Riemann's Contribution to Flight and Laser Fusion

Effective gap-to-chord ratioFigure 1THE BUSEMANN SUPERSONIC BIPLANEBusemann's design of a drag-free supersonic wing is a classical study in shock wave dynamics. The ordinaryreflection of a shock is shown in a. The arrows show the direction of the fluid flow (the flow of air around thewing): As long as the flow is parallel to the wall (or wing), there is no shock wave. Thus, as shown in b, bybending the wall, the reflected shock can be "canceled" by an expansion at the corner.The Busemann biplane at zero lift is shown in c. As the wings travel through the air at a'velocity V 0 , part of theexpansion wave at the corner cancels the compression wave from the leading edge of the opposite plane andproduces the symmetrical pressure distribution shown. The wave drag is zero.At slightly different speeds, the waves begin to leak out, as shown in d. Busemann describes this as the wingsacting like a nozzle. The graph, e, shows the drag as a function of the geometry of the wings, along with thereflections of the shock waves required to produce the various occurrences of zero drag.Surprises like this don't go so well when you can't affordto live on less than the total amount of your salary.Question: Was there a laboratory there in Dresden?In Dresden there was a laboratory for applications ofaerodynamics for engineering turbines and things likethat. And although you weren't supposed to say it, it wasfor airplanes, too. While I was at Dresden I got invited tothe Volta meeting [the 1935 European meeting in Italy thatlaid the foundation for supersonic aerodynamics]. Andthere we could say that Dresden was working on applicationsto aviation—but for 100 years in the future. But itdidn't take long—just 10 years later Germany had a war.Question: Were you thinking of those turbines for jetengines, or was it still the aerodynamic question of wingdesign?We had supersonic wing shapes, to have less drag andlots of lift. That was the subject I got to talk about at Volta,since I had worked on that. They invited all the peoplewho had worked on high speeds to the meeting in Volta,Italy in 1935. The subject was high-speed subsonic andsupersonic flight. And they invited all the winners of theSchneider Cup to talk about how they had built theirairplanes for this special use and what their thinking wasabout engine changes, the wings, and things like that.Question: Did Germany enter the Schneider Cup race?No. We were not allowed to enter. The first race was in1913, I think, and the last one was in 1931. But during theFirst World War, there were no Schneider Cup races. Idon't know whether Germany had a chance to take partbetween 1913 and 1914; and in 1918, they told Germanyin the peace treaty, "no more airplanes anymore for you."We would supposedly only try to make war with them, toshoot things and throw things at other countries.Prandtl, Ackeret, and I were invited to Volta. Ackeretwas another pupil of Prandtl. He is now 80 years old. He'salive in Switzerland.* He talked about wind tunnels.Prandtl talked about the experience of the early years. Italked about lift at supersonic speeds. And von Karman[Theodor von Karman, a Hungarian scientist working inGermany who emigrated to the United States beforeWorld War II] talked about drag at supersonic speeds.* Ackeret died March 27, 1981 at the age of 83.36 FUSION October-November 1981