02/28/2016. Remarks by Walter van Tilborg: "The Model 4 design of Drago K. Jovanovich and his J.O.V. Helicopters (formerly Helicopter Engineering Research Corporation) was a further development of the JOV-3 Proof of Concept aircraft. It attracted attention of the McCulloch Motors Corporation and Jovanovich joined the McCulloch Aircraft Corporation in 1951. When it became apparent that the MC-4 would not enter production, Jovanovich founded in 1957 his Jovair Corporation and in 1960 re-acquired the rights to the MC-4. Jovair then continued development and launched an improved four-seat version under the name Sedan. Although the Model 4E was type certificated, it did not enter production.

MC-4: This was the first aircraft built by McCulloch and was a two-seater with an 165 hp Franklin 6V4-165-B32 engine. The aircraft differed externally from the JOV-3 aircraft in having a redesigned inward sloping wind screen. The aircraft was first flown in March 1951.
MC-4A: McCulloch company designation reported for the USN HUM-1.
MC-4C: This improved three-seater had a 200 hp Franklin 6A4-200-C6 engine and it had prominent auxiliary tail surfaces to which so called endplate rudders were added.
4A: Stripped down utility version developed by Jovair Corporation and featuring an uncovered fuselage and cabin section. This variant first flown in prototype form in 1962 and was mainly intended for use as agricultural aircraft, as trainer or as flying crane with under slung loads. Only the prototype was completed and this had a 210 hp Franklin 6A-335 engine.
4E Sedan: First flown in 1963, this was the MC-4C modified by Jovair into a four-seater. Externally it differed from the MC-4C in having a redesigned sloping rear fuselage and different cabin window arrangement, but it retained the tail with endplates of the YH-30s. This aircraft was powered by a 210 hp Franklin 6A-335 engine.
YH-30: Designation for three aircraft of the MC-4C model ordered by the US Army for evaluation and built by McCulloch. One YH-30 aircraft later went to the US Army Aviation Museum.
HUM-1 (XHUM-1): This designation was used for two aircraft USN evaluation. Under the company designation MC-4A these were built in 1953 by McCulloch and based on the MC-4C/YH-30. Engine was also a 200 hp Franklin 6A4-200-C6. The HUM-1 aircraft later joined the collection of the Pima Air & Space Museum, Tucson, Arizona (BuNo. 133817) and Yanks Air Museum at Chino, California (BuNo. 133818).

The Jovair Model 4U dedicated crop sprayer version and Model 4ES Sedan were not built. The production rights for the Model 4 Sedan were sold to Hughes, but no further aircraft were produced. "