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$100 EDF Scratch Build Contest - EE Canberra

Old 10-30-2014, 04:50 PM
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quorneng
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Default $100 EDF Scratch Build Contest - EE Canberra

The English Electric Canberra is one of my favourites. A classic example of how to get the best out of the available power.

With this build the question is going to be can I get cheap 30mm EDFs to satisfactorily fly a scale (or as near as possible scale) airframe? I suspect it will be pretty marginal.

So which of the many Mks of Canberra? Actually the basic airframe changed little (discounting the big wing B57s!) so I think I will choose to model the prototype. Simple to paint as it was pale blue over all.
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This is actually a later T4 that was painted to look like the prototype in 1999 to mark the anniversary of the Canberra's 50 years in service with the RAF.

With the very limited thrust available (6oz in total if I am lucky!) it will have to be reasonably big to carry the weight efficiently but very, very light.

I think I have been here before!

Last edited by quorneng; 11-04-2014 at 10:01 PM.
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Old 10-30-2014, 06:16 PM
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Welcome on board, quorneng! Can't wait to see your build. The Canberra is another rarely modeled planes that deserves better. I got to see the full scale big wing B-57 you mentioned at the Pima Air & Space museum. Looked freaky! I think I read it was created sort of as a back up plan in case the U-2 project didn't work out. Good luck!
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Old 10-31-2014, 03:22 AM
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quorneng
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At the moment this post is more "thinking out loud" than a description of the build of a Canberra with 30mm EDFs.

To my horror Hobbyking quote the thrust of the AEO 30 at just 1.6oz (48g) but of course this is likely to be the 'free air' static thrust so rather less (30%?) when it is in what will be quite a long duct - even in a Canberra!

It would appear to me that for a small diameter fan in a relatively big light airframe its flying speed will be modest so it will pay to optimise the static thrust rather than worry how fast it might go. It follows this is best achieved by mounting the fan well aft to keep the thrust tube short and use the maximum possible inlet duct diameter within scale dimensions.

This is roughly the proportions of a Canberra engine nacelle.
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With a 30mm EDF actually as the scale jet pipe the thrust tube is the Fan Swept Area (FSA) and it is possible to have the whole inlet duct with no less than 3 times the fan area area. In this configuration it should hopefully develop pretty close to its 'free air' thrust figure.

With a 30mm scale jet pipe the Canberra would have a span of 29" (720mm) which sounds reasonable but to stand much chance of flying with no more than 3 oz thrust it should weigh no more than 6 oz (170g) complete.
Hmmm!


I understand the really big wing B57 actually came into being after Gary Powers had been shot down and U2 over flights were banned so they needed a high altitude plane that could carry the bigger payload of the sideways looking equipment that could be used safely from outside (just!) the Soviet borders.

Last edited by quorneng; 10-31-2014 at 03:37 AM.
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Old 10-31-2014, 05:12 AM
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Originally Posted by quorneng View Post
...


I understand the really big wing B57 actually came into being after Gary Powers had been shot down and U2 over flights were banned so they needed a high altitude plane that could carry the bigger payload of the sideways looking equipment that could be used safely from outside (just!) the Soviet borders.
I stand corrected. I'll have to do some more reading on the subject.

Looks like those little edf's may be a challenge. I hope it works well. I'm a little confused about you choosing very large intakes though. I can't speak from experience, only what I've read, and that is that a 90% fsa intakes area was optimum. Having more could create extra drag, as the edf can only pump so much air. Is that only in the faster edf's?
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Old 10-31-2014, 01:03 PM
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xmech2k
I estimate my Canberra will fly at about 20mph as a result of a very low wing loading whereas the fan exit speed will be perhaps 3 times that.
This would mean that the air would simply enter the inlet at more or less flying speed so it would not create any 'drag' as such, at bit like the big turbo fans that look to have a ridiculous frontal area for 600mph but of course they don't create drag either - as long as they are running!
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Old 11-01-2014, 02:54 AM
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You could always run an internal fan. The ducting is inefficient, but the fan is much more powerful. On the Comet I have around 22-23 oz of thrust, which on paper should fly the roughly 50" airliner given it's relatively light AUW for it's size.

I had the same concerns, as the 30mm EDFs have low thrust, but are as large as possible to maintain a reasonable scale appearance at somewhere in the 50" span range. 40mm EDFs have exponentially more thrust and would be much more practical, but would be too large for the nacelles for a reasonable scale appearance unless the jet grew to a size where the AUW would likely become unreasonable.

Some of the thrust figures I see advertised for 30mm EDFs seem a bit overstated. Of course I never experimented with the purchase ones, but the 30mm GWS EDFs I was remotoring with the 12mm Feigao inrunner would be lucky to produce much more than 1oz, and were still stressing those tiny fan blades to the point that I would have a difficult time seeing them withstand much more.
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Old 11-02-2014, 01:50 AM
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Bill G
That is a very interesting picture and represents another way of overcoming the inherent lack of efficiency of small fans.

I did use this sort of principle in my XB70 Valkyrie where a single 'buried' 70 mm fan fed six 28 mm diameter nozzles. It certainly works well enough although it does have the advantage of being a more or less 'straight through' duct.
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Old 11-02-2014, 09:51 AM
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I used one of those AEO fans in the 17" freeflight Mig 17 I build a few years ago (pic below). I got a lot more than 48g out of it. On a 2s LiPo it produced about 84g thrust in free air. But this did drop significantly when installed in the long duct of the Mig.

I tested a range of fans for the Mig, see picture below. From left to right is the GWS EDF30 with Turnigy 1015 brushless motor (48g thrust), the AEO 30mm fan (84g), the KP aero fan (74g) then the GWS and AEO 40mm fans. Also attached is thrust test picture of the AEO 30mm to verify my numbers.

Good luck with the project.

Steve
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Old 11-02-2014, 04:04 PM
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Steve
84g from each fan would certainly give me some useful performance.
I shall have to test mine in the same way to check.

To begin with I intend to build just an engine nacelle to find out how much thrust goes missing!
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Old 11-02-2014, 06:37 PM
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Originally Posted by quorneng View Post
Bill G
That is a very interesting picture and represents another way of overcoming the inherent lack of efficiency of small fans.

I did use this sort of principle in my XB70 Valkyrie where a single 'buried' 70 mm fan fed six 28 mm diameter nozzles. It certainly works well enough although it does have the advantage of being a more or less 'straight through' duct.
The Comet ducting certainly wasn't as ideal as something like the XB70. I probably lost something like 60% or more thrust, although 22-23oz still should fly the plane on paper. Done again it would have been a bit cleaner, but when you haven't finished a build it's difficult to envision the exact amount of room available to keep things reasonably scale. The joining "V" of the two exits would have been a bit further rearward, done again.


Originally Posted by JetPlaneFlyer View Post
I used one of those AEO fans in the 17" freeflight Mig 17 I build a few years ago (pic below). I got a lot more than 48g out of it. On a 2s LiPo it produced about 84g thrust in free air. But this did drop significantly when installed in the long duct of the Mig.

I tested a range of fans for the Mig, see picture below. From left to right is the GWS EDF30 with Turnigy 1015 brushless motor (48g thrust), the AEO 30mm fan (84g), the KP aero fan (74g) then the GWS and AEO 40mm fans. Also attached is thrust test picture of the AEO 30mm to verify my numbers.

Good luck with the project.

Steve
Very true. The raw spec is really optimistic when compared to mounted in ducting. Your photo got me thinking about how the GWS fans like the EDF40 and 50 are among the fewer small fans without a lip. When I tossed around the idea of mounting fans in Comet nacelles, the EDF40 was as appealing as the smaller 30mm fans, since it had no lip and would keep the nacelle diameter as scale as possible. Of course the 30 could always be hacked down, but some CF wrapping or something similar would be a good idea for rigidity. That KP fan looks interesting, appearing to have no intake lip and a reasonable wall thickness.
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Old 11-02-2014, 09:59 PM
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I actually machined off the lips of the four 40mm AEO I used in my Concorde with a lathe. I did not disassemble them but simply held the fan casing in a 3 jaw chuck and very carefully 'parted off' the lip section with a very fine (and sharp!) tool.
Quite nerve raking as the EDF could not be held that firmly in the chuck and if it did moved the EDF would be destroyed.

In the Canberra by making the EDF the actual jet pipe the scale nacelle is large enough to allow the lip to be retained.
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Old 11-02-2014, 10:02 PM
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On my Mig i just extended the inlet ducting into the throat of the fan, just far enough so it 'bypassed' the bellmouth.
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Old 11-15-2014, 02:15 AM
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As my current project is neraring completion I can start thinking about the Canberra.
First task is to create an 'outline only' 3 view.
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This has been developed from on a nice scale 3 view drawing so it should be reasonably accurate.
On reflection I think a B2 (camo top, all black under) will be more visible than the pale blue overall of the prototype.
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Old 11-22-2014, 01:57 AM
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A bit more drawing.
A scale Canberra nacelle with a 35mm EDF right at the back acting as a slightly over scale jet pipe.
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This allows virtually the entire inlet duct to be just over twice the FSA which should significantly reduce the duct losses.
However
Done like this the Canberra will come out rather larger than I had intended at 40" (1016mm)span.

Putting the EDF right at the front of the nacelle would allow the overall size to be reduced a bit to about 35" span, the fan bell mouth could be retained (good for low speed thrust) and the spinner would be a reasonable representation of the Avon's 'bullet' but I fear the losses resulting from the long 35mm exhaust duct would be greater than with the EDF at the back.

"I think I had better think it out again!".
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Old 11-23-2014, 11:03 PM
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I'm blaming you for this one Quorneng.
Since I've never gotten around to finding an adequate field for my larger version, I just printed out 30 sheets for a smaller, 33" span, hand launchable version with a centrally mounted EDF. There's something about these sleek, integral wing nacelles that draws us to these subjects. Not surprising, I believe Chris Golds has modeled both of these subjects.
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Old 11-24-2014, 01:55 AM
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Bill G, my (stolen from Chellie) offer to maiden that Comet for you still stands, if you care to make the short drive over here! Our did it happen already and you didn't tell us?
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Old 11-24-2014, 05:51 AM
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Originally Posted by xmech2k View Post
Bill G, my (stolen from Chellie) offer to maiden that Comet for you still stands, if you care to make the short drive over here! Our did it happen already and you didn't tell us?
Might think about it, with the weather as of late. May even think of going to the UK and having Quorneng fly it. Still better weather than here.
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Old 11-24-2014, 08:27 PM
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Bill G
If you come over, I would fly it!

A bit more doodling with a comparison of EDF at the front and the back of the Canberra engine nacelle.
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The EDF are the same size (a cut and past!) but as I hoped is does allow the nacelle and thus the entire airframe to be reduced by 15%. My biggest concern is the losses resulting from the long & small diameter exhaust tube.
I have shown an 'after body' behind the EDF that brings the 'annular' airflow from around the out runner bell efficiently to a circular duct of 27mm diam.

On balance I think I will try the 'fan at the front' option first as it will have a better scale appearance and the fact that the duct is a smaller diameter allows more space for the wing spar to go 'over and under'.

Last edited by quorneng; 11-25-2014 at 12:15 AM.
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Old 11-25-2014, 02:46 PM
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Still doodling away but it is starting to come together.
With a 30 mm EDF right at the front of each nacelle the Canberra will have a span of 28.4" (720 mm)
On this plan the RH nacelle with the EDF is in a 'direct' plan view where as of course in the plane the whole thing is canted nose up.
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The issue is going to be that long exhaust tube. To match the area of the 'annulus' around the motor it will be just 22 mm diameter, hence the need to build just one nacelle first to check the thrust actually available.

At 28" span it will have a wing area of just over 1 sq ft so if I can keep the all up weight to 4oz it stands a change of flying reasonably well on 3oz static thrust but it will be one heck of a light weight build.
HK suggest the 30 mm EDF can give 1.69 oz on a 2s so a lot is going to depend on the efficiency of that long exhaust tube.
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Old 11-26-2014, 07:45 AM
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To give you some optimism, my roughly 22" span ME262 and A10 flew really well, with anemic remotored GWS EDF30 fans, back when they were the only ones available. Changing hubs for the 12mm Feigao was a job, with the rotors also requiring aluminum adapter installation for the higher powered bl motor. What I learned from the 2 single engine EDF30 jets and 2 twin engine jobs, is that the added power of 2 fans at roughly the same span greatly outweighed the increase in weight. It was far beyond what I expected, given that I was expecting bricks at over 6oz, even considering the power increase. The single fan 4oz Vampire puts along and the 4oz Salamander a bit faster, but the much heavier A10 and ME262 at over 6oz really went. I remember the 262 possibly being in the 7oz range. My guess is that you could go a good bit over 4oz AUW. The little Vampire weighs over 4oz with restrictive ducting, and actually flew a good bit faster than this when the old 10c lipo was new, versus years later when I bothered to video the jet. It has scale like intakes with no cheater: https://www.youtube.com/watch?v=7QFH..._IhNe3uS3fLSoA
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Old 11-27-2014, 02:32 PM
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As weight is going to be the 'be all and end all' of this build a little bit of weigh comparison.
2mm Depron and copier paper
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Copier paper and acrylic sprayed tissue
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This rather confirmed the nacelle would have a rolled paper tube for the duct itself but supported by 2mm Depron formers with a 2mm planked outer skin.
So first a 'test' duct to check it can actually be made. The mandrel is a piece of 22mm plastic central heating pipe
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The formers are 'typical' rather than the exact size to test they can be glued onto the paper tube without distorting it.
The design requires a flared section taking the duct from the 30 mm of the EDF to 22 mm of the duct.
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A small 'after body' will be suspended in this section to keep a constant cross sectional area.
The test duct with the 30 mm EDF in place.
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The tube of UHU POR gives an indication of its size.
This duct was only ever intended to test the construction method which although fiddly seems to work well enough.
A complete 'working' nacelle is next.
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Old 12-01-2014, 12:12 AM
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The AEO 30mm EDF has a rather larger diameter out runner so it really needs the 'after body' to gradually bring the 'annulus' airflow down to a tube.
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This body will not be attached to the motor but suspended in the duct just behind it on 3 small litho plate fins.
The working paper exhaust tube with the formers glued on.
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The outer skin if the nacelle is planked (23 in total!) in 2mm Depron.
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The after body is installed using foam safe super glue.
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And the EDF glued into the front of the nacelle.
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Now to find out how much (or not) thrust is available.
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Old 12-01-2014, 01:13 AM
  #23  
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(Shakes head in amazement.) Another work of art, Quorneng. Hope it works well
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Old 12-01-2014, 03:44 AM
  #24  
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Looks like you have some nice, light nacelles now. Routing the wing panels across the nacelles is always an interesting task. Unlike a heavy, beefy foamy RTF, we can't just glue the panels to the thick foam nacelles and have reasonable strength. Are you planning something like a carbon rod spar behind the fan, used for a main spar section? Shouldn't be much loss with an airfoiled section sculpted from balsa, laminated around the spar.
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Old 12-01-2014, 09:04 PM
  #25  
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AWESOME! I hope there is enough thrust to make the project viable.
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