Spit/109 sea level speed comparisons in 1.08 beta patch

[Kurfürst]

Originally Posted by camber

I am still in the camp of the typical 109E doing around 475kmh at SL and 560kmh TAS top speed. IMO it is too much argument work to make the available flight tests match the 500kmh deck speed for series 109Es, as opposed to allowing that the aircraft were actually around the pass/fail level at SL (but OK at alt).

My view is that other POV, which simply wants to ignore the official specs and ignore test results in favour of uncorrected (engine powers not corrected) tests with very little detail (only very rough and extrapolated figures), with a differing engine fitting running at less boost and less power makes much less sense.

While there's a simply and logical explanation as to why how the V15a/official specs relate to the other tests, which is supported by the results themselves, the other way is simply to ignore a few tests in favour for the lowest possible values anyone can find.

Curiously, the most loud supporters of this agenda are the same people who want RAF planes modelled after the highest possible results, and ignore all but the most favourable data.

One thing that was brought up in the last thread, that the aircraft would be "failed" and sent back to Messerschmitt if they did <475kmh at SL. However, the 109G acceptance plot posted in this thread shows testing at a single altitude that varies but is closer to FTH than SL. It makes sense to me that acceptance tests would not be based on a full speed vs alt test regime, and especially not an actual test of the 109 belting along at sea level (a bit difficult to arrange except in CloD). So a 109 doing 470kmh at SL could still pass.

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...?

The other thing is considering 1.3ata vs 1.35ata. If the actual limit was 5 mins 1.3ata without the takeoff boost, I don't see that the fact the CloD 109s show 1.35ata suggests they should be made faster than historical (although we are getting toward hair splitting). Instead the CloD boost indication should be fixed or ignored. In the same way if the CloD Spit boost gauge showed +14psi, I wouldn't expect it to be made faster than historical to match the gauge.

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).

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)

One thing I really find interesting for 109s is combat use of the 1 minute takeoff boost. Whether or not it actually works except close to SL really depends on how it is designed...similarly to difference between the actual Spit II gated takeoff boost (will decay quickly with alt) and red tab combat boost (will work at any alt the supercharger is capable of delivering it).

Right now the 1.45ata works even up to FTH (odd), which seems very unlikely. But in real life it should certainly work if you are chasing or being chased low over the channel, but I have not seen a combat report or memoir that confirms this.

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.

This, along with the description of device makes it clear that the system employed a sort of fixed charge enrichment, providing a very rich mixture ratio to boost power for takeoff and low level. It was probably fixed for an optimum at supercharging ratio in the 1st gear of the engine, which became unsuitable as altitude increased to provide reasonable increase and there was no automatic mixture compensation for the 1-min rating. It could still be used up to near FTH, up to where the supercharger was phyisically capable delivering 1.45ata (I would guess - ca 3400-3500m in case of the 601Aa)but the decription notes that it only leads to increased fuel consumption and strain with very little increase in output. The manuals prescribe it's use only for takeoff, but its also evident from the warnings that there is no physical difficulty in using it any other time.

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).

Hope this helps.