Would a fiber optic FPV drone actually be useful for anything civilian?

The short answer is yes, a fiber tether setup is designed specifically for situations where radio frequencies are unusable, so your culvert issue is exactly the type of problem it solves. Standard 5.8GHz video and control signals simply cannot penetrate dense earth or long stretches of metal utility conduits, and that's where the fiber comes in. The tether itself is the link, carrying high-speed data from the drone's onboard camera back to a ground unit, completely bypassing the RF limitations that trip up typical FPV setups. While it might sound like something pulled straight out of a military spec, the practical civilian applications are focused heavily on infrastructure maintenance and inspection. Beyond storm culverts, these things are being used for assessing large industrial facilities, like those with heavy electromagnetic interference, or for internal surveys of massive, structurally complex spaces like shipping yards or decommissioned industrial silos. If you're looking at utility inspection, you could use it for checking integrity in bridge underpasses or complex underground drainage systems, which is a niche but real market.

As for whether it's clunky for a hobbyist, it depends entirely on how you define 'hobby.' This isn't a quick weekend setup you throw in a bag; it's specialized gear. The hardware involves a more complex tether system and specialized data processors on the ground. These drones are generally treated as professional inspection tools because of the engineering required to handle the fiber transmission while maintaining flight stability and managing the cable tension. Cost-wise, you're looking at a significant investment, more like professional surveying equipment than a consumer RC kit. If you're serious about the concept, look into commercial drone services that offer these advanced inspection capabilities rather than trying to source the parts yourself. The technology isn't just about better signal; it's about providing reliable, high-definition visual data inside environments that are otherwise impossible to safely or practically survey.

One thing I'd add is that the spool itself changes how the drone flies, since you're effectively towing a tail that catches on every rough edge and puddle, and a snapped fiber means instant total loss of link. A buddy let me fly his at a field day last year and even in open air you could feel the drag making the pitch feel sluggish compared to a normal quad. For a culvert specifically I'd honestly try a push-rod sewer inspection camera first, because unless your drone can hover in a confined tube against who knows what water flow, the flying part might be the harder problem than the signal.

For your culvert specifically, think about wether you even need flight. I do drain surveys as part of my job, and a push-rod crawler on a wheeled cart goes places a quad just can't, since there's no rotor wash kicking up silt and no spool dragging through standing water. I've pushed 300 feet of cable down a 24-inch line without much drama. A drone in a pipe that size has almost nothing to gain over a crawler, and the fiber tether gear costs multiples of what a decent push camera runs. The fiber rigs really earn thier keep in big open underground spaces like reservoir chambers, where there's room to actually fly.

Update: the push-rod crawler idea is where my head's at now. Renter-friendly question though, does anyone actually rent those drain cameras, or is it mostly a buy-your-own deal? My culvert's maybe a one-time look unless it turns out something's wrong down there. Also that point about rotor wash kicking up silt makes total sense, my quad allready stirs up enough muck on gravel to see it clearly.