I think I have decided on my next scale build.

On other forums there has been several DH Comet builds of one sort or another some small, some large, some with one EDF mounted in the fuselage, some with 2 or 4 mounted in the wings but as far as I can tell all have had to adopt over size ducts somewhere along the line.
So my intention is to build a Comet 1 - it has the biggest wing to fuselage ratio - using 4 EDFs with true scale ducts.

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You D love a challenge Q Watching this one with interest

Garry

Smashing aircraft, smashing project.
i shall enjoy this one.

Wow! I wish I was clever .I'll watch this one :woohoo:

No real decisions yet but I favour smaller rather than bigger maybe with 30 mm EDFs.
I used them on my Canberra so I can follow the same ducting principles.

With the Comet 1 the inlet and tailpipe areas are very small compared to the size of the air frame so it will have to built light - super light!
On the plus side the small scale tail pipe means the EDF also has to be small so there will be no problem fitting them inside a scale wing root. Thrust is another matter!
No decorating required for the prototype.

Except polished aluminium is almost impossible to reproduce!
The actual build will have a proper build blog.

There is a thread on RCME about a build of a Ballerina and he found a paint that looks very like polished ALI I think the guy is Belgian if that helps .

one tenor wrote: There is a thread on RCME about a build of a Ballerina and he found a paint that looks very like polished ALI I think the guy is Belgian if that helps .

try this link www.modelflying.co.uk/forums/postings.asp?th=113510&p=58

OT
That is very interesting but I suspect the original surface of his cowl was rather better than the normal Depron surface.
Obviously any surface can be made smooth with sufficient filler and sanding but I doubt I will be able to afford the weight to do so over a complete air frame.

So initial thought on the Comet.
I have to work out the best EDF option whilst retaining scale size inlet and exhaust.
This is the wing root using a 30 mm EDF with the scale exhausts set to 85% of the FSA.

Those small exhausts mean the EDFs fit in easily but the complete Comet comes out pretty big - like 60" span. :ohmy:
Whilst such a size is not a problem in itself it has to be remembered there would only be 12 oz thrust maximum so it really would have to weigh no more than 18 oz all up.
I fear that may be just a bit too optimistic! :woohoo:

"I think I better think it out again!"

Reviewing the situation Eh! Yep I think his cowl was balsa but there is no way to do that on Depron He He ! you've set yourself a task there all right Good luck

Some more options.
1. Fit the biggest EDF that would go inside, like this.

The issue with this is the exhaust would only be about 55% of the FSA so rather inefficient.
2. Use small EDFs but reduce the size of the plane so the exhaust will be under size but hopfully not too restrictive, about 78% FSA, something like this.

With 30 mm EDFs the Comet would come out at 1000 mm (40") span.
At this sort of size it could be built in one piece both saving weight and adding robustness.
The downside is the 30 mm EDFs are relatively expensive. I can get 70 mm one 22% cheaper but at that size the Comet would have a span of 2300 mm (90"). Impressive but a definite no/no!

The first task is to buy a single 30 mm EDF and build a test duct (with the 78% FSA) to see how much thrust is available compared to the same fan in free air.
That will then determine if it worth proceeding..

Still mulling over potential EDF configurations for my Comet 1
As a true skin flint I am still finding it hard to justify spending the best part of £90 on 4 tiny EDFs on what will be a 'small' foam plane.
I have come up with an interesting variation. 4 inlets, 4 exhaust, all scale ducts but only 2 EDFs.

Putting the EDF in the out board position gives an easier path for the rather complicated shaped bifurcated ducts.
Using 50 mm EDFs it will come out at 48" span. The combined exhaust area will be a bit small, about 75% FSA, but the 50 mm produces over 8 times the thrust of a 30 mm unit so even if it looses a bit it will still be much better off than a pair of 30's!
So two 50 mm EDFs ordered from Bangood and on offer! Hobbyking only had one in stock anyway.

Talking about the Ballerina builds on the RCME site a few have looked at using Depron in some bits.
So far I have resisted the temptation to 'chip in' with a true 'Depron' version. It would in any case be reduced in size a bit other wise it would have a ridiculously low wing loading.