"Sport 400"

Free plan

Wingspan 860mm (34 inches)
Wing Loading 36g/dm2 (12 oz/sqft)
Flying Weight 480g (17oz) with 7 cell Nicad, 380g (13.5oz) with 1300-2S Lipo
CG (percent of MAC) 21%
Motor Graupner Speed 400 6V
Propeller Gunther 4.9x4.3 or APC E 4.7 x 4.2 (5.5 x 4.5 with 2S Lipo)
Speed Control Kontronic Rondo400
Battery 7 x Sanyo 600AE (8.4V) or 2S Lipo (7.4V)
Receiver Hitec HFS04Mi+
Servos 3 x GWS Naro
Controls Ailerons, Elevator, Motor
Construction Sheet Balsa (foam-core wings)

The plans for this model are available for download at http://members.fortunecity.co.uk/slmohr/rcplan2.htm. The wing has a foam core (hot-wire cut) sheeted in 0.8mm balsa. It is quite strong even though there is no spar. I covered the wood with Solarfilm, using contrasting colors to make it more visible at a distance.

I made a few modifications to the plan:-

Extended nose length to get to get more weight forward, so that the battery doesn't have to be jammed up behind the motor for correct CG. A forward hatch allows for changing the battery without having to remove the wing. It incorporates a cooling air inlet scoop made from a plastic spoon. s400h.jpg
s400r.jpg Rear hatch for access to the elevator servo. It is secured with magnets (as is the forward hatch). The cooling air exit hole is sloped to reduce drag and turbulence. s400rh.jpg
The wing is secured with three powerful Neodym magnets. It will not disconnect during flight, but it can safely move if a wingtip catches in the grass on landing. s400w.jpg
Two aileron servos are buried in the wing to keep the fuselage interior unobstructed, and to permit differential (more up than down aileron movement to reduce adverse yaw) and spoilerons (to reduce lift when landing).

Light wing loading and low drag make this model a joy to fly. It can easily loop at less than half throttle, and rolls are fast and accurate, even at low speed. The only down side is that it glides forever on landing, which can be a problem on a small field. Hopefully my radio can be programmed for spoilerons, which should help bring it down a bit quicker.

Typical flight time is 6 minutes of aerobatics on a 7 cell 600AE pack. With KAN950's it should fly for at least 9 minutes.