1.  The wing takes shape
2.  ...and the
3. Thoughts about
Fin and Rudder
Tip floats
Fuselage (at last)
The beginning of the end
9. Covering with
Cowl front mouldings
Stripes and patches and details
Maiden flight and subsequent gallery



Oh dear; another bit of displacement activity while I summon the techniques needed to build the wings for the Duchess.

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 flaps as well as 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 .

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

This 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.

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!

...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?

So here we are: a scale rendition of the tailplane and sub-fins viewed from above.
I think a short visit to Mr Knife is called for, don’t you?

Ahh but...I have just visited the superb website http://www.seawings.co.uk/ and found a huge library of walk-round pictures of seaplanes, including four different 415s. It seems I was completely wrong (as was the little 3-view I was working from) and the sub-fins are set to induce a turn to starboard, logically correct but still a lot of offset for a model.

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 demonstartes 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!

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. 

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.

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.

They can be seen completed below

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.

The wing sits at 5 degrees incidence on an extension of the fuselage.  A triangular piece of 5mm at each corner will strengthen the pylon and provide a setting for four blind nuts, so that the wing, instead of being dowelled into a former, is bolted directly onto the structure.

This is the same situation as the Duchess, so I am practising for the next model!

Remembering what Trevor said about making the first attempts to define the location of the battery, I have waited until all the components are 2/3 built, in order to put them all together and make a very rough estimate of where that big lump of electricity will go.

I had in my mind that a tray between F2 and F3 would be necessary, with the cockpit being detachable, just like the Rapide and the Catalina, but because of the huge overhang of the motors and the central location of the wing, it seems that the battery will live just forward of the balance point, so that the top of the fuselage will need to detach, roughly where the Sealand has its hatch.

In this state, the model weighs 2.4 lbs, so after adding three servos, all the other hardware, battery, the rest of the balsa and the covering, I expect 4.5 lbs to be a reasonable target.

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.

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.

On display at the Club Night: one of the finlets got left behind!

At last, the fuselage is beginning to reflect the proportions of the full-size.  The nose block adds so much to the character of the aircraft.

The floats bodies are built on 2mm frame with soft 2mm planking.  The ply mounting plates have slotted holes to allow the front of the plate to slide under two small screws bedded into the main spar, with two more screws holding down the rear of the plate.  I rather hope that this will fix the floats securely enough to cope with water handling, but break off without damage if they hit something unyeilding.  They are fixed quite far out towards the wingtips, so will be very vulnerable to taxiing accidents! Afternote: the float legs are 1” shorter at this scale than I though, so I have cut off the offending inch and re-glued them.

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.

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 same afternoon, the tailplane and winglets were similarly treated and apart from the shine, don’t look too bad if you half-close your eyes.

Now then: do I mount the tailplane in the scale position, which means cutting a slot in the fin post, or opt for the easy life and slide it in between the LE and the fin post?

The cowlings are a pretty tricky shape to reproduce in balsa, so I carved up a master and sent it to Steve at Vortex Vacforms http://www.vortex-vacforms.co.uk/ 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).  Steve does a great job and at only 12 for the pair it represented very good value for money.  However, the guys at RC Model World (who published the plan) now provide moulded cowls from the same masters. Just Google RC Model World and then search for the CL-415. .

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

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.

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.

The trim stripes are gloss finish, the windows and doors are matted by rubbing with one of those green scrubbers from the kitchen.  (I told you experience of washing-up was useful).  The anti-glare panel on the nose is matt black paint and the wheels are a commercial item, stuck on with epoxy.

A last look at the wing and nacelle structure before covering begins.  I did have a “shall I fit flaps” moment this morning, but common sense prevailed.  The Vortex Vacform cowl fronts blend in nicely with the nacelles (at last) and the only seriously non-scale feature is the wing section, which just does not look right compared with the real thing.

The real thing has a mass of details over the whole airframe, but in the interests of sanity, I’m only going to reproduce the minimum needed to give the aircraft its character.  The bullet fairing at the tailplane (does it hide a hydraulic ram for trimming the angle of the subfins? There is an LE extension - not modelled - on the starboard tailplane between the fairing and the sub-fin that could hide the actuating arm.  It would explain why some photos show them at an angle and some do not). The massive hinges which dump the flaps into position are pretty obvious too, and are simple enough to make from layers of 1/16th balsa.

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

ARTF?  Well, she is not by any stretch of the imagination actually finished, but there are only a few essential bits and pieces to go before flight tests. Let’s say a fortnight....

Weight in this state (including the flight battery, but not the props and spinners, the SCs and maybe a flight battery), is 4 lb 2 oz, so let’s say 4.5 lbs maximum AUW, or about 10 oz/sq ft wing loading.  Not bad, eh?

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

The next day I took a trip up to Howard’s Field to take some Welkin photos for Trevor, and after that he flew the Canadair (and said it handled just like his Sealand - no surprise there).  While he wheeled it round the sky I took some photos.

“Ain’t she a beauty!”

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