Bf 109 engine management vs "Kommandogerät"

[andyw248]

Does anyone here know what the differences were between the engine management that the DB 601 in the Bf 109 provides, vs the so-called "Kommandogerat" used with the BMW 801 in the FW 190? From this publication on Kurfurst's site: http://www.kurfurst.org/Engine/DB60x/files/Flight_16April1942_DB601N_Engine.pdf I gather that the DB 601N already had one-lever control, which controlled boost pressure, fuel injection, and prop rpm. Did the "Kommandogerat" have any features beyond these?

[LLv34_Flanker]

S!

 

 Consider Kommandogerät as a mechanical ECU (engine control unit). It had more functions than Bf109's more simple system and took in account more inputs. It adjusted engine parameters according to the throttle lever position.

[Matt]

The Kommandogerät also switched the supercharger gear automatically.

 

Not that the DB 601 of the 109 would need that, but i guess if it would've had different gear stages, the pilot would've needed to switch those manually.

[Kurfurst]

I am not sure how the K-Gereat would actually control the engine system. The 109s system was rather simple - it simply had fixed certain propeller rpm to a given throttle (manifold pressure) position. The various sub systems took care of the rest - the throttle would open to give a set manifold pressure, the electric propeller govenor would maintain the said rpm etc. T

 

The DB series engine had 2+ supercharger speeds via a hydraulic coupling - the first one was a fixed "gear" ratio between the engine and the supercharger, the second one was variable anywhere between the first speed and next to no slip (3%) in the hydraulically driven supercharger, but the engine took care of that part via a barometric unit that controlled the amount of oil fluid in the coupling, and thus the slip and supercharger speed, with the result that the supercharger was only driven as much as the supercharging needs of the engine demanded at altitude (plus a bit of reserve). In short the automatic control was "built in" into the supercharger unit itself and it ruled out the very significant wastage of the usual fixed gear ratio systems between the low and high supercharger gears, sometimes amounting to several hundred horsepower... the BMW in that regard was somewhat backward, since it could only choose between two fixed s/c speeds, wasting several hundred HP between the too gears..

 

The direct fuel injection mixture was controlled by various sensors measuring manifold pressure, atmospheric pressure and induction temperature. From the F series onwards, the radiator flaps were also automatically controlled via a thermostat unit that was programmed to attempt to maintain coolant temperature at about 85 Celsius degrees by automatically opening or closing the raditor inlet and exit flaps. Manual override was provided though for emergencies or fine tuning.

 

From the practical standpoint the effect was the same, the pilot would only need concern himself with a single lever and forget about the rest. He controlled the throttle and RPM according to presets, while supercharger and propeller speed, mixture and radiator flap settings were were held in the range of the selected parameters. Maybe the K-Geraet did that with more finesse between interim settings, say between cruise and max settings, I do not know.  I guess you could say the BMW approach was a large "central brain" or sort of an engine computer, while the DB system was a series of conventional sub systems. Maybe the main plus was that all engine controls were contained in a single unit which was easy to be replaced with a a new one and inspected when time would permit, instead of tinkering with the whole engine, making the fighter unservicable.

[Sternjaeger]

the kommandogerat was a remarkable piece of engineering, it was an electro-mechanical-hydraulic mechanism (a rudimentary computer, if you wish), which could read the outside atmospheric pressure and adjust all the engine parameters (RPM, pitch, mixture) accordingly, yet still allowing the pilot to manually override the propeller pitch control if necessary.

 

 

 

In a way it was a classic example of German over-engineering, but it was truly remarkable for its time and quite dependable too apparently. 

 

My understanding is that the system used on the late 109s was a completely different thing altogether, but again Kurfurst probably knows more on the subject!

Edited January 6, 2014 by Sternjaeger

[andyw248]

Thanks guys for your insights and the diagram! This pretty much clarifies what the differences and similarities are.

[SharpeXB]

Will the prop pitch gauge on the 109F dash eventually function in BoS? I assume it will even though it's set automatically

[Anw.StG2_Tyke]

Will the prop pitch gauge on the 109F dash eventually function in BoS? I assume it will even though it's set automatically

It have to, because afaik the Pitchcontrol was set by the pilot while take off and landing. Afaik they turned of the automatic for those two things.