Titus Flags

Streamer-Based Hem Testing: Accelerated Wear & Force Simulation

How to Optimize a Fly-End Hem Stress-Test Streamer to Exceed ASTM D6193

Since making multiple 3×5 ft flags is impractical, streamers are a valid proxy for testing fly-hem durability—if you scale dimensions correctly to simulate real-world forces.

1. Streamer Design for Realistic Force Amplification

Key Variables:

  • Length-to-Width Ratio: Forces increase exponentially with length.
  • Tip Speed: Longer streamers generate higher dynamic loads at the free end.

Recommended Test Streamer:

  • Width: 2–3″ (at least 2X fly-end hem width).
  • Length: 8–10
  • Material: Same ripstop nylon + hem treatment (grosgrain/Tex 90/spar varnish).

Why This Works:

  • A 10 ft streamer in 15+ mph wind can simulate 2–3x the load of a 5 ft flag’s fly end due to whip effect.
  • Narrow width ensures forces concentrate at the hem (no distributed load “cheating”).

2. Wind Force Calculation (Simplified)

Force on a flag/streamer is roughly: F≈21​⋅ρ⋅v2⋅Cd​⋅A

Where:

  • ρ = air density (~1.2 kg/m³)
  • v = wind speed (e.g., 10 mph = 4.5 m/s)
  • Cd​ ≈ 1.0 (drag coefficient for flapping fabric)
  • A = area (e.g., 10 ft streamer × 0.2 ft = 0.18 m²)

Example:

  • 10 ft streamer in 15 mph wind: ~0.5 N force at tip (similar to gusts on a 3×5 ft flag’s fly corner).

Accelerated Testing Trick:

  • Use a fan at close range to boost effective wind speed (e.g., 20 mph fan = mimics 30+ mph natural wind).
  • Attach to vehicle for interstate speeds (70mph+10mph headwind).

3. Critical Test Metrics

Monitor for:

  1. Hem Separation: Stitches pulling out at the fly end.
  2. Fraying: Thread or ribbon degradation at high-stress zones.
  3. Stiffness vs. Flex: Does the varnish crack or inhibit natural motion?

Passing Criteria:

  • No seam failure after 1 hour of continuous flapping (≈ 1 month of moderate flag use).

4. Alternatives if Streamers Aren’t Feasible

  • Small “Flaglet” Test:
    • Make a 1 ft × 3 ft mini-flag with identical hem.
  • Tug Test:
    • Clamp hem in a vise and use a fish scale to apply gradual pull until failure.

Key Takeaway:

A 10 ft × 2–3″ streamer in 15+ mph wind (or fan airflow) will overstress the hem similarly to a 3×5 ft flag in normal use. Focus on the fly end’s stitch integrity and ribbon adhesion.