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Jul 16, 2017, 07:14 PM
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Build Log

A Depron Sea Vixen for 40 mm EDFS

Earlier I posted an experimental printed thrust tube for an AEO 40 mm out runner EDF.
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It proved to be quite efficient and light so it seemed logical to use two in a Sea Vixen.
The 40 mm AEO EDF only produces a modest thrust but it is quite efficient for the power that it uses. To make best use of the EDFS the Sea Vixen will be relatively large for a 'micro' at 35" ( 890 mm) span but built very light.
This front view shows how relatively small the 40 mm EDFs will be.
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It does have the advantage that scale inlets can be used without a significant penalty.
This plan view shows how the EDFs will be positioned right at the back of the fuselage.
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The Sea Vixen will follow the build principles I used on my 40 mm EDF DH Venom and although it will be twice the weight at 14 oz,( 395 g) all up it will still be built entirely from 2 mm Depron as a stressed skin structure without any additional reinforcing.
Well that's the plan.
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Jul 17, 2017, 06:37 AM
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Want to tag along for this. I have a set of Lockey's plan for the Sea Vixen. Was looking to convert to EDF, using twin Dr Mad Thrust 40mm EDFs. Build on!!!
Jul 17, 2017, 12:46 PM
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The FSA for the Dr Mad Thrust 40mm is 940 sq mm. How does that compare to the AEO 40mm?
Jul 17, 2017, 01:17 PM
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dr Thrust unit is similar to the Very poorly cast AEO shroud... sort of [As aside: the old GWS shrouds were very much better made... Grrr]
dr T uses the Same 40mm rotor so FSA is same.. albeit ultimately determined by the diameter of motor fitted
Ali shroud does differ from the blu plastic aeo thing, in that it has a machined 20mm ID motor tube.
No centralisation or blade rub problems there.
Making it imo.. worth every Gram of it's weight, being rigid and Accurately mfg'd.
Real weight differences are in the Inrunner motor which is 54gm in itself. (Dr T unit is ~62 gms ready to run)
But that's the price for significant thrust levels.
Your choice

as aside: There is also the thought of using One larger EDF unit :-)
Fan size increase is the Best way to get thrust up lower amp requirements.
Bigger is in fact often genuinely Better.. IF you can fit it?
Last edited by Bare; Jul 17, 2017 at 01:52 PM.
Jul 17, 2017, 02:06 PM
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I don't doubt the benefit of the Dr Mad units but in my case the principle is to go the other way round the weight/power spiral - light weight structure, less power, less battery etc.

This principle certainly worked on my AEO 40mm 810 mm span Depron Venom in that it flew for quite as long but not as fast as a 1100mm Durafly Vapmpire despite only having 1/5 the battery power.

The 'meat' of the Sea Vixen build is of course the fuselage and the EDF ducting within it.
With the EDFs almost at the rear the initial 6" (160 mm) of each inlet duct can be a simple rolled Depron tube supported by the fuselage formers.
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The tube has the same 42 mm internal diameter as the shroud and as the fuselage is big enough the original bell mouth has been left in place.
The remainder of the inlet will be much more complicated as it moves gradually out into the wing root whilst changing from a circular section to a triangle.
Jul 18, 2017, 04:45 PM
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The Sea Vixen has a remarkably complex fuselage with lots of double curves and odd shapes but unfortunately the 3 view I am working from only shows 3 sections so it is going to need many photos and some interpretation to create the 11 required!
The stack of 2 mm Depron formers for the main part of the fuselage.
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It is built as a planked 'half shell' over the plan.
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A time consuming process as each plank has to be quite narrow and individually shaped so it can easily follow the required shape and does not distort the structure.
As a stressed skin structure the fuselage will only achieve the required strength & stiffness when all the planking is complete.
Jul 19, 2017, 11:02 AM
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turbonut's Avatar
Your making good progress...
Latest blog entry: In flight
Jul 20, 2017, 03:07 AM
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With the first half of the front fuselage lifted from the plan the other half of the formers can be added.
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Just enough external planks are added to keep the formers 'square' without restricting access to plank the inlet duct on the inside of the holes in the formers.
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It is a process that simply cannot be rushed as each plank has to first shaped approximately by eye. then cold formed with the fingers as much as possible and then 'trial and error' adjusted until in fits adequately. As each plank in only 2mm Depron this is not quite as difficult as it sounds.
A thin bead of UHU POR on the mating edges, fit the plank and then quickly take it off again after the glue has spread to both surfaces, wait 10 seconds seconds and replace now relying the 'contact' characteristics of POR to hold it in place although a few pins may be required where the forces are too high until the POR fully sets.
It is best to work on alternate sides to avoid distorting anything but it can take up to an hour 'drying time' before the next adjacent plank can be added.
All I can say is it gets easier with practice and the structure also gets easier to handle as more planks are added.
The completed inlet duct adds considerable stiffness by itself.
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Now the external planking can be started although quite a large area of the top side will have to be left 'open' to install the motor wiring.
Last edited by Quorneng; Jul 20, 2017 at 03:14 AM.
Jul 20, 2017, 09:02 AM
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jumo004's Avatar
Amazing !!
Jul 22, 2017, 04:29 PM
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With the tube jet pipes added the planking can proceed.
The under side complete.
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It does give an idea of the rather complex curves although quite a bit of the top side has to be left 'open' to allow the motor wiring to be installed.
By comparison the wings are relatively simple with no ribs or spar just multiple 2 mm Depron shear webs.
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The wing section is scale, RAE104, which is a symmetrical laminar flow profile.
The tiny aileron servo is glued in before the top skin goes on.
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The RH wing completed.
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The only deviation from scale is to remove the mass balance on the aileron. With belly landings they tends to get knocked off.
Jul 22, 2017, 05:01 PM
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jumo004's Avatar
Just wondering on your wing construction. Why do you do it this way instead of one spar and maybe 3 or 4 ribs ?

Jul 23, 2017, 08:58 AM
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This is a fully stressed skin structure so in effect the top and bottom wing skins are the spar flanges. All that is then is needed, like any spar, is a suitable shear web structure between them
Even 2 mm Depron is quite thick for a wing skin so the shear web does not have to be continuous, like say a veneer covered foam core, but individually spaced out webs are quite adequate and it is of course much lighter than solid.
The relatively thick skin also means that providing the shear webs are all the correct depth ribs are not required to create the wing profile.
The result does give a very smooth shape all the way from root to tip.

However this sort of construction is really only suitable for super light weight planes with low aspect ratio 'fast jet' type wings.
Jul 24, 2017, 07:55 AM
corsair nut's Avatar
man, awesome project!!!!!!!!
Jul 24, 2017, 08:56 AM
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With the EDFs right at the back the motor wires are fairly long so to save weight lacquer insulated 'magnet' wire is used..
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To ensure the ESCs get adequate cooling their "bare" heat sinks are mounted flush on the inside face of the inlet ducts.
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At this point it is then possible to run up EDFs to ensure it all works.
Sea Vixen EDF test (0 min 28 sec)

I don't think there will be any problem hearing it!
Last edited by Quorneng; Jul 24, 2017 at 04:06 PM.
Jul 24, 2017, 03:52 PM
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