Trailing Edge Bond Voids: Detection on Thin Laminates

Author: RAS Thermal Co., Ltd. · Updated 2026-10-07

TL;DR Threshold: 6 mm volumetric floor as for the other primary bond lines. Geometry: thin tapering joint, tracked at 300 mm/s with compliant suspension. Coupling: full contact across the shrinking radius, gaps recorded as data gaps. Indexing: each void mapped to the blade model at plus or minus 0.1 mm.

The trailing edge closes clean but shows voids along the bond when the joint is scanned. The trailing edge is a thin, tapering joint, so the probe has to track a shrinking radius while holding coupling. Voids in that bond are small in absolute terms and sit behind a laminate that thins toward the edge, which makes the geometry as much of a problem as the defect. A compliant suspension that holds contact at 300 mm/s across the curve is what makes the pass repeatable, because a probe that lifts for a moment leaves a gap in the coverage map.

Common root causes

Root cause	What you see	Where it bites
Incomplete adhesive along a taper	voids where the bond thins toward the trailing edge	trailing edge bond line
Coupling loss on the curve	gaps in the scan where the probe lifted off the shrinking radius	thin curved trailing edge
Fillet shortfall near the closure	a joint thinner than the drawing where the shells meet	trailing edge closure
Trapped air at closure	voids at the interface with no surface sign	assembled trailing edge

What the numbers allow

The joint is scanned to the same 6 mm volumetric floor as the other primary bond lines under IEC 61400-5 Section 11, but the geometry raises the bar on the equipment rather than the threshold. A compliant suspension holding couplant contact at 300 mm/s on the curve is what keeps the coverage map complete, and the encoder indexes each void to the blade model at plus or minus 0.1 mm so a gap in coupling shows up as a gap in data, not as a clean result.

Threshold: 6 mm volumetric floor as for the other primary bond lines
Geometry: thin tapering joint, tracked at 300 mm/s with compliant suspension
Coupling: full contact across the shrinking radius, gaps recorded as data gaps
Indexing: each void mapped to the blade model at plus or minus 0.1 mm

How to confirm it

Work down this list in order. The first check that changes the result has found the cause.

Confirm coupling on the taper. Check that couplant contact holds as the laminate thins toward the edge, because a probe that lifts leaves a false clean result rather than a warning.
Track the radius smoothly. Let the suspension follow the shrinking radius at 300 mm/s instead of forcing the probe, since forcing it trades coupling for speed and loses the voids.
Set the volumetric floor. Dial in the 6 mm threshold from Section 11 as for the other bond lines, so the trailing edge is judged on the same basis as the web and spar joints.
Watch for coverage gaps. Read the coverage map for holes rather than only reading the indications, because on a curve an unrecorded gap is the more common failure.
Log voids against the serial. Record each void with its coordinates so the rework is scoped from the map and the closure can be reworked before finishing.

Prevention

Control the adhesive along the taper and hold the fillet profile to the drawing at closure. Then let the scan prove coverage rather than assume it, because on a thin curved joint the local failure is usually a lost coupling point rather than a missed defect, and the coverage map is where that shows.

Nothing here is rounded up for effect. Each value is the one on the equipment sheet or in the field report behind it.

Frequently Asked Questions

What acceptance limit applies to trailing edge bond voids?

The same 6 mm volumetric floor that IEC 61400-5 Section 11 applies to the other primary bond lines. The trailing edge is judged on that basis, so the challenge is coverage rather than the threshold itself.

Why is coupling harder on the trailing edge?

Because the joint is thin and tapers, so the probe has to follow a shrinking radius and hold contact throughout. A compliant suspension at 300 mm/s keeps contact, and any lift shows up as a gap in the coverage map.

How do I know the scan did not miss a zone?

By reading the coverage map, not only the indications. On a curved thin joint a lost coupling point shows as a data gap, and the encoder indexing to plus or minus 0.1 mm is what makes that gap visible.

Can a trailing edge void be repaired after closing?

It is far harder once the edge is finished, which is why the joint is scanned with the closure still accessible. Voids logged against the blade serial give the repair team a map while the joint can still be reworked.

Bottom line: The trailing edge is a thin tapering joint where the obstacle is coupling, not the threshold, so the coverage map matters as much as the indications. Hold contact at 300 mm/s, keep the Section 11 floor, and read the data gaps before reading the voids.