[JoeF]

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.
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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
  
  • 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.
    
  • 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.
  • 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.
  • Finite Element Analysis (FEA):
    Simulate load cases (axial compression, bending, torsion) to fine-tune the lattice design for optimal performance.
• 2. Material Selection
  
  • 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).
  • 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
  
  • 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.
  • 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.
  • 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.
  • Localized Reinforcement: Add reinforcement rings or solid sections at critical load points, such as joints or where spars connect to the wing structure.
  • Dimples and Perforations: Use small, shallow dimples in low-stress regions to further reduce weight without affecting stiffness.
• 5. Assembly and Integration
  
  • 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.
  • Modularity: Make the lattice modular so individual sections can be replaced if damaged.
  • Surface Treatments: Apply coatings (e.g., silicone, epoxy) inside and outside the lattice to improve aerodynamic smoothness and durability.
• 6. Analysis and Optimization
  
  • Finite Element Analysis (FEA): Simulate various load scenarios to ensure buckling resistance, particularly under compressive loads. Optimize lattice geometry iteratively based on FEA results.
  • 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.
  • 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:
  
  • Maximize the Effective Material Usage: Concentrate material only where stress is high, removing unnecessary weight from low-stress regions.
  • Enhance Structural Efficiency: Use advanced geometries like IsoTruss or hexagonal lattices, which are inherently efficient under compression.
  • 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
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..

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• 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.

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Euler's Buckling Formula
Euler's Column Formula
Euler's critical load
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[JoeF]

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.

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

• 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.

[JoeF]

For the record, Eddie Paul's ad in 1973 indicated
pack of 5 feet length:

EddiePaulWhitneyCLIP5ftdeclarationPack.jpg (23.83 KiB) Viewed 56 times

5'x1'x1'
That is five cubic feet.