WACO began production of their C-series 4-seat cabin bi-planes in 1932 and continued building the popular aircraft in various versions up until 1942. The aircraft were popular corporate aircraft and could be considered the “Learjets” of their day. Beginning in 1935, the company restyled the C-series as the Standard or S-series and introduced a new Custom series. One of the features of the WACO company was a wide variety of choices available to the buyers. Multiple engine and airframe styles resulted in a bewildering assortment of models each with its own three letter designation. The first letter refers to the type of engine installed, the second is the reference letter of the set of plans used to build the aircraft, and the third letter is the model series. Numbers referred to the number of designs in the model series. Thus, the ZKS-6 is a Jacobs L-5 powered Standard cabin bi-plane of type K and is the sixth model in the series.
WACO factory paint scheme, 1936
Pima Air & Space Museum