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Pinocchio pic

A near to scale 1/5 size PIEL CP90 Homebuilt sports aerobatic model with flight characteristics which can only be described as a "Dream Machine".

Article Frank Thomas * Photos by Brenton Thomas

A very near to scale model of the French PIEL CP90 homebuilt single seat sports aerobatic aircraft, PINOCCHIO is another product of Airborne's Design Staff and an excellent addition to their already fast growing Plans Service.

Pinocchio successfully combines pleasing scale lines and good handling characteristics with conventional construction methods.

It is well suited to the transition from simpler trainer style models to the more advanced scale designs and as such should provide an interesting challenge in building skills and attention to basic scale detailing.

While it is not a model for the tyro builder/flyer, those with good building skills and several trainer type models to their credit should have no great difficulty in producing a successful and very attractive model.

BUILDING COMMENTS

The prototype was built strictly as per plans, with the following minor exceptions: A commercial tail wheel bracket was used, the side line of the removable engine cowling was raised to the centre line of the nose block, and the top stringer from F7 to the tail post was replaced with a shaped balsa insert to simplify shaping.

An OS .46 FX motor was used (All Brian Winch's fault - as an OS fan from wayback, I couldn't resist his magic write up in March issue). The wing centre optional fibreglass reinforcing was omitted to test wing integrity.

If using a bigger motor I would suggest using the fibreglass to allow for increased stresses. (Editors note: Whilst the wing is very strong without fibreglass reinforcement, hairline cracks may appear along sheeting joints if fibreglass cloth is not used). With the .46 motor no balance adjustment was necessary to arrive at the initial projected C.G.

WING CONSTRUCTION

Pinocchio pic

N.B. For accuracy, check all parts against the main wing plan prior to cutting. The old saying "check twice, cut once" was never more appropriate. Prepare a basic wing kit allowing for final trimming as necessary.

As ribs W1 to W4 are identical size, these can be blocked and cut as a unit after cutting W4 as a template. Cut ribs W5 to W9 in pairs using the plan drawings. Check position of main spar slots against the main wing plan to ensure the accurate positioning of ribs during assembly. Leave the trailing edge pieces attached at this stage.

Cut the ply wing braces, checking slot positions and depth of cuts. Cut main spars, L/E and rear spars and aileron spars to length, allowing for final trimming.

I allow 3mm extra width and slot the leading edges 1.5mm top and bottom to provide support for the wing L/E sheeting. The leading edge and spars are then steam bent to curve as per plan prior to assembly. The rear and aileron spars, due to the cantilever wing shape, are thickest near the wing panel centre and taper towards both ends. These should be cut 20mm wide initially and shaped during assembly.

Cut 12 rectangular vertical grain shear webs 67.5mm x 37mm from 1.5mm balsa. These will assist as rib spacers and will be marked to final shape and installed after fitting the top main spar. Trace wing plan details on 1.5mm bottom T/E wing sheeting and cut to outline. Do not cut the out ailerons at this stage. Cut and join 1.5mm centre section sheeting from T/E to main spar. Note that the top and bottom T/E centre piece is 1.5mm ply.

Commence wing assembly with the centre section, as follows: Pin the bottom centre sheeting over the plan. Trim to length and glue main centre bottom and rear spars in place. Cut W1 ribs at rear spar and glue the four centre ribs in place. Attach the main wing brace and top centre spar. Add the L/E wing brace and leading edge.

Trim and fit the four T/E pieces of W1 ribs and the two filling blocks. If you use the centre mounted servo for aileron control, this should now be fitted. I prefer wing mounted servos for precise operation and ease of installation. Add the top sheeting. When this is all set, remove the wing section from plan and sheet the front bottom from spar to L/E. Shape the top centre L/E but leave the bottom square for addition of fuselage fairing.

Add the remaining two W1 ribs to form an attachment point for the outer wing panels. Centre section is now complete. Set up a hinged building boar, one side flat on the bench and the other angled to give 18mm dihedral at W9 as per plan. Tape the plastic covered plan in position and locate the wing centre section over the plan. With this firmly fixed in position, locate a 1.5mm spacer along the main spar line and cover with plastic. Glue and pin the bottom main spar and T/E sheeting in position over the plan. Cut the ribs to length, keeping the T/E pieces for trimming and fitting later. Attach the T/E spar. Glue in the ribs, using the shear webs for location and squaring. Fix the top spar. Now trim and fit the shear webs.

Add the front aileron spar. Trim and fit aileron and trailing edge ribs W2a - W9a remainder of rib T/E pieces, leading edge, support for aileron horn and 6mm square spruce aileron servo plate framing (if using wing mounted servos).

When all this is set, sheet inboard bottom section forward to main spar, fit and screw 1.5mm aileron servo plate in position and sheet between plate and T/E sheeting. Fit U/C blocks and drill outer ends for torque rods.

Mark position of aileron cutouts on outside of bottom sheet but do not cut out until wing sheeting is completed. Trim the rear spar and T/E to final shape and proceed with top sheeting and cap strips. Sheet bottom from main spar to L/E and add cap strips, ensuring that wing panel is perfectly flat.

Shape and fit tip block. Reverse the building board and assemble the other wing panel as above. Now cut out the ailerons and trim to shape. Hinge in place. Fit aileron horns and linkages. Dowels and wing bolts will be fitted later. Check the wing for lateral balance and give the lot a final sand.

While on the subject of flying surfaces and flushed with success at completion of that little project, let's try something a tad more relaxing before tackling the fuselage.

TAIL FEATHERS

These are built up over the plan from 9.5mm balsa and are quite straight forword.

Material width is mainly 15mm with 20mm elevator T/E. Strip off sufficient of these sizes for horizontal and vertical components. Trace and cut larger shaped parts, such as the rudder T/E and bottom, tailplane centre piece, fin bottom block and tip blocks before starting assembly. As for the wing, I used PVA glue, ensuring that all the end grain joints were double glued to ensure good structural integrity. After assembly, hinge both rudder and elevator before shaping to aerofoil section. A portable electric finishing sander works great for doing this operation. Finally round off the leading edges and tips.

FUSELAGE

Pinocchio pic

As the motor is fully enclosed, it will be worthwhile to give some thought to the location and type of fittings for fuelling, muffler etc. before building is commenced.

In the fuelling department I chose Dubro valves for both filling and overflow/muffler pressure, as these shut off one line when the nozzle is inserted. A small filler bottle with Dubro nozzle then takes care of overflow.

The OS .46 motor with standard muffler was used, this installation only requiring some extra carving under the engine and battery compartments in order to allow the muffler to fit in quite unobtrusively.

A standard muffler extension takes care of the exhaust gunk when flying.

Commence fuselage construction by cutting all bulkheads to shape. Epoxy F2a and F4a in place. Cut and sand the engine mount spacer for 2° right and down thrust, epoxy to F1 and drill for engine mount. Drill F1 for fuel lines and throttle cable. Drill 1/4" front wing dowel holes in F2/F2a as per plan and attach rear wing bolt fittings to F4/4A. Prepare the rectangular tank floor, ply doublers and fuselage sides - also 6.5mm square balsa and 6.5 x 3mm spruce longerons. Next step is basic fuselage assembly. To simplify assembly behind F7, cut the spruce top longerons to length so that they finish about 10mm behind F7, before attaching them to the top edge of the fuselage sides. Add ply fuselage doublers and mark in the bulkhead positions. With one fuselage side lying flat, set up and epoxy F1, tank and F2 in position.

Add the second fuselage side, checking carefully for square as a basis for accurate fuselage assembly. When this is all cured, set up in the fuselage jig. Glue in F3 to F7 and 9.5mm stern post. F3a and canopy frames will be added later. Steam bend the bottom longerons behind F7 to shape and glue in place. Cut a 6.5mm balsa filler to shape and fit in fuselage top from F7 to end post. Add the tailplane support block.

Fit the servo rails and install servos and control linkages.

I used a balsa pushrod and "Y" linkage for elevator, Golden rod rudder linkage and standard flex throttle cable. Sheet the bottom from wing back. Attach and square up the tailplane/elevator assembly. Fin/rudder was left till later to minimise hanger rash during work on the front end. Set the wing in position, check that everything is square and drill L/E dowel holes through F2/2a. Ensuring that wing is accurately aligned, drill trailing edge to accept wing bolts. Fit the motor in position and make any necessary modifications to F1 bottom area to accept the muffler. It may be necessary to make a semi-circular cutout in the bottom of F1 and enclose part of the battery area to prevent internal fuel or oil seepage around the muffler, depending on what type of muffler system is used. Make up and fit the chin and side blocks and nose block. Fit C2 and turtle deck sheeting, fuel tank and tank compartment top sheeting. Shape detachable top engine cowling and attach to top half of nose block. Paint cockpit floor (flat black) and set up cockpit instrumentation. Attach fin/rudder assembly, steerable tailwheel and top fin/fuselage fairing blocks.

Shape and fit the wing fairings, undercarriage fairings and wheel spats.

Finish off radio gear installation, linkage connections and any other finishing touch ups. Finally sand all over and the project should be ready for your personalised covering job. The cockpit canopy will be fitted later, when covering is completed. An excellent clear canopy is available from Airborne Plans Service.

COVERING

Everyone has their own preferred covering or painting methods. This is how I did it:
The U/C fairings and wheel spats were first sealed with dope, then dope and talcum powder, followed by several coats of Dulux water based spraypack sealer and finish coat. U/C trim was applied using Solartrim and car trim tape. All other covering was with Profilm, once again using car trim for line work. the motor compartment was sealed with epoxy resin after covering. All trim was then sealed using Feast Watson oiled based polyurethane clear.

FINAL PREPARATION AND FLYING

Having installed the motor, set up all control linkages, check the C.G. and ensure that all other pre-flight checks are completed, it is now time for the moment of truth.

In the flying department Pinocchio is a real "Dream Machine". Take-off is straight and true into the wind with virtually no rudder correction required.

A touch of elevator and steady application of throttle results in rotation within twenty-five metres with smooth, positive climb out.

Aileron response is crisp and sensitive, indicating that Pinocchio is in its true element as a scale model of the full size sports aerobatic PIEL CP 90.

While top speed is comparable with most .46 powered recreational aerobatic models, its excellent handling is evident throughout the throttle range. It will slow down until you won't believe it is still flying. Stall from level flight is almost a non-event, with no tendency to drop a wing. Landing is a breeze, with just enough speed to keep everything nicely in order.

SUMMARY

Developments in design of small homebuilt aircraft have provided an exciting range of new subjects which are especially suitable for scale modelling. Pinocchio (Piel CP 90) is a top sports aerobatic model for the recreational flyer or sport scale buff. 

The OS .46 FX motor provided adequate power and completely reliable operation. In my opinion, this is an ideally balanced combination which can be flown all day at half throttle for relaxation - turn up the power and you will be into aerobatics with plenty of scope to test your skill. Build Pinocchio accurately to the plans, dress it up in your favourite livery and you will not only get lots of accolades at the flying field - you will have a ball at the controls of your Dream Machine.