[camber]

Dear Kurfurst and others

Thank you for the response. That was exactly the critique I was looking for.

Originally Posted by Kurfürst

While Test 1 was made at 1,35ata and higher output, with known (measured) engine outputs Tests 2 and 3 were made with a 1,3ata - test 2/3 were flown at lower boost. This explains some of the difference but not all.

The important difference between Test 1 and Test 2/3 however is that while Test 1 is a performance test, and wanted to obtain accurate and absolute performance figures for the whole altitude spectrum, Test 2/3 were never intended to do the same.

Test 2/3 were about finding the relative difference in performance in various aerodynamic conditions, presumably for seeking out the viability for future improvements (guns installed not installed etc.). All they wanted to gain is relative speed difference on the same plane to get an idea how much drag penalty these items induce. They were never meant to be representative performance flight trials.

Also for Test 2 and 3. One part that is not mentioned in the table that all flight trials (none of which we know the supercharger setup) show very close agreement, within a few km/h to Test 1's performance with the high altitude supercharger speed in operation.?

I agree with you that Tests 2 and 3 are comparative (interestingly the changes made never affected performance). I consider them useful for consideration as they are among a limited range of official Messerschmitt 109E flight tests I am aware of, although they are certainly non-optimal (comparative, no height curve, sea level speed probably extrapolated etc.). More German speed tests would be be very useful, a few more and we could remove these ones if desired.

I would say however that provided the rated conditions are known, the "control" speed (i.e without configuration changes, not that this changed anything) should be considered in the data set in light of stated boost (1.30ata).

But I can't agree that (lack of) engine power correction is a good explanation of low altitude underperformance in multiple tests (i.e. other than test 1). It suggests that 109E underperformance due to DB601 defficiency is typical and might be a factor in actual production aircraft (unlikely). In this case the 109s underperform but it is a DB rather than Me problem.

Originally Posted by Kurfürst

There seem to be a misunderstanding. You seem to assume that the British used a boost controller, the Germans did not, and relied solely on the barometrically controlled hydraulic supercharger coupling and - did not have a throttle on the engine at all!

This is however a false assumption, as apart from controlling the supercharger, the DB engines had automatic boost controller as the RR engines did. In fact those engines that did not and the throttle was controlled manually were the exception.

The hydraulic coupling provided the apprx. amount of boost needed, usually a bit more just to make sure, but fine adjustment was made by the throttle on the DB, which limited boost to the nominal pressures.

Yes, I did make that (false) assumption. In my defense, I will say that I was seduced late at night by the romance of a boost control system engineered by hydraulic slippage of the supercharger by German engineering geniuses. I will look further into the total system but point conceded as the system you describe makes more sense.

This certainly knocks over one of the legs of my argument (but not all ). With separate boost control and provided ability to alter the variable oil pump operation, the coupling could indeed act similarly to a two geared system. However, it is still a hypothesis that the Swiss 109 was tested in high altitude mode at all altitudes (decreasing low alt performance). An alternative hypothesis is that the speed/height curve has been simplified as a straight line, similarly to the original 109E specification. Without actual data points we can't tell.

This unfortunately gets us back to the original problem of a somewhat large range of possible low altitude 109 performance, with reasonable grounds (in my opinion) to argue both ends of the spectrum:

* A guaranteed technical specification
* A prototype that meets the spec provided engine power is corrected
* Multiple flight tests (with boost variability) that are specification "passes" for max speed but around the pass/fail level at sea level speed. Some plausible but unproveable hypotheses are presented for underperformance in these real tests.

Originally Posted by Kurfürst

The guarantee was for 1.35ata performance, +/- 5% for 500 km/h. That means that anything between 475 km/h and 525/h is OK for acceptance, for an Emil with DB 601Aa and operating at 1.35ata.

Compared to that, it would the French got around 480 km/h at 1.3ata from a crashed aircraft and the Germans iirc 474 km/h for another test machine, again at 1.3ata. In both cases the nominal output of the engines was at least 55 PS less than that of the Aa engine.

Actually better, I get ~480kmh at 1.26ata from my pressure conversion for the French test. I'm not sure what the relevance is to the Aa export motor (comparison to Test 5?)

Originally Posted by Kurfürst

And this is based on which test or official data...?

Uhm, so by what connection how does 1.35 ata performance come into the picture? You basically show threww German tests (at uncorrected power) at 1.3ata, which only show performance for SL, and suddenly 1.3ata performance is now the same as 1.35ata performance?

How are uncorrected 1.3ata tests are in connection with 1.35ata performance?

Well, I admit that was rather sloppy, but we do have to deal with a set of tests with varying boost levels . It was a rough estimation of performance from the flight tests excluding the prototype and Russian test, to answer my original question : "if you had to derive a single set of figures, what would they be?". A better method would be to attempt to correct all speeds for a standard boost (1.35ata) in some manner, then average. Otherwise one can only say (based on flight tests minus tests 1 and 7)

SL speed 465-480kmh at 1.25-1.3ata
Top speed 547-565kmh at 1.25-1.3ata

With a theoretical correction to 1.35 ata, I would estimate we are looking at a low specification "pass" at SL and close to bang on spec at height.

Originally Posted by robtek

I've seen such a acceptance diagram from Meserschmitt 109's, but i don't know which series it was, anyway the general deviation was about 10 km/h below the guaranteed value, iirc. A few were above, the majority slightly below and five had to be refurbished because they've failed.
Found it: http://www.kurfurst.org/Performance_...catter_web.jpg

Looking at these tests for the 109G (Thank you), it appears (although the plot is a bit hard to make out) that acceptance testing was based on max speed only. The failed 109Gs are underperforming at height, and it doesn't appear that SL performance is being considered. The pattern of the true max speed average falling a little under the spec average seems rather plausible as well.

Based on this all, I would suggest that "typical" series 109Es
* Performed close (maybe a little below) to their max speed average spec at 5000m (572 kmh TAS)
* Performed close (but above) their minimum "pass" rate at sea level (475kmh IAS/TAS)

Based on the 109G test data I would hypothesise that slight deviations under sea level minimum spec might be possible in individual "passed" aircraft (provided they passed the max speed test at height).

From the CloD point of view we are perhaps over-focussed on the sea level performance. We spend a lot of time chasing and being chased at sea level in 1v1 battles, and when we "test" the aircraft we skim the waves in a way no actual test pilot would care to do on a routine basis

camber