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Another Andy Blackburn PSS Canberra

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Devon Slopes22/02/2018 17:49:15
15 forum posts
20 photos

I was looking for a first essay in scale modelling, mainly for the fun of building in odd moments of an evening. I thought about something to fly indoors, but our indoor venue is small, which is a bit limiting. Nor do I really have anywhere to fly an electric or glow model, as I'm mainly a slope soarer. But, a kind friend had bought me a year's subscription to RCM&E, and towards the end of the year saw the PSS Canberra. So, why not?

The other on-line resources I know about are Andy's blog developing the model, and Peter Garsden has started his own build blog which started just before mine - hopefully we can compare notes.

Edited By Devon Slopes on 22/02/2018 17:49:50

Devon Slopes22/02/2018 18:10:58
15 forum posts
20 photos

So, the first thing I did was order the Sarik Hobbies' Kit. As I said on Peter's Blog the acreage of Balsa is impressive.


Two closeups for those of you interested in what is really in there.



Devon Slopes22/02/2018 18:27:08
15 forum posts
20 photos

I'm still waiting for the balsa for the wing skins, so decided to start on the fuselage instead. Also, the construction intrigues me; it appears to be rather clever (Andy, if you are listening), and quite unlike anything I've done before, though I don't have a vast building experience. Anyway, the first task is to glue the two halves of each of the top and bottom keel's together. The balsa does not quite match the plan - but this is not a complaint, the kit is really nice - just a warning to other builders to make sure the two keels are the same length (whatever that may be).

I also sanded off a certain amount of the "cinder" from the laser cutting process from the scarf joints where the halves of each keel join, and where the formers slot into the keels. The down side of doing this is you have to be careful not to significantly change the shape of the slots, but the upside might be that the glue joint will be better. Does anyone out there know if this is helpful?

Anyway, as you can see from the picture at the head of the blog, I now have a top and bottom keel.

Mark Kettle 123/02/2018 05:26:45
2091 forum posts
1281 photos

I'll be following your build DS. The comment DS  -  'The balsa does not quite match the plan' -  is the keel size you are seeing in wood and the outer fuselage line on the plan including the outer skin planking?

Edited By Mark Kettle 1 on 23/02/2018 05:27:20

Andy Meade23/02/2018 08:47:47
2306 forum posts
596 photos

Good start , hope the wood issues aren't a show-stopper yes

Peter Garsden23/02/2018 08:54:08
1295 forum posts
884 photos

In answer to your question about filing off the scarf, I think it is a bit dangerous to file it off, because you could make the slots too big. It is really easy to sand away too much. I have not had a problem with glue sticking to scarf as it is actually just burn from a laser I think. The only place you have to file away is the wing spars where the joints are at an angle. Also the thick balsa has angled cuts because of the way the laser cuts the balsa. To be fair this is written on the 1/4 inch balsa by Sarik - attention to detail again.

Andy Blackburn23/02/2018 11:23:59
425 forum posts
482 photos
1 articles
Posted by Devon Slopes on 22/02/2018 18:27:08:

The balsa does not quite match the plan - but this is not a complaint, the kit is really nice - just a warning to other builders to make sure the two keels are the same length (whatever that may be).

I also sanded off a certain amount of the "cinder" from the laser cutting process from the scarf joints where the halves of each keel join, and where the formers slot into the keels. The down side of doing this is you have to be careful not to significantly change the shape of the slots, but the upside might be that the glue joint will be better. Does anyone out there know if this is helpful?

If you look on the original build thread, about half-way down page 1, you'll see that I also had a similar problem with the parts not quite matching the plan; there were two reasons for this:

  1. The first set of parts that I had made (by SLEC) were exactly as the plan but the laser cut isn't vertical - it's V-shaped, and is typically 0.7-0.8 mm wide at the top for 1/4" sheet. I corrected the laser parts patterns by adding a kerf of about 0.3 or 0.4 mm (memory is hazy) and just used the original parts by arranging them on the plan (see below) in about the right position, checked that the fuselage former at about F6 would still fit, pinned them down and stuffing bits of 1/32" balsa squashed into a v-section into any over-large slots in the keel. But I hope Sarik are using the corrected parts - I know that they have the DXF files, and from the picture it looks to me as though they are.
  2. The laser-cut parts will be the right size, but the plan, having been by pulled through a large print machine using a roller which will typically be subject to a small amount of slippage, might not be printed at 100.0% the correct size, and then the finished print will be subject to differences in temperature and humidity, so it'll change size anyway, and what's delivered to you will generally will be a slightly different size to what it should be. This has happened since time immemorial. Or, more accurately, since the invention of paper.

What you're seeing is probably a product of the plan not being the right size. Balsa doesn't change in size with temperature and humidity anything like as much as paper - Trust the parts.

On the "sanding away the cinder" thing, that depends on how you've done it. If it's to make the keel parts fit, and if you've done it carefully so that the sanded edge is exactly at 90 degrees to the face of the keel, then that's a good thing and in fact you have to do this with the keel parts (same applies to the fin, rudder and tailplane parts) for the reasons outlined above.

(The easiest way to do this is to hold the part on a cutting mat with a slight overhang, and then use a Permagrit block - which has 90 degree corners and a smooth bottom face - very carefully to true-up the edge. Sorry for teaching granny to suck eggs but it occurs to me that people who haven't done this before might find it useful).

But I wouldn't do it with anything else, though, unless you find that you have to do it - for instance, before planking or covering the fuselage when you have to sand it so that the edges of the formers fit the outer shin properly.

I should also point out that some of the keel slots are already intentionally a little bit big so that there's a little bit of wiggle room in getting everything to fit. Also, some of the supplied balsa might well be a few tenths of a millimetre under or over the nominal size (this is quite normal for balsa, although ply tends to be a bit more consistent) so having the slots over-size is usually a wise move. It doesn't seem to affect the strength of the overall component in any practical way - if you pile it into the side of the hill at high speed it'll still come apart in the same way, but mine hasn't (yet).


Edited By Andy Blackburn on 23/02/2018 11:34:32

Peter Garsden23/02/2018 18:55:29
1295 forum posts
884 photos

Wow Andy - that is a very proper explanation and quite accurate. Blew me away.

Whist you are online, I have noticed that there is no part cut for the 1.5mm wing root rib which fits onto the fuselage (I think from memory) and forms the join for the wing. It hasn't got a part number, and is something I will have to fashion myself. I am quite happy to do that but it is the one part I will have nightmares over because it has to be absolutely spot on or the incidence pins will be out of kilter. Just a thought if you are speaking to Sarik.

Parts D1 to 4, I think are also omitted, which again, I will do myself from carbon paper, but they could easily be incorporated onto one of the existing sheets where there is definitely space. Again, just a thought.

This really isn't a complaint, just an observation because, as I say the wood pack is very good.

Andy Blackburn23/02/2018 20:20:33
425 forum posts
482 photos
1 articles

Well, I'm pretty sure they were both on the original DXF files. I'll email Barry at Sarik.

Andy Blackburn23/02/2018 21:09:11
425 forum posts
482 photos
1 articles

OK, so I've emailed Sarik Hobbies to alert them to the issue. Obviously, I haven't seen the wood pack that Sarik have produced, so I obviously have no idea what's present and what's not, or if there are any other issues.

I sent Sarik all the DXF files for the parts that I used to build the prototype model, including the changes that were made as the prototype was built; I don't know what relationship the final wood pack has to my original parts patterns, I'm afraid - sorry.

Devon Slopes25/02/2018 09:50:55
15 forum posts
20 photos

More Balsa.

So the sheet and other material arrived during the week, to add to the already large pile. The new stuff is the pile between the laser-cut material and the building board.


Fitting together nicely.

Many thanks to all for the advice on sanding, part sizes and the fit. In future I will follow the rule that the laser-cut parts are the correct size. I dry assembled some of the formers on the top and bottom keels and found the slots in the keels are exactly as Andy says they should be, slightly oversize. But the former slots are slightly tight and some need a little opening out, again exactly as Andy says. And don't worry about "teaching granny to suck eggs" Andy, this is my first from-the-plan build, so any advice is welcome.

And more progress on the fuselage.

I found I had missed one jigging part on the fuselage, the one near the nose (I should read the plan more carefully). This you have to make for yourself, but its easy to do as you simply cut it out from the part of the "frame" which the nose for the keel came from. I also glued the stabiliser supports on the back of F10. Not sure exactly whether they should be close to the keel (as I've put them, with a bit of scrap to make sure the fit is OK) or further out.

(My excuse for slow progress is that I admit being drawn onto the slopes for a bit of flying yesterday.)


Andy Blackburn25/02/2018 10:42:41
425 forum posts
482 photos
1 articles

The jigging part on the picture above should have been part of the keel pieces; I'll add it to the list for Sarik.

Also, it looks as though the K6 pieces are cut from 1/4", but on the original (and on the first set of cut parts) they were 1/8" - as shown on the first page of the prototype Canberra build. But on the DXF files that were sent to RCM&E & Sarik, some fool (me) had somehow moved them to one of the 1/4" parts sheets. I think this was because they've always been marked on the plan as 1/4" parts, even though they weren't.

Please accept my sincere and abject apologies, and make yourself a couple of new parts from 1/8" sheet using the laser-cur parts as a pattern. And don't forget to add the servo mount (K6A) before glueing to the fuselage, otherwise they'll probably break as you're sliding them into the former slots - they're long parts and have a weakpoint where the servo goes. And don't forget that left and right K6's are mirror images - not that I'd make a mistake like that, I just made a spare in case it was needed. Ahem.

> And don't worry about "teaching granny to suck eggs" Andy, this is my first from-the-plan build, so any advice is welcome.

Then I admire your courage at choosing such a complex build for your first attempt! smiley

P.S. - your K7 pieces on the back of F10 look fine, although the original intention was to have them go right to the edge of the former. But what you have will be fine, it't only there to make sure that the stabiliser goes in the right place. It might look a bit confusing on the re-drawn plan because it looks as though it's showing the stabiiser - it isn't, the K7 parts are in the right place.


Edited By Andy Blackburn on 25/02/2018 11:02:14

Maurice Lester27/02/2018 20:22:16
15 forum posts

On the subject of missing parts we are also short of two wing ribs. The plan calls for two R4 in each wing but only two are included in the kit - again extras are easy to cut if you do it before glueing the originals!!!!

Andy Blackburn28/02/2018 08:51:35
425 forum posts
482 photos
1 articles
Posted by Maurice Lester on 27/02/2018 20:22:16:

On the subject of missing parts we are also short of two wing ribs. The plan calls for two R4 in each wing but only two are included in the kit - again extras are easy to cut if you do it before glueing the originals!!!!

Oh dear. I refer you to my previous remarks (the ones about everything being on the original DXF files)... I'll inform Sarik.

I suppose it's inevitable that on something with as many cut parts as this, there will be some nistakes...


Devon Slopes04/03/2018 09:40:47
15 forum posts
20 photos

List of parts.

In addition to the list created by Andy, and added to by Peter, you will need some 3/32” medium to make the false leading edge. I also think you will need three sizes of spruce:

¼” x 1/8” for the tail fin spar;

¼” x 1/16” for the tailplane spars;

1/8 x 1/8” for the incidence tube supports.

I’d forgotten the last one of these when ordering, but I guess I can cut it out from the ¼”x1/8”

Devon Slopes04/03/2018 09:49:55
15 forum posts
20 photos

My aim this week was to end up with a “dry assembled” fuselage, so I could understand how it all worked before committing to glue.

Battery Box and F10. I built my battery box on the bench, rather than using the formers as a guide, but it seemed to work fine. The end piece can be made from the same sheet as the sides are cut from. In a previous post Andy said that really the guides for the tail plane should have been closer to the edge of the former (though this was not crucial). So, honour has now been satisfied with the addition of two extensions to the guides.


Servos and K6. I’m hoping to use Hitec HS81s or HS82MGs, as I have some I can scrounge from somewhere else. Not as nice as the suggested servos (though they have a larger torque), but then as they would have said in my local model shop (sadly now closed) “with your flying you’ll never notice”! But, this means you have to adapt K6 and K6A to take slightly larger servos.

Hatch Doublers. Although I don’t need them yet, I cut the ¼” hatch doublers. There is some extra material at the bottom of the sheet that has the keels on, which is slightly wider than the doublers and just asking to have them cut out from it. Using the mantra “the wood is right” I cut the slots in the doubler which match the formers using K6 as a guide, not by matching it up with the plan; they fit fine. So here are both the F6s (laid out to make sure I have one of each hand, thanks for the warning Andy) and the hatch doublers.


Fuselage Dry Assembly. So, having pinned the bottom keel to the building board, I worked systematically through the fuselage formers testing them against the top and bottom keels, and opening out the slots if needed. Very therapeutic, especially as you see the Canberra shape emerging in skeleton. I then began to put the other pieces in place. The ones which form the slot for the tail fin (K5) look slightly longer than in Andy’s prototype, which is probably a good thing, but means the jigs have to go on the front side of F9 rather than (as in Andy’s photos) the rear side. I still have to put in the mount for the rudder servo, and I see Andy added extra ply on the back of K6A to take the servo screws.

And so here it is, dry assembled. I must say, Andy, I think it’s something of a design masterpiece on your part. Now I need to get out the glue.


Devon Slopes11/03/2018 12:50:30
15 forum posts
20 photos

Super 'Phatic. Why do I build model aircraft? It's only partly to get more model aircraft, because as we know it's often cheaper to simply buy them ready built. Nor do I buy the theory that it's entirely about the sense of satisfaction when its done. That sounds like the argument for banging your head against a brick wall (it's nice when it stops). It's in part because I like mastering new skills, and understanding why technology and techniques work. Thus I was rather shocked when I found myself thinking I could glue the frame together with something I knew and understood, aliphatic glue, by pulling bits off to put glue on them. Andy is quite clear in his instructions, put it all together and then cyano or Super 'Phatic the joints. Now, I dislike cyano; both the fumes and the thin stuff running all over everything (including your fingers). But Super 'Phatic I had never used. So I went to my local model railway shop and bought a bottle. Its brilliant, no fumes yet it seeps into joints rather like cyano. So, although this photo may not look very different from last week's post, it is now all glued together (though I may run some Super 'Phatic over the undersides of some joints when it's free of the building board).


I tried to make sure the outer surfaces of the keels did not end up below the outer edges of the formers, otherwise I might have a lot of sanding of ply to do. I also kept checking it was square as I glued it. At one point the top keel was not directly above the bottom keel, but a square double-sided sticky taped to the board nudged it over and fixed that.

Incidence Tube Jigs. I fretted a little about the jigs which hold the rods through the incidence tubes. In the end I double sided sticky taped the two jigs together, carefully measured the positions of the holes for the rods from the plan, and drilled them both together (starting with a fine drill but first). I wondered if I should put ply in the positions of the holes, as they would be better defined and more robust than the balsa, but actually the balsa works fine, provided the holes are drilled a little tight.

Planking - advice appreciated. Well, advice is always appreciated, but here it will be particularly welcome as I've not planked before. I've a couple more things to do before I start, but it would be nice if I get started on it this week. Andy said in his blog that he although he had used 7.5mm wide planks, 8.5 or 9mm might have been better for making them fit (to each other?) between the formers. So I'll do the experiment and try 9mm. But how to get them taper in the right way is what worries me. By using the diameter of the former as a proxy for the width the planks need to be, you can make the following plot (where the height of the planks is grossly exaggerated.

canberra-page-001.jpgSo the planks have to halve in width over about 20cm as you approach the nose. Andy used a gauge to get this right, but he's got much more experience than me and so will spot sooner if things are going awry. I'm wondering about making a plywood pattern.

In other news Peter is making rapid progress with his wings. I'm keeping a careful eye on his wing joiner ideas, as I had wondered about something similar, though it may be a bit far off piste for me.

Devon Slopes13/03/2018 18:29:21
15 forum posts
20 photos

Too Many Bits? I've now unpinned the fuselage from the bench so I can add formers F4A and F6A, which make the edges of the hatch. There are two each of these in the woodpack, but I only expected one of eac. Can someone check my sanity here to avoid me making a blunder? We do only need one of each, the others are spares?

Andy Blackburn16/03/2018 15:47:44
425 forum posts
482 photos
1 articles

> Planking - advice appreciated. Well, advice is always appreciated, but here it will be particularly welcome as I've not planked before.

WRT the planking; it's true that I used a couple of little plywood guages to get the right width, but after indenting each end I tapered the planks by eye using a coarse Permagrit block - you don't really need to use a guage.

All you have to do is make sure that you leave the middle bit alone, and then:

  1. Taper the nose part of the plank till it's roughly correct
  2. Taper the tail part, again 'till it's roughly right
  3. Finally, chamfer the edges in cross-section slightly (as per one of the fuselage cross-sections on the plan) so that adjacent planks will fit together.

Then it's a matter of glueing the planks in place (assuming that you've already chamfered the edges of the formers so that the planks fit), using medium cyano, and sandable woodworking glue (Aliphatic is best) to glue adjacent planks.

It takes me a few (4-5) minutes per plank; less fastidious people might be quicker. You'll have to cut some custom-shaped planks for the last bits.

Oh, and when marking each plank for the hatch formers, make a little indent with a razor saw otherwise the pencil mark will be sanded away...

Devon Slopes18/03/2018 19:06:44
15 forum posts
20 photos

Many thanks for the advice, Andy, though I think its going to be over a week before I get to the planking now, for reasons explained below.

I had become confused about the correct order for doing things when the framework is completed, so here is what I think should happen.

1) After most of the skeleton is completed remove it from the building board.

2) Then add the hatch formers (K4A and K6A).

3) Then add the hatch doublers (the 1/2" by 1/4" by 14" piece around the hatch opening). (You may want to have it back on the board jigged up when you do this; not sure).

4) Then smooth off chamfer the keels and formers.

5) Pin it back on the board.

6) Add the snakes and servos.

7) Start planking.

The hatch doubler, or Mistake One. I put the hatch doubler on before taking the skeleton off the board for the first time. This makes it more than tricky to get the hatch formers in. (And with respect to the above post about how many formers, I believe you are provided with two "spares".) Minor surgery was needed, in addition to that required to make the slots in the laser cut K4A and K6A match those in K4 and K6. But they are in, though I may need some small filling pieces after I've cut the hatch out to make up for what had to be removed to get them in.

Mistake Two. Avid readers of this blog will recall that above I said to make sure the keels did not end up inside the surface defined by the formers, otherwise there might be a lot of sanding to do. Well, I should have listened to myself! When I pulled the skeleton off the board, I found this hiding underneath...


So rather than sand the former I did this...


i.e added a thin piece of balsa to the keel and sanded it to the correct profile.

So, I'm now up to point 4 on the list above, which I think is going to take more time than I thought to get right, and also other things in life are going to intervene this week.

Rudder Servo Mount. To leave on a positive note, though, I thoroughly enjoyed making the bits for the servo mount, which will be put in after I have sanded everything off and re-mounted the skeleton on the board. I'm using slightly different servos from Andy, so minor changes were required.


Its far neater than it need be, but, as I said, I was enjoying myself! The servo fits snugly between the bits of spruce I placed on either side. I achieved this by double-sided sticky taping the servo in the right place, and then aliphatic gluing the spruce to the ply, pushing the spruce up against the servo. The grab of the aliphatic holds them in that position, and when its all dry a knife under the servo will spring it free.

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