Walter Kaaden. 1963.

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6. Walter Kaaden

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Walter Kaaden was a German engineer who transformed the performance of the two-stroke engine by understanding the role of resonance waves in the exhaust system; this is the story of the expansion chamber, an innovation in two-stroke technology and the fasinating route this information took to reach Peter Inchley.

Working for MZ, Kaaden laid the foundations for the modern two-stroke engine; his understanding of gas flow and resonance enabled him to make the first engine to achieve 200 bhp/litre.

He put this to practice on his old DKW, which he rode to work, and transforming it into a racer by adding his home built expansion chambers. He obtained this knowledge from his work during the Second World War, on the development of the rocket pulse jet engine.

But Walter is not the whole story, but he pulled the elements together, he was born in Pobershau, Saxony, Germany. His father worked as a chauffeur, to the sales manager at the DKW factory. At eight years old he attended the opening of the Nürburgring racing circuit, a formative event to which he attributed his enthusiasm for race engineering.

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“Go MZ”, the birth of the modern two-stroke race engine.

Kaaden studied at the Technical Academy in Chemnitz, and in 1940 he joined the Henschel aircraft factory in Berlin, he worked under Herbert A. Wagner, the designer of the HS 293 radio-guided rocket-propelled missile.

Despite many reports to the contrary, Kaaden did not work on the V-1 flying bomb nor under Wernher von Braun on the V-2 German rocket program.

From 1943 he worked on the development of the HS 293 at the Peenemünde Army Research Center as a ‘flight engineer’. But the bombing of Peenemünde in World War II in August 1943 destroyed the facilities.

The Germans then moved its missile production and testing to the secure, deep tunnel network built beneath the Harz Mountains at the Mittelwerk factory.

This is where Kaaden was captured and interned by the Americans at the end of the war; afterwards he stayed behind the “Iron Curtain”.

He eventually returned to Zschopau to start a timber business specialising in roof trusses that were in great demand to renovate bomb-damaged buildings and it was here, in his spare time, that he built his first racing motorcycle, it was based on the 1939, DKW RT 125 and he raced this himself in local events, testing it on the long straight in front of the IFA factory offices.


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Ewald Kluge / DKW 350cc 1951 / Expansion Chambers / Erich Wolf

In 1953 he was called in by the IFA (Industrieverband Fahrzeugbau) management and asked about his machine, they were so impressed he was asked to take over the management of their racing department, Kurt Kampf’s IFA 125cc racers had been outclassed by Bernhard Petruschke, riding the private ZPH (Zimmermann-Petruschke-Henkel) machine and they wanted to do something about it.

Like IFA, engineer Daniel Zimmermann had based his ZPH engine on the pre-war DKW RT 125, which he heavily modified by adding a disc valve, this allowed asymmetric port timing, with a longer duration inlet phase.

Zimmermann also used a new crankshaft providing ‘square bore and stroke’ dimensions (54mm x 54mm) and used stuffing rings to boost the primary compression ratio. However, the East German government didn’t like the competition between the two East Germans and persuaded Zimmermann to reveal his engine’s secrets to Walter Kaaden at IFA. The result in 1953 was the IFA racer, which featured a rotary disc valve.

Working with extremely limited resources, Kaaden then began to develop the expansion chamber, invented by Erich Wolf (the DKW designer), which had first appeared in 1951, on the 350cc, three cylinder, DKW racers. Kaaden applied his knowledge from the experiments on the pulse jet engine.

In 1952 Kurt Kampf had copied this DKW (Dampf-Kraft-Wagen) innovation and fitted them to the IFA racers. Kaaden used an oscilloscope to examine the resonance in the exhaust system and devised profiles to maximise the engine’s efficiency.

The net result of this development programme was that by 1954, Kaaden’s two-stroke 125cc racing engine was producing 13 bhp, more than 100 bhp/litre.

This engine was further developed to produce 25 bhp at 10,800 rev/min, he had recognised the potential of harnessing the pressure waves in an exhaust to not only aid the clearance of burnt gasses, but also to pressurise the combustion chamber while the exhaust port was still open, returning what would have been wasted charge back into the cylinder.

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