The three kinds of blade robot
External drones. A drone flies the length of each blade and photographs the surface. It is fast, needs no one on the blade, and produces good images of erosion, surface cracks, coating damage and receptor condition. It sees the shell, not the structure behind it.
External crawlers. A robot that attaches to the blade surface and moves along it, usually lowered from the nacelle or hub. External crawlers carry cameras and increasingly repair tools, so a leading-edge repair can be done without a rope technician. They also work on the shell.
Internal crawlers. A robot that enters the blade through the root hatch and drives along the inside, recording the shear webs, bond lines, spar caps and lightning conductor. This is the only robot type that inspects the load-carrying structure, and it is the one this article is mostly about. Detectra is an internal crawler.
What an internal crawler does that nothing else can
The alternative to an internal crawler is a technician in a confined space. The comparison is straightforward:
| Technician from the root | Internal crawler | |
|---|---|---|
| Reach | A short way past the root | Up to 80 % of the blade length |
| Person in the blade | Yes | No, the operator stays at the root |
| Record | A set of photographs | A distance-tagged 8K 360° recording of the whole pass |
| Time in the blade | Hours per turbine | About 15 minutes of capture per blade |
| Repeatability | Depends on the technician | Same position, same view, next year |
The reach is the decisive point. The middle of the blade, where the trailing-edge bond carries the most strain and the section is thinnest, is where the failures that end blades start. A technician never sees it. See What an internal blade inspection covers for why.
What a crawler has to solve
An internal crawler is a harder machine than it looks. Five problems decide whether it is useful:
Getting in and moving. The root hatch and the inside of the blade are the constraints. The crawler must be light enough to lift in by hand, small enough to pass the narrowing section, and able to drive over adhesive fillets, drainage channels and debris. Detectra weighs 3.7 kg, measures 350 × 250 × 200 mm and drives on four wheels at 0 to 3 m/s.
Seeing. Inside a blade there is no light and every surface is glossy resin. A camera that has to be aimed will miss things. Detectra records the full sphere in 8K 360° video at 24 fps, so nothing is aimed at during the drive and the looking happens afterwards. Its four LED panels are switched individually, because the way to see a hairline crack in a glossy fillet is to light it from the side, not from the front. See 8K 360° video for internal blade inspection.
Knowing where it is. A finding without a position is a photograph, not an inspection record. Every Detectra take carries the distance from the root, so a finding can be located on the blade and revisited.
Getting out. A robot that cannot come back is a serious problem inside a blade. Detectra drives back to the root or is pulled back on its cable.
Working offline. There is no network inside a blade and often none at the turbine. The tablet joins the crawler's own wireless link, and recordings are stored on board. See Offshore wind blade inspections for what this means at sea.
What a crawler cannot do today
It is worth being plain about the limits.
It sees surfaces. A camera, however good, sees the inner surface of the laminate. A delamination that has not reached the surface, or the depth of a crack, needs a measurement method. That is the reason for a second generation of crawler with NDT add-ons: Quantra, targeted for 2027, and the Detectra research crawler for groups developing their own sensors. NDT for wind turbine blades sets out the methods and where each fits inside the blade.
It does not reach the tip. The last part of the blade is too narrow for any wheeled machine, and the last part is also where water collects. Drainage and tip condition remain an external and manual job.
It does not repair. An internal crawler documents. Repair inside a blade is still a technician's work, and a good record is what tells the technician where to go.
It needs the turbine stopped. As with any internal inspection, the rotor is stopped and the blade locked. The gain is that the stop is short: about 15 minutes of capture per blade.
Review still takes time. A 360° recording of a whole blade is a lot of footage. Review takes about 3 hours per turbine today, with AI-proposed candidates in Fenestra that an inspector confirms, rejects or reclassifies before anything enters a report.
How to think about the mix
A fleet that is inspected well uses all three: drones for the shell on a regular cycle, external crawlers or technicians for repairs, and an internal crawler for the structure at the points where it matters most, such as before the end of the warranty, after a lightning strike, or when an external inspection finds a trailing-edge crack. The internal crawler is the newest of the three and the one most fleets are still missing.
Frequently asked questions
What is the difference between a blade inspection drone and a blade crawler?
A drone photographs the outside of the blade from the air. An external crawler moves along the outer surface to inspect or repair it. An internal crawler drives through the inside of the blade and records the structure: shear webs, bond lines, spar caps and the lightning conductor. Only the internal crawler sees the load-carrying parts.
How far can an internal blade inspection robot go?
Detectra drives up to 80 % of the blade length from the root. The last part of the blade is too narrow for any wheeled machine.
Does a blade inspection robot need an operator?
Yes. Detectra is remotely operated: the operator stays at the root with a tablet connected to the crawler's own wireless link, drives it chamber by chamber, and brings it back. The review of the recording is done afterwards, at a desk.