On May 23, 1928, the group took RAK 2 to the Avusring near Berlin. In front of 2000 spectators, the world's press, politicians and celebrities Fritz von Opel himself took the wheel. Pressing the firing pedal eight times, he accelerated to a record-breaking 148 mph in just over a mile. By that time Fritz was struggling to keep control, and when the front end started to lift dangerously he shut the car down, pulling up to applause from the crowd - and a kiss from actress Lillian Harvey.
Although it's been suggested Opel were only in it for the publicity, the group had always made it clear that rocket cars were just a first step. In a short speech after the run von Opel said "We also want to investigate the effect of acceleration on the human body - the final stage in our project will be to produce manned rocket propelled space ships". The publicity from the event more than repaid every pfennig that Opel had invested, and gave a significant boost to the then fledgling science of rocketry.
Further rocket car experiments followed. In June 1928 RAK 3, a rail mounted car with 10 rockets, set a new record for rail mounted vehicles at 158 mph watched by 20,000 spectators, before being destroyed on its second run. In the summer of 1928, RAK 4 - another rail car - was wrecked when a rocket exploded on ignition, setting off all the other rockets and making the car jump the rails. The railway authorities banned further tests, but by then the group had moved on, buying a glider christened Ente (duck), which they fitted with two 44 lb thrust rockets.
On June 11 1928 Ente flew just under a mile under rocket power, although on its second flight a rocket exploded, damaging the wing and setting the plane alight. Undeterred, von Opel commissioned Julius Hatry, a well-known glider builder, to make a bespoke rocket powered craft, the Opel - Sander - Hatry RAK 1. On June 30, 1929, RAK 1 flew two miles in 75 seconds, reaching 90 mph, before being destroyed in a crash landing.
That was the last time Fritz von Opel piloted a rocket-propelled vehicle, and soon afterwards the group separated, almost certainly as a result of changes at Opel. Perhaps realising what was soon to happen in Germany, the von Opels sold the company to General Motors later in 1929. Max Valier continued to experiment with rockets, moving from black powder to liquid fuel motors; he built two further cars, but was killed when a liquid fuel motor exploded on a test bed in 1930. Sander was twice arrested by the Nazis, who coveted his rocketry interests, and died in prison in 1938. 'Rocket Fritz' moved to Switzerland after the sale to GM; he lived until 1971, long enough to see the first manned landing on the Moon.