English Electric Canberra

[Jim Stewart]

Excellent build!

Makes my 6 mm depron efforts look agricultural!

Can I ask what glues and paint you used? Also, was there any preparation apart from rubbing down?

Would like to try something a little less ambitious for a first scale type.

Cheers

Jim

[Simon Chaddock]

Chris

One of the penalties (and benefits!) of Depron is its flexibility so a single thickness 'plank' as a moveable control surface is bound to flex a bit if driven from one end and even more so if there is an aerodynamic balance at the other.

With my very light planes I have no qualms about using small servos and relatively flexible control surfaces as a way of limiting the maximum stresses that can be imposed on the airframe - almost the equivalent of the rising stick forces with speed physically limiting how many 'g' a pilot can pull.

In the case of my small Canberra I will probably leave the elevator as a 'strip' without the scale counter balance but on a larger plane I would stick to scale for appearance if for nothing else although on both my rather larger Skyray and FD2 I have removed the counterbalances because as belly landers the counterbalance tips kept getting damaged.

Jim

The paint is nothing more than household emulsion (match pots). Homebase Dove Grey and Black Magic in the case of the Canberra. The semi gloss finish comes from a light coat of spray Simonix Clear Acrylic Laquer although this has to be applied very sparingly in several coats as a thick 'wet' layer will penetrate the paint and effect the Depron.

Sanding Depron is a mixed blessing as once you remove its 'skin' the surface is very porous and needs filling and/or coats of paint to give the same surface finish as bare Depron. It is all too easy to 'fill and sand' only to find you have exposed bit more underlying Depron in the process!

The really important aspect is UHU POR although an strong glue is very 'rubbery' so is difficult to sand and doing so tends it tends damage the surrounding Depron more than the POR!

To avoid this on the Canberra I stuck each plank to the formers with POR but used thick PVA (which dries hard and can be sanded) to stick each to its neighbour.

Obviously if the whole structure is covered in something like brown paper as Tony does this problem disappears although there is a modest weight penalty.

If you pick a suitable plane with little double curvature building true scale in Depron can fairly trouble free.

As a example my 40" all Depron Super Cub has one piece skins for the top and bottom wing surfaces. The tail feathers are flat, as they are in the full size, and the fuselage is basically a hollow box built up from 6 sheets over formers.

[Simon Chaddock]

My B2 Canberra came out at 246 g although to be honest not sub 250 by design, in fact the sub 250 g class was not an issue when I built it in 2014.

With tiny 35 mm EDFs I knew it was going to be short on thrust so one possibility was to build a Martin RB57D. It still was a Canberra but had a considerably increased wing span. With a lower wing loading the hope was it would fly slower and thus use a bit less power. In the end I stuck with the standard Canberra wing.

Now the 250 g class has meaning I wondered if I revisited the big wing span could it still keep within the weight limit? I like a challenge.

This compares the original Canberra wing against the RB57D.

Of course this was not the ultimate big wing the RB57H went even further but only the fuselage remained as the tail plane & fin were significantly revised and with completely different engines.

Rather than build a new Canberra I wanted to do a 'Frankenstein' and simply remove the old and add the extended outer wing panels.

Having read through this thread it shows the fuselage nose has been significantly rebuilt three times so a complete new RB57D nose, with a single seat cockpit, might actually save a few grams.

The original B2 wing build plan.

By a bit of judicious 'cut & paste' the RB57 wing build plan.

I have cheated a bit and made the ailerons a bit wider and longer than true scale.

To make life easier I printed out a set of rib 'masters' that would act as guides when cutting out the 2mm Depron ribs.

Really a bit of overkill as there are only 2 ribs required of each size! They are a true scale symmetric section.

I built the original wing using a rather odd technique, build the D box section first and then add the rest of the structure onto the back of it 'free hand'.

The D box has 4 surfaces, top, bottom front and back with 7 half ribs inside all in 2 mm Depron.

The first D box spar complete.

Remarkably stiff both in bending and torsion. It weighs just 6.8 g.

Next is the tricky bit, turning it into a wing.

Edited By Simon Chaddock on 23/02/2020 17:59:32

[Simon Chaddock]

The RH B57D RH outer wing panel.

I have cheated just a bit and made the aileron a bit bitter than scale.

In this state it weighs 10.1 g. Now to do the same for the other wing D box.

Before it can be tissue covered the ultra micro 2.1 g servos will have to be ;extracted' from the old Canberra wings.

[Simon Chaddock]

Moving on the extended wings against the original B2.

The additional diagonal bracing (2mm sq Depron) is to resist the effect of the shrunk tissue.

[Simon Chaddock]

The nose of the Canberra, apart from the 2 major rebuilds to move the battery forward also suffered a significant crash last year so is far from pristine and likely both weak and over weight.

So as it will in effect become a Martin B57D I might as well take the opportunity to build a new Martin nose which in the D had a single seat canopy.

First the 'tired' Canberra nose is cut off.

It weighs 17 g

The B2 had a battery hatch on the underside of the nose. With its gyro rx I was always concerned about connecting it when inverted and then turning the plane over although it did not seem to matter.

The B57D nose will use the canopy as the battery hatch so it will be loaded from the top.

Small radius planking in 2mm Depron is rather tedious.

[Simon Chaddock]

The complete Martin B57D nose.

The front part of the canopy is the battery hatch.

With the original Canberra outer wing panel removed it shows just how much bigger the B57D wing is.

By pulling through all the spare wire it will be possible to fit the servo in the new LH wing, however it is almost certain the servo wire on the RH side will have to be extended. not looking forward tot hat as the servo wire is tiny - 36AWG!

Edited By Simon Chaddock on 03/03/2020 17:30:27

[Simon Chaddock]

Both wing on and the servos wired up and tested.

Tissue, i coat of Eze dope and the ailerons connected.

Ready to go with a 950 mAh 2s it weighs 249.2 g so it is sub 250!

Calm this morning so it had its maiden. No problem except it does fly really slowly for an EDF. A bit sensitive in pitch (short coupled) but quite controllable.

Flying so slowly is not ideal for an EDF so its flight duration is likely slightly worse than it was when a Canberra it wasn't that long then.

It glides equally slowly and the ground effect is very noticeable so not hard to get a slow gentle landing.

Obviously when painted (silver) it will be a few grams over 250 so my OP number has to go on.

.

[Stephen Jones]

Very nice Simon,

And i guess it will be even heavier with your Op Number on it

Steve.