Swan (oz15289)

About this Plan

Swan. Radio control sport pusher canard model.

Quote: "The Swan, by AG Lennon. This month we're presenting an unusual .45 size pusher canard that features, among other things, flaps on both the fore and aft flying surfaces. It's an excellent flier and is guaranteed to turn heads at any flying field. The designer is a noted aerodynamicist and author of the book, R/C Model Airplane Design.

The Swan was designed in the winter of 1984-85, and was built in the spring of 1985, The following summer was devoted to test flying, modifications, and the inevitable repairs. Finally, in October 1985, this model aircraft flew to the author's satisfaction.

During test flights, takeoffs were good, climb was excellent, directional and longitudinal control and stability superb; flap deployment (of both fore and aft flaps) was adjusted to provide a good glide, flaps down. Surprisingly, deploying the flaps had no effect on longitudinal trim; the model seems to 'levitate' as it slows down. This is in sharp contrast to conventional models which require down-elevator trim to avoid nosing up when the slotted flaps are fully deployed. The annoying and persistent problem was a gentle 'wing-rocking' at low speeds. The model seesawed around itslongitudinal axis about 10° each way.

This mild instability did not increase in amplitude or become uncontrollable, and disappeared when the aircraft accelerated under power. Experienced canard fliers advised that this wing rocking was characteristic of canards; the cure was to speed up the model. This, the author did not accept. Landings at high speed are difficult and potentially damaging, and had no place in flapped canard design philosophy.

A variety of cures were attempted. First, the CG was moved forward 1/4 inch, by addition of ballast, and the foreplane's incidence upped by 1/4°, the rocking persisted. Next, chordwise wing fences of 1/32-inch plywood were installed at the outboard ends of the flaps and test flown without beneficial results - and were removed. NASA drooped leading edges ahead of the ailerons were installed; again to no avail - and were removed.

Finally, the author did what should have been done originally. He checked the incidence of both fore and aft wings and found the aft wing at a full 1° above design incidence. The incidences were adjusted to those shown in the drawings, and the CG moved forward slightly to the drawing position; by addition of a small amount of ballast.

In subsequent test flights, the model flew beautifully with no wing rock. Flaps were effective and slow speed, nose-high touchdowns on the aft wheel were made. Half-flap deployment resulted in shorter take-off runs and higher rates of climb.

The original linkage for lowering both fore and aft flaps simultaneously (which is mandatory) but still permitting overriding pitch control, proved reasonably effective, but not ideal. Several types were tried during the test flying period. Finally, the arrangement shown in the drawings proved very satisfactory.

The elevator servo is mounted on a slide and is moved back and forth by the flap servo which both lowers the aft flap as it rotates counterclockwise and moves the elevator servo backward, thus simultaneously lowering the forward flap. However, the elevator servo operates independently but under radio command, to raise or lower the forward flap for pitch control, without regard for its location on the slide.

Forward flap deployment of 20° balanced 35 to 40° of aft flap deployment and resulted in a slow, slightly nose down glide, which could be steepened to roughly 45°, nose down, without much acceleration due to the high flap drag. This permits slow approaches and slower, nose-high touchdowns under good control. This arrangement permits considerable flexibility in adjusting the deflection angles of both sets of flaps, through the use of different holes in the flap and elevator servo arms, and in the inboard aft flap horn.

The Swan will not stall or spin: the only other limitation is its limited ability to fly inverted. This is characteristic of canards using cambered (as distinct from symmetrical) airfoil sections on both fore and aft wings. The foreplane section is NACA 4415 and the aftplane NACA 2415.

Controls: The author uses a six channel Futaba transmitter, receiver and five 5128 servos. The flap servo is controlled by the slide switch that permits flap deflection proportional to the switch's movement. A retract snap-switch would necessitate only two flap positions; full up or full down.

To minimize the amount of ballast to properly locate the CG, all servos, a 700 mAH battery and the receiver, are located as far forward as possible in the fuselage.

The connection from servos to ailerons, aft flaps and engine are Sullivan flexible 'Gold-N-Rods.' The rudder servo and rudders are linked by fine nylon stranded cord that permits outward rudder action only. The elevator servo is linked to the foreplane slotted flap by ball joints and push rod.

The drawings show Futaba 5128 servos. The servo mounts may require modification to suit other servo types..."

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