Origins PH: Engine management systems
During World War II, the complexity of aircraft engines intensified at a stratospheric rate. The number of cylinders has increased, engine configurations have evolved, and new approaches have been adopted for cooling. Carburetors gave way to pressure carburettors, then pressure carburetors gave way to mechanical direct injection. Single-speed compressors have been replaced by two-speed units and the number of supercharging stages has increased; water, methanol and nitrous injection were introduced.
This rapid development led to tremendous increases in engine power. In 1936, for example, the first production Merlin V12 – with a displacement of 27 liters and fitted with an SU carburetor and single-speed, single-stage supercharging – delivered 902 hp at 2,850 rpm.
Just four years later, the Merlin XX equipped with a two-speed compressor could develop a maximum of 1510 hp at 3000 rpm. Two-stage fuel injection and supercharging, six years later, gave the powerful Merlin 130 and 131 a power output of 2,100 hp.
These production increases, coupled with the rapid evolution of aerodynamics, resulted in a dramatic change in the performance of the aircraft. Climb and dive rates exploded, straight-line speeds increased, responses improved, and high-altitude performance increased better and better.
However, pilots have often found that increasingly powerful plants can meet new challenges. In order to extract the best performance, the engines had to be carefully managed. While some aspects were often self-regulated, it was not uncommon for a variety of settings – such as fuel mixture, boost pressure, boost gears, chemical boost, water injection, fuel fuel flow and ignition controls – require pilot attention. This, too, was at the top of handling the throttle itself and, most importantly, the propeller pitch.
Combine this complexity with the ability to climb and dive further at an increased pace, requiring more frequent changes in engine settings, and pilot distraction became a real problem. More importantly, it increased the chances of the pilot selecting an incorrect configuration, especially in the heat of the moment. At best, this would lead to a decrease in performance.
BMW, busy developing radial engines primarily for transport planes and bombers at the time, suddenly found its twin-row, 18-cylinder “139” radial thrust in the limelight – as had been suggested by ‘it could power the upcoming Focke-Wulf Fw 190 The engine was dated and had its flaws, so a new iteration was offered. Four cylinders were removed, the displacement of the others was increased, and upgrades including direct fuel injection and sodium-cooled valves were installed.
This question of controlling the new “801” engine, however, was well on BMW’s radar. What the engine needed was an overall device that would regulate all the parameters required to automatically deliver the best performance. The pilot could then concentrate solely on the flight – or the fight – without having to worry about whether his plane was performing at its best; this was undoubtedly an issue raised by Focke-Wulf engineer and test pilot Professor Kurt Tank, who understood the realities of combat flight and saw automation as the key to improved efficiency.
According to BMW records, an engineer named Henrich Leibach then presented a solution. He proposed a device, fed by a myriad of inputs including pressure and temperature, which would manage the engine and its auxiliaries. The resulting mechanical-hydraulic analog unit, first used in production engines in 1939, was called Kommandogerät – “Control device”. It was, as noted in later studies of the units captured by American engineers, a real-time “automatic engine control system”.
The Kommandogerät had some 30 inputs and outputs – fuel flow control, propeller pitch, compressor settings, timing and flaps for the oil cooling ducts – and reduced the pilot’s engine control input to a single the sink. The 81.8-liter 801, with two-speed supercharging, developed 1,622 hp at 2,700 rpm so equipped. By the end of the war, development had brought the power of the popular radial to nearly 2,435 hp.
Either way, with its 801 engine fitted with Kommandogerät, the pilots had a much easier time piloting the new Fw 190 than they would have with the previous arrangements. The ‘Flight’ magazine, reporting the aircraft’s early developments, was less impressed. “Although intelligently designed,” he said, “the ‘manual gearbox’ was certainly built with total disregard for economy considerations. ‘
While somewhat neglecting the size and capabilities of the unit, the assessment was not incorrect – as high fuel consumption was deemed to be a potential issue with the Kommandogerät, as the boost and mixture could not be manually adjusted to provide maximum range when cruising. It was also extremely complicated, expensive and prone to waves, which made formation flying difficult. Additionally, damage could result in total loss of control, rather than system failure.
Despite this, other manufacturers have taken note. This advanced radial, with its innovative single lever control, showed that complete “engine management” systems could work. Efforts were made to develop similar systems for some allied fighters, but the rapid transition to much more mechanically simpler jet engines apparently led to most approaches being shelved.
Analog electronic controls were introduced later for jet engines, followed by digital units. By the early 1980s, advances in solid-state electronics meant that complete engine control units – capable of handling both fuel, sparks, and other variables – were feasible for automotive applications. Although far removed from the Kommandogerät, the basic concepts of simplifying control, automating and improving performance were the same.
By the way, in a copy of Flight magazine from 1945, Bristol engineer Sir Roy Fedden – responsible for one of the many investigations into German aeronautical engineering after the war – made special mention of the Kommandogerät at the following a visit to BMW. He said the “special single lever control for this engine combination” was “definitely a very good job”.
More importantly, he was also surprised by BMW’s proposal for a variable valve timing arrangement – which, unbeknownst to him, predated the company’s “VANOS” automotive variable valve timing system by 47 years.