Question: When was the aircraft manufacturer at which Klapmeier brothers was a co-founder founded? 
Sentence (from "Klapmeier brothers"): The Klapmeier brothers, Alan Lee Klapmeier (born October 6, 1958) and Dale Edward Klapmeier (born July 2, 1961), are American aircraft designers and aviation entrepreneurs who together founded the Cirrus Aircraft Corporation in 1984.
Relevant evidence: Yes