Complex sentence: The original Cougar design was marketed by Nesmith himself, but when a modified Cougar won an Experimental Aircraft Association (EAA) design competition in 1963, that organization took over selling plans.
Split into simpler sentences: The original Cougar design was marketed by Nesmith himself. When a modified Cougar won an Experimental Aircraft Association (EAA) design competition in 1963, that organization took over selling plans.