WimacWest

[Andre Germain]

For those following, I've changed the OpenSCAD solution so much using far simpler and better method - I'll post it when it's further along. I've been working hollowing out the wings. Where are the ribs you say? it's not easy to print such as the wing is printed vertically along its length, instead one relies on the skin which is actually an inner and outer skin with internal webbing done by the slicer app and printer. Here, ongoing internal view.. more to do.

[Andre Germain]

I got to test out printing LW-PLA, that is low weight PLA, which will expand (foaming) at higher temperatures. When printed at 200F, no expansion occurs, and the layers are easy to separate (not good for R/C), but at 250F with half the extrusion rate, the layers bond so well that I was not able to separate the layer with any reasonable force. You do have to print slower. Certainly looking promising for R/C.

I'm printing the right wing inner panel at the moment - was to be 36 hours on a 0.4mm nozzle, so I switched to 0.8mm nozzle and doubled layer height, its down to 9 hours. Patience!

I've attached yet another OpenSCAD revision, very much different and improved.

[Andrew Fernie]

Hi Andre. I have heard that the LW-PLA can be sanded and painted better than standard PLA. Do you think that is the case?

[Andre Germain]

I stopped the printing after 2 hours because some of the surface was messing up, but otherwise the wing section is very strong, light and shows much promise.

Andrew, when using the expanded temperature range, the surface is matte and appears sand-able. They say its also very paintable, looks likely. I've painted PLA with Tremclad flat black (!) on an optical tunnel that holds a cold mirror for the telescope, and that worked very well - educated guess is this material will paint even better.

I'm so encouraged by the LW-PLA that I'll be purchasing three reels of 1kgs this week (50$ each).

[Andre Germain]

I switched to UtilMaker for more control of the Cura slicer settings and the surface defects are no longer. Printed the largest section I could on a Creality CR-20S, 10" of span, 1/4 of the wing. 180 grams. Balsa + monokote sheeted foam would be lighter, stronger and survive bad landings better, but for certain LW-PLA is fine for fuselage and probably tail surfaces.

[Andrew Fernie]

Hi Andre.
I have built and flown one of these https://www.rcgroups.com/forums/show...s-Posted%21%29 and looked at a bunch of designs from 3dlabprints. They all seem to use thinner skins and more complex interior stiffeners. It seems like that is how they keep the weight under control. Have you considered that type of approach?

[Andre Germain]

Andrew,

yes I have considered it, I'd worry going less than 0.8mm skin as although its quite strong, you could puncture it with relative ease. The skin on those in the link are so thin, egg shells. My inner structure, at the same 0.8mm, quickly adds up and is a significant part of the total weight. See in the photo a cross section of the wing where the rod to connect the wing and fuselage has structure 100mm into the wing to explain that the inner and outer skin are 0.8mm. I still have to work the infill and add more layers around the rod for structural strength. I wanted honey comb, as per military A/C however the extensive transverse ribbing with variable filling circle radii is intriguing in the model you linked - I'll work that in this weekend and try it out (such variable infill are not native to Cura, will need to use a different slicer engine).

I did consider the first reel of LW-PLA for experimentation. The first few runs were to setup the slicers for R/C, followed by structural tests, and then further weight reduction, my flights are mostly touch'n'go's than flight! that punishes the structures. If I can manage VTOL or below stall CTOL, it should lessen such, more reason to shave off weight! 0.6mm nozzle is a logical next step. I'm musing of a hybrid wing where the leading and trailing edges are LW-PLA and the center is foam (skinned).

NEWS FLASH: the slicer had predicted 180gr, but I weighed it at 152gr. I plan for total wing weight under 450gr, so it achievable (the section I printed is ~1/4 of the full wing).

[Andre Germain]

I changed the wing from a skin shell to a single layer skin and used quarter cubic filling - as expected the surface in between the inner supports is softer, but overall the strength across the span and chord, and resistance to twist are improved, and the weight has dropped from 152 to 114 grams! That's quite viable and is under my target weight. Furthermore, as I was using Minkowski smoothing to create the shell and no longer need to, the trailing edge is sharper and thinner, not round as it used to be. Smells like a winner.

[Andre Germain]

Found the data on eSun LW, turns out 260C is just right for 220%.

I bought a 400x400x400mm build volume FDM printer to ease R/C build ups.