"Autorotation Learned from Flying Seeds" Experimental Kit

"Autorotation" is a fundamental concept regarding helicopter safety.
It is a complex phenomenon in which, following an engine failure, the airflow generated during descent causes the blades to spin and produce lift, enabling a soft landing.
However, in the natural world, there are "Winged Seeds" and/or "Flying Seeds" that utilize this very phenomenon to propagate their species.
While there are various types featuring one, two, or multiple blades but this kit focuses on the two-winged seed of the Dipterocarp (Lauan) tree as a model for studying "Autorotation".
I plan to upload a kit for three-blades type in the near future.
Please refer to the information available online and in books (particularly those regarding helicopters) for details on "Dipterocarpaceae (Lauan)" and "Autorotation."
This model comes provided with a Pre-Rotation devise, allowing you to learn through experimentation by varying the angle of attack and center of gravity using two similar wing designs.
Recognizing the difficulty of the challenge, I persisted through trial and error and finally managed to prepare the necessary components and equipment to conduct experiments on angle of attack and center of gravity.
The particularly difficult aspects were:
・ Designing, printing, and assembling the lightweight wings
・ The mechanism to allow vertical descent while spinning the rotor (pre-spin device)
Goal of this session (How to view the video)
"The rotation speeds up during the vertical fall from approximate 5 m height, and it continues to rotate at just landing on the ground. "

A. Features of this Device
① Observation of an actual "Dipterocarpus" (Lauan) seed... see photo (Reference Only)

② Fabrication of comparative Wing models
　(a) Curved type
　(b) 45 degree cone angle type

③ Specifications for each wing
　(a) Wing profile... original design... outer skin only for weight reduction
　　　Minimum thickness: 0.4 mm; Wing length: approx. 180 mm; Chord: 30 mm
　(b) Angle of attack (mounting angle)... hubs prepared for -5°, -10°, and -15°
　(c) Center of gravity... weighted sphere designed to mimic the seed (30 mm diameter, 0.8 mm thickness). Adjustable via shaft to positions at 0, 10, 20, 30, 40, and 50 mm

④ Drop experiments... indoor (2 m height) and at observation deck (approx. 5 m height)
　(a) Pre-rotation drop (pre-rotation device fabricated... gear and spring-loaded mechanism)

⑤ Experimental results... combinations yielding successful soft landings... see Video.
　(a) Curved type... -15 degree angle, 0 mm shaft
　(b) 45 degree cone angle type... -15 degree angle, 50 mm shaft

[Video] https://youtu.be/G6PW7KDJ0C0

B. Assembly Manual (PDF format, total 28 pages)
The detail assembly manual including "Parts-List", "After printing treatment" and "Assembly procedure" are prepared based on "Standard Skill (Filing, Drilling, Tapping, gluing and tightening)".

C. General Notes (Parts and Tools)
1. Piano Wire : φ1.2 x300L
2. Coil Spring : 10x20x0.6 (Optional)
3. Aluminum Pipe : φ3, 5, 6, 9
4. Wood Bar : 45x12x910L, 8x8x400L
5. Screw : M1.4, M2, M3 Nut : M2, Washer : M2 Wing Bolt : M4, M5, M6
6. Drill and Tap
　　My design hole diameter is considerably smaller than the finish hole diameter in order to ensure the wall thickness at the time of printing.
　　　Drill : φ1.1, 1.5, 2, 2.5, 3.2, 4, 5 Tap : M1.4, , M2, M3, M4, M5, M6
　　Use appropriate size of Tap for attaching screw otherwise specified in text.
　7. Please purchase your own tripod.

D. STL files
　Files: STL Files (52items)
“ws” of last 2 digits means “With Support” special designed.

E. Printing settings
Raft, Support, Layer Height, Infill: Depending on your experience.
My models were printed by "idbox" using with 0.4 nozzle, 1.75 PLA.
　Rotating parts such as Blade, Gear, Shaft are recommended 0.2 Layer, 100% infill.

F. Total Net Print Time: Approx. 80 Hr.
　(Estimated as case of PLA, 0.4mm Nozzle, 0.2mm Layer Height, 40% infill and No raft and support)
Note: When at actual print, each parameter may be adjusted by your experience.

[Update] 2026.08.06
Add Conversion Kit for 3-Blade Rotor
https://cults3d.com/en/3d-model/tool/autorotation-learned-from-flying-seeds-experimental-kit-2
[Update] 2026.08.12
Add Para. F

This model was created and verified using well maintenanced 3D printer with a 0.4 mm nozzle and 1.75 mm PLA filament, involving fine manual finishing work; please take this into consideration before downloading.

See Manual.