A printed plane or not as the case may be!

Indeed that exactly what the commercial printed planes do it.
However from a purely structural point of view a constant diameter carbon tube is a bit of a 'get out' for simplicity. About 50% of the material in such a tube is not really 'earning its keep'.

I would never claim a 'built up' printed wing is any sort of improvement over conventional structures, far from it, printed planes are weak for their weight. This is more of an exploration exercise to find out what the end result might be.

After about 11 hours the 5 sections of the box spar are complete, but not yet glued together.

The inner 200 mm section, which includes the 'built in' 3 degree dihedral, has nearly twice the material in its flanges as the 'light as can be printed' furthest out ones to try to give the spar a strength/stiffness proportional to its distance from the wing root.

Now to start adding on the ribs along with the leading and trailing edges working from the centre outwards.

More power to your printer Simon, I was as is my way only gently teasing you ( or should that be ribbing?? )

Are you printing the spars vertically Simon?

Klippy
No they are printed lying on the bed like this.

This allows CURA to apply a different number of top and bottom layers (i.e. the spar flanges) without adding to the thickness of the side walls.
This means the different sections of the spar can have a different strength/stiffness for what is basically basically the same external shape.
The fill of each spar is different as well.
The outer and lightest section uses a Gyroid fill as this provides the best level of support to its very thin side walls which are only 0.25 mm thick.
Not that it proves much but here the lightest of the spar sections (it weighs 4.9g) easily supports a centre load of 567 g (20 oz).

It could carry more but it will be used in the wing so I don't want to break it.

The wing centre section completed.

The outer spar sections are not yet added to make it easier to 'thread' on the next 5 ribs on each side.

Thanks Simon, somehow I thought they were hollow and was wondering why they weren't sagging, can we have a picture of a flat rib please? And do you have to cut out some of the infill in order to push the outer spars in?
Warning, it could be that I'm missing the point here!

Klippy
A picture of a rib as seen in CURA.

If you expand the view you can see most of the print settings used.

A similar picture of a spar showing the hollow end (note it alone has a double wall) and the infill pattern used on the inner spar sections.

The infill has been accurately positioned to create an exact wall to wall zig zag pattern. In addition the top and bottom filament runs are set along the length of the spar to give the maximum tensile strength.

I hope this helps.

Its an awful faff to set it all up and a practical result is by no means guaranteed. :ohmy:

Thanks Simon, that makes so much more sense now. You don't get too much sag when you close the top of the spar end?

Spent most of the day printing and building so now the basic wing is complete and it is shown in front of the fuselage it will eventually be attached to.

There are 40 individual pieces (12 different types) and in this state it weighs 80 g .
It is about twice as heavy as the Depron/Balsa wing it will replace and probably not as strong but it will certainly be adequate.
Ailerons and servo mounts still to print which will push the parts count to 58 with 17 different.

With the wing complete I started on the making the small Ballerina wing removable.
The first job is to cut the Depron wing out.

It proved to be rather tricky in fact by the time I had done it the upper flange of the spar was cracked so the Deprn wing will require some careful carpentry to restore its strength!
Then it needs some thought on how to secure both wings but in a fully interchangeable manner. I fear bolt locations that are good for the printed structure will not work so well on the Depron wing.
The aileron servos are installed.

Tiny but the same as in the Depron wing.
As a test I have covered one aileron and given it two coats of EzeDope.

Doesn't look that nice but it has dramatically increased its torsional rigidity for a weight penalty of 0.9g
That may not sound much but it is a 20% increase! :woohoo:

This is turning into a pretty impractical way to build a wing but as in Mastermind "I've started so I'll finish".
The wing in place.

but to make it fit the fuselage cutout for the Depron wing has required a number of specially shaped printed pieces. The problem is there is no mathematical model for the existing fuselage so these special parts have to shaped in CAD by eye, printed, then any CAD adjustments made and repeat. Doing well if it only takes 3 goes! :woohoo:

The good news is the wing uncovered is strong enough to pass the "lift by the wing tip test". I would expect the tissue covering to significantly improve the wing's stiffness.
The bad news is the uncovered wing weighs 99 g so 130 g? with ailerons, tissue and dope. The Depron wing complete ready to go is just 89 g. :ohmy:

Does dope attack the PLA?

He's using "eze dope" klippy...water based.

Klippy
I do not actually have any real Dope!
However I tried cellulose thinners and that has no effect apart from bleaching the colour a bit.
PLA is a starch based plastic so it is possible it will not be effected by conventional dope.

Spent most of the day struggling with the wing hold down bolts but eventually got them to fit as intended.
With the wing securely in place and the battery installed a 'wing tip' test.

Bends a bid but the test does generate a root bending load that is the equivalent (more or less) of pulling 4g aerodynamically. A gentle loop?
Just the servo connections to sort out then the covering can start.

A start on the tissue.

Although sold as model plane tissue it is horrible to use as it has absolutely no wet strength so it is hard to get an even level of tissue taughtness.
My theory being if the tissue is equally taught all over to start with it will water shrink more evenly too and reduce any tendency to induce a warp.
Bring back Modelspan!