BuiltWithNOF

MIKE ROACH’S MODEL AIRCRAFT

CATALINA DIARY

The Diary is NOT finished!  See crash and repair details below

Introduction

The wing

Tail surfaces

Fuselage formers

Fuselage stringers

Sheeting the Hull           

Solartex

A bit of pink foam

Wiring

Painting and decorating

Markings and details

Test and adjust

Flying..... Logbook

The crash

The repairs

And she flies (again)

The pylon

Retracts

Sheeting and Cowls

Cockpit hatch

Litespan

Glass-clothing

Building from an Ivan’s Plan: a summary after 4 months experience

Mid-2007.  Having followed the building of Trevor Hewson’s Ivan Pettigrew designs Short Sealand and being at the first flight, when it was obvious that she was a beauty, I looked for a twin for myself.  Ivan’s plans are simple, make lightweight models and are good value for money.  His website has some interesting video clips of his models in the air (even a looping Blackburn Beverley, if that’s your thing) so I sent off for the plans for his 84” span Catalina.  After a very short time, they arrived and I ordered what I hoped was enough balsa and hardware from Flitehook. 

On looking round the ‘net for colour schemes I found lots of pictures at Airliners.net with my favourite being the the lovely version here, which has camouflaged upper surfaces with the remainder white, and sufficient weathering to keep my airbrush happy.  The enlarged rudder is not on the plan, and the distictive gun blisters were not on the aircraft at this stage (although they were added later), so some decisions will have to be made later in the building programme.  There is also a very attractive American version in dark blue, white and yellow which would show up well and look good.  Ivan’s plans are for “sport scale” models and having seen the Sealand look fabulous in the air and close-up on the ground, I must resist the temptation to “improve” the model!

I’m hoping to fly the model at Howard’s Field, off the grass, just like Trevor does with the Sealand, and also at Christchurch Harbour when conditions are right.  I wonder what the effect of salt water will be on the airframe.....

Pause for the sailing season to finish...

Dec 07.  Ordered two Hyperion Z2213-24 brushless motors, two 25amp SCs (400265). and a programming card (400232) to go with them, on Trevor’s advice.  This will be the same set-up as he has in the Sealand, so by Christmas I will be brushless and cashless.  Cut the wood for the tip floats, and will start building over Christmas. The motors arrived two days later, an amazing performance during the Christmas period.  Laid down the 7’6” main spar on a specially-bought 6’ pine shelf from B&Q.  The whole wing build depends on constructing the centre section on the spar, then propping it up and building the wingtips.  The section looks like a Clarke Y, so the process will be very easy despite the size of the beast.  It certainly beats fiddling around with 1/32 square on an indoor Sopwith!  Ivan specifies a flat-bottomed section with a “NACA Cuff” on the outboard sections, to prevent tip stalling, but I’m going to build in 1/4” washout instead.

The tip floats went together easily enough and the tricky-looking scallop on the undersurface required no work at all, as it just formed itself when the sheet was bent to the profile.  I had to keep telling myself that the floats take no real dynamic load at all and are just there to support the wing at rest, and to look pretty when being retracted.  In other words, if they snap off, I’ve done something seriously wrong!

The tip floats are retractable and according to Ivan are only used in the very first and last stages of flight off water, and not used at all when flying off grass.  Each one weighed 20 grams when complete to this stage, although the wire actuating rods have yet to be fitted.

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2 days before Christmas.  Took advantage of the Queen on telly to nip upstairs and start the wing, having cut out all the centre-section ribs, decided on the position of the servos and the route of the snakes and the motor and SC loom.  In my experience, unless you cut the holes for snakes and wiring in the ribs before you start the building, you get a mare’s nest of rubbish splintered holes in the ribs, which have to be hidden by copious sheeting.  This is not going to be that sort of model... The wing section, although supposed to be Seelig 7055 is going to end up flat-bottomed (as are the tip sections) for ease of construction.

Would you believe the centre section was 0.5” wider than my 42” balsa?  I’m very tempted to build it the width of a sheet of 1/16th and have done with it.  A fancy scarf joint just to add 0.25” each side of a standard sheet is wasting time on a sport scale model, surely?  And who would know?  Apart from you and me of course. I also find that Ivan’s spars are not quite parallel on the drawing.  I shall build by the ribs I’ve cut, not by the plan!

28 Dec. The centre section went together pretty easily and I now have the tips framed up, but not after a lot of re-drawing and cut-to-fit.  I found the ribs just didn’t match the spars, so have a complete new set on paper to add to the plan when I have time. 

The wing in it’s “just off the board” state, not sanded, no fittings at all, lots of work to do, but the basis seems to be soundly constructed, if perhaps a little fragile!  In this state it weighs 72 grams (6 oz).

 (PS.  Ivan tells me that on his master plan the CS is 42” wide.  And in fact making a scarf joint so that the entire under surface sheeting was prepared at once (just like the main spar) would be a very good way of building the wing, and were I to make the wing again, this is how I would do it.)

As Trevor Hewson says “We seem to have established that Ivan's plans, whilst very detailed, are sometimes not to be taken too literally. I don't think they are unique in this respect and it always annoys me when modelling journalists advise one to 'cut out a complete kit of parts before starting work'. I can think of no better way to ensure a lot of ill-fitting parts. I much prefer to 'cut to fit' as I go”.

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3 Jan 08.  I got on with the tailplane and fin assemblies over the New Year, after having time off for an afternoon at Howard’s, flying the little indoor Spitfire and Walrus and then tightening the bicycle clips for 15 minutes with the Piper Cub.  It was a challenge after not flying much since April, but all went reasonably well and apart from one slightly short stumble into the weeds at the north end of the main runway, I managed to get her lined up and in the right place for each landing.  The only repair was a bent UC leg.  A record.  As an aside, before flying I charged up the Cub’s 2S and 3S  3700 mAh LiPolys (for the first time since April) and they only took 500 mA before the charger cut out, so they keep their charge pretty well.  After 15 minutes flying they needed about 1500 mA each.  Half an hour’s flying would be up agianst the bump stops, but 20-25 minutes seems well within their capacity.

The Catalina’s tail surfaces are symmetrical and taper along the planform, so although the actual balsa work is straighforward, there is a lot of careful packing up to do before the glueing begins.  The photos show the use of plain rectangular ribs which are planed and sanded to shape after the glue has dried.  Chamfering the spars before beginning work might make the “post building” work easier, but I have always done this after construction.

The square top to the fin is correct for the version I am modelling from the Airliners.net site, but can easily be reverted to the more usual curved top if necessary. The lower half of the fin will be sheeted later, then the slot for the tailplane packed up to provide one degree positive incidence.

The “Master” paid a visit and made some nice comments and reduced the size of some of the hurdles that remain in the construction sequence by drawing out the wiring diagram for the motors, SCs and the retract servo.  Thanks Trevor.  But he raised one hurdle much higher, and I’ve got to have another look at the way the floats retract, and how they fit into the wings once they have done so.  It seems I should have stuck to Ivan’s plan rather than making assumptions and sheeting the outer panels.  Where would we plan builders be if all modelling was as easy as ARTF?   Back to top

7 Jan 08.  After totalling the Cub yesterday (brain versus thumbs) I cut out all the fuselage formers using the method you see here, which adds strength to the corners of each one and creates a hole in the middle.

Each former was then “spatted” so they all stood up straight.

This afternoon I pinned down the 3mm square upper centre longeron and threaded the larger formers onto 4.5mm square rails, then (after a bit of trimming) glued them onto the aforementioned longeron.  Phew!

 ”Next” says Ivan in his instruction sheet, “attach the longerons to the sides of the fuselage where shown.”  Occasionally I lost the right balance between flexibility and strength in my stripwood, but this was an enjoyable exercise as the shape began to emerge and the need for a lot of sanding and shaping became clear.  The sheeting on the front undersurface is to be 2mm and you can see from the photos that there is quite a lot of twisting needed to get the correct chine shape flowing from the nose to the step.  I feel sure that it’s important to use as few sections as possible so that joins in the sheeting are reduced to the minimum in the interests both of structural integrity and waterproofing.  There are swathes of RC Groups http://www.rcgroups.com/forums/showthread.php?t=710485 devoted to Ivan’s models but none of them is much help when it comes to making paper patterns of the main sheeted areas.  I remember Trevor had to spend a lot of time sheeting the Sealand, and that was only the lower half of the “hull.” 

The process of adding the stringers was pretty straightforward, except for the obviously curved ones at the rear of the step.  Not only are they sharply curved, they are also cambered.  After a couple of half-hearted attempts to persuade a strip of 3 x 4mm round this double-curvature, I cut a strip to the camber from 3mm sheet and steamed it to the correct curve while making a cup of tea.  It worked perfectly.  Back to top

Sheeting the hull has proved fairly straightforward, although the end result does magnify the inevitable small errors that creep in.  I tried to stick to best practice: avoid joints by using the largest piece of sheet possible; where joins are necessary, support the joint; use a paper pattern to establish the shape of the area to be sheeted and finally, work to an achievable degree of accuracy.  The planing section of the hull is sheeted with 2mm medium soft (20 grams per sheet of 3” x 36), which was easy to “persuade” round the twist and curve at the front of the hull (the bow, we should call it)

On the left I have increased the surface area of the keel by adding soft 2mm strips either side.  This gives the best glueing area for a minimal weight increase.  The rebate on the left and right of the keel is 1.5mm, just about enough for a good glue joint.

On the right, the subsidiary step just needs sheeting over with 1.5mm and the hull will float!

 

 

 

 

 

The rather sharp compound curves at the bow make it difficult to sheet in one go.  After a rather half-hearted attempt I took the planking route - a skill I have not tried since a Keil Kraft control-line stunter about 50 years ago!  I used a variation on the method described by Henry Holcome in Model Airplane News (easily found on a search of www.modelairplanenews.com) where alternate strips are chamfered.  The bow section of the Catalina has a 1:2.5 ratio from formers A to D, so all the strips were cut 3mm wide at the A end and 8mm wide at the D end, thus forming a fan of strips along that part of the hull.  I hope the pictures make it clearer than the words.

The strips were chamfered using a knife and a steel rule.  This is the 8mm end of two of the strips showing how they lock together.  The bow is still un-sanded in this shot.  The narrow ends of the strips conform well to the sharp curves at former A.  Altogether a very satisfying technique.

One last job before I packed up for the family holidays (2 weeks in Tenerife!) was to sheet the fuselage side back to the rear of the top hatch section.  Despite looking easy, I had to rip off one sheet before it all fell really nicely into place - a case of measuring once and cutting twice: one of my weaknesses.

At this stage I would have assembled the various bits and pieces in the garden, so as to get the obligatory “uncovered” picture.  Unfortunately the wind and rain prevented it.

Those seeking more information on Ivan’s Plans need look no further than the link above, where all 13 pages are devoted to his models and the various techniques used in their construction, as well as countless links to full build diaries (the Martin Mars is really awesome) and this of course is where I did my homework on the planking business.

En passant, as they say, an “Ivan’s” model of the Saunders Roe Princess, at 1/20th scale, would have a wingspan of 132”.  The fuselage formers would be 14” tall and the wing ribs nearly 18” long.  Six 150 watt motors might be enough - weight 14 lbs??

Just joking, of course: I’d have to buy a new car!

Back to the real world

One last post: I put a 3S LiPoly in the battery bay and with the servos in the plan position the fuz only balanced at former E.  This did not seem good enough to me so I carved out the centre of former B and extended the tray.  This moved the balance point 2” further forward, and gives a much better margin of error.  As I’m not going to fit a nosewheel, the cockpit hatch can go between B and D, with the gap between A and B planked over.  If the plane balances with the battery further back I can always fit a stopper at B.  Not so easy to correct the other way round!

2 Feb 08.  Back from a refreshing couple of weeks in the sun, I have tried to get back the momentum I had before I left.  Not easy: there’s always so much to do and so many loose ends to tie up after a holiday. 

I was not looking forward to making the pylon, and at this stage I am wishing that I’d chosen an easier, more sensible design like the Grumman Goose, not this ridiculously fragile attachment of wings to fuselage.  Call me a pessimist, call me Eeyore if you like, but all that is holding the wing and fuselage together is the glue between the top of these balsa pillars, a bit of 1/8th over the top and some 1/16th sheet to fair it all in.  If this joint survives even one of my landings I will be very, very surprised.

 I must admit that by the time I had completed the pylon (all but one side of sheeting, to allow the wiring to be ducted through) my attack of mid-project Builder’s Funk had evaporated.  In this state it does seem strong enough to take the loads of flying and careful landing.  Must do something about that awful fit line though!

The part I was not looking forward to was making the holes for the various bolts and dowels.  By the time it is necessary to make them, the structure hides all the access you need... But my late father-in-law’s toolbox provided the answer in the shape of two reamers.  The first takes the hole from Dremel size, the next to just under the size of the bolt.  Perfect.  The bolt then drives a screw thread in the lite ply or plywood which is then hardened with cyano, thus avoiding the need for a blind nut to complete the fixing

I have taken a slight liberty with Ivan’s plan, preferring a more robust pylon hold-down than 2 triangles of ply.  You can see the thread cut by the reamers in both holes (with glasses).

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 After scrapping a failed version of the cockpit hatch, a break from fuselage work was called for.  All the control surfaces are now ready to cover and the fin/tailplane joint, something I had not been looking forward to, turned out quite well.  I’ve departed from the text again and installed micro servos for each aileron and hard-wired the leads together into a long “Y”.  The float retract mechanism is far simpler that Ivan’s but retains the central servo (although in an email he said he left out the operating crank on his Minicat and had a straight connection to the servo).  The system works but, like others, I find that the last bit of “up” closure is hard to achieve.  I suggest that a slight change to the angle of the float operating wire (the one that is glued and sewn to the float leg) might impart more force to that part of the operation.  After all, the “down” action is quite easy to achieve and not really critical.

Assuming a direct connection to the retract servo in each case, the force acting to keep the float fully up will be greater in the second case than the first, because the moment is greater.  The lack of force in the down position is not so critical on this model. I hope

Up

Down.  The angle on the arm probably needs relieving slightly to reduce any binding

22 Feb 08.  I took a long look at the two servos driving the ailerons and decided to take it all out and revert to the single servo in the centre section.  A GWS HS81 Micro (10.99 from Channel 4 models) has about 3kg/cm of torque, so should be more than capable of doing the job.  Fitting the servo, pushrods and linkages took a couple of hours and the end result is much neater, although my pre-cut holes in the ribs took a bit of a beating.  I also feel happier that there won’t be any interference from the leads.  I promise to put the retaining screw into the retract servo output arm! That servo is recessed into the pylon top.  I don’t feel too happy about it, but I can’t lie the servo down because the wing section is not tall enough to enclose the servo movement.

25 Feb 08. After inserting the motor wiring, I sheeted all the upper part of the D box, adding 7 mm washout at the tips.  The wing feels good and strong now and it is a relief to cover up all those wing ribs and wiring and make some forward progress.

Looking at the engine cowls and comparing the mounting system for my little Hyperion brushless motors, I’ve again departed from the score and have made up the motor mounts and cowl supports from 3 mm balsa sheet.  The photo shows how these will glue neatly under the wing.  Since there will be very little load on the structure there does not seem to be any need for any more reinforcement.

The cowls are a simple wrap of 0.8 mm ply round a 3 mm balsa disc, which is then fronted by two laminations of 5 mm soft balsa and a further ring of 0.8 plyThe ply ring keeps a nice sharp edge on the inner face of the cowling as well as being a guide to cutting out the scrap balsa.  Once sanded,  filled, varnished and painted it should all look like one surface.

27 Feb 08 At last, a nice day and enough structure built to put it all together and admire it!  As seen, it weighs 1lb 14 oz: let’s say 2lb 6 or 7 oz with the ailerons, floats, rear sheeting and cowls finished, making a target weight of 4 lbs seem reasonable.  That will give a wing loading of about 11 oz/sq ft, according to Ivan’s website, and thus a very similar flight pattern to Trevor’s Sealand. 

The rear fuselage sheeting went on relatively easily, there being no compound curves or tricky cut-outs.  The fin mounting still looks difficult though, and will need a bit more than just some epoxy and a heavy weight.

While the glue was drying, I cut out the half-inch sheeting for the nose-block and immediately tried to carve out the sectional shape with it on the wrong way up!  Another nose-block later, and very soon discovered that it is not an easy shape to cut, with the underside chine being very tricky.  I also discovered that Ivan had set a trap for trusting modellers, in that his plan view of the nose-block is 10 mm longer than his elevation.  Just his little joke, I expect... My view is that the elevation is correct, despite being the shorter measurement.  It all depends on where you want the highest point of the chine to be.

3 Mar 08.  All seems to have gone well with the fin mounting, though I glued two fillets under F1 from 5 mm balsa, which were sanded to conform to the curve of the fuselage and thus provided a much better seat for the fin.

The fin base on the full-size seems to have been a very wide affair, providing a lot of support for the tail assembly. 

Ivan’s plan shows a fairing which covers the fillet, back to the rudder line.  It’s one of those satisfying little jobs that makes a big difference to the strength of the fin and the appearance of the model, for very little effort!

Before and after filling the gaps with lightweight domestic filler

For years I have used the very lightest filler on the market. It keeps changing its name, but is now called “One Fill Pollyfilla” and I got mine from B&Q in Christchurch.  It blends well with balsa or Depron, dries quickly and sands very easily.  The fin base now looks as wide as it should and had I thought of it earlier, I could have used the fairings to camouflage the rudder and elevator control rods.  As it is, they are “lost” when looking from the front, but pretty obvious from the side.

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7 Mar 08.  I found the cockpit hatch rather tricky, and was going to abandon all the balsa work and make a foam “black windows” version, but for some reason found myself cutting 1/16th square from a sheet of hard balsa that had been in my spares box for a decade.  A few minutes later the outine of the cockpit was looking good, so after a couple of hours (and super-glueing my fingers to the wood at least twice) The version recommended by Ivan had taken shape.  The fit lines are terrible and will need some disceet filling, but as an “objet” it works, and has the distinctive squinty look of a Catalina office.  The pilot and his co-pilot are actually Harry Hawker and TOM Sopwith from one of my earlier models, carved from pink foam and painted up.  I will have to make something more warlike before fitting all that glazing. 
Two pairs of small magnets provided by Andrew Tubb complete the fittings, and the hatch snaps neatly and firmly into place, yet is easy to release.  Another hurdle overcome and the structure 95% complete.  The Solartex is calling!

Showing the model off at my Club’s pub evening (Christchurch and District MFC meet every month in the local pub) was a very rewarding experience and thanks everyone for the support and positive comments. Clive’s Sopwith Triplane also made a welcome appearance

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8 Mar 08.  Finally started the covering process, with some Litespan on the elevators.  These, together with the rudder, ailerons and wing, can be covered off the model.  Litespan is funny stuff and quite difficult to get a smooth wrinkle-free surface even on large models.  It’s worse on small ones!  I apply the Balsaloc to the film, not the model: this keeps the iron clean and saves a tiny amount of weight, so you feel virtuous when doing it.  I use a small domestic travelling iron and start on the nylon setting, but first I wipe a glue stick round the edge of the structure.  This grabs the covering sufficiently so that you don’t need three hands to get started.  Then I tack round in the usual way and seal all the edges, still on the nylon setting.  The curved edges need special treatment that can be seen in the photos.  For this and the next stage I turn the iron up to “wool” and go over the sealed edges again, then the curved parts, gradually shrinking and sealing as I go.  It still seems very much a matter of chance whether you get a wrinkle-free surface, though.  The iron settings of Nylon, Wool and Cotton equate to tack, shrink and far too hot.

Covering tacked round at nylon setting

Starting to seal and shrink at wool

Fully shrunk and sealed

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14 Mar 08.  Glass-cloth covering.  I have never attempted this before, and was very reluctant indeed to get involved in the epoxy method as described in many a modelling magazine.  I’m strongly allergic to cyano (but not to the odorless type, thank goodness) and mildly so to epoxy, and wish to continue using the latter for as long as possible without too many adverse effects.  But the hull needs some pretty good waterproofing, and Trevor’s glassed hull stands up well to landing on damp grass, so I have a limited range of options.  Ivan’s preference of using doped-on silkspan appealed, but I couldn’t find a source of the material, and although I like the smell of dope, neither Wendy nor the dog does!

I had read on the Ivan build thread about using acrylic varnish instead of epoxy as an adhesive, and talking to the ever-helpful staff at Channel 4, was introduced to Rustin’s varnish, which they had used with 0.6 oz glass cloth to cover the fuselage of an ARTF airliner.  I was impressed.  Here are the results.

Mr Rustin’s varnish: dries matt in 20 minutes, and is water clean-up

This is the underside of one of the tip floats.  The procedure I followed was fill any dents with the Polyfilla mentioned above and then give the balsa a coat of varnish (the effect is very similar to using sanding sealer) and sand off the fuzz, then lay a roughly cut strip of cloth over the surface and give another coat of varnish.  There does not seem to be the desperate need to wet out the cloth, nor to scrape off any excess, as the varnish is absorbed into the grain of the cloth and the balsa - anyway, I needed the structure to be waterproof and strong, and I have 16 oz to play with! Note how well the cloth conforms to the sharp double-curvature.

The fuselage is similar - just bigger!  I laid in a strip along the hull step and others round the water-rudder area and the subsidairy planing section, where the water would rush in and out in its uncovered state.  Then the hull surface got a full layer, then the top of the fuselage, then a final layer on the hull to provide yet more reinforcing and waterproofing.

Ahh: the “W” word! I described this technique on the Ivan’s Plans build thread http://www.rcgroups.com/forums/showthread.php?t=710485 and almost immediately got a post that the varnish was not waterproof, and checking the Rustin’s website, all it said was “water resistant.” Don’t Panic! I dumped a sacrificial tip float in a basin of water overnight, and was greatly relieved to find that, by morning, all I had to do was shake off the water droplets beading on the skin. Phew! I agree that the varnish probably isn’t “waterproof” in law, but it certainly seems waterproof enough for my purposes.

The covered fuselage has put on 25 grams, from 307 to 332 but I have a final layer of cloth to varnish onto the underside, with an overall coat of varnish to finish off.  Still, it looks as though for a 2 oz weight gain I’ve got a tough, water resistant (!) finish, with no smell, no clogged brushes or rolls of kitchen towel and no mess.  Can’t be bad.

27 Mar 07. I have never used Solartex before and after a day or so putting it off (as one does) I've finally covered the ailerons and the wing undersurface. What a wonderful material! No wonder 'tex users hate Litespan! I found I had to use a slightly higher setting to stick it down firmly, but a lower setting for initial shrinking works very well indeed.  The photo is slightly flattering, but I have to say, it does look good!

The top of the wing was covered in one piece of fabric: a slightly nerve-racking experience! It really does seem to have gone well and is almost ready for painting. 

You can just see one of the floats, which had to be attached in order to get at the linkage from the top, and therefore had to be painted.  A 3.25 spray can of Hycote Double Acryclic white undercoat from MDC worked perfectly.  Hycote is a dense colour, very quick-drying paint and is compatible with cellulose paints and modelling acrylics, and for use on plastic, metal and ceramics.  Balsa wood seems to fall intoone of those categories.  I’ve used it before on Depron with no problems.

Now: do they do the same thing in dark sea grey and dark green, I wonder!

One of the trickiest bits of modelling is making the fairings behind the engine cowls.  Planking or solid block take a long time and the results can be indifferent.  I’m used to working in pink foam, and these 4 stages (HWC blank, HWC rough shaped, fine sanded and glass-cloth covered) illustrate the ease with which complex shapes can be made from foam.  I know that it’s not “traditional”, but the fact that it took an hour or so to make these 4 fairings speaks for itself.

Foam is not strong on its own, and for the first time I glass-clothed directly over it, using my water-based varnish.  It worked perfectly, and there is no tendency for the varnish to attack the foam.  It is certainly a far better option than tissue and 50% white glue, which I have tried on another model.

Fans of disaster movies should have a look at this!  While I was wet sanding the fuselage I caught my hand on the water-rudder fitting...and the soldered joint inside the covered-up fuselage broke!  Trevor’s question came back to me immediately: “is it just a wire-to-brass strip joint?  Perhaps if you soldered the strip to a collet you would have a better join”  So, 10 minutes later, I had opened up the top of the fuz to get access, prepared and soldered up a collet with the actuating lever (brass strip), re-threaded the whole thing back into place and tightened up the grub screw..  Just got to fit the hatch back now.  Didn’t real Catalinas have a hatch here?

At last the model is beginning to look a bit more military.  Hy-Cote grey primer, which as you see has covered the dense white of the Solartex, is a bit light for Dark Sea Grey, but will provide a good base for the camouflage colours.  The fuselage has been sprayed white, after doing a successful float test and fitting the water rudder. The markings are a test sheet at model size, done using MS Word.

The control surfaces are fitted and the hinges epoxied and pinned.  The last lap seems to be here, and my list of actions is down to 9 serials, ending in “Fly!”  The aim is to get her to the Club scale competition evening on 7 May, if possible having had her first flight.

Gulp.

Masking curved colour lines is always tricky, but on this “sport scale” model I tried a new technique, using paper patterns and the sort of glue that you get on Post-It Notes, called “Scotch Up”.  I have no idea where to get it: I got some from Mike Stewart (his superb free-flight website is listed on my links page) and it works just as advertised: it sticks quite firmly and peels off easily. The resulting dividing line is not perfect, but

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“Scotch Up”, made by 3M in France and the not too bad dividing line.  Using car body primer in a spray can makes this sort of job much easier because it sprays cleanly and dries very quickly.

Markings are printed onto Lazertran transfer paper (www.lazertran.com) using an ordinary inkjet printer, having made a proof copy first to check the dimensions.  Designing the markings is a pretty simple process, using Microsoft Word and the “autoshapes” function.  All the markings have to be cut out before soaking off, as the backing film dries white.  This useful feature means that the white part of markings (the centre of the fin flash and the fuselage roundels) needs no special treatment, and the serial number, on a white background is just cut out in a rectangle.  Apparently the uncoloured part of the transfer can be made transparent (and thus take on the background colour) by using Krystal Kleer varnish.  I haven’t tried this yet. I wrote an article about making markings for AMI a few years ago.  You can see it at my techniques page.

The wiring is very simple (it has to be!).  The motors’ power leads are Y joined into Power Pole connectors.  The only splicing in the thin wires was between a small battery and the retract servo.  At the moment the two SCs are Y leaded into the throttle socket on the RX.  No-one is sure whether this is a good thing or not!

The various mechanical connections have been tested and everything moves in the right direction.  The motors have been run up.  The floats go up and down.  The model balances on the mainspar. All that is left is to..........................

Fly! 4 May 08. She flies, she flies! I had a really good maiden flight this evening at about 7.30pm. Went down to the Harbour and did a bit of taxying to make sure everything was going to work, then took my Sailing Club's safety boat out into the middle and moored up. With half a mile of clear water all round, there were no worries about hitting anything! She took off perfectly and climbed out strongly on 3/4 throttle. A lot of down trim was needed and a touch of left rudder and she flew hands off. Then I just concentrated on gentle turns. She seems to cruise on about 1/4 throttle and to land I just had the props ticking over. She landed herself with just a bit of up elevator over the last 20 metres or so.

Wonderful! Thanks to everyone who helped with advice and encouragement: photos next time!

A very happy Sopwith Mike

5 May

10 May

Building from an Ivan’s Plan.

After 4 months living with a Catalina, can I pass on some tips for other builders?

Will it fit in your car?

Span 84”, Wing area 835sq in (5.8sq ft), Length 52”, Weight 4lb 4oz (4oz more than Ivan’s), Wing Loading 12oz/sq ft
2 Hyperion Z2213-24 brushless outrunners with 30 amp SCs, 10x7 APC E props, 3-cell 3700mAh LiPo battery, 7,300 rpm at 30 amps, about 70 watts/lb. SCs WERE wired directly into the RX using a Y-lead, but this has not proved successful and there is now a conventional RX battery with the SCs running just the motors

Is it a scale model?

This is a “sport scale” model.  The fuselage is quite complex, but if you want a relatively easy build and a lot of modelling satisfaction, then just build it off the plan like I did.  If on the other hand you want a “proper” scale model, then start off by choosing a particular prototype or 3-view and change the plan outlines to conform to your aircraft.  The shape of the bow section , the curve of the pylon ends, the engine cowls and carburettor intakes, the divergent thrust-lines angle of the engines themselves, the gun turrets and blisters, the rudder and elevator hinge lines, the retracting floats, etc etc all need attention.

Is the plan and the parts accurate for the model?

There are a couple of draughting errors on the plan: the nose-block is a different length on the plan view than on the elevation and the floats are too short to fit neatly onto the wingtip.  Everything else is pretty good.  Like all plans, the fit of parts must be adjusted after each is cut out.  Don’t make a “kit of parts” as is sometimes advised in the magazines, because you will just have to cut most of them out again!  You might like to make the centre section of the wing exactly the length of your balsa sheets if you can get 42” stock, but splicing the whole of the under-surface sheeting in one go is probably a better way to approach the problem.

Retracting Floats

The retract mechanism on the plan is unnecessarily complex and a straight connection to the servo is all that is needed.  However, some form of restraint is needed to stop the float folding towards the fuselage when manoeuvring on choppy water.  I suggest a fishing trace arrangement, but some form of semi-scale linkage would look good.

Fin, Rudder and Tailplane.

I found no problems here.  Take care to block up the LE and TE accurately so you  get symmetrically constructed surfaces.  The hinge gap on mine is far too big (I made a mess of the hinge fitting).  The fin just glues onto the top of the fuselage, then the join is reinforced by the side fairings.  It might be possible to conceal the rudder and elevator pushrods inside this fairing: it might be possible to hide them altogether, but it would be a more complex build.

Wing.

The wing looks alarmingly flimsy at all stages of the build, until it is covered.  Just grit your teeth and build it with the plan wood sizes and take care at every stage to handle with care!  I did not use Ivan’s NACA cuff as I think it spoils the look of the wing, and I have not noticed and tendency to tip stall.  I put progressive washout along each wing outer section: about 1/4” I think.  My wing section is just a plain flat-bottomed thing, using the upper contour of Ivan’s.  Lazy I know, but it worked and made building and fitting to the pylon, and fitting the nacelles, much easier.

I did try to lie the servos flat in the centre as Ivan suggests, but the movement I needed on the retract servo meant it had to stand upright, and be let into the pylon top.  This has not been a problem so far.  I built a simple hatch to get access to the servos and this has proved essential.

Fuselage.

I built mine upside down, using the hardwood rails as a datum, and extending the smaller formers on “legs” so that everything ended up square and straight.  Even so, the fuselage is not perfect!  Once all the formers and stringers were in place, I fattened up the stringers where sheeting was to be joined with soft 1/4” strip, to provide a good glueing area for the sheet edges.  I think that without this reinforcement my fuselage would have been very weak.

Pylon

I have to say that this was the bit that made me most nervous!  It has to take all the bending and shearing loads of flight and landing and just looks so puny on the plan.  But once I had bitten the bullet, built it and sheeted one side, it all made sense.  It’s as strong as it needs to be.  If I were to built the plane again, I would add load-bearing struts in their scale locations, permanently attached to the wing and bolting into the fuselage.  The pylon could then be lighter still.

Covering.

I think that light glass-cloth covering applied with acrylic varnish is the bee’s knees and hope to use it again on sheeted structures.  It is completely waterproof, strong, light and sands, fills and takes paint very well.  I used Solartex on all the other surfaces except the elevators.  This probably explains why I had to add 3 oz of lead (now down to 2.25 oz) to the nose! Litespan on all the tail surfaces would have reduced the need for ballast.

Power.

Now that brushless motors and SCs are as cheap as chips, I see no point in using anything else.  The set-up I’m using gives 4lbs of thrust and will probably fly for half an hour and still have enough left in the battery to taxi home.  I have not done any aerobatics yet!

Flying.

After only 4 flights, I’m hooked.  She flies very well indeed and is stable in all axes, floats along on a few amps and almost lands herself.  Take-off can be very short on full power or nicely extended for a scale run, but she does need some up elevator to prevent the nose digging in.  This isn’t a serious problem.  Unlike Ivan, I have found that I don’t need to use the rudder in normal flight and since my thumbs are not coordinated, this is a good thing.  The water rudder is perhaps a bit small in windy conditions.

Summary.

Ivan’s plans are for builders.  You do need to use your grey cells to work out what he means and how you are going to achieve the end results, but that is all part of the challenge.  You model will be different from mine, but sticking to the spirit of his designs will give you a unique model, built to fly.

The crash.  A quote from my Model Flying Club’s magazine:

I expect you have heard that I fell into that perennial electric modellers' trap, the prop bite, one afternoon late last year. I ground-looped the Catalina, and in trying to get the cockpit canopy off so as to switch off and trudge back to the car, must have pushed the throttle stick with my coat sleeve. 3 slices later I had wrenched my hand out of the way and pulled one of the motors off its mount, fortunately without too much damage to either, although both looked much worse than they were. Both the model and my hand were repaired, the Catalina by Mr Epoxy and my hand by Nurse Wendy.

The model must have decided that it had had enough of being flown around the sky, and that if it could not self-destruct by biting me, then it would do so by deliberately changing the TX configuration while I was asleep. The next flight, which was to be its 50th, started with a good clean take-off, then a graceful but terminal wing-over to smack into the ground with a the most terrible crashing noise.

She is currently sitting on a high shelf waiting for a repair assessment, but it does look pretty bad. Nature is much better at glueing things back together...

Ah, the joys of aeromodelling!”

1 March 2009. And then there was this!  In mid to late December I took her out one frosty but calm day and as I described above, she smacked into the ground and made a large hole, which can still be seen today!  I didn’t have a camera with me (or was too dismayed to take a picture) but the next day the evidence was there for all to see.

The damage was extensive, and I laid the wreckage on a shelf and finished the next model, the Canadair “Super Scooper”, which I had started in November.  At the moment this is 99.9% complete but onflown.

As soon as space was available I laid out the wing and after taking off all the covering, cut out/shook off every broken item.

The floats and ailerons were undamaged and came off easily, to be stripped and stored.  The same could not be said of the engine nacelles and motor mounts, wich were junked, apart from the radial cowlings which survived reasonably well.  The main spar was unbroken (thank you, Ivan!) but the LE and all the ribs were in a bad way.  After cutting back the underside LE sheeting and sanding off the residue, it was time to start rebuilding.

Improvements?

I never got round to making the struts, the front gun turret or the observation blisters. Nor the exhaust manifolds for that matter.

Lots to do!

12 March 2009.  The wing is pretty well repaired, which required all the ribs out to the aileron break, most of the D box sheeting and the motor mounts to be replaced. The servos have been re-fitted.  The ailerons just need to be re-pinned in place and the retracting floats secured after covering. The nacelle cowlings needed to be completely re-made, but the job only took a couple of hours, using pink foam and a hot-wire cutter.

15 March 09.  The fuselage, looking pretty sorry for itself. So you would you if you had dived head-first into the grass from 50 ft! All the lower (hull) parts of the bulkheads are intact, except for A and B, and most of the side frames have some balsa left on them. After clearing out all the crud, I superglued all the splits in the 1/16th skin, made up and fitted new side frames from G forwards and replaced the horizontal reinforcement for things like the servo rails and RX mount. Despite the damage, it is beginning to seem as if it can be successfully repaired.

19 Mar 09.  Claimed Old Age pension. Continued repair of Catalina...

27 Mar 09.  Some tricky stuff needed for the new canopy/turret/hatch, and a lot of filler will be needed for the gaps.  The pylon is complete once again and seems to be as strong as ever.  Heard from Ivan today, so looking forward to flying the repaired plane next month and sending him a few photos.

And finished.  Even got the struts done this time!

As usual, the photograph flatters the model: I did not spend hours getting the shut lines exactly right, but this represents 433924, a Catalina belonging to the USAF Air Rescue Service in the late ‘40s and early ‘50s.  The colour (Tamiya Medium Blue) is not deep enough but is reasonably close.

The front turret is built up like the cockpit, but the engine fairings and the radome are pink foam.

Oh, and the observation blisters are being moulded by Steve at Vortex Vacforms.

Flight tests as soon as the weather is suitable!

Thursday 16 April 2009. Nearly a year after the first flight, she flies again!  There was a bit too much breeze for comfort, but she tracked straight on the water and did the usual leap into the air.  She seemed a bit twitchy on ailerons but looked wonderful.  The slightly bent shaft of the port motor sound pretty rough though.

Took in a bit of water taxiing back to the boat, but it all poured out again...

18 April 2009.  A very pleasant evening for flying, rather spoilt by the port motor giving up during a low flypast.  The subsequent heavy splash landing soaked the RX, which has had to be replaced, but there seems to be very little damage. I think the fault lies with the speed controller Y lead connection. Good pictures, though! The last one is after the big splash.

Looking rather forlorn.  The object in the water on the starboard side is the radome.  The wing hatch disappeared and one wing bolt came loose.  Lucky!

It turns out that it was the speed controller that was at fault, and this has been replaced, along with the slightly bent prop adaptor (not the shaft, as I thought). The model is now converted to Multiplex and has steering on motors rather than water rudder.  Despite the prang, there has been a lot of interest in the model, and nearly all “vintage” people recognise the type.

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