[Kurfürst]

Originally Posted by klem

OK, my bad. I forgot I had abook called Bf109 by William Green. In it he covers he entire development of the 109 and of V15 he says it was fitted wwith the DB601A and goes on to say that "this was the engine that powered virtually every Bf109 for the first eighteen months of the war". Yes, I know that's contentious.

V15 or V15a? In any case, the V15a tests note a "DB 601A", but they give the rating as 1,35ata (which is the Aa rating). Power ratings also match that of the Aa.

More memory problems, I forgot the 1C Manual for CoD which gives us the following max figures:

Take-off
Initial climb at 250 km/h.
Raise gear.
Raise landing flaps and adjust trim accordingly.
Max 2,468 rpm / 1.45 ATA

Climb
Max continuous 2,368 rpm / 1.35 ATA.
Oil temperature: 30 to 75 C, up to 95 in short bursts.
Water temperature: 80 C, up to 105 in short bursts.

Cruise
Max 2,326 rpm / 1.20 ATA.

These figures appear to come directly from the Bf 109E operating manual and were clearly for 601Aa. See: http://109lair.hobbyvista.com/techre...als/bf109e.pdf

Originally Posted by klem

Looking at the available figures again.....

V15 with the DB601A gave 485kph at SL on 1.31ata corrected to 498 for guaranteed engine performance and 561/4900m on 1.33ata corrected to 572/4800m. But did this represent a standard military loaded aircraft in 1938? It compares very favourable with J-347s DB601Aa 'true' performance a full 20 months later. Is this likely?

The answer to both questions is that V15a fully confirmed to serial production aircraft, as the test report clearly notes.

Me109E-3 J-347 ("The Swiss Tests") with DB601Aa gave 464kph at SL and 565kph at 5000m.

Also note the results achieved in the Swiss tests fully agree with the results achieved with V15a FS/H0henlader supercharger gear testing results. This cannot be a coincidence IMHO.

Like I said, if the two aircraft two speeds is virtually identical at altitude with the same rating, it means that power and drag is virtually the same too.

Drag doesn't change with altitdue, so any meaningful drag or aiframe conditions between E-1 V15a and the Swiss E-3 J-347 can be ruled out.

Propellers are the same.

The only thing that can be different between the two is POWER. V15a has obviously a lot more power at low levels. Now this might raise the question wheter V15a has some kind of ultra-brutal low altitude engine with much more power than the serial production aircraft, but this can be ruled out too, since [b]V 15a's engine was bench tested/b], and it has exactly the amount of power at low levels as a DB 601Aa should have.

So the J-347 has LESS horsepower at low levels.

And it matches V15a's high-gear / Hohenlander / FS gear speed curves almost perfectly.

I mean, HELLOOOOOO? It runs in high supercharger gear only.. That's perfectly suitable if one want to compare the factory VDM props performance under identical conditions to two other type of props (which is what the Swiss were doing).

E-1 1791 and E-3 1792 both with DB601A gave 475-476 at SL on 1.3ata (max 5 mins) and "These speeds are on normal temperature and right boost pressure regulator setting, nevertheless, not on guarantee achievement of the engine". This begs the question on two separate aircraft "why not?" and leaves the door open to speculation that the guaranteed engine figures were not being achieved. Although without corrections the SL figures aren't that far below V15 (uncorrected for guaranteed performance and therefore in the same circumstances as 1791/1792) and which used fractionally higher boost.

In other words: under similar testing conditions, boosts and correcting (ie. not fully corrected), both the pre production WNr. 1791 and 1792 fully support the WNr. 1774 (V15a) figures.

The Bf109E-? curves for 16th December 1939 give 462 at SL and 562 at 4500m, presumably at the max 5 min contiuous rating... but for the 601A or 601Aa?? I am assuming the 601A because of the date and the fact that it is from the handbook.

The December 1939 manual gives 1.3ata max ratings, so it's clearly for the 601A-1 version (early Lader).

Comparison the Manual's climb rates and speeds (at unknown rating) show practically identical match as the RAE trials which OTOH are known to have been performed at 1.23 ata 30-min rating, so in all likelyhood the manual also shows 30-min rating.

462 kph at the 30-min rating at SL is fairly believable for the 109E / 601A1.

Bf109E-3 French tests (DB601A) gives us about 475-480kph at SL and 550kph at 5000m.

Note the French aircraft is again a practically exact match with the V15a figures at low levels (as measured at 1.31ata, the French one was running at 1.3ata).

The French aircraft was not developing full boost over altitude for unknown reason (French oils used in tests are suspect) but only about ca. 1.2 ata. In other words, they achieved about 550 kph with 1.2ata.

Bf109E-3 US tests (engine unknown) give us 467kph at SL and 543klph at 5000m.

US tests did not measure the captured '109E' speed anywhere near ground level..

Lowest measured value was 336 mph at 12k feet (541 kph at 3657 m) using the low altitude supercharger. In comparison V15a achieved 532 kph at (uncorrected) 1.33ata, and 545 kph at (corrected) 1.35ata.

As a matter of fact at known measurement altitudes the US trial matches even exceeds the V15a data..

I realise I am going around the same circles as several other people and I am forced to the conclusion that 1C MG are modelling the Bf109E-3 on the DB601Aa and the Swiss Tests. The boost figures 1C give us are for the DB601Aa which the Swiss a/c had and the speed chart 1C give us for CoD closely resembles the Swiss results.

I Agree.

Whether they should be doing that is open to question. I have no idea when the DB601Aa was introduced and in what numbers.

It was introduced early and in large numbers.

I'm also inclined to disregard the V15 figures because everything else is against them including their date, the fact that it was a dev a/c (although at pre-production status) and full details of the aircraft loadout.

As demonstrated above, this opinion is decidedly incorrect.

The V15a results match other results exactly, IF THE SAME CONDITIONS AND CORRECTIONS ARE APPLIED. Problem is, most of the other tests being waved about are either uncorrected, simplistic or are for different conditions (different engine, different boost).

Also the V15a's loadout is as detailed if not more so than any other 109E tests (definietely more so than the completely unknown conditions of the Swiss test, for example).

One can't compare apples and oranges.

Unfortunatley the only set of DB601Aa figures seems to be the Swiss tests.

This is incorrect because both V15a trials and the Baubeschreibung Leistungsblatter also detail DB 601Aa performance.

The most likely reason 1c decided to model the DB 601Aa variant is that this is what was best documented (both in manuals and for performance tests).



Well the question is basically this:

Should we correct FM to match the airplane modelled, or match the airplane to the FM modelled?

Should we compare our exiting FM's accuracy with tests using different and lower powered variants of engines we have modelled or not?

Should we use official / guaranteed performance specs for all aircraft (which is the V15a figures) or just pick the worst ones for each plane we can find from the bottom of the tolerance limits?

Should we model aircraft after essentially undocumented speed curves, in which the actual flight conditions are completely unknown or based on tests which are well documented and all airframe conditions, engine outputs are documented, known and also - can be replicated in the sim?

Should we apply the above decision to all aircraft, or just apply it to some aircraft, as it fits our taste?


BTW ain't the Spitfire's FM based on the Spitfire prototype? No problem with this one, eh?