DKW's Remarkable Streamliners

The incredible photo below was taken on October 26, 1938, during ‘World Record Week’, a week of racing sponsored by the Ministry for Sport in Nazi Germany, on the new autobahn just outside Frankfurt-am-Main.  It’s a fairly straight and flat autobahn deemed suitable for land speed racing, and I presume the ‘Record Week’ meant that the various car and motorcycle factories had access to the autobahn for a period of time during each day, and the timekeeping facilities/staff were kept on hand full-time.

DKW participated 500cc model (a supercharged two-stroke twin of course, since that’s what the factory was racing at the time), and the body was designed by streamlining expert Baron Reinhard von Koenig-Fachsenfeld, the inventor in 1936 of the chopped tail on cars (later called the ‘Kamm’ tail after Wunibald Kamm developed the idea). The Baron used windtunnel testing at F.K.F.S. in Stuttgart – home of DKW – to find vehicle shapes with minimal drag. The tail on this bike (not a ‘Kamm’ tail – that was designed for cars as a production compromise to ‘ideal’ streamlining) features a novel ‘air brake’; the end of the tail fin has two flaps which can spread out to create drag.

I don’t know if those flaps are hydraulic, or if the rider had a ‘brake pedal’ to push, or perhaps even linked braking, as seen on Rudges of the period. There were aerodynamic problems with the DKW’s full enclosure, though, and a combination of handling issues (the record runs in ’38 had to be abandoned due to prevailing winds), and poor rider visibility/fumes/discomfort while sealed into the ‘egg’ put paid to this remarkable shape.

Thus, in later runs, the top of the streamliner was cut off, to the level shown on the pic above. This version still had handling issues, and the enclosure was cut down further to the shape seen below; interesting as this progression presages the trend from ‘dustbin’ fairings to ‘dolphin’ fairings in GP racing, post-war. Dustbins and other front-wheel enclosing streamliners are extremely sensitive to side winds, and can be dangerous at high speeds. Leaving the front wheel ‘in the breeze’ makes a huge difference to the ability of the machine to take an angular blast of wind, and remain stable enough to make course corrections.

Several factories in Europe experimented with enclosures on their fastest machines during the 1930s, most famously BMW and Gilera, and put up some very fast speeds before the War – almost 200mph from 500cc ohc engines.  They are amazingly sculptural, but not especially stable!

DKW began building motorcycles in 1922, the 142cc Reichsfahrmodell, and by the 1930s was the largest motorcycle factory in the world.  They always used two-stroke engines, even in their automobiles, designed by Hugo Ruppe originally.  Ruppe’s racing engines used the ladepumpe system, using an auxiliary piston to force the gas/air mix into the combustion chamber via the crankcase – a kind of two-stroke supercharging.  When Adolf Schnürle developed a new porting system for two-strokes (as used on every two-stroke motor since, and to this day) DKW were the first to license the technology in 1932, with Arnold Zoller adapting the design for DKW. Schnürle’s patented porting system, when used with a tuned exhaust (or better, with expansion chambers), produced excellent fuel scavenging principles and much more power than a four-stroke engine: they’re the reason why all GP bikes turned to two-stroke motors by the 1970s!

But for racing, the Schnürle system was problematic, especially with a supercharger, which blew the fuel mix right through the combustion chamber and out the exhaust pipe.  DKW’s solution was a split-piston design, in which fuel was drawn into one cylinder, then pushed into another cylinder for combustion, making it possible to compress the fuel mixture for maximum power, at the expense of complication!  Thus, DKW’s ‘twin cylinder’ two stroke racers of the 1930s actually had five pistons: two pairs of split-piston combustion chambers, and one supercharging Ladepumpe!  These made wickedly fast 250cc and 350cc road racers, of the type that won the Isle of Man Lightweight TT in 1938, with Ewald Kluge riding.  The 500cc two-stroke streamliners were not ultimately as successful as their smaller siblings, regardless their wicked bodywork. After WW2, DKW continued developing road and racing two-strokes, including their remarkable ‘Singing Saw’ three-cylinder racers, featured here.