The Airworld kit is an excellent base for a World Championship winning scale model or very detailed Sports Scale model. This kit has secured 1st and 2nd place in the last two World Jet Masters competitions.

The kit is fully moulded, glass/balsa/glass construction using the highest quality materials. We supply the kit with a CNC cut woodwork set and 2.7LTR fuel tank.
Epoxy is used for all moulded parts, so as consequence epoxy glue should be used for all joints. We used a combination of Pacer/ZAP epoxies and BVM Aero epoxy for construction of our demo model.

Only the rudder requires hinging, the ailerons, flaps and elevators are live hinged in the mould guaranteeing perfect alignment (and saving lots of time!)

No accessories are supplied with the kit. We used BVM carbon control horns on all surfaces. The Rudder and gear doors were all hinged with std 307 Robart hinge points.
The wings plug in on a single aluminium tube, the sockets are factory fitted ensuring perfect alignment. The tailplane halves can also be made removable or permently glued in position.

Seven servos are required for the main flying controls, we used 2x JR 8231 on ailerons, and 5 x JR 3301 “wing” servos on the remaining controls.

You then have the choice of a standard servo for nose wheel steering. Depending on the retract/gear door sequencer and wheel brakes you use you may use servo operated valves to open the gear doors and retract the U/C . Our demo model uses a single JR 368/361 servo to control the retract and gear door sequencing via two Ultra Precision Valves. Motors & Rotors can supply a diagram of how to connect these valves. The wheel brakes also use an Ultra Precision UP6 brake valve which is servo operated, again we used a DS368 or DS361.

We used Spring Air 701 retracts fitted with modified Eurokit trailing link oleos. Airworld supply HAWE air up/down sets when bought from them.

The nose wheel is a Sullivan 2” item and the mains use 2 ¾” 66mm dia wheels fitted with brakes. It is possible to use Intairco wheels.

The gear doors are opened using UP 5/16” Air Rams-¾” on the nose and 2-off 1”on the main doors.

The kit come supplied with inlet ducting only. We recommend the optional use of a bye-pass duct for the turbine-We used a Steve Brett duct made by Geoff Ferguson. Airworld also offer a bye-pass with spun aluminium rear cone.

Our tail pipe is a 3” diameter, straight single walled stainless steel tube that we covered with “Milton” Ceramic cloth.

1/7th Scale pilots can be sourced from Pete’s Pilots.

All the above parts are available from Motors & Rotors.

Our demo model is powered by a Graupner JetCat P80 turbine which provides ample power. Most of the flight is throttled back, using the P80 we achieve 10 minute flights from the 2.7ltr tank.

We have found that a Gyro fitted to the rudder removes any “fishtailing” that is present during gusty conditions. We did not fit a wing gyro mentioned in the German instructions and didn’t find it necessary.

The flying qualities of the L-39 make it a perfect first scale jet model. Take off tracks straight even without the gyro fitted and landings “stick” due to the three trailing link oleos.

The kit is supplied in six main moulded components, plus five moulded double skinned gear door pieces. A wood set, “Conformal” 2.7ltr fuel tank, a moulded canopy frame, and clear canopy glass and wing tip light covers. A sheet of ABS mouldings are also supplied with scale control ram covers.

Construction additional notes

It is possible to finish the wings and tail plane halves before starting work on the fuselage. Make all cuts with a fine toothed razor saw, this won’t damage the finished surface. We recommend using Permagrit tools for all sanding/filing.

Wings

Cut out the plain area marked out on the wing underside where the main retract units fit. This area corresponds to the supplied leg cover doors supplied. The retract mounts are factory fitted. We drilled and tapped the plywood to retain the retract units. Springair units push hard up against the ready cut opening.

Flap servo mounts are part of the retract mounting plate, with a factory cut hole for a JR3341/3301 servo.

Access to this area is via the lower wing skin. Access hatches for this and the aileron servos are cut using a fine tooth razor saw. The hatches are best retained with M2 x 6 CSK screws. Holding tabs of 1.6mm plywood are glued inside the corners of the openings and tapped for the M2 screws. The positions of the openings can be judged from the photos in the German instructions.

For full flap movement it maybe necessary to sand back the wing/flap hinge line overhang on the lower skins to allow sufficient movement. The root rib will also require easing in the full down flap position.

The aileron servo can be mounted in a cradle or glued directly to the wings top surface after being wrapped in masking tape.

BVM Carbon control horns were used on the flaps and ailerons. Linkages to the flaps and ailerons were made from 2mm pushrod wire. The flap linkage is designed to be external. It is possible to get a linkage inside the wing.

Tailplanes

Each tailplane half has a JR3341/DS3301 servo fitted from the root. Cut through the root rib with a sharp scalpel, removing an area equal to the size of the servo including the mounting lugs.

The servo arm protrudes through the lower tailplane skin and is connected to the elevators with 2mm pushrod material. We glued hard wood blocks in the tailplane halves so that the servos could be screwed in position.

Each tailplane halve is joined with the two light weight stainless steel tubes supplied.
A corresponding opening is cut in the fuselage side to allow servo lead access.

Fuselage

The first job on the fuselage is to remove the gear door openings; again the marked plain area is very accurate. The moulded gear doors supplied are used as a template to guide you during this work.

The hatch for turbine access is cut next, again using a fine toothed razor saw held against a straight edge. The size of opening we made differs from the size show in the German instructions.

Measuring back from the rear of the gear door openings approx 37mm there is a line of rivets, this is the front of our hatch, measure back 300mm, and this is the rear. Once the hatch has been cut-out we recommend that you attach fixing tabs (6) and re fix the hatch using more M2 x 6 CSK screws. This allows the hatch to be screwed back in position while the formers are being glued to guarantee the fuselage keeps its shape.
Next we recommend you fit the wings to the fuselage so that these can be used as a guide for aligning the tail plane halves and the vertical fin. The fuselage moulding seems very accurate so the wing root fairings on the fuselage can be used as basic alignment guides.

Open the main wing tube sleeve opening in the fuselage enough to allow a small amount of adjustment before the fibre glass tube is epoxied in position.

The main wing joiner is an aluminium tube, the rear wing spar is supplied as an 8mm stainless tube.

We set the wing roots flush with the fuselage root fairings and found the model fly’s straight. The dihedral is set by the factory fitted wing tubes.

We hold the wings to the fuselage with two M4 studs glued in the wing roots and M4 wing nuts accessed through the main gear doors. This is a neater solution than the spring shown in the kit instructions.

Once the wings are fitted, the tailplane halves can be dealt with next. If the tailplane halves are to be made removable, it is advisable to bond the tubes to the fuselage. We permanently fixed the tailplane halves on our model.

The vertical fin has a balsa spar bonded into the rear edge of the fin, recessed approx 6mm inside the back edge. This allows for the scale rudder hinge set-up.

Three Robart 307 hinge point hinges are used. Holding the rudder up to a light will give an indication as to the position of the factory installed woodwork. The hinge pivot line should align with the finish of the radius on the rudder/outer skin. Bonding the hinges into the rudder early in the construction does not interfere with any later work required. Ensure you allow sufficient swing on the hinges for the stated rudder movement.
The balsa fin spar has a plywood support glued to the lower wider end to act as a fixing former-The bond of this is critical to the rigidity of the vertical fin. The Rudder servo mount fixes to the front of this spar, a JR 3301/3341/3728 wing servo is used coupled with a short servo arm of approx 10mm radius. The ply plate has an offset hole to allow horn clearance. The rudder horn can be on either side, depending which way up you put the plate.

The next job is cutting the inlet access area from each side of the fuselage. The minimum lip is left around the fuselage edge to allow for clearance on the inlet Y.
The Y is positioned using the rear support former and the inlet covers.

Sand/file the covers to fit the fuselage before fitting the inlet Y. Tack glue the inlet covers in position and then work on the fit of the Y piece. The actual position of the Y rear former is only determined once the Y fits the inlet cheeks. The two Z shaped formers are fitted to support the wing joiner tube.

The “open” horseshoe former position is not critical and can simply be fitted where it is found to fit the shell. This will be towards the rear of the motor hatch opening.

The nose leg former position can only be exactly determined by trial and error. Due to the slim nose and forward retracting nose leg the former has to lean back slightly. The nose leg door closes with the leg up and down, requiring that the leg moves back into the fuselage section when extended.

Hinge the gear door with two Robart 307 hinge points mounted with the hinge pin centre flush with the lower fuselage skin. These are bonded in with the hinges folded 90 degrees in the gear door closed position.

The nose gear door is opened with a ¾” stroke U.P. ram mounted approx half way down the nose gear door. The actual position is determined by clearance of the nose wheel fork. Make a half former to mount the ram onto on the fuselage side.

The RX pack (2000mAH) is mounted on the opposite side of the nose again on a structure you make.

Hinge the main gear doors with two Robart hinge points on each door. Again the hinge centre on the lower fuselage skin to stop any off-set movement. The doors are operated by UP 1” stroke rams. The lower ram fixing and pivot is attached to the rear Y inlet support former.

Both the nose and main door horn attachments are cut down servo arm stars.
Use Sullivan control clevis, as these matches the UP air ram thread.

The L-39 needs as much weight built into the nose of the model as possible, so planning the installation with everything as far forward as possible in beneficial. We ended up with 5oz of weight in the nose of our demo model.

The fuel tank mounting lug is glued to the front lower edge of the tank. The rear of the tank sits on the wing spar tube. The lug is screwed to a rectangular plate fixed across the fuselage with a single M4 screw.

Our canopy frame is held in position with a carbon front peg and rear BVM hatch catch. Ejection seats can be made from light ply.

Parts list. Extras needed/used.

2” Sullivan nose wheel.
2 ¾” Main wheels fitted with brakes.
2 packets BVM Carbon control horns.
9 Robart 307 hinge point hinges.
1 Ultra Precision ¾” stroke 5/16” Ram.
2 Ultra Precision 1” stroke 5/16” Rams.
1 UP 1 Air valve.
1 UP 5 Spring Air speed control valve.
1 UP 6 Proportional brake valve.
1 pack of Robart air tube.
4 Robart quick release connectors.
22 M2 x 6 CSK Screws.
2 M4 x 30 screws and M4 wing nuts.
1 pack Sullivan snakes for clevis units.
BVM Hatch Catch.
Assorted screws and washers.