Optimizing CFRP Tube Manufacturing for Drone Landing Gear: Filament Winding vs. Roll Wrapping for Impact Resistance

In the design of UAV landing gear, the choice of manufacturing process for carbon fiber reinforced polymer (CFRP) tubes is critical to achieving the required impact resistance. This article compares filament winding and roll wrapping, focusing on mechanical performance, cost, and quality control. We provide a worked example using Toray T700S to illustrate the differences, and reference ASTM D3039 for testing standards.

Why Impact Resistance Matters in Drone Landing Gear

Drone landing gear must absorb repeated impact loads during landing, which can induce high strain rates and potential delamination. Unlike aerospace primary structures, landing gear tubes are often subjected to off-axis loads and point impacts from rough terrain. Therefore, the manufacturing process must produce tubes with high interlaminar shear strength (ILSS) and damage tolerance.

According to MIL-HDBK-17, the impact resistance of composite laminates is governed by fiber architecture, matrix toughness, and interfacial bonding. For CFRP tubes, the orientation of fibers relative to the loading axis is a key factor. Filament winding allows precise control of winding angles, while roll wrapping typically uses unidirectional or woven prepreg layers stacked in a mold.

Filament Winding vs. Roll Wrapping: Process Overview

Filament winding involves winding continuous fiber tows (impregnated with resin) onto a rotating mandrel. The winding angle can be precisely controlled (e.g., ±45° or helical patterns). After winding, the part is cured in an oven or autoclave. This process is highly automated and suitable for cylindrical geometries.

Roll wrapping (also known as sheet wrapping) uses prepreg sheets that are rolled onto a mandrel, often with a release film. The layers are oriented to achieve desired mechanical properties. This method is more labor-intensive but allows for hybrid layups (e.g., combining unidirectional and woven plies).

The choice affects fiber volume fraction (Vf), void content, and residual stresses.

Impact Resistance Comparison: Key Parameters

Worked Example: Predicting Impact Force Capacity

Consider a CFRP tube with outer diameter 30 mm and wall thickness 2 mm, made from Toray T700S fibers (tensile strength 4,900 MPa, modulus 230 GPa) in an epoxy matrix (Hexcel 8552). The tube is subjected to a drop impact from a height of 1 meter with a mass of 5 kg (typical for small UAV).

The kinetic energy at impact is: E = mgh = 5 × 9.81 × 1 = 49.05 J.

Assuming the tube behaves as a simply supported beam, the maximum stress due to impact can be estimated using energy methods. For a tube with length L = 300 mm, the bending stiffness EI is calculated from the modulus and moment of inertia. Using the rule of mixtures, the longitudinal modulus of the laminate (assuming 60% fiber volume fraction) is: E_l = Vf × E_f + (1 - Vf) × E_m = 0.6 × 230 + 0.4 × 3.5 = 139.4 GPa (where E_m = 3.5 GPa for epoxy).

The moment of inertia for a thin-walled tube is: I = π/64 × (D_o^4 - D_i^4). With D_o = 30 mm, D_i = 26 mm, I = π/64 × (30^4 - 26^4) = 1.58 × 10^4 mm^4.

The maximum bending stress is σ = M*c/I, where c = 15 mm. For a central impact, the maximum moment M = F*L/4. Using energy balance, the equivalent static force F can be found. For a 49 J impact, the force is approximately 2,000 N (assuming elastic response). Then σ = (2000 × 300/4) × 15 / (1.58e4) = 142.4 MPa. This is well below the material strength, indicating that a filament-wound tube with proper orientation can safely absorb the impact.

However, roll-wrapped tubes with lower Vf (55%) will have a lower modulus (E_l = 0.55 × 230 + 0.45 × 3.5 = 128.1 GPa), leading to higher stress for the same impact. Thus, filament winding provides better impact resistance.

Quality Control and Testing Standards

Both processes must adhere to ASTM D3039 for tensile properties and ASTM D7136/D7137 for impact resistance. At Flex Precision Composites, we use Zeiss Contura CMM for dimensional inspection and ultrasonic testing to detect delaminations. Our autoclave cure at 135°C ensures void content below 1%, achieving Vf > 62%.

For drone landing gear, we recommend filament winding for high-volume production where consistent quality is required. Roll wrapping is suitable for prototypes or complex geometries.

Cost and Lead Time Considerations

Filament winding machines have higher initial investment but lower per-part cost for large series (e.g., >1,000 units). Roll wrapping requires less capital but more labor, making it cost-effective for small batches. Lead times: filament winding can produce 100 tubes per day, while roll wrapping may produce 20-30.

For a typical UAV project, the total cost per tube (including materials and labor) is approximately $15-25 for filament winding and $20-35 for roll wrapping, depending on quality requirements.

Conclusion: Which Process Should You Choose?

For drone landing gear that demands high impact resistance, filament winding is generally superior due to higher fiber volume fraction, lower void content, and better interlaminar properties. However, roll wrapping offers flexibility for complex shapes and lower tooling costs. We recommend evaluating your specific load cases and production volumes.

At Dongguan Flex Precision Composites, we have both capabilities and can guide you through the selection process. Contact us for a consultation.