BMW iiia Engine Manual

[No.23_Starling]

Hi all, I just saw that BMW have digitized the original iiia engine manual from their archives. You can access it here: https://bmw-grouparchiv.de/irc/resultlist/detailpage?id=3052421 You might need to setup a BMW account but that should be free; once done so you can add this document to a workbook then view it and print as a PDF etc.

 

There's not a lot here that's revelatory and it reinforces what is largely said in secondhand sources, but it does conflict with the DVIIF and DXIIF in Rise of Flight and Flying Circus in terms of altitude throttle usage. There's some really helpful stuff in the document around operation of the altitude throttle, the workings of the carburetor, and technical drawings I'd not seen before.

 

A few things pop out:

 

Altitude Throttle Usage

The manual states that the three valves labelled 10, 13, and 14 are used for normal flight (see diagram) with the two lower valves labelled 11 and 12 are operated by the separate altitude throttle "from an altitude of 2000m", up to "4000m".

 

In the operating instructions it describes the operation at 2000, 3000, and 4000m:

"When flying, the following instructions must be strictly observed:
1. Climb to about 2000M: no further regulation.

2. Climb from 2000-3000m: at 2000m carefully open the altitude throttle until the engine gains about 20-30rpm; then continue to climb without further adjustment.

3. Climb from 3000-4000m: at 3000m open the altitude throttle until the engine gains another 20 revolutions; then continue to climb without further adjustment.

4. Climb above 4000m: at 4000m, open the throttle completely. From this altitude onwards, you can fly with the altitude throttle open at all times."

 

The whole process is reversed for descending until 2000m: "In order not to overload the engine, until at 2000m altitude the altitude throttle lever is completely closed."

 

It then strongly advises pilots not to err from these instructions: "The entire available power can be used at any altitude at any time using this one lever. However, the engine should not be loaded beyond the speed specified above unless absolutely necessary."

 

They lastly say that the pilot should experiment a bit to find the right positions and "mark the positions for 2000, 3000, and 4000, altitude on the segment of the altitude throttle."

 

Fuel and Benzene Addition

They address this directly stating that the fuel used should be petrol with a specific gravity of 0.72 - pretty standard stuff - but: "petrol with a higher specific gravity or benzene can also be used without any changes to the carburettor, but the performance will be slightly reduced, the engine will run a little harder and the carburettor transitions will not be quite as good as when using regular petrol."

 

FC Comparison

In terms of what this could mean for our in-game model @LukeFF, it looks like our engine allows for modest altitude throttle usage 1500m too low, and full usage a good 2000m too low based on BMW's recommendations (you can start using it at 500m and open it fully at 1500m in Flying Circus).

 

This advice around usage above 2000m is echoed in the words of Lothar von Richthofen (see Fokker DVII Aces of WW1, Franks) and we've no reason not to ignore him and BMW's own engineers.

 

The manual also eschews any mention of benzene allowing for low-altitude usage and actually states that it will reduce performance.

I'm not sure what apetite there is for altering the altitude throttle modelling but the evidence is pretty strong that something isnt correct.

 

I'd advise those of you with an interest in the engine to download a copy @Holtzauge @=IRFC=Hellbender @J99_Sizzlorr.

Do have a crack at your own translations and let me know if I've got anything wrong!

 

S!

 

 

[J99_Sizzlorr]

Nothing new we had the digital manual already 1 and a half year ago when we were discussing the matter with Fliegerbenzin. I just like to add the Höhengas operation during a dogfight. In which the Höhengashebel gets fully opened and then the engine get regulated by the Normalgashebel only. After the dogfight the Höhengashebel gets closed fully when und 2000m. If over 2000m altitude put the lever accordingly. Also the flight with configuration with the highest fuel saving is Höhengashebel fully open at 1000m altitude and then regulate with the Normalgashebel to not overrev the engine.

Edited August 26, 2024 by J99_Sizzlorr

[No.23_Starling]

1 hour ago, J99_Sizzlorr said:

Nothing new we had the digital manual already 1 and a half year ago when we were discussing the matter with Fliegerbenzin. I just like to add the Höhengas operation during a dogfight. In which the Höhengashebel gets fully opened and then the engine get regulated by the Normalgashebel only. After the dogfight the Höhengashebel gets closed fully when und 2000m. If over 2000m altitude put the lever accordingly. Also the flight with configuration with the highest fuel saving is Höhengashebel fully open at 1000m altitude and then regulate with the Normalgashebel to not overrev the engine.

The curious thing is that the FC model isn’t that far out with @Holtzauge’s model for the DVIIF climb. The issue seems more with when the altitude throttle is meant to be engaged. If it wasn’t engaged till 2000m then it would make things easier in-game.

[Zooropa_Fly]

I think in-game, as is the case in RoF - the 3 alt throttle stages kick in at 1500 / 2000 / 2500M.

That's going purely by the rasping / not rasping sound of the engine at full throttle.

So assuming the information in the OP is correct, it is indeed out a little bit.

[No.23_Starling]

7 hours ago, Zooropa_Fly said:

I think in-game, as is the case in RoF - the 3 alt throttle stages kick in at 1500 / 2000 / 2500M.

That's going purely by the rasping / not rasping sound of the engine at full throttle.

So assuming the information in the OP is correct, it is indeed out a little bit.

The last time I tried it a week back I could engage the altitude throttle at 500m then fully open it at 1500m. I can’t remember how it was in RoF. 
 

Either way the climb modelling is pretty good when compared with Anders’ models so it’s more an inconvenience than a problem!

[Zooropa_Fly]

Yes you're right - I muffed that one up !

 

It's 500 / 1000 / 1500M.. as indeed you say.

 

S!

[LukeFF]

22 hours ago, US103_Rummell said:

Hi all, I just saw that BMW have digitized the original iiia engine manual from their archives. You can access it here: https://bmw-grouparchiv.de/irc/resultlist/detailpage?id=3052421 You might need to setup a BMW account but that should be free; once done so you can add this document to a workbook then view it and print as a PDF etc.

 

There's not a lot here that's revelatory and it reinforces what is largely said in secondhand sources, but it does conflict with the DVIIF and DXIIF in Rise of Flight and Flying Circus in terms of altitude throttle usage. There's some really helpful stuff in the document around operation of the altitude throttle, the workings of the carburetor, and technical drawings I'd not seen before.

 

A few things pop out:

 

Altitude Throttle Usage

The manual states that the three valves labelled 10, 13, and 14 are used for normal flight (see diagram) with the two lower valves labelled 11 and 12 are operated by the separate altitude throttle "from an altitude of 2000m", up to "4000m".

 

In the operating instructions it describes the operation at 2000, 3000, and 4000m:

"When flying, the following instructions must be strictly observed:
1. Climb to about 2000M: no further regulation.

2. Climb from 2000-3000m: at 2000m carefully open the altitude throttle until the engine gains about 20-30rpm; then continue to climb without further adjustment.

3. Climb from 3000-4000m: at 3000m open the altitude throttle until the engine gains another 20 revolutions; then continue to climb without further adjustment.

4. Climb above 4000m: at 4000m, open the throttle completely. From this altitude onwards, you can fly with the altitude throttle open at all times."

 

The whole process is reversed for descending until 2000m: "In order not to overload the engine, until at 2000m altitude the altitude throttle lever is completely closed."

 

It then strongly advises pilots not to err from these instructions: "The entire available power can be used at any altitude at any time using this one lever. However, the engine should not be loaded beyond the speed specified above unless absolutely necessary."

 

They lastly say that the pilot should experiment a bit to find the right positions and "mark the positions for 2000, 3000, and 4000, altitude on the segment of the altitude throttle."

 

Fuel and Benzene Addition

They address this directly stating that the fuel used should be petrol with a specific gravity of 0.72 - pretty standard stuff - but: "petrol with a higher specific gravity or benzene can also be used without any changes to the carburettor, but the performance will be slightly reduced, the engine will run a little harder and the carburettor transitions will not be quite as good as when using regular petrol."

 

FC Comparison

In terms of what this could mean for our in-game model @LukeFF, it looks like our engine allows for modest altitude throttle usage 1500m too low, and full usage a good 2000m too low based on BMW's recommendations (you can start using it at 500m and open it fully at 1500m in Flying Circus).

 

This advice around usage above 2000m is echoed in the words of Lothar von Richthofen (see Fokker DVII Aces of WW1, Franks) and we've no reason not to ignore him and BMW's own engineers.

 

The manual also eschews any mention of benzene allowing for low-altitude usage and actually states that it will reduce performance.

I'm not sure what apetite there is for altering the altitude throttle modelling but the evidence is pretty strong that something isnt correct.

 

I'd advise those of you with an interest in the engine to download a copy @Holtzauge @=IRFC=Hellbender @J99_Sizzlorr.

Do have a crack at your own translations and let me know if I've got anything wrong!

 

S!

 

 

 

I've passed this along to our engineers in case they haven't seen it yet, thanks. 👍🏻

[No.23_Starling]

4 hours ago, LukeFF said:

I've passed this along to our engineers in case they haven't seen it yet, thanks. 

The BMW was also fitted to the DXIIF so applies to two of our birds