Can military drones fly high enough to not be heard?

Military drones vary in size and performance. Some are carried in a tube in a backpack and are used at low levels to let soldiers see over the next ridge. They might be heard, but they are very quiet. read more

In the USA if you’re flying as a hobbyist, and not within 5 miles of an airport, there isn’t a height restriction as long as you maintain VLOS (visual line of sight) of your drone. read more

The FAA Advisory Circular 91-57 is one page, dates all the way back to 1981, and states simply that model aircraft operators – in this case people flying drones – cannot fly their crafts more than 400 feet above the ground, must keep them within sight, and should not operate within five miles of an airport without first informing the airport’s operating authorities or aircraft control tower. read more