The Opel RAK.1 (also known as the Opel RAK.3) was the world's first purpose-built rocket-powered aircraft. It was designed and built by Julius Hatry under commission from Fritz von Opel, who flew it on September 30, 1929 in front of a large crowd at Rebstock airport near Frankfurt am Main. The RAK.1 plane was part of a series of rocket-powered vehicles that were developed and demonstrated within the Opel RAK program, the world's first large-scale rocket program. The idea to build and race a rocket-powered car as an intermediate step to realize rocket-powered aviation and even spaceflight was suggested to von Opel by Max Valier. After the World War I, Valier became highly interested in rocketry. Valier, in 1927, he was one of the co-founders of the German Verein für Raumschiffahrt, or "Spaceflight Society", a group of later highly influential scientists who would play a major role in making rocket spaceflight a reality. As an early spaceflight advocate, Valier was more interested in publicizing rocketry than marketing Opel automobiles but came to the conclusion that building a successful rocket-powered car would achieve both goals. Von Opel confirmed his interest in realizing Valier's proposal. On behalf of von Opel, Valier eventually contacted Friedrich Wilhelm Sander, a German pyrotechnical engineer who, in 1923, had purchased H.G. Cordes, a Bremerhaven firm famous for its manufacture of black-powder rockets used mainly for harpoons, signal devices and similar devices. Opel, Sander and Valier joined forces and combined into one entity the financing, the theoretical knowledge, and the practical capability necessary for success. Moreover, von Opel, Valier, and Sander said from the start that their experiments with cars were only a prelude to grander experiments with air- and spacecraft: They agreed on the final goal for Opel RAK of working on rocket-powered aircraft at the same time they were building their famous rocket cars, as pre-condition for the anticipated spaceflight application.
Preparatory work on rocket-powered land vehicles The group went to an Opel race car, “RAK 1.” The RAK 1 demonstrator was stripped of its engine and radiator to reduce weight. To help keep the car’s wheels on the ground at expected high speeds, the group attached behind each front wheel a small, wing-like stub, set at a negative angle of attack. For propulsion, they elected to use 12 black-powder rockets, mounted in four rows of three rockets each and ignited electrically. The propellant, similar to gunpowder, burned in a subsonic deflagration wave and not in a supersonic detonation wave. A demonstration for the press on April 11, 1928, in Rüsselsheim was arranged: Opel engineer and race driver Kurt C. Volkhart developed and tested the Opel-RAK 1, a converted racing car equipped with Sander rockets instead of an internal combustion engine, which was the first rocket powered automobile. During the April 1928 experiments, piloted by Volkhart, RAK 1 reached the symbolic speed of 100 km/h in just eight seconds. Von Opel, Sander and Valier were satisfied by RAK 1’s performance, and in particular by the attracted positive publicity for the science of rocketry, but also the Opel company. Nevertheless it was clear to the RAK program leadership, they had no plans to commercially produce rocket cars for end customers, the aim was the development and demonstration of a rocket-powered aircraft. The group continued their land projects and built RAK 2, designed by Volkhart from the ground up as a rocket car. It was far larger and more streamlined than its predecessor. The RAK 2 was powered by 24 rockets packing 264 pounds of explosives. On May 23, 1928, Fritz von Opel himself demonstrated the car, Opel RAK 2, on the Avus Speedway near Berlin. Prior to the start Professor Johann Schütte, Chairman of the Scientific Society of Aviation, and Fritz von Opel held prophetic speeches on the future of rocket-based aviation and spaceflight. After these introductory remarks, mechanics August Becker and Karl Treber then took the tarpaulin off the Opel RAK 2 and carefully pushed it to the start. Eventually the rockets were installed and connected to the ignition mechanism. Police cleared the AVUS track and von Opel drove the RAK 2 car to a record-setting speed of 238 km/h, successfully mastering the challenge of insufficient downforce from the wings for these velocities. The RAK 2 rockets were operational for a ride of circa three minutes, watched by 3,000 spectators and world media, among them Fritz Lang, director of Metropolis and Woman in the Moon, world boxing champion Max Schmeling and many more sports and show business celebrities: A world record for rail vehicles was reached with RAK3 on June 23, 1928, with the car attaining a top speed of 256 km/h over a 5-km stretch of straight track near Hanover. Some 20,000 spectators watched RAK 3 breaking the existing world speed record of railcars by nearly 40 km/h. The resulting international publicity after RAK2 and RAK3 demonstrations was enormous and gave the science of rocketry a major boost. A replica of the RAK 2 rocket-propelled car is on display at the Opel museum in Rüsselsheim, another one at the "Deutsches Museum" in Munich.
Pioneering phase at Wasserkuppe Mountain
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