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CA-15 plans are available from: Airborne Plans Service for AU$74.80 (3 sheets) plus $5.00 P&H2. Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).
Plan No. 578 
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CA-15 picture

by Adrian Hopgood

The Commonwealth Aircraft Corporation's CA-15 was considered by some to be the "ultimate" in single piston engine fighter designs. In its time the CA-15 was the most advanced aircraft designed and built in Australia despite the fact that only one prototype was ever built and test flown.

Designed as a long range, high performance fighter for the RAAF, it incorporated advanced structural and aerodynamic refinements. Originally it was intended for the CA-15 to be powered by a large radial engine but plans were later changed with the aircraft finally emerging with a Rolls-Royce Griffon 12 cylinder V- engine, giving it a maximum speed of around 450 mph.

It first flew in 1946 with tests continuing on and off until 1950 when the project was halted. As with other post WWII piston engine fighters, the development of the CA-15 was scrapped with the emergence of the jet age.

The model

CA-15 picture

The model is 1/6 scale yet even at this scale it is a reasonably big model. Interestingly the wingspan of 1.8m is the same as the length of the fuselage.

Scale drawings were obtained from the Commonwealth Aircraft Corporations from which highly detailed plans for the model were designed and drawn by Rodde Heslehurst. The only deviation from true scale was the aerofoil; the laminar flow type was substituted for a semi-symmetrical profile better suited for models.

The prototype model is powered with a 45cc Zenoah motor which proved to be adequate, but anything less powerful may not get the model off the ground. Flow through cooling is limited even though I did not experience overheating. The 51/2 diameter aluminium spinner was custom made.

CA-15 picture

Retractable main undercarriage legs were made especially for this model by Custom Retracts in NSW. The units are modified from the standard CR400 retracts to suit the correct angle of the CA-15 undercarriage legs. The struts are made of chromolly tube with investment cast scissor links and steel offset yoke. These units are pneumatically operated and are superbly engineered. Anyone wishing to obtain a pair of legs for the CA-15 can do so from Custom Retracts. The tailwheel unit which is also retractable is available commercially.

The model was entirely covered in metal using litho plates obtained from a printing factory. Although time consuming the end result complete with rivets and panels is astonishingly scale like.

All up weight of the model was 24lb, pretty heavy for a model with not that much wing area. A permit to fly the CA-15 was necessary being well over the 15lb (7kg) limit.

Building the CA-15

A project of this type should only be attempted by experienced modellers.

As previously mentioned the weight of this model could work out to be rather heavy, therefore selection of light timber throughout is advisable. Also it may be worthwhile to hollow out the plywood formers slightly more than what is shown on the plan. Any weight saving will help.

Only a brief description of building will be given as experienced modellers should be able to proceed independently.

The wing

CA-15 picture

Cut out all wing ribs carefully noting materials used for each. Prepare the leading edges, spars, trailing edges and wing braces ready for assembly.

Build up each wing panel over the plan in the conventional manner with gluing of ribs onto main spar, then adding the false leading edge, trailing edge spars, top spars and webbing. Check for symmetry. When dry lift the basic structure off the building board and join the two wing panels together with the dihedral brace. Cut away a section of leading edge between W4 - W5, then glue the hardwood undercarriage mounting blocks into place.

At this stage the ailerons and flaps can be built up and fully sheeted. Also skin the top surface of the wing with pre-joined 1.5mm balsa sheets.

Now install the retracts into the wing, cutting space out of the inner ribs as required to make fit.

Finally complete the wing structure by skinning the underside surface, then adding the leading edge and wingtips. Temporarily fit the ailerons and flaps onto wing. Sand the wing smooth. Add the wing locating dowels.

Tail surfaces

Build up the framework with ribs, spars, leading and trailing edges. The tailplane is joined with the dihedral brace, then skin all the tail surfaces with 1.5mm balsa skin.

The tailplane is set into balsa blocks which become part of the rear fuselage. The fin is glued on top of these blocks. Trial fit the rudder and elevators with hinges.

Fuselage

CA-15 picture

Before commencing fuselage establish how your engine will fit and make adjustments to plan to suit.

Cut out all the plywood formers and crutches. Hardwood bearers run from the nose ring well into the fuselage but engine should be mounted onto the firewall.

Assemble the cowl formers and middle fuselage formers onto wing seat crutches, then add stringers and spines from front to rear fuselage. A fuselage jig would be helpful here but sighting along the spine and fuselage datum line is how I did it.

The underside radiator is built up concurrently with the fuselage frame up. Skin the fuselage with 3mm balsa sheet rolled around the framework in sections, or use planking as recommended on plan. The underside of the engine cowl is removable. The exhaust pipes from brass tubes were made to function as cooling ducts.

Fit the wing onto the fuselage. Drill and tap through the mounting blocks for the wing bolts. The radiator is removable for access to wing.

Install the retractable tail wheel unit, and make up the elevator linkage.

The canopy is trimmed to size and cockpit frame made up. I chose to make mine a sliding canopy for scale effect.

Servo installation

The CA-15 has 11 servos to cover all operations. Servos for control servos should be heavy duty types as loads on them will be considerable. The rudder and elevator servos are positioned under the tailplane with access through a panel on the side of the fuselage.

The aileron and flap servos are installed inside the wing.

The undercarriage legs are operated pneumatically with a servo switching the air on and off. Separate servos operate each of the undercarriage and tail wheel doors. A retract sequencing system would be desirable on the CA-15 as opening or closing the undercarriage doors by manually flicking different switches on the transmitter is not just an open and shut case!

Covering the model

CA-15 picture

Being fully sheeted the model lends itself to a number of possibilities for covering. Plastic films may be used or the model can be painted. There IS only one colour to use - that being bare metal! For that reason I went the whole hog and covered mine in aluminium litho plate, an extremely time consuming process but very rewarding.

After polishing the metal skin roundels and other symbols were painted on to finish off the model. Balancing the model to correct C of G required an additional 1lb of lead in the nose even with a rather heavy Zenoah engine up front.

Flying the CA-15

The CA-15 is a real showpiece model which will attract a crowd wherever it flies, therefore it should been treated with respect and not flown in "hot dog" fashion as if it were a Sunday sports model.

All that hard work could be lost in an instant!

The model flies quite fast, very quick in fact. Take off runs will be long, allow plenty of speed to build up first before pealing away, even then climb outs must be extremely gentle or you could risk stalling and snap rolling into the ground.

CA-15 picture

Once flying speed is established though the CA-15 is very controllable with no vices. No changes in trim whatsoever were necessary. It tracked true and positively whatever direction it was given.

The model slow rolls beautifully and will perform other basic aerobatic manoeuvres such as stall turns, barrel rolls and with speed build up very wide loops, and of course spin. Do not attempt anything outrageous. This model easily becomes ballistic if out of control.

Stately circuit flying and high speed fly passes are more in character with this type of model and will help ease the shaky fingers at the controls.

The CA-15 power glides well, so far the engine hasn't stopped. The model should glide OK provided speed is kept up. Be careful not to allow the speed to wash off to the point where controls become mushy. Landing is straight forward and flaps help to lower the approach speed.

On one occasion the retracts failed to come down due to the air tube becoming twisted, so it was in for a belly landing with flaps up. Other than a broken prop and a little gravel rash on the underside the CA-15 was undamaged.

All in all the CA-15 has been a very rewarding project. With the metal covering it looks a "million bucks" and flies nicely too. Having put so much work into it though I will only be flying this model on special occasions.


SPECIFICATIONS CA-15

Type: 1/6th scale model Wingspan: 1.8 metre Length: 1.8 metre Weight: 10.8kg Engine: 45cc 6-7 channel radio control required

CA-15 plans are available from:
Airborne Plans Service
AU$74.80 (3 sheets) plus AU$5.00 P&H2
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).

Plan No. 578

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This page was last modified on the 19-May-02