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Old Jan 11, 2015, 01:29 PM
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A 'micro' English Electric Canberra

I like the English Electric Canberra. It always seemed such an elegant solution to the problem of packaging two long thin axial flow jets into an aerodynamically efficient airframe.
As a model the only problem is those long thin engine nacelles - they are completely the wrong shape for an EDF!

So following my 'big but light in Depron' technique just how big or small would a Canberra come out using 30 mm EDFs in scale ducts and more to point would it ever stand a chance of being light enough to fly on the thrust available?

The first decision was where to mount the EDF in the nacelle? Right at the back as the tail pipe allowing a generous inlet duct? I did this on my Fairey Delta 2.
Or right at the front to retain the EDF bell mouth but with a relatively long FSA sized duct? I did this on my V-1.

After doing some sketches the 'EDF at the front' was selected as the FSA sized thrust tube made it easier to arrange for the wing loads to go round it and the fan spinner would make a reasonable representation of the Avon's 'bullet' fairing.

I found a nice detailed '3 view' of a B2 and simplified it by removing most of the surface detail.
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To accommodate a 30 mm EDF in the nose of a scale nacelle gave a span of 32" (810 mm) and a similar fuselage length.
The first task is to build a test nacelle to get an idea of what happens when a long tiny (22 mm dia) duct is added to that cheap out runner AEO EDF.
Using a piece of 22 mm plastic pipe as a mandrel the thrust tube is formed from rolled paper with some of 2 mm Depron formers to hold the shape.
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The short tapered section on the front takes it to the 30 mm of the EDF.
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On my test stand it gave just over 2 oz thrust drawing 7A. The 'bare' EDF gave just under 3 oz. That long duct does indeed costs some thrust.

Still reasonably encouraged the next task is to build a scale Canberra engine nacelle which hopefully will be no less efficient however to work at all this is going to have to be a very light 32" Canberra.
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Old Jan 11, 2015, 06:58 PM
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Can you make the duct 30mm then taper it at the exit instead of the reduction just aft of the fan.
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Old Jan 13, 2015, 05:46 PM
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Turbonut
I could but if you look at the AEO 30 mm fan it has a substantial diameter out runner actually slightly larger than the fan hub so the exit annulus is actually slightly less than the FSA .
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The bluff end of the bell would do horrible things to the airflow creating considerable turbulence so I reasoned that it was better to get down to the FSA relatively quickly.
In the final version I intend there to be an 'after body' suspended in the duct to maintain a constant cross sectional area (and equal to the FSA) as it changes from an 'annulus' at the EDF to the circular duct of the thrust tube, just as in done in the full size Avon behind the last turbine wheel!
http://www.flightglobal.com/airspace...on-cutaway.jpg

So on with the 'working' engine nacelle.
As before a paper tube over the 22mm plastic tube mandrel but with the flared nose piece sized accurately from a turned wood mandrel.
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More formers to give the correct outside profile and even more planks, each one shaped to fit and all in 2 mm Depron.
The 'after body' suspended in the tapered part of the duct.
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It is located by 3 litho plate fins.
The complete nacelle with the mandrel removed and the EDF glued into front.
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A bit longer than the 'test' duct but on the test stand it delivers just over 2oz thrust.
So far so good. Now I've just got to make another and then build a Canberra round them that preferably does not weigh too much over 6 oz complete!
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Last edited by Quorneng; Jan 14, 2015 at 11:05 AM.
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Old Jan 14, 2015, 04:34 AM
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Old Jan 15, 2015, 06:35 PM
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The wing of the Canberra for its span has a very generous area which is good but for a very light build even the weight of 2 mm Depron is significant. Tissue is a lot lighter.

My intention is to use an all "D" box wing spar with a tissue covering to the trailing edge.
The outer wing D box lower skin and internal ribs.
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It uses the scale symmetrical RAE wing section.
The D box complete and the ribs and trailing edge added.
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It is all 2mm Depron. No reinforcing is used.
The complete outer panel fixed to the engine nacelle.
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It took careful fitting to get the wing to exactly match the nacelle contour (the nacelle points up a bit relative to the wing datum) but once achieved it was then simply glued on!
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Old Jan 20, 2015, 12:10 PM
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Next the wing centre section.
Built in exactly the same way and in one piece (it has no dihedral). The centre section of the fuselage is built on it.
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The centre section complete.
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The underside skin of the fuselage has been left off as the radio and battery will go in there - somewhere! The exact position can only be determined when the fuselage and tail feathers are complete.
The other nacelle and outer wing panel are next and will have to be very carefully fitted to ensure the dihedral and incidence match both sides!
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Old Jan 21, 2015, 11:04 AM
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Nice work!
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Old Jan 22, 2015, 11:38 AM
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The next bit is a bit boring building the second engine nacelles and its outer wing panel.
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The wing looks massive compared to those tiny EDFs!
More interesting is the fuselage tail section built as a half shell over the plan.
First temporary keel pieces are pinned down and the formers glued on.
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It then planked with shaped planks.
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UHU POR is used to glue each plank to the former but thick PVA is spead along the edge of the plank to join it to its neighbour. The reason for this is although a POR joint is strong the glue remains 'rubbery' so is almost impossible to sand. PVA is weaker but dried hard so the planks can be easily sanded to give a smooth profile.
The temporary keel strips are peeled off. This is possible as POR does not reach full strength for several days.
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The other half of the formers are added. The big 'solid' former is also temporary and will be removed just before the tail section is joined to the rest of the fuselage.
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It is then planked.
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The result is a very light stressed skin monocoque structure with no internal members at all apart from the 'ring' formers.

It works well but it is not particularly quick to do!
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Last edited by Quorneng; Jan 22, 2015 at 07:39 PM.
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Old Jan 22, 2015, 12:02 PM
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Very cool !!
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Old Jan 24, 2015, 06:09 PM
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The fuselage nose section is built the same way.
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To save weight even the solid cockpit canopy is part of the stressed skin structure.
The nose complete.
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Joining two parts of a stressed skin monocoque is actually quite simple, you just join the skin. There is nothing else!
The bare airframe.
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The underside of the mid section is still not skinned as all the electrics apart from the EDFs have still to be installed.
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Old Jan 26, 2015, 03:39 PM
killickb
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Very, very nice design/construction, how can it not succeed! Canberra has been on my list for years. I have Chris Golds plans and I know that GreenAir kits one but have never got around to building/procuring either. Many years ago begged Dan Savage to kit his NASA B-57 but he never did.
As a boy used to stand at end of runway at RAF Wyton to feel/smell/tremble in the exhaust of their Canberras.
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Old Jan 26, 2015, 03:49 PM
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The 4ch Orange micro 3 axis stabilised radio goes in.
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A quick CofG check indicated that the battery would need to slide in forwards.
The underside of the fuselage could then be made good and with a side hinged hatch.
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The 'slide in' battery box.
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It is sized for a 950mAh 3s Nanotech
With the 2.5g aileron servos tested the open bits of the wing can be tissue covered.
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With the battery in it weighs just a fraction over 7oz (200g) giving a wing loading of 4oz/sqft.
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Old Jan 26, 2015, 09:27 PM
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you have almost 2 sq ft of wing????
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Old Jan 26, 2015, 11:34 PM
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looks like it!
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Old Jan 27, 2015, 07:27 AM
killickb
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The Villages. Florida
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I love it! Maiden cannot be far away? And design to completion in only 15 days ! I would imagine this is going to tend toward the "underpowered" regime but at least you will be able to fly close in and enjoy --- indoors maybe?

Your construction methods sure seem that they would lend themselves to a larger scale. If successful, any thoughts on providing us a plan ?
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