Q for our German-speaking members

[tomo pauk]

Hello,
Reading a bit about the DB engines, in some charts the term 'Geblaesedruck' can be read. Compared with the term 'Ladedruck, it is in most of the cases (always?) bigger, and it seems that is dependent to the altitude. Maybe someone might shed some light on that matter?
A chart where those can be read: here.

 

[pbehn]

Hello,
Reading a bit about the DB engines, in some charts the term 'Geblaesedruck' can be read. Compared with the term 'Ladedruck, it is in most of the cases (always?) bigger, and it seems that is dependent to the altitude. Maybe someone might shed some light on that matter?
A chart where those can be read: here.

They translate to blower pressure (Geblaesedruck) and charge pressure (Ladedruck)

 

[Shortround6]

Geblaesedruck may be the peak pressure the supercharger can deliver at the altitude in question while Ladedruck is the allowable pressure the engine can handle and the controls are set for?

 

[tomo pauk]

Never thanked for these replies

The Geblaesedruck is indeed a pressure the supercharger was able to provide. The term 'Gebläse' is the synonym for the term 'Lader' (compressor), just as the supercharger, compressor and blower are used to describe the same thing in ww2 aero-terminology.
In the DB-6 series of engines, the throttle plate is installed 'after' the compressor, in order to, well, throttle the amount of the pressured air into the engine intake manifold. Due to the operation of the throttle plate (partly closed until full throttle altitude is attained, then fully opened), the pressure of the air is indeed limited to the value the cylinders can withstand. Hence the term 'Ladedruck' (not 'Laderdruck') - basically, the manifold pressure in US terminology.
It is questionable how much the cost was in engine power, that was used to drive the supercharger to make up to 1.8 ata at low level, just to have that pressure cut down to 1.3 ata? The difference/loss between Geblaesedruck and Ladedruckabove full throttle altitude is still 0.5 ata (per above linked chart), or about 1.5 in Hg.
Once the Germans were to install the 'swirl throttles' in their engines (Jumo 213, DB-605 L and 603L), they dispensed with throttle plates, the swirl throttle being used instead.

Soviet terminology also made difference between the supercharger-delivered pressure and manifold pressure for their Klimovs and Mikulins, due to installation of throttle plates (and carburetors, of course) between supercharger and cylinders.