Modular RC Airplane

This design provides the components to construct a modular RC airplane. The components are slid onto an 8mm carbon fiber backbone. The wing sections and ailerons are slid onto three 4mm carbon fiber rods. Except for wing end caps, no glue is used, instead everything is fastened using M2.5 and M3 bolts and screws. This allows you to easily do things like adjust wing size and slide components on the backbone rod to adjust the center of gravity.

I used PLA+ for printing, where it provides a better strength to weight ratio than lightweight PLA. The tires for the landing gear were printed using TPU. The total weight of the plane shown in the picture with all components, motor, servos and battery is 644 grams.

My implementation uses the popular 2.4GHz Express LRS (ELRS) for radio controls. This involves a 4 channel receiver, three servos and an electronic speed controller (ESC) , as well as an ELRS transmitter. I have chosen these components from Radiomaster.

The (non-printed) parts list includes:

Three 500mm 4mm carbon fiber rods as spars for supporting wing sections
One 330mm 8mm carbon fiber tube for airplane backbone
8x4.5 (8045) 2 vane propeller
Four 1.3mm pushrod connectors with 1.2mm push rods for connecting servos to control surfaces
Two 1.5mm stainless steel rods for landing gear
Three SG90 servo motors for rudder, elevator and aileron controls
One A2212 KV2200 brushless motor (suitable for a plane of up to 800 grams and can use a 2S or 3S battery)
One Radiomaster ER4 receiver module
One 40A brushless ESC to control the motor (supports both 2S or 3S batteries)
1400mAh 11.1v 3S Lipo battery (different battery sizes are possible, and testing shows a 3S is likely needed, see note below)
XT60 connectors (for circuit between toggle switch and battery)
Toggle switch (to disconnect battery)
Assorted M2.5 and M3 bolts and screws

Note that the battery mounts are sized for either a 2200mAh 2S (7.4v) battery or a 1400mAh 3S (11.1v) battery. A 3S battery will generate about 50% more thrust than a 2S battery due to the higher voltage. The battery mounts are also used to hold the 1.5mm rods used for the landing gear. Use of other sizes of batteries would require adjustments to the size of the battery mounts. The center of gravity of the plane is adjusted in part by the specific weight and placement of the battery.

The hardest part of construction is to properly bend the stainless steel rods used for landing gear and push rods for the ailerons. Need to be sure that the rods for the ailerons don't interfere with those for the rudder and elevator. Note the bends in the rods for the landing gear so that they attach to the wheel mounts securely and keep the wheels aimed straight ahead. Pictures are provided.

Amazon provides a low cost 'RC plane motor kit' with the brushless motor, ESC, propeller and servos. There is also a kit for push rods and connectors. All of the listed non-printed materials (except for the toggle switch) were purchased on Amazon.

The design uses four channels (which is why the ER4 receiver is a good choice) which are very/most common for RC planes:

Aileron/roll
Elevator/pitch (set up with an inverted output in transmitter)
Throttle (set up with an inverted output in transmitter)
Rudder/yaw

Some of the design parameters realized using the provided STL files are:

Length (from propeller tip to elevator) of 500mm
Wing span of 650mm
Wing chord of 120mm
Aileron length of 140mm
Aileron area of 126 cm**2
Wing area of 690 cm**2
Propeller diameter of 200mm
Thrust of 650-750g using A2212 2200KV motor, 3S battery and 200mm (8 inch) propeller
Total weight of 644 grams

This is marked as a WORK IN PROGRESS, as I am currently testing everything thoroughly before actual flight. I am using a Radiomaster transmitter. I strongly recommend getting familiar with your transmitter by connecting it to a flight simulator before you attempt actual flight. You will likely want to invert a couple outputs in your transmitter (as noted above) Also, with motor disconnected, make sure your control surfaces are operable and properly set with your transmitter. When connecting your brushless motor, you need to be sure it rotates in the correct direction. Do this before you attach the propeller. If it rotates in the wrong direction, you just need to reverse any two of the three wires to the motor. It's a good idea to mark the wires with colored tape so you can reattach properly in the future. Note that you will likely need to update the firmware and configuration on your receiver (i.e. the ER4) before it will connect to your transmitter.

The OpenSCAD file used to generate the STL files is provided. The OpenSCAD files for landing gear wheels and tires are from my other designs at https://www.thingiverse.com/thing:7316286 and https://www.thingiverse.com/thing:7317402.

Version History:

V1-V10: Development, not published
V11: Initial published release
V12: Strengthened motor mount
V13: Battery mounts modified for 1400mAh 3S, slots for wires added to nose

See my other RC projects at https://www.thingiverse.com/thing:7328990, https://www.thingiverse.com/thing:7326362 and https://www.thingiverse.com/thing:7073846.