Originally posted by gripen
Isegrim,
The critical altitude of the DB 605 given in the specs (5800m at 1,3ata 2600rpm) is with some RAM (about climb speed). See for example spec chart posted above. Quick and dirty estimate for the unrammed FTH of the DB 605A is about 5200m at 1,3ata 2600rpm.
Hate to disagree, but it`s not.
Your confusion comes from the DB 605 A power curves, which were printed on standard milimater papers that say it`s 'statisch und dynamisch' power outputs. They say it for all engines... However in case of the 605A`s, it`s only static output, the dynamic outputs are missing from the paper...
http://www.x-plane.org/users/isegrim/Motor/DB605Agraph.jpgThis can be confirmed from the DB 601E power output curves, notice they have the same standard note on the right, but they also give the dynamic pressure gain (staudruck) in the curves themselves, unlike the 605A curves.
As you can see, the qouted 1200 PS at 4.8km value is for
static output at 0 kg/m2 Staudruck..
Also note that not even that curve chart is free from small typo errors, i.e. 1200 kg / cm2 is
quite a pressure gain, eh?
(on 601N chart it`s 1200 kg /m2, which is the correct one ).
Studying the 601E dynamic powers vs 109F-4`s VDH (6200m) in flight tests also shows the 109F gained 800 kg / m2 dynamic pressure at full level speed flight, or about 1100 m FTH increase in max. level speed.
Applying the same (in fact it was more because of higher speed of 109G, and larger air intake) gives 5800 + 1100 = 6900m VDH for the 109G (unless if you would like to claim that the 109G would gain a whole 300m only for some mystic reason, 1/3 that of the 109F gained, as it did in the engine swap test MW likes to show. The reason is obvious in his case, though.).
It`s also tells you why the TSAGI`s speed curves are correct. RAM effect as we know decreases the output with fixed s/c ratios, as in the case of the 1st fixed speed on DBs as well. The dynamic pressure is the highest at low levels, so is the power loss; it decreases as altitude increases, so does power increases. Thus it`s not a linear line, but for a rough example, the curve at SL at max. level speed flight is valid for 1200 kg/m2, but at 500m it`s only 1100, at 1000m it`s 1000 etc. The power output varies with varying dynamic gain.
In other words, the decreasing IAS speed w. altitude gives a curved pressure gain curve, which gives a curved power output curve instead of linear, which again gives a curves max. speed curve instead of linear, as all these things interact with each other. In most curves these are simplified however, and shown with a weighted straight line. And that`s why the Soviet curves shapes are accurate.
For MW,
http://www.x-plane.org/users/isegrim/109/climbfinnG-2MT215-13ata.jpgClimb results obtained in the Finnish tests with Bf 109 G-2 MT 215
at 1.3ata.
at 0m : 21.7 m/sec = 4270 fpm
at 1900m : 24.2 m/sec = 4760 fpm.Which tells us why Miky didn`t put up this speed graph as well, `cos then he would also have to show the climb results
at 30-min reduced power outputs..
Since the DB 605 A developed 1310 PS at 1.3ata, but 1475 at 1.42ata, it`s reasonable to belive that the climb performance at the full 1.42ata rating would be
As a sidenote, the Finn climb tests are in perfect agreement with the dataset of Rechlin and Tsagi for the 109 G-2 at altitude w. 1.3ata. The Rechlin results fell between the two others at low altitude, that`s 21 m/sec or 4133 fpm at 1.3ata reduced power.
edit: The FAF speed tests on Bf 109G-2 were flown the radiators at shut position. [/B]
This exactly means what mm ? Same setting at whole altitude range?
