An Allison V-1710 with a two-speed supercharger in 1942 (4 Viewers)

[Shortround6]

Sure but both the Merlin and domestic P&W etc. types were potentially available to Allison in 1941-42. So we aren't necessarily talking about designing from scratch so much as adapting something.

Wright R-1820 engine used a two-stage supercharger with an 11in impeller and two gears. Low = 7.14:1 and High 10.0:1. Granted the R-1820 only turned 2500rpm but with the size of impeller and the gear ratio the tip speed was 1,199fps. R-1820 was rated at 1000hp at 13,600ft (?). So using the existing Wright R-1820 supercharger was not going to work on the Allison.
Idea being to gain power, not lose it
Perhaps there was room in the R-1830 supercharger. 11 in rotor, 8.57 supercharger gear, 2700rpm, tip speed 1,097fps. R-1830 was rated at 1050hp at 13,100ft.
Maybe it they could have (would have?) used a higher tip speed with the higher rpm engine but it doesn't look like a lot room.
P-W upgraded the supercharger used in the later R-2000 engines (C-54 engines) to 11.3in impeller and used a 9.52:1 high gear ratio.
At 2700rpm they got 1100hp at 16,000ft using a 1266fps tip speed. An awful lot work to pretty much match what the Allison could do with a set of 9.60 gears.

Wright got the late R-1820s up to 1000hp at 17,000ft in the FM-2s, in part by getting the engine up to 2600rpm and later up to 2700rpm. Not sure what, if anything they did to supercharger.

Now maybe you could have tried using the supercharger off of an R-2600 but that really seems to be like a lot of work. It also doesn't offer much change in pressure even if a lot more volume and with changing things you are going to trading volume for pressure and quite possibly pushing the supercharger into a less efficient operating area.

Using a two-stage supercharger, in theory, offered better efficiency and with either the P&W system (3 speeds) or the Allison system (variable speed) better matching of the airflows through the two supercharger stages.
This was the advantage of the GE turbos. In theory, constant pressure and volume to the carburetor inlet on the engine supercharger.

The 'miracle' of the two-stage Merlin was that Hooker and the rest of RR managed to get two stages that were fixed in rotation to each other (both impellers were operated off the same shaft) to cover a wide range of pressures and air flows without either choking each other or limiting each other to any great extent.

For Allison in 1941 (test labs or drawings) and 1942 was teh two speed supercharger seen as 1938-1940 technology and the two-stage seen as the future?
If Allison had limited resources for R&D which path do they take?

Now it turns out that two stage superchargers are a lot harder to work out in practice than in theory. How far (or how long) did Bristol and Napier get? How far did Wright get?
How far did Continental get (even using a turbo)?
France, Germany and the Soviet Union, for bombers, all tried putting an engine in the fuselage driving a large compressor to supply high pressure air to the wing engines.

By the time the US got any working Japanese two speed engines back to the US it was too late? Japanese did pretty well with two speed engines.

 

[Shortround6]

USA was not cut off from the rest of the world.
People in the aero engine business in the USA knew by 1938 that supercharger on the Merlin was phisically bigger, and accurately pointed out that the altitude performance of the engine will be better because of that. The benefits of 2-speed drives for S/C were known before ww2, ditto for the 2-stage mechanical supercharging.

Until the big orders in April/May 1939 The market share of the military was small in comparison to the commercial market.
Big US military orders were relative compared to the rest of the world. The April 1939 P-40 was smaller (in number of aircraft) than the June 1936 initial order for Hurricanes.
The US interest in two speed supercharges and RR interest in two speed superchargers was not really for altitude performance but to get large aircraft off the ground, without losing what altitude performance they did have.
US already had better propellers. The US had to get airliners over the Rocky Mountains and the 4,000-5,000ft Appalachians.
People were looking at airliners with pressurized fuselages, but these were flagships. A two-speed engine that peaked in the mid-teens was good enough for the late 30s and very early 40s for commercial aviation
As we have mentioned may times before. The P-40 was what the Army could get quickly, not what they wanted. They wanted turbos, altitude problem solved, ......except...... that turbos were 2 years away from squadron service, hence P-40s...............except...............turbos were actually three years or more away from actual squadron service, at least in fighters.
How much of this was the turbos themselves, how much was lack of proper engines and how much was the fighters that the turbos were supposed to go in (XP-39, XP-43, XP-44, XP-60 etc) were largely failures we can argue about. USAAC ordered about 60 Turbo charged A-20s in 1939, They built and tested one. The other 59 planes were completed without turbos.

 

[Howard Gibson]

The whole point of the thread is when could Allison have designed and moved a single stage, two speed V-1710 (roughly equivalent to Merlin XX) into production, and could it have been done by early 1943. I think two-stage ala Merlin 60 or R2800 etc. would inevitably happen later.

The two-speed two-stage Merlin 61 was in production in 1942 for Spitfire_IXs. It's available for any other mischief anybody wants to get into.

Let's not forget that Allied success in 1943/44 was fighter performance at 30,000ft. This means two stages of supercharging.

 

[Steamed_Banana]

The two-speed two-stage Merlin 61 was in production in 1942 for Spitfire_IXs. It's available for any other mischief anybody wants to get into.

Let's not forget that Allied success in 1943/44 was fighter performance at 30,000ft. This means two stages of supercharging.

The thing is, that is the apparently permanent assumption about WW2, but I really don't believe that it's true.

Let's examine this statement by Geoffrey to dig deeper:

It is a basic rule when air forces fight each other altitude goes up, if the army and/or navy are involved altitude tends to go down.

The thing is, this is partly true, but there is a really important bit missing. What determines whether the air battle (e.g. involving fighters) goes up or down, or stays in the middle, is almost entirely dependent on where the bombers are. And this, in turn, depends on the type of target and type of fighting.

During the pivotal year of 1943, or you might extend that to 1942-very early 1944, most of the fighting is taking place on a series of battlefields around the world:

Spoiler: Theaters of active combat in the mid-war

MTO
North Africa
Middle East
Mediterranean Sea (including major convoys)
Sicily and Mediterranean Islands (Sardinia, Corsica, Malta, Crete, Pantelleria, Lampedusa etc.)
Italy
Balkans

PTO
New Guinea
Solomon Islands
Other South Pacific Islands
Philippines
Aleutians

CBI
China
Burma / India
Pacific Rim
Indian Ocean

Russia / Eastern European front
Russia
Ukraine
Balkans
North Atlantic (Convoys and Fjords)

In each of these Theaters, targets during 1943 were generally Tactical or Operational, not Strategic. The Strategic bombing campaign did not really get going until later in 1944.

Strategic day-time bombers (e.g., the US heavy bombers in this case) can fly at high altitude, how high depending on the exact type (B-24 not as high as B-17, B-17 not as high as B-29), but they are only really useful against Strategic targets at that 20,000' / 6,000m + ft altitude.)

Where the ground armies are fighting, Operational targets like airfields, bridges, ports, supply depots, large artillery positions etc. can be targeted including by heavy bombers, but they will typically do so from much lower altitude. Partly this depends on the Theater and prevailing weather, as well as the season, local air defenses etc., but generally speaking, against Operational targets combat is at lower altitude. 8,000 - 20,000 ft, usually on the lower end of that band.

Ships can be either Tactical or Operational, or even Strategic targets, but regardless - to target them you have to get down pretty low, as in below 5,000 ft. They tried hitting them by dropping bombs from altitude but that almost never worked.

Tactical targets are of course typically below 8,000 ft, usually down around 2,000 ft or less, assuming low ground / near sea level.

Fighters will often fight for high ground / altitude advantage well above the bombers, but in order to win this fight some of them will have to be right where the bombers are.

In North Africa, though the skies were usually clear, the fighting rarely got higher than about 20,000 ft, and most of the fighting was down around 5,000-10,000 ft or lower.

Russia saw even lower altitude, as did SW Pacific and Burma, often due to weather and cloud ceiling. Same in Italy. Same in Normandy and through the Low Countries into Germany once the fighting started in NW Europe.

But it's in this middle part of the war that the thread is focused. There is nothing inevitable about air war in WW2 that says fighting is going to be at 30,000 ft. In fact, usually it wasn't even close to that.

 

[drgondog]

Just a couple of notes.
There were three CBI groups with P-51A, the 23rd, the 51st and the 311th. The 51st and 311th both also flew the A-36. All started receiving ships in September thru November 1943 timeframe. In addition the 1st Air Commando received P-51A ('used') when the 311 and 51st converted to P-51B.

P-51B/C were first allocated to theaters in which high-altitude strategic bombing doctrine was adhered to, same with P-51D. RAF had different approach, rarely operating bombers above 18,000 feet. Ditto SWPA and CBI.

CBI got P-51B/Cs when they didn't really need them save for long range strikes on targets like Rangoon. Their allocations were imposed largely because Chaing had enormous influence with Roosevelt.

Delivering the P-47D-25 to MTO in mid 1944 made further replacements by P-51B/C, on other groups than in 15th AF, not required. Ditto, to a degree in SWPA - whereas operations attacking Japan favored P-51D selection over P-38J/L and P-47N.

Many Mustang III were returned to US control via political pressure applied to Portal by Arnold after second Schweinfurt mission. Additionally Portal agreed to direct existing Mustang III's to assist in mid-range 8th AF penetration and withdrawal support, which they did beginning in March 1944 timeframe. Neither Portal nor Leigh-Mallory were overjoyed in losing control of IX Fighter Command to 8th AF in the run-up to Overlord, but the planned transition from P-38 and P-47 to P-51B/D only occurred in earnest beginning late April/May 1944.

In light of the planned assault on LW and airframe/engine industry beginning Feb 20 1944, Arnold issued several important orders. Namely all P-51B/D to be devoted to ETO 8th AF and MTO 15th AF; No further conversions to F-6C until inventory sufficient; All new P-38 FGs to the 8th, 9th and replacements for the three P-38Fgs in MTO.

 

[Shortround6]

But it's in this middle part of the war that the thread is focused. There is nothing inevitable about air war in WW2 that says fighting is going to be at 30,000 ft. In fact, usually it wasn't even close to that

This is true. But the altitudes they were expecting to fight at went back and forth.
And you have to order the planes you want to fight with 1-3 years ahead of time.
Poland and France were fought in the under 20,000ft range, mostly. Yes a lot was done in the 8,000ft and under range.
The US was already (1939) planning to go higher, much higher, with the ordering both fighters and bombers whose engines peaked at 25,000ft. As noted above for various reasons the USAAC was not able to take delivery of the desired aircraft in the numbers they wanted.
The US desire for high altitude aircraft was reinforced by the 1940 BoB which turned out to be something of an aberration. With the armies 20-100 miles apart (English Channel) a lot of the air fighting (except shipping strikes) was more operational and strategic. The opposing fighters were often flying 5-10,000ft higher than the bombers. Or at least doing it often enough to fighting at around 30,000ft to become a requirement. A high-flying fighter can often fight at lower altitude better than a low altitude fighter can fight at higher altitudes.
A big reason the Hurricane got the Merlin XX and not the Spitfire. A Hurricane, even with a Merlin XII engine was in trouble against later model 109Es with newer DB 601 engines.
The Hurricane needed the Merlin XX just to stay close to the later 109s (later than the E-3/E-4).
Germans introduced the 109Fs in small numbers in the fall/winter of 1940 and things did not look good for fighters that had trouble over 20,000ft or even in the high teens. Germans started attacking at night and the altitude race was put on hold. That is to say there was very little new data and the British/Italian fights were not given enough credence. Both sides were not using up to date fighters and bombers. Summer of 1941 and information about the Russian front is scarce. North Africa is still in the hands of older aircraft on both sides (mostly) and thus not a good set of data on what was needed for 'new' aircraft. The war in NA is using not only older aircraft but not a lot of them and with a lack of strategic targets the air fighting does descend to lower altitudes in general (Except for recon). The War in Pacific is mostly fought at low altitudes. In part becasue the British are using obsolete aircraft and the Japanese are only using high altitude engines (two speed) in a very few planes.
The 'experts' fully expect altitudes to climb once newer planes show up. And to some extent they do. Japanese have trouble bombing at night (no radio beam systems) and since the bombers can fly in the 20,000ft+ range they do it to lessen losses. And now the Americans/allies are in trouble. The American 'high altitude planes' have either failed to show up or only showed up in small quantities. It also turned out that high altitude bombing was very, very difficult for everybody. It was hard enough to actually fly at over 20,000ft with large formation of bombers (over 9-12), hitting the intended target/s from those altitudes with a small number of bombers was much harder. Both sided have to fly lower to increase effectiveness.
The Soviets are not as forthcoming as they might be about operations.
With 20/20 hindsight we can find all the problems (or the wishful thinking of the time) but no country/side wanted to cede the upper levels of the air to the enemy. They often did so because they had no choice. And then they tried to pick times/places/conditions that would minimize the enemies Hight advantage.

 

[Shortround6]

There were three CBI groups with P-51A, the 23rd, the 51st and the 311th. The 51st and 311th both also flew the A-36. All started receiving ships in September thru November 1943 timeframe.

Just using this to reinforce the lead times the US dealing with.
A-36 production started in Oct 1942 (?) and ended in March 1943.
P-51 production started in March 1943 and ended in May 1943 (?)
1st operation mission of the A-36 was June 6th 1943 over Pantelleria Island.
About 4-5 months to get the P-51As to the CBI? 15 months after the P-51A had been ordered?

 

[Steamed_Banana]

This is true. But the altitudes they were expecting to fight at went back and forth.
And you have to order the planes you want to fight with 1-3 years ahead of time.
Poland and France were fought in the under 20,000ft range, mostly. Yes a lot was done in the 8,000ft and under range.
The US was already (1939) planning to go higher, much higher, with the ordering both fighters and bombers whose engines peaked at 25,000ft. As noted above for various reasons the USAAC was not able to take delivery of the desired aircraft in the numbers they wanted.
The US desire for high altitude aircraft was reinforced by the 1940 BoB which turned out to be something of an aberration. With the armies 20-100 miles apart (English Channel) a lot of the air fighting (except shipping strikes) was more operational and strategic. The opposing fighters were often flying 5-10,000ft higher than the bombers. Or at least doing it often enough to fighting at around 30,000ft to become a requirement. A high-flying fighter can often fight at lower altitude better than a low altitude fighter can fight at higher altitudes.
A big reason the Hurricane got the Merlin XX and not the Spitfire. A Hurricane, even with a Merlin XII engine was in trouble against later model 109Es with newer DB 601 engines.
The Hurricane needed the Merlin XX just to stay close to the later 109s (later than the E-3/E-4).
Germans introduced the 109Fs in small numbers in the fall/winter of 1940 and things did not look good for fighters that had trouble over 20,000ft or even in the high teens. Germans started attacking at night and the altitude race was put on hold. That is to say there was very little new data and the British/Italian fights were not given enough credence. Both sides were not using up to date fighters and bombers. Summer of 1941 and information about the Russian front is scarce. North Africa is still in the hands of older aircraft on both sides (mostly) and thus not a good set of data on what was needed for 'new' aircraft. The war in NA is using not only older aircraft but not a lot of them and with a lack of strategic targets the air fighting does descend to lower altitudes in general (Except for recon). The War in Pacific is mostly fought at low altitudes. In part becasue the British are using obsolete aircraft and the Japanese are only using high altitude engines (two speed) in a very few planes.
The 'experts' fully expect altitudes to climb once newer planes show up. And to some extent they do. Japanese have trouble bombing at night (no radio beam systems) and since the bombers can fly in the 20,000ft+ range they do it to lessen losses. And now the Americans/allies are in trouble. The American 'high altitude planes' have either failed to show up or only showed up in small quantities. It also turned out that high altitude bombing was very, very difficult for everybody. It was hard enough to actually fly at over 20,000ft with large formation of bombers (over 9-12), hitting the intended target/s from those altitudes with a small number of bombers was much harder. Both sided have to fly lower to increase effectiveness.
The Soviets are not as forthcoming as they might be about operations.
With 20/20 hindsight we can find all the problems (or the wishful thinking of the time) but no country/side wanted to cede the upper levels of the air to the enemy. They often did so because they had no choice. And then they tried to pick times/places/conditions that would minimize the enemies Hight advantage.

The hindsight factor is key here, obviously, with some caveats.

The fighting from the second half of 1941 through 1942, both in the Pacific and North Africa, and I think at this point, some data was emerging from the Soviets as well, as part of the Lend Lease negotiations, was going up to a certain point, depending on the target type. Bombing from 20,000 feet was very hard against small targets, but ports and airfields (like at Darwin, Port Moresby, Henderson field) it could be effective, and it was worth bombing from that altitude due to the danger of the AAA. This means fighters were operating at 25,000-28,000 feet, basically as high as they could fly.

In the MTO fights, the bombers were mostly down low, but the fighters went up above them, to 15, then 20,000 feet to get the high ground so to speak. Here, the Hurricane II was given a new lease on life by the Merlin XX. It arrived in Theater starting in Feb - April 1941, and demonstrated an edge over the Fiat G.50, the Macchi 200, and even the Bf 110. In April 1941 when JG 27 arrived with the Bf 109E4 and E7 Trop, the Hurricane II was clearly at a disadvantage, but it could at least compete, in part thanks to the engine. When the Bf 109F4 arrived in late 1941 however, the Hurricane II was in trouble. The Tomahawk started to take the lead. Here altitude performance was not it's strength, but it could fight up to about 16,000 ft, ceding the high ground to the Bf 109s of JG 27, but it could turn the tables in sustained fighting down low, such as if they tried to attack escorted bombers instead of picking off the high cover. I think it was obvious to anyone paying attention that the Tomahawk while capable, really needed better altitude capability.

In the Pacific, though in 1942 the Japanese fighters did not yet have two speed or two stage superchargers, they were so light that they could still perform fairly well up to around 20,000 ft and a bit more. But here the Wildcat, otherwise outclassed by the A6M and Ki-43, could hold it's own due to it's (somewhat mediocre) two-stage supercharger. That gave it enough extra power to have a bit of an advantage at altitude, which no doubt saved a lot of lives. This was certainly clear by the end of Midway in June 1942.

The first combat for the P-40F was in the late summer of 1942 with a few aircraft from the 57th FG, followed by more US units arriving in the fall. They apparently knew the Merlin XX powered versions were going to work out better, because all of the US Fighter Groups got them (much to the annoyance of the British, who were hoping to get a lot more than the two squadrons worth they got). But it was certainly clear by the end of the year (1942) that the two speed supercharger offered a significant advantage in combat performance for the P-40.


So depending on when somebody developed the nice hindsight inspired vision, which depending on who does something slightly different could have happened as early as mid 1941 or so, to as late as late 1942 which is probably too late.

Then again, how long did it take to convert the P-40 to the Merlin XX and get the V-1650-1 into production? That seems to have happened pretty fast.

Anyway, if something is done by say, mid 1942, it seems to me like you might have some aircraft avalable in early 1943. If the British payed a bit more attention to North Africa, they may have added this request to the Americans, and who knows if the Americans pay attention or not (for all I know, they did point this out). Someone clever did in fact suggest putting the merlin XX on the P-40 in time to be useful, so it's not too far of a jump to Allison making a V-1710 with some kind of version or hack of a Merlin XX supercharger.

Arguably.

 

[Steamed_Banana]

Just a couple of notes.
There were three CBI groups with P-51A, the 23rd, the 51st and the 311th. The 51st and 311th both also flew the A-36. All started receiving ships in September thru November 1943 timeframe. In addition the 1st Air Commando received P-51A ('used') when the 311 and 51st converted to P-51B.

P-51B/C were first allocated to theaters in which high-altitude strategic bombing doctrine was adhered to, same with P-51D. RAF had different approach, rarely operating bombers above 18,000 feet. Ditto SWPA and CBI.

CBI got P-51B/Cs when they didn't really need them save for long range strikes on targets like Rangoon. Their allocations were imposed largely because Chaing had enormous influence with Roosevelt.

Totally disagree- Chiang may well have had undue influence, but they did absolutely need them in Theater. The P-51B/C were a huge step up in outcomes. The P-40s were holding their own but lacked range for a lot of important missions in Theater. The British were still using Hurricanes well into 1944 and Spitfires only slowly trickled in. Neither the P-51A nor the small number of P-38s in Theater were making much of a difference.

Delivering the P-47D-25 to MTO in mid 1944 made further replacements by P-51B/C, on other groups than in 15th AF, not required. Ditto, to a degree in SWPA - whereas operations attacking Japan favored P-51D selection over P-38J/L and P-47N.

P-47s didn't do all that well initially in the MTO or in the CBI. Nor did the P-38s, though obviously in both cases this changed when the improved variants became available.

 

[tomo pauk]

Until the big orders in April/May 1939 The market share of the military was small in comparison to the commercial market.
Big US military orders were relative compared to the rest of the world. The April 1939 P-40 was smaller (in number of aircraft) than the June 1936 initial order for Hurricanes.

You were specifically inquiring this:

I keep asking, without getting any real answers, were was Allison supposed to got to for answers/Guidance in supercharger design in the United States?

Questions/answers and guidance about the supercharger design is not something that a costumer of your engines is supposed to do, but the engine company itself. It is about what the engineers and technicians can do, not what the costumer might or might not want.

The US interest in two speed supercharges and RR interest in two speed superchargers was not really for altitude performance but to get large aircraft off the ground, without losing what altitude performance they did have.

Too much of the mutually exclusive details of the supercharger designs get lumped into 'just make 2-speed S/Cs and Bob's your uncle'.

Most of the people discussing the aero engine superchargers are not even aware of the Merlin X (I know you are not one of them). It incorporated the improved impeller design, that gave a slight boost of the altitude performance (perhaps 30 HP above 17500 ft vs. the Merlin III?). Then we also have another intermediate step that - increased ratio of the gearing, from 8.588:1 to 9.089, that added another ~20 HP vs. the Merlin X, despite using the impeller from the Merlin III, or about 50 HP over the Merlin III; all for the altitudes above 17500 ft.
Then, finally, we have the Merlin XX, that introduced the much improved air intake as well as the even 'faster' gearing (9.49:1), as well as the impeller from the Mk.X, so we're finally at ~1170 HP at 17500 ft, where the Merlin XII was doing about 1040 HP.

While the Merlin X was indeed used as a bomber engine, the much improved all-around power of the Merlin XX meant that it ended up in fighters - Hurricane II, Beaufighter II, Defiant II, and not in bombers.

 

[Shortround6]

Then again, how long did it take to convert the P-40 to the Merlin XX and get the V-1650-1 into production? That seems to have happened pretty fast.

The V-1650-1 was the 3000 engines (actual delivers were around 2700-2800) from the Sept 1940 contract.
They are not going to start showing up until the abut year later (fall of 1941) but the US has to figure something to do with them.
They won't fit in P-39s. They won't work in P-38s with turbos. A P-38 with V-1650-1s is going to be lower in performance (at high altitudes) than an turbo Allison P-38.

That leaves the P-40 as the only logical choice.
They tried to use one Merlin (British built) in one of the XP-60 prototypes and it first flew on 18 September 1941. But the XP-60 had 275 sq ft wing and a proposed armament of eight .50 cal guns which is a bit much for a Merlin XX family engine.
It appears that the XP-40F (converted P-40D) was first flown June 30th 1941 and delivered in Nov 1941. These dates may be in error.
The first production P-40F was delivered in Jan 1942 but production was slow due to the low production of Packard Merlin engines and the need to share production with the British. Merlin powered Fs were built alongside Allison powered Ks.
So it appears that production took over year after the decision was made.
Curtiss had to tool up to make the Fs on a production basis and to do that they had to design and test the new radiators, oil cooler, air intake, cowling and figure out how to fly it
Only part joking. Due to the heavier Merlin engine compared to the Allison the Fs were flown with a minimum of 35 US gallons in the rear tank to keep the CG where they want it.
Es and Ks were supposed to take-off on the forward tank and then go through either the drop tank or rear (fuselage) tank and the back to the wing tanks. The Fs took off using the forward wing tank, then the drop tank if fitted and then burned down the fuselage tank to 35 US gallons remaining and then to wing tank/s and used the 35 US gallons in rear as reserve. P-39Es and K s used the forward wing tank (if fitted) as reserve after take-0ff.
Getting enough P-40Fs built to equip a fighter group in the Spring of 1942 took a while but with much increase Merlin production in April, May, June P-40F production increased.
June 1942 Merlin production exceeded Sept 1941 through March 1942 production combined.

For perspective. The P-47 was running late. the First 171 P-47s (all of the Bs) are ruled not combat capable. The P-47 was supposed to go operational in May of 1942 after being ordered in Sept 1940. The 56th fighter group is declared operational in the US in Nov 1942, they have been training (and crashing) since June. They go operational in March/April 1943
P-47 is running at least 6-9 months late.
Now at some point in mid 1941 the P-40F may have been seen as improved P-40E with a bit more altitude performance. The USAAC was planning on having a lot more P-47s in operational units at the end of 1942. The P-40F has to fill in for the P-47 and for the failure of the P-39 and for the shortage of P-38s.

How it was used in NA in Sept 1942 onward is not how things were supposed to go.

 

[Shortround6]

Questions/answers and guidance about the supercharger design is not something that a costumer of your engines is supposed to do, but the engine company itself. It is about what the engineers and technicians can do, not what the costumer might or might not want.

For most of the 1930s the engine makers built engines they thought would sell. If you designed and built really gee-whiz techno engines that few people bought you went bankrupt.
Engine makers were looking 4-6 years down the road. Unfortunately for them, it took longer to make a new engine than it did to make a new airframe, even a large airframe like the B-19. Wright went for the R-2600 and got Boeing to buy some for the 314 Clippers. Wright was also planning on using the R-2600s in what would be the C-46. They switched to the P&W R-2800s in production versions. Neither plane used a pressurized fuselage that would require two stage superchargers.
About 1/2 of the Boing 307 had pressurized fuselages (?) but they used very low pressurization and used two speed superchargers.
The Airlines refused the buy the Douglas DC-4E

and the sole example (with it's R-2180 engines) was sold to Japan.
US airline companies had to make a profit. They were not operating with a government subsidy (or not much of one) and were not seen as Government prestige or propaganda.

While the Merlin X was indeed used as a bomber engine, the much improved all-around power of the Merlin XX meant that it ended up in fighters - Hurricane II, Beaufighter II, Defiant II, and not in bombers.

That is true and it shows the difference even 2 years can make. But you needed a heck of engine for the Beaufighter
Merlins were stuck in Beaufighters in desperation due to a shortage of Hercules engines.
Hurricane with Merlin XX was the quick fix.
Defiant II was a mark of desperation. Anybody that thinks the Battle was mistake has never looked at a Defiant II.

But back to the Merlin X. As we both know, the increase of about 200hp in take-off power using 87 octane fuel over the Merlin III was a major improvement, the increase of 1500ft in FTH was nice but it was a lot less important.

 

[tomo pauk]

For most of the 1930s the engine makers built engines they thought would sell. If you designed and built really gee-whiz techno engines that few people bought you went bankrupt.

If someone thinks that V-1710 - especially without a turbo attached - was a gee-whiz engine per the standards of the day, I have the Brooklyn bridge on sale, real cheap

 

[SaparotRob]

If someone thinks that V-1710 - especially without a turbo attached - was a gee-whiz engine per the standards of the day, I have the Brooklyn bridge on sale, real cheap

I ain't selling it. Geez.

 

[Steamed_Banana]

If someone thinks that V-1710 - especially without a turbo attached - was a gee-whiz engine per the standards of the day, I have the Brooklyn bridge on sale, real cheap

Yeah, but I definitely get his point about lead-times and the need to somewhat accurately anticipate the future, which was definitely not an easy thing in 1936-1941

 

[tomo pauk]

Yeah, but I definitely get his point about lead-times and the need to somewhat accurately anticipate the future, which was definitely not an easy thing in 1936-1941

We can take a look from 1936 backwards.
Every year saw the improvement of both the total engine power, the engine power vs. altitude, and the increase of flying altitude. The power/weight ratios were going up. Aircraft were growing larger and heavier, thus further pushing the aero engines to be more up to the task. The company XYZ will do bad planning if they assumed that the bar will not go up both due to the efforts of the company OPQ from the same country, as well as from at least half a dozen companies abroad.

 

[Howard Gibson]

The thing is, that is the apparently permanent assumption about WW2, but I really don't believe that it's true.

Let's examine this statement by Geoffrey to dig deeper:



The thing is, this is partly true, but there is a really important bit missing. What determines whether the air battle (e.g. involving fighters) goes up or down, or stays in the middle, is almost entirely dependent on where the bombers are. And this, in turn, depends on the type of target and type of fighting.

During the pivotal year of 1943, or you might extend that to 1942-very early 1944, most of the fighting is taking place on a series of battlefields around the world:

Spoiler: Theaters of active combat in the mid-war

MTO
North Africa
Middle East
Mediterranean Sea (including major convoys)
Sicily and Mediterranean Islands (Sardinia, Corsica, Malta, Crete, Pantelleria, Lampedusa etc.)
Italy
Balkans

PTO
New Guinea
Solomon Islands
Other South Pacific Islands
Philippines
Aleutians

CBI
China
Burma / India
Pacific Rim
Indian Ocean

Russia / Eastern European front
Russia
Ukraine
Balkans
North Atlantic (Convoys and Fjords)

In each of these Theaters, targets during 1943 were generally Tactical or Operational, not Strategic. The Strategic bombing campaign did not really get going until later in 1944.

Strategic day-time bombers (e.g., the US heavy bombers in this case) can fly at high altitude, how high depending on the exact type (B-24 not as high as B-17, B-17 not as high as B-29), but they are only really useful against Strategic targets at that 20,000' / 6,000m + ft altitude.)

Where the ground armies are fighting, Operational targets like airfields, bridges, ports, supply depots, large artillery positions etc. can be targeted including by heavy bombers, but they will typically do so from much lower altitude. Partly this depends on the Theater and prevailing weather, as well as the season, local air defenses etc., but generally speaking, against Operational targets combat is at lower altitude. 8,000 - 20,000 ft, usually on the lower end of that band.

Ships can be either Tactical or Operational, or even Strategic targets, but regardless - to target them you have to get down pretty low, as in below 5,000 ft. They tried hitting them by dropping bombs from altitude but that almost never worked.

Tactical targets are of course typically below 8,000 ft, usually down around 2,000 ft or less, assuming low ground / near sea level.

View attachment 873734

Fighters will often fight for high ground / altitude advantage well above the bombers, but in order to win this fight some of them will have to be right where the bombers are.

In North Africa, though the skies were usually clear, the fighting rarely got higher than about 20,000 ft, and most of the fighting was down around 5,000-10,000 ft or lower.

Russia saw even lower altitude, as did SW Pacific and Burma, often due to weather and cloud ceiling. Same in Italy. Same in Normandy and through the Low Countries into Germany once the fighting started in NW Europe.

But it's in this middle part of the war that the thread is focused. There is nothing inevitable about air war in WW2 that says fighting is going to be at 30,000 ft. In fact, usually it wasn't even close to that.

The Americans were doing daylight strategic bombing of Germany in 1943. This is when P47s shot down and killed experienced Luftwaffe pilots. Mustangs in late 1943 were the coup de gras (sp?).

If the big mission in the ETO in 1943 had been ground attack, the Fw190s would massacred the P47s. B17s and B24s came in at 25,000ft plus. The B17's better altitude performance made it desirable in the ETO. 30,000ft was where you wanted to fight in a P47.

 

[MikeMeech]

Hi
I thought Dowding's comments on air fighting at high "ceiling" might be of interest, from his 'Battle of Britain Despatch', paras 212-217 are relevant:

Mike

 

[Steamed_Banana]

The Americans were doing daylight strategic bombing of Germany in 1943. This is when P47s shot down and killed experienced Luftwaffe pilots. Mustangs in late 1943 were the coup de gras (sp?).

If the big mission in the ETO in 1943 had been ground attack, the Fw190s would massacred the P47s. B17s and B24s came in at 25,000ft plus. The B17's better altitude performance made it desirable in the ETO. 30,000ft was where you wanted to fight in a P47.

Daylight strategic bombing started in NW Europe in 1943, but it was not yet effective or really significant to the outcome of the war, particularly in comparison to the very intense ground and naval combat going on in the various Theaters I listed. The end of the Battle of Stalingrad, the Battle of Kursk, the siege of Leningrad, the eviction of the Nazis from North Africa, the invasions of Sicily and Italy (and capitulation of the state of Italy), the end of the Battle of Guadalcanal, the Battle of the Bismarck Sea, the invasion of Lae, the Battle of Tarawa were all turning points in the war.

The limitations of Strategic bombing in 1943 were in large part because Allied bombers were being forced to out-range their escorts, (including those P-47s), in order to attack targets of Strategic significance. The P-47s, P-38s, and Spitfires which comprised most of the available fighter escort at this time, had limited range which was gradually being improved but not fast enough to solve the problem during 1943.

The partially escorted raids on the ball-bearing plants at Schweinfurt an Regensburg in August and October 1943, which resulted in losses casualties so severe (60 bombers in the first raid and ~80 severely damaged, 550 aircrew MiA or PoW; 77 heavy bombers lost in the second raid) that they forced a pause on unescorted missions.

Strategic daylight bombing clearly had potential to be significant, but in 1943 that potential had not been realized. That didn't happen until fighters were available that could escort the heavy bombers all the way to their targets and back. Which eventually P-47s and P-38s could do, but it fell upon the P-51s in the long run as a policy decision.

That said I certainly agree that the P-47 fought best at 25-30,000 feet, and that this is where it had an advantage over German fighters. As improved versions of the P-47 became available they became more capable at fighting at lower altitudes as well, and were brought into the Tactical and Operational fighting quite a bit more.

Strategic bombing was still essentially a sideshow in 1943, and combat at those kinds of altitude remained rare until 1944, as I originally noted. You could argue that Big Week in Feb 1944 was the resumption of effective Strategic bombing and the beginning of the Strategic bombing campaign becomming criticall important in NW Europe. The first major Strategic bombing raid against Japan was in June of 1944, but really ramped up after the capture of the Marianas in November 1944.

 

[drgondog]

Daylight strategic bombing started in NW Europe in 1943, but it was not yet effective or really significant to the outcome of the war, particularly in comparison to the very intense ground and naval combat going on in the various Theaters I listed. The end of the Battle of Stalingrad, the Battle of Kursk, the siege of Leningrad, the eviction of the Nazis from North Africa, the invasions of Sicily and Italy (and capitulation of the state of Italy), the end of the Battle of Guadalcanal, the Battle of the Bismarck Sea, the invasion of Lae, the Battle of Tarawa were all turning points in the war.

The limitations of Strategic bombing in 1943 were in large part because Allied bombers were being forced to out-range their escorts, (including those P-47s), in order to attack targets of Strategic significance. The P-47s, P-38s, and Spitfires which comprised most of the available fighter escort at this time, had limited range which was gradually being improved but not fast enough to solve the problem during 1943.

According to Speer, the threat to strategic targets like Schweinfurt compelled a diversification effort to reduce risk of losing ball bearings - essential to all mechanized vehicles, compelled a re-focus from broad range of air assets to fighter production, compelled hidden mobilization and volume of anti-aircraft artillery and gunners which greatly reduced Wehrmacht resistance to Soviet armor. He also expressed the opinion that had 8th AF immediately followed up with additional strikes at Schweinfurt it would have been catastrophic.

I would re-arrange critical battles to include Moscow and Stalingrad/Midway and remove Italy, the capture of Lae and Tarawa as 'critical'. The latter were important but the resources applied to Italy, fopr example, were out of proportion to the German assets destroyed. Kesslering deserves the accolades for the Italian campaign. That said southern Italy very important to 12th and 15th AF, bringing Ploesti and Munich/Leipzig/Vienna into frequent attack range.

P-38s didn't not return until August/September, only one of the two P-38 FGs was operational the day after the second Schweinfurt mission and the 20th, only the last week of December. They were important but not 'effective' due to the myriads of operational issues experienced at high altitude. That said the two P-38Fgs and the one P-51FG operational in December did perform escort to Bordeaux on December 31st - nearly 200 miles farther than the P-47 escort.

The partially escorted raids on the ball-bearing plants at Schweinfurt an Regensburg in August and October 1943, which resulted in losses casualties so severe (60 bombers in the first raid and ~80 severely damaged, 550 aircrew MiA or PoW; 77 heavy bombers lost in the second raid) that they forced a pause on unescorted missions.

'Partially Escorted' is an understatement. The 'escort of P-47s just barely reached Achen.

60 B-17s MIA on October 14. 138 returnees were Damaged, have to research the ones written off, but the crews returned to fight another day. I saw a youTube video that looked AI that presented '77', but that figure is incorrect.

Strategic daylight bombing clearly had potential to be significant, but in 1943 that potential had not been realized. That didn't happen until fighters were available that could escort the heavy bombers all the way to their targets and back. Which eventually P-47s and P-38s could do, but it fell upon the P-51s in the long run as a policy decision.

The P-38J with extra leading edge fuel was able to escort to all the targets attacked until May when the 8th stepped up strikes into Poland and Czechoslovakia. Range wasn't the issue that forced them out of 8th AF. Simply, the Mustang was a better escort/air superiority fighter due to combined attributes of performance, range and economics. The P-47 was forced out for the same reasons.

That said I certainly agree that the P-47 fought best at 25-30,000 feet, and that this is where it had an advantage over German fighters. As improved versions of the P-47 became available they became more capable at fighting at lower altitudes as well, and were brought into the Tactical and Operational fighting quite a bit more.

Strictly speaking both the Bf 109G-6 and FW 190A-5 and -8 performance peaked at ~ 22,000 feet whereas the Turbo-equipped P-47 increased speed and power loadings up to 30,000 feet so it was a wide envelope. The Paddle blades introduced in early 1944 certainly helped improve climb performance but fighter vs fighter advantage, save speed for 109, favored the FW 109 and Bf 109 through 20,000 feet. The basic difference in combat results increasingly favored US due to pilot skill and experience as the air war continued.

Strategic bombing was still essentially a sideshow in 1943, and combat at those kinds of altitude remained rare until 1944, as I originally noted. You could argue that Big Week in Feb 1944 was the resumption of effective Strategic bombing and the beginning of the Strategic bombing campaign becomming criticall important in NW Europe. The first major Strategic bombing raid against Japan was in June of 1944, but really ramped up after the capture of the Marianas in November 1944.

The first Effective raids on Japan occurred beginning March 1945 when Lemay though out of the box and began burning down Japanese cities at low/medium altitudes at night. The original plank holder, Hansel couldn't seem to break the code that Japan was not the same as Germany and that the crossing jet streams destroyed 'pickle barrel' bombing from high altitude.