Spit/109 sea level speed comparisons in 1.08 beta patch

[TomcatViP]

I am

[JtD]

Great, so what's your explanation? I seem to have missed it.

[MiG-3U]

Originally Posted by TomcatViP

no again. Sry. But you are in inviscid and incompressible.

Those eq are valid only bellow Mach 0.3. Btw 0.3 and O.6, this can do a nice guess-estimate if you had a coeff. Above 0.6, you can't rely on this way for calculating perfs.

Remind that 0.X is the LOCAL maxima of speed.

Thx however for the details you pushed here.

REM: If you had used your calculation to estimate the time of accel from Stall speed to 200mph, I won't have said anything (if you have added a coef in 2Pi*Alpha). Or the cruise speed (WWII).

~S

Well, Mtt used exactly same rough calculation as Holtzauge to estimate the speed at different power. When the speed difference is around 10-15kmh, the changes in induced drag, propeller thrust and drag coefficient due to compressibility are so small that the error is less than 0.5kmh. That is certainly good enough, given that most data here is without compressibility corrections.

However, field is open for you interpretation, of course.

[camber]

Thank you Kurfurst for the helpful reply and Holzauge for the extra calculation info.

Originally Posted by Kurfürst

Yes of course there were a lot of 109E's that just passed the minimum specs and were still accepted into service. So were Spitfires and Hurricanes. So why should be 109Es modelled after the worst possible specs instead of the nominal/guaranteed/tested and confirmed specs, while Spitfires and Hurricanes get special treatment and are modelled in optimistic conditions? Especially as the CLOD engine models wear of the airframe, so worn/badly manufactured planes and the scatter in performance can be easily modelled...?

This is a good point, made critical by the fact of having a single aircraft cloned exactly across the whole battle theatre is rather unhistorical really. My position is that the (may he exist) CloD FM czar should make a good faith attempt to find an "average" performing variant (which will always incorporate some subjective calls), then fiddle within plausible historical performance ranges to make CloD work best.

With the 109E, my position is that based on what flight testing/ etc. information is available, at 1.3ata the SL performance was around 475kmh. This close pass/fail performance on the Messerschmitt chart was however not an issue because the acceptance was based on an altitude performance test, where the typical 109E was close to the guaranteed average spec. I think we maybe overstate how important SL top speed was to the Luftwaffe of the time, as they were overwhelmingly interested in altitude performance, where the 109 performed inspiringly. In CloD however we like to chase each other just above the deck a lot more, I suspect.

Originally Posted by Kurfürst

The Spitfire II analouge is limping, since it essentially says that if the performance doesn't match the engine outputs, decrease the engine output until it matches the wrong speed. It's akin to say that if Spitfire speeds do not match the +12 performance levels, but they match the + 6 1/4 boost, simple set the gauge to show 6 1/4 (which is unfortunately the current situation in the sim). Moreover the Spitfire I / II had only one type of engine fitted (M III or XII).

I agree, the situation is a bit theoretical anyway because FM fine-tuning may not occur anyway in CloD. I do think (if we had to choose what was fixed) that it is better to have the aircraft end performance historical with wrong boost indications, rather than correct performance but for an unhistorical boost. Which brings us to the next point, about what boost the 109E SHOULD have:

Originally Posted by Kurfürst

The Me 109E in contrast had at least four fitting and used during the Battle of Britain, with different boost and outputs.

The DB 601A-1 with the old type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4000m.

The DB 601A-1 with the new type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4500m.

The DB 601Aa with the old type supercharger, 1.35 ata for five min and 1045 PS, and 1.45 ata for 1 min and 1175 PS. Rated altitude being 3700m (altitude output was otherwise very much like the DB 601A-1 / old s/c, though it is an open question wheter the new s/c was fitted to the Aa as well. So far no evidence to that though.)
This is the type we have in the sim.

The DB 601N, 1.35 ata for five min and 1175 PS. Rated altitude being 4800m. (there was a second type of 601N, mounted in one in the 109F had better supercharger and IIRC 5200 m rated altitude)

Therefore, it is pointless to compare our 601Aa equipped Emils performance (1.35ata) to real life tests of DB 601A-1 equipped Emils at 1.3ata. It should of course match the real life DB 601Aa at 1.35ata (V-15a, Baubeschreibung "5%" specs, Swiss trials of serial no. 2404)

This is a really interesting point. Googling back, I see the DB601Aa is a bit controversial in discussions going back a long way, in that is it just only an export version, or was it widely used in Luftwaffe 109s. As you say, CloD seems to have put a DB601Aa in every 109E on the channel coast, which seems an odd choice but not a demonstrably wrong one (like a Me262 Jumo jet engine would be ). If I was CloD FM czar, I would consider re-engining all 109s to one of the DB601 A-1 variants and giving it 1.3 ata 475kmh/560kmh performance. If I stuck with the 1.35ata DB601Aa, I would increase speeds by an appropriate theoretically derived increment from the extra 0.05ata (e.g. using the formulae Holzauge provided), thus using the 1.3ata 109 data as a baseline.

Going on to the extra boost:

Originally Posted by Kurfürst

The 109's 1-min Startleistung of 1.45ata worked different from the Spit II gated boost: like the Spitfire I, it had an automatic boost control which maintained 1.45ata up to near rated altitude. The primary difference was, evidenced from the DB 601Aa power curves is that just above the 1st supercharger speed, the power output with the 1 min rating suddenly dropped quickly, and although it still brought some very marginal power increase.

(snip)

So there's not much wrong with the 1-min rating being usable up to FTH, what is wrong is how it's modelled. At low altitudes, it should bring a MUCH more noticable boost in power than currently, given that it boosts the engine by 110-130 HP, but above ca. 1.5 km it should amount next to nothing (with fuel consumption still being sky high).

That seems reasonable to me, provided the 1.45ata FTH is reduced to the correct level (below 1.35ata FTH) for the supercharger capability. Right now in CloD the 1.45ata seems to be still working when around the 1.35ata FTH (without changing rpm). The one thing that concerns me is that I haven't read reports of 109 drivers reaching first for their clockwork boost buttons when in a sticky situation, in the same way RAF drivers went straight for the boost lever or tit.

Cheers,
camber

[NZtyphoon]

As for the Spitfire and Hurricane "get(ting) special treatment and are modelled in optimistic conditions?" While the British fighters are badly handicapped, what with engines blowing up after just a few minutes at higher boost settings, and badly under performing in other respects? Hardly "special treatment'', but there are some who don't mind.

[Holtzauge]

Originally Posted by NZtyphoon

As for the Spitfire and Hurricane "get(ting) special treatment and are modelled in optimistic conditions?" While the British fighters are badly handicapped, what with engines blowing up after just a few minutes at higher boost settings, and badly under performing in other respects? Hardly "special treatment'', but there are some who don't mind.

Well I would hope that any adjustment of the Me109E would be coordinated with a corresponding adjustment of the Spitfire speed: So if the Me109 was raised to around 475 Km/h for the DB601A variant at 1.3 ata then I would expect the Spitfire to get approximately 283 Mph for +6.25 boost and 314 Mph for +12 boost.

BTW, doing a rough calculation for the DB601Aa for 1.35 ata would yield circa:

v=460 x (1045/910)^(1/3)= 482 Km/h

In addition, Cambers question is interesting: How many DB601Aa were there on the Channel front? Was it a mix of DB601A1 and Aa? If so what were the proportions?

Concerning which engine to model, even given a free choise, I'm not sure I would opt for the DB601Aa: If the Spitfire uses +12 boost the 109E is outclassed down low either with the DB601A1 or Aa. On the other hand the DB601A1 with "Neue Lader" has superior altitude performance while the Aa is outclassed on both accounts. So why give up the altitude advantage for a mere 7 Km/h more on the deck when the result is still far below the 505 Km/h the Spitfire will do on +12 boost?

[Al Schlageter]

Shikhov:

But seems too early to make a final conclusion what was the 601Aa.
I'm completely satisfied of 601Aa installation on Bf109E-7 detailed example.
Quite strange plane - used Arado E-1 airframe (3380-3664 block) and equipped with rare enough Aa engine produced 3 years before.
Great example, but may be exist some more?

As far as I understand 1168 is the total Aa/Ba number were produced. Some of them were installed on Swiss and Jugoslavian Emils (153), may be some Do215B were also equipped. Abt. 1000 of rest DB601Aa were on LW hands.
Therefore a figure apeared 1000/4000 E = ~ 1/4 (like Olivier already showed).

Many thanks to Kurfurst for work and new documents - DASA sheets for DB601A-0, A-1, Aa, N. But new question was born - when tables was printed ? It seems in same time no later then mid of 1939.
Please compare with Auszuege aus Fl.datenblatt Bf109E-1, E-3 nach L.Dv.556/3 powercurves (p.22) and Tabelle.
DB601A in Dec.1939 in their final condition was enough different as if for 1937.

From another side as we can see DB601Aa really developed since 1936 and therefore no matter for auslandisch version of A-1 can't be at the time.

Paid attantion for more point:
DB601N offer too little performance growth compare with DB601Aa for
30-min settings:
Aa at 1,27 ata 1050 hp (4100 m) in manuals for foreign cust. 1025 (4200 m)
N at 1,35 ata 1050 hp (4800 - 4900 m)
I can't see difference and any reason for using highly expensive (5 times) and available in small quantity at the time 100 octane C-fuel if LW has on hands so powerfull and reliable engine as DB601Aa.

Seems something wrong in this story.

All the best.

Igor.

olefebvre (Butch2K) replies"

I don't believe the Luftwaffe intended to use the 601Aa in the 109 at first, it seems really associated with the introduction of bomb carrying 109. The reason being the increased power output of the take-off rating.

You correctly underlined the few differences between the Aa and the N, and indeed the differences are not that important. Keep in mind that the E-7 which was basically an E-4/B with droptank support was intended to use the DB601N at first. Yet the DB601N proved problem prone, and it's production was at first very slow. So i believe the introduction of the Aa on the /B and E-7 ac was a quick expedient to replace the DB601N until it proved reliable and could be really mass produced.

There were few 109 really equipped with DB601N engines, they simply did not provide any significant advantage at the time. With the introduction of the higher performance blower when the Friedrich entered production, then it provided an advantage.

[TomcatViP]

Really did you read at least what I wrote on the last page?

(Edited on request).

[JtD]

Yes I did, assuming you are referring to this one. But it only states a few principles of aerodynamics, doesn't quantify them or provides a calculation illustrating that if this is taken into account, the numbers add up. I agree on the trend, but I doubt that they will account for the full difference.

Thank you for editing your post.

[MiG-3U]

Originally Posted by JtD

Yes I did, assuming you are referring to this one. But it only states a few principles of aerodynamics, doesn't quantify them or provides a calculation illustrating that if this is taken into account, the numbers add up. I agree on the trend, but I doubt that they will account for the full difference.

Thank you for editing your post.

Well, the logical problem with Tomcat's argument on Holtzauge's calculation is that Mtt calculated that claimed 498km/h at sea level exactly same way as Holtzauge. So if we prove either of them seriously unaccurate, the other is just as unaccurate.

However, generally there is no steep rise on the Cd until mach numbers well over 0.6 so the error caused by compressibility is very small given the speed differerences around 15kmh talked here.