PH Origins: Engine Management Systems

During World War II, the complexity of aero engines escalated at a stratospheric rate. Cylinder counts climbed, engine configurations evolved and new approaches were taken to cooling. Carburettors gave way to pressure carburettors, then pressure carburettors gave way to mechanical direct fuel injection. Single-speed superchargers were replaced with two-speed units, and the number of supercharging stages increased; water, methanol and nitrous injection were introduced.

This rapid development led to terrific increases in engine output. In 1936, for example, the first production Merlin V12 - displacing 27-litres and equipped with an S.U. carburettor and single-speed, single-stage supercharging - belted out 902hp at 2,850rpm.

Just four years later, the two-speed supercharger-equipped Merlin XX could hammer out a maximum of 1,510hp at 3,000rpm. Fuel injection and two-stage supercharging, six years later, endowed the hard-hitting Merlin 130 and 131s with an almighty 2,100hp.

These hikes in output, in conjunction with rapidly advancing aerodynamics, led to a dramatic shift in aircraft performance. Climb and dive rates went through the roof, straight-line speeds escalated, responses improved and high-altitude performance grew better and better.

Pilots, however, often found that the increasingly potent powerplants could serve up new challenges. In order to extract the best performance, the engines had to be carefully managed. Although some aspects were often self-regulating, it wasn't uncommon for a variety of adjustments - such as fuel mixture, boost pressure, supercharger gears, chemical supercharging, water injection, fuel flow and spark controls - to require the attention of the pilot. That, too, was atop of managing the throttle itself and, crucially, propeller pitch.

Couple this complexity with the ability to climb and dive further at an increased rate, necessitating more frequent changes to the engine's settings, and pilot distraction became a real issue. More pressingly, it increased the chance of the pilot selecting an improper configuration, particularly in the heat of battle. At best, this would result in reduced performance.

BMW, busy developing radial engines primarily for transport and bomber aircraft at the time, suddenly found its two-row, 18-cylinder '139' radial thrust into the limelight - as it had been suggested it could power the upcoming Focke-Wulf Fw 190. The engine was dated and had its flaws, though, so a new iteration was proposed. Four cylinders were deleted, the capacity of the remaining ones increased, and upgrades including direct fuel injection and sodium-cooled valves were fitted.

This issue of controlling the new '801' engine, however, was well on BMW's radar. What the engine needed was an overarching device that would regulate all the required parameters to automatically deliver the best performance. The pilot could then concentrate solely on flying - or fighting - without having to worry whether his aircraft was performing at its best; this was no doubt an issue pressed home by Focke-Wulf engineer and test pilot Professor Kurt Tank, who understood the realities of combat flying and considered automation key to improving effectiveness.

According to BMW's archives, an engineer called Henrich Leibach then presented a solution. He proposed a device, fed with myriad inputs including pressure and temperature, that would manage the engine and its ancillaries. The resulting mechanical-hydraulic analogue unit, first employed in production engines in 1939, was called the Kommandogerät - 'Command Device'. It was, as stated in subsequent studies on captured units by American engineers, a real-time 'automatic engine control system'.

The Kommandogerät had some 30 inputs and outputs - regulating fuel flow, propeller pitch, supercharger settings, timing and oil cooling duct flaps - and reduced the pilot's engine control input to effectively one lever. The 41.8-litre 801, with two-speed supercharging, produced 1,622hp at 2,700rpm so equipped. By the end of the war, development had raised the output of the highly regarded radial to almost 2,435hp.

In any case, with its Kommandogerät-equipped 801 engine, pilots had a far easier time flying the new Fw 190 than they would have using previous arrangements. 'Flight' magazine, reporting on the aircraft's early development, was less impressed. 'Though cleverly designed', it stated, 'the "mechanical box" was certainly built with complete disregard for considerations of economy.'

While somewhat overlooking the significance and capabilities of the unit, the assessment wasn't incorrect - as high fuel consumption was reputedly one potential issue with the Kommandogerät, as the boost and mixture could not be manually set to deliver maximum range when cruising. It was also ferociously complicated, expensive and prone to surging, which made formation flying hard work. Additionally, damage could lead to a complete loss of control, instead of the failure of one system.

Despite this, other manufacturers took note. This advanced radial, with its pioneering one-lever control, showed that comprehensive 'engine management' systems could work. Efforts were made to develop similar systems for some Allied fighters but the rapid transition to mechanically far simpler jet engines seemingly led to most approaches being sidelined.

Analogue electronic controls were later introduced for jet engines, followed by digital units. By the early 1980s, advancements in solid-state electronics meant complete engine control units - capable of managing both fuel, spark and other variables - were feasible for automotive applications. While far removed from the Kommandogerät, the core concepts of control simplification, automation and improved performance were the same.

As an aside, in a 1945 copy of Flight magazine, Bristol engineer Sir Roy Fedden - responsible for leading one of many investigations into German aviation engineering after the war - made special mention of the Kommandogerät following a visit to BMW. He said that the 'special single-lever control for this engine combination' was 'undoubtedly a very fine piece of work'.

More prominently, he was also taken aback by BMW's proposal for a variable valve timing arrangement - which, unbeknownst to him, preceded the company's own production automotive 'VANOS' variable valve timing system by 47 years.


P.H. O'meter

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Comments (29) Join the discussion on the forum

  • astrsxi77 12 Feb 2018

    Interesting and informative. Top effort!

  • Plug Life 12 Feb 2018

    PH Origins said:
    Professor Kurt Tank
    Proper name.

  • fido 12 Feb 2018

    The article missed out the most important reason for EMS - emission controls introduced in the 60s/70s. You simply can't compute to the level of accuracy required with a mechanical system, or deal with complexities in a closed loop system.

  • unsprung 12 Feb 2018

    An illuminating article, thanks.

    Ideal engine parameters for essentially every condition. No more need to "warm up the car" (because a cold engine would stall).

    Now... If we can follow the advances in ECU software with complementary advances in engine hardware -- for example, electronically-activated valves which require no cam -- we will truly master the internal combustion engine.

    Battery-electric vehicles are fabulous, but petrol is not going to die, not even from legislation.

  • Turbobanana 12 Feb 2018

    "Although some aspects were often self-regulating, it wasn't uncommon for a variety of adjustments - such as fuel mixture, boost pressure, supercharger gears, chemical supercharging, water injection, fuel flow and spark controls - to require the attention of the pilot. That, too, was atop of managing the throttle itself and, crucially, propeller pitch."

    And, you know, avoiding being shot at.

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