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Introduction

Strange how things work out. During the day at work I kept thinking I must start building another model, I had itchy hands. For a long time I had been planning to build a Nomad and had decided to start that night.

Upon arriving home from work my daughter informed me that John Rogers from Airborne had rung re: building another plane. I immediately returned his call and was asked if I was interested in building a sport scale Winjeel Trainer. I jumped in boots and all, because in my early years I used to sit in a boat fishing on Port Phillip Bay while watching the student pilots flying over head practising their aerobatics and wishing I was up there with them.

The RAAF requested in 1948 for a piston engined aircraft to replace the ageing Tiger Moth's and Wirraway's. The Commonwealth Aircraft Corporation responded with their own designed CA-22 later call the "Winjeel" which is an Aboriginal name for "Young Eagle". The first two prototypes were test flown in 1951 but failed the RAAF requirements mainly because they would not spin properly. So the CAC redesigned the tail section by moving the fin and rudder forward, enlarging the wing fillets, improving the canopy, and repositioning the engine which solved the problem.

The RAAF was happy with the new version designated CA-25 and placed an order for sixty two aircraft late in 1951 of which the first were delivered in September 1955. The "Winjeel" served the RAAF as a basic trainer till 1975 when it was replaced with the CT4 air trainer but some CA-25's were kept in service till late 1994 when it's role was replaced by the Pilatus PC-9. The Winjeel served the RAAF for almost 40 years as a basic trainer.

The aircraft I have decided to replicate is A85-432 which is now located at the Oakey Army Aviation Museum in Queensland. It was delivered to the RAAF in August 1956 and is still airworthy.

THE MODEL

So much for the history lesson now to the nitty gritty of constructing the model.

The Winjeel is not a beginners model but it is an ideal project for a first scale model for builders with a bit of experience.

A product of Airborne's in house plans department the model Winjeel retains true to scale outlines but simplified structure including use of strip ailerons makes it a sport/scale type.

My waiting time was short lived as the plans and materials arrived three working days later by post. After studying the plans and comparing them with original drawings and photo's my enthusiasm was boiling over, I decided to kit as much of the parts as possible to enable the assembly of each section to be assembled quickly and as smoothly as possible.

FUSELAGE ASSEMBLY

Place the 3mm balsa fuselage sides on a flat surface inside up, position and glue 1.5mm ply doublers with PVA glue, next position and glue 3mm x 6.5mm spruce longerons with PVA glue, then position and glue the rear 3mm balsa doubler.

I use a heap of lead sinkers to hold glued sections flat until glue sets, making sure you have a pair of sides not identical sides. Also assemble formers F7 and F8 using PVA glue. We will now assemble firewall come tank housing consisting of firewall F1 two 3mm ply sides and two 6mm ply top and bottom, after checking down and side thrust is correct glue this assembly together with 5 minute epoxy.

Depending on your motor and mount selection (I chose a Saito 65 four stroke on soft rubber mounts). This box section has to have correct distance (to accommodate motor and mount) between front of cowl and former F1, I slid this box section back into formers F2 and F3 to give correct clearance between propeller and front of cowl. Once correct location has been identified glue box section into formers F2 and F3 with 5 minute epoxy.

Carefully mark the locations of all formers on the inside of both fuselage sides.

If you have access to a fuselage jig it will make the next stage of fuselage assembly very easy. I found I could completely assemble the fuselage without glue to check for fit and trueness, when satisfied with all adjustments I could then remove completely and then start final assembly with glues. 5 minute epoxy was used to glue formers F2 and F3 to fuselage sides. When epoxy on formers F2 and F3 has cured glue in F4, F5, F6, F7, F8, F9 F3a and rear of fuselage sides with PVA glue. Recheck assembly for trueness.

I decided the best way to fit the removable cowl by using 4 x No.6 x 1" caphead bolts through the four corners of former C4 to four blind nuts fitted into the four corners of former F2.

Attach former C4 to former F2 with bolts etc. with washers the thickness of a fine saw blade between C4 and F2, assemble and glue C4, C3, C2 and 5mm square stringers using 5 minute epoxy, when cured fit 3mm balsa sides to cowl. Fit 5mm square stringers to front deck, the cowl top and front deck can now be sheeted with 3mm balsa. I deviated from the plan by using solid sheet instead of 6.5mm strips, when 3mm sheet was steamed it bent around formers without effort.

When glue is fully cured remove fuselage from jig, remove four caphead bolts and washers. Carefully run fine saw blade between C4 and F2 to cut outer sheeting, when completed refit four caphead bolts and spacer washers through cowl into fuselage and refit fuselage back into jig upside down. Fit glue 5mm square stringers to bottom of fuselage, then sheet with 3mm soft balsa sheet.

When dry remove complete assembly from jig and with a fine saw cut remainder of sheeting between cowl and fuselage. At this stage the spacer washers can be removed and cowl fitted flush onto fuselage.

Fit tailwheel assembly to fuselage, I chose to have a steerable tailwheel by using flexible auto speedo cable between tailwheel and rudder. Refit fuselage into jig right way up and fit tailplane and fin as per plan checking to make sure it is square. Fit rear deck 5mm square stringers and 3mm sheeting Canopy frames two by CF1 and CF2 can now be fitted. We will leave the fuselage at this stage and start on the wing.

WING ASSEMBLY

This will be assembled in three sections, centre section and two outboard sections.

Cover plan with grease proof paper or Glad Wrap. Cut two 6.5mm square spruce spars 37.5cm long, lay bottom spar on centre section of wing plan and hold in position with weights or pins. Position and glue ribs W1, W2 and W3 in their correct positions then glue on top spar. Fit and glue 1.5mm balsa shear webs with the grain vertical. Fit and glue 6.5mm balsa trailing edge spar. Fit and glue 6.5mm balsa leading edge between two W1 rib's. Fit and glue 6.5mm balsa leading edges from W1 to W2 and W3. (Do not glue to W3). When glue has cured cut through ribs flush against rear face of spar. Width of saw cut to equal thickness of dihedral brace (DB2). An ideal method is to use several hacksaw blades tapped together at both ends to equal the thickness of DB2. Glue brace DB2 to main spar then glue ribs W1, W2 and W3 to DB2. Check alignment.

Fit balsa fill blocks between ribs W1 and W2 to support wing bolts. then glue 1.5mm balsa top centre section sheeting. Fit and glue hardwood undercarriage mounting blocks, and glue 6.5mm balsa triangle supports for undercarriage mounting blocks. Fit and glue 6.5mm hardwood wing locating dowels.

OUTBOARD WING SECTIONS

Cut four 6.5mm spruce spars 53cm long. Place one over plan and hold down with weights or pins, position and glue ribs W5 - W11. Using dihedral angles position and glue W4 into position, position and glue 6.5mm square spruce top spar, position and glue 6.5mm balsa aileron spar to ribs W4 through to W11. Fit and glue 6.5mm balsa leading edge to ribs W5 through to W11 but do not glue to W4. Fit and glue 1.5mm balsa shear webs with vertical grain between all ribs. Fit and glue 3mm balsa corner gussets. Fit and glue top 1.5mm balsa strip also 1.5mm sheeting between W4 and W5. Now repeat the above steps to assemble the opposite side outboard wing. Next cut slots in ribs W4 flush with rear edge of main spars to accommodate main spar dihedral brace DB2.

The three sections of the wing can now be mated and glued together checking for correct alignment and dihedral.

The front ribs W3 and W4 need to be trimmed to allow the fitting of dihedral brace DB1 which can now be glued into position.

The decision now has to be made whether to use outboard mounted aileron servos or centre mounted servo and bellcranks. I chose the latter and mounted bellcranks behind mainspar in between ribs W4 and W5. Now is the time to make provision before underside 1.5mm balsa sheeting is fitted.

Check for correct washout before removing construction tabs from ribs. If all OK remove tabs and fit and glue underside 1.5mm balsa sheeting as per plan. Inboard sections of outer wing panels can also be sheeted as well. Fit and glue balsa wing tips.

Main wing can now be trail fitted to fuselage. Check and adjust fit. Also check and adjust main wing incidence.

Cover top centre section of wing with Glad Wrap and refit wing. Now glue in 1.5mm balsa wing root fairing with grain running at right angles to fuselage, fit and glue in fillets F4a, F5a and F6a. Top of wing fillet 1.5mm balsa sheet with grain running length ways from F4a to rear of wing fillet. I chose to use Micro-fill balsa filler from F4a round to front of wing. At this stage we might as well finish the engine cowl. Build up two layers of 12.5mm balsa to form C1 then glue to front of cowl. Sand to shape inside and out. Next carefully mark and cut out engine cooling vents on cowl sides, then fit C5 and sand to shape. Dummy air intake for oil cooler and carby can be either shaped from solid balsa or fabricated from scrap sheet. I chose to use scrap 6.5mm balsa. Once shaped it is then glued to cowl. At this stage it might pay to fit engine. Then fit cowl to give engine clearance and cooling and exhaust outlet.

TAIL FEATHERS

The plan shows these are cut from soft 9.5mm sheet balsa for simplicity. I chose more scale like feathers because the original was fabric covered. I cut the rudder and elevators from 3mm soft balsa sheet,, glued 3mm x 9mm balsa strip on top and bottom leading edges, cut 3mm square balsa strips and glued these top and bottom where ribs are. When dry sand the airfoil shape into rudder and elevators.

Fit 9.5mm balsa fillet to front of tailplane to fuselage, sand tailplane to form correct airfoil section. The fin can also be sanded to shape.

The ailerons are cut from 9.5mm balsa then shaped for correct fit. Be sure to allow for washout when shaping ailerons. Fit trailing edge to centre section panel.

Basic construction is now complete. Finely sand fuselage and wings and prepare for final finish. I chose silver grey Solarkote covering for wings and fuselage.

Prepare all balsa surfaces with Balsa Loc or similar product to help adhesion of covering. Apply covering as per manufacturers instructions.

Install all control surfaces. Install undercarriage, fit fuel tank, motor and radio gear. After cockpit detail has been fitted canopy can be glued into position. At this stage my canopy is only temporarily fitted and held in position with black and silver duct tape because I haven't finished all cockpit detail.

Control surface throws are as follows:
Rudder Left 30mm Right 30mm
Elevator Up 15mm Down 15mm
Ailerons Up 7mm Down 5mm

FLYING THE MODEL

After checking all systems I decided to start the motor (Brand new never been run). Very soon the Saito 65 was purring like only a Saito can. Taxiing around the yard showed very good ground handling characteristics. So out to the strip for a test flight and shakedown.

After doing range check the Winjeel was refuelled and started preflight check was again completed taxiing trails started. Ground handling was excellent so a high speed run down the runway was commenced. with all systems go the Winjeel was starting to float begging to become airborne, so a bit more power was applied. After a good smooth lift off and steady climb out it started to bank and turn left, so three clicks of right aileron and two clicks of right rudder had it flying level and in a straight line. There seemed to be oodles of power so the throttle was reduced to half power. Flight seem very predictable with no apparent vices, control surfaces were very effective. Loops, Cuban eights and rolls very very smooth and predictable.

The Winjeel was then taken high and throttle was reduced to idle to test stall characteristics. No problems so now to test spin characteristics. Spin was good and when controls were released spin stopped within a quarter of a turn. No wonder the full size Winjeel was such a popular trainer.

Next thing is to try for a landing with minimum power, it floated down smoothly on main wheels then the tail settled down beautifully. I was over the moon as the Winjeel performs just as well as it looks. A real crowd pleaser.

SUMMARY

A very rewarding project, even for modellers with minimal experience with scratch building.


Look for these exciting plans in future editions of Airborne.
F/A-18 Hornet, F-11 & Red Arrow 'Hawk'


CA-25 Winjeel plans are available from:
Airborne Plans Service

AU$52.80 (2 sheets) plus AU$3.00 P&H2
Plan No. 628

Moulded Canopy AU$33.00 plus AU$6.00 P&H2

Click here to order this plan

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This page was last modified on the 21-May-02