Otto Frenzl

Otto Frenzl (born November 12, 1909 in Graz , † November 1, 1996 in Innsbruck ) was an Austrian engineer . Frenzl is considered to be the authoritative discoverer of the area rule, which is important for aviation .

Life and accomplishments

Drawings for "Patent Specification 932 410"

Frenzl had studied electrical engineering at the Technical Universities of Graz and Vienna . In 1937 he went to the Junkers aircraft and engine works in Dessau, where he worked in the fluid engineering department under Philipp von Doepp (1885-1967). There he built a high-speed wind tunnel , the HK 900, with a cross-sectional area of ​​900 cm² and an intermittent steam jet propulsion system , and equipped it with the measurement technology. From 1942 Frenzl was directly involved in the development of high-speed aircraft.

There he discovered the connections between the area rule when he was looking for an explanation for the greater resistance of a W-wing compared to a continuously swept wing in the transonic area. On December 17, 1943, he wrote an inventor's report on the subject, entitled Arrangement of displacement bodies in high-speed flight , which was rewarded with 50  Reichsmarks . Using the measurements for the Junkers project EF 122, he describes how the critical Mach number could be increased from 0.72 to 0.77 by shifting the engine nacelles. The results of this research were presented to a broad group of interested parties in March 1944 by Theodor Zobel at the German Academy of Aviation Research in the lecture Fundamentally new ways of increasing the performance of high-speed aircraft . Together with Heinrich Hertel and Werner Hempel , he was granted patent no. 932410 on March 21, 1944, in which the principles of the area rule were set out.

From December 1943 Frenzl was involved in the planning of a much larger ejector wind tunnel in Muldenstein , which the Dinglerwerke should build.

After the war he worked at the SNECMA in Melun-Villaroche . There he built and looked after an ejector wind tunnel based on his experience with the HK 900 with a measuring cross-section of 0.4 × 0.6 m. It was used for jet engine development. In 1956 Frenzl received his doctorate from the TH Graz as Dr.-Ing. with the work flow of evaporating water in nozzles , which was based directly on his experience in the design of the ejector wind tunnels he had designed up to then. Frenzl also worked on the Sigma 4 wind tunnel, which was commissioned by the Institut Aéro Technique in 1962 with a measuring cross-section of 0.85 × 0.85 m in Saint-Cyr-l'École . In 1967 the DFVLR also began to work in Trauen with a high-speed wind tunnel with a measuring cross-section of 0.7 × 0.7 m, which was intended for the development of ramjet engines . Frenzl was also involved in this. These two systems worked with hot water in accordance with his habilitation thesis.

In the 1970s, Frenzl also took part in developing a desalination plant in Roswell (New Mexico) . In Lone Star (Texas) a dedusting system works according to a process that Frenzl was able to sell to Friedrich Krupp AG .

In 1984 he applied for several patents for the development of a stationary surf wave generator .

Publications

• About the development of intermittently working wind tunnels with jet propulsion , 1955
• Motor nacelle wing interference at high speeds (The Area Rule) , 1957
• Surfing pool as a ski slope simulator. Düsseldorf: Krammer Verlag 1977