Planeprint Learjet 35 : 50mm

davidk · December 06, 2025, 06:30:03 PM

Here's the start of the 50mm Planeprint Learjet 35. Downsized to 71.4% this allows a 50mm EDF to fit and most carbon fiber tubes and rods to fit. 25g Retracts seem to fit nicely. The full version comes in at around 3900g flight weight and so far the parts are coming in between 43% and 51%. The 50mm size should come in under 1800g flight weight and the 50mm EDFs put out 900g each. Have to keep an eye on the weight.

The FMS 70mm EDF weighs 255g... the 50mm EDF weighs 75g... so the 2 50mm come in at 105g less than half of the 70's. Overall, I think I'll get a thrust ratio of more than 1:1.

My biggest issue is servos. I need a small metal gear servo to fit in the 71.4% servo pockets. There's an EMAX ES9052MD that weighs 5.5g. It's a tiny bit big, but I could make it fit. There's also a GoTeck GS-4308MG that weights 4.3g and fits perfectly... but I've never heard of GoTeck.

Michael's going to build one of these as well so I'll leave the build process up to him to report. I'll post progress pics.

msatin · December 06, 2025, 10:19:20 PM

Looking forward to seeing the progress.
FYI - MotionRc recently came out with a line of digital servos called xWave.
The have a 5g servo. It's not a MG, but it is digital.
Perhaps it can fit.
https://motionrc.com/products/xwave-x5-5g-digital-nano-servo-xwa6005-003

davidk · December 08, 2025, 03:20:46 PM

Thanks Mark... that would fit, but I really want a metal gear servo for the Elevators and Rudder. And I would prefer metal gear for the Ailerons. I can probably get away with plastic for the Ailerons, but if a metal gear will fit, I'd prefer it. I need 2 servos for the Elevators. The Rudder is a bit different because I can use the full size parts... I don't have to scale down the Rudder servo parts in order to use them. I do have to abide by the pockets for the Elevators and Ailerons when sized down for a 50mm.

davidk · December 09, 2025, 12:17:41 PM

If I follow the instructions for servo installation then I'm really limited in servo choice. In the attached pic you'll see the servo pocket (1) that is built into the part, and then a servo insert (2) which slides into the servo pocket. This lets you glue the servo attachments (3) to the insert, and the insert provides attachment points for the servo cover (4).

This is all good and works well for a full sized build. For the 50mm build the servo insert (2) and the servo attachments (3) take up too much wall space.

I think I'll do away with the insert and attachments and hot glue the servo into place. I still want a servo cover so I'll design a platform for the servo to sit on while not taking up wall space. I think it will be simply be a case of adjusting the existing insert, removing the walls, making the floor thicker, and keeping the cover attachment points.

This will let me use the slightly larger metal gear servos.

davidk · December 11, 2025, 09:57:08 AM

Box-o-Learjet is building.

davidk · December 30, 2025, 04:35:16 PM

While other parts are printing I decided to start on the rear fuselage. There are CF rods that run the length of the Fuselage and were relatively easy to CA for the full size LJ. Not so much with the 50mm version. You could get your whole arm into the full size, although CAing was still tough. No chance with the 50mm. This is my first print and build of a downsized model and so I'm going very slowly, trying to ensure that stuff fits. I'm going to CA the CF Rods in place in each section as I go along instead of trying to get them in place after the full Fuselage is built.

I didn't think the lengths of CF Tubes and Rods would translate in a downsized model... but they do.

Here Fus7 and Fus8 have a CF rod crossing between them for reinforcement. The 2 CF rods used to secure the HS size down perfectly at 71.4%.

Michael · December 30, 2025, 09:24:18 PM

Nice!

msatin · December 30, 2025, 09:50:40 PM

Looking good Dave

davidk · December 31, 2025, 12:30:39 PM

Not hard to do, but a bit finicky. The 2mm CF Rods are projecting out to a larger diameter than the part being glued. I just need to be careful while fitting so I don't pull off the glued rods. This is the only way I can think of securing the 3 715mm rods.

piker · December 31, 2025, 03:20:55 PM

Very cool, Dave!

A lot cleaner than building with Balsa. No saw dust!

davidk · December 31, 2025, 03:46:55 PM

That's true, but it is life we're dealing with here... and so there's always a replacement problem for every solution.
This is what's inside the printer... there's a lot more that escapes. Little bits, strings, etc. that are all over the floor and tend to stick to stuff... and make their way everywhere.

And balsa shavings smell better.

davidk · January 02, 2026, 03:05:16 PM

I was a bit worried about the front gear. I needed the parts to fit when downsized but I still wanted to use a full-size 12g metal gear servo. So, some parts were adjusted in Tinkercad to accommodate.

The mechanism and design by Rene at Planeprint is so clever.

The cutout in Fuselage 1 for the gear was almost big enough. I needed another 5mm at the front and a small notch at the side for the axle.

Michael · January 05, 2026, 01:27:06 PM

My 50mm Learjet' printed kit' is ready. I've paid for a file, and David has printed the parts for me. I'm starting the assembly/construction. It's similar to the bigger model, but the smaller size makes the work just a bit more challenging.

I'll post my progress, here in this thread, but will avoid duplicating David's information. I'll mostly just highlight any difference between David's and my plane, and any significant differences between this model and the bigger 70mm fan model, if any arise.

davidk · January 05, 2026, 02:21:23 PM

Another adjustment needed was for the 50mm EDF units. We're using X-Fly 50mm 4S EDFs. The length of the housing is a bit shorter than required. I could have created an attachment point that pushed the EDF forward but that looked really complex. Instead I created an extension ring that lets the EDF sit on the original attachment points. I hope this will work out for balance. The extension ring slides over the original structure for the nacelle.

Michael · January 05, 2026, 08:50:21 PM

I just had my first problem with construction. The parts are fine; my gluing technique was not so fine.

I used medium CA, when I should have used slow CA, and one fuselage glue joint dried before I could fully join them. They are solidly glued, and they have carbon fiber support, but they left about a 0.5mm gap.

To fill the gap, I used some light-weight filler mixed with a near exact colour water-based paint. A little more sanding, and the joint will not be visible once it is painted.

I intend to paint the plane the same colour as is printed. This is to keep the 'skin' opaque, so that the infill (a patterned, supporting and strengthening structure under the outside skin) will not be noticeable in sunny/bright conditions.