compartment, the rear of F1, the 3⁄8in. bottom sheet and the side framework 1⁄8in. sheet latex or synthetic rubber sheet to act as shock absorption to the DEAC cells. Note: Plastic foam is not sufficiently resilient for lining purposes but ideal for holding the batteries loosely in position within the battery compartment.

3. Add top 3⁄8in. nose sheeting and a nose block consisting of three layers of 3⁄8in. sheet.

4. Draw in the fuselage ends and glue in position formers F5, F6 and the tail block with 1⁄16in. ply plate end, and 1⁄8in. sq. cross members. When all is set the top and bottom 1⁄16in. sheeting can be added, including the 1⁄16in. ply for the main undercarriage and the 16 gauge ‘piano’ wire tail skid bound to 1⁄16in. ply.

5. The escapement rubber winder consists of a plastic nose bush with a slot cut in the rounded end for the winding hook to engage. The nose bush is prevented from rotating by filing a flat onto the side of the nose bush shank conforming to a similar shape hole in the fuselage and plate.

6. Thoroughly sandpaper the fuselage, fill the grain and sand again.

Covering and Finish
The model should be covered in heavyweight tissue. Pin down all flying surfaces when doping to prevent warps. Colour dope should be kept to a minimum as this represents wasted weight but the model should be thoroughly fuel proofed to avoid seepage of fuel into the structure, particularly beneath the engine.

Escapement Installation
1. The escapement is mounted on a 1⁄16in. ply former in the normal way. Although the former must be glued to the fuselage, there is not room to slide the escapement in and out. Cut a piece of 12 or 14 g. brass tubing 11⁄16in. long and flatten the ends in a vice. Drill two holes each side approximately 9⁄16in. and 13⁄16in. from centre to centre. Solder this rocker arm onto the drive hook of the escapement. With the wings in position cut two 18 g. piano wire pushrods to length, bend one end at 90° and solder to the rocker arm with cup washers. Cut small lengths of 16 g. tubing, flatten the ends and drill to receive the 18 g. aileron horns and solder them to the pushrod arms so that the ailerons are level.

2. Test the linkage for freedom of movement. The amount of ‘throw’ will depend on which hole on the rocker arm is used.

3. When satisfied with the action, cover the area below the engine, following the fuselage curve to the horizontal top of the rear fuselage, with heavy gauge celluloid. Two small holes must be cut in the celluloid for the pushrods to project through, and the rear of it must be well fuel proofed before fixing in position, and externally after fixing. An impact adhesive is the best for fixing this screen in position, the purpose of the screen being to protect the escapement area from the excess fuel from the engine.

Radio Installation
Due to the variety of radio control equipment presently available, no specific instructions are given for installation
but the use of Deac’s is strongly recommended for the
reasons of nose weight and reliability.