by Andrew Curless
Plan No. 670
I copied the formers and wing shapes using A4 white paper. Just trace the wing rib or former onto the paper then cut out the shape with a pair of scissors and you have yourself a template. Now pin the template to your timber and run a soft pencil or fine tipped felt pen around the outside to transfer the shape onto the material and you have the shape required. Next cut all your parts and assemble them into components i.e., tail group, wing group, fuselage group, etc.
Now that you have your kit cut out and piled into little groups on your work bench it is a good time to "PANIC", this is where I start to wonder if I have bitten off more than I can chew. This is also a good time to hide all the components except the ones you need to start building. I always like to start with the wing so that is where we will start our CL215.
The wing is a one piece built up unit with no dihedral, it is fully sheeted with 1.5mm balsa and has two motor pod bays set into the leading edge. Don't forget to drill service holes in the ribs for servo leads etc. Lay out the plan on your work bench and cover with plastic wrap to protect it, then pin down your trailing edge spar and bottom main spar, using a small square lay out the W2 wing ribs gluing as you go. Once all the ribs are in position pop on the top main spar then fit the wing brace into the centre, remembering to check all the ribs are square as you go. Let all the glue joints dry then fit and glue all W1 ribs and the 3mm false leading edge and WB2. This is a good time to make up the ply motor pod boxes, when assembled mark one left and one right then using them as the spacers cut away the false leading edge and fit and glue ribs W2a for a snug fit making sure not to glue in the motor pods, remove pods once W2a ribs are secure and fit wing shear webs, (this is where keeping your ribs square pays off), then the throttle cables, fit WM3 and fill up the gap with some scrap balsa.
In constructing the motor nacelle start by constructing the ply wood motor pod. When built ,fit into the wing in between W2A making sure to fit the 1/2" balsa spacer underneath EB, remember to draw your throttle linkages through the motor pod as your fit it into position. Then with your ruler mark the centre lines of the nacelle onto the wing and taking measurements from the plan glue formers E3 to E6 into position. Now fit the tank hatch onto motor pod and glue in formers E1 to E3A. Sand and fit E7 and two E8s into position to give the construction rigidity and ready it for sheeting with 3mm balsa. With this done sand nacelles to final shape for sheeting with balsa. My next step was to sheet the nacelles starting at the wings at E8 on both sides working to the top centre at E7 using 20-25mm strips of balsa. While time consuming it was the best method to achieve the best contours. Next make up the rear balsa blocks out of 12mm balsa and glue into position then sand to shape the entire nacelle and cut out the tank hatch. Now refit the hatch with pins and screws to lock in position for service to the tank bay.
The plan shows a built up engine cowl manufactured from 3mm balsa wood. Assembly the cowl rings with 61/2 mm spacers then edge glue 3mm planking, (cut to the length of the cowl jig), and paint with cloudy ammonia and wrap around the cowl jig and hold in place with rubber bands until dry. This process ends with a rounded pre-shaped planking which can be trimmed and glued into position easily. Build up two layers of 3mm planking on the interior front of the cowl and one 3mm layer on the rear exterior. When dry the cowl can be sanded to shape and fibre-glassed or finished as you require. Finally fit cowl to nacelle, sanding as required to achieve a good fit. I mounted mine with four small hardwood blocks.
Next pin both fuselage sides together and sand to required shape, then split apart and fit one over the plan and mark positions of all formers. Transfer positions to opposite fuselage side. Now fit all doublers and longerons to fuselage sides, remembering to make a left and a right side because it's a real bummer if you have two left sides! Next I began to fit formers F2, F3, F4 and F5 to one side of the fuselage making sure they were all square also fit wingmount plates WM1 and WM2 into position. After the glue joints have dried sand the tail post to the required wedge shape and fit the opposite fuselage side to all formers then glue in the tail area. Position fuselage over the plan to check for alignment and pin and tape until all glue joints have cured. (Upside down on plan.) Now fit formers F5a, F6, F7 and F8 into the rear of the fuselage. F1 now has to be fitted to the front of the fuselage this requires some skill to pull the nose of the fuselage from F2 into F1. I painted the balsa sides with cloudy ammonia to aid in the bending of the timber then with liberal glue added to the edges of F1,I pulled in both sides of the fuselage with the aid of masking tape and when satisfied, left to dry over night. Once all formers are fitted take a sanding block and sand bottom of formers to get a uniform finish. When satisfied, fit in the centre keel to the rear of F5 to the tail post and from F5 forward to just short of F1 where the hard wood nose gear block is to be fitted. Subsequently cut hard wood nose block to profile shown on the plan and fit into F1 butting up to the keel and aligning with the 3mm ply gusset. When complete take a sanding block and shape both keels to a triangle section ready for planking the bottom of the hull.
Turn the fuselage over, check shape and sand to requirements the top of all formers and fit 61/2 mm square stringers between F2 and F4 and between F6 and F8. Now plank the top of the fuselage between F2 and F4 and F6 to F8 with 3mm balsa sheet. From F8 to the tail post I fitted one piece of 10mm sheet then sanded to the profile required. Once happy with the tail shape temporarily fit the fin to the top of the fuselage cutting locating slots as required. (This is to determine location for flexible control rods to the rudder and elevator.) When happy with the control rod locations glue them into position and remove the fin from the fuselage. Now turn over the fuselage and make up the planking for the front of the fuselage bottom from F5 to F1. Sand to shape and glue into position. Now we can make up the nose pod and cabin area at the top of the fuselage, I made mine out of 1/2" balsa sheet. I copied the profile off the top view of the plan and made a series of horizontal horse-shoe shapes. Starting at the centre of the nose area, I layered the sheet one on top of the other to the full height of fuselage sides reducing in size as you build towards the extremities of the nose pod. (Note: It's better to be slightly oversize then undersized.) The cabin was built in a similar fashion using a solid block on the top of the cabin. When happy with basic outline construction it is time to sand to final shape, (I suggest outside on a windy day). I recommend a 6inch sanding disk in a 10mm pistol drill to quickly grind unwanted balsa away, (but be very careful, itís easy to grind too much away). When close to the size required, change to a sanding block and complete hand shaping until happy with profile. By now you have a fairly wobbly fuselage which will not sit on your bench very well, a trip to your green grocery to pick up a foam fruit or vegetable box is a good idea as this can be quickly cut to fit the fuselage profile and make it much easy to work on your aeroplane. Glue in ply undercarriage plates, (FD), to the rear of F5 on inside of both sides of the fuselage. Mark and drill holes for undercarriage tubes, make up from scrap balsa with support packing for undercarriage tubes and fit and glue into position. In front of the wing saddle between the top of the fuselage planking and F4 fill with scrap balsa blocks and sand to shape. The same needs to the done at the rear of the wing saddle behind F6. This basically completes the fuselage construction except for the planking to the bottom of the fuselage behind F5, this will be done after the fin has been fitted to the fuselage and locked into place.
I always start by fitting the wing to the fuselage first. Make sure the wing is sitting symmetrically on the fuselage. Then I triangulate the wing tips to the tail post, this guarantees a wing that is square to the fuselage centre line. Once in position pin then drill pilot holes for the bolts, remove wing and drill and tap wing mount plates. Enlarge holes in wing to correct size and re-fit wing to fuselage.
Now fit the fin into the tail of the fuselage, which is mostly a case of trial and error, until happy with the position of the fin to the centre line of the fuselage and 90∞ to the wing. The fin post extension protrudes over the keel at the bottom of the fuselage and because of the forward slope requires two packing pieces of balsa fitted between the fuselage sides and the front face of the fin post, this ties the fin post to the full depth of the fuselage and is the reason why the rear bottom planking was not fitted previously. Now the fin is fitted, the rear bottom planking can be cut and sanded to shape and glued into position. Next we have to fit the tail plane into the fin between R3 and R3a. Slide the tail plane into position, sanding R3 and R3a until the tail plane and the wing are level and square to each other and glue into position. Elevator and rudder can be hinged and fitted at this point, (but not glued yet).
This is also a good time to fiber glass the hull bottom from F5 to forward of F1 although if you are not planing to fly off water you could bypass this step.
Next fit your motors to the nacelles to determine the location of the access holes through the motor cowls for the motor heads, exhausts and needle valve.
There are many options open to finishing off the model, I went for a painted finish using aircraft dope, talc and a mixture of tissue paper and Sig Coverall since all surfaces are sheet balsa.
The whole model is sanded to final shape with 200 grade sand paper and then doped a couple of times, then sand off the raised fluff. This is when I fill any dents or hollows, slap on one more coat of dope then when dry re-sand. Next apply tissue over complete fuselage using dope as the adhesive, when complete I Iike to give the whole fuselage one extra coat of pure dope then two coats of a mixture of dope and talcum powder, sanding between coats with 400 grit wet and dry, this will give you a nice smooth finish to apply the undercoat.
The wing and motor nacelles were covered in the same fashion except I used Sig Coverall which is a shrinkable fabric that I find very useful for going around complex curves and odd shapes. I filled the weave of the coverall with the dope and talc mix to get a nice fine finish, then sprayed the whole plane with auto primer and sanded it back with 400 wet/dry.
Automotive enamel was then used for the finishing top coat.
Having had some experience with twin engined models in the past I cranked up both motors with some confidence only to find when both engines were running at full throttle that I had very bad engine vibration in the left engine.
Why is this so? I changed engine mounts which failed to stop the vibration but did reduce it. What to do? Then I remembered reading somewhere in the Airborne Engineer about motor vibration and harmonics in twins with side mounted engines, so I decided to change the motors to an inverted position which after some fiddling around with control cables has solved the vibration problem. (Maybe Brian Winch the Airborne Engineer can give us some clues as to the cause of the vibration).
So with both motors running smoothly and reliably it was off to the local dam for some flying. On arrival the CL 215 bomber was assembled, radio checked and both motors run up and needle valves set, then the engines shut down and fuel tanks were refilled. We decided to take some photos, (just in case), before I committed the aircraft to the sky. With the photos out of the way I restarted the engines put the plane into the water and tried to taxi out from the bank.
Wrong. This baby don't taxi at low throttle. After recovering the plane I decided to put her in the water and just cranked her right open, which resulted in the plane pulling quite sharply to the left even with full right rudder and aileron applied, after approximately 5 meters the controls had airflow over them and good control was available the Canadair Water Bomber rose gracefully into the air.
With both motors running well the plane was trimmed for neutral flight and flown in a scale like manner around the dam, (read no aerobatics). First flights are always heart stoppers and this proved no different, although all control throws proved to be more than adequate. Ailerons 20mm up and down, elevators 20mm up and down and rudder 30mm left and right. Center of gravity was set at 30% of the wing cord, (on the spar), a water rudder is required. The only changes done to the plane as built off the plan is 1degree of down thrust on both motors and to invert them.
This aircraft has proven to be an eye-catcher and gracefully flyer. Though not a beginners scratch built model it is an excellent step up into either stand-off scale or a seaplane when you want to be a little different.
A most satisfying and rewarding project.
There is an excellent Web page on the SuperScooper and the address is http://www.superscooper.com