Printing with Light Weight PLA

The number of times I've had a slight offset on one arm, so I've moved it one tooth on the spline - only to get an offset the other way!
It's even worse with the bigger Futaba servos, with a square output shaft, so you can only adjust in 90' increments!
Modern gear, where you can 'tweak' the centre by 1 degree or less save an awful lot of swearing!

After seeing the all-in weight of the LW-PLA printed wing (nice as it looked and as nice as being able to print a longer section on the diagonal) but it was essentially the same as the hybrid rib-spar-foam wing.... I went back and had a think about the vase mode design with a limited number of vase-imposed ribs running along the span of the wing vs running along the chord and tried a compromise (see figure).

It keeps the leading edge ribs, the rib at the spar and the trailing portion of the wing has ribs at 15mm intervals.  It is quite stiff, resists crushing and twist. Probably as strong as the very complex vase-mode wing I designed a few weeks ago with the oval voids.  Much simpler from the CAD side.

It is 10-12g less weight of the hollow version with a 3% gyroid fill and thus prints faster and has zero stringing (as one would expect with a vase-mode print). So an 180mm span with a chord tapering from 175mm-156mm comes in at 29g.  I could see that spacing the vase-ribs at 20mm intervals might be a good compromise to drop off a few more g.

The only niggle is the open top of the print. I am thinking of making a few U shaped bits of LW-PLA to glue between the ribs to increase the contact area for gluing.  Or to print a 10mm wide sleeve to join adjacent sections.
 

That latest vase print looks very neat.
Does the vase printing make the longitudinal ribs double thickness?

I have come to a similar conclusion that an external sleeve is by far the best way to join such structures as it transfers the load from the skin to the sleeve via the glue in shear which is ideal and then transfers it back to the skin again.
How important the wing joint is will of course depend on how much of the bending is taken by the inserted carbon spar..  

The technique of getting a vase mode internal rib involves a 0.1mm slice into the body of the wing stopping just short of the opposite site.  The extruder goes along the perimeter and then into the wing at that slice and then out before it continues along the perimeter.  So one gets a two layer fused rib so roughly double the thickness of the single perimeter. 

So there is a simple loft of the Clarke-Y from which is extracted the void for the CF spar.  There are then a group of very thin blocks which are slightly elevated above the base of the wing and which pass through the upper wing surface.  These are grouped together and then subtracted from the wing thus forming the path for the vase option in the slicer to work with.

 

That is most Interesting but it is using techniques that are a bit beyond my capabilities in FreeCAD.
I will certainly look into that sort of Vase printing technique. 

I certainly used up quite a few M of LW-PLA exploring this.  I went overly complex and then perhaps overly simple. Nice thing about CAD is to think of some simple case and explore and then see what it is like in the slicer and then what it is like when printing.  Certainly I halted prints early because I it was a) not quite what I was looking for, b) the 'offsets' were a bit much and it did not fuse properly.
Certainly has been fun to explore while waiting for the weather to be less horrible.

Tony - I am so looking forward to a 'joint CAD project'!  We can even do it during a quite time when the beasties are taking a siestia....

Managed to fly the 1010 mm printed wing this afternoon.
Rather short because of a mechanical failure. The RH aileron horn broke free resulting a severe flutter   but managed to land safely with one aileron. 

I extracted this short clip of the flutter.

Later in the afternoon at 5 pm, just as it started to rain,  I flew the now repaired 1010 mm printed wing again. It was by then a bit dark to video.
The flight was still cut a bit short a) because the rain was getting harder and b) the transmitter battery indicator nudged the red sector!
Nevertheless I did a serious power dive and a loop which the wing survived no problem. 
Needed a bit more right trim than I would like. The wing must have a bit of a warp although it looks pretty true to me.
. 

Well done with the printed wing!  From the video it seems to handle well (most of the time). Does it feel different from the usual wing?

Yes it is a bit different.
I expect mainly  as it is both a plank wing and Clark Y section whereas its current wing is tapered, mildly semi symmetric and with only about 80% of the area.
There will be a 'proper' video of the printed wing as soon as the conditions are suitable.

I have added PLA bracing strips glued to both the top and bottom surfaces of the inner wing panel.
 
You can see the braces are not only tapered but have a different thickness root to tip to match the likely forces involved.
The improvement in stiffness, although maybe not the ultimate strength, is quite impressive which is why I felt confident to loop it.

This set me thinking and following the quip by the satirist Tom Lehrer "Don't shade your eyes but plagiarise although always call it research" I did followed your principle of a vase printed wing.
Such vase printing will allow an "indent" in the top and bottom surfaces so the PLA brace would be flush with the wing surface. Furthermore by using multiple close layers it would be possible to mimic the elements of a classic "I" section beam but still be incorporated in the wing print.
Something like this
 
When printed in LW-PLA the intention is the adjacent lines stick together so in principle once the PLA top and bottom "brace" is added the wing will have an integrated spar along these lines.
 
I have also discovered that such a file can also be conventionally printed. It is a bit less tidy with more LW-PLA "tails" but it does mean the wing can have an infill. In addition it could  be lofted and thus be tapered.

First to try printing a simple "integrated spar" wing panel. 
Well that's the plan.

Nice idea to design an inset for the PLA and bringing about a spar that has some of the characteristics of the balsa top and bottom flange.

I have a PLA solid rib-at-the-end to protect the aileron and the LW-PLA - a few g but perhaps worth it to reinforce a bit of the wing which might get the most abuse in landings....

A short and cut down test piece of the vase printed I beam wing with the flush PLA flanges added.
 
With a 4% Gyroid infill it is very stiff in torsion and strong in bending. The down side is it takes a very long time to print, about 6 hours. As the infill covers the whole wing even it is a few grams heavier that the current wing which has the benefit that different fill densities can be used either side of the 'spar' line.

The biggest advantage of a vertical print is it can be lofted so to see how it looked I created a tapered two panel wing each of 235 mm which is the tallest I can print . The root is sized to fit the Blue Dragon fuselage. The tip is tapered to 77% of the root chord.
The inner panel.
 
The outer panel with a recess trailing edge for the aileron.
 
To save a bit of weight the vertical part of the spar on the outer panel is only two thicknesses whereas on the inner panel it is four. 
Lofting also means the inserted PLA flange is also tapered allowing it to reduce so matching the wing bending load.

It would take well over 24 hours to print the whole wing (2 inner, 2 outer, 2 ailerons and a centre dihedral section) and to make matters worse I don't have enough LW-PLA left on the roll to do it.
An interesting exercise but I am not sure I really want another wing just at the moment!    

Just for interest more than reality this is a 1000 mm tapered wing "assembled" in CAD from four lofted panels and a dihedral centre section giving a 6 degree dihedral..
 
The taper is 2:1.and the top and bottom "indent" for the PLA 0.5 mm thick insert is tapered from 12 mm wide at the root to 2 mm at the tip.
Whilst in theory it would be possible to loft an aileron I seriously doubt it could be printed. I suspect they would have to be individually constructed out of foam.

Interesting to do but there will be no further action.   
  

I'm having difficulty following much of this but I must say you and Jon have really pushed the envelope on this one.

having difficulty following - - I  drowned a while back!