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



## gjs238 (Jun 11, 2015)

Much has been discussed here of multi-*stage *superchargers, but less of multi-*speed *single-stage superchargers.

The DB engines used a hydraulic fluid coupling with a barometric control to achieve multi-speed drive with a seamless power curve.
Other engines featured multiple speeds, kinda like a stick/manual/standard shift transmission in a car, with a jagged power curve.
The V-1710 was stuck with one speed.

- Wasn't one reason for using the V-1650 in the P-40 because it had a 2-speed drive?
- Could an excellent multi-speed drive somewhat mitigate the effects of having only one stage?
- Which engines and aircraft had multi-speed drives? Which had only single speed?
- Whatever else comes to mind


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## Shortround6 (Jun 12, 2015)

> - Wasn't one reason for using the V-1650 in the P-40 because it had a 2-speed drive?
> - Could an excellent multi-speed drive somewhat mitigate the effects of having only one stage?



In 1941 (Summer/Fall) the Merlin had a better supercharger than the Allison, *period*. Packard was building the Merlin XX, not the single speed Merlin 45 so that is what the P-40 got. Advantage of the Merlin XX over the Merlin 45 was it gave 1280hp for take off instead of 1185hp at the same boost and rpm. Difference at altitude was only few dozen HP or around 1000 ft. The most marked difference between a plane equipped with a Merlin XX instead of a Merlin 45 is going to be at the lower altitudes where the Merlin XX offers around 100hp more than the Merlin 45 while in low gear. 

It would't matter how many gears you used on a Merlin XX/45 supercharger (they were the same for all practical purposes) the inlet/impeller/housing was pretty much maxed out at around 19-20,000ft. (with RAM) It was flowing all the air it could at as high a pressure as it could while maintaining decent efficiency. Using a 3 speed drive might give you a bit more take-off power and take out the worst of the "dip" between low gear and high gear it wasn't going to do much, if anything, for altitude. 

A two-stage supercharger does NOTHING for very low altitude performance as any even mediocre single stage supercharger can deliver all the manifold pressure an engine can stand at sea level. SO a multi speed (more than 2?) single stage doesn't do anything for low altitudes and doesn't do anything for altitudes over the 16-20,000ft range (or less depending on how good the single stage supercharger is) leaving your extra gears (over two) very little to do on a single stage engine. 

You can only drive a single stage impeller so fast before the tip speed exceeds the speed of sound in the conditions inside the supercharger (temperature and pressure) and starts up shock waves that interfere with the airflow. It doesn't matter how excellent (or how bad) the supercharger drive mechanism is. The two are not related. 

You will find that the vast majority of superchargers (and engines) at the beginning of the war had critical altitudes of around 11-14,000ft. This is due in large part to the fuel. with 87 octane there is only so much boost you can use (or how much you can compress the air in the supercharger) even at 12,000ft before detonation sets in. US 100 octane helped but US 100 octane was also only 100 octane when running rich so while it may have helped point the way to needing better superchargers ( Like the P&W two stage or the turbos) but it didn't allow for the over 5 to 1 pressure ratio used by the Melrin 60/61 two stage. 
The basic superchargers needed to be improved (better inlets, better impellers, better guide vane set ups and better diffusers) to get better altitude performance before fooling around more complicated supercharger drives.

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## tomo pauk (Jun 12, 2015)

gjs238 said:


> ...
> - Wasn't one reason for using the V-1650 in the P-40 because it had a 2-speed drive?



Nope, that was not the reason. Main reason was redundancy - USAAF was not 100% sure that Allison will be able to supply all these V-1710s needed for P-38/39/40 in numbers needed. In 1940, the Merlin was a known quantity, the V-1710 less so - that was an insurance in case the V-1710 turned to be a lemon, or a dead end when it is about further development. For same reason, the P-44/47B were started, so not all the eggs are in one basket, engine-wise.


> - Could an excellent multi-speed drive somewhat mitigate the effects of having only one stage?



In case the V-1710 is slated for bombers, the 2-speed drive would've helped. Otherwise, no much gain IMO.


> - Which engines and aircraft had multi-speed drives? Which had only single speed?



Single speed S/C drive - vast majority of the Mikulin's engines, Italian radial engines, Bristol Mercury Taurus, also some Hercules engines, Merlin I/II/III/VIII/XII/30/45-50 (and 'M' versions), Hispano X12/Y12.



> - Whatever else comes to mind



Want a V-1710 to perform above 20000 ft? Crank up the work on the 2-stage variant (and stick it on the P-51 for starters), or design an aircraft with turbo in mind.

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## Shortround6 (Jun 12, 2015)

I would add as far as the P-40 goes that it was the only logical choice. The Original contract for the Merlin engine with Packard was for 9,000 engines of which the British were to get 6,000 and the US 3,000. They had to go in _something_ and they sure weren't going to work in P-39s. Much as members here fantasize about P-38s with Merlin engines that wasn't going to happen either in early 1942. A a pair of engines offering 1100hp at 20,000ft (Merlin XXs ) or a pair of engines offering 1150hp at 25,000ft (turbo Allison's). Please remember it took around 6 months from Prototype P-40F to first production example. Messing around with the P-38 in the fall of 1941 could have meant hundreds fewer P-38s built in 1942. 
Leaves the P-40 to use up the Merlins by default.


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## SpicyJuan11 (Jun 12, 2015)

Forgive me for going a bit off topic, but how do (multiple) turbochargers compare to a 3 speed supercharger (thinking BMW 802 vs BMW P.8011?


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## gjs238 (Jun 12, 2015)

No multi-speed single-stage R-1830 or R-2800?


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## Shortround6 (Jun 12, 2015)

You had two speed R-1830s and two speed R-2800s. what is the 3rd gear going to do? 

The engine in the early B-26 used an 11in impeller and used a 10.0:1 high gear. If I am doing the math right that means the impeller tip speed was 1247fps. The impeller tip speed in a Merlin XX (V-1650-1) was 1272fps. 2% faster? 

Military rating was 1500hp at 14,000ft, and you can't spin the impeller much faster. At the 2400rpm max continuous (or climb?) the critical altitudes were 7500ft in low gear (1500hp) and 13,000ft in high gear (1450hp). A 3rd gear would smooth out the dip at 10,000ft? 

R-1830s also used an 11in impeller but I have no idea if it used the same number of blades or if it was even near the same thickness. ( thicker means more volume per revolution of the impeller) high gear was usually 8. 47. and most R-1830s were good for 2700rpm. 

Late war R-1830s were rated at 1350hp for take-off at 2800rpm and used the same gear ratios and same diameter impeller, I don't know if there were other changes. High gear Military rating went from 1050hp at 13,100ft to 1100hp at 13700ft with the impeller spinning 847rpm faster due to the higher rpm limit. Most of the power was coming from the extra rpm. Part of the R-1830s altitude problem came from the fact that it was using 48in (9lbs boost) for it's take-off and low altitude (low gear) military ratings. It needed more boost to get similar power to the Allison. Low gear was used to get better take-off performance but a single stage R-1830 needed more than spinning the impeller faster to make power at altitude. Impeller tip speed was 1097fpm.
Power needed by the supercharger is proportional to the sq of the tip speed. An impeller running at 1250fpm tip speed needs just under 30% more power than one running at 1100fpm, every thing else being equal.


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## gjs238 (Jun 12, 2015)

By "multi-speed" I meant more than one speed, not necessarily three-speed.


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## kool kitty89 (Jun 13, 2015)

Shortround6 said:


> I would add as far as the P-40 goes that it was the only logical choice. The Original contract for the Merlin engine with Packard was for 9,000 engines of which the British were to get 6,000 and the US 3,000. They had to go in _something_ and they sure weren't going to work in P-39s. Much as members here fantasize about P-38s with Merlin engines that wasn't going to happen either in early 1942. A a pair of engines offering 1100hp at 20,000ft (Merlin XXs ) or a pair of engines offering 1150hp at 25,000ft (turbo Allison's). Please remember it took around 6 months from Prototype P-40F to first production example. Messing around with the P-38 in the fall of 1941 could have meant hundreds fewer P-38s built in 1942.
> Leaves the P-40 to use up the Merlins by default.


The only other sensible option would have been the Mustang, and for that to work, the USAAF would have needed to take interest sooner AND North American would have to put emphasis on adopting the V-1650 from the start (at very least in parallel with the Allison powered prototypes). With the existing British interest in that design, importing a British (or Canadian) Merlin XX for prototype expedience may have made sense as well.


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## gjs238 (Jun 13, 2015)

Shortround6 said:


> I would add as far as the P-40 goes that it was the only logical choice. The Original contract for the Merlin engine with Packard was for 9,000 engines of which the British were to get 6,000 and the US 3,000. They had to go in _something_ and they sure weren't going to work in P-39s. Much as members here fantasize about P-38s with Merlin engines that wasn't going to happen either in early 1942. A a pair of engines offering 1100hp at 20,000ft (Merlin XXs ) or a pair of engines offering 1150hp at 25,000ft (turbo Allison's). Please remember it took around 6 months from Prototype P-40F to first production example. Messing around with the P-38 in the fall of 1941 could have meant hundreds fewer P-38s built in 1942.
> Leaves the P-40 to use up the Merlins by default.



Or the P-51?
"Messing around" with the P-51 may have been less risky than with the P-40 (and with hindsight, more rewarding.)


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## Shortround6 (Jun 13, 2015)

With at least the first 620 Mustangs being built to British orders and being paid for by the British cash, not lend lease, the Americans had very little interest in powering British aircraft with engines form the American allotment of the production total. What the British choose to do with their first 6,000 Packard built Merlins was up to them. Please note it took until April of 1943 to complete the first 9,000 Packard Merlins. I don't know if the US actually took ALL 3,000 but in the Spring, Summer and Fall of 1941 when allocations and production planning for 1942 was going on The Mustang was hardly a blip on the American plans. The first flight (work started when?) of the XP-40F was _before_ a production P-40D was delivered to the Air Force and was, in fact less than 2 months after the last production P-40C was built and less than 2 months after the the first P-40D (prototype?) flies. It is also about 7 weeks _before_ the first XP-51 shows up and Wright Field to be ignored. 
So even if Wright Field HAD flown the P-51 extensively in the first week they had it, decided it was the greatest thing since sliced bread and cold beer combined AND figured out the advantage of Sticking a Merlin XX engine in it you are about 4-6 months behind the P-40F in timing. Without commandeering even more of the British aircraft The Americans aren't going to get any P-51s with either engine until the Summer/Fall of 1942. First P-51A (first lend lease aircraft) is delivered in July of 1942. First flight of a P-51 (NA-91) took place back on May 29th 1942 BUT please note that the order for the P-51s (lend lease) was placed on July 7th, 1941, 8 days after the XP-40F first flew. 

Now I may have mixed up a date in their (or two?) but I hope you get the idea. Orders were placed and plans of engine (and other resources) allocations were made months if not a year _before_ the aircraft began to come out of the factory doors, let alone make it to service squadrons. Some last minute changes might be made but the people in charge were very hesitant in case something went wrong and one factory or another was left with dozens if not hundreds of airframes waiting for engines. In 1941 the Army was rationing Allisons at times to the 3 manufacturers that needed them and lets remember that in 1943 North American early production of P-51Bs easily out stripped the supply of V-1650-3 engines for a few months.


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## tomo pauk (Jun 13, 2015)

The British can choose to give the Mustang/Merlin a chance, once both Packard and NAA deals are signed. Just like they provided the Merlin XX for the 1st prototype of the P-40F. 
Based on experiences of the BoB, they can add two and two together, and conclude that a V-1710 powered Mustang (with 1150 HP at 12000 ft) will not cut it as good as Merlin powered one (1150 HP at 18500 ft) at altitude. The USAF can test the resulting aircraft and then decide it is worth their attention.
The production of 1-stage Packard Merlins amounted to 4850 pcs in second half of 1942, and ~4500 pcs in 1st half of 1943. 

Other, non-Merlin options (with caveat that Curtiss produces 'A-40', so fighter funds can be re-allocated to NAA):
- push for Mustang with 9.60:1 supercharged V-1710 instead of A-36
- two stage V-1710 for Mustang


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## Shortround6 (Jun 13, 2015)

tomo pauk said:


> Other, non-Merlin options (with caveat that Curtiss produces 'A-40', so fighter funds can be re-allocated to NAA):
> - push for Mustang with 9.60:1 supercharged V-1710 instead of A-36
> - two stage V-1710 for Mustang



Uh, time line check, P-51As got the Allison V-1710-81 with the 9.60 gears, They just don't show up until march of 1943. They were ordered in June of 1942. Now here is the 'funny' thing. P-40s didn't get the Allison V-1710-81 with the 9.60 gears until the M model (deliveries start in Dec of 1942) and the N models, N-1 is the "stripper" and doesn't show up until _surprise_, March of 1943. 
You can play all the 3 card Monte you want with trying to change engines around between P-51s, A-36s, P-40s and_ A-40s_ but the 9.60 engines don't show up until the winter of 1942/43. Mustangs got them only a few months after the P-40s.


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## tomo pauk (Jun 13, 2015)

The AHT lists both P-39 and P-40 with 'faster' superchargers 1st delivered in November 1942 (the P-51A indeed 1st delivered in March 1943), a month after the A-36 is 1st delivered. The A-36 are in N. Africa in April 1943 - so the 'early P-51A' should enter the combat in May 1943, instead in September 1943?


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## Shortround6 (Jun 13, 2015)

We have a bit of confusion as to built and/or delivered and/or delivered where. We especially have a bit of a problem with getting aircraft to specific war zones. 
1. A Factory can a roll a plane out the door and declare it "built". 
2. A plane can be test flown (or acceptance flight) at the factory airfield and upon being signed off on (accepted by government representative) declared "delivered" to the Army or Navy. 
3. A plane can be declared "delivered" when it arrives at an Army or Navy depot for any additional work required or for issue to using unit. Once things got going planes rarely went directly from the factory to the service squadron.
4. For delivery of Curtiss and Bell aircraft vs North American Aircraft to the Med or to Britain you have the voyage through the Panama canal just to get to the Atlantic ocean. Figure 3-4 weeks minimum extra travel time if not more (several weeks) depending on convoy schedules. It's either that or "knock down" the plane (remove wing) crate them and ship cross country by train to Atlantic Port. 
Now if you are sending planes to the South Pacific the Mustangs should have had an advantage


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## tomo pauk (Jun 13, 2015)

I'm trying to use the 'A-36 rule of the thumb' - counting from the 1st delivered example, it took 6 months for them to be in a war theater (North Africa). With 'early P-51A' 1st delivered in Nov 1942, we add 6 months for them to be in a war theater (be it North Africa, or, maybe UK - the distance from California is similar)- meaning it is May 1943.


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## Shortround6 (Jun 13, 2015)

are you really going to get enough to make any difference to the war, not just the Mustang record book?

In the Oct-Dec of 1942 Bell was building just under 300 P-39s a month. Curtiss was building 360-404 P-40s a month. It took NA from Oct to March to build 500 A-36s. NA never exceeded 86 Mustangs a month until April of 1943. Perhaps they could have gained some speed had not the production lines been disrupted by the A-36 (fitting dive brakes and such) but it would take a while to build up any meaningful number of 9.60 gear Mustangs. 2-3 squadrons per month?


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## kool kitty89 (Jun 13, 2015)

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.


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## tomo pauk (Jun 13, 2015)

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.



> are you really going to get enough to make any difference to the war, not just the Mustang record book?



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?


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## wuzak (Jun 13, 2015)

Shortround6 said:


> You had two speed R-1830s and two speed R-2800s. what is the 3rd gear going to do?



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


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## kool kitty89 (Jun 13, 2015)

tomo pauk said:


> 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)



wuzak said:


> 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.


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## Shortround6 (Jun 13, 2015)

kool kitty89 said:


> 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.


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## Shortround6 (Jun 13, 2015)

tomo pauk said:


> 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.
> ...



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.


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## kool kitty89 (Jun 14, 2015)

Shortround6 said:


> 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?


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## kool kitty89 (Jun 14, 2015)

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.


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## tomo pauk (Jun 14, 2015)

Shortround6 said:


> 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.


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## wuzak (Jun 14, 2015)

kool kitty89 said:


> 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.


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## Koopernic (Jun 14, 2015)

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.


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## Shortround6 (Jun 14, 2015)

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.


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## Koopernic (Jun 14, 2015)

Shortround6 said:


> 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.
> 
> ...



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.


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## wuzak (Jun 15, 2015)

Shortround6 said:


> 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.
> 
> ...



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.


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## kool kitty89 (Jun 15, 2015)

Koopernic said:


> 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?




Shortround6 said:


> 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.






tomo pauk said:


> 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)


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## tomo pauk (Jun 15, 2015)

kool kitty89 said:


> ....
> 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):


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## Denniss (Jun 15, 2015)

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.


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## tomo pauk (Jun 16, 2015)

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.


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## Denniss (Jun 16, 2015)

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.


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## tomo pauk (Jun 16, 2015)

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


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## Denniss (Jun 16, 2015)

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.


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## kool kitty89 (Jun 16, 2015)

tomo pauk said:


> 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.





Denniss said:


> 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)


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## Koopernic (Jun 17, 2015)

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.


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## wuzak (Jun 17, 2015)

Koopernic said:


> 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.



If the two stages were on different shafts, with one having two speed ratios and the other having one speed ratio the supercharging system would still only have 2 speeds. If both shafts had 2 speeds then they would have 4 speeds all up.

The P&W R2800 used in teh Corsair and Hellcat had the supercharger impellers on different shafts as you say, with the engine supercharger having a single, fixed, ratio, while the auxiliary supercharger had two ratios (Hi and Lo) and a neutral (impeller not spinning).


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## wuzak (Jun 17, 2015)

kool kitty89 said:


> 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)



You have to look at what they wanted the high altitude engine for. Mostly it was to combat USAAF bombers, which often flew 25-30,000ft) and their escorts (which usually flew higher).

The V-1650-7 was introduced to the Mustang to give it better performance and middling altitudes, especially concerning climb rates. When the P-51H was introduced it had the -9, with the critical altitude raised to the same as the -3, if not higher. 

Of course the boost affects the critical altitude. The higher the boost, the lower the critical altitude.

Perhaps the Griffon is a better comparison. It is the same capacity, and later versions were fitted with a 3 speed supercharger. In the Griffon's case, the extra gear was for low altitude. The supercharger was redesigned to slightly increase critical altitude in full supercharger gear (S). Can't recall if medium supercharge gear increased as well.

In Rolls-Royce rating terms all the two speed 2 stage engines were rated RM-##SM, where S and M stood for fully supercharged and Medium supercharged.

Similarly 2 speed 2 stage Griffons were RG-##SM.

The three speed Griffons were RG-##SML, where L stood for low supercharged.


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## tomo pauk (Jun 17, 2015)

Denniss said:


> 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 comparative drawing shows that 1st stage is always feeding the 2nd stage with compressed air - in case the 2nd stage is not clutched in, the internal S/C losses would be huge.









kool kitty89 said:


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



Lets remember that S/C gearing was calculated/designed with MW 50 operation in mind, as such it makes plenty of sense to tailor the 3rd gear to 9.5 km rated height. With MW 50 in use, the rated height would be at around 8-8.5 km, but it took a while to introduce the version of 213E that would allow for MW 50 operation also in 3rd gear. 

@ Koopernic:


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



The second impeller looks like the carbon copy of the DVL-designed impeller, used on Jumo 211F and subsequent.


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## kool kitty89 (Jun 17, 2015)

tomo pauk said:


> The second impeller looks like the carbon copy of the DVL-designed impeller, used on Jumo 211F and subsequent.


Looking at that diagram, it also appears the impellers for the 2 stages were identical or nearly identical in diameter, but the first stage used a taller/broader pitch for the blades/vanes of the impeller. (so larger area and should be getting higher mass flow)


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## Koopernic (Jun 17, 2015)

Technically it might even be 3 stages, note the axial flow fan in front of the two centrifugal stages. This probably functioned in a similar manner to the inductor fan in front of Heinkel Jet engines providing a low level of compression to smooth the airflow. In other words high volume low pressure.

The first stage of the centrifugal compressor looks unshrouded, the second stage seems to have integral shrouding on the impellor.


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## kool kitty89 (Jun 17, 2015)

Koopernic said:


> Technically it might even be 3 stages, note the axial flow fan in front of the two centrifugal stages. This probably functioned in a similar manner to the inductor fan in front of Heinkel Jet engines providing a low level of compression to smooth the airflow. In other words high volume low pressure.


I believe that would actually be the variable inlet guide vanes used in leu of butterfly type throttle plates. (I thought it was an impeller too, the first time I saw it, but this feature was discussed in a few other threads and also explains the smooth power curves for each of the speeds -the swirl inlet was much more aerodynamically efficient than simple butterfly valves)



> The first stage of the centrifugal compressor looks unshrouded, the second stage seems to have integral shrouding on the impellor.


I thought so too, at a glance, but looking closer, I think that first stage impeller is fully shrouded as well (the shroud projecting out of the cut-away casing/bell housing)

Junkers tended towards shrouded supercharger designs, including to the detriment of the odd 'spouted' impeller used on the Jumo 210 and 211 prior to the F model. (the versions shown above from the F and later models is a vast improvement, possibly with more real advantages over unshrouded impellers)

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## Koopernic (Jun 17, 2015)

Yes, you can see the pitch adjustment mechanism.


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## kool kitty89 (Jun 21, 2015)

Hmm, looking over all the V-1710 charts again (especially those on Peril's P-40 site), it looks like all the pressure altitude charts for actual power at altitude for given manifold pressure and RPM are plotted entirely with throttle wide-open and power only being limited by RPM and atmospheric pressure (and ram for charts plotting for ram effect). They also specifically list take-off power at much lower RPM (but identical power and slightly higher boost) than the "Specific Engline Flight Chart" does. (in the case of the V-1710-39/F3R with 8.8:1 superhcarger, that lists 1150 hp at 3000 RPM 45.5" Hg while the pressure-altitude chart plots take-off power at 2200 RPM with 46" Hg)

Wouldn't controlling the RPM setting on a constant speed propeller give a good deal of automatic control for setting engine speed? (obviously this wouldn't apply to 2-pitch or maualy controlled variable-pitch propellers) And couldn't a barometrically regulated prop speed governor be implemented similar to the supercharger regulator used on the DB-601/605/603 engines?


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## Shortround6 (Jun 21, 2015)

The more "automatic" controls you put on an engine the easier a pilots job is (and the harder the maintenance personnel have to work). You also have Murphy's law 

One of the bigger problems P-38s had in early/mid WW II was mis-rigged turbo controls. Whirlwinds had a lot of trouble with the engine controls (which was often lumped into blaming the basic engine), and the story goes it became a court marshal offence for British "erks" to openup and mess with the control boxes on Sabre engines. 

The US finally went to single lever controls on some planes and a lot of progress was made from 1941/42 to 1945 but trying to get too tricky too early in the war with engine controls just may backfire.

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## kool kitty89 (Jun 22, 2015)

Shortround6 said:


> The more "automatic" controls you put on an engine the easier a pilots job is (and the harder the maintenance personnel have to work). You also have Murphy's law


I was thinking more in line with what was done on the DB-601 early war but applied to the prop controls rather than the supercharger. I suppose the variable speed supercharger control unit itself would increase failure rates and maintenance (and obviously manufacturing cost, complexity, and weight). Let alone the engine computer BMW introduced on the 801. (Bramo had previously used single-lever systems on the 323 -and I assume developed them for the 329- so there was a good degree of background work there already) 

Having automatic limiting/control systems oriented towards avoiding catastrophic failure would probably be more important. (I'd imagine the V-1710's automatic boost control helped to some degree in avoiding detonation, at least on the 9.6:1 models -with 100/130 fuel it seemed near impossible to induce detonation even wide-open at SL at 3000 RPM, at least with a rich mixture; damage due to excessive power levels overstressing components would be less immediate and more related to intentional abuse or prolonged pilot error -or calibration error- rather than the rapid onset cylinder damage caused by detonation) 

Aside from that, manual or semi-automated control on the pilots end should still be useful for higher power levels and not just cruise. Even prior to clearing engines for WEP ratings, more power (and better specific fuel consumption) at military rating below critical altitude and take-off would seem fairly straighforward. Manually operated variable pitch propellers would make that more difficult, but constant speed propellers should have simplified that a great deal. (2-pitch propellers would be a good deal worse but not really be a factor in USAAF use)

I'm not sure if all newer USAAF aircraft had adopted constant speed props by the start of the war, and I recall references to constant speed propellers on the P-38, P-39, and P-40, but that term is sometimes misused in the more general context of variable-pitch propellers.


It's possible that individual squadrons adopted unofficial ratings and procedures on their aircraft, but it seems far more useful to actually provide official ratings for optimal performance and practical procedures to implement as standard. (having pilots constantly checking boost and RPM during climb/combat wouldn't be practical, but setting lower RPM+high boost take-off procedures along with lower RPM mil/WEP settings in steps similar to those used for supercharger gear changes would seem more practical)

For take-off purposes (at SL), the V-1710-39 could manage 1325 HP at 2400 RPM wide-open at 50" Hg.

The older V-1710-33 chart has slightly lower power levels across the board (and also lists the supercharger gearing at 8.77:1 rather than 8.8:1; that doesn't seem like a rounding error given Allison tended to give values to 2 decimal points when applicable). I haven't seen details on the overall changes between the C and E/F series V-1710s, but I suppose there were at least some modifications to the supercharger installation. (though the V-1710-39 specification sheet also lists the -33 as having 8.8:1 supercharger gearing)

In any case, the V-1710-33's chart puts it at 1260 hp at 2400 RPM at SL pushing something close to 49.5" Hg.


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## Shortround6 (Jun 22, 2015)

The US was a bit ahead of the game on constant speed props. Not only was Hamilton Standard an American company but a large number of US airlines had been using the constant speed props for several years before 1939. In fact over 20 airlines had started using fully feathering props by 1939. You also had Curtiss trying to compete with Hamilton Standard. This goes deep, Hamilton Standard was part of the United Aircraft group which included Pratt Whitney. Boeing at one time was part of United Aircraft but split off in the mid 30s. Vought and Sikorsky were also part of United Aircraft. SO Curtiss Wright was competing against them with airframes, engines and their own Curtiss propellers. 

AS far as plying games with propellers on take-off, you might want to think about that *very* carefully. The whole idea of the "constant" speed propeller or variable pitch was to use the optimum pitch of the blades for each flight condition. For take-off you want a shallow pitch even if high rpm to move the the maximum amount of air. Reducing rpm and increasing pitch in an attempt to use the same engine power results in a steep pitch on the blades. Cutting the rpm to 2400rpm is a 20% reduction in prop rpm and you are going to need a steeper pitch. trouble is at slow speed the angle of attack of the blades would be wrong and the blades are part stalling and part thrashing the air instead of producing thrust. 

Those old Schneider trophy racers had fantastic power to weight ratios but lousy take-off performance because the high speed props were such a mismatch. Using a constant speed (or variabe pitch ) helps a lot but you are throwing away part of the advantage if you try this trick. Spitfires with 2 pitch props used fine pitch for take off and 2850rpm. which cut about 100rds form the take-off run of the fixed pitch wood prop planes, which were taking off using a lot less than 2850rpm. At 170ASI and 2000ft the prop was shifted into course pitch where it stayed pretty much until the plane landed. Shifting to high gear dropped the engine rpm to 2070rpm and 6 1/4lbs boost. One can only imagine the power drop. 

This not what you are suggesting and a prop than use an infinite number of pitches won't suffer like this but playing games with the rpm and pitch and the wrong air-speeds is NOT going to increase performance.

basic propeller theory says that for transmitting about 1000hp you need a prop about 10-12% bigger in diameter for a 1200rpm prop than for a 1500rpm prop. This may be for fixed pitch props but you get the idea.


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## kool kitty89 (Jun 23, 2015)

Shortround6 said:


> AS far as plying games with propellers on take-off, you might want to think about that *very* carefully. The whole idea of the "constant" speed propeller or variable pitch was to use the optimum pitch of the blades for each flight condition. For take-off you want a shallow pitch even if high rpm to move the the maximum amount of air. Reducing rpm and increasing pitch in an attempt to use the same engine power results in a steep pitch on the blades. Cutting the rpm to 2400rpm is a 20% reduction in prop rpm and you are going to need a steeper pitch. trouble is at slow speed the angle of attack of the blades would be wrong and the blades are part stalling and part thrashing the air instead of producing thrust.


Right, prop pitch control is a bit like gearing in an auto transmission (and constant speed props are a bit like using a torque converter in an automatic transmission while 2-pitch propers would be akin to a very coarse 2-speed manual transmission). I overlooked that issue, so the 2400 RPM case would likely only be useful at high airspeeds.

It still seems like dropping to 2800~2850 RPM for take-off with moderately increased manifold pressure might have advantages for take-off, but more likely for climb. (2400 RPM at high power and coarse pitch would probably still be too low for useful prop efficiency in climb, but something in the 2600-2800 high-boost range seems potentially useful depending on the aircraft's best climb speed)

There's also the issue of fuel burn, and when not in combat but still climbing to cruise altitude (let alone cruising) optimal raw performance and maximum thrust isn't as important as thrust (and drag) relative to fuel consumption. The significantly improved efficiency of very low RPM cruise (1600 RPM) combined with high boost and lean mixture conditions proved ideal for maximizing range on the P-38. And while the high boost aspect would vary a good deal more without the turbos, it should still apply at low altitudes (especially for the 9.6:1 engines) as well as pointing to conditions at modest speeds and relatively high torque/coarse pitch propeller settings. (ie not low-power low-RPM at relatively fine pitch)


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## Koopernic (Jun 23, 2015)

The automatic controls on the German engines did a lot more than control pitch, which I believe was done via vacuum from from the Venturi in allied engines rather than a governor. According to the pilots throttle lever demand the controls selected the optimal rpm, pitch for that airspeed. They even controlled rich/lean mixture. In a dive the propellor would automatically feather. It often took a long time to set up an allied fighter for combat or setup for a dive and I've seen an interview with one P38 pilot who expressed great personnel regret that he had lost a bomber he was escorting due to the time taken changing from cruise to combat settings, I got the somewhat sad impression that he was unnecessarily blaming himself. Selecting emergency power did often require operation of a switch such as MW50, GM1 or rich mixture injection into the supercharger.

Obviously allied aircraft improved their controls but it seems only slowly. Supposedly allied pilots thought the could do better in setting up their engines for lean cruise or in precise control in formation flying but I suspect this is a case of boosting their own moral.


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## kool kitty89 (Jun 24, 2015)

Koopernic said:


> Obviously allied aircraft improved their controls but it seems only slowly. Supposedly allied pilots thought the could do better in setting up their engines for lean cruise or in precise control in formation flying but I suspect this is a case of boosting their own moral.


Effectively manually leaning out the mixture to effectively improve maximum range and endurance proved true in the Pacific after Lindberg shared his experience with USAAF pilots. (this was at least true in the Pacific, I'm not sure if the same techniques were applied in the ETO)

I know this specifically applied to the P-38's range and the V-1710, but I wonder if similar attempts were made with the P-47, particularly given (like the P-38 ) it could take advantage of the turbocharger for relatively high manifold pressures at very low RPM.


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## Zipper730 (Jul 6, 2020)

From what I remember you have a pump which is connected to the engine's shaft, and hydraulic fluid is directed through there and spins it in the process. A stator is located in the middle and better directs the fluid into the turbine, which makes it spin, after which it flows around and back again: By varying the amount of hydraulic fluid, or the spacing between the pump and turbine, one can vary the RPM of the impeller's effective gear-ratio.

This variation was similar to a turbocharger except at higher RPM more horsepower actually *was* taken off the shaft, and there was a smaller gear-ratio range than a turbocharger (similar to a twin-speed supercharger it seemed): I'm curious if there was anyway with the technology of the time to vary this by both varying the amount of fluid *and* increase the spacing between pump and turbine?

Also would it have been beyond the capability of the time to design the stator to vary this? I do remember the USSR developing a swirl-throttle that helped reduce throttling losses to nearly nothing.


S
 Shortround6
, 

 Snowygrouch
, 
W
 wuzak


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## Zipper730 (Jul 6, 2020)

Shortround6 said:


> It would't matter how many gears you used on a Merlin XX/45 supercharger (they were the same for all practical purposes) the inlet/impeller/housing was pretty much maxed out at around 19-20,000ft. (with RAM)


The engine critical altitude was around 16250 right? If that's right then the engine got 2750-3750' of altitude from ram compression. That's actually pretty good for the time.


> You can only drive a single stage impeller so fast before the tip speed exceeds the speed of sound in the conditions inside the supercharger (temperature and pressure) and starts up shock waves that interfere with the airflow.


While this might be a slight detour from topic, it's something that I've often been curious about: For propellers and superchargers, it was considered a no-no to have the airflow be supersonic. Then you'd see gas-turbines have tip-velocities that would be supersonic, and root-to-tip conditions at cruise speed, and it supposedly generated superior pressure-ratios than subsonic designs offered.

To make it even better, turbofans also had supersonic fan-stages and they, too, also saw improvements in performance, despite the fact that they acted like propellers.



SpicyJuan11 said:


> Forgive me for going a bit off topic, but how do (multiple) turbochargers compare to a 3 speed supercharger (thinking BMW 802 vs BMW P.8011?


I didn't know there were any two-stage turbochargers developed in the war that saw operational use. From what I remember, most turbocharged engine designs had one stage of supercharging and one of turbocharging.



wuzak said:


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


Well, not exactly: The main-stage blower only had one speed, and the neutral stage simply had the auxiliary stage unclutched (it didn't spin), with low and high being different speeds.



kool kitty89 said:


> 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.


I never knew any 9.6's were ever used in the war. I knew the Mustang Mk.II was faster than the Mk.I/IA, but I thought it was due to a change in the radiator design.


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## MiTasol (Jul 6, 2020)

gjs238 said:


> By "multi-speed" I meant more than one speed, not necessarily three-speed.



Do you mean like the late model Allisons with the second supercharger driven by a variable speed drive.


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## wuzak (Jul 6, 2020)

Zipper730 said:


> Well, not exactly: The main-stage blower only had one speed, and the neutral stage simply had the auxiliary stage unclutched (it didn't spin), with low and high being different speeds.



Well, 0 Low and High looks like 3 speeds to me.


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## glennasher (Jul 7, 2020)

Which production block of Allisons went to the PT boats, and when did they siphon off those engines to go to the boats? I wonder how much that effected the need for the Merlins to go into P-40s and Mustang B's. Did the US Navy need enough to alter the plans for those aircraft?
That's just a thought, as the Allisons weren't just for aircraft after all.


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## gjs238 (Jul 7, 2020)

glennasher said:


> Which production block of Allisons went to the PT boats, and when did they siphon off those engines to go to the boats? I wonder how much that effected the need for the Merlins to go into P-40s and Mustang B's. Did the US Navy need enough to alter the plans for those aircraft?
> That's just a thought, as the Allisons weren't just for aircraft after all.



PT boats didn't use Allisons.
PT boat - Wikipedia


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## Zipper730 (Jul 7, 2020)

wuzak said:


> Well, 0 Low and High looks like 3 speeds to me.


Well, one stage only has one speed, the other has three speeds. I guess it's just harder to write down than to say "two-stage supercharging"


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## MIflyer (Jul 7, 2020)

The fluid coupling used in the BF-109's DB engine gave it at least one tactical advantage over the Merlin Mustang and Spit IX. On the P-51 and Spit IX the low to high speed switch over occurred at about 18,000 ft, controlled by an aneroid device (y'all ever try to calibrate one of those?) . Canny BF-109 pilots knew that and tried to fight at that altitude, the speed switch going in and out and thus really screwing up the Allied pilot's throttle setting. And of course manufacturing and calibration tolerances meant that no two Mustangs or Spits were set up exactly the same, with the result that a lead and his wingman had a hard time staying together when maneuvering at around 18,000 ft.

Some Mustangs on Iwo Jima had their spring loaded supercharger high speed switches changed to regular toggle switches so they could engage the high speed manually at a lower altitude. The Packard tech reps strongly recommended against this practice.

Late in the war, or perhaps postwar the Merlin supercharger speed switchover was changed from an altitude setting to ram air pressure. I guess this makes sense, because it you are going slow presumably the throttle setting is low as well and there was less chance of overboosting the engine. Then when speed built up the high speed would switch over to low. I know someone who flies a Mustang regularly and says theirs has had the aneroid device removed, the manual supercharger high speed switch being operated for test purposes only once in a blue moon.

The Japanese tried 3 speed single stage superchargers in the Raiden.

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## MIflyer (Jul 8, 2020)

Zipper730 said:


> Well, one stage only has one speed, the other has three speeds. I guess it's just harder to write down than to say "two speed supercharging"



Confusion is aided further by the fact that many older articles and books referred to "Two Stage Supercharging" when in reality it was "Two Speed Supercharging."


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## tomo pauk (Jul 8, 2020)

MIflyer said:


> Confusion is aided further by the fact that many older articles and books referred to "Two Stage Supercharging" when in reality it was "Two Speed Supercharging."


If there is one stage, and then another stage, that is a two stage supercharging.


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## Snowygrouch (Jul 8, 2020)

MIflyer said:


> Confusion is aided further by the fact that many older articles and books referred to "Two Stage Supercharging" when in reality it was "Two Speed Supercharging."



Very true, including otherwise very well written books like "FIGHTER" By Len Deighton.


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## Mike Williams (Jul 8, 2020)

MIflyer said:


> The fluid coupling used in the BF-109's DB engine gave it at least one tactical advantage over the Merlin Mustang and Spit IX. On the P-51 and Spit IX the low to high speed switch over occurred at about 18,000 ft, controlled by an aneroid device (y'all ever try to calibrate one of those?) . Canny BF-109 pilots knew that and tried to fight at that altitude, the speed switch going in and out and thus really screwing up the Allied pilot's throttle setting. And of course manufacturing and calibration tolerances meant that no two Mustangs or Spits were set up exactly the same, with the result that a lead and his wingman had a hard time staying together when maneuvering at around 18,000 ft.



Not necessarily: 

http://www.wwiiaircraftperformance.org/Oxsbring-72sqdn.jpg

http://www.wwiiaircraftperformance.org/mustang/ppf-p-51-mods.pdf

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## MIflyer (Jul 8, 2020)

Snowygrouch said:


> Very true, including otherwise very well written books like "FIGHTER" By Len Deighton.



I also have a problem with "Fighter" in that he describes BF-110's escorting bombers from Norway and leaving their rear gunners on the ground so they could carry the huge extra fuel tank, and that apparently never occurred.


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## Reluctant Poster (Jul 8, 2020)

MIflyer said:


> The fluid coupling used in the BF-109's DB engine gave it at least one tactical advantage over the Merlin Mustang and Spit IX. On the P-51 and Spit IX the low to high speed switch over occurred at about 18,000 ft, controlled by an aneroid device (y'all ever try to calibrate one of those?) . Canny BF-109 pilots knew that and tried to fight at that altitude, the speed switch going in and out and thus really screwing up the Allied pilot's throttle setting. And of course manufacturing and calibration tolerances meant that no two Mustangs or Spits were set up exactly the same, with the result that a lead and his wingman had a hard time staying together when maneuvering at around 18,000 ft.
> 
> Some Mustangs on Iwo Jima had their spring loaded supercharger high speed switches changed to regular toggle switches so they could engage the high speed manually at a lower altitude. The Packard tech reps strongly recommended against this practice.
> 
> ...


There was a difference between RR and Packard built 2 stage Merlins. Packard used the boost control unit from the Merlin 28. From Rolls Royce and the Mustang by David Birch: “The USAAC had reported oscillations of the boost control and its failure to control satisfactorily.........It was considered that the problem was caused by having too small a boost control unit.......Although a complete cure was not affected a considerable improvement was achieved by fitment of stronger springs in the boost aneroid and relay piston.”

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## MIflyer (Jul 8, 2020)

One thing I have wondered about. A friend of mine joined the RAF before Pearl Harbor and flew Spitfires and Hurricanes in the UK. I do not think he got past training over there because after 7 Dec 1941 he ended up in the Pacific flying B-24's. So he was likely flying Spit MK 1's and II's in training.

In any case he described having to reach down and "turn on" the supercharger in the Spitfire. This does not sound right but I have not dug into the pilot's manuals to see what he could be talking about. In any version of the Merlin could you engage and disengage the supercharger? That could be done with the R-1830 of the F4F and R-2800 of the F6F, F4U, and P-61 but was not possible with the V-1710.


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## wuzak (Jul 8, 2020)

Spitfire Is had single speed Merlins, which did not have a neutral gear. The supercharger was engaged at all times.

Maybe manually adjusting the throttle. Not sure when they got automatic boost control.

The R-1830 of the F4F and the R-2800 of the F6F were two stage engines, where the auxiliary stage had High, Low and Neutral positions, while the main supercharger stage was always engaged and had a fixed speed relationship to the crank.

Most V-1710s were the single stage type, which was the same situation as the Merlin.


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## Shortround6 (Jul 8, 2020)

MIflyer said:


> In any case he described having to reach down and "turn on" the supercharger in the Spitfire. This does not sound right but I have not dug into the pilot's manuals to see what he could be talking about.



He might possibly have been referring to the boost override switch. This had a number of nicknames.
Basically the British engines had an automatic boost limiting device (an aneroid device) that prevented the pilot from overboosting the engine. On the early Hurricanes and Spitfires they were limited to 6lbs of boost for most flying. However in an "emergency" a button or knob could be pressed that changed the aneroid device to a 12lb setting. If the plane was flying at near full throttle and below the critical altitude activating this switch would provide a very noticeable kick in the pants. About a 29% increase in manifold pressure if the plane was at the right altitude.

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## MIflyer (Jul 9, 2020)

Yes, that would make sense. Eric Brown mentions the need to be careful with the early V-1710's, since they lacked an automatic boost control. I read of the RAF finding a number of Hawk 81A's still stored still in their crates and deciding while they were not much good for fighter duties they could be used for training bomber crews in dealing with fighter attacks. They assembled the Hawks, put RAF in them and sent them off. The first one was not up for long at all. The pilot had shoved the throttle all the way in and went roaring off, but the V-1710 blew its top right after takeoff.

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## Kevin J (Jul 9, 2020)

MIflyer said:


> Yes, that would make sense. Eric Brown mentions the need to be careful with the early V-1710's, since they lacked an automatic boost control. I read of the RAF finding a number of Hawk 81A'd still stored still in their crates and deciding while they were not much good for fighter duties they could be used for training bomber crews in dealing with fighter attacks. They assembled the Hawks, put RAF in them and sent them off. The first one was not up for long at all. The pilot had shoed the throttle all the way in and went roaring off, but the V-1710 blew its top right after takeoff.


I've always wondered what happened to each Mohawk they received, because there's uncertainty between different sources as to the exact number received and operated. Does anyone know?


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## MIflyer (Jul 9, 2020)

Some of the French Mohawks were left, still in their crates, in various French colonial possessions and rotted away.

The Profile publication on the Hawk 75 describes the various versions and some info on where they ended up.


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## Kevin J (Jul 9, 2020)

MIflyer said:


> Some of the French Mohawks were left, still in their crates, in various French colonial possessions and rotted away.
> 
> The Profile publication on the Hawk 75 describes the various versions and some info on where they ended up.


Thanks, but I was looking for something more detailed than this.


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## soaringtractor (Jul 9, 2020)

gjs238 said:


> Much has been discussed here of multi-*stage *superchargers, but less of multi-*speed *single-stage superchargers.
> 
> The DB engines used a hydraulic fluid coupling with a barometric control to achieve multi-speed drive with a seamless power curve.
> Other engines featured multiple speeds, kinda like a stick/manual/standard shift transmission in a car, with a jagged power curve.
> ...


BULLSHIT !!!! The P40 with the Allisons still out performed the Packard V1650-1 merlin in speed, climb, the only slight advantage the P40F Melin version had was a slight advantage in service ceiling, giving up top speed, climb to the Allison version, according to the performance figures I read !!!! nd remember the merlin was about 300# heavier !!!!! negating any slight increase in HP !!!


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## tomo pauk (Jul 9, 2020)

Is that a new standard of conversation?


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## Shortround6 (Jul 9, 2020)

New standard of facts?

A number of squadrons did overboost the Allison engined P-40s before the WEP rating came out in late 1942. 
But that only works below the critical altitude of the engine, which for the 8.80 geared airplanes was around 12,000ft without ram and depended a bit on intake manifold and backfire screens. 
the high powers quoted for the Allison in the P-40E and K are for altitudes of around 5,000ft and under (including some RAM).

climb figures (time to altitude) are hard to compare because the Allison used 3000rpm for the first 5 minutes and then used 2600rpm for th erest of the climb while the Merlin powered versions used 2850rpm for the entire climb and not the full 3000rpm at any point in most tests. 
Given the above limitations the P-40F was over a minute faster to 20,000ft. 

The Allison powered P-40s were better at low altitude if over boosted. But once the altitude got into the low teens there wasn't much contest. The Merlin steadily got better.

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## MIflyer (Jul 9, 2020)

In regard to the presence of bovine excrement, note the attached chart form "America's Hundred Thousand"







It would have been child's play for Allison to have built a two speed singe stage V-1710, and given that the V-1710 supercharger/accessories section was a separate part from the main block and the reduction gear sections, commonality could have still been maintained. And either the V-1650-1 or a two speed V-1710 in a P-51 would have been a heck of a performer, no P-51B in speed, but still better than just about anything else around in 1942.

Also the "300 lb heavier" compares a single stage V-1710 to a two stage Merlin 61.

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## Shortround6 (Jul 9, 2020)

MIflyer said:


> Also the "300 lb heavier" compares a single stage V-1710 to a two stage Merlin 61.



Well, the V-1650-1 is supposed to weigh 1510lbs according to RR. 
The V-1710-39 in the P-40E is supposed to weight 1310lb so there is 200lbs, not 300lbs. 

I haven't looked up the difference in radiators, coolant, oil system and other "accessories". 
And there may be a difference it what was considered "dry weight" depending on source. 
Usually generators, starter motors/systems, gun synchronizers and any auxiliary pumps (vacuum, hydraulic, etc) are not included. Sometimes the exhaust gaskets, flanges, nuts and washers are but pipes/stacks are not.

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## xylstra (Jul 15, 2020)

gjs238 said:


> Much has been discussed here of multi-*stage *superchargers, but less of multi-*speed *single-stage superchargers.
> 
> The DB engines used a hydraulic fluid coupling with a barometric control to achieve multi-speed drive with a seamless power curve.
> Other engines featured multiple speeds, kinda like a stick/manual/standard shift transmission in a car, with a jagged power curve.
> ...


The first NAPIER 'Nomad' prototype employed a CVT mechanical drive. Fairly crude one.


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## PAT303 (Jul 15, 2020)

Shortround6 said:


> He might possibly have been referring to the boost override switch.


http://www.spitfireperformance.com/spit2pnfs3.jpg
They call it the boost cut out switch here but it's the same thing.


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## MIflyer (Jul 16, 2020)

I believe the P-40M was the first production aircraft to have an automatic boost control on the V-1710. Since the P-40M was built exclusively for RAF and Empire nations use, that makes sense. They were used to having the automatic boost control in the Merlin and no doubt they had far more pilots who expected the V-1710 to have one as well. 

On the other, there is a statement in the book "Vees for Victory" that the RAF found it a good idea to take the automatic boost control off the V-1710 and let'er rip.

The later P-38's had an automatic boost control as well, but since the turbo already had a form of boost control it was common for the two regulators to fight one another, leading to jerky flight at times (any of y'all ever try hooking two pneumatic or electronic regulators in series?). Perhaps this was not too much of a problem with fighters but with the recon F-5's it was unacceptable. So at at least some recon P-38 units, such as the 9th Photo Recon, the automatic boost control unit was removed.


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