Thank goodness I missed this ridiculous bun fight.
The Ju-390 has been quoted as using both the BMW-801D and BMW-801E engine. The "E" engine was experimental and never saw widespread use. The "E" engine had 2.5% better fuel performance.
The "E" engine differed in gearing for higher altitude and a better cooling fan/compressor. The figures for a BMW-801E are so marginally different as to be minimal and if you insist on the Ju-390 having flown to New York with BMW-801E engines then so much the better because that engine had slightly better fuel performance.
Drgndog you've quoted figured like 56 inches boost. That's claptrap!
drgndog said:
You believe a Truth but you don't have any of this to demonstrate you have an assembly of relevant facts? Nor does Kiwi.
I see however where you've made the mistake drgndog and it is understandable.
Yes you've published a report on BMW-801D performance in a range of rpm settings from 2150rpm to 2750rpm. (post#93)
What you seem unaware of Drgndog is the BMW-801D (and E) had an automatic fuel control system.
When run above 2150rpm the automatic fuel control switches the supercharger from low to high gear and fuel from lean to rich. That is why you have a table with much higher fuel consumption. It pays to cite facts in context.
The context is that this engine would not have been run at such settings by the Ju-390 except on take off and even then only for limited time.
You've cited a table for a fighter plane performance at high boost, high rpm and rich fuel mixtures. That does not translate to a Ju-390 at lower rpm with lean mixture and low boost.
I got involved because I saw an analysis that seemed reasonable to me based on the numbers presented. I got into this in more detail when Kiwi posed that nobody knew what they were talking about and proceeded to a.) get the math wrong by nearly 20% on his own figures and assumptions - much less any assumptions based on a referencable source that applied to the case in question.
As I have stated before I did not get the math wrong. I rounded down because I did not accept given the low wing loading that the climb would have been so protracted.
An Fw-190 A5 would reach 20,000ft in 15 minutes. I calculated that a Ju-390 would reach 20,000ft in 25 minutes because that is the time a fully laden B-29 needed to reach 20,000ft.
Then I rounded it down as you say by 20% because the Ju-390 has only 55% of the B-29's wing load and 18% more power. The Ju-390 also had an 85% better power to weight ratio than the B-29.
A realistic figure for the ju-390 to reach 20,000ft would be about 20 minutes, so please stop misleading people.
I did not get the maths wrong. I rounded down because I knew that the fuel consumption for a 25 minute climb was excessive and not supported by fact.
The math which you say I got wrong was an "ESTIMATE" for the climb. The maths for the cruise was essentially correct. the climb to altitude was an estimate... nothing more ...nothing less.
If you want to split hairs drgndog, had I assumed the same 15 minute time to altitude figures I could have halved the fuel estimate for the climb and you'd be none the wiser so please stop engaging in cheap shots.
If you want an honest debate then don't use intellectual dishonesty to win the debate.
In an altitude range of 14,000ft to 20,000ft with the early two stage supercharger used on "D" and "E" engines the manifold pressure at cruise settings of 1700hp and leaned fuel was 27 inches of mercury.
The supercharger did not change gear until 2150 rpm.
I'm willing to believe any performance figures based on either well founded calculations based on exhaustive wind tunnel results with at least one test flight to reference areas of agreement versus differences from the theoretical.
I am glad to hear that drgndog because NACA performed the tests you've referred to on the BMW-801D2
My information comes from the National Advisory Committee for Aeronautics (NACA) forerunner to NASA, Memorandum report #E5D19 "Characteristic of the BMW 801D2 Automatic Engine Control."
Flying at lean cruise settings and supercharger low gear up to 20,000 ft, the BMW-801D engine only burned 56.66 US Gals per hour. The "E" engine used 2.5% less fuel per hour.
I too believe that the service ceiling of the Ju-390 was higher than 6 km, probably 8-9 km, but no more as the BMW-801 lost performance rapidly above 20,000 ft.
Soren the BMW 801D2 would reach 36,000ft if pushed, but that tripled the fuel consumption. Critics of the New York flight cite BMW-801 fuel consumption at maximum power with rich fuel mixtures and high boost to justify claims that the flight couldn't have happened.
It's intellectually dishonest to cite such power settings as typical of a New York flight. No aircraft cruises at maximum power on a long range flight.
Through a process of logical deduction the cruise speed for such a mission appears to have been a very slow 167 knots at 20,000ft.
BMW-801E
The BMW801E engine: Version E was in fact modified D-2 used for prototype testing. It would have developed 2000hp in bench tests. It seemed to be produced in small number and to be delivered under designation TG and/or TH.
At take off power the BMW-801D used 200 US Gal per hour but could only maintain this for 3 minutes before overheating required throttling back.
At take off power the BMW-801E used 195 US Gals per hour. It also used water methanol injection to the supercharger intake at take off.
The biggest difference was a centrifugal air compressor which pushed air pressure from 1.39 atmospheres for the BMW-801D up to 1.62 atmospheres for the BMW-801E.
