The enigma of the Bf-109

[Kurfürst]

Never heard that happening. Somewhere I read the VDM prop automatism was quite satisfactory in limiting the RPM, and as for the Merlins overspeed limit, the Spit II manual is the only one mentioning such high rpm of 3600, but its noted that it tolerates it for 20 secs only. http://www.fourthfightergroup.com/eagles/spit1pn2-a.jpg

The Merlin equipped P-51D`s flight manual by the USAAF notes on page 65 :

"The maximum diving engine overspeed is 3300 rpm"

and

"Overspeed between 3300 and 3600 rpm neccessiates an inspection of the engine before further flight. If rpm exceeds 3600 rpm, the engine must be removed for overhaul."

Appearantly R-R was willing to take more risks when authrozing max. limits of the engine than DB.

[joeblogs]

Well that would explain why fuel consumption charts for German fighter engines are so flat compared to the American ones. I was not aware of this, although I guess I should have given their use of fuel injection systems.

-Blogs

Originally posted by pasoleati
Crumpp, at least on the 109G there was no manual mixture control expect for stopping the engine. I don´t see that as a problem. Later Merlins and Griffons adopted the same principle. For some reason Americans kept putting 4-position mixture controls on their fighters even in 1945. Though e.g. the Hellcat is a favorite of mine, I have no envy for the pilot who has 8 engine related controls (throttle, prop, blower gear change, mixture, carb air inlet, oil cooler doors, cowl flaps and intercooler flaps) to manipulate in flight!

[pasoleati]

Blogs, that is not the explanation for the flatness of the curves. First, these curves are relatively flat with only Jumo and DB engines, that of the BMW 801 resemble American curves in shape. The real reason for the flattish curves of the first two is that they, for some reason never satisfactorily explained as far as sources available to me are concerned, is that they don´t use overrich mixture as a means to prevent detonation. For example, DB 605A´s minimum sfc is around 205 g/hp/hr, i.e. around the same as that of the Allison. At WER, the figure (all info at sea level) is around 240 g/hp/hr while the Allison´s corresponding sfc goes over 300 g/hp/hr. Since according to Allied post war studies (e.g. Ministry of Power report on German fuels) German fuels had very good rich mixture qualities for liguid cooled engines, it is indeed surprising that it wasn´t taken advantage of.

[joeblogs]

Well then I remain at a loss too.

-Blogs

Originally posted by pasoleati
Blogs, that is not the explanation for the flatness of the curves. First, these curves are relatively flat with only Jumo and DB engines, that of the BMW 801 approach American curves in shape. The real reason for the flattish curves of the first two is that they, for some reason never satisfactorily explained as far as sources available to me are concerned, is that they don´t use overrich mixture as a means of detanation preventing. For example, a DB 605A minimum sfc is around 205 g/hp/hr, around the same as with e.g. the Allison. At WER, the figure (all info as sea level) is around 240 g/hp/hr while the Allison´s corresponding sfc goes over 300 g/hp/hr. Since according to Allied post war studies (e.g. Ministry of Power report on German fuels) German fuels had very goof rich mixture qualities for liguid cooled engines, it is indeed surprising that it wasn´t taken advantage of.