Welcome to Pt.2 of our ongoing low-wing sports/aerobatic ARTF R/C model assembly and flying adventure. Are you ready to get to grips with a beautiful backside and a nifty nose? You are? Good! Lets get going
Before gluing the horizontal tailplane and vertical fin in place, cut away the Monokote from over the fuselage horizontal stabiliser (stab) openings and the rear-end control rod exit holes with a sharp scalpel. Its recommended that a 3/32 flap of covering be left within the top edges of the fuselage openings to act as joint-seals when the horizontal stab is permanently settled. I didnt bother doing this, opting instead to use separate 1/2 strips of self-adhesive Solartrim to achieve the same junction-smoothing effect at the final finishing stage.
Bolt the wing to the fuselage, ensuring that its centred in plan-view by taking measurements from each aileron trailing edge to the stern-post centreline. Test-fit the horizontal stab through the fuselage openings and slide it about laterally until the trailing edge measurements are equal either side of the stern-post. When the dimensions are equal, stick a pin through the fin slot into the stabs trailing edge and fuselage structure to hold it in place.
Push a stout modelling pin into the middle of the firewall top edge using the pre-indented (Biro line-extended) firewall centreline as a guide. Tie strong non-stretch thread around the anchored pin and cut the thread in-situ with scissors 12 longer than the fuselage itself.
Loosely fold a piece of paper masking tape over the tailplane end of the thread to form an alignment flag and draw an arrowhead on it in Biro or fine-point black felt-tip pen. Slide the masking tape along the hand-tensioned thread until the arrowhead points to one trailing edge corner of the horizontal stab. Swing the thread over to the same position on the other trailing edge corner of the stab and note the dimensional difference relative to the arrowhead mark.
Rotate the stab slightly in top-view and tweak the alignment flags position until it is no longer necessary to move the masking tape arrowhead reference point to obtain the same dimension on either side. When this position is achieved the stab is centred in plan-view. Mark the fuselage outline on the stab centre section top and bottom with a fine-point black felt-tip pen.
Remove the stab and cut 1/16 inside the marked fuselage outline top and bottom with a super-sharp scalpel. Use only enough Monokote-cutting force to slice the covering and not the balsa wood itself. Heat-seal the cut covering edges in case the slicing process disturbed them.
Mix up some one-hour epoxy and evenly coat both fuselage opening edges and the stab centre section top and bottom. I suggest that the stab be stuck in place using a different technique to that recommended in the manual. By first cutting away a small chunk of fuselage from behind the stab-engagement openings, it is possible to push it in from behind. This is a much less messy/worrisome procedure than the lateral insertion route advocated. On my model, the excavated fuselage chunk was replaced when the stab was glued solid; Solartrim strips subsequently disguised the area.
Ensure that the stab is re-aligned with the previously-established fuselage marks and wipe away excess epoxy with kitchen towel and meths. If possible, use a Robart foam carrying stand (available in all good model shops) to support the model as you need to check the front/rear as well as plan-view stab/wing alignment before the glue sets. If you dont have the Robart stand, make sure that you have plenty of viewing room so that the stab/wing relationship can be easily checked from about ten-feet away. Get the stab level relative to the wing in head-on view by inserting small scrap balsa wedges into the fuselage openings above or below the stab centre section as required. Allow the glue to cure and then fit the fin.
Anchoring the fin is simple! Dry-fit it in its slot and mark the fuselage lines either side with the black fine-point felt-tip pen. Remove it again and scalpel-cut the covering away 1/16 below the marks, heat-sealing the cut covering edges if needed. Remove the pin and thread paraphernalia from the stab-alignment exercise and mix up a small dose of one-hour epoxy. Feed the glue with a cocktail stick into the fin slot and spatula it on to the bare wood fin base. Lovingly insert the fin into its slot and wipe away the squeezed-out adhesive with the kitchen towel and meths.
The Mk. One Eyeball is fine I find, for setting the fin relative to the fitted horizontal stab and wing. Use modelling pins or masking tape to keep the fin sit straight if needed. Allow to dry and relish the sight of your rapidly coming together hot ship!
HINGE AND BRACKET
Before attaching the large rudder, the steerable tailwheel unit is mounted on the lower rear fuselage. Insert the tailwheel wire through the alloy bracket, then bend the wire through 90-degrees with vice-grips where recommended so that it can engage in the rudder. Make sure that the bent wire is in line with the tailwheel. Tweak if necessary to achieve a straight relationship.
Temporarily position the tailwheel assembly (the wheel itself comes pre-fitted) beneath the lower rear fuselage and mark the location of the two mounting screws. Remove the tailwheel assembly, drill two 1/16 holes in the ply plate and wick some thin cyano in to strengthen the screw purchase. Screw the tailwheel assembly down tight when the cyano has cured.
Test-fit the rudder and mark where the tailwheel wire will enter through its leading edge; make certain that this line is at right-angles to the rudder hinge-line. Carefully drill into the rudder leading edge, cautiously monitoring that the drill doesnt go crooked! Take it easy here; its better to start undersize and work up to the required hole size. Groove the rudder leading edge from its bottom edge up to the drilled hole with a piece of 1/8 diameter sharpened brass tube; this allows the upright portion of the tailwheel wire to recess within the rudder leading edge when its bent part engages through the hole.
Cyano the hinges into the rudder only using the procedure advocated for the aileron attachment last time. Sparingly coat the tailwheel wire where needed with half-hour epoxy. Use a cocktail stick to get the adhesive into the rudder leading edge groove and hole. Feed the rudder onto the projecting tailwheel wire and gently slot the hinges into the fin trailing edge. When the rudder/tailwheel wire alignment is spot-on, zap the hinges solid in the fin trailing edge. Wipe away excess epoxy with kitchen towel and meths and allow to dry.
Zap the hinges into the independent elevator halves and then mount em on the stab trailing edge. Zap the mounted elevators in-situ when accurately aligned, as described for the ailerons last month.
Your rear-end is now fairly well sorted, so remove the wings and lets turn our attention to some up front behaviour!
The engine can be mounted at 45-degrees or fully inverted. I chose the latter configuration as it entails the least amount of cowl material removal.
Cut the engine mount-positioning paper template from the back cover page of the assembly manual and temporarily tape or paste it to the firewall using the factory-indented (Biro-extended) bulkhead marks as a guide. Drill through the template where shown; this gives the correct bolt hole spacing for anchoring the adjustable engine mount to the firewall. Remove the template and lightly clamp the mount halves to the firewall using the four anchor bolts provided.
With the mount halves making a sliding friction-fit on the firewall, place your chosen engine on the mount arms and adjust to suit the crankcase width. When the engine fits snugly, centre the pre-indented tick marks on the mount with the factory-scribed firewall marks. Now fully tighten the mount-retaining anchor bolts.
Slide the engine forward or back on the mount so that the prop rear face is the prescribed distance from the firewall. Get this dimension right as it sets up a tidy spinner/cowl gap when the time comes. When the mounting distance is correct, hand-hold the engine steady and mark through the holes in the engine lugs onto the mount arms with a stout modelling pin or a specialist hole locator device available in the better model shops. Whatever hole-marking method you use, make sure the initial marks are centred with the holes in the engine lugs. Check several times that youve got em accurate before drilling through the mount arms.
I attached my Irvine 53 with large self-tapping screws for a totally satisfactory grip, but you could tap the drilled holes to suit the supplied bolt thread if you have the necessary equipment and skill.
If your engine is short (for example, an O.S. 40LA), you may have to glue the optional 1/2 thick scrap ply mount-spacing plate to the firewall with fifteen-minute epoxy before the mount goes on. If this is the case, youll need longer anchor bolts to compensate for the increased firewall thickness.
TUBE AND TANK
The throttle linkage is now installed, the tank bay is fuel proofed and the fuel tank is put to bed. The throttle linkage is a wire pushrod running in a plastic outer tube. Drill the firewall to suit and roughen the outer tube with 180-grit glass-paper where it will pass through the firewall and former F2 at the rear of the tank bay. Insert the outer tube through the former holes and adjust its fit so that it projects beyond the firewall by 1/2 while its rear end extends into the radio bay back to where the servo tray will sit. Zap the outer tube solid with medium cyano or fifteen-minute epoxy applied with a cocktail stick. If using epoxy, rotate the tube around in-situ to spread the applied adhesive in a pleasing, conical shape.
When the tube-holding glue has set, fuel proof the tank bay interior as best you can with Clearcoat applied with a long-handled 1/2 flattie artists brush.
Assemble the fuel tank as directed. The three metal tubes are first passed through and aligned in the rubber bung, but dont tighten the bung-compressing screw until the bung and tubes are correctly inserted in the tank. The tubes arent pre-bent so its easy to kink em if one isnt careful! To save unnecessary hassle, I simply used pre-bent tubes from an old tank. Note that both the filler and vent tubes are best inserted with the bend facing upward at first, otherwise they wont go through the tank neck opening. You can rotate the fill tube inverted with pliers as suggested when its fitted, but I left both the filler and vent tube facing upwards with no ill effects. Tighten the bung-compressing screw securely when the tube fit is correct.
Push the tank into place it goes in easily. The suggested scrap balsa crosspiece behind the tank is necessary to prevent it migrating backwards. Before adding the crosspiece, pack the tank bay with rigid foam to stabilise the tank and minimise the fuel frothing effects of the engine vibes.
The servo installation and throttle, elevator, rudder pushrod hook-up happens when the ply servo tray is glued in place with medium cyano, aliphatic resin or half-hour epoxy. However, well leave that task until next time and concentrate on the cowl for the time being.
Draw a vertical line 1/2 behind the firewall each side of the fuselage with the black fine-point felt-tip pen guided by a set square. Test-fit the cowl onto the fuselage with the silencer removed. Push the cowl all the way up to the lines each side and centre the cowl ring with the engine crankshaft. Temporarily fitting the prop and spinner aids the alignment process. Aim for an even-looking 3/32 gap twixt the spinner backplate and the cowl front face.
Visualise where the carb sits inside the cowl and mark the exterior GRP skin with the black fine-point felt-tip pen freehand around the area in preparation for the formation of an air intake hole. Remove prop, spinner and cowl and cut away the lower carb air intake hole and two air-cooling cheek openings in the cowl. Begin the openings 1/4 undersize and slowly enlarge to the required size. Periodically re-fit the cowl to ensure that the lower air intake hole evenly exposes the carb.
Two cowl hole-formation techniques are possible. My bog-standard method entails perforating the outlines undersize with a series of 1/16 holes, then using a Junior hacksaw to cut the material away followed by a final edge shaping/clean-up with files and block-wrapped 180-grit glass-paper, used wet. A more high-tech and less labour intensive route is a rotary grinding tool in an electric mini drill.
Draw a vertical line in black fine-point felt-tip pen guided by a set square 1/4 from the cowls rear edge either side. Mark the horizontal intersection points onto the vertical lines as instructed in the manual this is to establish the cowl-retaining screw hole locations. Re-fit the cowl over the engine and centre/space it accurately once more with the spinner and prop fitted, and tape the cowl to the fuselage.
Drill through the cowl into the fuselage at the marked horizontal intersection points. Be extra vigilant that the cowl remains centred/spaced accurately relative to the spinner while doing this! When the four holes are drilled, screw the cowl down properly with the small self-tappers provided. Remove the masking tape holding the cowl to the fuselage. Take the spinner, prop and cowl off again and wick some thin cyano into the cowl-retaining screw holes to toughen the timber and increase the hold-down screw bite.
The silencer/pressure line exit holes, glow plug and needle valve orifices are now marked out and cut away. With the cowl still removed, use cereal card strips to determine the location of the holes. Cut four card strips about 2 wide and 12 long and tape them to the fuselage. Position them so that the forward ends extend over and beyond where each cowl hole will be made. Using the mounted engine as a guide, mark in Biro or felt-tip pen the precise silencer opening, pressure line exit point, glow plug access hole and needle valve hole on the card strips. The meaning of this will soon become clear.
Re-fit the cowl, prop and spinner and securely screw down the cowl. Keep the card strips in place while doing this its a simple matter to gently bend them back as the bonnet goes on.
Now, allow the card strips to overlap the fitted cowl so that they take up their original positions. By drilling through the card at the pre-marked points into the GRP material you have automatically found the correct locations for the holes. Remove the card strips, spinner, prop and cowl and fully form the remaining cowl holes as previously described.
To tighten/remove the silencer bolts, two holes may have to drilled on the opposite cowl side. Mark these hole centres by passing a metal meat skewer through the engine holes from the silencer side until it hits and dents the cowl inner surface. Then drill holes and enlarge as required.
The cowl material becomes quite ragged when forming the various holes, so the suggested application of thin cyano really helped to harden up the GRP weave prior to finish-smoothing the edges. The cowl is now sitting pretty.
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