Luftwaffe with just B4 fuel

[z42]

I'd beg to disagree.
2500 rpm and 1.30 was the max allowable rating before late 1941 (or maybe before January 1942?) - ie. Start & Notleistung setting (= 2700 rpm, 1.40 ata) was banned. The ban was lifted very early in 1942.

Interesting, perhaps I was misunderstanding what I read. I based my statements primarily on the following two quotes from TSHPR:

1. Page 304 (summary of 1942): "..the DB 601E withdrawn as the injection system was under-developed with the fuels available...".
2. Page 452 (Technical overview of DB, about the fuel atomization issue): "This was progressively improved by raising the opening pressure of the injections from 5 to 90 bar over the course of two years, and many developments with the L-Orange company on injector spray pattern changes". So it took two years, from the realization that the atomization was problem, to having an adequate solution. Too late for the 601E.

Of course, this doesn't mean they couldn't have come up with some interim solution (if so, what exactly?) that allowed them to get rid of the derating on the 601E much sooner? Or that the "full" solution with 90 bar opening pressure and new injectors was only needed for the very late war 605 variants cranking out ~2000 PS on C3?

 

[Deleted member 68059]

I'd beg to disagree.
2500 rpm and 1.30 was the max allowable rating before late 1941 (or maybe before January 1942?) - ie. Start & Notleistung setting (= 2700 rpm, 1.40 ata) was banned. The ban was lifted very early in 1942.

The banning "dates" are a notoriously difficult metric to use as an indication of when the problem emerged or when it was solved.

For example, its clear the issues occured a long time before things got noticed enough to result in the official de-rating, and despite
dates being mentioned, I have never actually found THE letter saying the ban had been lifted on any of the engines.
(I`m not saying such a letter does not exist, just that I`ve never seen it).

Its also clear that they thought they had things solved a few times, when in fact they were not.

Personally I`m not really sure there actually is an exact date when everything was suddenly ok again, because the solution involved retrofitting thousands of
existing engines with new valves, and engines still on production lines with new valves, that would have taken months to complete, also because the
chroming process was very laborious and took time as well.

Indeed as various changes to fuels and more boost were used as the war went on, problems with the valves and detonation did occur
still occur (in smaller severity and frequency) right up until the end of the war, and the chroming was never more than an
acceptable workaround, it was never as good as having valves with the desired quantity of Chromium/Nickel with full Cobalt rich coatings etc in the first place.

In other words, the problem was never actually 100% solved, right till the end.

 

[tomo pauk]

The banning "dates" are a notoriously difficult metric to use as an indication of when the problem emerged or when it was solved.

For example, its clear the issues occured a long time before things got noticed enough to result in the official de-rating, and despite
dates being mentioned, I have never actually found THE letter saying the ban had been lifted on any of the engines.
(I`m not saying such a letter does not exist, just that I`ve never seen it).

FWIW, this is from the manual for the DB 601E & G, dated February 1942:



(text in red notes that 2700 rpm operation is allowed if the automatic RPM limiter is installed, that pilot cannot override)
I haven't find any other notes or reasons of 'ban' in the manual, nor what the mods were incorporated in the engine type so the 2700 rpm operation is allowed.
We also can see the graph on your site & book, that notes Start & Notleistung on the 109F-4.

As for the ban -
Here is the table, dated 29th Nov 1941, where the ban is on the Start & Notleistung is noted ("z. Zt. gesp." - "zur Zeit Gesperrt" - blocked for the time being) at the top right corner. Unfortunately, Mr. Rausch mis-interpreted the note into a directly opposite term, as it can be seen when German language option is selected.

 

[mack8]

If the DB 601N stays as-is, runs the same RPM, pushes the same boost (without pre-detonation happening - this might be the kicker) etc, the resulting power should be as it was - no decrease.



Upping the boost further, to ~1.40 ata, will see the increase of another 5%? That is more than 1200 HP for TO.
Again - on a same engine type, the lower octane fuel and greater boost are usually mutually exclusive things. I'd strongly suggest reduction of compression ratio, preferably to 6.5:1, if not to the Merlin's value (6:1). Yes, some power will be lost for same boost and RPM, but there should be peace of mind for B4 operation.


601N was running at extra 200 rpm at rated altitude vs. the 601A, so we indeed should be getting better power at altitude.



Going with increased CR is fine and dandy if engine can take it. Otherwise, staying conservative with CR is probably less troublesome approach.


Time for the experts to chime in

Well what we think the germans should do in regards to the CR and what they will actually do are two different things. DB at least kept pushing the CR up even on B4. But at least in this TL since they don't have C3 fuel they can't go to really CRs such as the 8.5 of late DB-605 (and probably 603) or Jumo-213 models.

Probably the lowest CR they might go for this ALT DB-601N is 6.9, the same as on the DB-601A models, but me i think they will go for 7.2 like the C/D or E models. If they go for a CR of 6.9 and 1.35 ata at 2600 rpm you think they will still run into detonation on B4? This sort of combines the CR and ata of the A-1 and Aa models, most of the extra power coming from the higher rpm and the improved supercharger.

 

[Engineman]

FWIW, this is from the manual for the DB 601E & G, dated February 1942:

View attachment 753991

(text in red notes that 2700 rpm operation is allowed if the automatic RPM limiter is installed, that pilot cannot override)
I haven't find any other notes or reasons of 'ban' in the manual, nor what the mods were incorporated in the engine type so the 2700 rpm operation is allowed.
We also can see the graph on your site & book, that notes Start & Notleistung on the 109F-4.

As for the ban -
Here is the table, dated 29th Nov 1941, where the ban is on the Start & Notleistung is noted ("z. Zt. gesp." - "zur Zeit Gesperrt" - blocked for the time being) at the top right corner. Unfortunately, Mr. Rausch mis-interpreted the note into a directly opposite term, as it can be seen when German language option is selected.

Without trying to quote about the power restriction limitations that I believe are not easy to follow and, possibly, we lack all the orders and limitations of, I would point out that the note in red in the top corner of the DB 601 E engine performance table posted above is a restriction of the use of the Start.-und Notleistung power setting to ONLY with the use of the Automatik propeller control. This is nothing to do with a power limitation, it is a limitation of not using greater than Steig- und Kampfleistung power setting in HAND (Manual propeller control).
This was because it was difficult to manually control rpm at the high power settings. So, this say's 2700/1.42 is allowed in Automatik control.
Additionally, the DB 605 A was similarly limited to it's 2800/1.42 Start. und Notleistung power setting only with the use of Automatik propeller control for the same reason.

Eng

 

[Engineman]

In addition, it is worth noting that the Automatik propeller function was a fairly new system for pilots who were also known to use the Hand (manual) pitch control in combat to reduce pitch and obtain higher rpm that increased the firing rate of the synchronised MG17 guns. Overall, the DB 601 E and 605 A were very close to their rejection rpm limits of 2750 and 2850 rpm. There is no doubt that in combat, using Hand propeller pitch control at Start und Notleistung would cause inaccurate pitch control and over-reving with consequent possible engine damage and rejection.

Eng

 

[tomo pauk]

Without trying to quote about the power restriction limitations that I believe are not easy to follow and, possibly, we lack all the orders and limitations of, I would point out that the note in red in the top corner of the DB 601 E engine performance table posted above is a restriction of the use of the Start.-und Notleistung power setting to ONLY with the use of the Automatik propeller control. This is nothing to do with a power limitation, it is a limitation of not using greater than Steig- und Kampfleistung power setting in HAND (Manual propeller control).
This was because it was difficult to manually control rpm at the high power settings. So, this say's 2700/1.42 is allowed in Automatik control.
Additionally, the DB 605 A was similarly limited to it's 2800/1.42 Start. und Notleistung power setting only with the use of Automatik propeller control for the same reason.

Eng

In addition, it is worth noting that the Automatik propeller function was a fairly new system for pilots who were also known to use the Hand (manual) pitch control in combat to reduce pitch and obtain higher rpm that increased the firing rate of the synchronised MG17 guns. Overall, the DB 601 E and 605 A were very close to their rejection rpm limits of 2750 and 2850 rpm. There is no doubt that in combat, using Hand propeller pitch control at Start und Notleistung would cause inaccurate pitch control and over-reving with consequent possible engine damage and rejection.

Eng

Question - where was the automatic control for the prop mentioned in German docs wrt. the 601E allowed for 2700 rpm?

 

[Engineman]

Hi Tomo,
The DB 601 E propeller pitch control on the Bf 109 F3/4 was very similar to the installation on the DB 605 A on the Bf 109 G. Do you need some detail?

Eng

 

[tomo pauk]

Hi Tomo,
The DB 601 E propeller pitch control on the Bf 109 F3/4 was very similar to the installation on the DB 605 A on the Bf 109 G. Do you need some detail?

Eng

I'm curious why would you note that prop rpm limiter is in play, when the note on the table does not mention it.

 

[Engineman]

Because although the note in red is a bit strangely written, it means you must use Auto prop control at Start. und Not.
This is the same in the Bf 109 G, although the limitation on only using 2800 U/min in Auto is better worded. This is nothing to do with the power limitations that were imposed.

Eng

 

[tomo pauk]

Because although the note in red is a bit strangely written, it means you must use Auto prop control at Start. und Not.

You will hopefully have no problems in me staying skeptical on this.

 

[Deleted member 68059]

You will hopefully have no problems in me staying skeptical on this.

I happen to know who "engine man" is in real life, I'd be inclined to believe everything he tells you about Daimler Benz v12s, he is not an armchair enthusiast.

 

[tomo pauk]

I happen to know who "engine man" is in real life, I'd be inclined to believe everything he tells you about Daimler Benz v12s,

He will probably forgive me asking questions.

he is not an armchair enthusiast.

I've figured that some time ago.

 

[Deleted member 68059]

He will probably forgive me asking questions.


I've figured that some time ago.

This might help a bit E Engineman tomo pauk

 

[tomo pauk]

Excellent, thank you.

 

[Engineman]

Thanks Calum,
It should be noted that this is something of a "wild card" instruction in the very early days of the Automatik prop control and at the time Hand control of pitch and rpm was normal, but inaccurate. The latitude shown here with rpm was withdrawn about 8 months later and as we know, did not apply to the DB 601 E or the DB 605 A. Of note, the "short time" is not defined! Furthermore, the last sentence is inaccurate about a future system giving automatic increase of max rpm above FTH, this never happened.

Eng