Canberra by Andy Blackburn PSS

[Andy Blackburn]

+1 for the two laminations of 3/32" - I did that on one nacelle, actually, works fine as long as you use a sandable glue (e.g. balsa cement).

Or you could put the 3/16" sheeting on with the grain spanwise; I did that on the other nacelle, and it works fine.

[Bob Jennings 1]

Nice one Pete, fascinating reading. I may have a go after the Hurricane build.

[Peter Garsden]

Good thoughts chaps on the sheeting. I will go for the 3/32" x 2 laminations as that will bend nicely and be stronger.

I just thought also that I would show you something which helps the paper template for the nacelle skins

It sounds obvious but the template is 3D as Andy says and you have to snip the paper at the leading edge and trailing edge so as to avoid twisting the paper and skewing the pattern. If you don't do this, you will end up with a pattern that is too small at the front top over the sheeting/

See what I mean about a gap at the top of the leading edge sheeting with the lack of a 3D perspective. The gap at the front is normal and has to be remedied by the application of masking tape to cover the space, then it works fine.

You can see the various wedges which are covered in sellotape to stop them from sticking to the superglue

[Peter Garsden]

Sadly Andy, I have found another part cutting error. N4 should have a flat edge top and bottom, but the one which has been cut in the pack has a curved edge on one side. This led to me not being sure I had got it the right way up.

[Andy Blackburn]

Posted by Peter Garsden on 24/03/2018 18:43:50:

Sadly Andy, I have found another part cutting error. N4 should have a flat edge top and bottom, but the one which has been cut in the pack has a curved edge on one side. This led to me not being sure I had got it the right way up.

Oh dear. That's clearly not right.

My prototype was built using parts patterns that I had laser-cut by a third party, and everything fitted (obviously). Your parts are produced by Sarik, and the fact that there are errors that were not present in the original parts set tells me that Sarik have produced their own patterns from the Canberra B.2 plan.

I have to ask - have you contacted Sarik to let them know that there are error(s)? You should really let them know, since they produced the parts that you bought and if corrections are required, it will be Sarik's responsibility to make them.

I should stress that I have no connection to Sarik, and I have no control over what they produce.

Having said that, though, I should point out that:

1. The plan shows the part the right way up
2. The reason that the slot in N4 is higher than the centreline is that - cunningly, I thought - it will only fit one way
3. You can cut or sand a flat on the incorrectly-cut N4 and all will be well.

Edited By Andy Blackburn on 24/03/2018 21:06:49

[Peter Garsden]

We've definitely got a full extra set of parts for the nacelles. Sadly these will go into the bin.

I think that I will contact Sarik and point out the errors.

Edited By Peter Garsden on 26/03/2018 18:29:45

[Andy Blackburn]

What, a complete set??

Extraordinary.

Mind you, as we have seen, getting a set of printed parts absolutely correct is a significant undertaking; I think the only way you can expect to have a decent shot at it is to cut the parts and then try a test build with the actual parts, correcting and repeating as necessary. That's what Traplet did with the Jet Provost parts, and they were almost 100% correct.

I think talking to Sarik is probably the right thing to do.

[Peter Garsden]

Thanks Andy. I have emailed Sarik and referred them to my blog. In many ways the wood pack is very good - lots of bits I wouldn't expect included and good quality machining with the name of the part printed on each one.

I was talking to Phil who said he did a beta test build with the Hurricane and he is still finding corrections. You can't spot everything. It is like editing text.

Anyway I will be adopting radio silence whilst I build the Hurricane, so you can avoid getting annoyed for a while!

I am thinking how difficult it might be to cover the nacelles in a different colour of solarfilm to the rest of the wings - not looking forward to that one. Here are the finished wings.

[Peter Garsden]

One off one on - Hurricane finished so the Canberra is back on. The goal is to finish both models by the next PSS event in 5 weeks is it?

I started by joining the top and bottom keels over the plan. I have read the very polite description by Devon Sloper that the parts do not line up with the plan. I reckon that the keel parts are a good 10mm longer than shown on the plan.

When the same thing happened with the wing - see above - I assumed that the parts did not line up with the plan, but I think that the plan is undersized. It is a free plan from RCM&E so the acid test would be to test the purchased plan with the parts. Curiouser and curiouser said Alice in Wonderland wasn't it?

Lined up here you see at F1

By F5 we are about 3mm out

I guess it doesn't matter that the fuselage is 10mm longer than the plan as long as the formers line up. Here I have made up some dummy formers (they are round) to check the top and bottom slots line up.

[Andy Blackburn]

I had a long conversation with the tech guy at Sarik about this; between us, we eventually sorted out what was going on. Don't know if you've spoken to them but I should think that they'll be happy to send you some replacement parts that are of the right size.

I always put a couple of 100mm lines at right-angles in the top left-hand corner of the plan to guard against scaling issues, but after this experience I think in future I'm going to do the same on the printed parts patterns.

However, if you decide to just go with it as it is I think it'll be fine, just remember to assemble the finished wings onto the bare fuselage structure to check that the holes (2 incidence pegs, wing joiner and servo lead hole) are all in the right place. The worst that you'll have to do is to either move some formers by elongating the slots or shim the incidence peg locations. There's a fair margin or excess strength in the fuselage so as long as you fill any large slots, it won't make any difference.

[Peter Garsden]

Yes I agree Andy, I am not too bothered that the plan is not the same as the parts with the fuselage because all it will do it affect the moment arm, which is not an issue on a model like this, or indeed any model where the fuselage is 10mm longer.

The most important thing is the angle of incidence which remains the same so no problem.

Fortunately, your excellent self assembly system gets round the problem as the whole fuselage fits together nicely. It makes the job so much easier.

I really don't want to find things, but I noticed that when you had parts cut, they included the incidence pin supports that sit either side of the fuselage and are made from 1/8 balsa. They aren't included, however, in the wood pack, so maybe better to make them myself. Whilst I will have to make them over the plan, the plan doesn't match the parts, so I am hoping that Sarik will cut me some supports and send them on. I will ask.

Oddly, I fashioned the inner plywood 1.5mm ribs myself from the plan and they seemed to match, which is rather odd. I can always match up the holes with the wings.

[Peter Garsden]

This is such a clever design, and so easy to build (so far). The whole thing goes together perfectly with the slotted formers if one follows the instructions in the RCM&E Article, as well as diagrams on the plan, such attention to detail. Mind you I would expect nothing less from Andy B.

The servos have to go in at an early stage. The rudder servo is the trickiest because one cannot get at the horn and adjustment once the planking is on. I am trying to work out how to adjust the clevis if need be. Very much like aileron servos in a mouldie wing. I think I will have to cut down my allen key, and make all the adjustment at the tail.

All the holes cleverly made in the formers are for the SLEC snakes, which I have not used before. Only the swivel and pinch type servo snake holders will do, which can, of course come loose unless the grub screws are treated with Locktite - so set up the rudder servo so it is correct before applying planking

Like Devon Sloper, I too and using and HS82MG Hitec servo for the rudder which is bigger than the rudder servo plate, but the method he suggests is spot on ie double sided tape to hold the servo in place then glue the beech supports with aliphatic, and apply clamps till dry. And clamp the servo with a ply plate.

I am going to change the suggested support of the servo by adding another piece of 3/8" balsa to make it more in line with the end of the snake.

[Peter Garsden]

This shows the extra piece of 3/8 for the servo mount. Easier to do this before planking.

You can see how the dummy 1/8 supports work here to enable you to line everything up so that it is square before the incidence wing wires and glued in place with epoxy. One can also try out a piece of fin. So clever.

When I tried my battery down the long battery box tube before it went into the fuselage, I found it bound on the battery and I couldn't get it out. This was because the connector and wire were jamming it. Don't want that to happen when the battery is in situ, so I applied hot glue to the wires and the connector to hold it in place.

Incidentally, much better to make the battery box using the battery as a former. Quite difficult to get square. I am sure I have seen them in other kits with tabs, which make it easier to assemble - Andy don't know how easy it would be to redesign?

[Andy Blackburn]

> The rudder servo is the trickiest because one cannot get at the horn and adjustment once the planking is on. I am trying to work out how to adjust the clevis if need be...

You probably won't need to adjust it at all, but if you really think you'll have to then you can use a ball-link rather than a clevis. To adjust it, you pop the ball-link off using a screwdriver or bent bit of metal and remove the servo, make the adjustment (fingers/needle-nose pliers), pop the ball-link back on using fingers and then re-install the servo.

> Incidentally, much better to make the battery box using the battery as a former. Quite difficult to get square. I am sure I have seen them in other kits with tabs, which make it easier to assemble - Andy don't know how easy it would be to redesign?

Well, the design is now the property of RCM&E so a re-design isn't on the cards...

However, I've never had a problem getting a square battery box; assemble it first using a bit of masking tape inside a couple of the formers with square holes, then square it up at each end with a couple of the square off-cuts rammed into each end (shimmed with masking tape if the laser cut is a bit wide) and then hit it with a bit of cyano. Using the battery as a former might be a bit risky because as you have discovered, they're not necessarily square.

Edited By Andy Blackburn on 12/08/2018 20:36:18

[Peter Garsden]

Ah...wise word indeed sir, thank you - quite right....post propter hoc and all that...

[Peter Garsden]

Romantic I may not be but no planking ceremony for me (what a planker do I hear?) or a bit of a plank? No surely not.

So question Andy - is my maths correct?

The fomer F4 is 100mm. F1 is 60mm, so the ratio is 3 to 5 and my planks are 9mm so they should reduce at the nose to 5.4mm - correct, measured from F4 to F1 and the same height from F4 to F7? So the same theory applies to the tail?

I laid 2 planks as shown but they are too wide at the nose and tail? I will make a handy tool as shown in your blog out of 1/16 ply to gauge the widths

[Peter Garsden]

Hate being negative but, as Devon Sloper hinted at, there are duplicate F4A and F6A. I am gong to use them to make the thickness 1/8 instead of 1/16 which is what they are but out of - or could be 3/32, anyway I have had to trim them because they are cut for the top of the former rather than the bottom, yet a slot is cut into them for the hatch doubler, which is rather strange - one for the Sarik list methinks.

Edited By Peter Garsden on 15/08/2018 06:01:51

[Andy Blackburn]

> So question Andy - is my maths correct?

Without checking the numbers, the principle is correct - apart from the middle bit of the fuselage that's parallel, the ends of the planks taper in the same ratio as the former size. Just don't forget to chamfer the edges a bit so that if there is a gap between planks (perish the thought!) then it's on the inside and will be filled with glue.

However, you don't have to be dead accurate with the planks because you can always make a couple of odd-shaped planks to get everything back to where it should be.

[Devon Slopes]

On the subject of the plank taper I found that the planks needed a different taper depending on their position round the fuselage, see especially my 18th June post in this blog, though remember I have not finished planking yet, so I've not shown it works for definite! 

Edited By Devon Slopes on 16/08/2018 00:10:52

[Trevor]

FWIW, my approach to this is to eye up the largest former and mark out plank widths on it which are as broad as possible compatible with the degree of curvature. Count how many planks are needed, then mark each of the other formers into the same number of divisions. Hint: arranging to have, say, 8 planks rather than 7 will make this a much easier job!

Then cut out the first plank slightly oversize, offer it up and sand it back until it is somewhere near the marks on the formers. There's no need to be precise about this - much more important to keep the edge of the plank smooth so that the next plank easy to fit to it. Offer up the next plank, again oversize, sand the mating edge to get a good fit to the previous one, then sand the other edge to get somewhere near the next set of marks. Use Aliphatic resin between the planks and pins or cyano to hold them to the formers.

Trevor

[Peter Garsden]

Well planking I have found to be far easier than I thought, me being a planking virgin as it were. The balsa bends nicely round curves, and it is relatively easy to fill in gaps. I think the shape of the fuselage with no complex curves helps a lot.

Gets a bit tricky round the front where the curve intensifies

The instructions say fill in the tail before you turn it over, which will be a bit tricky. but hey ho. Feeding the tubes through the right size holes might be a challenge.

[Peter Garsden]

The instructions also say lay up some dummy tailplane stubs so as to work round the shape with the blocks. I decided to assemble the tailplanes anyway. Again we have extra bits in the woodpack I don't need.

[Peter Garsden]

 

The rear of the fuselage I found a bit tricky. It has to be done before taking the fuselage off the bench from the top decking to firm things up. You can see I enlarge the holes for the elevator snakes which pass through the 6mm balsa pieces (2 per side) which extend from the front to the back of the elevator.

You can also see that I made some dummy tailplanes and fin which must be remove afterwards to leave gaps.

I couldn't work out how to keep them in position. I spot glued them with cryano, attached the lower support pieces, then removed them for pinning back in position from underneath as they were now supported.

I then put some block balsa of 6mm thickness from scrap left from the wood pack. I used some clear selophane to protect then top of the tailplane and sides of the fin from being stuck to the block again to remove them after drying.

You can see I made a new F11 as the supplied version had indentations for strip wood which does not extend to the tail and stops at F10.

I will insert packing pieces to the bottom when the fuselage is upside down and I am attaching the bottom planking as then I will have proper access.

Edited By Peter Garsden on 22/08/2018 18:49:56

Edited By Peter Garsden on 22/08/2018 18:51:07

[Peter Garsden]

Here we see the dummy tailplane half, fin, and some upper blocking, which will be planed away once the fin and tailplane are removed. The snakes do get in the way.

[Peter Garsden]

Once dry, the whole assembly is removed from the board and turned over for the planking underneath the fuselage. One also gets access to the rear underneath for blocking out.

I made some supports from scrap bits of foam left over from packaging of a model through the post. I cut out diamond shapes in the foam then used my Permagrit coarse files to finish them off.