Originally posted by Viking
For the DB 605AS as well? (I notice you did not post a link to a DB chart)
The DB 605AS as well as the DB 605A charts can be found from Valtonen's article and Raunio's article in SILH 1/2005. Charts on GJ+FX can be found from TOCH.
Originally posted by Viking
You chose to compare the DB 605AS with the V-1650-3 and -7 (that I compared it to earlier not realizing it actually was a -3).
Here is a piece of news that might surprise you: The DB 605AS is also a high altitude engine.
As you can see, at 10000m so called high altitude DB was nearly equall with low altitude (or medium altitude if that suits your needs better) version of the two stage Merlin.
Originally posted by Viking
Yes. They are not problems at all and the use of the word “problem” is inappropriate. You’re basically saying the supercharger had “problems” because it could have been even better than it already was.
Have a look
here.
Ladedruck = manifold pressure
Gebläsedruck = pressure between impeller and the throttle valve
As you can see the DB does quite large overpressure all the way up to the 2nd FTH. That means that large part of the theoretical advantage is lost.
Besides the oil system of the supercharger caused continous problems.
Originally posted by Viking
Edit: The fact of the matter is that the DB supercharger was more efficient at a much wider altitude range than the RR supercharger. The RR supercharger was marginally (you mention 4%) more efficient at its two FTH’s, but those only peak at very narrow altitude bands.
Perhaps you should actually try to understand the data posted above. Direct mechanical supercharger is more efficient everywhere else except between the 1st and 2nd FTH.
Originally posted by Charge
The advantage is not "when the second oil pump starts to increase speed etc. but all the way to critical altitude if need be. The choice of impeller gear ratio could be more radical but that would mean more excess heat generated by the clutch which would again need to be wasted. So it needs to be a compromise.
Well, the possible advantage lies only in the area where hydraulic coupling works enough effectively. The DB 605AS had 1st FTH around 2500m without RAM and around 3000m with RAM while roughly comparable V-1650-7 had 1st FTH around 1900m and around 3000m with RAM so there is no any advantage for the DB but losses due slip and heat (direct mechanical gear has no these losses).
Originally posted by Charge
I don't follow your logic. The pressure is controlled due to barometric conditions. How is that inaccurate considering that the aneroid is working correctly.
Aneroid does not measure MAP but outside pressure on it's orifice . The optimal impeller speed depends on needed MAP. See the link above giving the MAP and "Gebläsedruck".
Basicly the aneroid using outside pressure gives just rough adjustment and rest is done with throttle valve, therefore the engine is running more or less throttled up to the 2nd FTH. Just look the MAP and Gebläsedruck values in the graph linked above (there is several similar graphs in that site).
Originally posted by Charge
The throttle is supposed to cause loss -without it the plane would not stop. The point is that at what altitude you can open the throttle fully and what charger configuration will not let you do it. In DB you can open the throttle fully at any altitude and the charging control itself does not prevent it.
You see the problem; you don't understand at all how the adjustment of the hydraulic coupling and MAP worked in the DBs. That NACA report presents just optimal case which is not reality with the DBs.
Originally posted by Charge
Nope, the 4% loss can be compensated by simply rotating the impeller faster. The only drawback is the excess heat which needs to be get rid of.
Well, direct mechanical gear does the same with less power and without losses due to heat and slip. Other way to think the same issue is that at same gear ratio on direct mechanical gear spins 4% faster and without losses due to slip and heat.