Mini Canberra bomber - RC Groups
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Oct 17, 2010, 09:36 AM
It must have a machinegun
Scaledown's Avatar
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Mini Canberra bomber

Pusher prop jet models donít seem to be quite as popular as they were a few years back when jetset44 started pumping out designs for park jets. But I still like them. In the case of the plane Iím about to start building, I donít have much choice because they donít make a 25mm dia fan.

Iíve drawn up plans for a 55cm (22Ē) English Electric Canberra bomber. It was also built in the US as the B-57. The target weight is 110g (4oz), so itís a calm weather park flier.

My first thought was to build it from Durabatics foam, but when I went to order some I found that the guy who makes it had passed away. So then I thought of 1mm depron, but you canít buy it in Australia, so I decided to make my own by taking 2mm depron and shaving one side away. It means there is only one skin, so its not nearly as stiff, but I hope it will work OK.

I used my electric planer set to a cut depth of 0.7mm. Then I finished it with an orbital sander with 80 grit paper. I tested the planer on a piece of scrap 6mm, because I didnít know what it would do. I thought it might ingest the whole sheet like a mulcher, but it worked OK. The planer makes a bit of a mess, so itís a good thing I did it outside. The finish was a little rough but the sander smoothed it out. I could have done the whole job with the sander but it would have been too hard to maintain a consistent thickness. I donít know if anyone else has tried shaving down depron.
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Oct 24, 2010, 07:16 AM
Registerd Beaver
Smokin' Beaver's Avatar
G'day Scalemeister,
good to see another project on the bench.

I'm subscribed of course.
Still scratching away at the Mavis (what a job it turned into) multi's seem to take forever.

Oct 24, 2010, 08:29 AM
Registered User

I agree on scratch built foams.

I use 4' long sanding boards. 1 has 33 grit & the other is 80 grit. I also made 2 round closet poles into sanding boards for the inside curves.
I found the high humidity is my friend.

I did 1 day on a 20% humidity. HA HA HA. " It is the Michilen tire man. "
Oct 27, 2010, 08:38 AM
It must have a machinegun
Scaledown's Avatar
Hi Phil
Agree with you about multis. This will be my last for a while. At least its a simple build.

4' sanding board? That would take a bit of effort to use I expect. That's a nice collection of planes you have there.

I've attached a pic of the wings under construction, ready for the top skin.
I've designed it for positive Gs by gluing a single kevlar thread to the bottom skin (for tension) and a 2mm square balsa spar under the top skin to stop it from buckling in compression. Most of the ribs are balsa because foam is too flexible at that size.
Oct 30, 2010, 09:14 AM
It must have a machinegun
Scaledown's Avatar
The top skins are on. To get the right amount of washout as the skins glue, I twisted the building board. The board was a piece of 3mm MDF. By stapling three corners down and chocking up the fourth corner I was able to get the washout exactly the same on both wings. I've given it a fair bit of washout on the outer panels because there's quite a bit of taper in the wing plan.

I'm going to use the boiling water method to curve the foam for the fuselage and engine nacelles. The rear fuselage and parts of the nacelles will be tapered tubes, so I carved a mould with the correct taper out of blue foam, and I'll be wrapping the foam around this in the water.
Nov 03, 2010, 08:20 AM
It must have a machinegun
Scaledown's Avatar
I've hinged the ailerons, carved some wing tips and joined the wings. I've used 1mm carbon torque rods. Hopefully they are not too flexible for the job. I just made the motor mounts. I hope to get a bit of cooling air passing through the nacelles.

The motors are 5 gram Hextronic 2000kv units, driving 4x2.5 GWS props. The speedies are Castle Creations Thunderbird 6.
Nov 07, 2010, 05:04 AM
It must have a machinegun
Scaledown's Avatar
I've been working on the engines. I found when I curved the 1mm sheet in the boiling water, it had much more springback than normal depron with both skins. So I tried curving it around a smaller diameter tube first, then the correct diameter and the springback was much reduced. Maybe I was breaking the grain more with the smaller diameter.

You can see in the pic I glued some balsa strips to the edges. These act as handles so I can pull the sheet evenly and tightly around the mould (in this case a wooden dowel) without needing 13 fingers. I always cut the piece oversize then trim it down later, because the edges can swell and warp a little.

The pics give a good idea of the size of the plane now.
Nov 07, 2010, 08:44 AM
Registerd Beaver
Smokin' Beaver's Avatar
That's quite a job there & came out very nice.
So the air/jet pipe duct goes over & under the wing skin to cool the motor?
This model looks like it will really fly well - lots of wing, lots of power...
Nov 07, 2010, 08:58 AM
ToxicToast's Avatar
Looking forward to seeing how this one turns out!
Nov 08, 2010, 06:56 AM
It must have a machinegun
Scaledown's Avatar
That's the plan Phil. Normally I would include a former or two, but I can't in this case because it would block the flow. I was thinking of putting the ESC in the tube for cooling but it won't fit.
Nov 09, 2010, 06:00 AM
It must have a machinegun
Scaledown's Avatar
The engines have been sanded to a smooth curve now. Later I will apply some lightweight spackle to the sanded areas (where the skin is now gone) to fill the pores before I paint it. I'll also be adding some paper tailpipes to hide the motors. I've run the motor wires through the wings to the motor mounts already. I used enamelled wire to save weight.

Now its time to build a fuselage.
Nov 14, 2010, 09:07 AM
It must have a machinegun
Scaledown's Avatar
The fuse is coming together with pre-curved pieces. Things are beginning to go wrong now. I messed up a measurement when assembling the fuselage. "Measure twice - cut once!" Now I have an extra construction joint that I didn't intend. Then when I installed the control horns onto the aileron torque rods, I discovered that the carbon torque rods are way too flexible. The ailerons were just flopping around. Its probably unflyable. I've started extracting the rods to replace them with steel - not easy without butchering the wing, and I wanted to avoid the weight of steel anyway.

Come to think of it, I had the same problem with another plane a few years ago. You would think I'd learn.

Let the word go out around the world from this day onwards:

You can see in one of the pics that I reinforced the fuselage near the wing leading edge with some bits of carbon, and some balsa strip. This is because if I have a hard landing (inevitable) the biggest stress will be at this point, trying to break the nose off in front of the wing.
Nov 14, 2010, 11:16 AM
No Guts No Glory
kestrel2003's Avatar

Looking forwared to see it fly!

Always nice to see a canberra beeing built. Looks realy nice to far. Any idea on the finish? A black night intruder, a sand color recon version or a silver finish? rgds mv
Nov 17, 2010, 05:10 AM
It must have a machinegun
Scaledown's Avatar
At the moment I'm leaning towards the RAAF scheme. Black looks cool, but it might be hard to pick its orientation at a distance. I've got a heap of silver planes already. I must say yours looks nice.
Nov 17, 2010, 12:00 PM
No Guts No Glory
kestrel2003's Avatar

Raspberry ripple

I may try building a 1m span baby canberra, impeller not pusher. If I do the its raspberry ripple time. I have a weakness for target tugs. Looking forwared to see yours.

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