This is almost certainly illegal. If the hats actually hit anyone, it's possible to be sued for reckless endangerment and/or assault. If they don't, it's littering.
If you're asking dumb things like "how could a propeller hat dropped 50+ feet hurt someone?" then I encourage you to imagine getting hit in the eye by the spinning propeller if you happen to look up.
If you're asking dumb things like "how could a propeller hat dropped 50+ feet hurt someone?" then I encourage you to imagine getting hit in the eye by the spinning propeller if you happen to look up.