The Chapparel is the latest in a line of thoroughbred designs which now conforms with the new 2 x 2 Pattern Aerobatic rules. Apart from the clean aerodynamic and well balanced lines, the aim of this design is to achieve the lightest weight structure to achieve the highest power to weight ratio possible. Indeed with an OS 140, as used on the prototype, the Chapparel's effortless and unlimited vertical climb on half throttle is astounding. You can literally hang the model on its prop then apply full power and rocket up vertically again. Of course the pattern schedule will require a more disciplined approach to flying.
Building the Model
The model has balsa skinned foam core wings and tail feathers. The fuselage is built up from balsa, foam, plywood and fibreglass. Selection of the lightest weight materials is essential.
Cut the wing panels out of white foam blocks. Before the wings are skinned with balsa you will need to prepare them with cut outs for the wing rods, servo bay, wheel well, retract undercarriage braces, plus reinforcement with carbon ribbon strips. For further weight saving I drilled holes out of the wing cores evenly spaced out over the entire span.
The ply undercarriage bracing needs to be interlocked and epoxied into the wing panels with the wing retaining tube in place. This needs to be set up with the wing panels upside down on the building board with the centre section lifted up for dihedral. (See plan diagram.)
Finally, skin the wing, add leading edge, aileron spars, wing tip blocks and root ribs. Sand to shape.
Cut out ailerons, temporarily install aileron servo. Fit hinges to aileron and control linkages.
Cut out the tail surfaces from foam blocks. Cut out channels for the tailplane rods and make up square tubes out of balsa. Set up carefully for 0 degrees dihedral.
Skin the panels, leading edge and tips, then cut out elevator and rudder. Add spars, then hinges to the control surfaces.
The sides are cut from 1.5mm balsa sheet, reinforced with balsa doublers and 3mm sq. balsa longerons and bracing. The central fuselage is a box section with a cut out foam turtle deck on top and carved out balsa block on the bottom rear. Accurate alignment is very important for this type of model.
The only ply components are the engine mounting plate, firewall and root ribs, which are cut out and fitted appropriately.
The fin and tailplane section are glued into the rear fuselage and blended in.
The canopy and underside pan can be shaped from balsa block, however a lightweight fibreglass canopy and pan are available from the designer Adrian Hopgood (Phone (03) 5248 1195).
Covering and Finishing
The surfaces of the model were coated with dope and talc and sanded smooth until all the wood grain was filled. It was then covered with tissue and dope.
Automotive primer was then sprayed over, smoothed with fine wet and dry paper. The model was then painted with automotive acrylic paints. The canopy was also painted.
The radio gear, engine, fuel tank and undercarriage were then installed. By careful positioning of radio gear the model was balanced to correct CG position without addition of lead.
Flying the Model
It is difficult to describe the flying characteristics of a pattern model apart from saying that the Chapparel does it all with ease. It flies gracefully and very smoothly throughout all manoeuvres.
As mentioned in the introduction, the high power to weight ratio produces a phenomenal climb rate therefore pilots will need to take it easy on the throttle to keep the aerobatics within a reasonable flight envelope.
Overall the Chapparel is magic to fly and modellers can expect to take out many competition wins or placing's with this model.
SPECIFICATIONS Chapparel IV
Type: 2 x 2 Pattern Aerobatic Model
Chapparel IV plans are available from:
Plan No. 669
To return to Airbornes
This page was last modified on the 4 May 1999