Tiger 72 Manual

This expanded instruction manual is intended to complement the printed manual supplied with the plan. The expanded manual contains a wealth of photographs to help clear up any uncertainty in the written instructions, but if all else fails do get in touch with us and we will help out however we can.

The Tiger 72 is based on a much earlier design, called Ruhig Tigre (roughly translated as “Quiet Tiger” or “Peaceful Tiger”) which was a sports model of 60” wingspan designed by Colin Dickinson and featured as a pull out plan in Radio Modeller magazine in 1990. I built a Ruhig Tigre from the original plan and it flew like a dream for a number of years. Colin had begun work on an enlarged version but sadly died before the larger model was completed. I took Colin’s plan as my inspiration for this model and, although the outline is very close to the original, I comprehensively redesigned the structure to take advantage of modern construction methods – back in the 1990s, the idea of a modeller having access to computer aided design software and laser cut parts was the stuff of daydreams.

If this is your first foray into the world of traditional modelling, you should find nothing difficult here, although you would be well advised to read up on traditional construction methods – there is an enormous amount of information available online as well as in numerous books on the subject. The most important piece of information I can give is to say that, if at any stage you are unsure of how best to proceed, STOP and don’t continue until you are happy that all is clear.

Before opening the glue bottle, take time to look through the sheets of pre-cut parts and familiarise yourself thoroughly with the drawings – it should be clear which pieces fit where.

The model is built in a series of sub-assemblies – tailplane, wings, fuselage etc., which are then brought together towards the end of the build. For each sub-assembly, begin by identifying all the laser cut parts on the laser cut sheets. Each part is retained in its sheet by short “bridges” which are gaps in the laser cut lines. These bridges will need carefully cutting through with a scalpel or Stanley knife to free the parts from the sheet. An inevitable side effect of using a laser to cut out balsa and ply parts is that a certain amount of scorching of the wood occurs – this leaves a sooty black residue around the cut lines. The soot will not affect the ability of the glue to stick the parts together, so there is no need to remove the residue before assembly, however, in handling the parts, you will inevitably get some soot on your hands which will then transfer itself to the wood (and anything else you touch) giving it a “grubby” look. While this may look unsightly during the building process, any surface grubbiness will disappear during the sanding process after construction. Assemble the parts over the plan (after first covering the plan with non-stick clear plastic sheet) using aliphatic resin.

Tailplane, elevators, fin and rudder.

Note – it is fine to build the elevators at the same time as the tailplane, but if doing this be careful not to accidentally glue the elevators to the tailplane!

1. Pin the laser cut parts in place over the plan, using aliphatic glue to join the mating faces.

2. Add the strip balsa structure. The straight fore/aft pieces fit in first and must be cut from lengths of 1/4×3/8” (6x9mm) strip balsa to fit into the notches in the cut parts. Once all these have been fitted, the diagonals can be added. The ends of these will need to be cut to fit into the corners as shown on the plan. It is important that the fit of these pieces must be snug but not too tight – they should not need forcing into place, but neither should they be loose.

TOP TIP.

Fit the longest pieces first – that way, if a piece is accidentally cut too short, it may be possible to use it for a shorter piece later on.

3. Once all the glue has thoroughly dried, remove the structures from the board, sand smooth on both sides and then shape to the profiles shown on the plan before setting aside.

Do not glue the fin in place in its locating slot on the tailplane yet – this will take place immediately before the whole tail group is fitted to the completed (and covered) fuselage.

Fuselage.

Construction of the fuselage is a quick and straightforward task, with a number of pre-cut parts simplifying the task of creating a light yet strong and accurate structure. The laser cut formers have tabs in their sides which locate into corresponding slots in the fuselage sides, however if you are cutting your own parts by hand, these tabs and slots may be omitted as they serve only to aid location and, while they add some strength to the structure, it will be perfectly satisfactory without them. Also, steps 1 and 3 below call for laminating two pieces of 3mm ply to make 6mm thick parts – this has only been done for convenience, since it was found that laser cutting 6mm ply caused excessive scorching. If you are making your own parts it doesn’t matter whether you make them up from 2 thin laminations or one thick piece.

1. Each fuselage side is made by laminating two pieces of 3mm lite ply to make 6mm sides. Pin the pre-cut lite ply fuselage sides in place over the plan. The sides have a number of slots cut in them which will be used later to locate the formers – ensure that these slots are clear as they can get small pieces of wood trapped in them during transport.

2. Glue the upper and lower longerons in place using aliphatic glue. Take particular care to ensure that the upper longeron accurately follows the line drawn on the plan as this will ultimately dictate the incidence angle of the tailplane, which is a critical angle.

3. The tailplane supports (also made from two laminations of 3mm lite ply) at the rear of the fuselage can be added at the same time as the lower longeron.

4. Add the vertical and diagonal strips of 1/4” balsa between the upper and lower longerons.

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5. Once all the glue has dried, the completed fuselage side can be removed from the building board and sanded on both sides then returned to the board, this time with the clear film on top of it, and the second side built over the first to ensure accuracy.

6. Once both sides have been completed and left to dry thoroughly, hold or pin them together and sand the outlines so that they are identical.

7. Return one of the sides to the building board and locate formers F3, F4 and F5, gluing these in place and supporting them while the glue sets to ensure they are accurately perpendicular to the fuselage side.

8. While the glue is setting on these pieces, now would be a good time to locate the spiked blind nuts in the holes on F4a.

9. Glue the two 1/4” reinforcement strips in place on F2 and the servo tray as shown. These strips can be cut from leftover lengths of the fuselage longerons.

10. Locate F2 in its slot on the fuselage side but DO NOT GLUE IT IN PLACE YET.

11. Take the second fuselage side and glue it in position over F3, F4 and F5 and at the same time trap F2, F4a and the servo tray in place between the two sides. Place weights on top of the second fuselage side to hold everything securely in place while the glue dries.

The fuselage structure can now be removed from the building board and rotated the correct way up.

12. Add formers F6 – F9 and join the two ends of the fuselage. Take care at this stage to ensure that the fuselage is straight and not twisted or bent – a fuselage building jig will help enormously here.

The fuselage sides, when viewed from above, will take on a slight curve from F5 – F9. A certain amount of fitting may well be required to ensure an even curve with no bulging or waviness. dry fit each former in place (without glue) and trim the sides with a sanding block, or add thin strips of balsa if required, to achieve a smooth line along the fuselage sides. The correct vertical position of each former can be checked by laying a strip of balsa along the tops of the formers (locating it in the notches cut into F4 and F9) and checking that it just touches each intermediate former.

13. Add the 1/4“ square balsa stringers to the upper rear fuselage. The locating slots in F4 (and, to a lesser extent, F9) may need easing out with a needle file to achieve a close fit. F5 – F8 do not have locating slots, the stringers can be secured to these with a drop of glue. Once completed, the load on these glue joints is minimal and so there is no need for each former to have a locating slot for the stringers.

14. Fit the 3/16” support rails between F4 and F5. The ply turtle deck will attach to these rails in the next step. Also, fit a piece of 1/2″ x 1/4″ strip (cut from the end of one of the cyparis wing spars) behind F5. This will prevent F5 from bowing backwards later on when the underside covering is shrunk in place.)

15. Using a piece of paper, make a template for the 1/32” ply turtle deck then carefully cut and glue this piece in place. Accurate positioning of this piece is essential to avoid a mess so take your time and don’t go near it with a glue bottle until you are certain that it fits and you are confident of your ability to clamp it in place while the glue dries. Either aliphatic resin or thick cyanoacrylate are suitable for this task – aliphatic gives more chance to reposition the piece if the positioning is not quite accurate first time, but does require a good number of clamps, tape and elastic bands to ensure it can be held in place while the glue sets. On the prototype I used thick cyano and held it in place with finger pressure, but that method leaves little margin for error!

16. Add 1/4” x 1/16” capping strips along the top of each stringer and sand flush with the ply turtle deck.

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17. Infill the space behind F9 with triangular pieces cut from scrap ply. If you already have your tailwheel to hand, it will be easiest to drill mounting holes for this in the lower ply piece before fitting it to the model, but if not, it will not be a difficult job to drill these holes later.

18. Where the rear fuselage ends meet, sand them square and add the stern post from a piece of 1/4” balsa. Don’t try to trim the tailcoats to final shape just yet – this will come later once the tail assembly is trial fitted as the stern post must match the front edge of the rudder.

19. Make up the tail block spacer piece as shown on the plan using two pieces of scrap 3/8” balsa. If you have no 3/8” balsa to hand, it can be made up from any combination of thinner balsa – what is important is that it is the same thickness as the fin and elevator.

20. Position the tail block spacer on the tailplane seat but DO NOT GLUE IT IN PLACE. Take two soft balsa blocks and cut them approximately to the shape of the tail blocks – leave them oversize for now. Glue the blocks end on to the rear face of F9, trapping the spacer piece between them. Take care not to get any glue on the spacer itself.

21. Once the blocks are firmly glued in place, use a plane and sanding block to shape them to match the curve of the rear fuselage. Take great care during this process – the tail blocks are only attached to F9 by a small glue area. The spacer piece helps to support them in place but even so, care must be taken not to disturb the glue joint. Now slide the spacer piece out to the rear.

22. Add F3a, ensuring the holes for the wing dowels align with the holes in F3.

23. Carefully pull the front fuselage ends together, gluing F1 and F2 in place. A fair amount of pressure will be required to pull the sides together – this can be reduced by making a series of thin saw cuts on the inner faces of the fuselage forward of F2 (although this was not required on the prototype). Use slow setting epoxy resin to fix F1 in place and leave it clamped securely while the glue sets, and until after the triangular reinforcement pieces have been added behind it.

24. Add the undercarriage mounting plate, reinforcing it with triangular balsa along its inner edges where it meets the fuselage side. Again, it will be easier to drill mounting holes for the undercarriage before fitting, if possible, however it is possible to drill these holes later if needed.

25. The 1/8” balsa floor can be added forward of the undercarriage plate, or it can be left off until a later stage to facilitate access to the motor mount and battery bay.

26. Make up the motor mount from the four pieces of 6mm birch ply. Note that the mount pieces fit together in such a way as to give RIGHT thrust when fitted to the model – the mount is not supposed to be square. Asymmetric tabs in the ply pieces reduce the possibility of building it incorrectly but it is still possible to assemble it in such a way as to give side thrust to the left – the opposite of what is required.

27. Fit the assembled motor mount to the front face of F1, adding triangular strips around the edge to strengthen the joint.

28. Add the cockpit sides from thin ply, using the paper template trick described earlier to help you.

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29. Make up the battery hatch from the three formers and the supplied hatch base – it is best to do this on the model to ensure that a good fit is achieved, but protect the bay with clear film first to avoid the hatch becoming permanently glued in place. Once the base and formers have been joined, remove the skeleton hatch from the model and complete it with strips of 1/8″ balsa wood.

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30. Whether you are using a moulded cowl (available from Nuviation) or making up your own, now is the time to check the fit and adjust it as necessary to suit your chosen motor and achieve a smooth transition into the lines of the forward fuselage.

31. Fit the two battery support ribs through the holes in the fuselage sides. Now is a good time to make up a suitable tray to hold your battery, the motor mount has been designed to allow most batteries to slide well into it to facilitate correct cg (centre of gravity) location later on. If you wish, you can fix the tray permanently in place now or leave it until later to keep access easy into the bay below. Whenever you do decide to fix the tray, make sure that it will clear the cowl once this is in place.

The fuselage is now complete except for the windscreen, which will be dealt with after covering.

Wings.

Construction of the wings is made slightly unconventional by the symmetrical aerofoil section, however there is certainly nothing difficult about building them.

1. Make up the upper and lower wing skins from 1/16” sheet balsa, sanding them smooth and placing to one side. Never leave the surface sanding until after the skins have been added to the wing structure as to do so will inevitably lead to uneven sanding of the skins and make a mess.

2. Pin the main spar in position over the plan.

3. Take one rib and position it over the main spar so that it sits level – i.e. with the leading and trailing edges off the board such that the slot for the upper main spar will be vertically above the lower. Now take a length of any straight pole – I used 1/2” balsa dowel for this but a thin broom handle or similar will do just as well – and roll it into position underneath the rib such that the rib is supported in position. Ensure the dowel/broom handle is exactly parallel to the spar and pin it in place. From now on, as you add ribs to the structure, the position of the spar on the board will dictate the location of the forward part of the rib, while the broom handle will ensure that the tail of the rib is held off the building board by exactly the required amount.

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4. Glue all ribs in place, noting that the innermost rib must be set at an angle to accommodate the dihedral – the required angle (88.5 degrees) is shown on the plan and a suitably shaped template is included in the cut wood pack. Having a symmetrical section, it is not immediately apparent which side of the wing is the upper surface and in fact it doesn’t matter whether you build the wing the right way up or upside down. When you come to build the second wing, you will use the same drawing and build the other way up – i.e. if you build the first wing the “right” way up, you must remember to build the second wing upside down.

Take great care at this stage as the ribs are made of very thin lite ply. Once the structure is complete, they are more than up to the job required of them, but at this stage they are very weak and inadvertently catching a sleeve on a rib will surely break it.

When you get to R5 you will see that there is a recess in one side of the rib – this is to accommodate the servo housing and must be on the lower side of the wing. At the risk of labouring a point, this means that when you build one wing the recess will be beneath the structure, on the side facing the board, and when you build the other wing the recess must be uppermost, facing the ceiling.

5. Add the upper spars and the shear webs in front of the main spar. Note that the grain on the shear webs must run in a vertical direction.

6. The 1/8” false leading edge can be added to the front of the ribs and the upper edge of this can be very gently trimmed to sit flush with the upper edge of the ribs. Take care with this stage as the wing will have very little rigidity. Although rather wasteful, it is helpful to make up this false leading edge with a piece of balsa which is wide enough to have its lower edge resting on the board while it is being fixed to the ribs. Doing this introduces a little rigidity to the part built structure and the excess can be cut away once the wing has been turned over.

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7. Add the 1/4” linings to the aileron bays.

8. Add the upper sheeting, starting with the forward wing skin (including the extended portion over the innermost ribs), followed by the servo housings, trailing edge strip and finally the capping strips along the tops of all the ribs.

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9. Once all glue has dried, the wing can be lifted from the board, flipped over and the lower skins added after trimming the lower edge of the false leading edge. The servo housings can also be made up from the 1/16” cut ply pieces and glued in position.

10. The forward edge of the skins should now be trimmed flush with the forward face of the false leading edge and then the 1/4” leading edge itself can be glued in position before shaping to the profile shown on the plan.

11. The wing tips can be assembled from the cut parts and glued in place on the outermost rib.

12. The trailing edge of the wing now consists of two edges of 1/16” balsa and is finished by having a strip of hard balsa attached along the full length which is then planed and sanded to match the profile shown on the plan.

13. Construction of the centre section is broadly the same, with a just a few differences – the entire centre section is fully sheeted top and bottom and W4 must be fitted along with W1, 2 and 3 which will support the wing dowels later on. It will be necessary to cut holes in the upper and lower skins to line up with those in W4. The easiest way to do this is by using W4 as a guide to cut the holes in the lower skin before adding the upper skin, and then do the same to the upper skin by passing a sharpened length of brass tube through the holes in the lower skin and W4 after the centre section is complete.

All that remains now is to join the three sections to make a complete wing.

14. Slide the ply dihedral braces into position in the slots behind the main spar in the centre section and ensure that the outer panels can be slid into place on the outer sections of the dihedral braces. This job may be a little fiddly and require some trimming of all parts to achieve a good, close fit.

15. With the centre section flat on the bench, each outermost rib needs to be supported 13mm off the bench to give the required dihedral angle. Have a couple of dry runs at positioning the wing panels and, once you are happy that all is as it should be, apply a liberal coating of epoxy resin to the mating faces of the ribs and the dihedral braces, slide all into place and support in position until fully cured.

16. The wing joint can now be reinforced with glass fibre bandage on both sides of the centre section.

17. Check the fit of the wing against the fuselage and make any minor adjustments as required to get a good fit. In particular, ensure the wing dowels will match up with the holes in F3a, and ensure that the wing retaining bolts pass cleanly through the holes in the wing centre section and into the blind nuts in the fuselage.

18. Make up the ailerons on the board, remembering to build a left and right version (the only difference being that the ply plate which will accept the aileron horn must be on the underside of the model and so, like the servo housings earlier, will need to be uppermost when building one aileron and lowermost when building the other.) The 1/4” balsa strip that makes up the leading edge of the aileron will need to be chamfered slightly to allow it to sit correctly on the building board – as the aileron ribs are positioned against the board the angle at the leading edge will be somewhat more than 90 degrees and this must be accounted for when fitting the balsa leading edge. Add reinforcement blocks behind the aileron leading edge and in the wing to accept the hinges. The prototype used “Robart” type hinges – note the slots cut into the ailerons to conceal the hinges.

19. The belly pan is made up by supporting the complete model upside down and fixing the parts shown to the underside of the wing centre section so that they match up with the sides of the fuselage. Take care at this stage to glue the belly pan only to the wing and not the fuselage itself. It will be helpful to use clear plastic sheet around the wing/fuselage joint to prevent glue getting where it is not wanted.

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The model is now substantially complete and ready for covering and installation of your chosen radio gear and powertrain.

Finishing.

1. The prototype was covered in Solartex, doped and then painted. Although this is a heavier option than using film covering, it does produce a very durable finish. Heat shrink film is, however, perfectly acceptable and substantially easier – especially for builders who do not have access to spraying equipment.

2. Cover the fuselage and tail pieces separately, making sure to leave an uncovered space in the tailplane and fin where they will touch the tail blocks (this ensure that they are fixed in place with a wood – wood glue joint) then fit the piano wire joiner to the two elevator halves. Attach these to the tailplane using furry Mylar hinges then trial fit the fin in its slot. You should find the rear of the fin overhangs the rear of the tailplane by a small amount. This is to provide a space, when the rudder is in place, to allow the elevator joiner to move. If you find that there is no such space, perhaps due to over zealous sanding of the rear of the fin, make a small notch in the leading edge of the rudder to achieve the same purpose. The fin and rudder can now be joined with Mylar hinges, making sure that the rudder has an extra hinge added below the level of the tailplane which will locate in a slot cut into the fuselage stern post. The fin, tailplane, elevators and rudder can now all be slid into location between the tail blocks after first coating the bare surfaces with Aliphatic resin.

3. When fitting the windscreen, make up a template from paper and hold it against the fuselage to see if you are happy with the shape. Once you are happy, cut the required shape from thin acetate sheet. The windscreen will forever be vulnerable to being knocked off, so it is strongly advised that you make small tabs in the lower edge of the screen to locate into carefully cut slots in the forward fuselage, rather than relying on a glue joint along the lower edge of the acetate. The exact amount of rake and the size of the screen is very much a matter of personal taste and will not affect the flying qualities.

4. The prototype used standard sized servos on the elevator and rudder and 16g mini servos on each aileron. Make sure to use good quality servos all round – especially for the mini servos. The aileron servos were fitted by attaching thick plywood blocks to the inside of the servo hatches and drilling holes in these to accept screws through the servo lugs. Pushrods were then used to connect the servos to bespoke fibreglass control horns although commercial nylon control horns would work just as well.
Once complete the model should balance in the middle of the mainspar. It may be necessary to add ballast either to the nose or tail to achieve this – for early flights err on the side of caution and keep this suggested balance point as the rear limit until you are used to the model and wish to experiment.

Flying notes.
After a busy couple of years designing and building, not to mention moving house and having all my fleet in storage pending the erection of my new workshop, I have been unable to fly models for a very long time and, having invested an awful lot of time and effort into designing and building the Tiger, I was reluctant to trust my (mediocre on a good day) flying skills to undertake the test flights, so I persuaded David Ashby to do the honours. The first flights took place with a 4s set up and, while David reported that the handling was smooth and the model flew well, he also felt that it was under powered. An upgrade of the powertrain was clearly in order and so it was back to the workshop for some modifications to accommodate six cells, a more powerful motor and a bigger prop. The model was transformed! With the 50% increase in thrust afforded by the new powertrain, the Tiger does everything I had hoped for and more. Loops from level flight are easily achieved, as is prolonged inverted flight. The thick wing section gives a creditable slow speed performance too, so the Tiger will feel safe and assured for intermediate pilots while experts will have fun wringing it out with all the performance you would expect from a full blooded sports aerobat. Do please note that this model was never intended to be a racer so full throttle dives from height are bound to overstress the airframe! Remember that the throttle stick moves in both directions and save full power for rapid motion uphill! I must admit, I am pretty chuffed with this one; Colin Dickinson knew what he was doing when he designed the original, smaller version and I hope he would be pleased with the tweaks I have made while enlarging his model.

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