The MW 50 System as an Alternative to the GM-1
Bf 109 G-10 W.Nr 490 617 ‘Blue 2’, Uffz. Gerhard Reiher, 8./JG 3, Alperstedt, 1944. Behind the circular antenna on the spine, a triangular label is visible adjacent to the MW 50 filling point [Martin Reiher]
in the Bf 109G and K
Text: Pavel Raška
This technical discussion supplements the article describing the GM-1 system in the Messerschmitt Bf 109 in the November, 2024 newsletter.
Even before World War II, Dr. Otto Lutz (1906-1974) came up with the idea of injecting nitrous oxide into an engine to increase performance. He later published (as late as 1942) a scientific paper on the subject "Über Leistungssteigerung von Flugmotoren durch Zugabe von Sauerstoffträgern", or roughly translated, ‘On increasing the performance of aircraft engines through the addition of oxygen compounds’.
Just before World War II, BMW engineers Dietrich Singelmann (1903-1989) and Helmut von Zborowski (1905-1969, a native of Terezin) began to independently experiment with the injection of a mixture of water and methanol. They discovered that by mixing water with methanol and adding a drop of an anti-corrosion additive, they obtained a problem-free liquid that, unlike nitrous oxide, could be stored in ordinary canisters at an airfield. Although it was not recommended as a drink, it does not normally burn or explode and generally exhibits benevolent properties. The 1:1 ratio of water to methanol proved to be the most advantageous not only in terms of engine performance, but also against the risk of the mixture freezing. The injection of water and methanol was first tested in 1939 on the Bramo 323-A engine. Later, both gentlemen devoted themselves to the development of rocket engines.
The GM-1 system described in our previous article was not very popular among fighter pilots, it could not be used at lower altitudes and it was deemed just ‘dead weight’ which worsened flight performance. The situation was better for high-altitude reconnaissance units. Readers of Clostermann's ‘The Big Show’ will certainly remember the duel between Spitfires and the Bf 109 at high altitude. The Bf 109 was equipped with the GM-1 system, but its pilot made the mistake of trying to save himself by diving. However, just above sea level, the GM-1 could not be used and the reconnaissance Bf 109 ended up being shot down over the ocean.
The wreckage of Bf 109G-10 WNr. 151556 from JG 300 and Bf 109G-14AS WNr. 784998 from IV/JG 53 after emergency landings in early 1945. Both aircraft show open MW 50 fuel tank filler ports on their spines.
The new system, which was supposed to eliminate the shortcomings of the GM-1, was designated MW 50. The original thermally insulated tanks for the GM-1 were initially produced by the Büssing-NAG company in relatively small numbers at about fifty per month. The GM-1 installation used in the Bf 109G could be used for injection in the MW 50, but problems arose with valve corrosion. By installing a modified valve, the entire system could be used for one or the other mixture (GM-1 or MW 50).
The developmental experiments that were conducted yielded a second, simplified version of the MW 50 system. It no longer required the use of nitrous oxide, eliminating the need for thermal insulation of the tank. In addition, the compressed air bottles in the wings were eliminated and replaced with compressed air from the compressor. This resulted in a further weight saving. The injection nozzle was replaced with a different type, because the pressure from the compressor was lower. This simplified type of MW 50 was apparently standard equipment on the Messerschmitt Bf 109 G-14 and G-10. A characteristic modification of the design, visible even to modelers, is the square ‘box’ behind the pilot's head, covering the battery. In the later development variant of the Bf 109 K, the internal equipment was redesigned and although the MW 50 was standard, the aforementioned box behind the pilot's head disappeared, because the battery was moved to another place within the fuselage. The MW 50 tank could also be used as an additional fuel tank in the K version. There was a MW 50/Kraftstoff switch on the instrument panel and depending on its setting, the relevant valve switched either to inject the mixture into the compressor or to pump the contents into the main fuel tank. Of course, it was important to pay attention to the position of the switch depending on the contents of the tank.
At this point, it is necessary to take a detour and discuss the Messerschmitt fuel system. The aircraft were equipped with an L-shaped fuel tank with a capacity of 400 liters located under and behind the pilot's seat. The Bf 109 E version had a sheet metal tank, while a new special rubberized self-sealing SB Sackbehälter tank was developed for the F version. This SB was also developed for C2 fuel used with the DB 601N engine, but in normal operation, C3 gasoline was used, which caused unexpected problems with the DB 601N. Finally, after a long time, it was discovered that in the rubberized SB tank, C3 gasoline chemically reacted with the tank material, which degraded the gasoline used. Therefore, the SB tank had to be modified so that this reaction did not occur. Some Messerschmitt Bf 109s of the F version were still equipped with the older sheet metal tank on the production line. The additional three-hundred-liter droptanks were not equipped with a fuel pump and compressed air from a compressor was blown into the auxiliary tank to move fuel from it into the main tank. When the tank for the MW 50 was filled with fuel, the valve was set to pump its contents into the main fuel tank and the pumping was again done with compressed air. With the droptanks and the MW 50 filled with fuel, the Messerschmitt Bf 109 could double its range. In the Czechoslovak Avia S-199, the MW 50 tank was used exclusively as a fuel tank.
Bf 109K fuel system diagram from a period manual with the MW 50 mixture tank indicated.
The protrusion on the access hatch to the battery and additional storage compartment allowed for the former’s relocation forward, which freed up space for the MW 50 tank in the fuselage behind the cockpit. Bf 109G-14, Oblt. Rolf Schlegel 10./Jagdgeschwader 4, March 1945 [JG 4 Archive - Museum of the Air Battle over the Ore Mountains on September 11th, 1944 in Kovarska]
Notes and clarifications to the November, 2024 article:
- The code word MONA used for the very first version of the GM-1, refers to, according to Baumgartl, da Vinci’s Mona Lisa. It would appear that the model inhaled some nitrous oxide gas, resulting in her mysterious smile, once and for all solving an age-old riddle at last!
- I had some reservations about the circular tank of the GM-1 for the F-4/Z version of the Bf 109. Baumgartl states that there really was a GM-1 tank made of thin sheet metal wrapped with piano wire, but he doubts that it would have made it into production aircraft. Those who remember will certainly recall the glass siphon bottles with metal mesh popular under socialism, filled with carbon dioxide cartridges - the principle is the same and the container withstands internal pressure well.
A little bit of a glossary:
Sonderstoff = A special material (used specifically with the GM-1 or MW 50 systems)
Kraftstoff = Fuel
Sauerstoff = Oxygen
Behälter = Tank
Leistung = Performance