Section 51F. Any airport commission may let or lease, for a period not exceeding twenty years, those land areas at any airport under its control which are used for airport purposes, under such terms and conditions as it may prescribe, for hangars, shops, storage, industrial purposes, offices and other space rental, and for concessions, and may lease any other areas at such an airport for any purpose. With the approval of the mayor and the city council in cities or the approval of a town meeting, as the case may be, said commission may so let or lease for a longer period; provided, that no such airport in the cities of New Bedford and Beverly shall be let or leased except with the approval of the mayor and the city council, or in the town of Southbridge by vote of the town.