Daimler-Benz DB 007 / DB 670 / ZTL 109-007 / ZTL6001
After initial studies on gas turbines in the late 1920s, Daimler-Benz lost interest in them until 1939 with the arrival of Karl Leist. Work began immediately on the DB 670 (aka ZTL 5000), a ducted fan with compressor feeding an afterburner, driven by a DB 604 X-24 engine delivering 1,864 kW (2,500 hp). At a weight of 3,748 lb (1,700 kg), with an expected thrust of 6 kN (1,323 lbf) at a speed of 900 km/h (559 mph) and altitude of 19,685 ft (6,000 m) the DB 670 was abandoned due to the very low power/weight ratio. After a brief interlude studying pulse-jets Leist began work on what was to become the DB007.
Previous design efforts in Germany had investigated ducted fans (turbofans / by-pass turbojets) and contra-rotating compressor spools, but Leist incorporated both into the ZTL6000 (precursor to the ZTL 6001 / DB 007), resulting in a very complex design. Another novel feature was a turbine which passed alternately through the combustion chamber efflux and cooling air tapped from the bypass flow. By the Summer of 1942 design goals had been revised down and the new engine was given the designations ZTL6001(company) and DB 007 / ZTL 109-007 (RLM), ZTL being an acronym for Zweikreiststurbinen-Luftstrahltriebwerk (two-circuit turbojet engine).
Air entered the engine through a conventional air intake, flow splitting after the initial guide vanes to the compressor inside and the ducted fan outside, with a by-pass ratio of approximately 2.45:1. The compressor consisted of seventeen stages of blading, eight carried on the inner drum, rotating at full engine speed, and nine on the outer drum which rotated in the opposite direction at 0.5:1 engine speed. Although extremely complicated mechanically, a compressor efficiency of 80% was expected with a very credible pressure ratio of 8:1. For comparison, typical engines of the era offered pressure ratios on the order of 3.5:1.
Further complication arose from the ducted fan which consisted of three stages of blading attached to the outside of the rotating compressor casing, with stators attached to the inside of the engine outer casing. Calculated efficiency of the fan section was 84%.
Air from the compressor passed to the four linked tubular combustion chambers, spaced evenly around the circumference with gaps to allow cool bypass air tapped from the by-pass duct to cool the turbine directly. Although this resulted in relatively poor turbine efficiency, at 74%, the cooling allowed a far higher Turbine Inlet Temperature (TIT) increasing the overall efficiency of combustion.
The turbine consisted of hollow nickel steel blading on a forged steel turbine wheel which drove the compressor via a hollow shaft and flexible coupling. The inner compressor drum was driven directly but a reduction gearbox drove the outer drum at half speed.
Structural materials comprised mainly of cast aluminium alloys forward of the combustion chamber and welded sheet steel from the combustion chambers aft.
Only bench testing began on a test-bed on 27 May 1943 before the program was cancelled in May 1944 by order of the RLM.
DB 007 / ZTL 6001