A tissue covered 3D printed structure?

[quorneng]

The joys of own design printing to very tight limits, both in dimensions and weight and it was still not quite right.

As soon as you complete one you find a detail that would make it better and/or lighter.
The only plus is they are very light so use little filament. Each only weighs 6 g that's about 2.5 m of filament.

 

[Boberticus]

at 25 bucks a kilo, thats just 15 cents a try!

 

[quorneng]

That is exactly why 3D printing makes a good 'experimental' medium even if it is not ideal structurally.
The first fuselage just held together with tape.

The slot in the wing platform is to allow the aileron servo wire to pass through to the rx which will be underneath.
The nose cowl is really a bit of a luxury.

I doubt it will make much difference aerodynamically but it looks nice!

 

[quorneng]

The 1000 mm plank wing is built in traditional style but as it is hopefully going to be sub 250 g all up the spar can be lighter built with a thinner wing.

This time the leading and trailing edges are in effect hollow sections that are simply glued on to the front and rear of the ribs.
Slightly heavier but stronger and simpler to do.

Once the 3.7 g aileron servo are installed it can be tissue covered, water shrunk and doped in the normal way.

The ailerons are similarly built up and tissue covered with simple top tape hinges.

The wing, tail boom and fuselage complete with motor and battery weigh just over 200 g so provided the 'tail feathers' with the elevator servo come in at less than 50 g the 250 g target looks achievable.

 

[quorneng]

The completed 3D print and tissue covered "Print Tractor"

And it weighs 248 g. Phew!
It even flies pretty well but it is not as 'nice' to fly as the Depron Light Tractor which by comparison is a 'delight'.
It needs some thinking to see what might be done to both improve the aerodynamics and reduce the weight.

 

[FoamyDM]

The completed 3D print and tissue covered "Print Tractor"
View attachment 177425
And it weighs 248 g. Phew!
It even flies pretty well but it is not as 'nice' to fly as the Depron Light Tractor which by comparison is a 'delight'.
It needs some thinking to see what might be done to both improve the aerodynamics and reduce the weight.

Great project! Excellent documentation, thank you. I think my skillset need a strong 3d modeling infusion. I have to go back and find that bulldog thread by local fiend

 

[quorneng]

Having satisfied myself that a tissue covered 3D printed plane under 250 g was possible I wanted to see if I could do it better.
The biggest single part is the wing so rather than a plank I decided it would be structurally more efficient if it was tapered both in chord and thickness. At small sizes aerodynamics favour thinner sections so the concept would be a thicker 10% t/c ratio at the root for structural reasons but thinning down to 6% t/c ratio at the tip but otherwise built in the same way as before.

To reduce the tendency to ground loop on landing due to the very shallow fuselage the wing was also given modest polyhedral to give a bit more tip clearance.

The conventional tail was replaced by a V tail both to save weight and improve the durability. As there is no rudder a single servo in one half of tail moves both surfaces only as elevators.

With a single link rod this is geometrically impossible but with this flexible elevator horns it actually works well.
The completed Mk2 version with a bit of 'rattle' can paint for visibility.

Same motor, battery and over dimensions but it now weighs just 219g.
Now just needs the weather to calm down a bit!

 

[FoamyDM]

Ooh this is so exciting. Is your file just a wing section, solid, but printed with no top or bottom layers, or is it a grid "cut" to profile in the modeling stage?

 

[quorneng]

FoamyDM
The wing is made up of the normal parts of a 'stick and tissue' wing but each part (spar, ribs, leading and trailing edges) are 3D printed. They are then glued together in the conventional way and tissue covered.
Obviously the spar is the most complex bit as it is 1000 mm long yet the print bed has a maximum print length of 290 mm (across the diagonal) so it has to be made up of a number of interlocking parts glued together to give the required bending strength.
By using a polyhedral wing even the longest leading and trailing edge pieces are within the 290 mm limit.
Everything else, ribs, tail and the fuselage, is really an exercise in designing & printing ultra lightweight parts.
This is one of the wing ribs.

The initial layer is 0.15 mm thick, the wall thickness is 0.25 mm. It is 2.5 mm 'thick' with no top layer. The infill is 6% 'triangles' but carefully positioned to give 'diagonal' bracing. It weighs 0.6 g.
It takes longer to print all the parts than it does to glue them together but at least making another is just a matter of 'pressing a button', well almost!

 

[quorneng]

Calm weather finally arrived so a maiden was possible and it flies pretty well with more than enough power. With such a generous wing area and limited weight it is very sensitive to turbulence. It will need some adjustments and removing a small warp in the right wing before I will be really happy with it.
Then I will do a video.

 

[quorneng]

A short edited video of the final 220 g version of the printed stick and tissue "PrintTractor II" flying this morning.

Plenty of power. It loops nicely and even without a folding prop it glides really well.