Effects of multi-speed superchargers (or lack of the same) (1 Viewer)

[kool kitty89]

Better/longer ranged fighter coverage of Italian possessions in mid/late 1943? Earlier introduction of second (and third?) source for Mustang? Freeing more P-38s for ETO and Pacific? Hammering home the fact that P-47 needs both a better drop tank facility and more internal fuel, earlier than historically? No P-63? Earlier increase of internal fuel for mainstream Spitfire variants and the Tempest?

Also something to challenge the Fw 190 other than the Typhoon and Spit IX, perhaps faster than any of those down low or maybe even all altitudes? (should be faster down low than the 8.8 and 9.6 1710 at all altitudes at mil power -and more in WEP too if rated similarly to British engines)

Better range for escort than the early P-47s too, at least once wing pylons were fitted, but worse high alt performance. (still not bad compared to the 109 and 190 of '42 and '43) If the P-47 had gotten 200 gal pressurized belly tanks around that time it might have been a bit more equal though. (that or just less draggy wing pylons)

Surely the R-1830 and R-2800 had 3 speed superchargers? LO, HI and Neutral.

The single-stage engines came in single and 2-speed versions, as did the R-1820 and R-2600, but P&W's
2-stage engines were 3-speed, yes.

 

[Shortround6]

Unless the 9.6:1 Allison engines enter production sooner than they did historically, wouldn't the V-1650-1 still be the better bet time wise? This applies both to Mustang I/IAs and A-36s (and the few dozen P-51/F-6As taken from the Mustang I production block). Of course, British deliveries would be taking engines otherwise earmarked for British ordered Kittyhawks or Canadian Hurricanes.

Or taking engines away from..........ominous drum roll...............BOMBER COMMAND

You don't really have a unified supply system between the Americans and the British. Especially in late 1941 and part of 1942. You have airframes bought and paid for with British gold and engines bought and paid for with gold. You have British lend lease aircraft/engine which are paid for by the Americans and promised to the British (and obviously more subject to repossession by the Americans) . And you have American aircraft with nothing to do with the British.

The British only got about 250 Kittyhawk IIs with the Merlin engines. Now the question is (since engines were government furnished equipment, not supplied by the air frame maker) were these P-40-Fs powered by "american" Packard engines or by "British" Packard engines? And while the V-1650 certainly showed up in a much more timely fashion than the 9.60 gear Allisons (which had originally been promised for the end of 1941) and Packard is cranking out about 800 engines a month from July to December of 1942 the beginning of the year didn't look so rosy. 109 engines in Jan (36-37 to the US?), 149 in Feb ( 50 to the US ?) 333 in March (111 to the US?).

The A-36s, if kept at low level didn't need the Melrin XX engine. Their engines had 7:48 supercharger gears and they had more take-off power than the Merlin was allowed normally and with WEP ratings they could hit 1500hp down low without abusing the engine. Now if people want to try and take the A-36 up stairs and play air superiority fighter with it then yes, you need a different engine.

 

[Shortround6]

Agreed all the way.

Re. post # 18:
The NAA produced 86 Mustangs for the 1st time in April 1942, 68 was produced in Dec 1941, 84 next month - a bigger monthly production than the F4F that has 1 year of headstart in production. All of those Mustangs are for the RAF.
What NAA needs is a signed contract with USAF (along with provision for prioritized items/materials), pronto - 8th Dec 1941?, so both NAA and USA can devote more resources for the production of P-51. That way we'd see the increase in production, like it was case for P-38/39/40, whose production doubled from late 1941 to late 1942. The production of F4F went into triple digits in mid 1942, for example.
So we'd see the Mustang production making maybe 150 pcs monthly by the end of 1942, when P-39 was going to 300 pcs (already in Aug 1942 it was 306), the complicated P-38 at ~150, the F4F at almost 200. Even the P-47 was produced in 142 pcs in Dec 1942, despite a bit later start of production than P-51, but 3 factories started producing the Jug by then.



Better/longer ranged fighter coverage of Italian possessions in mid/late 1943? Earlier introduction of second (and third?) source for Mustang? Freeing more P-38s for ETO and Pacific? Hammering home the fact that P-47 needs both a better drop tank facility and more internal fuel, earlier than historically? No P-63? Earlier increase of internal fuel for mainstream Spitfire variants and the Tempest?

Ok, now you are not just changing the from one engine to another it the historic number of airframes produced but totally revamping the entire US fighter production scheme. And changing budget allocations and changing factory expansion and or construction and moving thousands of workers around. Given enough resources and unhistorical dictatorial powers I guess you can up with any result you want. Of course you have to realize the Mustang is THE war winning airplane 5-6 months before it ever fires a shot in anger or even equips a full squadron in actual service.

A lot of pilots liked the way the F2A flew in it's early versions and the P-36/Hawk 75 also had a number of fans. Didn't mean they were war winning airplanes.

 

[kool kitty89]

You don't really have a unified supply system between the Americans and the British. Especially in late 1941 and part of 1942. You have airframes bought and paid for with British gold and engines bought and paid for with gold. You have British lend lease aircraft/engine which are paid for by the Americans and promised to the British (and obviously more subject to repossession by the Americans) . And you have American aircraft with nothing to do with the British.

I wasn't so much suggesting engines being 'taken away' from existing contracts, but more changing planning and orders made in 1940 relating to the NA-73 project, V-1650s, and V-1710s. For ANY of that to make sense, the NA-73 project would have needed to planned as Merlin powered from the get-go (or intended for both the Merlin and V-1710) and prototyped as such. Now, whether all of those were Packard V-1650-1s allotted to the British batches or American, of if British manufactured engines were to be installed, or a combination of all of the above, I'm not sure. (the British manufactured Merlin case seems a bit impractical though; it might be plausible from an objective logistics standpoint to have engineless airframes shipped to Britain for final assembly, but I'd think there's a lot that could go wrong with that, including greater difficulty in quality control and testing before leaving the factory, or unnecessary added work -such as test engines being fitted and then removed before transport)

The A-36s, if kept at low level didn't need the Melrin XX engine. Their engines had 7:48 supercharger gears and they had more take-off power than the Merlin was allowed normally and with WEP ratings they could hit 1500hp down low without abusing the engine. Now if people want to try and take the A-36 up stairs and play air superiority fighter with it then yes, you need a different engine.

The Mustang Mk.I/IA did use 8.8:1 supercharged engines (and the Mk.II of course used 9.6) so my previous comments at least still apply there.

Again, for the case of US Army planning for engine allocation to seriously consider the P-51 to receive priority for available V-1650 engines, they would have had to take much greater interest in the design in 1940. (and, again, North American would have had to include a Merlin XX powered prototype early on, in parallel with or preceding the Allison powered variant)

The 7.48:1 supercharged V-1710s would also be just as useful for P-40s dedicated to low level intrusion/ground attack, or P-39s for the same purpose (a role the USAAF seemed to prefer for the P-39). That, and it's something that failed to come up in the brief discussion in another thread regarding possible Allison powered Canadian Hurricanes. (admittedly again heavily dependent on military planning earlier on, but a low-alt V-1710 powered Hurricane could have made tons of sense for both fighter-bombers and the heavy cannon equipped IID equivalents)


On that note, though, does anyone have access to detailed military planning charts or performance/altitude graphs for any of the 7.48:1 supercharged V-1710s?

 

[kool kitty89]

One thing that hasn't been addressed yet is regulating engine RPM to control supercharger speed. (it's also something I overlooked here: http://www.ww2aircraft.net/forum/av...stions-military-vs-wep-43434.html#post1209492 )

Raise or lower engine RPM and you raise or lower supercharger RPM as well, so even with a single-speed supercharger you've got some potential for varying supercharger speed and at some altitudes (especially those well below FTH) the reduced power consumption of the supercharger and reduced charge heating results in a net increase in power. Additionally, less charge heating would allow maximum boost limits to be raised, further increasing potential maximum power at lower RPM.

In the above linked discussion, Soviets running V-1710s at 75" Hg manifold pressure was mentioned, and while this seems implausible at max RPM (especially with the 9.6:1 blower's heating and detonation limits and Allison's own testing of the 8.8 blower at SL maxing out closer to 70" with ram on the P-40 -P-39 should be less), it may very well be possible to run the 9.6:1 engines at 75" at low altitude and reduced RPM.

I have no idea what actual Soviet operating procedure was, but a good general example would be running a 9.6:1 supercharged V-1710 at 2800 RPM. This would result in the supercharger running at 2800x9.6 = 26,880 rpm compared to 26,400 rpm for an 8.8:1 engine at 3000 RPM. (or equivalent to a 8.96:1 ratio at 3000 RPM) With that modestly higher supercharger speed, the right conditions for intake temperature and supercharger performance may indeed have allowed 75" manifold pressure at low level (the low temperatures on the Eastern Front would also help). Additionally, lower RPM for a given torque value will mean less power and less stress on the engine, possibly making the overall strains closer to standard WEP ratings at 3000 RPM.

This would also apply to more modest boost pressures (again due to reduced charge heating and power consumed by the supercharger) and it may very well have been more optimal to run in the 2600-2800 RPM range at lower levels with both the 8.8 and 9.6 supercharger ratio V-1710s, possibly even closer to 2500 hp for take-off in the 9.6:1 case.

The standard procedure of using 3000 RPM for take-off and initial climb for USAAF aircraft seems somewhat ironic and counter-productive in this respect as well. Starting at 2600 RPM and shifting up to 3000 RPM once close to the FTH would make more sense and likely result in significantly improved initial and average rate of climb. (not to mention better specific fuel consumption) Similar should apply to the single-speed Merlin models and any single speed engine that doesn't have its FTH at very low level.


Assuming torque remains fairly constant for a given supercharger RPM and manifold pressure, nominal power output should remain proportional to engine RPM, so a 9.6:1 engine at 2750 rpm should have very nearly exactly 91.67% the power output of an 8.8:1 engine at 3000 RPM under similar conditions (altitude/ambient pressure and temperature, ram conditions, etc). So with the 8.8:1 engine capable of 1490 hp at 3000 RPM with 56" manifold pressure at 5000 ft, a 9.6:1 engine should be able to manage approximately 1366 hp at 2750 rpm.

 

[tomo pauk]

Ok, now you are not just changing the from one engine to another it the historic number of airframes produced but totally revamping the entire US fighter production scheme. And changing budget allocations and changing factory expansion and or construction and moving thousands of workers around. Given enough resources and unhistorical dictatorial powers I guess you can up with any result you want.

By Dec 7th 1941, the NAA has 15 thousands (15000) of employees, per AHT - there would be a change of where a hundred workers eng up, not thousands. There is no need for major change of revamping the US fighter production scheme - produce 120-150 Mustangs in 1942 monthly, vs. 80 P-51s or A-36s.
The NAA has a contract for LL (to RAF), dated July 7th 1941, to produce 150 of the cannon-armed P-51s (some of those end up in USAF service as photo recons). Plus 300+320 for Mustang I, to be paid by UK.

Of course you have to realize the Mustang is THE war winning airplane 5-6 months before it ever fires a shot in anger or even equips a full squadron in actual service.

USAF can test the XP-51 in late 1941 instead on March 1942 and come to some conclusions, the 1st XP-51 arrived at Wright Field in Aug 24th 1941.

A lot of pilots liked the way the F2A flew in it's early versions and the P-36/Hawk 75 also had a number of fans. Didn't mean they were war winning airplanes.

Those pilots were wrong, just like the Japanese were wrong until too late to emphasize maneuverability above other qualities of a fighter.

 

[wuzak]

I wasn't so much suggesting engines being 'taken away' from existing contracts, but more changing planning and orders made in 1940 relating to the NA-73 project, V-1650s, and V-1710s. For ANY of that to make sense, the NA-73 project would have needed to planned as Merlin powered from the get-go (or intended for both the Merlin and V-1710) and prototyped as such. Now, whether all of those were Packard V-1650-1s allotted to the British batches or American, of if British manufactured engines were to be installed, or a combination of all of the above, I'm not sure. (the British manufactured Merlin case seems a bit impractical though; it might be plausible from an objective logistics standpoint to have engineless airframes shipped to Britain for final assembly, but I'd think there's a lot that could go wrong with that, including greater difficulty in quality control and testing before leaving the factory, or unnecessary added work -such as test engines being fitted and then removed before transport)

Rolls-Royce suggested installting the Merlin XX and Merlin 61 in the P-51 after tests of the first Mustang to arrive in Britain. In the end none of the airframes given to Rolls-Royce were converted to Merlin XXs, instead they all received 60-series Merlins.

By the time this work was going on the Spitfire IX was in production, or was nearly so, and the same for the Merlin 61. So using the Merlin XX would only appeal if it were Packard engines being used.

The proposal from Rolls-Royce was to do exactly as you suggested - ship engineless airframes to the UK where a Rolls-Royce conversion facility would install the Merlin 61. This never eventuated as NAA were only months behind on the P-51B prototype, and it made little sense to have Rolls-Royce converting Allison models for a few months before the P-51B was rolling off the production line.

The other suggestion by Rolls-Royce, rejected by NAA as requiring too much work, was to install the Griffon 61, which Hives suggested, at that time, was the finest fighter engine in the world.

 

[Koopernic]

The only single stage 3 speed supercharger I have heard of is that of the BMW801F which was to equip the Fw 190A10, it was never built over tooling and bombing issues. Little information is available on it.

Nevertheless a study of the speed curves of aircraft with two speed and superchargers shows a number of jagged peaks and fall offs in speed that would have been smoothed by more than 2 speeds and by interpolation added a 10 or more mph speed advantage over many altitudes.

A BMW801D2 was easily able to maintain 1.42 ata to its critical altitude of about 20,000ft where air pressure is about 0.5 ata. I.E. pressure ratios of about 2.8:1 were practical. (It's often claimed that the British had superior centrifugal compressors that could handle higher ratios) If through good impellor design and an extra speed or two the supercharger can operate over say 4:1 or 4.5:1 our critical altitude would go up by 5000ft easily. This would have made a big difference to German fighters challenging American bombers and their escorts at around 25,000ft. The problem is that these ratios lead to temperature increases and would need to be dealt with by an intercooler, Water/Alcohol Injection or Rich mixture injection of high octane aromatic fuels to precool the superchargers.

The tendancy to 'overboost' engines to gain power as fuels became better rather than to increase compression ratios also must have challenged supercharger performance and surge limits.

 

[Shortround6]

I would note that the best centrifugal compressor in a jet engine reached about 4.8 and that was several years after the war if not in the early 50s. Maybe they do better now but anything over 4.0 to 1 was just unreachable outside of a laboratory in WWII. The DH Goblin compressor was 3.6 for example, Derwent I was 3.9 .

It was also a known fact that a two stage compressor to less power and heated the air less for a given level of compression than a single stage compressor even if the singe stage could reach the pressure desired.

Building 3 speed drives is a bit more difficult than 2 speed drives. They are going to be heavier and bulkier in addition to the added mechanical complexity. Depending on the engine the drive may have to handle anywhere from 100 to 350hp (or more, R-2800 took around 350hp just to drive the auxiliary supercharger in high gear.) Early Allison drive system couldn't handle the load of 9.60 gears and the Merlin needed a beefed up (larger diameter ?) driveshaft to the supercharger gears to reliable go above 15/16lbs boost.

Is the added cost and complication worth the result? Some countries were, at times, limited in their gear cutting ability. Fewer planes with slightly better supercharger set ups vs more planes with two speed drives?

raising compression ratio in the cylinder will not make anywhere near the same power with a given fuel as raising the boost.

 

[Koopernic]

I would note that the best centrifugal compressor in a jet engine reached about 4.8 and that was several years after the war if not in the early 50s. Maybe they do better now but anything over 4.0 to 1 was just unreachable outside of a laboratory in WWII. The DH Goblin compressor was 3.6 for example, Derwent I was 3.9 .

It was also a known fact that a two stage compressor to less power and heated the air less for a given level of compression than a single stage compressor even if the singe stage could reach the pressure desired.

Building 3 speed drives is a bit more difficult than 2 speed drives. They are going to be heavier and bulkier in addition to the added mechanical complexity. Depending on the engine the drive may have to handle anywhere from 100 to 350hp (or more, R-2800 took around 350hp just to drive the auxiliary supercharger in high gear.) Early Allison drive system couldn't handle the load of 9.60 gears and the Merlin needed a beefed up (larger diameter ?) driveshaft to the supercharger gears to reliable go above 15/16lbs boost.

Is the added cost and complication worth the result? Some countries were, at times, limited in their gear cutting ability. Fewer planes with slightly better supercharger set ups vs more planes with two speed drives?

raising compression ratio in the cylinder will not make anywhere near the same power with a given fuel as raising the boost.

I think overall you are correct, I see the main advantage of three speeds on a single stage engine actually at low altitude (rather than high) due to the practice of over boosting engines to gain WEP. Three speed drives were starting to make an appearance at the end of WW2; in the case of Junkers there was the Jumo 213E and 213F (the same engine, differing in intercooler) that actually saw some service in the Ta 152H and Fw 190D12 respectively. These were both two stage engines but they would start making an appearance in single stage engines simply because they had been developed and were available. The BMW801F supposedly was to get it. Incidentally Dietmar Herman in 'long nose' notes that the first 200 Jumo 213E/F were defective due to a weak supercharger drive shaft which caused quite a few problems in the Ta 152H. I'm not quite sure how much more complex they were. I would have though 4 speeds might be easy in a sort of double clutch arrangement as used in some Borg Warner Gearboxes on modern VW cars. The small steps in speed would reduce the shock of changing gear. At a certain point a hydraulic drive becomes attractive perhaps due to the 'gentleness' of the stress on the gears and shaft from the lack of sudden shifts as we saw on the Allison V1710 and DB series. The DB603N had the usual DB variable hydraulic drive but actually two mechanical speeds on top that could be selected as too mission type.

Modern centrifugal compressors can handle 10:1 pressure ratio since about 1970-80. It hasn't lead to return of the centrifugal compressor, but they do show up in the turboprops and some small turbofans with high bypass ratios and complex double reverse flow combustion chambers.

 

[wuzak]

I would note that the best centrifugal compressor in a jet engine reached about 4.8 and that was several years after the war if not in the early 50s. Maybe they do better now but anything over 4.0 to 1 was just unreachable outside of a laboratory in WWII. The DH Goblin compressor was 3.6 for example, Derwent I was 3.9 .

It was also a known fact that a two stage compressor to less power and heated the air less for a given level of compression than a single stage compressor even if the singe stage could reach the pressure desired.

Building 3 speed drives is a bit more difficult than 2 speed drives. They are going to be heavier and bulkier in addition to the added mechanical complexity. Depending on the engine the drive may have to handle anywhere from 100 to 350hp (or more, R-2800 took around 350hp just to drive the auxiliary supercharger in high gear.) Early Allison drive system couldn't handle the load of 9.60 gears and the Merlin needed a beefed up (larger diameter ?) driveshaft to the supercharger gears to reliable go above 15/16lbs boost.

Is the added cost and complication worth the result? Some countries were, at times, limited in their gear cutting ability. Fewer planes with slightly better supercharger set ups vs more planes with two speed drives?

raising compression ratio in the cylinder will not make anywhere near the same power with a given fuel as raising the boost.

Having the extra gear on a single stage engine helps only if the supercharger has a high critical altitude. Like for the Merlin 46/47. It helps with the lower altitudes.

Also, changing gears isn't instantaneous, so there must be some loss of performance if there are many changes.

 

[kool kitty89]

At a certain point a hydraulic drive becomes attractive perhaps due to the 'gentleness' of the stress on the gears and shaft from the lack of sudden shifts as we saw on the Allison V1710 and DB series. The DB603N had the usual DB variable hydraulic drive but actually two mechanical speeds on top that could be selected as too mission type.

This again make me think about RPM limiting to regulate supercharger speed. Matching (close to) optimum RPM and boost for given altitude/atmospheric pressure within alloted power/RPM limits on a given engine design would seem to have at least some of the same advantages of the hydraulic system (including on single-speed superchargers -the early DB-601s just have one smoothed power curve with a peak, so single gear vs 2 on the 601E and 605).

Now, you'd either have to have pilots manually regulate all that, or have an automatic rev-limiting system on top of automatic boost control (or one or the other, leaving the pilot to make up the difference). Could linking prop pitch control to an altitude (or altitude+throttle setting) defined rev limiter be practical for the time?

Early Allison drive system couldn't handle the load of 9.60 gears and the Merlin needed a beefed up (larger diameter ?) driveshaft to the supercharger gears to reliable go above 15/16lbs boost.

On the note of the V-1710's supercharger gear/teeth load issues, would putting RPM limits on an earlier 9.6:1 engine (say in the -39 or even -33 vintage time period) below critical altitude avoid the strain on the drive gears? (and, like the DB 601, allow overrev -ie full 3000 RPM in this case- at some point above critical altitude at the lower speed -say 2750 or 2800 RPM, the former literally running the supercharger at the same speed as 8.8:1 would at 3000 RPM) Or would the lower tooth count on the gear still end up causing it to be too weak in spite of less power actually being transmitted?

The early V-1710s seem to have left quite a bit of headroom for boost increase without risking detonation (even on 100/100 octane fuel -let alone 100/130), so dropping RPM and increasing boost limits while staying within structural tolerances seems feasible.

Those pilots were wrong, just like the Japanese were wrong until too late to emphasize maneuverability above other qualities of a fighter.

I'm not really sure that's relevant to the P-36 or F2A, at least given the contemporary competition. (P-40 and F4F-3) Brewster's manufacturing and management woes aside, was the F2A-3 actually worse on the whole than the F4F-3? (or F4F-4 -let alone the jumble of single-stage R-1830 and R-1820 powered versions) British test pilots complemented the Buffalo Mk.I's handling characteristics in spite of it being weighed down with protection roughly equivalent to late BoB Spitfires/Hurricanes and P-40Bs. (metal tanks covered in self-sealing material, armor plate, armor glass windscreen)

Is there any actual USN/USMC combat where both F2A-3s and F4Fs were present?

And while the P-36 wouldn't beat the P-40 in speed, had it kept getting similar engines to the contemporary F4F (both single and 2-stage) along with upgraded armament and protection of the P-40, it should have held up better than the F2A or F4F taking advantage of energy tactics while possibly having better altitude performance (perhaps more so climb than level flight) than the similarly configured P-40.

But as far as up-arming/armoring those fighters vs leaving them lighter, yes that's certainly preferable AND that weight is a major part of gaining superior dive performance (the lighter Export Hawk 75s dove slower than the Spitfire I due to a combination of drag and lower weight -it still shared the superior high speed control of P-40). That might be an area the F4F beats the F2A. (but it'd still probably be close -the F2A might have the lead had it been adapted to the narrower R-1830, probably more significant drag difference than the F4F saw -it's bulky enough that the wider R-1820 Cyclone doesn't make as much difference)

 

[tomo pauk]

....
The 7.48:1 supercharged V-1710s would also be just as useful for P-40s dedicated to low level intrusion/ground attack, or P-39s for the same purpose (a role the USAAF seemed to prefer for the P-39). That, and it's something that failed to come up in the brief discussion in another thread regarding possible Allison powered Canadian Hurricanes. (admittedly again heavily dependent on military planning earlier on, but a low-alt V-1710 powered Hurricane could have made tons of sense for both fighter-bombers and the heavy cannon equipped IID equivalents)

The 7.84:1 supercharged V-1710 (like the V-1710-87 (F21R) on the A-36) have had military power of 1325 HP at 3200 ft vs. 1150 HP at 12000 ft on the earlier 'F' models - slower spinning S/C meant it will use less power, while a bit greater boost (46.5-47 vs. 42-44 in Hg) will be manageable for extended period of time due to less charge heating. The WER will be lacking, though, with no ram we would see ~1460 HP at ~51 in Hg at SL as the best value.

On that note, though, does anyone have access to detailed military planning charts or performance/altitude graphs for any of the 7.48:1 supercharged V-1710s?

To the gold mine: table. The table agrees with the chart found at pg. 272 of the 'Vee's for victory'.

edit: with ram, the power values are listed in this table (kindly provided by krieghund, open the pic separately):

 

[Denniss]

Do we have sources confirming a 3-speed superchanrger on thwe 801F ? I have only seen 2-speed with improved alt performance and more power through all alts.
Jumo 213 E/F supercharger is at least for me somewhat mysterious, power graphs look more like two speed charger like 213A but with an additional high alt stage.

 

[tomo pauk]

Von Ghersdorf et al do not list the 3-speed S/C for the 801F, nor it does list the MW 50, of course. These are changes, vs. 801E, listed in their book: reinforced cranskhaft, counterweights (on the crankshaft) with dampers, bigger inlet and outlet valves withing a bigger 'Ventilhub' (valve case; head?) and changed valve timing, bigger injection pump, external air intake with entrance in the wing 'nose' (ie. wing leading edge), 'increase' in S/C gearing (= S/C will turn faster RPM per same crankshaft RPM), improved internal and external aerodynamics of the 801TF power egg. Designed with easier attachment for the turbo-charger. Take off power 2400 PS, climb power up to 2200 PS, rated height expected to be at 7-8 km of altitude. Bench- and flying tests successfully passed. At test bench 2600 PS achieved. The power egg 801TF was expected to power a version of Ta 152, 250 mm of increase of power egg (??, probably requiring a longer engine bearer than what V-12 had) would be required to meet CoG requirements.

The power graph of the Jumo 213E shows that MW 50 operation ('Sonder-Notleistung' power setting, start at 2050 PS at sea level) is allowed only for 1st two S/C speeds. When looking to the second best power setting ('Notleistung', start at ~1730 PS at sea level = take off power, or 'Startleistung'), 3 'kinks' for 3 S/C speeds are easy to spot, as they are on other, less 'agressive' power settings. The GM1 operation has 3 small lines, each line for a different amount of the mixture injected.
Additional stage would mean additional impeller/supercharger, it already featured 2 impellers somewhat in Merlin 60s style.

 

[Denniss]

power loss and fuel consumption in the second 'kink' are diferent to the first one, either a massive rpm increase for the supercharger or just the second stage kicking-in.

 

[tomo pauk]

The second stage, or second impeller, was turning on the same shaft as the 1st impeller. The faster the S/C is turned, it's efficiency is dropping. So it should be the significant increase of S/C RPM when 3rd gear was shifted in, that increased the consumption.

edit: picture showing 1-stage S/C on the Jumo 213A and 2-stage on the Jumo 213E

 

[Denniss]

Are you sure the second stage was always active? Your comment sounds like it was. Then it would require a higher gear to get high alt charging.
I'm a bit suspicious about this but I don't have exact sources about this system.

 

[kool kitty89]

The second stage, or second impeller, was turning on the same shaft as the 1st impeller. The faster the S/C is turned, it's efficiency is dropping. So it should be the significant increase of S/C RPM when 3rd gear was shifted in, that increased the consumption.

edit: picture showing 1-stage S/C on the Jumo 213A and 2-stage on the Jumo 213E

Given the figures on the chart, it seems like that 3rd speed is a bit beyond the really useful performance (and efficiency range) particularly given the high critical altitude. (that or lowing all 3 speeds, but it's the high gear that seems problematic) Targeting the 3rd stage crit alt 1-2km lower seems like it'd make a lot more sense while still giving a smoother power curve than the contemporary 2-stage Merlin series. Granted, the same shift occurred between the V-1650-3 and -7, except A. the -3 still wasn't tuned quite as high as the 213 appears to be here, and B. the 3 speeds means it could better compromise and avoid the larger altitude performance gap between the -3 and 7. (ie more like if the Merlin could be arranged to use the -7's MS gear as low, middle gear between the -7's FS and 3's MS gear range, and high gear similar to the -3's FS gear)

Or in short, just optimized so high gear was in the ~8 km range rather than over 9.5km.


Though I suppose, using the exact same engines, simply running one of the lower RPM settings at higher boost pressures might come close to the same effect. (you'd need more specific testing for detonation limits at given supercharger RPM, or at least re-applying existing data for different operational conditions in service -ie supercharger RPM at high engine RPM and lower gear should be similar to lower engine RPM in higher gear, and detonation test results should be mostly comparable aside from any quirks related to varying piston speed)

Low RPM and high boost should also give better fuel consumption than similar powers at similar mixture proportions at higher RPM and lower manifold pressure.

Are you sure the second stage was always active? Your comment sounds like it was. Then it would require a higher gear to get high alt charging.
I'm a bit suspicious about this but I don't have exact sources about this system.

The 2-stage merlin and griffon used similar arangements with 2-speeds and both impellers on a single shaft. The same would apply to a multi-speed single stage arrangement, there's an optimal mechanical efficiency range for any compressor and additional issue of density losses due to heating (so that part of efficiency keeps going down as impeller speed goes up, even in the 'sweet spot' of mechanical efficiency of best pressure gain for given power consumed). So it's just likely that the 1st and 2nd supercharger gears are closer in efficiency (mechanical and thermal/charge density related) than the 2nd and 3rd gears are, at least with the engine running at max RPM. (lower engine RPM = lower supercharger RPM, which should push the high gear into a more competitive efficiency range at low engine RPM)

 

[Koopernic]

Page 129 or Hermann's book on the Ta 152H specifically states that the Jumo 213E had a two stage 3 speed supercharger. I suppose there is the possibility that this consisted of a single speed first stage that could be declutched combined with a two speed second stage but that sounds like a complicated arrangement. It was used on the PW R2800 Corsair/Hellcat engines. He also notes that a weak drive shaft ruled out the use of the highest speed something that was fixed in the Jumo 213E1 (ie the E0 must have been defective and we hear of numerous supercharger failures on the descriptions of Ta 152 missions). In "long nose", Hermann's book on the Fw 190D, he notes the problem also existed in the Jumo 213F, the first 200 Jumo 213E or F had this problem. The Fw 190D did not have room for the Jumo 213E1 intercooler but it seems that the intercooler on the Jumo 213EB was arranged such that it could be used in both the Ta 152 and Fw 190D.


Given the practice of increasing engine power via high ratios of overboosting I suspect that even if a 3 speed single stage doesn't increase critical altitude it will smooth the power curve at low altitudes and moreover lead to improved cruising performance, the latter might be quite important.

Post edit, given Tommo's picture its clear it used a single combined shaft for both impellors. The second impellor looks most unusual.