An Allison V-1710 with a two-speed supercharger in 1942 (9 Viewers)

[Shortround6]

The P-40Q s were about 2 feet longer than a P-40K or N. Partially to house the longer engine and partially, like the Fw 190D, to extend the tail to counteract the longer nose and keep stability. I don't know what else they took out of the P-40Q between the engine and the instruments and rudder pedals. The radiator and oil cooler were out in the wings. Location of oil tank and coolant header tank?
It could be done but it was not easy, it was not a firewall forward conversion like converting from the Allison to the single stage Merlin (and that was a bit harder than it appears).

The problem with the Allison is that they had to change the back of the engine block/crankcase to fit a larger diameter supercharger and that is what they really need to do, not just try to use a different gear and spin the existing supercharger impeller inside the existing housing.
Allison got lucky. The engine was (by late 1941/beginning of 1942) very strong and could take a lot of boosting, and they got the better fuel that allowed for over boosting at low altitudes. This took away a lot of the need for a two speed supercharger or at least the pressing need for a low gear.

Things changed quickly in the late 30s and early 40s.
The RR Merlin X with two speed supercharger used just about the same supercharger as the Merlin III. But the low gear in the supercharger allowed the engine to make 1065hp for take-off on 87 octane fuel compared to the 880hp that the Merlin III offered in late 1938. Getting an extra 185hp per engine for take-offs in a bomber was huge for very little weight.

 

[Shortround6]

They probably figured the turbos would be easier than they actually were, since they were being used in airliners already by 1940 at least.

It was just, as you or somebody else noted, not as easy to put one in a fighter.

Don't believe everything you read in Wiki
While the Boeing 307 used the wings, landing gear and some tail structure from the B-17s they never used turbos. They did use two speed superchargers, not two stage superchargers.

 

[Geoffrey Sinclair]

2 speed 2 stage supercharging, like the Merlin 60 series or the R-1830-76/-86 in the F4F-3 and 4. Merlin 20 were 2 speed 1 stage, as was the R-1830-90 in the F4F-3A. The V-1710 1 speed 1 stage, relying on turbo supercharging for altitude performance, the design decisions made early made it hard to change the engine driven supercharging.

War Production Board report,
V-1650 1 Stage August 1941 to December 1944 (no production in 1945), 49, 7,246, 9,503, 7,255.
V-1650 2-stage, November 1942 to December 1945, by year 5, 2,792, 15,736, 13,346
V-1710 2-stage, December 1942 to December 1945, by year 1, 514, 2,867, 1,645, main user the P-63, which developed its best speeds above 20,000 feet.

After building 112 engines May to July 1943 V-1710 2-stage production dropped to 2 then 1 in August and September, rebuilt to over 300 engines a month in Q1/44 then back to 11 then 12 in August and September 1944, another rebuild to over 300 a month mid 1945, when V-1710 production was phased out in favour of the jets, mostly the J-33.

The USN reports 10 V-1710 built in 1946, then 603 in 1947 and 145 in 1948.

The US built Merlin 28, 29 and 31 in 1941/43, switching to Merlin 33 and 38 in 1943, with the first 2 speed 2 stage engines for Britain in November 1943. All single stage engine production was for Britain apart from 2,813 engines August 1941 to March 1943. Almost all 2 stage production was for the US, the main exception was the Merlin 266 for the Spitfire XVI. There was nothing stopping the US making more Merlins if the requirement was there. To end 1943 Packard Merlin for Britain were 5,200 Merlin 28, 480 Merlin 29, 560 Merlin 31, 880 Merlin 33 and 6,862 Merlin 38. Merlin 31 production ended in February 1943, Merlin 33 mostly April to July 1943. Packard had built Merlin production to around or over 800 a month from July 1942, dropped it to around 600 a month in March and April 1943 as the M28, M31, and V-1650-1 went out of production and the M33, M38 and 2 stage versions began, production in May was 1,222, production in the second half of 1943 was about 50% more that of the second half of 1942. By end 1943, ignoring the need for spares, there were enough M31 and M33 for actual Canadian and Australian Mosquito production until into 1945.

Canadian built Hurricanes arriving in Britain had any US Merlins removed, Canadian built Lancaster and Mosquito kept their US Merlins. The RAF restricted use of British and Canadian built aircraft with US Merlins to Britain and North West Europe.

The P-40 was the USAAF interim design, the best way to obtain a better performing fighter than the P-35 and P-36 in numbers quickly. To be replaced by the turbo P-38/39/43/47 "soon".

The RAF spent most of 1940 to 1942 trying to plug gaps, firstly at home, then in the Middle East, then USSR then Far East, as well as greater needs for anti submarine operations. That meant a dilution in quality of aircraft and aircrew to make up numbers. On top of that it had little ability to force Luftwaffe to fight by day. The amount of time the armies in the western desert fought divisional or larger sized operations is days in the 3 years of the campaign. As over France, the Luftwaffe could usually operate to the strengths of its fighters in good tactical situations while limiting exposure of other aircraft types.

As of end 1941 the USAAF was not expecting to keep large numbers of aircraft operational in the tropics, nor until late 1942 large numbers operating in North Africa, nor then the campaign to clear Tunisia would last as long and initially would have the axis air forces better able to mount operations and force the allied air forces into fights. Then after about mid 1943 having the need for the latest fighters in Italy substantially decrease as the Luftwaffe withdrew to defend Germany.

As of early 1943 the USAAF was looking at phasing out the P-39, using the P-40 as a fighter bomber and the P-47 as the air superiority fighter. The P-38 as twin engine air superiority and escort, the Merlin P-51, even if it lived up to the prototype results, was still more listed as headed for units like the 9th Air Force. As the 8th Air Force in particular proved the need for more long range fighters things changed, it also meant more theatres around the world would have to wait for the latest types until the 8th had enough, and the 9th for that matter given the expected timing and importance of Operation Overlord.

The P-51 airframe was obviously superior to the P-40 one, making the P-51 the better candidate for the better engines. While the Red Air Force preferred the P-39 to the P-40 and kept asking for them. When it comes to numbers 4,454 P-40 in 1942 and 4,258 in 1943, P-47 532 and 4,428, P-51 634 and 1,710, it made the P-47 a second half of 1943 and the P-51 a 1944 fighter in terms of arrival in numbers.

A problem for the British was ramping up 2 stage Merlin production, the Spitfire VIII was meant as the overseas service version, 795 in 1943 compared with 1,769 mark IX and 1,328 mark V. Fighter Command found itself taking a back seat for IX allocations in the first half of 1943 at least, the Australians received their first VIII in October 1943. Until around mid to end 1943 every front was seeking the latest Spitfires in numbers as an urgent requirement. The P-51 took over that position in 1944.

Remember the starting positions, the aviation industry was small in the 1930's, then had to compete with all the other priorities in the 1940's Canada increased airframe output about 100 times from mid/late 1930's to 1944 peak, the US 30 times. To help do this Canada largely avoided building engines and propellers.

First order for Canadian made Hurricanes in 1938, first production in February 1940. There was no combat worthy P-40 design in production until the Tomahawk II in October 1940, factor that into a Canadian P-40 time line, more sensible to create a second US line. In mid 1941 came an export order for 400 Hurricanes, to be sent across Pacific and having US engines, became what most references call the RCAF order, 50 more built as Sea Hurricanes. Also a mid 1941 idea was importing US engines for Hurricanes retained in Canada to equip fighter OTU. Canadian Hurricanes built for the RAF were incomplete airframes, requiring brakes, instruments etc. before issue.

In 1942/43 the 8th Air Force lost 737 heavy bombers to enemy a/c, which meant they probably shot down around 500 Luftwaffe fighters, the US fighters in theatre made 458 claims. It was 1944 when the US fighters took over the role of shooting down Luftwaffe aircraft.

The Hurricane and P-39 and P-40 and other types remained in production for so long thanks to the laws of mass production, the cost of creating and tearing down production lines, the forecasts of future needs, their usefulness in secondary roles and so on. In the Hurricane case add the problems with the Sabre engine and Typhoon airframe.

 

[MIflyer]

The P-51 airframe was obviously superior to the P-40 one,

But in some respects inferior for ground attack, due to the vulnerability of the belly mounted radiator. P-51 pilots in Korea mostly would have traded their Mustangs for Warhawks, unless a P-47 was available.

 

[BarnOwlLover]

But in some respects inferior for ground attack, due to the vulnerability of the belly mounted radiator. P-51 pilots in Korea mostly would have traded their Mustangs for Warhawks, unless a P-47 was available.

I think I brought this up a long time ago, but I doubt that radiator positioning mattered that much. Especially given that the P-40 and Typhoon had them in the nose which from ground attack missions I'd argue were even more vulnerable to small arms fire.

Of course, the Germans weren't really using "small arms" to down strafing aircraft. They used 20 and 37mm cannons when possible, often in twin or multiple mounts. Even a P-47 wouldn't survive very much of that. And the North Koreans did much the same in the Korean War.

Also, most Japanese aircraft had radial engines, and the USN had a lot of success using 40mm Bofors and similar weapons to shoot down Japanese planes, especially when proximity fuses became common. Things would've been worse for the IJA/IJN if the autoloading 3"/50 caliber AAA was available in World War II.

Not to mention that in Korea that I did read on this forum that the P-51 and F4U had basically identical loss rates per mission, despite the F4U having a radial engine.

 

[Shortround6]

The P-43 is a way to look at a single engine fighter using a turbo on a 1939-41 engine.
There was also a Seversky fighter using the P&W two stage like the engine used in the Wildcat and there was Curtiss Hawk 75 using the same engine (?).
There are crap load of miss-identified photos of these planes so be careful of going by captions.

The Turbo was bulky as was the intercooler needed for either the mechanical two stage or the turbo.
But the turbo allowed for around 1100-1200hp at 25,000ft while the mechanical two stage (P&W) only allowed for about 1000hp at 19-20,000ft. It did require a smaller intercooler.
The existing 1938-39 engines (P&W, Curtiss and Allison) with single stage superchargers were offering around 950-1040hp at around 14,000ft.
Only Curtiss had a 2 speed supercharger at this time (1939) and they used it to get 1100-1200hp for take-off.
Army favored the Turbo, Navy favored the mechanical two stage.
US army and navy were cooperating better than the Japanese army and navy but only just enough to say so
At least the US forces pretty much agreed on guns and ammo.

For Allison it was the lack of decent intercooler set up that doomed the P-39. The Army was looking at the turbo YP-37s but only to figure out operational problems which is why they ordered the lower tech P-40s in large numbers.

This is the set up for 1942. Now in 1942 The Army wants better altitude performance from everything but is somewhat stuck by decisions made back in 1939 (and before) and by the continued failure of any of the Gee-Whiz hyper engines to actually stay together on test stands while making enough power to fly airplanes.
As far as supercharges go, as mentioned in many old threads, in the early to mid 30s there was ONLY one supercharger company in the United States and that was GE and they sold complete superchargers, supercharger parts and supercharger designs/drawings to Packard, Wright and P&W but they weren't really that good. Allison actually made supercharger parts for GE under subcontract to supply to either Wright or P&W. This means there was a real lack of experienced supercharger designers in the US to hire. Allison tried to use the same size impeller on both stages of their first 2 stage design. Hooker sidestepped that mistake by looking at where he wanted to be airflow wise (around 1000hp at near 30,000ft) and figured that is what the Vulture engine would do so he just grabbed a Vulture supercharger and had it feed into the Merlin supercharger. It was pretty close. P&W had the only working mechanical supercharger in the US (working in the sense that it was in production and service) and it doesn't seem to actually be that good. Merlin 45/XX and a number of Japanese two speed superchargers came very close using only a single stage.

The US needed a better single stage supercharger design before a 2 speed supercharger would have really done them any good. You need airflow (pounds of air per minute or hour) at a good pressure ratio. Air at 20,000ft is 0.533 times as dense as sea level air while the pressure is even worse. About 46% the pressure at sea level.

If you want 1150hp from the Allison engine at 20,000ft instead of the 12,000ft of -73 engine in P-40K (42in) you have to figure out how to get about 30% more cubic feet of air into the air intake to get the same number of pounds of air into the supercharger and then you have to increase the amount of compression from 2.17 times to about 3 times without sending the temperature through the roof.
You can trade some power (50-100?) and/or altitude (19,000ft instead of 20,000ft) but the existing supercharger isn't going to really work. The engines with 9.60 gears lost 25hp and needed 2.6in more boost to get that 15,500ft.

 

[tomo pauk]

If you want 1150hp from the Allison engine at 20,000ft instead of the 12,000ft of -73 engine in P-40K (42in) you have to figure out how to get about 30% more cubic feet of air into the air intake to get the same number of pounds of air into the supercharger and then you have to increase the amount of compression from 2.17 times to about 3 times without sending the temperature through the roof.
You can trade some power (50-100?) and/or altitude (19,000ft instead of 20,000ft) but the existing supercharger isn't going to really work. The engines with 9.60 gears lost 25hp and needed 2.6in more boost to get that 15,500ft.

1150 HP at 20000 ft with the V-1710 and it's small impeller is really a tall order. Not even Merlin XX or 45 was able to do it, and probably not even the Merlin 46.
IMO, the best compromise would've been that the impeller is spun at 10.52:1 ratio, that should give perhaps 1100 HP at 17500 ft? Use the 8.10:1 or 8.80:1 for the low gear in the 2-speed drive.

Alternatively, move on to the bigger impellers, with either 2-speed or variable-speed drive.

 

[Shortround6]

1150 HP at 20000 ft with the V-1710 and it's small impeller is really a tall order. Not even Merlin XX or 45 was able to do it, and probably not even the Merlin 46.
IMO, the best compromise would've been that the impeller is spun at 10.52:1 ratio, that should give perhaps 1100 HP at 17500 ft? Use the 8.10:1 or 8.80:1 for the low gear in the 2-speed drive.

Alternatively, move on to the bigger impellers, with either 2-speed or variable-speed drive.

The Merlin 46 might have done it, just. But the Merlin 46 lost about 85hp for take off at 12lbs due to the larger impeller and the associated problems compared to the Merlin 45.
Merlin 46 is using 9lbs (48in?) of boost so the Merlin 46 supercharger is not going to deliver 1100hp at 44 in.

 

[tomo pauk]

The Merlin 46 might have done it, just. But the Merlin 46 lost about 85hp for take off at 12lbs due to the larger impeller and the associated problems compared to the Merlin 45.

This is why I've suggested that either 2-speed or variable speed drive is used.

 

[Shortround6]

Very good suggestion. I am just saying that a two speed or variable drive without changing the impeller and housing won't get the results desired.

 

[tomo pauk]

I am just saying that a two speed or variable drive without changing the impeller and housing won't get the results desired.

Depends on what is desired? If mimicking the Merlin XX, DB 601E or the 2-stage R-1830 or is desired, the legacy supercharger might come very close. If mimicking the DB 605A is desired (even the de-rated values), then indeed a bigger S/C is needed.

 

[Howard Gibson]

1150 HP at 20000 ft with the V-1710 and it's small impeller is really a tall order. Not even Merlin XX or 45 was able to do it, and probably not even the Merlin 46.
IMO, the best compromise would've been that the impeller is spun at 10.52:1 ratio, that should give perhaps 1100 HP at 17500 ft? Use the 8.10:1 or 8.80:1 for the low gear in the 2-speed drive.

Alternatively, move on to the bigger impellers, with either 2-speed or variable-speed drive.

The Merlin_61 put out 1600hp for take-off, presumably using the low gear. When the switched to its high gear, the output was 1200hp, reflecting the extra power needed to drive the supercharger. The Spitfires and Mustangs with two-stage Merlins reached their top speeds in the thin air at 26,000ft.

 

[tomo pauk]

The Merlin_61 put out 1600hp for take-off, presumably using the low gear. When the switched to its high gear, the output was 1200hp, reflecting the extra power needed to drive the supercharger.

Low gear was certainly used for take off
TO power of the Mk 61 was 1280 HP (+12 psi); max power in flight was 1565 HP in low gear, and 1390 HP in high gear (+15 psi for the later two power values). Per 'The Merlin in perspective' book by RR HT; the chart from the Polish flight museum gives a bit lower values for in-flight power, ~1515 and ~1360.

 

[Steamed_Banana]

From the operational histories, if you look at Axis losses, US bomber crews, especially the heavy bomber crews, clearly overclaimed much more than the fighter units did. It's impressive that they did in fact shoot down Axis fighters but it was at a fairly low rate, and often overclaiming was in the realm of 20-1 or 15-1 claims vs actual enemy losses. I seriously doubt that bomber crews shot down as many Axis fighters over Europe in 1943 as Allied fighters did.

More important IMO is that the defensive guns on those bombers allowed them to survive quick and short interceptions (i.e. as opposed to lengthy, sustained interceptions where they could still be vulnerable), whereas older, slower and / or less heavily armed types took prohibitively heavy losses almost any time they got caught, and the either faster and / or better defended bombers aborted their missions less often and as a result hit more targets. In my opinion this was the real value of the defensive guns, and a higher speed complimented this, while it also meant less time over target, shorter interception window for enemy fighters, being harder to hit by enemy AAA over the targets etc. I suspect a smaller size also helped.

I am certain that more Axis fighters were destroyed on the ground by bombs than were shot down in the air by either defensive gunners or Allied fighter pilots, at least in the PTO and MTO. Dropping bombs on Axis airfields was the best way to destroy Axis fighters, at least in those Theaters.

Early Baltimore I with open .30 cal gun, late Baltimore V with twin .50 cal power turret

'Anecdotally', one of the best surviving Allied Bomber type in the MTO was the fairly lightly armed Martin Baltimore, which became the main bomber type of the DAF. It did not do well initially when sent out un-escorted, but with even what you might call 'limited' or 'intermittent' escort, (i.e. Allied fighters were at least in the vicinity in the early part of the mission but often disappeared especially after the bomb release), managed to survive numerous raids over North Africa, Sicily, Sardinia, Italy, and the Balkans. The Baltimore had a top level speed of about 300 mph and could reach a high speed well over 400 mph in a shallow dive. Early versions just had a few .30 cal machineguns, though the later version used in Italy had a power turret with two 12.7mm.

Second highest Allied survival rate for Allied bombers in Theater was (allegedly) the substantially larger, slower (~280 mph max), but much more heavily armed B-26 which also fended off Axis fighters when friendly escorts weren't around, you can see a couple of examples of that in the operational history that I recently posted in the P-38 thread. But the defensive gunners overclaimed a huge amount, for understandable reasons. In a given formation of bombers, as many as 20 or 30 gunners could be shooting at the same aircraft. If they see it show signs of damage- begin smoking, lose parts, go into a spin, pilot bail out etc., they all think they are the one that got it.

The B-26 also carried a much heavier bomb load than the Baltimore. Baltimores carried 1,000-2,000 lbs of bombs depending on the mission, B-26 marauder was more like 3,000-4,000 lbs depending on the mission profile, potentially as much as 5,800 lbs for 'extreme' loadouts.

 

[Steamed_Banana]

P-51 was clearly the superior aircraft to the P-40 in the long run, but it did not manifest as such until they put the merlin engine in it. P-51A were mediocre in combat in the CBI and P-40 units like 23rd FG, 51 FG, and 80 FG did much better in 1943 and early 1944, when they started switching over to P-51C etc. The majority of Allied fighter victories in Theater were by pilots flying P-40s.

P-39 was I think, originally hoped to replace the P-40 but didn't work out for the US. There was only one P-39 Ace in US service. The Soviets did indeed love it though not all Soviet P-39 units did well, about half of them did. It may have just been better suited for that Theater.

The Spitfire VIII made a big difference when it became engaged in the CBI and Pacific, but it's range was limited compared to the P-51 or P-38 by that point, which kept it out of the fight somewhat, and it arrived rather late. The Spit Mk V didn't do particularly well either in the Pacific or CBI.

P-47s did not make a big impact in 1943, nor did P-38s or Corsairs, though al three types showed promise and added some strategic / operational capabilities that were superior to the P-39 and P-40. All through 1943 P-40 units like the 7th and 8th Sqns of the 49th FG (9th Sqn was P-38s) out of the New Guinea area, and the 44th FS operating out of the Solomons, and the various Australian and New Zealand P-40 units in both areas, were really bearing the brunt of the fighting in the SWPA in 1943, and along with Navy Wildcats, inflicting most of the enemy aircraft losses in the air (and sometimes on the ground).

 

[Steamed_Banana]

Speaking of these fighters, anyone know the origin of this roll rate chart?

 

[Jugman]

The later Allisons didn't use the remote supercharger stage that the earlier engines (as used in the P-63) had. The late Allisons were still longer than the Merlin, but the difference was in inches, not the 2.5 feet that it would've been with the remote supercharger stage.

They most certainly did. Depending on where the carb was, the auxiliary supercharger added ~16-22 inches to the nominal length of the engine. Practical installed length increased by about 12in. over the single stage single speed models

 

[Steamed_Banana]

If you want 1150hp from the Allison engine at 20,000ft instead of the 12,000ft of -73 engine in P-40K (42in) you have to figure out how to get about 30% more cubic feet of air into the air intake to get the same number of pounds of air into the supercharger and then you have to increase the amount of compression from 2.17 times to about 3 times without sending the temperature through the roof.
You can trade some power (50-100?) and/or altitude (19,000ft instead of 20,000ft) but the existing supercharger isn't going to really work. The engines with 9.60 gears lost 25hp and needed 2.6in more boost to get that 15,500ft.

I mean, they got it to work in the P-40F and L with the Merlin XX, so what's the difference then exactly?

 

[tomo pauk]

I mean, they got it to work in the P-40F and L with the Merlin XX, so what's the difference then exactly?

Do you point out at Curtiss that made the P-40F & L reality with the V-1650-1, or at RR that made Merlin XX a reality?

 

[MiTasol]

I mean, they got it to work in the P-40F and L with the Merlin XX, so what's the difference then exactly?

I mean the P-51 model with the highest top speed was powered by an Allison so what's the difference then exactly?