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Re: The 5 ft-packed-HG Movement

Postby JoeF » Mon Dec 16, 2024 8:55 am

Preamble emphasis: Retain telescopic nestability for tiny packing of spar and beam segments of a tpHG while optimizing the use of mass. Thus, keep individual spar segments with ODs and IDs that are globally constant. That is, this note is about not using vanilla COTs beams but rather using high-design for beams. Geodesics with density variations comes to mind. We might be able to get higher resistance to buckling with the use of less mass and still be able to telescopic nest spar and beam segments for tiny packing.
================================================================

Alternative titles for this technical note that refines or reframes the concept:

"Optimized Cylindrical Latticed Spars: Constant OD and ID, Variable Mass Distribution"
"Cylindrical Latticed Spar Segments: Lightweight Design with Constant Outer and Inner Diameters"
"Innovations in Latticed Spar Design: Constant Dimensions, Optimized Strength"
"Lightweight Latticed Spars with Global Constant OD and ID"
"Structural Efficiency in Cylindrical Latticed Spars: Uniform Dimensions, Variable Strength"
"Cylindrical Spar Design: Constant OD/ID, Adaptive Lattice Mass Distribution"
"Advanced Latticed Spars: Uniform Geometry, Optimized Material Use"
"Engineering Latticed Spars with Global Constant OD and ID"
"Cylindrical Latticed Spar Segments for Lightweight Structural Applications"
"Latticed Spar Technology: Uniform Cylindrical Dimensions with Optimized Mass"


or for some fun:
"Holey Spar Segments: Latticed Design for Lightweight Strength"
"Holey Cylindrical Spars: Optimized Perforated Structures with Constant OD and ID"
"Holey Yet Strong: Advanced Latticed Spar Segments"
"Holey Spar Segments: Revolutionizing Weight-to-Strength Ratios in Cylindrical Designs"
"Holey but Mighty: Latticed Spar Segments for High-Performance Applications"

How to design and build latticed spar segments that optimize mass and effectiveness in tpHGs?

    User Prompt:
    How to design and build latticed spar segments for tpHGs? (tiny-packed hang gliders)

    Aim for lighter spar segments that keep constant OD and ID, but that still structurally taper via mass distribution and lattice design. Variable geodesics on the virtual cylindrical shell perforated by dimples, valleys, etc. at various densities from beam end to beam center to beam other end. Aim for resistance to buckling by best use of mass to get beams better for the tpHG than plain constant-mass distribution and plain constant-lay distribution for the CF beam. Analyze how low-mass a strong beam could be by making the beam with variable lattice along its length.

    Response:
    • 1. Design Principles
      • :arrow: Constant OD and ID with Tapered Mass Distribution:
        Maintain a uniform outer diameter (OD) and inner diameter (ID) for compatibility with nested spar segments and assembly. Use a lattice structure to distribute mass where it’s most effective, concentrating material where compressive forces or bending moments are highest.
      • :arrow: Variable Geodesics on a Virtual Cylindrical Shell:
        Define geodesic paths (curves on the cylindrical surface) that adapt to the stress profile along the beam. Incorporate perforations (dimples, valleys, or voids) in low-stress regions to reduce mass without compromising strength.
      • :arrow: Buckling Resistance through Optimized Geometry:
        Vary lattice density and strut thickness along the length of the beam. Use curved or arched lattice elements to enhance stability under compression.
      • :arrow: Finite Element Analysis (FEA):
        Simulate load cases (axial compression, bending, torsion) to fine-tune the lattice design for optimal performance.
    • 2. Material Selection
      • :arrow: Carbon Fiber Composites: Use braided carbon fiber for struts to achieve high stiffness-to-weight ratios. Optimize layup patterns (e.g., unidirectional along struts, biaxial for joints).
      • :arrow: Hybrid Materials: Combine carbon fiber with Kevlar or Dyneema for impact resistance at high-stress joints. Explore lightweight metals (e.g., titanium or aluminum) for reinforcement at lattice intersections.
    • 3. Manufacturing Techniques
      • :arrow: 3D Printing: Use Direct Ink Writing (DIW) or Continuous Fiber Reinforcement (CFR) additive manufacturing for precision lattice construction. Print lattice structures with integrated end caps and couplers.
      • :arrow: Mandrel-Based Construction: Create a cylindrical mandrel with removable sections to facilitate laying up a variable-density lattice. Apply braided carbon fiber over the mandrel in a pattern that follows the geodesics of the lattice design.
      • :arrow: Perforation Methods: Start with a solid cylindrical composite tube, then use CNC machining, laser cutting, or water jetting to create the lattice pattern. Ensure smooth transitions between lattice and solid regions to avoid stress concentrations.
    • 4. Lattice Configuration
      • :arrow: Variable Strut Thickness and Density: Use thicker, denser struts near the ends of the beam (where axial loads are higher). Gradually thin and space out struts toward the center.
      • :arrow: Localized Reinforcement: Add reinforcement rings or solid sections at critical load points, such as joints or where spars connect to the wing structure.
      • :arrow: Dimples and Perforations: Use small, shallow dimples in low-stress regions to further reduce weight without affecting stiffness.
    • 5. Assembly and Integration
      • :arrow: End Couplers: Integrate lattice-compatible Joe Couplers to maintain nesting and alignment. Design the couplers to distribute loads evenly across the lattice at beam ends.
      • :arrow: Modularity: Make the lattice modular so individual sections can be replaced if damaged.
      • :arrow: Surface Treatments: Apply coatings (e.g., silicone, epoxy) inside and outside the lattice to improve aerodynamic smoothness and durability.
    • 6. Analysis and Optimization
      • :arrow: Finite Element Analysis (FEA): Simulate various load scenarios to ensure buckling resistance, particularly under compressive loads. Optimize lattice geometry iteratively based on FEA results.
      • :arrow: Weight and Strength Trade-offs: Compare the weight of the lattice spar to plain spars with equivalent buckling resistance. Analyze whether the variable-mass lattice significantly improves the strength-to-weight ratio.
      • :arrow: Experimental Validation: Build prototypes and test under load conditions to validate FEA predictions.
    • 7. How Low-Mass Can a Strong Beam Be?
      To minimize mass while retaining structural strength:
      • :arrow: Maximize the Effective Material Usage: Concentrate material only where stress is high, removing unnecessary weight from low-stress regions.
      • :arrow: Enhance Structural Efficiency: Use advanced geometries like IsoTruss or hexagonal lattices, which are inherently efficient under compression.
      • :arrow: Leverage Tailored Composites: Tailor fiber layup direction to align with principal stress paths.
      A well-designed lattice spar can be significantly lighter than a constant-mass distribution spar while achieving comparable or superior performance, particularly in buckling resistance. This is ideal for tpHGs, where portability and strength are critical.

mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmA paper of similar focus mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
Recent progresses in lightweight carbon fibre reinforced lattice cylindrical shells
Authors:

Ming Li, Hengyi Zhu, Changliang Lai, Wenyi Bao, Han Han, Renbang Lin, Weiping He, Hualin Fan
Received 1 June 2022, Revised 27 September 2022, Accepted 30 September 2022, Available online 14 October 2022, Version of Record 14 October 2022.

Abstract Here
Abstract wrote:Abstract
Owing to their high strengths and stiffnesses, carbon fibre reinforced composites (CFRC) are widely used in aerospace engineering for lightweight structural designs. The introduction of a wide variety of lattices into composite cylindrical shells is considered one of the most promising strategies for improving the mechanical properties and simultaneously reducing weight. Herein, the configurations and manufacturing methods of three typical types of lattice structures, namely lattice, lattice sandwich, and lattice stiffened shells, are demonstrated. Experimental investigations are presented to discuss the mechanical properties of these cylindrical shells under compression, along with their free vibration characteristics. Further, non-destructive methods, which can identify the mechanical properties and buckling loads of such shells non-destructively, are demonstrated. Moreover, multi-failure theories proposed to predict the failure loads and failure modes are presented. Finally, the development of CFRC lattice cylindrical shells in lightweight designs is summarised..


==============================================================================================================

  • What is Anisogrid?
    An anisogrid is a type of lightweight structural component designed with an open lattice or grid-like pattern that exhibits anisotropic properties—meaning its strength and stiffness vary depending on the direction of the applied load. These structures are commonly used in aerospace, rocketry, and other high-performance engineering applications due to their excellent strength-to-weight ratio and ability to be tailored for specific loading conditions.
  • Key Features of Anisogrid Structures:

    • Lattice Design
      - The structure consists of interconnected ribs (or struts) that form a repetitive geometric pattern, such as triangles, hexagons, or other polygons.
      - The grid is designed to handle loads along specific directions, providing optimal strength and stiffness where needed while minimizing material use.
    • Anisotropy
      - Unlike isotropic materials (uniform properties in all directions), anisogrid structures are engineered so that their properties are stronger or stiffer along particular axes (e.g., axial or hoop directions in a cylinder).
    • High Strength-to-Weight Ratio
      - By placing material only where it is structurally necessary, anisogrids significantly reduce weight without compromising mechanical performance.
    • Customizable Properties
      - The lattice pattern, rib thickness, and material choice can be customized to meet specific requirements for load-bearing, vibration damping, or thermal resistance.

  • Applications:

    • Aerospace
      - Used in launch vehicle fuselages, payload fairings, and pressure vessels due to their ability to withstand high axial and hoop stresses while being lightweight.
    • Civil Engineering
      - Applied in bridge components and structural reinforcements where tailored strength is needed.
    • High-Performance Tubes
      - Cylindrical anisogrids are often used in spars, trusses, and shafts where rotational stiffness and buckling resistance are critical.

  • Advantages:

    • Material Efficiency
      - Eliminates unnecessary material, focusing on load paths and reducing overall weight.
    • Directional Strength
      - Strength and stiffness can be aligned with expected load directions, improving structural efficiency.
    • Buckling Resistance
      - The lattice design effectively resists buckling by distributing loads through the grid geometry.

  • Challenges:

    • Complex Manufacturing
      - Producing an anisogrid involves advanced fabrication techniques such as automated filament winding, 3D printing, or CNC machining.
    • Cost
      - Precision manufacturing and high-performance materials like carbon fiber can make anisogrids expensive.
    • Analysis and Design
      - Designing an anisogrid requires detailed simulations to predict behavior under different loads and optimize the grid pattern.

  • Relevance to Hang Glider Spars:
    Incorporating an anisogrid structure in your TPHG spar segments could:

    • Provide tailored stiffness along the length of the spar to resist bending and buckling.
    • Enable mass distribution optimization, aligning with your goal for constant OD and ID spars with variable lattice designs.
    • Leverage carbon fiber reinforcement to maximize weight savings while maintaining structural integrity.


============================================================
:arrow: Euler's Buckling Formula
Euler's Column Formula
Euler's critical load
============================================================
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Re: The 5 ft-packed-HG Movement

Postby JoeF » Wed Dec 18, 2024 4:56 pm

Four wheels used via strap-on tpHG tote pack may become two sand-friendly wheels for a Dockweiler tpHG.
The wheels on hard axles will very quickly disassemble for bus-time toting of the tpHG pack; the wheels will be fully isolated and ready to use on the glider. During assembly of the glider, the side flying crosslines will be fed through the wheels' hubs and moved adjacent to the bottom of the queenposts. An easy placement of a wrap tie will keep the wheels in place in case the wheels are needed in some landing. So, the wheels will play double duty: wagon making and flight landing, if necessary.

======================================
For sand landing, are skis better than bulbous wheels? [ ]

right or wrong, opining ChatGPT wrote:
  • Advantages of Wheels:
    • Lower Friction: Wheels roll more easily on sand, reducing the risk of the glider stopping abruptly and pitching forward.
    • Versatility: Wheels can handle various terrains, including compact or loose sand.
    • Ease of Installation: Many hang gliders already have mounts compatible with wheels.
    • Control: Wheels allow for smoother deceleration and controlled stops.
  • Drawbacks of Skis:
    • High Friction: Skis tend to dig into loose sand rather than gliding over it.
    • Limited Use: Skis are better suited for snow or very fine, compact surfaces.
    • Difficulty in Steering: Skis provide limited directional control, making landings more unpredictable.
  • Recommendation: For sand landings, wheels are the better option. Opt for large-diameter, low-pressure "sand wheels" to distribute weight and prevent digging into soft sand.
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Re: The 5 ft-packed-HG Movement :: or less tpHG

Postby JoeF » Thu Dec 19, 2024 3:32 pm

For the record, Eddie Paul's ad in 1973 indicated
pack of 5 feet length:
EddiePaulWhitneyCLIP5ftdeclarationPack.jpg
EddiePaulWhitneyCLIP5ftdeclarationPack.jpg (23.83 KiB) Viewed 1056 times

5'x1'x1'
That is five cubic feet.
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Re: The 5 ft-packed-HG Movement

Postby Semper Fidelis » Sun Jan 05, 2025 4:28 pm


WAHOO... ERIC MADE A GREAT JOB ! :thumbup: :thumbup:

WITHIN TWO DAYS ALREADY 13k VIEWS :shock: :shock: :shock:

GOOD NEWS, I'VE ALSO WORKED THIS WEEKEND
AND NOW YOU CAN (FINALY) VISIT AND FORWARD

http://www.hangglifter.com

A lot of links and pictures, I'd like the "blue guy" to contact me.
I'll finish to upload the texts in the TPHG page.

HAPPY NEW YEAR FRIENDS, MISS YOU !

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Re: The 5 ft-packed-HG Movement

Postby JoeF » Fri Jan 17, 2025 1:02 pm

Hang glider sail that uses many zippered sections: Why? Still allows compound curves. Allows multiple transport pack options against having to roll up one big global sail. Allows trade-outs for repair or size experiments or decoration.

Hang Glider Sail with Zippered Sections: Why?

  • Allows Compound Curves:
    Smaller, zippered panels enable precise tailoring for aerodynamically efficient shapes. This modular approach makes complex sail designs achievable without needing to sew a single large piece.
  • Multiple Transport Packing Options:
    Zippered sections let the sail be divided into smaller, manageable parts that are easy to fold or roll individually. Ideal for compact packing needs, such as in Tiny Packed Hang Glider (TPHG) designs.
  • Ease of Repairs:
    Damaged panels can be replaced or repaired without affecting the rest of the sail, saving time and reducing costs compared to replacing an entire sail.
  • Customization for Experiments:
    Sections can be swapped out to test different materials, sizes, or shapes, allowing for rapid prototyping and iterative design improvements.
  • Decorative Options:
    Individual panels make it easier to incorporate unique patterns, colors, or branding into the sail design.
  • Environmental Benefits:
    Damaged sections can be recycled or replaced incrementally, reducing waste compared to discarding a single large sail.
  • Weight Distribution Management:
    Different materials can be used for specific sections (e.g., heavier-duty fabric in high-stress areas, lighter materials elsewhere) to optimize performance.
  • Versatile Adaptation:
    A zippered sail design allows for adjustments to suit varying flight conditions or pilot preferences, such as resizing sections to modify wing loading or control characteristics.

This modular sail approach enhances portability, versatility, and repairability, making it a practical choice for modern hang glider designs.


But:

Costs and Considerations for Sectioned Hang Glider Sails with Zippers

Costs:

  • Material Costs:
    High-quality zippers (e.g., UV-resistant, marine-grade) are more expensive than standard fabric.
    Additional fabric reinforcements are needed around zipper seams to prevent tearing under tension.
  • Labor Costs:
    Increased time and skill required for precision sewing and alignment of zippers during sail fabrication.
  • Maintenance Costs:
    Zippers may require periodic lubrication or replacement due to wear, especially in high-stress areas.
  • Weight Costs:
    Zippers add weight to the sail, which may affect performance and packing volume.

Considerations:

  • Structural Integrity:
    Proper reinforcement around zippers is crucial to ensure durability and maintain tension across the sail.
  • Aerodynamic Impact:
    Zippers and their seams must be designed to minimize drag, such as by using flat, low-profile zippers.
  • Packing Efficiency:
    Sectioning enables compact folding, but the weight and bulk of zippers could reduce the overall benefit.
  • Design Complexity:
    Sail designs must account for zipper placement to avoid compromising the airfoil's shape and performance.
  • Repair and Replacement:
    While individual sections are easier to replace, ensuring consistent fit and tension after a panel swap can be challenging.
  • Environmental Exposure:
    Zippers are vulnerable to sand, dirt, and corrosion, requiring regular cleaning and maintenance in harsh environments.
  • Customization Opportunities:
    Enables modular experimentation with different materials, colors, or sizes, but requires careful tracking of compatible sections.
  • Production Scalability:
    Manufacturing sectioned sails with zippers may be less efficient than producing a single-piece sail, affecting cost per unit in small production runs.

Conclusion:
While sectioned sails with zippers offer significant advantages in portability, modularity, and repairability, they come with added costs in materials, labor, and maintenance. The benefits must be weighed against these trade-offs, especially for lightweight, high-performance designs.

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Re: The 5 ft-packed-HG Movement

Postby JoeF » Thu Jan 23, 2025 8:45 pm

Study with eye toward topic:

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Re: The 5 ft-packed-HG Movement

Postby JoeF » Mon Jan 27, 2025 5:51 pm

Here is how I am coding projects that fit this topic:
myWing1, myWing2, myWing3, myWing4, myWing5
where the numerals indicate quantity of length in feet.
Also, myWingOneMeter is used.

The lengths indicate targets for the tiny packs involved in transporting a hang glider.
Packs are to be of a weight and shape that permits polite and safe transport by a pilot while using
public buses, trains, and sidewalks. Such packs will also transport well in small cars.
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Re: The 5 ft-packed-HG Movement

Postby JoeF » Thu Jan 30, 2025 9:47 pm

Compression member exploration for splinted air beam:
The airbeam helps to keep compression member from buckling when the airbeam and compression member are well integrated (hugging each other, embracing, married, ...). In some TPHGs (tiny-packed hang gliders) that use the splinted airbeam for spars, there may be compression members that are "segmented". The longest segment might force the transport packs to be about the length of that longest segment.
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Re: The 5 ft-packed-HG Movement

Postby JoeF » Thu Feb 13, 2025 8:51 am

Have one face open. Open nesting and then stack reverse wise to allow compression member making.
Blocks001.JPG
One face is open allowing telescopic nesting. Open. Stack opposingly. Compress with central cable. Explore the concept.
Blocks001.JPG (20.33 KiB) Viewed 75 times

Blocks002.JPG
Blocks002.JPG (33.06 KiB) Viewed 74 times

Blocks003.JPG
Blocks003.JPG (32.7 KiB) Viewed 74 times

Blocks004.JPG
Blocks004.JPG (19.5 KiB) Viewed 74 times

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Re: The 5 ft-packed-HG Movement

Postby JoeF » Thu Feb 13, 2025 11:57 am

Hang Glider Spar Concept Using Nestable Shells and Compression Cables

Overview
This concept explores a hang glider spar composed of nestable shells with an open face, which can be stacked in reverse order to create a tall structure and then compressed using cables. The structure would provide both compact packing and efficient load distribution under flight conditions.

Structural Concept

  • Nestable Shells: Each spar is formed from multiple shells that nest within one another when packed. During assembly, they are stacked in reverse order, forming a long structural member.
  • Open-Faced Design: The shells have one face open, which may serve as an access point for cable routing, weight reduction, and aerodynamic shaping.
  • Compression System: Once stacked, a central or multiple siding cables tighten the structure, holding the sections together under tension.


Compression Mechanism
[*] Central Compression Cable: A single cable runs through the center of the stacked shells, tightened at both ends to maintain axial compression.
[*] Siding Compression Cables: Multiple cables run along the exterior or within grooves of the shell walls, distributing tension forces more evenly and potentially allowing dynamic stiffness adjustments.

Cross-Sectional Shapes
Various cross-sections can be explored to optimize aerodynamics, structural integrity, and nesting efficiency:

  • Square: Easy to align, good structural integrity, but potential for stress concentrations.
  • Elliptical: Aerodynamically favorable but requires precise shaping for nesting.
  • Round: Efficient in handling loads but may have nesting inefficiencies.
  • Triangular: Strong shape but difficult to nest efficiently.
  • Pentagonal/Hexagonal: Good balance of strength and packing efficiency.
  • Heptagonal/Octagonal: Approaching roundness while retaining flat surfaces for interfacing with cables.
  • Polygonal Hybrid: A blend of flat and curved faces to optimize nesting and structural performance.


Wing-Specific Spar Nesting

  • Dual Nesting: Two separate nests, one for the left wing spar and one for the right wing spar, allowing independent assembly and packing.
  • Shared Nesting Core: A single nesting structure that splits into two wing spars, reducing component count and improving weight distribution.


Additional Considerations

  • Locking Mechanism: Simple mechanical interlocks or friction-based engagement to prevent slippage between shells.
  • Material Choice: Carbon fiber, composite laminates, or lightweight aluminum alloys for optimal strength-to-weight ratio.
  • Dynamic Adjustability: Potential for adjusting spar length or stiffness mid-flight via cable tensioning systems.
  • Assembly Ease: Tool-free or quick-lock mechanisms to facilitate rapid field setup.


Next Steps
[*] Prototyping small-scale models to test nesting and compression mechanisms.
[*] Simulating aerodynamic and structural performance for different cross-section shapes.
[*] Evaluating potential for adaptive stiffness control through selective cable tensioning.

This concept holds promise for a compact, efficient, and adaptable hang glider spar system. Further development and testing will refine the design for real-world application.

Ah! I see what you're getting at—your method involves reversing the blocks before stacking, rather than simple telescoping extension. This is different from traditional telescoping structures, as it relies on the open face of each shell to nest and then invert for compression stacking.

Are There Industries That Use This Approach?
While this exact method is rare, there are a few areas where similar reversed nesting or inverted shell stacking principles are applied:

1. Packaging & Storage Containers
Nestable Storage Bins & Crates – Many plastic storage bins are designed to nest inside one another for compact transport, but when flipped, they can stack into a stable column.
Russian Doll (Matryoshka) Design – The concept of nesting items within each other and then reversing their order for use is similar to your approach.

2. Structural Engineering & Architecture
Modular Stackable Housing – Some disaster relief or prefabricated housing units use stackable shells that nest for compact storage and then reverse-stack for full-size assembly.
Collapsible Bridge Structures – Some military bridges or portable shelters use modular plates that fit inside one another and then flip for deployment.

3. Military & Aerospace Applications
Reversible Armor Plating – Some military vehicle designs use stackable armor plates that can be rearranged in a different order for transport vs. deployment.
Deployable Space Habitats – Concepts like expandable space stations or lunar bases consider modular shells that nest for launch and then reverse their order for assembly.

4. Consumer & Industrial Products
Collapsible Buckets & Funnels – Some designs use concentric rings that nest, but when reversed, form a stable structure.
Folding Furniture & Stackable Chairs – Some chairs stack compactly one way but, when flipped or rotated, create a stable arrangement.

5. Robotics & Kinetic Structures
Variable Geometry Trusses – Some robotic arms or morphing structures use shell-like elements that nest and then reverse their order for expansion.

Why This Might Be Unique for a Hang Glider Spar?
Unlike traditional telescoping spars that slide out in a linear manner, your approach would:
Allow extreme compactness when stored.
Provide high rigidity when tensioned.
Potentially allow variable stiffness based on cable tension.

This could be a completely new approach for ultralight aviation and deployable wings!


Please explore with me a slight indent at the top of each block to prevent side sliding of subsequent blocks when the stack is in compression. We do not want the separate shells to slide off the underparent.
ChatGPT said:
A slight indent at the top of each block could act as a stabilizing feature to prevent side sliding when the stack is in compression. Here are some key considerations for implementing this:

1. Indent Geometry & Depth
Shallow Groove or Lip: A small inward step or groove at the top of each shell would create a natural alignment feature when stacked.
Curved Recess: A concave lip could cradle the convex base of the next shell, increasing lateral stability.
Angled Shoulders: A tapered edge could provide a mechanical stop against lateral motion.

2. Preventing Jamming vs. Providing Stability
The indent must be shallow enough to avoid jamming during stacking/unstacking.
The transition between indent and main shell should be smooth to prevent stress concentrations.
The indent could also serve as a visual guide for assembly, ensuring proper nesting orientation.

3. Material Considerations
Carbon Fiber or Composite Laminates: Can be molded with an integrated lip.
Aluminum or Metal Shells: The indent could be machined or formed with press techniques.
Polymer Coatings: Adding a non-slip surface (such as rubberized edges) could complement the indent.

4. Locking & Friction Aids
A textured surface or grippy insert within the indent could increase friction and resist sliding.
Magnetic or mechanical interlocks could further prevent unintended movement.
A cable-preloaded system could ensure compression aligns each block tightly.
Would you like to explore a physical test using 3D-printed models or material simulations?

You said:
yes.
ChatGPT said:
To proceed with a physical test, we can follow these steps:

1. Define the Indent Shape & Test Parameters
We need to decide:

Indent depth: How shallow or deep the groove should be to prevent sliding while allowing easy stacking/unstacking.
Indent shape: Flat, concave, or a tapered angle.
Materials: Initial tests can use 3D-printed models in plastic before trying composite or metal versions.

2. 3D Modeling & Printing Prototypes
I can help design a parametric 3D model for the shells with adjustable indent depth and shape.
You can print test pieces in PLA or PETG using an FDM printer, or resin printing for finer details.

3. Compression & Sliding Tests
Stack multiple shells with different indent variations.
Apply compressive force and observe if side sliding occurs.
Try different surface coatings or textures to see how they affect stability.
Would you like a 3D model file (e.g., STL or STEP), or should we start by sketching variations of the indent geometry first?


:arrow: I note that the tension cables could also play an anti-slide-off role. Also, castellated rim to holes might be chosen.


https://www.youtube.com/watch?v=sfX3aWluU20 shows a toy stacking that has interlocking rims on the edges of the reverse nestables.
ChatGPT said:
The video you mentioned demonstrates a toy stacking system where interlocking rims on the edges of the reverse nestable pieces help keep them stable and prevent slippage when stacked in compression. This is a great example of how reverse stacking can be made effective through design features such as interlocking or grooved edges that prevent lateral movement.

Similar design principles are used in various industrial applications, like those found in packaging systems or modular containers where items nest within each other for compact transport. These often feature interlocking edges, grooves, or lips that stabilize the stack, ensuring they don’t slide off when pressure is applied.

For your own application with spar components or modular systems, this principle could be applied by designing a slight lip or groove on the edges of each shell to prevent side-sliding during compression. This design would effectively allow the blocks to nest in a stable manner while maintaining their position even under force.

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