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From Sam Chui's video, there are tiny circles on the surface of three fan blades of next generation Trent 1000 engine. Why aren't they present on remaining fan blades? Below comments suggest they are for optical purposes. What optical information can be inferred from these circle?

My prediction: They are embedded explosive charger to test explosion testing(specifically Blade off testing of an engine.

enter image description here

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  • $\begingroup$ At about 14:11 in the linked video the engineer talks about installing an explosive bolt to test engine containment. He's not referring to the small circles, so whatever they are for, it's not that! $\endgroup$
    – CatchAsCatchCan
    Commented May 20, 2020 at 12:01
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    $\begingroup$ Explosive charges would be at the root of the blade, not distributed of the entire Surface. They could be static pressure measurement points or strain gauges. But I suspect they are markers for an optical measurement system. $\endgroup$
    – DeltaLima ♦
    Commented May 20, 2020 at 12:01
  • $\begingroup$ my guess is that they're nails to keep the blades in place with the frame, but I'm not sure. $\endgroup$
    – Air Canada 001
    Commented May 20, 2020 at 14:23
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    $\begingroup$ @DeltaLima since they are on both the composite painted surfaces and the stainless leading edges I'm going with stickers for some optical purpose also. $\endgroup$
    – John K
    Commented May 20, 2020 at 14:35
  • $\begingroup$ I'm guessing that they are all on a slightly different radius. That would make it easier for a laser to focus on one at a time and so measure defomation/vibration under load at that point. $\endgroup$
    – Martin James
    Commented May 24, 2020 at 6:25

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These are certainly targets for an optical CMM (coordinate measuring machine) using laser, structured light or stereoscopy. The targets help define common points on the model from one scan to the next.

@mins linked a perfect example of this in his comment below, from which this image is taken. When doing 3D scanning, you want the dots in a random pattern as in the OPs image, rather than the uniform pattern seen below. This helps the identify and match the dots when going from one scan to the next (called "tie-points"). For the vibration analysis process linked by @mins, the requirements are probably different as the camera doesn't move, so it makes sense to place the dots in a grid pattern. Source https://www.gom.com/metrology-systems/aramis.html

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    $\begingroup$ @eleventyone: I think the poster means "It is 100% certain that these are targets..." $\endgroup$
    – TonyK
    Commented Aug 8, 2020 at 11:35
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    $\begingroup$ So do I, but what I think is irrelevant. $\endgroup$
    – eleventyone
    Commented Aug 8, 2020 at 11:36
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    $\begingroup$ Likely used with ARAMIS sensors and software for deformation/vibration analysis. $\endgroup$
    – mins
    Commented Aug 8, 2020 at 13:30
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    $\begingroup$ Before anyone comments that they seem to be randomly placed: the "randomness" makes it possible to identify each blade from a scan. The blades are also numbered, but this pattern variation is another blade indentification method. $\endgroup$
    – Jpe61
    Commented Aug 8, 2020 at 17:30
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    $\begingroup$ You updated you aswer just as i posted my comment 😂 $\endgroup$
    – Jpe61
    Commented Aug 9, 2020 at 18:28

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