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A Depron Sea Vixen.FAW2

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Simon Chaddock07/07/2017 23:10:26
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My 32" span Depron EDF DH Venom FB1 is relatively large and light for its 40 mm EDF but nevertheless flies really well and with a substantial cruise endurance (10 minutes+!) for a 'micro' EDF.

The next project is to try to achieve the same with a Sea Vixen but powered by two 40 mm EDFs

PlanviewS

The problem is the cheap HK AEO 40 mm EDF use an out runner whose motor bell is significantly bigger than the diameter of the fan hub. Concerned at the turbulence losses that would be cause by such a large 'bluff end' directly in the duct I designed and 3D printed an 'exhaust tube' that incorporates an inner 'after body'.

ThrustTubeAfterBody This not only streamlines the air flow downstream of the motor bell but in conjunction with a reducing diameter exhaust tube keeps the duct area constant at 85% of the FSA.

One advantage of 3D printing means the second exhaust duct is just a matter of pressing a button!

TwinEDFs

Each exhaust duct weighs just over 3g..

Now all I have to do is to build the plane. wink 2 Of concern is the fact that the fuselage of the Sea Vixen has a remarkably complex shape!

Edited By Simon Chaddock on 07/07/2017 23:14:26

Stephen Jones07/07/2017 23:31:26
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2885 forum posts
1657 photos

Hi Simon,

Have you measured the output of the motors with and without the ducts.

And checked the heat of the motors .

Would be interesting to know.

Steve

Dave Hopkin08/07/2017 02:24:34
3672 forum posts
294 photos

Looking forwards to this one Simon,,,......

McG 696908/07/2017 05:55:32
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I will be following this one too, Simon. yes

Cheers

Chris

Simon Chaddock08/07/2017 11:31:22
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Stephen

The intention with this exhaust tube is that any benefit from the reduction in turbulence in the exhaust duct would off set the increase in skin drag from its extra surface area.

Within measurement accuracy this has proved to be the case as the EDF gives the same static thrust (140g on a 2s, 90W, 13A) with or without the thrust tube attached.

There will of course be some further losses from the inlet ducting although it should be limited as each inlet will maintain about 1. times the FSA.

The hope is that ready to go the Sea Vixen will achieve an 80% thrust to weight ratio which is about the same as my slightly smaller DH Venom and that has significant power to spare.

At these modest power levels motor cooling is not too much of an issue. The high velocity air passes directly over the outer surface of the motor bell as well as any air stirred around by the rotating magnets.

To maintain the streamlined nature of the air frame I suspect cooling the ESCs tends some attention.

Of course this could all prove to be wrong! wink 2

Edited By Simon Chaddock on 08/07/2017 11:32:21

Ian Jones08/07/2017 15:22:11
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3229 forum posts
1401 photos

An efficient ducted fan is one of the 3D printing projects on my list. I don't have the design skills (yet!) so I will be watching very closely.

Edited By Ian Jones on 08/07/2017 15:24:00

Simon Chaddock09/07/2017 22:29:37
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This front view with the EDFs shown in blue demonstrates the "large and light" concept and suggests that true scale inlets will have sufficient area about 1.2 FSA.

Intakefront

However this concept only works if the air frame is built ultra light!

The fuselage of the Sea Vixen is rather a complex shape and I only have 4 fuselage sections! It will take quite a bit of interpretation with the aid of many photos to create a full set of about 11. Then there is the problem of building the fuselage up around the inlets ducts.and still keep it all super light.

So I 'chickened' out and decided to build the wings first as in comparison they are a relatively simple shape.

According to the Incomplete Guide to Airfoil Usage the Sea Vixen used an EC1040 section, The only problem is the name is not recognised by any airfoil database!

What is available is RAE 104 which is a symmetrical 10% thickness section with its maximum depth at 40% - good enough!

RAE 104 section Although a bit bigger and twice the weight of my Venom it will still follow the same "all Depron stressed skin structure" and like the Venom it will have no wing ribs!

The lower LH wing skin and shear webs all in 2mm Depron.

Ailservo

The wing is thick enough to just cover the 4.1 g aileron servo.

A composite picture of the completed wing and an edge view showing its symmetrical section.

RHwingskin

So far so good but it really is a daft way to build the wing of an EDF! wink 2

Edited By Simon Chaddock on 09/07/2017 22:32:56

Colin Leighfield09/07/2017 22:34:58
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That's definitely a laminar flow wing section Simon. What do you reckon the limiting Mach number is going to be?

Mark Kettle 109/07/2017 22:47:22
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1580 photos

Well the full wing span is 51' X 12" = 612 inch divide by 32" = est scale is 1:19 th. So would the speed of the model by 1/19th of the top speed of the full size ( 690 mph ) = 36.3 mph ?

Can depron take such speed, I bet it can. 

Edited By Mark Kettle 1 on 09/07/2017 22:49:10

Simon Chaddock10/07/2017 19:01:21
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5777 forum posts
3055 photos

A little bit further with both EDFS and part inet tubes fixed together by the fuselage formers.

Twin Inlets 1

So far so good but the front part of the inlets is much more complicated, in fact I have not even worked out how I am going to do it!

Stephen Jones10/07/2017 23:41:12
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2885 forum posts
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You are a quick builder that is for sure Simon,

Watching with interest.

Steve

Chris Walby11/07/2017 08:37:52
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1326 forum posts
332 photos

Hi, Very interesting build, have you considered where the C of G will end up (just I have a pusher Vulcan with motor at one end and lipos at the other just to get the C of G in the right place!).

+ those fans are going to suck hard on the inlet tubes, perhaps a plenum approach then if you need to add cheat holes the option is there.

Only suggestions and great building skills...if only my Depron looked that good!

Edited By Chris Walby on 11/07/2017 08:38:36

Simon Chaddock11/07/2017 13:14:35
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5777 forum posts
3055 photos

Chris

I have run up a fan to full power with inlet tube as above with no problem.

Of course a cylinder with reasonable external support is pretty good at resisting low pressure, however the rest of the inlet duct is more complex and basically changes to a triangle so collapsing may become a issue. The saving grace is the inlet area is quite large at 1.2 FSA so it should keep the duct 'under pressure' to a minimum.

With such a light structure i am not too worried about positioning the CofG as its 2000mAh 2s Lipo weighs quite a bit more than both EDFs combined and each ESC, which needs to be close to the battery, weighs nearly as much as its EDF.

Hopefully the battery will end up in the Cockpit area which then makes it easier to disguise the hatch..

Well that's the plan. wink 2

..

Simon Chaddock12/07/2017 21:39:12
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As the fuselage with its ducts was going to be the most difficult to build I though I had better find out if it was indeed possible

Quite a stack of vey thin fuselage formers. It took quite a time to work out the intermediate ones from just the 3 I had!

Former stack

Built as a half shell over the plan with lots of individually fitted planks.

The really hard bit was planking the S shaped inlet duct on the inside of the formers. After 12 hours non stop I ended up with the left half of the fuselage.smile o

L half fuse2

There are 8 formers and 42 planks, every one different and individually fitted.

L half fuse1

So far so good but the real killer is I will have to it all over again for the other side! wink 2

..

Chris Walby12/07/2017 21:53:57
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1326 forum posts
332 photos

Looking good there...and once the other half of the fuselage is finished you'll have a couple of booms to do!

My initial post was I was concerned with the throttling effect of long parallel ducts to the fans as I have a couple of PNP edf's which have large inlets/plenum right up to the fan impeller (and short discharge tubes) with one having a bunch of cheat holes as well. I have no technical basis that its an issue.

Would you be prepared to provide your plans at some point?

Stephen Jones12/07/2017 23:06:10
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2885 forum posts
1657 photos

Wow,

12 hrs none stop without a break or a biccy i don`t Know how you do it.

Keep it up though i like watching your builds.

Steve

Simon Chaddock13/07/2017 19:24:10
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5777 forum posts
3055 photos

The formers added to the other side,

RH hal ffuse1

Then the tricky bit -p Planking the inlet duct on the inside to the formers. After a good few hours, you have to let the glue set on each plank before you can do its neighbour, the duct is complete.

RH duct

It actually take a bit longer as the rather delicate structure has to be handled whereas for the first half it was held flat on the building board.

The outer skin can now progress...

Simon Chaddock15/07/2017 16:36:14
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5777 forum posts
3055 photos

With some of the fuselage skin in place a trial f"placement" fit to make sure things are more or less the right size and shape. wink 2

Wing fuse1

All in the picture, which includes the EDFs and aileron servos, weighs 5.1 oz (144g).

With the weight of the EDFs now 'built in' the fuselage needs very delicate handling so completing the majority of the skin planking is vital.

Simon Chaddock16/07/2017 22:57:01
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5777 forum posts
3055 photos

Planking the complex curves is slow going but at least the underside is done.

Fuse under1

Thee next job is to wire up the and install the ESCs to allow most of the top decking to be added of course having tested it still all works! wink 2

Edited By Simon Chaddock on 16/07/2017 22:57:29

Colin Leighfield16/07/2017 23:51:00
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6007 forum posts
2505 photos

Another painstaking super efficient build! You can see how DH evolved from their early commitment to tail-less designs as shown by the Swallow to this, adding a conventional tail via twin booms. Despite its early problems, I think this was a more effective design than the Javelin, seem so odd that the RAF rejected, it for the problematic Gloster design. If both services had ordered variants of the original 110 I'm sure the design would have evolved and we'd have got a more effective plane for a lot less money.

Edited By Colin Leighfield on 16/07/2017 23:51:31

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