The RMI-1, also known as X/H, stands as a testament to Hungary's innovation in aircraft design during World War II. This Hungarian destroyer and reconnaissance aircraft was marked by its forward-looking features in that never beend used in any domestic Hungarian aircraft design, including a full metal shell design and ambitious plans for the application of the groundbreaking Jendrassik CS–1 turboprop/gas turbine engine.
Designed by György Jendrassik in 1937, the Jendrassik CS–1 was a revolutionary propeller gas turbine engine and in some perspective it was the world's first of its kind. To keep the development of the engine hidden and prevent Germany from seizing the prototype, the engine was given a code name that implied it was for a boat ("CS" meaning boat).
The CS-1 engine was the intended powerplant for the RMI-1 aircraft and under the leadership of aircraft designer László Varga, the design of the X/H aircraft commenced in 1940. The choice of the CS-1 propeller gas turbine engine was motivated by its low structural weight and high performance, promising favorable flight characteristics for the aircraft. The construction of the airframe took place at the Székesfehérvár plant of the Aviation Technical Institute.
The development of the gas turbine engine faced challenges, particularly with the annular combustion chamber of the CS-1, leading to a halt in 1941. Despite this setback, the development of the RMI-1 aircraft persisted. Another aspect of the groundbreaking kind of work was that this project required innovative approaches to calculating the strength of shell structures and developing aerodynamic test methods for wind tunnel tests which was revolutionary aproach at the time.
To overcome the challenges with the gas turbine and keep the development of the airplane on schedule the X/H underwent some modifications, replacing the CS-1 engines with Daimler-Benz DB 605 piston engines, manufactured at WMM Csepel. Ground tests with the new engines began in the fall of 1943.
During ground testing, the X/H briefly took flight but experienced a mishap, damaging one of its landing gears. The testing had to be suspended for repairs. Unfortunately, before the repairs were completed, the aircraft fell victim to an American bomb raid in the summer of 1944.
Although the RMI-1 did not reach its full potential nor reaching the development stage to have its maiden flight due to the challenges faced during its development and testing phases, it remains a symbol of Hungary's ambitious foray into advanced aircraft design during World War Two.