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Electric Ducted Fan Jets Discuss electric ducted fan jets here including setup tips, power systems, flying techniques, etc.

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Old 09-05-2017, 12:56 AM   #1
quorneng
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Default A Depron DH Sea Vixen for 40 mm EDFs

This project really started when wondered if I could 'print' an exhaust tube for a 40 mm EDF.
The current model of 40 mm AEO EDF uses a 23 mm diameter out runner which a looks huge in a 40 mm duct and to make matters worse is actually 2mm bigger diameter that the fan hub!
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The previous version of this EDF although less powerful at least used an out runner that exactly matched the fan hub. It was quite a bit lighter as well.
So the task was to print an exhaust tube that also had an inner 'cone' to avoid the sudden change in duct area caused by the end of the motor bell.
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The resulting exhaust tube has a constant area along its length ending at 32 mm diameter which corresponds to about 92% of the FSA.
After much experimentation I found I could print both the inner and out parts in one piece with benefits in strength and weight reduction.
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The thrust tube is simply glued onto the plastic shroud and being printed it is no problem to make two!
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The question was could a scale Sea vixen be built big and light enough to use scale size inlets and still fly on the modest thrust of the AEO EDFs?

My all Depron scale DH Venom flies very well at 6.5 oz (185 g) using the earlier lower power 40 mm AEO unit so with two more powerful EDFs my 'target' weight is 14 oz (396 g).

I obtained a good 3 view which included some basic fuselage sections.
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Obviously this drawing would have to be clean up a bit to remove unwanted surface detail before it could be used as a building plan.
Finally scaling up the Sea Vixen inlet to give the same area as a 40 mm EDF gives it a span of 36" (915 mm).
In fact not much larger than the 32" of the Depron Venom but at over twice the weight it might be stretching the concept of using the same 'super light' Depron structure.


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Old 09-05-2017, 01:41 AM   #2
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I have one of those and they are quite powerful considering their size. Just hogs on batteries.
Very neat job of the exhausts.
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Old 09-05-2017, 08:01 AM   #3
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This is interesting as I was looking at Thingiverse yesterday and found a 70mm duct for printing ...

I was actually looking for possible cowl to replace on a WOT4 ... just in case I needed one !

Watching this thread with great interest.

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Old 09-05-2017, 11:59 AM   #4
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Panther
Yes indeed.
Even on a 2s they draw some 20A which means a battery capable of a genuine 40A.

Given the 'optimism' of most battery ratings this suggests something like a 2000 mAh 35c 2s and even then it would only give 3 minutes with a degree of throttle management!
The Sea Vixen is aerodynamically quite an 'efficient' air frame (but a rather complex shape!) so hopefully it will fly well at reduced power where the efficiency (thrust/W) of these small fans increases significantly.

The short thrust tube means the small EDFs will in effect be 'right at the back'.
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Such a layout maybe unusual although it does have some advantages given the need to extract the maximum possible performance from the fans.
The battery has to go well forward to compensate so is thus well clear of the bifurcated inlets ducts.
The inlet ducts themselves can be larger than the FSA (a 40 mm diameter tube is actually 1.2 times the FSA) so the overall duct losses are lower than a mid mounted fan with a longer smaller (FSA) diameter thrust tube.

Enough of the theory - I just have to build it!


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Old 09-05-2017, 12:32 PM   #5
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Knowing your skill at keeping frame weight down and flying with limited power - I am sure of your success.

Me - I'm a chicken .... I would opt for pusher prop at back end of fuselage given the boom arrangement !

Looking fwd to that flight video to come ...

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Old 09-06-2017, 05:05 PM   #6
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The more I look at the Sea Vixen the more I get worried by its rather complex shape and each of those booms represents a complete fuselage on its own!
So I chickened out and started with the wing outer panels as they are simple and I knew I could make them.
Each is a rib-less fully stressed skin structure made entirely in 2 mm Depron.
The bottom skin and shear webs. The webs form a true scale EC1040 wing section when the top skin is pulled over them.
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The tiny 4.2 g aileron servo is completely built in and looks almost insignificant.
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With no ribs running the servo wire though the wing is not a problem.
With the top skin added it become surprisingly rigid.
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Note its maximum thickness is at about 50% chord typical for a transonic section of the period.
The Wing of the DH110 prototype was actually thinner and permitted supersonic (just!) flight. The thicker wing of the Sea Vixen's was definitely sub sonic.

Well that's the easy bit. Now onto the fuselage.


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Old 09-07-2017, 09:09 PM   #7
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The 3 view shows that the fuselage and wing is effectively in 3 sections with a straight joint just inboard of the booms, however the fuselage itself is rather a complex shape and with twin ducts will have to be made is a number of pieces.
The first job is to cut out the complete former 'stack'.
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Each duct has a parallel tube section so this is built first and carries 4 major formers.
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The L & R are glued together on the center line.
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'Silly fragile' at this stage but hopefully if all works out it will become the major load bearing part of the the wing center section.


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Old 09-11-2017, 12:53 PM   #8
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The forward part of the wing/fuselage is built as a half shell over the plan but first is the full former 'stack'.
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The LH side under construction.
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Only enough of the planking is completed to allow the fuselage half to be lifted from the plan and handled but still to allow enough access to plank the inside of the inlets ducts.
The completed half fuselage.
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Planking the complex shape of the inlet duct is time consuming to say the least!
The other half will be built onto it rather than over the plan. Doing it this way ensures the other half is structurally integrated rather than having to rely on one big center line glued joint.


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Old 09-15-2017, 12:38 AM   #9
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The RH half of the fuselage center section being built up from the LH half.
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Before any external skin goes on the inlet duct has to be planked.
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Not easy working on the inside of the formers.
The next job is to glue on the rear portion of the inlets with the EDFs attached.


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Old 09-15-2017, 02:57 PM   #10
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Impressive, as usual.

Did you consider a single larger fan and bifurcated ducts?

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Old 09-15-2017, 09:28 PM   #11
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pmullen503
To my mind a single bigger fan, like the HobbyKing Sea Vixen, although significantly more efficient would almost be like cheating!
Twin fans sound better too.

I wanted to test the efficiency of the 'printed' exhaust duct and inner cone. I am not sure I could have printed a bifurcated one!
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Old 09-16-2017, 01:01 AM   #12
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I know with my CAD skills the bifurcated ducts would be a challenge but it could surely be done. I'm working on a BV-215 using a single, larger EDF instead of two smaller units. In that case, the single EDF was the obvious choice. But it does feel like I'm cheating.

I've thought about using a 3D printed mold for the exhaust ducts. Making the ducts themselves with glass and epoxy. Lost foam casting is so messy.

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Old 09-16-2017, 05:20 PM   #13
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I did use a single fan with six outlets (sexfurcated?) on my B70 Valkyrie.
It worked well enough but I suspect the benefit of the performance of the big fan was almost negated by in efficiency of the ducting.
On the other hand six small individual EDFs would have been seriously expensive!
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Old 09-17-2017, 02:13 AM   #14
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6 into one was pretty impressive. Was the area small enough to maintain the eflux velocity?

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Old 09-17-2017, 06:47 PM   #15
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My XB70 uses a plenum chamber (actually the rectangular section of the fuselage) aft of the fan. The chamber has a cross section several times the FSA to keep the duct losses down. The fuselage gradually changes to a wide narrow rectangle with 6 individual 28 mm nozzles at its end.
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The six nozzles side by side match the scale fuselage cross section.
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As it was always likely to be a hand launched slow flyer I wanted maximum static thrust.
It needed a working canard (in conjunction with elevons) to give adequate pitch control but it flies pretty well with an impressive ground effect on landing.


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Old 09-18-2017, 01:00 PM   #16
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Back to the Sea Vixen.
With nose section planked sufficiently to be handled the EDF section is glued on taking great care to ensure the inlet tubes match up exactly to the formed inlet ducts.
This allows the wing roots to be skinned and the underside of the fuselage to be planked.
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The centre portion of the upper surface is left open to enable the 'electrics' to be added at a later stage.

The wings can now be glued on.
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As the wings have no ribs or spar and the fuselage is entirely Depron the joint strength relies entirely on the "skin to skin" joint.
A narrow Depron strip is added around the inside covering the joint to increase the glue area.
It may sound daft to rely purely on such a joint but the whole principle of these lightweight Depron structures is to keep the loads 'spread out' and avoid concentrating them anywhere at all.
Note the solid "magnet" wire from the motors to the ESCs. For a given current capacity they are only half the weight of silicon insulated multi strand!

It currently looks remarkably like the ill fated DH108 Swallow!


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Old 09-21-2017, 04:43 PM   #17
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The booms are next.
Each is almost equivalent to a complete fuselage so it is built as a 'planked' half shell over the plan with lots of formers!
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Once lifted the other half is built on.
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The boom underside is left open as it will be glued directly to the wing skin.
It is all 2 mm Depron. Compared to the Vampire the booms are fatter and relatively short so no reinforcement is required - I hope!
It is all rather tedious and slow to do but at least the L & R booms are identical.


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Old 09-25-2017, 03:40 PM   #18
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The booms are glued in place.
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Next is the fin that includes the end of the boom. Another all 2 mm Depron structure.
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The RH fin glued to boom.
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Before going any further a 'pull through' will have to be installed so the elevator servo cable (its servo will be in the tail plane) can be pulled through.


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Old 09-25-2017, 04:26 PM   #19
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Beautiful work!

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Old 09-26-2017, 04:30 PM   #20
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Both fins in place.
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The ESC heat sinks are mounted on the inner face of each inlets as it is a convenient flat surface. will have significant airflow across them and are close to the position of the battery.
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With a final test of the 'electrics' the rear part of the fuselage top skin can be completed.
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The pinion tank nose cones are also added.
The 2000mAh 2s LiPo will go in the navigators position.


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Old 10-04-2017, 01:30 AM   #21
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Planking the cockpit area.
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The 'solid' cockpit behaves as the fuselage skin and is fully load bearing.
The 'coal hole' battery hatch.
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The 2000mAh 2s slides well forward into the nose.
A simple color scheme, dark sea grey on top.
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White under sides.
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35" (890 mm) span and 13.25 oz (375 g) ready to go.


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Old 10-07-2017, 05:31 PM   #22
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It does fly well enough.
A short rather poor quality video of its second flight.
https://www.youtube.com/watch?v=n95GPHlZkfw
Just need some calm weather to try it out further!
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Old 10-07-2017, 07:34 PM   #23
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Congratulations, she looks great in the air, seems to have a fair turn of speed for a lightweight model too!

I built a Sea Vixen from the old KeilKraft plan a few years ago. It's a tricky design for freeflight as they tend to spiral without RC to keep the wings level. i did get it flying ok in the end.
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Old 10-09-2017, 01:22 AM   #24
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Nice! Well done.

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