Varga RMI-1 X/H; The First Turboprop…almost

April 16, 2024

In the run up to the start of the Second World War, air forces across the world were not just building up their respective strengths, they were exploring new concepts and designs that they hoped would give them the edge when conflict broke out. And the twin-engine heavy fighter was one of the ideas that just about everyone was interested in.

These offered the prospect of being able to carry far heavier armament than their single-engine brethren, along with greater fuel loads and respectable enough payloads to enable them to match many light bombers of their day.

Suffice to say, the range of aircraft that got into service or indeed were just subject to serious study ranges across the good, the bad and the ugly.

But of all these designs, one was truly innovative. Not for its expected role or performance, which mirrored that of its contemporaries, but for the fact that it was originally planned to use a previously unused idea providing it with a revolutionary powerplant.

The Hungarian Varga RMI-1 X/H; intended to be the world’s turboprop-powered aircraft.

Now Hungary doesn’t spring to mind as a powerhouse of aeronautical innovation, but in the years running up to World War Two they did have an aero industry that was building indigenous designs. They also had one György Jendrassik, a rather talented engine designer who in 1937 built an experimental gas turbine engine. With the success of this Jendrassik started work on a larger version, the Cs-1, intended to be the world’s first turboprop engine for aircraft use.

For those who don’t know, a turboprop is essentially a jet turbine, but whereas a jet engine achieves its thrust by shooting out superheated gas straight out the back as exhaust, a turboprop uses that energy to turn a propellor to provide its propulsive power. Benefits of this is that a turboprop is much more fuel efficient than a jet engine, as well as, theoretically, simpler to build.

Jendrassik projected that his Cs-1 would be able to produce 1,000hp, which by the standards of the late-1930s was about comparable to piston-engine designs, but the advantage the Cs-1 would have was that it would be considerably lighter than these conventional competitors, providing a significant advantage over more powerful but much heavier piston engines.

Certainly, the Hungarian authorities were interested enough that they decided the Cs-1 might be a splendid powerplant for a new heavy attack aircraft, and so in 1940 they commissioned the construction of the Varga RMI-1 X/H.

Even without the novel powerplant, the aircraft was pushing the bounds of the Hungarian aero industry. Intended to be a three-seat attack aircraft, the RMI-1 was the first Hungarian aircraft built entirely of metal. Armament was expected to be four fixed forward firing heavy machine guns in the wings, with three rifle-calibre weapons protecting the rear of the aircraft.

Payload was up to 300kg (660lb) in an internal bomb bay and projected speed with the turboprops was 340mph (547 km/h), a very respectable speed for an aircraft of this type in 1940.

Unfortunately, as I am sure you expected, things started to go wrong rather quickly. The Cs-1 proved only capable of producing 400hp in bench tests, despite Jendrassik’s best efforts, and in 1942, with Hungary now involved in the war on the side of Germany, it was decided that the Varga would be cancelled. Instead, a licence for the Messerschmitt Me 210 aircraft and its associated Daimler-Benz DB 605 engine would be acquired for use by the Royal Hungarian Air Force.

Unfortunately for the Hungarians the Me 210 turned out to be a bit of a lemon, acquiring a dreadful initial reputation with Luftwaffe testing units and needing substantial redesign work before it could get into service.

So, in 1943 they once again decided to look back at the Varga, and with the single prototype languishing partly completed, they decided to try it out fitted with the DB 605 piston engines they were now making. This presented fresh problems, as the Daimler-Benz was about 50% more powerful than the originally intended Cs-1’s, but also considerably heavier and with a very different centre of gravity.

Considerable work had to be done to see if the conversion could even be made to fly, but while this was ongoing the Hungarians took the opportunity to build a potential trainer aircraft closely modelled on the RMI-1 X/H. This, the Varga RMI-2 X/G, was a much simpler aircraft that used mixed material construction for simplicity and which was engined with two Argus piston engines that produced 240hp each.

This aircraft even had the privilege of undergoing flight testing, which is more than can be said for its bigger sibling.

The complexities of fitting the DB 605 to the RMI-1 meant that additional weight had to be added to the aircraft’s tail for balance, and thus it wasn’t until late 1943 that the aircraft was able to begin taxi trials. For an aircraft as cursed with misfortune as the RMI-1 this obviously couldn’t progress smoothly, and an accident damaged the aircraft.

Repairs would be necessary, but now were far from a priority because in 1944 the Hungarians began to take delivery of their home-produced Me 210Ca-1.

Somewhat ironically the delays in getting these operational meant that the Hungarian machines had had the major issues in the design ironed out and as a result they found the aircraft extremely effective, a sharp contrast to the earlier German experience with the type. Thus, there really wasn’t any urgent need for the Varga RMI-1.

Despite this, gradual repairs were made on the prototype and preparations made for flight testing to begin in mid-1944…when the final calamity befell the type. In June 1944 an American bombing raid destroyed both the RMI-1 and -2, finally sealing the fate of the aircraft.

To be honest, the chances of the RMI-1 actually getting into service with the Cs-1 turboprop were extremely slim as the engine’s design, though it had some remarkably advanced features, was just not likely to work properly – always a danger when dealing with brand new technology.

But it does lead to the Varga RMI-1 X/H being an intriguing “what-if” aircraft.

Related / Sources

https://en.wikipedia.org/wiki/Varga_RMI-1_X/H

https://hu.wikipedia.org/wiki/RMI%E2%80%931

https://en.wikipedia.org/wiki/Jendrassik_Cs-1

https://balaton-modell.gportal.hu/gindex.php?pg=3083346&nid=614830

https://aviationtrivia.blogspot.com/2015/08/the-jendrassik-cs-1-worlds-first_25.html

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