Table schema:
CREATE TABLE table_29087004_2 (written_by VARCHAR, united_states_original_airdate VARCHAR, directed_by VARCHAR, canada_original_airdate VARCHAR)

Question: Who wrote the episode directed by Jos Humphrey that had an original Canadian air date that was unknown and a United States original air date of August 27, 2011?
SQL: SELECT written_by FROM table_29087004_2 WHERE directed_by = "Jos Humphrey" AND canada_original_airdate = "Unknown" AND united_states_original_airdate = "August 27, 2011"