Question about Bf 109K-4

[Kurfürst]

Originally Posted by Juha

Hello Kurfürst

Your pages are very interesting as is Your message on 2000hp DB 605s. Have You seen the article on DB 600 series engines in Aeroplane Monthly May 2005? IIRC it seems to emphasis the importance of sparking plugs in achieving the 1850 and 2000hp in late DB 605 models.

Unfurtunately not, AM isn`t available here (hardly any foreign magazine is), but it sounds interesting and I`d love to read it. If it`s possible, could you take me a few shots on the article and send it to my mail address at kurfurst@atw.hu?


On 109K, IMHO its worst feature was low permitted Vmax for a 1945 fighter. In Finnish manual for Bf 109 G-2/6 the Vmax permitted was 750km/h.
...
I have also seen a pilot manual for Bf 109G/AS, date Aug. 44, which gave permissible Vmax as 750km/h at 0-4km altitude, 700km/h 4-5km, 600km/h 5-?km and 500km/h ?-?, I cannot remember the higher altitudes. The speed should be IAS. I don’t know the position error of Bf 109’s speedometer, so I cannot convert the speeds to TASs. Can You help me in this?

IAS and TAS are greatly different things, as a rule of thumb, decrease TAS vs. IAS by 10% for every 1500m altitude, but that`s pretty rough....

If you refer to here : http://www.pbase.com/isegrim/image/5288901, you`ll see how it works. Ie. you noted 750 kph IAS for 0-4 km altitude, where the G-2 would obtain only 492-525 kph in level flight. I also believe Mtt was quite conservative in his limiations, for the known Lukas Schmidt dive reached something like 890 kph TAS on a 109F without trouble, and they dared 906 after limiting aileron deflection, which isn`t really structural but compressibilty related with the Frise ailerons.

Results plotted vs. limitations :



As for the 109K, the diving limitations were increased over the 109G to 850 kph or 527 mph. That`s a pretty high figure imho even for 1945. The limitations are given in the 109K handbuch, 850 kph TAS at SL w. or w/o gondolas, and 800kph TAS at 10 kph - the 109K had altitude compensating speed gauge with two, TAS and IAS needles, and the limit was given in TAS.

[Juha]

Wunderbar Kurfürst

I'll will try to take a passable photo on the DB 605 page(s ) but not on whole article for not to breach too badly the writer's copyright. And I'll give the bibliobraphic data also. please give me day or two for doing that.

What is the source of the most interesting table? I knew the max. Mach number reached from one of my friends but haven't see the table before.

Why was it possible to increase the diving limitation so much for K? I cannot recall any significant reinforcement of structures in K when compared to G. But my knowledge on K is pretty limited.

Juha

[Kurfürst]

Thanks. You can find the report on the 109lair, I think along the tail unit changes stuff, but if not, I can email you.

As for why the change, I don`t know, perhaps because the undercarriage was to be fully retractable and covered on the 109K. Dive limits are more of a function of aerodynamics, rather than raw structural strenght..
But there`s more conservatism involved imho than pure technical neccesity - it`s enough to look on the fact that all 109F and G models, despite quite a variaton between them aerodynamically, had exactly the same dive limits.