Introduction
This page complements a journal paper (submitted) on VELUM, a lightweight coated low-density polyethylene (LDPE) membrane for small lighter-than-air (SLTA) vehicles. It provides extra visuals and brief highlights only.
Conventional envelopes present trade-offs: polyurethane (PU) is durable yet heavy and more permeable, whereas Mylar® is light and gas-tight but brittle. The proposed coated LDPE reduces mass and leakage and improves tear tolerance while retaining simple, scalable fabrication.
Manufacturing Concept
Envelopes of identical geometry were made from different materials: LDPE was built in our lab, while PU and Mylar® came from industrial manufacturers. Mylar was later excluded due to brittleness, so comparisons focused on LDPE versus PU.
Coating
Multiple tests were performed on small LDPE samples to identify the most effective coating method. The selected method, detailed in the paper, achieved superior surface coverage and was applied to the final envelope, thereby improving gas retention and durability.
Tests & Results
Just a brief overview is presented here; the full data and methods are detailed in the submitted paper.
- Weight: Coated LDPE remained lighter than PU, with only a minor mass increase after coating.
- Durability: Tear resistance higher than Mylar; seam strength remained reliable under stress.
- Leakage: Lowest leakage-to-mass ratio among all three materials tested.
- Hydrophobicity: Highest water-repellency (contact angle >117°).
- Burst test: LDPE ruptured in a controlled slit (safe failure), PU failed at lower pressure, Mylar failed explosively.
Leakage test setup with the envelope suspended from a 50 N load cell in a controlled environment, as shown below:
Burst tests (800×1200 mm samples; compressed air) replicated biaxial loading; Mylar carried the highest pressure before catastrophic rupture, PU failed first after ductile thinning, and LDPE ruptured at 3.08 kPa along a controlled slit—evidence of strong seams and a non-catastrophic failure mode (shown below).
Deployment
To validate VELUM’s real-world feasibility, we conducted a deployment trial in a partially flooded cave environment, characterized by narrow passages and high humidity.
The coated LDPE envelope maintained helium retention and structural integrity during field tests, demonstrating stable flight and durability under harsh conditions.
Pre-Deployment Flight Tests
Bench and indoor flight trials to verify buoyancy, controls, sealing integrity, and handling before the cave mission.
LDPE Envelope
PU Envelope
Field Deployment in Cave Environment
Validation in a partially flooded cave with narrow passages and high humidity. The airship maintained stable flight, strong helium retention, and resilient handling in a confined setting.
