The board shall have power and authority, under conditions herein set forth, to appropriate money from the general fund or from the gasoline fund for the construction and maintenance of any airport project within the county, and may participate in any such project sponsored by any incorporated town or city within the county, and in the purchase or lease of land therefor, provided and upon conditions that the board is given representation on any board or committee named or selected for the purchase or lease of land therefor, or authorized and empowered to construct and maintain such project, and further, that any land acquired or leased for such project shall be leased or purchased with the county as joint lessee or owner.