by exosequitur, published
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Very long flights are possible with this tiny glider when launched with a rubber band or off of something high.
With practice, it is hand launchable by holding between the wing and empanage.
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I think I know what the issue is - I have a fractional first layer ratio set, .6 ish, I think (slicer is busy right now) . 3 Layers should work too, but the cg might end up a bit aft due to the thicker first layer. If you cant get it to fly stable, try a tiny bit of weight forward. (on a tiny flying model like this, the details count)
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Now, U2A and U2B Version STL's, longer wings (a is long, b is very long)
....and a U2C version, slightly lighter, hollow fuselage and easier to build correctly. (reworked vertical stabilizer) . This one may not slice correctly if you have a nozzle width other than .35.
These 'U2' versions are more challenging to print and tune, but offer the possibility of better performance and slow flight capabilities. These use more than 100mm of build space.
Updated , cleaner models and STL Files, a double print STL for larger printers, and a new .STL with.6mm wing spar heights for anyone having trouble getting the layers to work out. This new .6mm spar model has not been tested, but I do not expect any problems. If you print it, please comment on the results... thanks!
Your printer will need to be capable of printing smooth 1 and 2 layer .15mm prints. Adjust your first layer settings to achieve solid layers with no surface debris or curling.
Some cleaning of print artifacts and fit checking is a good idea prior to getting out the glue...
Layer height matters, as does fill ratio. Increasing the fill ratio for the fuselage will shift the CG forward, which may be desirable depending on your results.
I am using .15532 layer height and a bottom layer height close to 50% (.08ish) - you will want to be as close to this as possible, or calculate a layer height that gives 4 layers at .50mm on your setup.
The important thing is that the web of the flying surfaces should be two layers, and the spars and wingtip reinforcements should be 4 (3 Layers should work too, but the CG might end up a bit aft due to the thicker first layer. If you can't get it to fly stable, try a tiny bit of weight forward. On a tiny flying model like this, the details really count).
More layers should also be ok as long as they are very thin so that weight does not increase too dramatically....I am using 300mm of 3mm filament
My nozzle is .35mm, but a .5 should work fine. If your nozzle is smaller than .33, adjust the perimeters accordingly.
The wing must be very flat. Use care when removing the wing and tail sections from the bed. Peel up from the tips toward the fuselage with a thin blade or spatula, lifting only as much as needed to break free, being careful not to disturb the spanwise symmetry. If the wings are not perfectly symetrical when viewed from the front of the aircraft, adjustments will be required for proper performance.
Glue the tail and canopy / hook into place with a tiny drop of superglue.
Known working instructions:
Print the chickadee using ABS, .155 layer height with a .5 first layer height (or close). Use 2 perimeters, and 2 solid layers, 30% rectalinear fill (you can increase the fill ratio to move the CG forward if desired) . Use a fill orientation of 0 degrees to the axis of the fuselage (natural axis of the print). 45 degrees works also, but causes uneven flexing of the wings under load, resulting in a strong turning tendency at high launch speeds.
Print the launcher with 3 perimeters (2 for .5 nozzle), 2 solid layers, and .35 line fill. Two perimeters are not enough, and will break. Scale the part to your preference - it is not layer critical.
Fly with eye protection if using the rubber band launcher! The plane is tiny, hard to see, and may return to the point of launch at high speed. (yes, I did hit myself in the eye flying this plane)
Carefully bow the wings upward to give a slight rounded dihedral.
Carefully bend in a tiny bit of up elevator so the plane does not dive towards the ground. Adjust elevon surfaces further as needed until the plane flies straight and level.
Put on your safety glasses, a nice stretchy 2mm cross section (12-18" extended) rubber band on the launcher, and fly!
A small amount of weight (1/2 of a 3mm washer, etc) can be glued to the fuselage aft of the hook for more stability or longer flights.
Except in extreme cases, do not bend ailerons in the wing. Use the elevators as elevons instead. Using the rudder will cause side-slip drag, and will result in shorter flights. If the model seems to be skidding, use the rudder to align the fuselage to the direction of flight, then elevon tweaking to get straight and level or any other desired flight profile.
A neat trick is to adjust the pane for straight looping flight, then launch at about a 30 degree roll angle, slightly upward. Keep adjusting launch and control profiles until the plane circles around so that you can catch it.
Other materials and layer heights may work as well, please post your results!
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