Comment by ssl-3
Sure, they'll move around in the prop wash.
But that's fine, isn't it? If they're intended to detect fixed objects, then noticing that one or more of them have ceased to be blown around in that way may be a good way to detect unanticipated contact with a fixed object: When the signal becomes less noisy, then maybe something is in the way.
And the whiskers don't have to be all floppy like a wet noodle. I myself am thinking that something rigid or semi-rigid might be good. Perhaps something akin to armature wire, or thin spring steel. Maybe even literal bamboo chopsticks.
They can also be constrained so that they don't get sent into the props.
My little brain thinks that the drone-end of the whiskers can be attached to potentiometers, with light return springs to bring them back towards center, like the mechanism used by an analog stick on a PS3 controller.
Rigid whiskers have other sets of problems. Below someone mentioned that rigid whiskers will break when they contact objects. If the whisker is as rigid as the drone itself, it plausibly breaks the same cables that the drone breaks. You also have the problem that in the event of drone failure, you now have a spike-covered drone falling out of the sky. What kind of damage does a bamboo chopstick or thin piece of steel do when it hits someone or something at ground level at drone-falling velocity with the mass of a drone behind it?
It's quite possible that these problems are solvable and can be engineered around, that there's a whisker-based solution, but I don't see it. It's certainly not an obviously workable solution.