Angstron 6in - planta e arquivos

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 Download files at https://www.thingiverse.com/thing:4263525

Angstron 6in CLG is my best design since 2017 for small CLG events. My best model flies consistently 72s outdoors not because the sink rate is great but because the incredible altitude it can get during launch, it weighs 3.4g.

That demands a very aggressive trim with AFT CG and neutral rudder which is I could only make possible by using tail boom flexibility.

The original model is fixed so if it finds a thermal it is gone. Hence I decided to do a DT version.

All versions use exactly the same flying surfaces as the original, all CNC milled only varying thickness +- 0.2mm according to balsa density. This consistency made possible the gradual improvements in the fuselage and mechanism design.

The DT concept is simple and not original. A string and rubber run from bottom of the fuselage over the wing, loops around the boom, right at the wing trailing edge and comes back to the nose where it meets the viscous damper. (10mm diameter 100gcm torque, 0.22g). The wing is glued to a support which is hinged to the fuselage via a M2 nylon bolt (later glued and sanded). A 10mm rubber attached to a 0.4mm wire hook in the wing rotates the wing to a 45-60deg negative incidence.

Version 1 was created as a concept and is impractical as flexibilities were too high and too nose heavy.

Version 2

  • Timer after the launching hook
  • Hole to attach the DT string
  • Flies ok but bunts hard during launch so altitude suffers. Very sensible to rudder. Some of the flexibility come from DT
Version 3:

  • Shorter nose
  • Improved wing support
  • 3 pannel wing (flat center)
  • Fuselage encloses the boom, is 8mm longer towards its direction, printed at 30% infill with 2.5mm at the thinnest section.
  • Thicker DT rubber
  • This version bunts a lot less than the previous but still not close to the fixed model. No more DT influence in pitch.
Version 4

  • Fuselage increased to 2.6mm
  • Boom shortened by 10mm
  • Elevator airfoil facing upwards
  • Bunt not noticeable anymore. Glide is good, weight is too high at 4.2g. Still sensible to rudder input, much more than the fixed one
Version 5 - Final model
  • Thinner wing (0.5g weight reduction)
  • 2.8mm fuselage, infill and shell strategy changed to save 0.15g
  • Longer wing support to avoid fuselage flexing while attaching DT.
  • 3.8g final weight. No bunt, more consistent. Climbs very well and glides as expected.
Conclusion
PLA 3D printed nose sections proved to be very robust at reasonable weight. Being easy to assemble prototyping is accelerated and are a great choice for these parts.
Carbon booms and CNC Milled flying surfaces help a lot in either speed of construction and consistency so convergence is quicker.
The fixed model is way simpler and it is much better suited for the beginner and will deliver higher performance at the risk of losing in thermals. DT version is a lot of fun as really small fields are not a problem with 10s DT and saves the model from time to time of being lost.
I leave here the stl files for all flying surfaces, the fixed and the DT fuselage and its parts an the model plan. Please note that changes to design are encouraged but remember 6in CLGs are very sensible!
More important than any technique keep in mind to fly and HAVE FUN! 

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