Opel RAK.1
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.
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.
On behalf of von Opel, Valier eventually contacted Friedrich Wilhelm Sander, a German pyrotechnical engineer who, in 1923, had purchased H.G.
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.
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.
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.
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.
After testing at Wasserkuppe, in June 1928, Fritz von Opel had purchased an Alexander Lippisch-designed sailplane, the Ente, and fitted it with rockets.
Before a large crowd assembled outside of Frankfurt, the intrepid von Opel made a successful flight of almost 3.5 km in 75 seconds, reaching an estimated top speed of around 150 km/h.
The Mannheim Museum of Technology, Technoseum, has a replica of RAK.1 as the world's first dedicated rocket-plane on display, the execution of which Julius Hatry himself supervised.
According to Frank H. Winter in SPACEFLIGHT magazine,[9] the initial plan was a course from Frankfurt to Rüsselsheim, site of the Opel Automobile Works and about 16 km due southwest.
As for the press and public, von Opel this time sincerely wished to keep them within limits, "to avoid any possible trouble with the unruly crowds."
According to Winter, von Opel had invited a few newspaper media and granted exclusive American rights to The New York Times and Fox Movietone for filming.
Nevertheless, Universal Newsreel of the US also found a way to report on the flight with film footage as "Speeds through air in rocket airplane - Fritz von Opel, millionaire daredevil, goes one and a quarter miles in flying inferno".
Winter reports on a comment by von Opel: "Felmy's willingness to risk his position to protect my first rocket flight from bureaucratic prohibitions is something I will never forget."
"...For today's flight I have trained for a year... For an hour before this morning's start I inspected the course and personally went over every detail of the plane — cables, fittings and rockets...
At a speed of 80 mph (129 km/h) this was a difficult feat, and Opel hit the ground with a crash as the landing-skid broke and the cockpit floor was shaved away, leaving him hanging by his safety-belt with an inch to spare."
Officially, von Opel had been aloft for an estimated 75 seconds, attaining a maximum velocity of 95 mph (153 km/h) and had traversed a distance of circa 3 km.
Sander was eventually engaged in the 1930s in German military projects under General Walter R. Dornberger but was imprisoned for treason by the Nazis and forced to sell his business, he died in 1938.
The experiments, not only the first rocket-powered flights but also the speed records of the land vehicles, were described in the media as the start of a new era: »… Nevertheless, few, if any, among the many thousands of onlookers who witnessed the demonstration on the AVUS track could help but feel that we are poised at the beginning of a new era.« (…) P. Friedmann, Das Motorrad No.
12/1928, June 9, 1928 »The amazing thing about Opel’s rocket run on the AVUS track in Berlin is not just the daring feat itself, but its aftermath: Both the public and academics have finally seen the light and have begun to believe in the future of the rocket as an engine for new rapid transit devices.« Otto Willi Gail, Illustrierte Zeitung, Leipzig, 1928 Opel, Sander, Valier and Hatry had engaged in a program that led directly to use of jet-assisted takeoff for heavily laden aircraft.
The German Reich was first to test the approach in August 1929 when a battery of solid rocket propellants supported a Junkers Ju-33 seaplane to get airborne.
The Opel RAK experiments excited also the interest of the German military, which provided funding for further development of rockets as a replacement for artillery.
Walter J. Boyne, Director of the National Air and Space Museum in Washington, DC, concluded "Working together, von Opel, Valier, and Sander had thrown a big rock of publicity into the mill pond of science.
