Designing and Building Modular 3D Printed Planes

Hi, I'm Joseph Maloney a 16 year old who loves 3D printing and aeronautics. I spend much of my free time working on STEM based projects and I have many hours of CAD experience.

The problem that inspired this project is that every 3D printed plane model I found on the internet was fragile and assembled in a way that prevented easy repairs. One of the main reasons to 3D print a plane is the ability to replace broken parts; if you break one part you can print a replacement and be ready to fly again with minimal effort. However, all three of the 3D plane models I found online used superglue to connect the pieces. Superglue cannot be easily removed so the only way to fix a broken section is too reprint the entire wing or fuselage.

Another reason I designed a 3D printed plane is that 3D printing allows for highly customizable designs, which can be tailored to specific preferences or requirements.

IMPORTANT!

Most anyone can print and build my design, however designing your own plane will require significant experience in fusion 360 and with RC planes. It is highly recommended that you at least start out by designing a simple flying wing design like the one my example. With that said, anyone should feel free to attempt this project. If I saw this message when I was learning I probably would have ignored it. However this will just make the design process take much longer, and you may have to restart at least once. I had do this with my first design and lost many hours of work.

This instructable will guide you through the steps of 3D modeling RC planes for 3D printing. If you aren't able to 3D model your own plane, you can print mine and fly it without ever opening fusion 360. The directions for making my plane are on step 12.

For my design and designs like it, you'll need the following supplies:

• ~300 grams of PLA or PLA+
• ~200 grams of light weight PLA or foaming PLA (LW PLA - amazon)
• 1 meter long 10mm square carbon fiber tube (10mm CF tube)
• CA glue and activator
• Computer with fusion 360 license

For my design and designs like it, you'll need the following electronic components (these are simply suggestions, similarly sized parts will work just as well).

• 2207 2300kv brushless motor or similar 4 cell capable motor (2207 motor)
• 2 of any 9 gram servo (9 gram servos)
• 200mm of 1mm linkage wire (linkage wire)
• 4 cell LIPO battery 1000-1400mah (LIPO battery)
• 4 cell capable 30+ amp ESC (40 amp ESC)
• 3+ channel receiver
• radio controller

One of the most important parts of 3D printing anything that is made of 2 or more parts. In my plane designs, I don't use print in place tolerances because they make the printing process much more complicated than it needs to be. For making planes there are 3 tolerances to keep in mind

• solid to solid body is 0.15mm
• solid to surface body is 0.35mm (add 0.2 to the solid to solid tolerance)
• surface to surface body is 0.55

The reason that surface bodies add 0.2mm to the tolerance is because they are sliced with the print line going along the surface body's cross-section. This makes the line width of 0.4mm offset tolerance.

It is important to note that all printers have slightly different tolerances so you can adjust these as necessary but I recommend at least doing a test print beforehand.

Developing a shape and outline is a challenging step since it will be the foundation for your plane. You may be concerned with many factors such as printability, aerodynamics, the center of gravity, and many other factors all of which are very important, but most of these issues you can worry about later. Just make a rough outline of how you want your plane to look. You can do this mainly on the XY plane however utilizing the YZ plane can be critical especially if you are making a more traditional looking plane. In many cases. your plane will end up looking slightly different than your outline, but usually this is for the better. Keep in mind that in the next step you will be using this outline to make your wing profile and/or fuselage shape.

Selecting a good airfoil profile is an important step however it doesn't need to be perfect, there are many RC planes that fly just fine without an airfoil. With that in mind, when selecting your airfoil you first need to classify your plane.

• Flying wing designs like mine, need an airfoil with some amount of reflex. Reflex is a characteristic some airfoils have, and it means that the trailing edge of the airfoil is curved up.
• Aerobatic style planes need a more symmetrical style of airfoil.
• Gliders or high efficiency planes need thinner airfoils that create less turbulence.

There are other categories that require different types of foils, but you can always look up the type of airfoil required. In most cases you will want to choose a pre made airfoil from an airfoil database. Most of these have already been tested and are likely to work for your purpose.

Once you have selected your airfoil, you need to design your general wing shape. Create a sketch of the airfoil profile, and then either sweep it across a path and guiderails or use a loft.

For most of this design you will be working in the sheet workspace this is because the plane is designed to use what could be called an exploit in the slicing engine. This exploit allows for one perimeter continuous walls with a custom infill structure.

During the entire modeling process of the outer shell you will also be working with the infill. The infill structure is always offset 0.6mm from the outer sheet body in every single case. This is because when you get to the slicing step you will want the infill structure to join with the outer shell and not overlap.

For the majority of the modeling process you will keep the infill body as one solid shape, like the example on the right. Only when you are done with the outer shell you can move onto actually making the structure of the infill.

With the infill always in mind, the next step is adding an area in the back for the motor. The further you indent it, the easier it will be to achieve a good CG with a light battery. However if you indent it too far it will look weird and there will not be enough space for electronics. Don't worry about how the cutout affects the airfoil as the motor will create lots of turbulence anyways. You should start thinking about how you want the plane divided up so it can fit in you 3D printer. The overhang created from making the motor cutout will not be printable unless you support it or make it less steep.

At this point its good to bring up that your plane is almost completely symmetrical so you will only ever need to design half of it. At the end you can mirror the parts and print them.

Creating your elevons or control surfaces will require some type of hinge. The different types vary in modeling difficulty, reparability, durability, and some even require different materials. Here are the main types listed in order of how hard they are to model and how to make them

• chamfer paper hinge: This is where one or two sides of the hinge is chamfered allowing movement. To model this you have to have the elevon separate from the main wing. The part that does the actual bending is a piece of tough paper or another flexible thin material. You may have to model a slot into the chamfer to accommodate the paper. You can use superglue to fix the paper in place just don't get any on the part of the paper that bends.
• external or separately printed hinge: This is where you print or buy a separate hinge, and during the assembly process you add it in. To model this you have to have the elevon separate from the main wing. You will also need a slot or indent for the hinge to fit in. The best way to fasten it is with glue. Remember to leave space for the hinge to move.
• wire hinge: This is a more traditional hinge design. First you model two interlocking pieces then you thread a thin wire or rod through to secure them. This can be much more difficult to model especially if you are trying to achieve tight tolerance.
• fully printed hinge: This is basically the same as the wire hinge except that the "wire part" is printed into either the control surface or wing. The example above is a fully printed hinge.

When modeling all of these hinges the main thing to keep in mind is the axis of rotation for the control surface. Make sure that it's the same and scaled correctly throughout the whole hinge.

This step is all about creating the right shape that looks good, has good aerodynamic properties, and is printable. I usually make an offset from my wing, and then using the form workspace, draw the shape of my hatch. Make sure that you don't create overhangs that are over ~60 degrees from the printing orientation. Once you've created the shape make an offset for the infill base like you did with the wing. This can be difficult because the offset tool doesn't always work correctly when offsetting from complex surfaces created in the form workspace. You may have to offset separate parts and stich them together. Make sure the infill base is a solid body. The last part of this step is to hollow out part of your cover infill base so that there is room for electronic components. Remember to keep some areas thicker for strength. In the image above the black material is the finished infill base while the white material is the finished sheet body.

There are two main ways to integrate servos into your design. The first is a simple indentation in the wing that is the shape of the servo. This is very simple to model just don't forget to make sure your overhangs aren't too steep. The other way is a clip or something that holds the servo in from the other side. This is more difficult to model but provides benefits in areas like aerodynamics, reparability, and assembly. On the elevon side, I found the best way was to model and glue on a separate piece that the linkage wire attaches to.

The goal of these components are to provide a place to mount the motor and to lock the cover in place. I chose to make my cover lock from a simple extruded ellipse. The cover lock has to have a solid, permanent connection to the wing and a temporary connection to the cover. To achieve this I made my cover lock glue onto the wing and used a screw to keep the cover in place, however, some sort of buckle or strap would work just as well if not better. This piece also has to provide a place to mount the motor, either with a separately printed mount or mounting holes on the cover lock.

In this step you will take both the infill base for the wing and the cover, then define how you want your infill to look and support your plane. This step is more complicated so I split it into parts.

• Preparation: Make sure that both your infill bases are up to date and are exactly 0.6mm away from their corresponding sheet bodies. For the cover sheet ensure that you included space for your electronics and wires. This is your last chance to make any changes to the overall shape of the infill without impacting the integrity of your plane.
• Creating the first sketches: This is where you actually define how the infill structure looks and reinforces your sheet body. You should do this step in separate sketches for the wing and the cover to avoid confusion when extruding. I do this step on the XY plane however, it could be interesting if you did it at a slant or on multiple planes to create a more complex and potentially stronger structure. I found that to create a strong wing while minimizing weight, it is important to have long spars running through the length of the wing. Support is also needed across the wing to keep the airfoil shape from flexing too much. Everywhere you don't want infill, make a closed polygon. Everywhere you do want infill, there MUST be a 0.1mm gap between polygons. For a visual, look at the image above. I found the best way to create this structure is through the rectangular pattern tool. Make sure the sketch covers the whole plane, and remember that there should be no angle greater than 60-70 degrees from the X axis.
• Extruding the sketch and refining the structure: Once you are finished with the sketch a simple extrusion through the whole wing will create your structure. Make sure you extrude only the polygons, and not the 0.1mm gaps between them. Save your project before this step because it is possible that fusion will crash. Once you have the basis of your structure, you can add holes to reduce weight.

Repeat these steps on any body that needs to have one perimeter and a custom infill.

This is one of those last details that is very simple yet incredibly important. Vertical stabilizers are very easy to model, just draw the general shape of your stabilizers, then subtract the wing from them. In my experience it is easiest to cut them out of foamboard after making the rest of the plane because 3D printed vertical stabilizers are very heavy. If you want to 3D print them, they need to be thin.

Slicer: Although many slicers work for this type of printing, I recommend using Cura version 4.13.1. Any version before 5.0 works well. In version 5.0, with the new slicing engine, your prints end up having a much more visible seam where the internal structure connects to outer skin. You can easily install earlier versions of Cura by visiting this page. 

Settings for solid parts: Use your standard slicer settings with the modifications below:

• Manufacturer recommended PLA temp
• Wall line count: 2-3
• Infill: 40% 

General settings for thin wall printing: For “thin wall printing”, which is where you are creating a part with one perimeter, you will need to copy the following slicer settings:

• Layer height: 0.2mm
• Line width: 0.4mm
• Wall line count: 1 
• Infill: disabled
• Top layers: 0
• Bottom layer: 0
• Cooling > 30%
• Disable all “mesh fixes” settings

Settings for PLA or PLA+: These settings are further recommendations for PLA parts: 

• Flow: 102%
• Hotend temp: 210c - Use the max temp for your specific filament or close to it

Settings for LW foaming PLA: These settings are further recommendations for light weight PLA parts:

• Flow: 55%
• Temp: 240c
• Speed: 50mm/s
• Disable retraction
• Enable Combing mode

Tips for slicing: 

• If the part is within 5 grams of the recommended weight for that part, then it should be sufficient as long as it's strong.
• If you are having bed adhesion issues add a brim.
• If your parts have bad strength or layer adhesion, increase your temps.
• If you notice that when you zoom in on the part in the slicer, especially on sloped surfaces, there will appear to be gaps in between the layers, ignore this as it will not affect your actual print.

If for any reason you aren't able to 3D model your own plane here's the STL's for mine! Follow the instructions in the PDF and fly!

The following steps are specific to my plane, however, many of the same concepts can be applied to any 3D printed plane.

Preparation: Make sure your build plate is clean, and that you have good bed adhesion. The wing sections can have bed adhesion issues because they have a small surface area in contact with the build plate. I like to use a glue stick for bed adhesion.

Print time: It will take somewhere between 40-60 hours of printing to manufacture the whole plane. I recommend that once you get it down, you print multiple parts at once and run prints overnight.

Post processing: After removing parts from the build plate, remove the brims if you added them. Then clean up any strings or blobs which are especially prominent on the light weight PLA parts due to disabled retraction. Lightly sand the light weight PLA parts to smooth up the surface, if you plan to paint them this is very important. Clean out the hinge holes and remove anything that would get in the way of the hinge moving.

Piece specific post processing: 

• For V2_Cover, you need to remove the support piece highlighted in red.
• For V2_Cover_Lock, you need to remove the support piece blocking the slot for the motor mount.
• For V2_Cover, and V2_Inner_Wing, you need to remove the indented area with the text “remove with hot knife”.

Measurement: You do not actually need to measure the spar with a ruler. In fact, it is much easier to insert the spar all the way through one of the wing halves, and cut it flush to the plane where the two halves join. If you want to know the actual measurements, they are below. However it is quite difficult to get the correct inner angle without using the wing section. 

Cutting: I recommend that you use a hacksaw or similar. To stop the ends from fraying, tape the area where you are cutting. When cutting carbon fiber, it is critical that you wear a mask. Carbon fiber dust can severely harm your lungs; this applies to sanding as well.

Sanding: Sanding the ends of the spar after cutting reduces the risk of cutting yourself. It also helps prevent the ends from fraying.

NOTE: Although this plane is mostly modular some gluing is required. Many parts need to be joined together as replaceable subsections. Most of these glue joints are along the line of symmetry of the plane. This is because there is no way to join the faces that where in contact with the build plate without adding more parts and complexity

Gluing: CA glue and accelerator is the best way to join PLA parts together easily. You need to glue the following mirrored pieces along the line of symmetry: 

• Inner wing
• Cover
• Nose piece and camera pod

You will also need to glue the inner and outer elevon pieces together with the prongs facing away from each other. Once you have glued the inner wing pieces together, glue the cover lock piece on the back where it locks in. Gluing the spars in is optional, it depends on if you want to buy new ones if you break the center section. After gluing the cover together, glue the printed nut into the hexagonal hole on top.

Wing assembly: To assemble the wing slide the spars into the center wing section that you glued together. Then sandwich the elevon between the middle and outer wing sections. Make sure that all the prongs go into the wing sections. Finally slide the middle and outer sections onto the spars protruding from the center section.

Securing the cover: To secure the cover, slide it all the way over the center wing section and insert the bolt through the cover lock into the cover. Tighten with a penny till the cover feels secure.

Servos and linkages: The servo installation is as simple as sliding the servo into the servo clip, and clipping the clip into the center wing section. Cut and bend your linkage wire to an appropriate length (somewhere between 6mm and 75mm). Insert the wire into the servo horn, then glue “Linkage_Elevon_Side” onto the elevon. I recommend about 5-10 degrees of reflex.

Motor installation: To install the motor, simply screw it into the motor mount, then slide the mount into the cover lock. I prefer to secure the motor mount with hot glue so that it is removable, However, CA glue works just as well.

Everything else: The flat area in the back is designated for the ESC and the receiver can just be tucked in anywhere that there is space. If you are using a camera then install it in the camera pod. The flat area on top of the spar is designated for a flight controller.

Getting the correct CG: The indentations on the bottom of the wing indicate the farthest back recommended CG. For the first flight I recommend flying with the CG 5-10mm past the indentations. The optimal way to adjust the CG is by moving the battery, adding weight in the front or back should be a last resort.

Elevon configuration: If you don’t know how to configure elevons, I recommend you look up a tutorial for your specific radio. The end result should be:

• When you move the stick forwards and back, the elevons move up and down.
• When you move the stick left and right, the elevons move in opposite directions to roll left or right.
• When you put the stick in the corner only one of the elevons should move.

Rates: The rates I recommend are:

• 10-15 degrees on ailerons 
• 15-20 degrees on elevator
• 30% expo for all