Operating UAS In Certain Airspace
§ 107.41 Operation in certain airspace.
(a) A small unmanned aircraft may not operate in Class A airspace.
(b) A small unmanned aircraft may not operate in Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless the operator has prior authorization from the Air Traffic Control (ATC) facility having jurisdiction over that airspace.
Here is a graphic of national air space (NAS) classifications:
Class A is 18,000 feet and above
Class B is from the surface up to 10,000 feet above ground level (AGL) over the busiest airports. It looks like an upside down wedding cake. All aircraft have to have air traffic control (ATC) permission to operate in Class B
Class C is generally from the surface up to 4,000' AGL at less busy airports, such as Des Moines, Moline, Springfield, MO, etc. You have to have ATC permission to enter Class C. It also looks like an upside down wedding cake. The inner core is from the surface to 4,000' AGL in a radius of 5 nautical miles from the airport and from 1,200 AGL to 4,000 AGL in a 10 NM radius from the airport.
Class D is around smaller towered airports like Dubuque, Waterloo, Rochester, MN, and is a cylinder from the surface to 2,500' AGL in a 5 NM radius from the airport. You have to have ATC permission to enter.
Class E airspace is controlled airspace other than the above. It may start at the surface, at 700' AGL or 1200' AGL and sometimes at other heights. You need to consult an aviation chart to know. Class E goes up to the next lower letter of controlled airspace.
Class F - there is none in the US NAS
Class G - uncontrolled airspace. Whatever is left. You can fly UAS here within other limits without asking ATC.
Many smaller airports with no tower are in Class E airspace. That is so they can have an instrument approach for airplanes. Examples would be Mason City, IA, Iowa City, IA and so forth. A small grass strip may be in Class G airspace.
For each commercial UAS operator, the question is would you need to operate within 5 nautical miles of an airport in Class E airspace? You have to consult an aviation chart to know where that is.