Basic balsa wood kits to build model glider are now almost none existent in the world. We therefore decided do something for this yawning gap in the market and offer readers a choice of a plan, a short kit, and added wood pack and details of an easy way to buy all the hardware to build my “Mont-3” my glider first featured in the October 2009 R.C.M.&E. magazine.
Never built a model? You really have been missing fun and a rewarding challenge but I hope old hands will forgive me for providing so much building information to help newcomers who have not had years of practice! What we have made available is:-
1. The plan is case you want to do the whole job yourself
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2. Cnc cut parts short kit of all the wood parts precision laser cut. Formers, wing ribs, braces and fuselage doublers
3. Wood pack option to buy a full set of all the balsa, spruce sticks and sheet materials.
4. Suggested list of adhesives and glass products.
5. Option to buy all the hardware needed – snakes, clevises, horns etc from one supplier
Our wood and CNC packs are very complete.
RCM&E's web pages have step by step building instructions taking you through each stage of Mont-3’s composite construction. Don’t be put off by “composite”. Epoxy resins for glassing set pretty slowly so if you have not used them before, there is no need to panic. The glass and carbon tows are simple to use in this model and give it enormous strength for less than featherlike landings or when on occasions, it gets eaten by a tree.
Impecunious youngsters do not need to lay out the total cost of the model instantly. Spread the cost by buying items as you go along but to help newcomers I have indicated sources for products I trust and use.
Delux Materials – See www.deluxmaterials.com
Aliphatic Resin wood glue (wood to wood gluing – sands well)
4 Minute Speed Epoxy (two pack ply and balsa to glass or carbon fibre)
Aeropoxy laminating resin (Two pack inside fusealge)
Glassfibre Laminating fabric 78gm (Inside fuselage)
ModelLite (Light filler for filling T.E. notches and dented balsa surfaces damaged while building.
Carbon Fibre Filament Tow (Main spar reinforcement) Look on web pages.
Carbon Fibre Tow 3k – 20 metres (Cost around 12p per 1m. plus VAT + postage) – Useful material so buy a some extra! Many suppliers on web pages
Radio Active Mfg – Tel 01905 776073 for all hardware:-
2 x CA116 Fluted control rod set (Snakes)
1 x Pkt. CA143 Mini Metal Pin Hinges.
4 x CA124 M2 threaded Metal clevis links.
4 x CA127F M2 Threaded connectors for CA124 into CA152 inner)
1 x Pkt CA128 M2 Nuts (For locking clevis to CA127F)
2 x Pkt AA1087 100mm (4”) White rubber wing elastic bands
1 x Pkt AA1064 Foam Wing Seating Tape
2 x CA108 Small Control Horn (for rudder and elevator)
Wing joiner tubes and matching ¼” and 1/8”Piano Wire as per plan
Cover the plan with clear plastic sheet to protect it. Nothing could be simpler than cutting and pinning down balsa sticks on the plan. Just make sure the building board is dead flat. Tailplane, fin and rudder are constructed in exactly the same way.
To me, this is the time demanding job in the building. Control surfaces must move easily. Poor hinging is bad for servos.
Good hinging drops by gravity.
Mini metal pin hinges were used but Mylar is okay. Cut all hinge slots, test fit but do not glue hinges into place until all covering is completed. Drill the holes for the 16 s.w.g. elevator wire joiner.
Later after covering you will lay the two elevator halves flat and insert the joiner with epoxy glue. Ensure the fin, top and bottom of the tail plane that are later glued onto the fuselage remain “wood to wood” and are not glued onto any plastic covering. When complete, all leading edges are rounded with glass paper. The elevator halves are wedge shaped and tapered down about 1/16” thick at the trailing edges and rounded at the leading edge. Not shown on the plan are two reinforcing 1mm ply pieces which are glued on the underside of the elevators halves where the first outboard hinge and the joiner spikes enter the balsa. Simple eh?
Tail plane pinned and glued but not yet fully sanded L.E.
Fuselage – Tick off each number as you complete each job
1. Start with the two balsa 3/32”fuselage sides. Mark a left hand and right hand inside each of the two sides. Laying each side in turn on the plan mark two lines for each former position from F1 to F6 where they will later be epoxy glued.
2. Glue a ¼” triangular balsa stick along the bottom of each side. The top one will run the full length from behind F6 to the tail and will both have to be tapered there so that the sides join properly at the tail end.
3. Fit the 3/32 short balsa piece at the extreme end of the fuselage.
4. Cut out the all the formers F1 to F6 from 3mm birch ply and check that they will fit in the positions drawn on the fuselage sides. The 1/16” ply doublers are epoxy glued to the top front edges of the fuselage sides.
5. Lay one fuselage side flat on the bench and using a set square and some kind of a support epoxy glue F4 at its precise position;
Bulkhead 4 is epoxy glued to one side
Note – The snake holes already drilled in formers may need modifying later which is easily done with a rat tail file.
6. When set, bring the second side up to the first checking that it notches into position and that it too is at right angles to F4. Use the plan view. Use a block of wood to keep the tail end apart will ensure the second side really is ay 90 degrees to F4. Use epoxy glue and leave to set.
7. Bring the tail ends of the sides together with an elastic band and trial fit F6 still over the plan view. Take care. You do not want a banana shaped fuselage. Elastic bands or masking tape will keep F6 in place while the epoxy glue sets.
8. Dry fit F2 and F3 after using a “G” clamp to pull the nose together and dry fit F1. Always use scrap wood underneath clamps to protect the balsa. When the two sides curve evenly to F1 then epoxy glue it in place.
9. Now start the 3/32” bottom sheeting slightly behind F4 first working forward and then with F5 loosely in place, backward to F4. Leave F2, F3 and F5 dry to retain the fuselage shape while sheeting the bottom. Remove them later for interior glassing between F1 and F4 and F4 to F6.
10. Use a needle file to cut the left and right hand fuselage snake exits. Left looking forward will exit the rudder snake and right the elevator snake.
11. The tow hook is made from 16s.w.g.piano wire.
The tow hook bent up as shown but leave the right angled bend at 45º (furthest away in photo) to get the hook through the ply bottom reinforcing plate and bottom planking. It is finally bent to this shape after epoxy gluing it in place. It will later be reinforced with glass cloth and resin (glassing F4 to F6)
12. Glassing. There are two jobs to do:-
a) Use glass cloth and epoxy resin to reinforce the fuselage
b) Use carbon tows to reinforce the 4 inner wing panel spruce spars
Take your time get materials all ready and mix the two part epoxy resins thoroughly. At ordinary room temperature moulding resins set pretty slowly so take your time.
- Surgical gloves protect your skin.
- Cheap brushes can be thrown away or a small jar of epoxy thinners to clean them.
- Small plastic container or clean fish paste jar.
- Small graduated syringes can be used to extract the right ratio of resin to hardener.
Check manufacturers resin/hardner proportion for the mix. I found that about 12cc of the 2 part mix would do one spar and one compartment. In the photo one compartment (left) is glassed and has reached the “green stage” and one side been trimmed level at the top. The other (right) has had the cloth roughly pushed down into it ready for the resin mix.
Cut two pieces of cloth to fit between F1 and F4 and F4 to F6 leave plenty of upstanding cloth on both sides to trim at the green stage.
Cloth resined in between F4 and F6 and nearest side trimmed at the green stage. Nose section between F1 and F4 dry fitted with plenty to trim away late
Weight forward gives enormous strength and saves carrying excessive lead . Some lead will be needed to achieve the correct the Centre of Gravity (C.G.). As resin begins to set it reaches the “green” stage when it is still supple but not yet rigid. This is the perfect time to trim off the excess with a sharp knife. If allowed to set fully it is extremely difficult to remove the tough waste cloth.
The green stage timing depends on the workshop temperature. The warmer it is the faster the set. Wet out cloth by dabbing resin in the bottom and working up the sides, make sure the cloth is perfectly saturated and no air is trapped under it. Strength is gained if the cloth slightly meets up the front and back of formers. At F1 the battery compartment is a tight fit for the battery so do not be too generous. Aft of F4 a piece of cloth is glassed in which covers the width of the fuselage and ½” up each side and this terminated 5” in front of the tail end. Alternatively 4 carbon tows can be glassed over both sides of the fuselages on top of the bottom triangular balsa strips.
13. The lower inner wing panel spars need a simple jig using a piece of melamine faced chipboard that is dead flat and either two pieces of strip wood that the 3/8” spruce will fit tightly between when polythene sheet of placed between them or as in this photo aluminium strip and iron bar.
My “L” shaped aluminium strips hold the 3/8” spruce between .
I went to a scrap yard and got some “L” shaped aluminium strip and a piece of 3/8” iron bar used to press the tows onto the spruce to get a perfectly straight and make the enormously strong spar. The wing nut ends hold the four carbon tows tight on top of the spruce spars as the resin sets.
Work as follows:-
Cover whole of jig in polythene sheet than force the spruce spar down into the “U” shaped channel. Epoxy resin the top of the spruce and then spread the four tows evenly over its width dabbing them down with more resin. Use a piece of scrap wood to distribute tows evenly over the width of the spar. Cover with more polythene and after a short “soak” place the iron bar on top and leave to set.
When the spar is taken out the jig it will need some rough sanding where a little resin has escaped. Use as mask when sanding carbon.
14. With the fuselage glassed now start to fit F2 F3 and the servo tray. I prefer the switch to be on the tray so it cannot be accidentally knocked to “off” during a launch. However this means that the switch needs to be built into the tray before the tray is glued in. The servos are removed until final assembly.
Radio test – This is a good time to check out the onboard radio gear.
Servo tray testing all the radio gear.
Using the TX programme, check that the servos move and the switch works. Proper & final radio installation takes place when the model is completed.
15. Now ensure that space between F1 and F2 still gives easy access for the battery. If glassing has been over generous then F2 can be moved back slightly but check your RX (radio) as well as these vary in length.
16. The glassing means that you must now sand F2 and F3 to fit the modified shape. Use epoxy and ensure F3 allows the servo tray to fit properly.
17. For 35 MHz installations only – If using a 35MHz RX then fit a plastic tube running from just in front of F5 and terminating at the bottom of the end of the fuselage. Drill an extra holes in F5,F4 and at the bottom of tail block. Cut the tube to length at the tail. Epoxy in place as it passes formers and the tail filler block.
For 2.4GHz Rx – Use the compartment under the wing for the Rx where there is more room for the aerial
18. Fit the switch to the tray and epoxy glue the servo tray into place.
19. Now fit the rudder and elevator snake “outers” leaving excessive length at both ends. They are trimmed to length later.
Where outer snakes pass through formers they should be epoxy glued to prevent flexing. As they pass through F6 they should be left slightly loose in the hole so that when connected to their respective servos they will have a small angular movement produced by the servo arm. Initially the tube and inner snake should line up perfectly with the servo arm in its neutral position. Servos must never “buzz” when at the full extent of their travel but later servo travel on the TX is used to allow them to give the correct throw to the control surfaces.
Leave control snake and aerial outlet protruding till later
20. Now finish off all the top planking as per plan as far at tailplane.
21. Hatch – this is the only time you can put pins through the balsa planking to hold the curve on each strip. Masking tape may also be used. The 1/8” hatch bottom has its formers angled to meet F6 and F1. Epoxy glue F1A, F3A and F4A to the base and use some thin cling film under it to prevent it sticking to the fuselage. Cut 1/8 sheet so that each length is chamfered on its edge to meet the next plank as evenly as possible. A slow job but even if it looks rough there should be enough thickness to sand it to a perfect rounded shape. A small peg is inserted into the front of the canopy that will plug it into a hole in F1.
Making the hatch cover
22. DeLuxe BalsaLite fills any gaps in the canopy planking.
23. Balsa Nose is carved from a block of balsa First rough cutting it to the side view on the plan and then the top view. Drill out hole shown on the plan to take a cast lead slug that will helps achieve the correct C.G.
Casting lead weight for the nose
24 . A wood block was used to cast molten lead but you can buy DeLuxe Materials liquid ballast to make the job easier.
25. Glue in two pieces of 1/2” X 1/8” balsa between F4 and F6 to provide better wing seating. Later, after painting cap the wing seat top with foam plastic tape. Cut wing fixing dowels to length but do not glue in.
The aluminium skid is bolted through the fuselage
26. The aluminium skid contributes strength and its weight forward helps that C. of G. I haunt scrap yards! The ¼” skid was cut from 1/8” sheet then drilled and countersunk for M2 x 15 mm bolts. The forward end was slightly countersunk into the nose block and the strip ends just in front of the tow hook. The skid is be fitted immediately after glassing but if you have fitted the servo tray, mark the bolt holes so that you can get at the heads inside to fit the nuts. Remove the skid until after the fuselage is finally finished. A wood scew secures the skid into the nose block and later resined into it.
Tip – Use scrap ¼”sq.balsa with dab of putty or Playdoh on the end and stick an M2 nut in it to reach inside bolt heads.
The completed fuselage tail plane and rudder
Building the wind
No bird or aircraft can fly efficiently with less than a perfect wing. Take time with this job.
Ribs 1 to 4 in each inner panel – The most demanding job is to precisely mark and drill the first 8 ply ribs that take the wing joiner tubes. All holes must be aligned precisely to ensure the correct dihedral on each wing half. The root ribs are specially angled and not glued into their final place until both halves of the inner wing panel are ready for joining. Use a pair of dividers to take precise measurements off the plan to markthe tube holes. Forward tube use centre dotted line for measurements noting that the hole on R1 is immediately under the main spar and other holes lower down at each successive rib. Mark off the aft holes for aluminium tube in a similar way so that this tube is perfectly parallel with the main tube.
Number the ply ribs and using the wing section on the plan mark off the drilling centres
Build the two inner wing panels on the board at the same time to ensure each half is identical. Study the wing cross section to see how spars, tubes and upper and lower sheeting work. You are building on a flat board and that means that wing rib R1 and cover rib and Rib AO at the join are angled and not upright.When the inner panels are built you can match the R1’s so that you have a perfect wing joint.
Inner wing panels
The lower spar is a of composite Spruce and Carbon Tow. Two spars are made using a simple jig built as previously shown or see R.C.M.& E July 2003. For gentler winch launching plain spruce may be substituted.
Composite spars use 4 pieces of carbon tow about 40 inches long. You will never fear a fierce bungee or winch launch again!
1. Try a dry fit both tubes into ribs R1-R4 but do not glue until later as you have to cut slots and insert the 1/16” ply web.
2. Cut, lay and pin the bottom spruce wood spar onto the plan. Cut one 3ft X1/16” sheet to length (R1 to R14) and glue its 1/16th edge to the front of the bottom spar making certain both are dead flat along their whole length. (Avoid rumpled plastic sheet underneath them!)
3. Mark and cut the 1/16”notches in the Trailing Edge (T.E.) section balsa. Pin the T.E. down on the plan.
4. Cut and glue the centre section lower sheeting behind the spruce spar and at the front edge of the T.E. Aft of the spar the 1/16” sheeting will need some slight packing under it so that it conforms to the under camber of the ribs.
5 Cut scraps of 1/16” sheet and place in front of the T.E. so that when the rib is glued into the T.E. there will be a 1/16” space for the bottom capping to run flush onto the T.E.
6. Spar notches that accommodate the bottom spars will need slight sanding to deepen them so that the extra thickness of the carbon allow them to fit perfectly flush. Dry this depth first.
7. Epoxy glue R2 to R14 upright to the bottom spar only using the epoxy glue over the carbon and slightly in front of it. Later wood to wood joints all use wood glue.
8. Now dry fit the top spruce leaving an extra bit over at the over inboard end. Leave both R1 ply ribs until wing halves are joined so that they meet at the correct angle without any gap.
9. The lower L.E. sheeting must be bent upwards along its front edge to comply with the curved front edge of the ribs. The ribs in front of the lower spar were not glued earlier. Now weigh each half wing down on top of its main spar and push short (1”) scrap triangular pieces of balsa under the front edge of the sheet at each rib station to curve the sheet up to meet each ribs bottom curve. An old piece of trailing edge balsa can also be used to get this upward curve along the whole length of the L.E. Dry test the first and then glue to each rib.
I use iron weights but pins are the normal way to hold parts in place while the glue dries.
10. Check with a long straight that every rib will meet the ½” X 3/8” sq L.E. and the lower sheeting along the length of the inner wing. Coarse glass paper glued to a dead square piece of wood can be used to level the front edge of the lower sheeting so that when glued it will land square onto the L.E. It should need absolute minimal sanding to achieve strong joints.
11. Dry fit the 3/8”x ½” leading edge using masking tape to hold it in place. Check that its bottom edge lands perfectly onto the bottom sheet and that there is still a 1/16” deep land for the top sheet to fit perfectly up to when it is later fitted.
12. Cut webs from 3/32 inch sheet with vertical grain and fit and wood glue them to the rear of the main spar from R6 to R13.
13. When both inner wing halves are built test fit the tubes and joiners again to see that each produces the 1 5/16” at the outer wing joiner. Now fit in the brass and aluminium joining tubes and lightly epoxy glue them to the ribs. Use shaped balsa wedges above and below them fully epoxy all into place.
Note – The main 1/4 inch wire joiner is 8 inches long but can be extended to 113/4” inches for increased ballasting. Use a small dab of nail varnish in its centre to stop wire entering the tube too far and losing it.
14. Use a Razor Saw to cut down R1 to R6 as far as lower sheeting to fit the 1/16” braces that are epoxy glued for and aft of the main spar.
15. Use the saw to cut down R13 and R14 ready later to fit the dihedral brace. The brace is built onto the wing tip section as it is built.
16. Now build the outer wing panels first chamfering the top and bottom plain spruce spars down from 3/8” to ¼” at the tip. Build simultaneously in exactly the same way as the inner panels but leave ribs AO out as these are glued in when the outer dihedral joint is completed.
17. Build in all the 3/32” vertical grain balsa webs on all wing panels.
18. Joining wing panels
I use a 2ft length of 4” x 2” timber to rest the wing tips on to get the correct outer wing panel dihedral. The tube holes will automatically give the inner panels their correct dihedral. The inner panels are laid flat on the building board and the outer panel wing tips tilted up 4 1/4” to sit on the timber.
Immediately you bring the outer to inner wing panels up to each other you see they do not fit! The L.E , T.E and spars need to be chamfered to an angle to bring them together .You can use a length of properly angled templates, timber with glass paper glued to it or as I did get a piece of slotted angle steel, bolts and wing nuts to make a variable angle sander.
19. When these parts land on their opposite parts perfectly, use epoxy glue to join them and after it is set, add the triangular reinforcements.
Templates and sanding jigs for sanding the wings at the panel joints
20. Start with the inner wing panels laid flat on the building board . The front edge of the 1/16” sheet must be chamfered so that it lands on the L.E with no gaps. It must fit over R1 to R14 but is only wood glued where it will land on the L.E. and a small dab of glue at the front of each rib.
21. When set thoroughly, bend the sheet back as far as the rear of the webs and cut off any excess. Use a paint brush to dab glue onto the top of each rib and all along the top of the spar and web.
22. Use masking tape to putt the sheet down and you can then put it down flat again weighted along the spar.
23. Add to tip sheeting from the spar back to the T.E and all the top cap strips.
24. Top sheet the outer panels by tilting the inners up on the 4” x2” so that the outer wings are now dead flat on the board. Sheet them in the same way.
25. Hold the centre joiner rib down vertically on scrap 3/32” balsa and draw round and cut two covering ribs. Drill them where tube holes are then glue and sand them to the R1’s to make a perfectly tidy join.
26. Use a small plane to start rounding the L.E and finish off with glass paper. Perfection takes hours! I use dilute PVC (50% water to glue) to raise the grain before final fine sanding. This helps the covering to stick well to balsa.
27. With the wing complete the final job is the streamlining blocks that fit the wing smoothly behind F4. First cut a full width block that fits behind F4 and length to the highest part of the aerofoil (about where the wing spar is. Now mark the wings aerofoil on each side of the block and carve away to it fits the top sheeting perfectly. Shape the lock to the round section of F4. Cut the shaped block in half lengthways and glue each half to each half of the wing.
Balsa fairing pieces are shaped then glued to each wing half
28. Finally I pinned and banded Mont-3 together just to make sure everything fitted and had been fine glass papered ready for covering.
You will need some basic tools to cover the model with one of the plastic film covering materials such as Solarfilm. This company (www.Solarfilm.co.uk Tel 01257 267418) offers beginners a DVD and their packages also contain instructions. I would suggest that the underside of the model has some dark panels which will give good visibility against the sky. Additionally put your address and phone number inside the model as you don’t want all this effort to be lost.
Covering tools you might need. I often only use scissors, sharp balsa knife and a Covering Iron with 1m.steel rule. Film does get hot so cotton gloves for smoothing down are a must. The Heat Gun (right) is useful for shrinking large areas but not vital.
The fuselage is the only part painted and to be perfectly honest it does not need special model paints. The only criteria for them is that they should not add too much weight. Use a good light filler/ undercoat and using wet and dry sandpaper rub almost back to the balsa and then give a final coat before the gloss to obtain a superb finish.
Before every full size flight, a pilot does a visual check to see the wings are still on, that the fuel tank has been filled before he does a full cockpit check. Forget the fuel tank but a glider needs just as careful checking. Flying a model aircraft should be exactly the same as full size every flight. Experienced buddies in clubs are there to help and willingly give beginners their time. Their help costs nothing but your thanks.
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