The Van's RV series has become the most popular kit-built aircraft in the world. As of April 2019, the RV-4 is the fourth most popular RV model. As of October 2019, 1436 RV-4s had been completed and flown worldwide. Richard VanGrunsven designed the RV-4 in the mid 1970s as a two-seat development of the single-seat RV-3. The RV-4 prototype first flew in August 1979. The RV-4 is a new design based upon the concepts proven in the RV-3 and is not merely a stretched RV-3. The RV-4 airframe will accept a range of engines up to 180 hp (134 kW), including the Lycoming O-360. The RV-4 has a new wing, with increased wingspan and wing area over the RV-3. The RV-4 is designed for sport aerobatics. The RV-4 has proven to be a capable cross country aircraft in service, able to carry two modest sized people and baggage on longer trips. RV-4s have been flown around the world, notably by an Australian, Jon Johanson, who completed world-girdling RV-4 flights on two occasions. Unlike most later RV series designs, RV-4 kits are only available with conventional landing gear, although some may have been constructed in tricycle configuration by builders. At least two RV-4s have also been built with retractable landing gear (mostly for the engineering challenge, as the performance gains were modest). The Harmon Rocket is a higher performance derivative of the RV4, with clipped wings, a 300 hp (224 kW) Lycoming IO-540 engine and a razorback turtledeck.
