L-39 Albatross by Planeprint

davidk · April 05, 2024, 01:15:40 PM

Still can't fly... might as well continue printing and gluing.
Sticking with a bit of a Reno Air Race theme, this is the L-39 Albatross.
Printed in LW-PLA, it's has an 1100mm Wingspan running on a 6S 70mm EDF.

davidk · April 06, 2024, 03:34:01 PM

Tail is on, nose is on.

The nose incorporates the mount for the front landing gear retract. Not only is the mount glued to the fuselage, but 2 6mm CF tubes are also glued to the mount and follow through into the fuselage.
Hopefully this will make the front gear mount and front fuselage strong enough to withstand a landing.

davidk · April 11, 2024, 03:23:35 PM

Well conceived feature for the elevator servo. The main bracket is glued to the fuselage and the servo is screwed to the small bracket which is, in turn, screwed to the main bracket.

bfeist · April 11, 2024, 03:33:56 PM

This really looks great. I've been following the 3d printed plane idea for a while but I haven't done it. I'm curious, being PLA, will you be glassing or otherwise sealing the surface somehow?

davidk · April 11, 2024, 05:01:01 PM

Quote from: bfeist on April 11, 2024, 03:33:56 PMThis really looks great. I've been following the 3d printed plane idea for a while but I haven't done it. I'm curious, being PLA, will you be glassing or otherwise sealing the surface somehow?

No, doing anything like that would add a lot of weight. Some have done that, but it changes the characteristics of a well designed plane. I'm not even one to paint, so I print in colours instead. This isn't PLA, it's active LW-PLA so the texture and finish are really nice. Not on this L-39 though. This was a print experiment using PrusaSlicer and has a terrible finish to it.

LW-PLA with a gyroid infill has a very balsa-like feel and strength to it.

For the OV-10 Bronco I printed I used OrcaSlicer and BambuLabs LW-PLA settings with perfect results. Same printer, Prusa MK4, but dialed in settings with OrcaSlicer.

The design is the most important part for a nice looking finish and Rene from PlanePrint thankfully understands this. His designs produce really good results.

davidk · April 12, 2024, 02:01:50 AM

Landing Gear on printed planes has always been the weak point. With the L-39 it may just have a chance to survive the first landing. 100% infill PLA printed retract servo mount tied into 2 6mm Carbon Fiber tubes all glued into the fuselage. And... a Planeprint version of trailing link gear. 1mm piano wire is used to give the gear some suspension. I think it might actually work. Since the tires are printed as well, I can adjust how soft or hard they'll be by changing the amount of infill. Right now they're 15%. I may try 10% for a softer tire.

davidk · April 12, 2024, 02:29:27 PM

One wing complete. The Flap and Aileron Servos are back to back in one section. Servo attachments are screwed onto the servo and then glued to the servo cover.
2 types of wingtips are provided... Reno Air Race and standard tanks. Of course... the tanks look cooler.
Parts are included for quick wing connects using MPX connectors. I was looking forward to this before I realized I'm never going to take the wing off. I'll use the MPX connectors for the OV-10 Bronco that's up next.

msatin · April 13, 2024, 12:16:09 AM

Looks fantastic Dave

davidk · April 13, 2024, 01:05:43 AM

I'm using the EDF from a Viper 70. 6S 3300mAh. A thrust tube is securely taped to the EDF and the EDF is solidly mounted.
So many nice features from Planeprint. The landing gear wheel wells also double as Air Intakes for a bit more takeoff power.
The Air Intakes are incorporated into a piece that also houses the wheels and is the EDF Cover.
This EDF Cover is secured in place with the rear 10mm Carbon Fiber tube.
I don't know how Rene thinks all this stuff up... it's very cool.

davidk · April 15, 2024, 09:39:56 PM

Taxi test today. Very good, but I'm not happy with the way the landing gear attaches to the servoless retracts.
It's just a 3mm bolt going through plastic against the retract flat spot.
Retract 3D landing gear is always an issue. If you over tighten just a bit the plastic is stripped. If the wheel turns at all while landing you'll tear out a whole wing and then things get really bad.
I'm trying a 100% solid part instead of a 15% infill that is originally called for.
I'm also going to try, for the first time, threaded inserts. I have just enough room... I think.

My only other complaint about this plane is that is requires an 8 channel Rx. In most planes the Aileron servos are installed opposite to each other and so a "Y" cable can be used. All good in this plane. Normally, the Flap servos are installed in the same direction... again a "Y" cable can be used. In this plane the Flap servos are installed opposite to each other... no "Y" cable. Also, the front gear steering servo is installed so that it's backwards to the Rudder... again no "Y" cable. Count 'em up and you get an 8 channel Rx.

I toyed with, and actually installed, 2 servo reversers. They worked and all is good... but... I don't quite trust them.

The difference in cost between an AR620 and an AR8020T is $40. This pretty little plane is worth a few more dollars.

sihinch · April 16, 2024, 07:07:25 AM

Very nice and good choice on the additional spend.

Good luck with the gear.

GuyOReilly · April 16, 2024, 07:44:09 AM

Impressive!

bfeist · April 16, 2024, 09:11:15 AM

One positive for using individual channels per control surface is you'll have precise trim, though with such a precisely produced model you might not need it.

davidk · April 18, 2024, 11:42:25 PM

I could not get the landing gear to bolt solidly to the retract pin with 3mm machine screws. They slide around even when taxiing a bit.
I've wanted to try threaded inserts for a while and got some and some attachments for my soldering iron.
The inserts melted into the PLA in about 1 second.
The retract pin is 4mm so I put a 4mm steel rod into the landing gear to ensure I didn't go too far when putting in the threaded insert.
Then, instead of using a machine screw I used a set screw. With a bit of Loctite I can really tighten the gear on now without fear of stripping PLA threads.
I feel using a threaded insert and a set screw may solve this issue with 3D printed landing gear.
The threaded insert is 3mm x H4. It is 4mm in length and 4.2mm in diameter. After they were installed I screwed in a long 3mm bolt and tried very hard to pull the insert out. It wouldn't budge.
We'll see how it all does on grass.

msatin · April 19, 2024, 04:07:33 PM

Very clever solution Dave!