Blade surface pressure mapping
A strain gauge tells you the load arrived. It cannot tell you where it concentrated, or whether the peak on the trace is a real load path or the fixture touching unevenly. A pressure field separates the two.
Total force is the wrong number
A blade panel in a test fixture is loaded through pads, clamps or a press. The number that decides whether the test is valid is not the force the machine reports — it is how that force is spread across the surface. A single-point sensor placed where you already expect the peak confirms your assumption. It cannot falsify it.
What matters in practice is the ability to tell three different failures apart, and they look identical in a strain trace:
A real load concentration
A stiffness transition, a ply drop or a geometry change genuinely concentrates load. This is the case you want to find, and the one worth designing around.
A contact artefact
The pad or the fixture face touches unevenly. Total force is correct, the load path is not. Nothing about the blade is wrong; the test is.
A defect under the surface
A bond-line void or a delamination redistributes pressure locally. Invisible from outside, indistinguishable from a load peak in a single channel.
What the grid has to resolve
Pitch is not a preference — it has to be shorter than the feature you are looking for. A useful rule: the spacing between points should be at most half the distance over which the pressure gradient of interest changes.
| Build | Points | Sheets | Collectors | Why you would pick it |
|---|---|---|---|---|
| Config A | 40,960 | 10 × 490 × 520 mm | 10 × PXS064mini | Finest granularity over the full area. Best when the gradient you are hunting is shorter than 10 mm and you cannot predict where it sits. |
| Config B | 20,480 | 5 × 490 × 1040 mm | 10 × PXS064mini | Half the seams of A, collectors small enough to mount off the part. The usual choice for a full-field panel test. |
| Config C | 20,480 | 5 × 490 × 1040 mm | 5 × PXS128 | One collector per long sheet, so fewer boxes and cable runs on the fixture. Suits strip-shaped measurements such as a bond line. |
All three builds cover the same 1040 × 2480 mm surface. A long sheet still carries 4096 points (64 × 64), so its pitch along the long axis is roughly 16 mm against 7.6 mm across — a trade that suits a narrow band and not a full field.
If you cannot yet state that distance, start on a smaller area with the finest grid you can afford (Config A) instead of covering the whole part coarsely. A large map at 11 mm pitch answers "roughly where", a small map at 7.6 mm answers "exactly here" — and the second one is usually what the design review needs.
What a map changes in the decision
A pressure field does not just confirm a prediction; it localises the error. In the panel test published on this site the measured maximum sat 60–80 mm inboard of where the model put it, and it was localised rather than distributed — which meant one region could be re-examined instead of the whole panel being re-qualified.
That is the practical difference between a field and a set of points: scope. A single channel says "higher than expected". A map says "higher here, not there, by this much" — and that is a statement a structural engineer can act on without re-running the whole campaign.
The same question, already measured
Configuration, method and finding are published as delivered; the client is not named.
20,480 points across a 2.5 m² blade panel
Five long sheets and ten compact collectors merged into one continuous map over 1040 × 2480 mm, then compared against the aerodynamic model.
Where this setup stops working
Every one of these has cost somebody a re-test. They are listed here rather than discovered on site.
20 Hz is not dynamics
This is quasi-static and steady-state work: press closure, hold, creep, slow loading. Blade vibration, flutter or impact transients need a different acquisition chain and should be quoted separately.
The film measures what it touches
Thick paint, contamination or an uneven bond under a sheet reads as pressure error, not as surface condition. Surface preparation is where most of the error in a real installation comes from.
A 0.3 mm layer is part of the stack
In a thin contact the film itself changes the interface slightly. Where the gap is thinner than the film, the sensor is measuring itself; that has to be designed for or removed before the next run.
The standard range starts at 400 kPa
The published build covers 400–6000 kPa, configurable. Aerodynamic surface pressure is two orders of magnitude lower. If that is the target, the range has to be specified and validated as a separate project — this page is about contact and structural loading.
Cabling is a real constraint
Ten collectors mean ten cable runs to one PC. The layout drawing, not the sensor, is where most of the schedule risk sits.
Durability is rated, not unlimited
Over 10,000 cycles. For long-duration cycling, sheet replacement and per-sheet recalibration should be budgeted from the first day.
The parts this measurement is built from
Film, collectors and software are quoted as one chain — the sheet count follows the surface.
4096-point sensing film
Sensing principle: Piezoresistive · Thickness: 0.3 mm
Compact 4096-point collector
Model: PXS064mini · Dimensions: 90 × 40 mm
Config B — 20,480 points
Sensing sheets: 5 × 490 × 1040 mm (active 487 × 1034 mm) · Collectors: 10 × PXS064mini (two per long sheet)
One session, all sheets
Platform: Windows desktop application · Input: Multiple collectors via docking hub
Frequently asked questions
Yes. The film is 0.3 mm with a 1.5 mm sealed border (3 mm where sheets combine) and a 300 mm lead, extendable to 500 mm. It is bonded with an adhesive layer and can be covered with a protective top layer, so the aerodynamic profile is not altered. Surface preparation is the part that decides whether the measurement is worth anything.
20,480 points (Config B or C) gives roughly 11 mm equivalent pitch across 1040 × 2480 mm; 40,960 (Config A) gives about 8 mm. Choose the finer build if the gradient you are looking for is shorter than 10 mm or you cannot predict where it sits.
It is a compliant layer in the interface. In a thick contact it is negligible; in a gap thinner than 0.3 mm it is not. Where that matters, the film is used to characterise the interface and then removed, or the stack-up is designed to accommodate it.
Collectors sample at 20 Hz / 12 bit, which suits press closure, hold and creep. It does not resolve vibration or impact. If the phenomenon is faster than about 50 ms, tell us at the enquiry stage rather than after the installation.
Rated for over 10,000 cycles, and reused routinely — but each sheet is inspected and recalibrated before a new campaign, and a sheet that has been through a full cure cycle is checked before it goes back on a part.
It answers a different question. Taps give accurate absolute pressure at a handful of points; film gives a dense relative field over the whole surface. Where both are available, the film is usually used to decide where the taps should go.
Different surface, same method
Bond-line pressure, read before cure
A press reporting the correct total force can still leave half a bond line starved. The number that matters is pressure…
Contact pressure across a bolted joint
Torque is an input, not a result. Two joints tightened to the same torque can carry very different pressure…
Send us the surface and the decision it has to support
Area, peak pressure, the feature you are looking for, and what happens if you miss it. That is enough for a first assessment.