Robin, The

When I designed the Robin, I wanted it to be larger than the usual .46-powered plane for better in-flight visibility and yet remain easy to transport. I wanted it to have a weight-to-power ratio (power loading, or P/L) of not more than 250 ounces per cubic inch of engine displacement (cid). This means that powered by a .46 engine, the model's maximum weight had to be no more than 115 ounces (.46 x 250). With a maximum wing area of 828 square inches, the wing loading would work out to be 20 ounces per square foot.

I reduced drag by carefully selecting the wing and tail airfoils, by contouring the fuselage and engine cowl and by using fairings on the landing-gear wire. I also tried to strike a balance between stability and maneuverability, as too much stability would inhibit the model's maneuverability. I also wanted the Robin to be spirally stable.

For short takeoffs and gentle landings, I incorporated large, slotted flaps into the Robin's wing. To obtain effective aileron control at high angles of attack (AoA), I used the NASA "safe wing droop" at the leading edge (LE). I incorporated differential aileron control to help avoid adverse yaw during turns and, to help prevent flutter, I added mass balance to the ailerons, elevators and rudder.

The model's stressed-skin construction produces a light yet strong, warp-free structure. The engine cowl provides adequate engine cooling while also offering a pleasing, turbo-prop-like appearance.

The Robin's performance exceeded all my expectations. Powered by an O.S.* Max .46 SF engine turning an APC* 12x7 propeller, the finished model weighs 110 ounces fueled and ready to fly. The wing area is 819 square inches, and the model's power loading is 239 ounces per cid. It has true short takeoff and landing (STOL) capability and with flaps fully extended, the stall speed is l5mph. I estimate that its maximum airspeed is 80mph.

CONSTRUCTION

I suggest that you cut out all the parts as indicated on the plans before you actually begin construction. Also, to reduce time and effort, use small power tools such as a scroll saw, a drill press, a belt or disc sander and a high-speed drill. Photocopy the small component drawings and use the copies as templates. For example, the eight plywood flap supports can all be made at one time by lightly cementing a stack of 1/16-inch ply blanks together and then rubber-cementing the photocopy to the top of the stack. You can then drill and cut all eight parts at one time. Cut close to the line, then use a sander to sand the parts to final shape.

ASSEMBLY

To assemble the small parts, I use 1/2inch-thick plywood surfaced with 1/4inch-thick cork as fixture boards cut in a variety of shapes and sizes. These are shown in the construction photos. Start construction with the wing, as it will be needed to position formers 5 and 6 in the fuselage later in the process.

Using an alignment fixture board to accurately duplicate the parts, assemble the flap supports on ribs C and E. Having identical parts is essential for good flap action. Next, assemble and sand the ailerons and flaps to shape, as these will be needed to precisely locate the flap support ribs span-wise in the wing structure. Cement the tube anchors to ribs D and G and then glue the FI ribs to the F ribs. Note that these rib assemblies are built as right- and left-hand assemblies. Assemble the rest of the ribs, spars and square, 3AIe-inch LE strips and install the spar shear webs.

Before you install the flexible pushrods in the wing, bend the plastic outer tubes to the shape shown on the plans while using a heat gun. Then manually bend the cables. Install the plastic tubes using CA, then cement the top sheeting to both wing panels. When cementing the bottom sheeting to the wing, first place the upper side of the left wing panel on the left building fixture rails and weight the panel down to maintain straightness until the cement sets. Use masking tape liberally to cement the wing sheeting to the LE Strip. When the left panel is done, do the same for the right panel. Now, install the aileron servo mount and the wing hold-down bolt pieces. Cement the wingtips securely into place, then sand them to shape as shown on the plans.

FUSELAGE

When assembling the fuselage sides and bulkheads, two 12-inch-long, lh-inchsquare blocks placed at right angles to the fuselage, between bulkheads 2 and 3 and bulkheads 9 and 10, will keep the sides level. Assemble the various bulkheads over photocopies of the plans, then make the battery/receiver box. Assemble bulkhead 10 and attach the tailwheel mounting bracket. Assemble the fuselage sides, doublers and triangular supports for the tank and servo rails, then install pushrod tube anchors for the rudder (on the right side only.)

Check that both sides of the fuselage are identical by positioning them together (outside surface to outside surface). Bolt the motor mount to bulkhead 2 and add the canopy hold-down dowels. Assemble the cooling-air outlet and attach to the forward, bottom sheeting that will fit just aft of the firewall. Install the bulkheads between the sides but do not cement formers S and 6 into place at this time.