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Old Oct 23, 2012, 12:29 PM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
Build Log
Design Print Fly - 3D Printed Organic Design

Greetings! I hope a 2-ft span plane is small enough to fit in this forum, I wasn't sure where else to put it, and I was drawn here from Lupus78's Hellcat thread.

I too am beginning to design 3D-printed RC planes, thanks to the ease and relatively cheap process made available by Shapeways.

I've done a few 3D-printed parts already; a pod-fairing and a motor mount - both of which performed beautifully. The nacelle/mount part is actually INCREDIBLY tough, and I've revised my future designs to cut down on weight and volume/cost. I've learned that even at 1mm thick, a part made from WSF can be made quite stiff, if you integrate return flanges and/or stiffening ribs. Here is a video log of my last plane. The parts performed great, the plane did not...

This time though, I'm taking it a bit further. I want to see if I can print the entire plane, skin and all. The biggest challenge is how far can I push the cost down if I restrict myself to a 2-foot wingspan, since 25" is Shapeways longest limiting dimension.

The main reason, for me, to print everything including the skin is to showcase the ability to make complex-curvatures and 'organic' custom designs. To that end, I incorporated a bird-like wing design and gave it a complex supercritical-airfoil cross section. Click here to see it on Shapeways.

I've made it as hollow as possible, integrating mounts and openings for all the electronics, along with internal ribs and spars. The only 'extra' openings are those needed to drain the excess material from the hollow wings. I realize a supercritical shape probably isn't the most efficient airfoil for this scale, but it's more about showing the feasibility of the process than the performance (but given the 3800kv motor I'm throwing at it, it should pull through the air just fine ). Also, I chose the supercrit section because it provided me with the thickness I needed for the wing servo. :P

All in all, the plane comes from Shapeways at about $300 including shipping. All that's left for me to do is install my components, and attach the tail to the body with a square CF tube or basswood square dowel. For a custom-designed, ARF, weird-azz plane like this, I think ~$300 isn't too crazy, but I could be drinking my own cool-aid here... (I'm sure I don't have to invite opinions on this subject )

NOTE: Some proportions have changed slightly since the attached images were made; I lengthened the nose a bit to make room for wires. Also, since the tail is attached after the fact, the length of the tail-boom is entirely customizable/variable, making for very easy CG/handling refinements.

The link below here goes to Sketchfab, a web-based 3D-viewer; I uploaded my latest 3D model so you can see it better than in just a few static images.
Wind Skimmer DPF2.ac (click to view in 3D)
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Last edited by pakrat961; Oct 23, 2012 at 02:41 PM.
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Old Oct 23, 2012, 04:42 PM
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That is way cool! I don't know what it will be like weight wise and with yaw stability, but the overall design and idea are great. It's general shape reminds me of a Swallow beatiful design!

B36
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Old Oct 23, 2012, 04:55 PM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
Quote:
Originally Posted by b36roxs View Post
That is way cool! I don't know what it will be like weight wise and with yaw stability, but the overall design and idea are great. It's general shape reminds me of a Swallow beatiful design!

B36
Thanks! Yeah, it's going to be a bit on the heavy side; maybe close to a whole pound, but that just means it'll be fast.

I originally created the design in X-Plane, and modeled it after the Black Skimmer. So I know it's a feasible, flying configuration, it's just a question of how it will handle once scaled down. I've made room for a V-tail mixer, so I'll be able to control yaw independently and make coordinated turns. And because the V-tail is inverted, the induced roll-yaw coupling will actually be complimentary, not counterproductive in turns. If there's room, I might even experiment with adding a piezo-gyro for active yaw-damping.
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Old Oct 26, 2012, 01:24 AM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
Update!

So since I've already gone so far as to model this whole thing in UG-NX, I decided to use the built-in FEM tool to see how my structure performs under load. I mean, why not, right?

Shapeways has their material properties online, so all I had to do was plug 'em in and set up the system. I don't have my final total weight yet, but I figured a pound was probably a pretty good starting point for analysis. And actually, the deflection was so small I upped it to 2 pounds just to see it. So technically what you're seeing in the following images is a theoretical 2-g load case. And even under 2 g's the max deflection is only 0.138" at the wingtip.

More interesting is what goes on in the centerbody area. As the wings are deflected up, they pull the sidewalls outward, and I was concerned about how much it deflects there. As you can see, it's basically imperceptible.

Also of note is the actual max stress observed; only 633PSI, while the max tensile strength of the material is over 6900! Basically meaning I've got a factor of 10 before I get anywhere near yielding the material. Granted, these are just static loads, I'm not accounting for anything dynamic yet, but at least I know it shouldn't tear itself apart.

Click each link to see the animated GIF's, and click the images below to enlarge:

Displacement Animated GIF

Stress Animated GIF 1

Stress Animated GIF 2

Stress Animated GIF 3


Bottom view 1, Stress:


Bottom view 2, Stress:
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Old Dec 03, 2012, 10:10 AM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
Just a quick update to let y'all know I finally ordered my first print of the plane! So as soon as it comes from Shapeways I'll update you further with an unboxing and assembly video.
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Old Dec 03, 2012, 06:35 PM
No place like cloud base......
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I was waiting!
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Old Dec 03, 2012, 08:08 PM
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Joined Nov 2007
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I can give you a rough estimate of its mass if you can provide me with the total volume.
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Old Dec 04, 2012, 12:49 AM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
I have the volume and density of the model framework, so I just need to add up all the components. Thanks for the offer though!
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Old Dec 20, 2012, 09:36 AM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
It has arrived!

Here's a video of the unboxing. More detailed pictures will follow.

BSAV - 3D Printed Plane Unboxing! (5 min 41 sec)


I can also report that it is very sturdy, and all the pre-modeled compartments fit their respective components perfectly. I'm VERY excited to put this thing together and fly it over the holiday break, although I have been advised that I should add a straight vertical surface on the tail for more positive yaw stability. Timing couldn't be more perfect.
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Old Dec 20, 2012, 11:35 AM
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Elmhurst, NY (Queens in NYC)
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Looks great!

I admit to being impressed. I hope it flies well, but even if it doesn't I'm totally convinced that you will be able to modify the design and try again.

I look forward to the next post, and/or video.

(Struggling to learn 3D design)

Pete
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Old Dec 20, 2012, 01:41 PM
KK4EHM--FPV Mon!
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United States, FL, Sebastian
Joined May 2005
1,333 Posts
That came out really nice. Great job man!
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Old Dec 20, 2012, 06:34 PM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
Update with pictures!

I've now got all the parts and pieces, now all that's left is to assemble it.
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Old Dec 20, 2012, 07:46 PM
Supersonic hover
Esprit440's Avatar
Michigan, United States
Joined Sep 2003
1,043 Posts
Very cool! Nice to see some RC history in the making. This is the first plane with printed skin I've seen done by a hobbyist.

Was there a lot of unsintered powder left in the wing bays or did those little relief holes do the trick?

-Matt
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Old Dec 21, 2012, 11:28 AM
I make planes I want to fly
pakrat961's Avatar
Southern Cal.
Joined Mar 2004
282 Posts
There was almost no unsintered powder left in the wing/body piece, the drain holes worked well.

However, I didn't provide similarly good drain holes in the tail pieces, and I had to do a bit of scraping and draining of leftover powder myself.

I've made a bunch of notes on minor improvements I can make for the next version, to make it more user-friendly and more truly "Almost Ready to Fly". I'm also hoping I can reduce the cost further by removing unnecessary volume; the first version is always a bit conservatively overbuilt.

Thanks for the comments guys, stay tuned for more assembly updates over the holiday break!
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Old Dec 21, 2012, 11:44 AM
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centennial/aurora colorado
Joined Mar 2008
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cannot.......resist......urge.......to ........buy.............plane........arggghhh, when you go into offering these please let me know, i need this plane. heck i could high altitude test it for you
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