Make It Glide - 120mm Build Plate Version

Description

This is the same as my "Make It Glide" model. I just partitioned the wings into 2 more sections, shortened the CFUS, and split the tail. Unlike that model, this one will require glue, to join the tail section to the boom. 

Here is the model in a brief backyard flight: https://giphy.com/gifs/z99bBJSQ7GdbpQd7LE . 

Recommended Print Settings

• All parts are already oriented in intended print direction
• 1 wall count
• 2 top/bottom layers
• 2% infill
  • 10% for CFUS
  • Up to 100% for FFUS and nosecone, if you want to reduce or possibly eliminate the use of ballast.
• Brim
• Layer height 0.2mm
• No supports
• 50 mm/s print speed or lower, especially as you get up to the wingtips
• Lightweight PLA (LW-PLA) 

I would also recommend Cura 4.13.1, as that was the slicer I used when designing certain aspects such as the wing spar cutouts. With the above settings, Cura will add extra material as intended to form an I-beam spar in the wing to provide sufficient strength. Loading into Prusa Slicer 2.5.0 did not give the results I was expecting/intending. That could be due to lack of experience on my part though.

I have included an image of the wing in my slicer, showing the intended result.

General Design

General stats of the design of the aircraft:

• Wingspan: 480 mm
• Root chord: 61 mm
• Wing area: 231 cm^2
• Aspect Ratio: 10.1
• E216 airfoil
  • High lift to drag ratio, with sufficient thickness for structural strength
  • Also has a thicker trailing edge compared to similar airfoils
• Elliptical planform
  • Results in an Oswald Efficiency Factor of 1.0
• Elliptical “dihedral”, wingtip is 45mm above the root
  • Provides roll stability in a unique way
• Elliptical sweep, wingtip is 78mm aft of root chord leading edge
  • Purely done to look cool. Would be useful if flying transonic

Balancing

For stable flight, all aircraft need their center of mass to be located in a specified region. For this aircraft, that would be about the middle of the wing. Too far forward, and the plane will nosedive. Too far aft, and the plane will not be aerodynamically stable, and will crash uncontrollably. Too far forward for this design would be balancing near the leading edge of the wing. Too far aft would be balancing near the trailing edge of the wing.

To balance, add pocket change to the front of the FFUS. The compartment hole is large enough to accommodate coins the size of an American nickel. Add enough so that the aircraft balances near the center of the wing. It might be possible to avoid the use of coins as ballast altogether if the nose cone is printed at 100% infill.

Flying

Fly in an open, outdoor space. Preferably with soft grass like a field or park. Hold at the fuselage behind the wing, and throw hard at a slightly upward angle. With minimal infill and a single layer wall thickness, this model is not very durable when it comes to crashes. Expect the fuselage to get beat up. The wing will usually be saved with its non-rigid attachment.

The final weight of the model is going to be a large determining factor in how it flies. The heavier the aircraft, the faster it has to fly achieve enough lift to hold itself in the air. That also means the faster it hits the ground if it crashes. See the below table for the calculated stall speeds (slowest the plane can controllably fly) of various total aircraft weights.

I would highly recommend printing a lighter weight PLA. There are some versions out there that will foam as they are printing, giving greater than 50% weight savings. Foaming LW-PLA is pretty difficult to work with, I still haven't gotten a full model to successfully print with it.

There are some pre-foamed LW-PLA's on the market that while having less of a weight savings (~20%), it is much easier to work with.

With the additional structural joints of this 120mm model, weight is going to be an even bigger factor.