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EL-39 - Semi scale RC jet for 120 mm EDF

3D model description


Uploaded a new Fuselage02 and Fuselage03 with tiny changes because it caused a layer shift in my printer today. I also uploaded my Simplify3D settings for fuselage parts as JGAurora

Uploaded a new Nose02 because of issues with the model.

Added small glue holes on the bottom of the flaps and elevators to more easily identify which side is up and which side is down. Add thin CA to the holes to secure the surface to the carbon hinge pin after assembly.

Length: 1858,5 mm
Wingspan: 1451 mm
All up weight: 7,2 kg
CG: 83-90 mm from the leading edge at the wing joint with the gear in the up position. There is a protrusion on the top of each wing surface to indicate the safe 83mm/25% MAC position. Gear up or down should make little difference because of the low weight of the nose gear. The prototype flies with CG at approximately 90 mm.

Appropriate pilot figure:

Video of the prototype without flaps:

High speed fly bys:

Build notes. Most of the plane assembly is pretty self explanatary, but here are some explanations. Read carefully:

300x300 mm print area is required for the largest parts. Many parts fit on a 200x200 bed, and some even smaller printers. I use a JGAurora A5 with TMC2100 stepper drivers for the big parts and a Wanhao Duplicator i3 for the smaller parts.

Good quality PLA should be used for the entire model. I recommend PrimaValue PLA:
Main tires, nose tire, fanrubber and fanseals need to be printed from TPU or other rubber like filaments.

Fuselage 01-07 should be glued together with CA and indexed with four 4x16 mm carbon rod pieces between each joint. I use thick CA and apply kicker to the edge after joining. The fuselage sections can be lightened by removing the bulk of the mating faces of each part. The example below shows the same part lightened and not lightened. It saved 30 g on this part alone, which adds up to a lot of weight on the finished plane. Make sure you leave a decent edge for glue to stick to when mating the parts, and make sure the different openings on the face are connected by solid material when you lighten them:

Nose03-Nose05 should also be glued together with CA and 4x16 mm carbon rods like the fuselage pieces. Nose01 and Nose02 should be installed with M3 screws. These two need to be replaceable to aid with access to the nose components and for replacement in case of damage.

Wing01, or Wing01-flap if you want flaps, must be glued to the fuselage with the 9x11x576 and 11x13x576 carbon tubes. The outer wing panels slot into these carbon tubes.This is done so that the plane can stand on the wheels during service, storage and transport.

Horizontal stabilizers should be joined and connected with the fuselage with 5mmx660 mm and 5mmx344 carbon rods or tubes. Glue the tubes in the stabilizer on one side and use screws on the other stabilizer to hold it all together. That way they can be removed to access to the servos.

All control surfaces use 3mm carbon rods and 3x6x2,5 mm ball bearings as hinges. Use two 3 mm split lock washers between the control surface and bearings to center each control surface, as shown in one illustration photo. Position them in slots that keep the control surface centered.

The shock absorbers need to be modified with the 3D printed pistons Shockpiston02 and 10000CST differential oil in order to dampen the heavy airplane on landing impact. The springs can be stretched slightly to increase tension.They should be very heavy to compress. Shockpiston01 can be used with thicker oil than 10000CST or for tuning if lighter damping is needed. One should also install an O-ring or rubber grommet on the exposed shaft between the housing and bottom cup to work as a soft end stop. The main gear will most likely bottom out when sitting on the ground, but will stretch on take off and be ready to absorb the landing shock when you land. Airplane shock absorbers are not designed to give a good ride quality, but to absorb the huge impact of the landing.

Glue the 11x51 mm carbon tubes into Maingear02 and then attach the exposed end of the carbon tube in the retract units. To install Maingear01 to Maingear02 use two 3x6x2,5 mm ball bearings and two M3x10 mm screws:

Assemble the nose gear as shown in the illustration:

The ESC should ideally sit inside the compartment over the intake duct, with wires going forward to the receiver and battery. This ensures adequate cooling. Extra capacitors need to be installed in such a way that they fit in the cable tube inside the fuselage.

If the 3D printable fan is used, the recommended HET motor should also be used with the heatsink. I do not know how well it will work in a very hot environment. 3D printed high power is still at an experimental stage for me. The motor shaft should have a hole drilled half way through it for one of the M3-16 mm impeller grub screws, because heat soak from the motor can cause the impeller to come loose if just a flat spot is used. The prototype fan pulls 83 A at full throttle on a fresh 12S charge when installed in the plane.

Part list. Some links have my affiliate code, which helps me pay for project development:
3x Shock absorbers:
10000 CST diff oil for the shocks:

M2x16 mm screws for the wheels.
Assorted M3 screws, cap head and countersunk head. 8-mm to 35mm length.
Assorted M3 grub screws.
Coutnersunk M4x38 mm screws for the main wheel axles.
#1 countersunk self tapping screws for the servo hatches.

Adjustable pushrod connectors for wheel doors:
4x 12x2 mm round magents for securing the canopy:

24 3x6x2,5 mm ball bearings for control surface hinges and landing gear hinges:
2x 12x18x4 mm ball bearings for nose wheel steering:
7x Nylon clevises for control surfaces:
7x M2 metal pushrods for control surfaces:
7x Snap link clevises for control servos:
1,5 mm piano wire for gear door links and hinges.

1x 5mmx660 mm carbon rod for horizontal stabs
1x 5mmx344 mm carbon rod for horizontal stabs
assorted short lengths of 4 mm carbon rod for indexing when joining fuselage parts.

2x 3x225 mm carbon rods for aileron hinges
2x 3x340 mm carbon rods for flap hinges
2x 3x286 mm carbon rods for elevator hinges
1x 3x276 mm carbon rod for rudder hinge

2x 6x8x400 mm carbon wingtip tubes
2x 7x9x440 mm carbon wing tubes
1x 9x11x32 mm carbon tube for nose gear strut
2x 9x11x51 mm carbon tubes for main gear struts
2x 9x11x440 mm carbon wing tubes
1x 9x11x576 mm carbon wing tube
1x 11x13x576 mm carbon wing tube

-12S 5000mAh lipos
-7x Control surface servos. The prototype flies with these:
Other servos with a case profile of less than 30x15 mm will also fit. A stronger digital option is Corona DS-236MG
-4x Landing gear door servos and nose gear steering servos: 9-12 g servos with metal gear are recommended. Not SG92R servos as they go crazy when used with the sequencer.
-ESC: 12S 120A+ ESC. I recommend Castle Creations Talon 120 because it has a strong integrated BEC.
The prototype flies with an Aerostar Advance 120A:
-Extra capacitors with low ESR for the ESC because of extended battery wires. At least 660uF.
-Retract and door sequencer:
-90° outward operating retracts with 11 mm strut clamp are required to use the 3D printable trailing link suspension. I use this (might require some adjustment to operate perfectly):
Other retract units will fit. The gear and wheel bays are roomy.
-Motor for the printable EDF:

3D printing settings

Most parts should be printed with one 0,4 mm perimeter only. The exceptions are hinge pieces, small parts and landing gear parts which should be printed with many walls or solid infill.

Fuselage-parts need 3 bottom layers and six top layers.

  • 3D model format: STL and ZIP



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