3D Printed Infinity Wing Design

Here is a great post by 3daeroventures about his 3D printed wing design.

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Hi all,

I just wanted to share my latest 3D printed infinity wing design with the group. I've attached some pics. Feel free to ask any questions about the design and build.

You can also check out the design, build, and flight video here:

3D Printed Inifinity Wing RC Airplane! (11 min 36 sec)

Technical Specs:

  • Wingspan: 50"
  • Length: 33.75"
  • Weight(Loaded): 1490 grams
  • Motor: Eflite Power 15
  • Battery: 3S 11.1V 2200mah LiPo
  • No. of Channels: 3 (throttle, elevons)

I'm working on making the STL files and a build guide available for sale. If the interest is high enough I'll have it ready by the end of the year.

Last edited by Jim T. Graham; Nov 20, 2019 at 01:05 PM..
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Nov 19, 2019, 08:28 PM
Registered User
Looks great!

I'd be keen to try printing one when you publish the plans.
Nov 19, 2019, 09:13 PM
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tspeer's Avatar
Count me in, too!

Have you considered adding a rudder? Or landing gear?

FWIW, I was the flight control system architect for this plane, which was to be a modified S-3 Viking. It had two control surfaces on each panel, plus ailerons and rudder. All the control surfaces were used for control around all three axes all the time - there weren't dedicated ailerons, elevators, etc.
Last edited by tspeer; Nov 19, 2019 at 09:33 PM.
Nov 19, 2019, 09:14 PM
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Thread OP
Thanks guys. If you sign up through the website I'll send out an email blast when it's ready.
Nov 19, 2019, 09:46 PM
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Thread OP
Quote:
Have you considered adding a rudder? Or landing gear?
That's awesome! It would be very easy to add a rudder to my design- I was just trying to cut some weight by eliminating a servo for the initial design. Now that I know it flies well I can add a rudder.

As far as landing gear I think I'll just add a single wheel to the belly for smoother landings but leave it as a hand launch.

I have a few more designs in the works that are scale conventional setups.
Nov 20, 2019, 02:12 AM
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Warbirdmadman's Avatar
I'd be in too.

Looks great and flies well too.

Well done.
Nov 20, 2019, 07:41 AM
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Dirty Dee's Avatar
Nicely done!

Question on your modeling/slicing workflow. With making all surfaces extruder width for manifold STLs, which slicer and setting did you apply so that the exterior surface remained smooth? did you offset the internal structures to be spaced away from the external shell, or were they combined?
Nov 20, 2019, 07:45 AM
Trust me, I'm an engineer !
Khan's Avatar
An interesting design for sure, and it looks great !

About the change in the design, and moving the CG Forward : now that you have the CG sitting on top of the front wing, doesn't that mean that the back wing is acting like a conventional horizontal stab ?
Nov 20, 2019, 10:56 AM
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Thread OP
Quote:
Originally Posted by Dirty Dee
Nicely done!

Question on your modeling/slicing workflow. With making all surfaces extruder width for manifold STLs, which slicer and setting did you apply so that the exterior surface remained smooth? did you offset the internal structures to be spaced away from the external shell, or were they combined?

I used Simplify3d.

The CAD model is actually all solids, not surfaces like a lot of other RC plane models (like 3DLabPrints). So the internal structures are all combined with the external shell. The outer surfaces are the same quality to something like 3DLabPrints.
Nov 20, 2019, 12:23 PM
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Silent Air Taxi


Hi there,

Congrats to your Plane. And thanks for sharing the difficulties on the first attempt.
It remainds me to a startup project we have here in Germany for the use (on day) as autonomus urban air vehicle:

https://e-sat.de/en/silent-air-taxi/

First time I saw a design like this fly.

Patrick
Nov 20, 2019, 12:46 PM
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Thread OP
Quote:
Originally Posted by Khan
An interesting design for sure, and it looks great !

About the change in the design, and moving the CG Forward : now that you have the CG sitting on top of the front wing, doesn't that mean that the back wing is acting like a conventional horizontal stab ?
The back wing must be providing a decent amount of lift. I'm assuming the Center of Lift is right in between the 2 wings.

All I know is this wing configuration makes for a very stable airplane. And I'm assuming the wrap around winglets help mitigate any wingtip vertices, reducing the risk of tip stalling at low speeds or high angles of attack.
Nov 20, 2019, 01:11 PM
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tspeer's Avatar
Quote:
Originally Posted by 3daeroventures
...
As far as landing gear I think I'll just add a single wheel to the belly for smoother landings but leave it as a hand launch. ,,,
That would work. I was mainly thinking of protecting the prop, although it would be nice to be able to shoot touch-and-gos. If you do add a single wheel, I think I'd be tempted to modify the stl to have the same attachment to the fuselage, but turn it into a conventional gear.

BTW, I've been experimenting recently with printing springy wheels. Even though PLA is a brittle material, when it's thin enough it flexes nicely. They are stiffer than I wanted at the size shown in the first photo, but the ones with larger diameter work better. I could do the smaller ones with fewer and thinner spokes if I really wanted more give to them. I was concerned about aerodynamic drag from all the cavities on the large wheels, so I wanted a smooth cover. But it had to be stretchy to allow the wheel to flex. Would you believe dental dams were the answer? I wish there were more choices of color, though. (I went with unflavored, but your plane may prefer mint or grape flavor.)

I think a conventional gear with some wheels like these would look awesome on your design.
Nov 20, 2019, 01:50 PM
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tspeer's Avatar
Quote:
Originally Posted by 3daeroventures
The back wing must be providing a decent amount of lift. I'm assuming the Center of Lift is right in between the 2 wings.

All I know is this wing configuration makes for a very stable airplane. And I'm assuming the wrap around winglets help mitigate any wingtip vertices, reducing the risk of tip stalling at low speeds or high angles of attack.
For any plane to be stable, the aft lifting surface must be more lightly loaded than the forward surface. So the aft wing does not produce as much lift as the forward wing. That's why you needed to move the center of gravity forward.

There are two reasons for this. The first is you want the plane to pitch down when there is an increase in angle of attack. When the aft wing is more lightly loaded and both wings receive an increase in angle of attack, you can think of the increase in lift being a greater percentage of what the lift was in the balanced condition, so the aft wing produces more pitching moment. That makes the plane want to pitch into the new apparent wind direction and return to the original angle of attack.

The second reason is easier to understand if you think about the moments about the neutral point. The pitching moment is independent of angle of attack when the moments are taken about the neutral point. So you can think of it as the center of lift for the whole plane. If the c.g. is at the neutral point, then the pitch stability I talked about above vanishes, and there is no change either way when the angle of attack changes. For speed stability, meaning you want the plane to pull up if it starts heading downhill (and vice versa) so it maintains level flight, you need to have a positive (nose up) pitching moment about the neutral point when the plane is in trim. This requires the c.g. to be ahead of the neutral point. You can think of it this way: with the c.g. ahead of the neutral point, gravity is trying to pull the nose down, while the positive aerodynamic moment is pulling the nose up just enough to support the weight. But the aerodynamic moment is proportional to speed squared, while the gravitational moment is independent of speed. So when the plane speeds up from the trimmed speed, the aerodynamic moment becomes stronger than the gravitational moment and the plane pitches up. The opposite happens when it slows down, lowering the nose when the plane slows down as it starts to climb. The end result is the plane flies level at the trimmed airspeed.

The wrap-around wingtips don't eliminate the trailing vortices, but they do spread them out somewhat. If you think of the lift from the forward wing wrapping up into the wing tip, and then consider how the lift on the aft wing wraps down into the wing tip, you'll realize that these two effects are of opposite sign. So the lift can't wrap all the way around the tip, but must still go to zero somewhere between the two wings just like the lift has to go to zero at the tip of a single wing.

The common explanation for the trailing vortices is they arise from flow around the tip of the wing, but this is misleading. The vortices really arise from the fact that the wing is producing lift over a finite span. No matter how the wing is shaped, there will still be vortices shed at the edges of the wake. You can see why when you picture the flow around a canoe paddle. When you draw a paddle through the water, you are moving a slug of water sideways, and that requires a force on the paddle. A wing pushes air downward, which results in a force on the wing. After you draw the paddle from the water, you'll see the water you accelerated continue to move. The moving slug of water pushes water aside in front of it, and water comes in to fill the void that would otherwise be left behind. The vortices are simply water that is circulating from in front to behind intensely over a short distance. The exact same thing is happening along the edges of the wake left by the wing. The air moving downward displaces other air and is replaced by air coming from above. The trailing vortices are at the edges of the moving wake vs the more stationary air mass surrounding it. You cannot eliminate this any more than you can eliminate the vortices you see swirling around the edges of a canoe paddle.

If you want to calculate the lift and interference between the wings and tips, you can use a tool like AVL. It will tell you where the neutral point is and show you how the load is spread along the wings. Of course, you've already worked out where the c.g. needs to be, but if you wanted to really understand what's going on with the aerodynamics of the joined wing, AVL is the tool to use.
Nov 20, 2019, 02:01 PM
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tspeer's Avatar
I have two 50 mm EDFs sitting around that I bought at a clearance sale. What would be awesome, and solve the prop strike problem without landing gear, would be a twin EDF version with the fans mounted mid fuselage like the 3-view I posted. Given where you want the c.g., they might even be located at or ahead of the forward wing leading edge.

BTW, I think the reason your plane handles well without a rudder is because of the anhedral of the aft wing. Differential deflection of the elevons not only produces a rolling moment, it also produces a yawing moment in the same direction. This yawing moment will compensate for the adverse yaw of the ailerons, or even to the extent of producing proverse yaw.

So you might not need to add a rudder after all. The main use of the rudder would be to slip the plane to steepen the approach angle or compensate for crosswinds. It wouldn't be needed to coordinate turns.
Nov 20, 2019, 02:21 PM
Registered User
I love the look of this plane!
And I appreciate your honesty to show your failed first attempt and that you had the ambition to go on. Keep doing what you do!


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