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

3D model description

The human is not included.

Flight videos:

Onboard videos:

Maiden video:

Added new Nose 3 with extra holes for JP retractable landing gear.

I added new plain wingtips without tanks today. Wing03-notank.STL is the right wing panel to use if the tip tanks are not used. Wingtip01.STL is the first wingtip I designed without a tank.

Added droptanks for the wing mounts. Droptank01 is one tank. The alignment holes are designed for 1,75 mm filament and are offset so that the parts only go together one way. Droptank02 is the mounting brackets between the tanks and the wing weapon mounts. The tall one goes in the front and the short one in the back. Glue them to the tank and secure the tank to the wing with M3 screws.

Also uploaded new wing parts that have integrated mounting holes for the weapon mounts in the correct location. If you already printed wings you can drill them through the mounts when positioned as I described below.

I added some scale detail. Look up photos of the full size to see exactly where they should go.
Airbrake01 - Fake airbrake shapes for the bottom of the fuselage.
Flares01 - Flare discharge openings for the bottom right rear fuselage.
Sensors02 - Antenna thingy on top of the fuselage.
Sensors03 - Ice accretion transmitter. Goes on the left side of the nose by the landing gear door.

Added two new canopy parts that resemble the canopy of the Aero L-59. I have not tried to print them yet. The file names are L-59-canopy02 and 03.

Also added weapon mounting points for the underside of the wing. Weaponmount01 is the inner mounts and 02 is the outer. They should be mounted with the centerline 10 mm and 110 mm from the wing joint respecitively, with the front screw hole through the center of the front carbon wing joiner.

Also added lightweight covers for the retract units on the bottom of the wing. They should be trimmed slightly to fit if they don't go in all the way, and secured with hot glue so that they can be removed if necessary. Retractcover01.

Addet a tiny part. A printable bottom shock eyelet for the main gear. It can be used on the nse as well. It prevents the spring collar from being pushed down the stock eyelet during high loads. These shocks aren't made to absorb such high loads.

Added a version of Fuselage01 with an integrated latch for the canopy. Make the latch from 50 mm long pieces of 3x5 tubing and 3 mm rod. Use a 4x0,3x20 mm spring and an M3 screw as the handle on top according to the illustration:

When using a latch in the rear for the canopy, glue Canopy01 in place on the fuselage, and add a pin to the top of Canopy02 so that it slots into Canopy01 and then is locked in place i the rear by the latch. Add a hole to the rear of Canopy03 for the latch.

Added a canopy handle (Canopylatch01) and flap fairings (Flapfairing01-02). The flap fairings can be glued to the top of the wing at 60 mm fron the inside and outside edge of Wing01-flap and 02-flap, like the photo shows. They should be glued to the static part of the wing, not the flap, obviously.

Added new Canopyplug01-03 which work better for vacuum moulding canopies. Can also be used to 3D print canopies using the spiral vase function with a clear filament. I recommend Prima EasyPrint clear filament for the best clarity. multiple clear coats of paint increase the transparency.

Added new Fuselage03-bigESC and 04-bigESC with larger ESC cavity in the top, for those with bigger ESCs than the original recommendations. Up to 30 mm tall and 59 mm wide ESCs can be fitted in the hole.

Added new Nose03-05 and Vstab01-05 with more internal structure to reduce the chance of buckling when printing.

Uploaded nose wheels for ball bearings. The file is Nosewheel01-bb and it uses the same ball bearings as all the control surfaces. Main wheels for bearings should follow soon.

Uploaded a slightly changed Fuselage05 to improve the top layer quality and reduce the pull on the side walls as the top layers are printed.

Uploaded a new Fuselage03 with slightly more internal support to improve print quality when the top layers are printed.

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 (prototype #1 ), 8 kg (prototype #2 ), 7,5 kg (prototype #3 )
CG: 83-103 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 maidened with CG at approximately 90 mm. 103 mm CG has been tested and flies very well.

Initial control throws:
Elevator: Up 18 mm / Down 16 mm
Ailerons: Up 20 mm / Down 15 mm
Rudder: 15mm / 15 mm

Use 30% exponential on all surfaces to reduce center sensitivity.

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:

Fuselage02 and Fuselage03 have small hinge lines for the main gear doors. These should be drilled or checked with wire before they are glued together because it's hard to do after assembly. If you didn't check them in advance and they are tight, you can use a 1 mm piano wire in a drill and use it as a flexible drill bit to open them up.

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. As of 03.07.2018 I have flown the 3D printed PLA impeller in 21°C ambient temperature, and the motor got too hot to hold my hand around for longer than a couple of seconds. I will recommend that the PLA impeller is not used for hot environments because of this. Hotter materials may work but that's more experimental than using PLA, and there are other properties that come into play, like elasticity.

Here's how you open up the hinges for the wheel doors. Use the same piano wire you use as the hinge pins to open up the holes with a drill. Cut the end of the wire to make a flat spade shape before drilling for easier drilling:

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 5mmx500 mm carbon rod for horizontal stabs (rear rod)
1x 5mmx344 mm carbon rod for horizontal stabs (front rod)
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 5000+mAh lipos. Two of these will work and give five minutes of safe duration. I recommend XT90 connectors instead of the included XT60:
-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
-Optional servo reverser if you are unable to reverse one flap and one gear door servo by other means:
-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. The highest quality option is probably the Electron ER-30evo, which should fit with some adaption:
-Motor for the printable EDF:

File name descriptions:
Aileron01 - Ailerons.
Airbrake01 - Fake airbrake shapes for the bottom of the fuselage.
Canopy01 - Front part of the canopy.
Canopy02 - Middle part of the canopy.
Canopy02 - Rear part of the canopy.
Canopylatch01 - Scale non functional outside handle for opening the canopies.
Canopyplug01 - Plug for vacuum forming the middle part of the canopy.
Canopyplug01 - Plug for vacuum forming the rear part of the canopy.
EDF-housing01 - EDF ousing and motor mount.
EDF-Impeller01 - 11 blade EDF impeller for 8 mm shaft.
EDF-tailcone01 - Tailcone for the back end of a HET 800-motor.
Elevator01 - Inner elevator parts.
Elevator02 - Middle elevator parts.
Elevator03 - Outer elevator parts.
Fanintake01 - Tube to guide air from the fuselage duct towards the EDF housing.
Fanrail01 - Mounting rails for the engine compartment. Pre-made holes for the printable EDF and Changesun 120 mm fan with captive M3 nuts.
Fanrubber01 - Mounting grommets for EDF installation on the fanrails.
Fanseal01 - Flexible seal between the front of the EDF and the rear of Fanintake01.
Fanseal02 - Flexible duct between the rear of the EDF and the exhaust tube of the fuselage.
Flap01 - Innermost flap parts.
Flap02 - Outermost flap parts.
Flap03 - Hinge brackets for the flaps. Fits in Wing02-flap.
Flapfairing01 - Dummy inboard flap fairing for the top of the wing.
Flapfairing02 - Dummy outboard flap fairing for the top of the wing.
Flares01 - Flare discharge openings for the bottom right rear fuselage. Look up photos of the real L-39 to find it.
Fuselage01-07 - Fuselage sections, from forward to rear.
Fuselage01-Latch - Fuselage part with integrated channel for a latch.
Fuselage03-bigESC -Section with larger hole for bigger than normal ESCs.
Fuselage04-bigESC -Section with larger hole for bigger than normal ESCs.
Hstab01 - Inner parts of the horizontal stabilizer.
Hstab01 - Outer parts of the horizontal stabilizer.
Hstab02 - Tips of the horizontal stabilizer.
Intake01 - Intake lips for the air intakes. Separate to simplify painting in a separate color.
L-59-canopy02 - Middle part of L-59 style canopy.
L-59-canopy03 - Rear part of L-59 style canopy.
Maingear01-02 - The main landing gear trailing link assembly.
Maingeardoor01 - Main gear doors to attach to the main landing gear.
Maingeardoor02 - Left inner main gear door.
Maingeardoor03 - Right inner main gear door.
Maingeardoor04 - Horns for the links to close Maingeardoor02 and 03.
Maingearmounts01 - Heavy duty mounting beams for the main landing gear in the inner wing parts.
Maintire01 - Main landing gear tire.
Mainwheel01 - Main landing gear wheel.
Mainwheel01-bb - Main landing gear wheel for 4x7x3 ball bearings.
Motorhatch01 - Hatch for the EDF compartment in the fuselage.
Nose01 - Tip of the nose.
Nose02 - Nose part and nose landing gear compartment.
Nose03-05 - Parts of nose under the cockpit area.
Nosegear01-03 - Nose gear trailing link assembly.
Nosegear04 - Internal part of the nose gear strut.
Nosegear05 - Top bearing cap of the nose gear strut.
Nosegear06 - Mounting and steering beam for the nose gear.
Nosegear07 - Nose gear steering link eye.
Nosegeardoor01 - Nose gear door.
Nosegeardoor01 - Nose gear door hinges with intergrated link hole.
Nosetire01 - Nose landing gear tire.
Nosewheel01 - Nose landing gear wheel without bearings.
Nosewheel01-bb - Nose landing gear wheel for 3x6x2,5 mm ball bearings.
Pitot01 - Pitot tubes for the wings.
Retractcover01 - Covers for the retract bays.
Rudder01 - Bottom part of the rudder.
Rudder02 - Top part of the rudder.
Rudderfence01 - Plate that goes under the top of the vertical stabilizer, over the rudder. Not all L-39 have this. Look up photos of the real L-39 to find it.
Sensors01 - Three rods that fit in the holes under Nose01.
Sensors02 - Antenna thingy on top of the fuselage. Look up photos of the real L-39 to find it.
Sensors03 - Ice accretion transmitter. Goes on the left side of the nose by the landing gear door. Look up photos of the real L-39 to find it.
Servohatchaileron01 - Aileron servo hatches. Install with #0 or #1 screws.
Servohatchrudder01 - Rudder servo hatch. Install with #0 or #1 screws.
Shockpiston01 - Two slot shock piston for heavier than 10000 CST oil.
Shockpiston02 - One slot shock piston for 10000 CST oil and lighter weight.
Tiptank01 - Rear parts of wing tip tanks.
Tiptank02 - Middle parts of wing tip tanks.
Tiptank03 - Front parts of wing tip tanks.
Tiptank04 - Tip tank front light glass.
Vstab01 - Bottom front part of vertical stabilizer.
Vstab02 - Bottom rear part of vertical stabilizer.
Vstab03 - Middle part of vertical stabilizer.
Vstab04 - Middle part of vertical stabilizer.
Vstab05 - Top part of vertical stabilizer.
Wing01 - Inner part of the wings without flap.
Wing01-flap - Inner part of the wings with flap.
Wing02 - Middle part of the wings without flap.
Wing02-flap - Middle part of the wings with flap.
Wing03 - Outer parts of the wings.
Wing03-notank - Outer parts of the wings for wingtips without tip tanks.
Wingtip01 - Plain wingtip without tip tank.
JGAurora - Simplify 3D profile for fuselage sections with JGAurora A5 printer.

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 for the most part.

Fanrail01 need to be printed solid if you plan to drill them for an aftermarket EDF.

Maingearmounts01 should be printed with six perimeters and twenty top layers to give something for the retract mounting screws to grab on to. Bottom layers can be just four or five. Infill isn't important. Iuse zero infill.

Maingear01-02 should be eight 0,4 mm perimeters, twelve top and bottom layers and at least 50% infill. The same goes for the nose gear parts.

  • 3D model format: STL and ZIP



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Welcome !
My question would be how much 3D printing would cost me home. I have a CR10 S5 printer and I would like to print this model. But I do not know how much it would cost me and what material I would use because I want to try 3D printing for the first time. I like Challenges and Airplanes.
If you would please and help me in this I would thank you.
Welcome to Csanád Gál

Check the files for updates and you will find a new wheel with ball bearing pockets. :)

New update: test taxi runs have gone great! Found a little flaw. Going back and forth a few times at high speed, heats up the axle and melts the main strut after some long runs down the runway. I’ve fixed it since and finishing the gyro setup. Hopefully next week I can maiden it.



good afternoon I wanted to buy the files for the L39 my printer has an area of ​​210 * 210 * 205, can scale to this dimension, or sell the cad, wanted to use a 90mm EDF.

It's 1:6,5 size. I cut my own paint stencils with a vinyl cutter.

Got the retracts all working. I'm looking at some graphics, but what size is this? 1/6? I thought I saw on another site as 1/6.5. Thanks for the help as usual!

Ok, I'll try it out. I'm using a 6.6V LiFe. It's getting close!lol

No they don't need a sequencer. What voltage did you try them with? Try spinning the shaft a little first to bring the unit out from the end point.

One of mine had a tendency to stick on one end because the magnet in the moving beam was too far away from the circuit board. I pushed the magnet out and that fixed it. It shouldn't be necessary though.

Hey bud, I bought 3 of those retracts from HK that you linked too, and I tried to use a servo tester on them. They didn't work. Are these the type of servoless retracts that need a sequencer to work? I'm stumped. I even tried using three different servo testers.

Maingeardoor01 contains both parts attached to the main gear. Maingear02 and 03 are the inboard doors.

what's the name of the stl file that has the main gear covers? Not the main gear doors. Thanks!!

Everything is all printed up! Now just getting in the parts to finish it. All the guys fly at my field are turbines and 90mm this size, and no one has an extra 120mm edf laying around!!lol For now, I'm saving for Jetfan 1120 pro and the HET 800-72-590. At least that is the plan!!lol Servos are coming in soon as well as, the carbon fiber rods. Also have to wait for the servoless retracts to come in. Damn! So much stuff to buy, no time to wait!!lol

Thanks as always!


They should fit in the bay. The width should only just fit but there should be plenty of room for the diameter.

The 3D printed tires on my EL-39 are quite hard. It's a heavy plane.

I've tried using flexible filament before, but in the humidity of South Florida near Ft. Lauderdale, you can't get the same flex as you could being up north! To much moisture, unless you have a perfectly controlled room an temperature. I just ordered the same size from Tower hobbies. Robert wheels model ROBQ1534. They sure look like the same size!!lol

If you were going to choose a robart main wheel, which would you use? It's my only hiccup now.

It's possible to make Robart 669L and 669R spring struts fit. They need to be cut and bent to fit. Other struts may fit, but I don't have any to test with. The printed struts are very strong. Check out my videos. I make a few very hard landings and haven't had any failure of the main landing gear yet. The nose gear is more fragile, but should never be the first thing to hit the ground.

The nose wheel is 60x20 mm. That's the max size that will fit.

The main wheels are 85x22 mm. The biggest you can fit is ~85x24 mm

What size is the nose wheel, if I were to buy one, and what size main gear wheel?

It doesn't go inside Nosegear04. It goes inside Nosegear03, and then Nosegear04 goes inside 03 on top of the shock. I attached a photo in the Thread on RCGroups.

The hex nut is the same as the outside width of that cylinder it needs to go inside. I must be missing the step. The graphic shows how it goes together, but what does you hex nut look like? Is it in a file I'm missing?

I do have a question regarding the nose gear. I have printed most of the pieces for it and I'm not sure if the shock absorber goes into nosegear04. Because the shock you told me to get, doesn't fit in it. Any pictures, not the computer pic, that shows you doing it would be great!!!

Thanks again!


I added two photos now showing the inside of the nose and main wheel wells wher ethe door servos reside.

You know, after I wrote that, I thought that was what they were for!! Not technical!!!lol Are there any pics of how you attached the servo to the nose gear door/ main gear doors? And how you put the servo in and how the retract looks, up? Any pic that is a close up of major parts, would be perfect! Also, if I can't print the landing gear to be good enough, like yours, do you know of any links for ones that might be bought online? Thanks again!
Awesome jet!!!

Those are there to support the center piece as it's built from a tiny surface up. I could not get it to print without them. Just snip them off after printing that section. They will leave minimal spots to clean up.

Ask away. There are probably more people wondering about things, and I don't know about all the things that need explaining.

I am following that thread! Pictures are a big help for me. Not a very "technical" person. I've adopted the "keep it simple" approach!!LOL Now one more question and I'll be out of your hair, what are those 6 ovals, almost floating, in the air intakes? Did I skip something in the thread regarding them?
Thanks for all the help!

Thank you, sir! Now, if I can figure out your nose gear door, I should be ok.

Thanks again!

Thanks for the response! What is the name of the file for the top piece of the tail? In your picture above, it is the part above the purple section. I have the two tan/brown pieces, the red and the purple, but not the pink top. Sorry to be a pain!!

Hi, Larry. There is no third part of the rudder. It got added to the list of parts by mistake. :) The rudder only has two parts.

Awesome L-39! I bought the files, but it seems to be missing the rudder03 in the downloaded files. Last part I need to finish the tail!! Any way I can get that one?

Hi, really nice model and good idea. I have buy your plans, but it's a little difficult how to assembly, specially the nose gear. Could you upload one video explaning how it is the correct way to assembly and especially how work the nose gear steering system? I have to buy 3 units of 90 degree retract servos, with no integrated steering, right?