The Canadair/Bombardier CL415 is the forest fire water-bomber par excellence and has perfect proportions for a model version.  A number have been made already, but my aim is to stick as closely as possible to the building techniques and materials popularised by Ivan Pettigrew.  The model will be 72” span, weigh about 4.5lbs, be powered by the same brushless electric set-up as the Catalina, have the usual 4 functions and be decorated in the garish scheme seen above.  You can see more about the real thing at http://www.oognok.ca/415/415.shtml which includes some very good pictures.

I took the basic 3-view from “Rotorheid”’s account of building a 1 metre version in a mere few days (I recommend his posts - they are very funny as well as being informative) at  http://www.rcgroups.com/forums/showthread.php?t=909913  (Afternote) but there is now a much more accurate plan available on the Seawings website - a visit strongly recommended!

So here goes.  The little plan is now 72” wide.

The wing should look familiar to all Ivan builders: a vertical mainspar with hardwood strips top and bottom, a false LE and a rear spar from 3mm balsa and lots of 1.5mm ribs!  The ailerons and flaps have yet to be added, but the structure is sound.

All the holes in the ribs are for rod-in-tube linkages for ailerons and flaps.  I’ve drawn up a neat double-bellcrank system for the flaps, so they operate in a scale way, but since Ivan would not consider flaps necessary on a lightly loaded model and they just add a large layer of complication to a relatively simple model, I think perhaps I’ll just leave them off!

6ft of wing looks quite a lot indoors, but it will be perfectly manageable when it is covered.  The complications of a 2-piece wing just didn’t seem worthwhile.

22 02 Jan 09

The rear of the wing went well, but I always seem to stutter over ailerons, which seem to need far more work than their size merits.

The nacelles will fit in the bigger gap between the 4th and 5th set of ribs out from the centre, cantilevered off some liteply supports. 

Lots more to do, but getting the wing off the table and preparing the board for the tail group always seems a big step.

The tailplane is typical of the aeroplane: tough, chunky and utterly functional.  And very easy to make, as a result. One of the unique features of the plane is the offset subfins.  Easier, I suppose, than offsetting the entire fin and rudder as has been done on a number of aircraft.  The fins will just slot through the offset ribs and who knows, may just make my take-offs straighter!

03 18 Nov 08

...but here’s a thing.  Which way should the offset go on the model?

I would have thought the aim would be to steer the plane to the right (ie the same as right side-thrust), but on the real thing it’s the other way round.  Perhaps their engines rotate anti-clockwise?

(Afternote) Details of the sub-fin offsets are shown on the Seawings 3-view.

09 19 Nov 08

The main undercarriage is an apparently simple parallelogram where the wheel is kept in the same plane throughout the retraction sequence and when full “up” lies against the side of the fuselage, very much like the Catalina and Sealand.  This simple “stick and pin” model demonstrates how easy it would be to make a working example for the plane: but then you have to make a working nosewheel and waterproof everything!  No thanks!

UC 05
UC 03
UC 02
UC 01

The fin and rudder are huge! There is a slight complication to the very simple structure, in that the rudder and elevator hingle lines coincide, so some “special circumstances” have to be invoked.  (I’m an Iain M Banks fan, if you were wondering, and if you were not, it doesn’t matter).  The only non-Ivan practice will be to hinge the rudder with Robart point hinges, to allow a nice close fit.  The fin post is backed with triangular strips which are then sanded away to make a smooth “hollow ground” section. The hatched section of the fin post will have eventually  to be cut out to allow the tailplane to be fitted.

Framing up the nacelles took rather longer than I anticipated, as they are not quite as simple as they appear, and I have rather over-engineered them!  The one nearer the camera weighs well under 2 oz though.  The motors will be the little KEDA 2217/20 from Giantcod RC, used by Trevor on his Rapide, with Hobby Wing guard 25A SCs. 

21 13 Dec 08

Although is it a very old and well-established method, I have never used triangular section round a curve before, but found that cutting 3/4 the way through the inside of the section made bending it to the nacelle profile very easy.  As you can see, it carves and sands nicely.  The cowl fronts are a much more complex matter, however, and will take up hours of carving and sanding, or maybe I’ll try a moulded front end from acetate. Then you only have to carve and sand the once!  It must be time to thread some power wires through the wing, but first a trip to Channel 4 tomorrow.

13 float close-up

Frankly, I had thought to make the floats from pink foam, as they are pretty curvy and tricky to sheet and plank.  But once started, it’s not all that difficult and the basic 3mm framework and the 1.5mm planing surface went together very easily.  Just waiting to buy some nice light soft 2mm for the upper surfaces.

Looming out of the December darkness comes the brick-built fuselage, from 5mm square and a few 3mm formers, with part of the 1.5mm sheeting already applied.

The front hull is the scale section, but I’ve reduced the “V” at the step in line with Ivan’s advice.  A deep V section gives very good sea-keeping and a comfortable ride in a seaway, but a flatter section gives better planing performance (but more bounce on landing) and of course is necessary if it’s going to take off from grass without someone running alongside keeping the tip floats out of the weeds.

29 11 Jan 09

2009.  I’m at that stage where there is still a heck of a lot to be done before covering can begin, and each little job takes at least an hour, but the end seems to be in sight!  The fuz is fully sheeted (the rear sides are going to be left open, and just covered with film) and the wing/fuz join is nicely faired in.  The wing has its LE now but is not completely closed up, waiting for final decisions on motor wiring and whether to cover the under-surface before glueing the nacelles in position. The top hatch and the cabin are taking shape, but only after cutting out several cardboard templates.

26 07 Jan 09

The cockpit roof, the cockpit itself and the nose of the aircraft are quite difficult to visualise, even with the superb “walk round” photo essays available on http://www.seawings.co.uk/ . Unfortunately none of the pictures are taken from above the aircraft, so there is a bit of guessing going on.  The rather neat triangles, which enable the cockpit to blend into the upper fuselage seem to be the key to getting the shape about right.
The battery access hatch should fair gracefully into the wing glacis plate, but what is possible in metal is not always so easy in balsa!
The next step is to glue the cockpit onto the fuselage and build up the stringers over the front formers to make the correct and somewhat tricky shape.

23 05 Jan 09 25 05 Jan 09

The cockpit is pure Ivan, with balsa sticks between the roof and the fuselage, to be covered in with acetate.  I am not a fan of detailed cockpits and even considered Trevor’s approach of having a “frosted glass” windscreen.  I would rather spend time on a consistent level of detail all over the model rather than having to concentrate on just one aspect.  With this in mind, I have lined the cockpit with plain card (actually, a cornflakes packet) and intend to find a couple of 1/12th pilots’ heads to add some degree of realism when it flies past.

You can’t see into the cockpit when it’s in the air.

32 12 Jan 09
41 15 Feb 09

This is the first time I have used Profilm, and so far it is a very impressive covering medium.  The rather thick backing paper makes it easy to mark for cutting out and the film itself adheres well and shrinks perfectly.  It is probably too glossy for a realistic finish, but some discrete rubbing down with fine wire wool, or even a kitchen “green pad” will take the edge off.

The Canadian Fire Service aircraft are Cadmium Yellow all over, with lots of black and white trim. Each leading edge has this typical sweeping design, which obviously needs to be quite accurately marked.  Profilm (aka Oracover) recommend that trim like this can be done with the same type of film - taking great care not to trap air bubbles - and so Lesro Models, an Oracover stockist, who sell by the metre rather than the roll, was raided.

After one abortive attempt to shrink the whole thing in one go, a template was cut out of the ubiquitous Cornflake packet, and four of each “hand” cut out, allowing a couple of mm to wrap round the LE.  The result is very pleasing and brings a whole lot more character to the simple sub-fin, as you can see from the two photos.  And being black, it’s difficult to see the air bubbles!

The cowlings are a pretty tricky shape to reproduce in balsa, so I carved up a master and sent it to Sarik Hobbies with the excellent results you see here.  Any imperfections are down to my rushing to job in my haste to get away for our annual trip to Tenerife (and the fact that my first attempt was 1/16th too small all round). 

Just one tip.  Get the mouldings first and build the cowl to fit them, and NOT the other way round!

(Afternote). The cowls are moulded in white ABS now.

Another milestone passed - the floatation test: 30 minutes in the bath, ballasted to 4 lbs at the balance point.  No leaks, and she floats nicely in a slight nose-up attitude, and is stable side-to-side.  This seems very important for relaxed flying off water, as an instability in this axis (ie a tendency to tip sideways) would seriously affect take-off and water-handling.

37 04 Feb 09
36 01 Feb 09

Now the fun part! Making the black and white stripes down the fuselage and up the fin seemed like an easy “afternoon” job...  The fin stripes were reasonably easy but three tries later I was still in trouble with the curved transition.  It won’t look too bad with the white centre lining.  All this decoration was added with Solartrim. 

The elevator servo is located in the fin: the simplest solution to a very embarrassing mistake, whereby the intended cable exit was positioned far too far back.  A complete rear fuselage rebuild was one option!

The arrowhead finlets add even more character to this amazing aeroplane.

Solartrim is reasonably easy to work with as long as you adhere (sorry!) to the soapy water discipline: cut out the shape needed and release it from the backing paper underwater, in a soapy water solution (the amount of soap seems pretty unimportant, but about twice the amount you would add to do the washing-up - and don’t say “what washing up?”)

The trim can then be slid into place quite easily, and patted dry.

48 25 Feb
50 25 Feb
43 15 Feb 09

The wing LE is sheathed in a black trim (surely not a de-icing boot?) with Dayglo patches. 

I used Profilm for this application, and found that the best way of having a bubble- and wrinkle-free surface was to tape down the trim and use the lightest setting on the iron, working back from the LE, adhering the black to the yellow before going to “hot” to seal the trim in place.  It seems to work.

The Dayglo (should have been red, not orange) is Solartim, applied wet.

The “work” room photo is just to give some idea of the terrible conditions us builders labour under, with junk almost everywhere.  You can see the Catalina on the right, waiting for the AAIB. Other planes are (L to R) DH2, the wheels of a Sopwith Tabloid prototype, Butterfly chassis, Walrus, Sopwith Bee and profile Auster Aiglet

49 25 Feb

2 April 2009.  After all the research, designing, building and testing, she FLIES!  Despite the high thrustline and short-coupled design, she flies just like the Catalina.  She weighs about the same, is roughly the same size and has the same power, so it’s not a surprise, but my goodness, it feels good! I was HOTAC (hands on TX and Camera), so did not get much in the way of flying shots, but the compulsory evening sunshine at Christchurch Harbour was the sort of photo-opportunity you just can’t miss. Just the spinners to sort out, and she’s done

54 3 Apr 01
53 2 Apr 09 03

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