Curtiss Kittyhawk Mk III (oz14596)

About this Plan

Curtiss Kittyhawk Mk III. Free flight scale model WWII fighter. Wingspan 780 mm, for .5 cc motors. Scale is 1/12.

Direct submission to Outerzone.

Update 2/6/2023: Added article, thanks to RFJ.

Quote: "1/12 scale 780 mm span, for .5cc motors. Curtiss Kittyhawk Mk III. Free Flight Scale, by John Coker.

THIS DESIGN for the Kittyhawk was inspired by the success of the Free Flight scale Spitfire VB (oz1641) designed by Stan Cole, which led Cedric de la Nougerede into designing the P-51B Mustang (oz2322) published in Aeromodeller, June 1979 edition. The structure is very similar to both the above-mentioned models as I see no point in changing something which has proved to work so well.

For keen scale types the only deliberate deviations from the full size are an increase in dihedral of 3°, the tailplane is 25mm further aft than scale and the fuselage is slightly deepened to accommodate the flat bottomed section. In fact the model seems to be quite stable in pitch and so I wonder if moving the tailpane aft (which was done to counteract the long nose) was really necessary - let me know if you're brave enough to try it!

The original model flys quite happily on the DC Dart and 7x4 propeller as shown on the plan as I suspect that more power could cause problems - above all I think that light weight is of prime importance in a model such as this and so every attempt should be made to keep the weight down.

FUSELAGE: Begin construction by building the 12 x 3 mm crutch over the plan view, this can be cut from a sheet of 3mm medium balsa which saves money and ensures consistant hardness, When dry remove the crutch from the plan and add formers F2 to F9, the spines and the engine bearers. Fit the centre section ribs CS1, CS2, the LE, TE and then sheet the top of the centre section to inboard of where the fuselage sheet will meet it.

The fuselage should be sheeted next, this is not difficult if tackled patiently. Work in sections and moisten the outside of the balsa panel before glueing in position with PVA white glue. Use plenty of pins and rubber bands to hold the panel in position until set and let each panel dry thoroughly before going on to the next. Before cutting the balsa sheet make stiff paper templates to obtain the correct shape, several may have to be made for each panel, but it is cheaper than wasting balsa and the fitting of the balsa panel is then much easier if the shape is correct.

Considering one side of the fuselage only, the sheet panels are as follows and should be fitted in this order. Above the crutch, from F5A to T1 = one panel (do not cut out the aft side windows at this stage). From F5A forward to F2 and from crutch to centre spine = one panel. Below crutch from F5 to F9 and down to centre spine = two panels. The Joint line of these panels runs from the sharp corner of F6 to about halfway round the curve of F9 and should start as a sharp line at F6 becoming a continuous curve at F7 and on to F9. From F5 forward to F3 and from crutch to wing centre section = one panel.

The rear cabin windows may now be marked and cut out, the pieces of sheet cut away are then fixed in position so as to conform to the concave curve in former F5A, there should be a 1.5mm deep ridge around all of the window edge. The blocks and thicker sheeting around the nose are now added. Fit the lower block between F2 and F3 first then make up and fit the exhaust duct and finally add the side panels. The forward top block can also be fitted and the cowling assembly built up and carved to shape.

WINGS: The wing construction is quite straight-forward apart from the 0.8mm diagonal ribs which should be fitted as oversize blanks and then carved and sanded to shape so as to conform to the section of the main ribs. The wing panels should be built complete with their boxes taking care to build in the 2.5mm (3/32in) washout on both tips.

Make the wing tongues and assemble to the centre section dry, fit the wings and check alignment/dihedral etc. When satisfied add the 3 x 3 mm strips against the CS1's and securely glue the tongues in place and leave to dry thoroughly.

Mark the position of the slot for the wing retaining springs on the undersides of the boxes and then drill through the boxes into the wing lockplates, remove the wings and finish the location slots in the lockplates.

The underside of the centre section can now be sheeted and the air duct made from block and fitted. Fine surface polyfilla is useful for getting a really smooth blend between the blocks and sheeting, but only use the minimum as it is very heavy. Fit the 1.5mm trailing edge root fillets and then the acetate root fairings, these incidentally are only single curvature and so not as difficult as might be imagined - use very thin acetate or draughting mylar film, as when glued down all round they become very stiff, but are easier to fit if thin and flexible. Mark the fairing edge positions on both the fuselage sides and upper centre section sheeting and then having sanded the back to roughen them, glue in place using five minute epoxy. Finally make the forward part of the fairing from balsa block.

TAIL UNIT: Check that the negative incidence angle is correct and fit the tailplane. Fit T2 to the top of the tailplane ensuring that it is central and then add the two 1.5mm sheet fin/rudder sides, cement them to the fin post T1 and T2 also glueing the leading edges together. When dry slip in T3 and the soft block piece, with the aid of clothes pegs glue the trailing edges together. When dry round off the edges. Cut out trim tab and fit hinge, finally adding tailplane fairing blocks and sand to shape.

FINISHING: Give the entire airframe one coat of sanding sealer, sand with flour paper and cover using heavyweight tissue for the outer wing panels and lightweight on all remainder. After doping give the entire model one more coat of sanding sealer and again lightly sand with flour paper.

Paint with matt enamels and then seal with matt polyurethane varnish - seal the engine bay and exhaust duct well with a hard fuel proofer before installing engine. The canopy back to the front frame was moulded on the prototype and the remainder was made from flat panels with external framing from masking tape.

Panel lines and weathering are a must with this type of model which otherwise looks very plain, the lines and rivets can be drawn on with black ink and a draughtsman's pen or with a soft grade pencil. Weathering is a mixture of painted-on chips and highlights, together with dry-brush scuffing and pencil shadows on rudder/aileron leading edges etc - a few oil stains about the cowling and wheel bays using brown gloss enamel wiped on finishes the job. Don't be afraid to experiment, the golden rule is a little at a time, although if you decide that you have overdone it a wipe with a turps-dampened rag will take off the excess paint if you catch it before it dries.

There are many colour schemes for the Kittyhawk, but I chose not to use the more common shark's mouth, and went instead for a RNZAF scheme as on the aircraft flown by Flg Off GB Fisken at Quadalcanal - now I am forever being asked if it is a Hurricane!

FLYING: Do pick a calm day, try to find a ldng slope and having checked the CG, test glide the model noting its behaviour. The prototype needed about 2mm of up elevator measured at the widest point of the elevator TE and also needed an increase of washout plus some tip ballast on the starboard wing to correct a consistent tendency to drop its port wing. Do not try to get a floating near the stall type glide, a fairly fast, straight and stable glide suits the model better.

Only when the glide is satisfactory should power flights be attempted. Correct any further trim problems with thrust line adjustments aiming for a wide left hand circle under power. Having achieved a successful flight pattern you're now ready to go in search of the opposition, good hunting!"

Supplementary file notes

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