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'Printed' wing ribs

A 48" span lightweight wing with 3D printed ribs

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Simon Chaddock03/02/2017 00:54:05
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This started out as an experiment to see if it was possible to use load bearing 3D printed components in a 'lightweight' wing structure.

Printing a complete rib showed that whilst it was admirably strong and stiff it was also very heavy, The neatest solution appeared to be to print just the rib outline 3 mm wide and then 'infill' it with 3 mm Depron sheet glued in. The resultant rib is virtually as strong and stiff as the fully printed one but less than half the weight.

Depron infill Rib

However it does require the Depron 'infill' to be accurately cut to shape and size to both maintain the correct rib profile and to fit snugly within the rib.

The solution was remarkable elegant. By surrounding the rib outline with a stout printed surround it creates a jig that will cut out a Depron blank that would fit exactly inside the rib outline.

Dprn infill 2

My printer could print 6 outlines at once quite quickly and once they were removed from the bed it was just a matter 3 clicks to tell it to print 6 more.

As the rib is so stiff and the fact that the 'printed' profile completely surrounds the Depron it raised the possibility that it could be used in conjunction with dope and tissue, something that is not possible on any Depron surface.

So a very conventional looking tissue or film covered wing with a balsa spar and leading and trailing edges but with printed ribs?

The half of a simple wing built to test the construction method.

Ribs 2

The leading and trailing edges are 'notched' and the ribs glued in. When dry the spar is threaded through a hole cut in the rib Depron infill and glued in place.

Although the spar is a constant width depth it is a built up balsa/Depron/balsa sandwich. To save weight each balsa flange is tapered from 5 mm deep at the root to 2 mm at the tip and the Depron cut deeper to compensate.

Up to this point it was really only a 'test' piece but it has gone to together remarkably well so the intention is now to complete the wing and fly it but it does mean I will have to 'back fit' an aileron.

At least I will be able to incorporate the necessary changes when I build the other half. wink 2 .

Tony Richardson03/02/2017 04:41:32
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Don't know anything about this kind of printing but is it possible to "print in" the spar notches? also could you not print a few cross members between the top and bottom frame of the rib or was this tried and came out too heavy.

cymaz03/02/2017 06:07:10
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Posted by Tony Richardson on 03/02/2017 04:41:32:

Don't know anything about this kind of printing but is it possible to "print in" the spar notches? also could you not print a few cross members between the top and bottom frame of the rib or was this tried and came out too heavy.

Simon did something like that on this thread....looks good

Colin Leighfield03/02/2017 08:54:41
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Good luck Simon, you're onto something here I'm sure.

Simon Chaddock03/02/2017 13:00:59
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Whilst is is perfectly possible to print in the spar notches this would negate much of the benefit of the continuous 'cap strip' effect of the one piece rib outline.

By cutting out the infill and inserting the spar through the rib (quite common practise in full size) the structural integrity of the rib is not compromised.

The next application of a printed component is the dihedral braces.

Brace 1

On refection I should have made the brace longer to increase the glue area as I am not sure how well PLA sticks to balsa using UHU POR. wink 2

Tony Richardson03/02/2017 19:05:50
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Ok I now see the issues with weight, absolutely amazing what can be done with a 3D printer.

Tony Richardson03/02/2017 21:58:22
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Simon I don't think I will ever have the knowledge to program a 3D printer but the technology fascinates me, I was prompted to search for other objects made in this manner and came across THIS I did take not the reference to weight several times throughout the video.

Simon Chaddock04/02/2017 21:57:15
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Tony

Yes that P38 is an amazing example of 3D printing, however Josh does point out that it is relatively heavy and definitely 'not a foamy'. He also voiced a concern at it potential robustness.

You have to admire the designers abilities and on the surface it is enormously attractive to be able to simply 'make' a scale plane from a set of electronic instructions but is printing the complete air frame in this way structurally efficient? I would have to say that on balance it probably is not. I suspect it relies quite heavily on the amazing power to weight of the brushless/LiPo combination syill there is nothing wrong with doing that.

I suppose it is a sign of the times that the amazing aerial camera shots came from a quad and that it looked like it had little difficulty keeping up!

Tony Richardson04/02/2017 23:04:20
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Yes I would imagine in cooler temps it would be quite brittle.

Simon Chaddock05/02/2017 20:23:58
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The complete 'bare' 48" wing.

48 bare

A couple of more printed bits. Thin backing pieces for the leading and trailing joints.

LE brace

Aileron servos next then I have to decide what to cover it with. wink 2.

Simon Chaddock07/02/2017 00:33:28
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Still a bit concerned at the ultimate strength of the dihedral braces or rather the abilities of the glue I decided to add spar cap stips top and bottom over the dihedral joint.

Spar caps

My usual test of a wing is to pick the 'ready to go' plane up by its wing tips. This puts a root bending load roughly equivalent to a pulling a 4g manoeuvre.

Although still uncovered the wing will indeed support the fuselage complete with motor, rx, servo and flight battery. wink 2

Load test 1

When covered with film or tissue (not decided yet!) it should add significant extra stiffness.

Aileron servos next.

Edited By Simon Chaddock on 07/02/2017 00:34:15

Colin Leighfield07/02/2017 10:43:54
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Interested to see that you keep a bed in your workshop Simon, perhaps I should do that. Great to see the HP115 and Canberra in the background.

I think your 3D printed wing project is excellent, there are so many possibilities here and we are just beginning.

Simon Chaddock07/02/2017 12:36:22
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Colin

It is of course a test bed!

Strictly its the other way round, my bed room is the 'plane' workshop (and literally my 'hanger'!). My 'mechanical' workshop is in the cellar. wink 2.

As the wing is to be film covered the aileron servo arms slots have to be protected.

Ail arm slot 1

This sort of small item is where 3D printing excels. Quick and cheap (1 p material cost and 1 minute to print a pair) in fact if they do not quite fit right just modify and print some more.

The revised slots in place.

Ail arm slot 2

Nearly ready to cover.

Colin Leighfield07/02/2017 16:51:25
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Simon. There is no prospect of me being allowed to build planes in the bedroom. There's no way of getting a bed into the shed, although a hammock is a possibility if it doesn't bring the roof down, which it probably would.

i have managed to sneak the 3D printer into the house though, it looks as if you need to keep the temperature above 15C for best results, so it wouldn't be working properly for most of the year if it had to go in the shed, not there's any room left in there anyway.

Simon Chaddock11/02/2017 16:48:39
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The final bit of printing, lead outs for the aileron servo wires.

Aileron wires 1

The 48" wing bare.

48 bare

Complete and tissue covered.

48 inch complete

Done with heavy weight Modelspan. Only moderately successful (rather more delicate when wet than I remember!) but then it at least 25 years old and going yellow! Nevertheless adequate with a coat of Exe Dope.

I had forgotten just how many operations are required with a conventional tissue covered structure. I could put together a Depron skin version in half the time and it would be stiffer and probably lighter. wink 2

Sitting on the Wing Dragon.

48 inch Wing Dragon

Ready to go the printed rib wing is the same weight as the 40" wing made of 5 mm foam insulation.

Perhaps more telling is the 44" true Depron wing is also exactly the same weight. Not only is it much stronger and stiffer but it also has two extra servos for the flaps. wink 2

Whilst the printed rib/inserted spar technique works well and being 'printed' you can create any wing section you like but equally the same principle can be applied to a Depron rib & skin construction and it is much quicker to put together.

For me the best part was designing and making the little specialist bits like the lead outs. With 3D printing you can create them exactly how you want rather having to 'make do' with commercially available items.

Simon Chaddock11/02/2017 16:48:40
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4881 forum posts
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The final bit of printing, lead outs for the aileron servo wires.

Aileron wires 1

The 48" wing bare.

48 bare

Complete and tissue covered.

48 inch complete

Done with heavy weight Modelspan. Only moderately successful (rather more delicate when wet than I remember!) but then it at least 25 years old and going yellow! Nevertheless adequate with a coat of Exe Dope.

I had forgotten just how many operations are required with a conventional tissue covered structure. I could put together a Depron skin version in half the time and it would be stiffer and probably lighter. wink 2

Sitting on the Wing Dragon.

48 inch Wing Dragon

Ready to go the printed rib wing is the same weight as the 40" wing made of 5 mm foam insulation.

Perhaps more telling is the 44" true Depron wing is also exactly the same weight. Not only is it much stronger and stiffer but it also has two extra servos for the flaps. wink 2

Whilst the printed rib/inserted spar technique works well and being 'printed' you can create any wing section you like but equally the same principle can be applied to a Depron rib & skin construction and it is much quicker to put together.

For me the best part was designing and making the little specialist bits like the lead outs. With 3D printing you can create them exactly how you want rather having to 'make do' with commercially available items.

Simon Chaddock14/02/2017 12:26:30
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I flew the printed rib wing this morning and it flies. Which is rather to be expected as it is very conventional.

The section I used is a bit thin (9.7%) with a relatively sharp leading edge along and this along with the changes is section due to the tissue sagging between the ribs, means its stall characteristics are a bit 'uneven'!

On the plus side it is has 15% more area for the same weight the 'base' wing so it climbs well.wink 2

Mark Kettle 114/02/2017 16:18:12
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Great Simon, It's good when you try something different and it works.

Simon Chaddock17/02/2017 16:12:16
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Second flight this time with a video.

Most of the 12 minute flight was exploring its flight manners so a number of landings and take offs were included.

The current V tail (no rudder) on the Wing Dragon is set up for a smaller wing with strong aileron differential so with the bigger area and no differential it exhibits significant adverse yaw.

The thin wing section does mean it can fly quite fast but the low wing loading also means it can go slowly although the sharp leading edge does give a very pronounced and random wing drop.

The single spar construction and all tissue covering means it really did like the damp conditions (it was just beginning to spot!) so the wing had little resistance to warping either natural or induced by flying loads.

Nevertheless 12 minutes of 'positive' flying and undamaged so it can't be that bad, although I still prefer the rigidity of Depron! wink 2

Edited By Simon Chaddock on 17/02/2017 16:13:52

Ian Jones17/02/2017 16:36:28
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I do like a happy ending, I could watch those landings all day!

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