An Allison V-1710 with a two-speed supercharger in 1942 (7 Viewers)

[MiTasol]

I am fairly sure that was covered in Dan Whitney's V's for Victory but my copy is down in Brisbane and I am 400km away for the next 3 months at least.

I have a foggy memory of 28 staff in 1938 but I cant remember if that was total or just design or what.

Don''t forget that, despite it's small size and GM severely limiting its budget the Allison company designed the bearings used in the Merlin and several other aero engines.

 

[Howard Gibson]

Too high a compression combined with a high inlet temperature to the cylinder resulting from high boost pressure results in detonation and that takes only a very short time to destroy an engine - usually by burning holes in the pistons. Pistons with holes in them do not produce much power and have very short lives.

This one is complicated. On a non-supercharged engine, the compression ratio affects the temperature ratio, which directly affects efficiency. A high temperature and compression ratio is more efficient, up until the engine knocks.

Okay, we are supercharged. The air is at whatever the atmospheric pressure is for the altitude. The supercharger increases this pressure up to some level. Basic gas laws tell us that the temperature of the air will increase when you compress it. The hot, compressed air is fed into the cylinder where it is again compressed, its pressure multiplied by the compression ratio. Again, due to gas laws, it heats up. If the air reaches the ignition temperature of the fuel vapour, it combusts, and on a spark ignition engine, you get knocking. Knocking is caused by high temperature. Your pressure at cylinder top-dead-centre, prior to ignition, is the atmospheric pressure, plus supercharger boost, all multiplied by the compression ratio.

If your air/fuel mixture has gotten well above ambient temperature, you can pass it through an intercooler, and the reduced temperature will more than make up for the fluid losses. The fuel, and any water and methanol you inject into the incoming air will vapourise, and reduce the temperature. With reduced temperatures by whatever means, you can let the supercharger apply higher boost pressures without knocking.

Supercharged engines are built with lower compression ratios than normally aspirated engines. I assume that there is a sweet spot for compression ratio and supercharger boost. Given the variation in compression ratios in World War II, nobody (or perhaps a lot of people) did not know what this was. The Naper Sabre's compression ratio was 7.0:1, which compare's to the Rolls Royce Merlin_XX's 6.0:1. Merlins ran at substantially higher manifolds boosts for reasons that are obvious if you read the above carefully.

 

[Micetro]

As others have previously allayed to I doubt that the development staff, prototype engineering machinery or flight-testing requirements would have been sufficient to allow a two-stage supercharger to be progressed into production in significant enough numbers to be useful until late 1943, looking at the previously signed contract production rates and completion dates required for single-stage variants.

At that early stage of the war Rolls themselves took many months to get from Hooker's initial eureka moment to a usable two-stage two-speed unit and even then the operation of it was not user-friendly or combat ready until many of the quirks had been ironed-out.

Also the contracts for the machine tools required to manufacture the parts very likely were only just being signed by that point and again took months to get into the machine shops.

A really great thread with some excellent information and debating

Tom

 

[tomo pauk]

As others have previously allayed to I doubt that the development staff, prototype engineering machinery or flight-testing requirements would have been sufficient to allow a two-stage supercharger to be progressed into production in significant enough numbers to be useful until late 1943, looking at the previously signed contract production rates and completion dates required for single-stage variants.

The 2-stage supercharged V-1710s were powering the P-63s made (not only) in the late 1943. Not that these were very much adding to the Allied war effort, though.
Now, if Allison can make a working, reliable 2-stage supercharged V-1710 by the late 1942, even if these are not as great as the Merlin 60 series of the time, that would've been excellent.

The upgraded 1-stage S/C for the V-1710, be that with a 2- or 1-speed drive, could've also used the better time table, say availability by the early 1942 instead of late 1942.

At that early stage of the war Rolls themselves took many months to get from Hooker's initial eureka moment to a usable two-stage two-speed unit and even then the operation of it was not user-friendly or combat ready until many of the quirks had been ironed-out.

(my emphasis)
Any specifics you have in mind wrt. the bolded part?

A really great thread with some excellent information and debating

True.

 

[Steamed_Banana]

As others have previously allayed to I doubt that the development staff, prototype engineering machinery or flight-testing requirements would have been sufficient to allow a two-stage supercharger to be progressed into production in significant enough numbers to be useful until late 1943, looking at the previously signed contract production rates and completion dates required for single-stage variants.

At that early stage of the war Rolls themselves took many months to get from Hooker's initial eureka moment to a usable two-stage two-speed unit and even then the operation of it was not user-friendly or combat ready until many of the quirks had been ironed-out.

Which is why we are really focusing mainly on just a two-speed supercharger

Also the contracts for the machine tools required to manufacture the parts very likely were only just being signed by that point and again took months to get into the machine shops.

I think the two stage is maybe too far a leap for the US in time for early 1943, though I'd like to look a little closer at the R-2800 and R-2600

A really great thread with some excellent information and debating

Agree and thanks!

Tom

 

[tomo pauk]

I think the two stage is maybe too far a leap for the US in time for early 1943, though I'd like to look a little closer at the R-2800 and R-2600

The XF4U was powered by a 2-stage supercharged R-2800 for it's 1st flight (Spetember 1940) and on. F4F-3 was in service use by 1941, powered by the 2-stage R-1830. The XF6F-1 was powered by the 2-stage supercharged R-2600 in early 1942.

The 2-stage superchargers were known to work in the 1930s, with companies like Bristol, Farman, Junkers/Jumo and Piaggio making such engines that were powering the actual aircraft. Daimler-Benz and Alfa Romeo used the 2-stage superchargers on the record-setting/racing cars in the late 1930s.
Interestingly enough, there was no in-service military aircraft powered by the 2-stage supercharged engines from these 6 companies, bar the Ta-152 barely making it by 1945 (Jumo and DB 2-stage engines).

 

[Steamed_Banana]

The XF4U was powered by a 2-stage supercharged R-2800 for it's 1st flight (Spetember 1940) and on. F4F-3 was in service use by 1941, powered by the 2-stage R-1830. The XF6F-1 was powered by the 2-stage supercharged R-2600 in early 1942.

yes I'm aware, but the two stage supercharger which was used on the F4F while helpful at altitude, was notoriously weak and inefficient. Is that correct?

I want to plunge a bit deeper into the wartime F4Us and F6F, as these are more confusing to me. Were the wartime production R-2800 as installed on these fighters both two stage and two-speed as I am reading, and was the two-stage supercharger efficient / effective? General consensus seems to be that these fighters are not as effective at altitude above 25,000' as a P-47 or a P-51 or a Spit IX etc.

I'm also unclear as to the timeline of various versions of the R-2800 in these fighters.

The 2-stage superchargers were known to work in the 1930s, with companies like Bristol, Farman, Junkers/Jumo and Piaggio making such engines that were powering the actual aircraft. Daimler-Benz and Alfa Romeo used the 2-stage superchargers on the record-setting/racing cars in the late 1930s.
Interestingly enough, there was no in-service military aircraft powered by the 2-stage supercharged engines from these 6 companies, bar the Ta-152 barely making it by 1945 (Jumo and DB 2-stage engines).

That is indeed interesting. It may be that it's just one of those things that works in prototype but is very tricky to get reliable and effective enough for broad military service.

For the US it was extra tempting to go to turbo because they had developed commercial air-liners which used them. So they knew they could work, and they did pretty early on for bombers. It just turned out fitting them into a fighter was tricky.

 

[tomo pauk]

yes I'm aware, but the two stage supercharger which was used on the F4F while helpful at altitude, was notoriously weak and inefficient. Is that correct?

The impellers were with straight blades, so indeed the efficiency left a lot to be desired from. OTOH, as a complete package, they were considerably better than the 1-stage superchargers from the P&W (that were also with the straight blades), and were still bette than the 1-stage S/Cs as installed on the V-1710s before the late 1942.

I want to plunge a bit deeper into the wartime F4Us and F6F, as these are more confusing to me. Were the wartime production R-2800 as installed on these fighters both two stage and two-speed as I am reading, and was the two-stage supercharger efficient / effective?

A 2-stage S/C driven just via the 1-speed drive would've been horribly ineficcient - depending on the gearing chosen, it will be either lacking the power at low altitudes, or at high altitudes.

The engine-stage S/C (here being the 2nd stage of compression) on the US-designed engines with 2-stage S/Cs was driven via a 1-speed gearing.
The auxiliary S/C (here being the 1st stage of compression) was driven via the gearbox with high, low and neutral gearing on the P&W engines (neutral setting allowed that the aux stage can be bypassed at low altitudes, so it a) does not use any power from the engine, and b) does not heat the compressed air too much); the V-1710 used the variable-speed drive for the aux S/C.

The 2-stage S/Cs as installed on some (but important) RR engines was with both impellers being driven by the same shaft, via a 2-speed drive; both impellers were turning the same RPM. Huge advantage was the compactness and simplicity of the set-up - a major thing when someone wants to up-engine the existing aircraft type. That 2-stage system was adopted by both Jumo and DB for their (very late) 2-stage supercharged engines, that were driven via a 3-speed gearbox (Jumo), or via the variable-speed drive (DB).
RR went with the 3-speed drive for the post-war Griffon 100 series for the Spiteful/Seafang, to gain extra power down low.

The 2-stage R-2800 gave a lot of power at all altitudes, powering the heavy and draggy US fighters at around 400 mph, and at 440-450 mph by the late ww2. That means that it scores high as far as I'm concerned.

General consensus seems to be that these fighters are not as effective at altitude above 25,000' as a P-47 or a P-51 or a Spit IX etc.

How much a fighter is effective is a sum of many factors; there is also a thing of 'horses for courses'.

The big & heavy F6F and F4U were designed around the heaviest and most powerful engines available, while also supposed to be good at low speed, with longer range than the previous designs. All of that drove the size and weight up, both of the things that will tone down the performance. The P-51 was a much smaller aircraft, powered initially by a V12 engine with a modest S/C, with next-gen aerodynamics and without the carrier suitability for the designers to take into account. Stick the modern V12 on it, and it becames an over-performer.
The P-47 didn't have the carrier requirement, but the R-2800, the associated turbo, big fuel tankage and 8 guns battery resulted with a fighter that was better above 25000 ft than the Navy birds. It was not much of a climber, though, due to the excessive weight.
F4U was of the performance similar to the Spitfire IX - not a mean feat considering the thin wing and light weight of the Spitfire. F6F was a bit worse. Both of the US fighters were also the much better carrier birds than the Spitfire/Seafire versions. F4U-4, with the much improved R-2800-18W, was comparable with the Spit XIV.

I'm also unclear as to the timeline of various versions of the R-2800 in these fighters.

The A series -4 powered the XF4U; 1850 HP max.
The B series -8 powered the F4U-1; the -10 powered the F6F-3 and -5, as well as the P-61. The -8 and -10, as well as the 8W and 10W, were basically the same engines, apart fro the carb and some small bits & pieces.
The C series -18W powered the F4U-4; took part in ww2 in 1945.
The E series -32W powered the F4U-5, a post-war model; that engine was with two small superchargers (so-called 'sidewinder' layout) feeding together the engine-stage S/C.
'W' denotes water-alcohol injection.

That is indeed interesting. It may be that it's just one of those things that works in prototype but is very tricky to get reliable and effective enough for broad military service.

Press on with development and testing - same as for any piece of kit that ups the state of art.

For the US it was extra tempting to go to turbo because they had developed commercial air-liners which used them. So they knew they could work, and they did pretty early on for bombers. It just turned out fitting them into a fighter was tricky.

Military application of turbochargers predates the commercial application of turbochargers.
Indeed, fitting the turboes on the fighters, even the bespoke ones made around the turboes was not easy.

 

[Micetro]

The 2-stage supercharged V-1710s were powering the P-63s made (not only) in the late 1943. Not that these were very much adding to the Allied war effort, though.
Now, if Allison can make a working, reliable 2-stage supercharged V-1710 by the late 1942, even if these are not as great as the Merlin 60 series of the time, that would've been excellent.

The upgraded 1-stage S/C for the V-1710, be that with a 2- or 1-speed drive, could've also used the better time table, say availability by the early 1942 instead of late 1942.


(my emphasis)
Any specifics you have in mind wrt. the bolded part?


True.

Hi Timo,

The early Spit IXs that were converted from MKVs had very much embryonic systems compared to the earlier versions. They would have been very pilot-heavy for operation for a number of reasons;

• Fuel wobble-pump for engine startup - the later versions used a boost pump. This wouldn't be such an issue once airborne and at altitude but sometimes on takeoff/final approach it might be required.

• Coolant radiator flaps - these were manually controlled on the early IXs and as such would have required regular monitoring and adjustments which is far from ideal in combat situations.

• There were numerous issues in plumbing the Oil, Coolant and Intercooler radiators and it took many variations to get to a workable layout when everything was standardised with the MKVII/VIII. Early machines often suffered from leaks which could spring up at any point whilst airborne.

• The delay in the introduction of the Injector Carburettor caused many issues in combat as there were still problems with bunting over into a negative-G dive.

• Carb intake duct - the delay in the incorporation of an air filter and carb heat meant that the aircraft was unsuitable for use in North Africa or the Mediterranean until the development of the Aboukir Filter was completed and introduced. The lack of carb heat also meant certain operational limitations in use by Fighter Command units.

So summing-up these developments took nearly a year to implement, time that would have been required for any newly-developed engine, sadly nothing can happen overnight in quantity.

Tom

 

[tomo pauk]

Hi Timo,

The early Spit IXs that were converted from MKVs had very much embryonic systems compared to the earlier versions. They would have been very pilot-heavy for operation for a number of reasons;

• Fuel wobble-pump for engine startup - the later versions used a boost pump. This wouldn't be such an issue once airborne and at altitude but sometimes on takeoff/final approach it might be required.

• Coolant radiator flaps - these were manually controlled on the early IXs and as such would have required regular monitoring and adjustments which is far from ideal in combat situations.

• There were numerous issues in plumbing the Oil, Coolant and Intercooler radiators and it took many variations to get to a workable layout when everything was standardised with the MKVII/VIII. Early machines often suffered from leaks which could spring up at any point whilst airborne.

• The delay in the introduction of the Injector Carburettor caused many issues in combat as there were still problems with bunting over into a negative-G dive.

• Carb intake duct - the delay in the incorporation of an air filter and carb heat meant that the aircraft was unsuitable for use in North Africa or the Mediterranean until the development of the Aboukir Filter was completed and introduced. The lack of carb heat also meant certain operational limitations in use by Fighter Command units.

So summing-up these developments took nearly a year to implement, time that would have been required for any newly-developed engine, sadly nothing can happen overnight in quantity.

Tom

Cheers.
Is there a good, easily available source that underscores these issues, and how much of these issues were a thing?

 

[Steamed_Banana]

Hi Timo,

• Carb intake duct - the delay in the incorporation of an air filter and carb heat meant that the aircraft was unsuitable for use in North Africa or the Mediterranean until the development of the Aboukir Filter was completed and introduced. The lack of carb heat also meant certain operational limitations in use by Fighter Command units.

That really explains a lot, as to why the Spit IX arrived so late in Theater, but also including the fact that I can't remember ever seeing a Spit IX or VIII with a Vokes filter. The combination of having these arrive with Aboukir type filter plus the new engine etc. would have been a huge boost in performance.

So summing-up these developments took nearly a year to implement, time that would have been required for any newly-developed engine, sadly nothing can happen overnight in quantity.

Tom

Maybe still time for Allison to come up with the two speed though

Thanks for the very interesting contribution.

 

[Steamed_Banana]

The impellers were with straight blades, so indeed the efficiency left a lot to be desired from. OTOH, as a complete package, they were considerably better than the 1-stage superchargers from the P&W (that were also with the straight blades), and were still bette than the 1-stage S/Cs as installed on the V-1710s before the late 1942.



A 2-stage S/C driven just via the 1-speed drive would've been horribly ineficcient - depending on the gearing chosen, it will be either lacking the power at low altitudes, or at high altitudes.

The engine-stage S/C (here being the 2nd stage of compression) on the US-designed engines with 2-stage S/Cs was driven via a 1-speed gearing.
The auxiliary S/C (here being the 1st stage of compression) was driven via the gearbox with high, low and neutral gearing on the P&W engines (neutral setting allowed that the aux stage can be bypassed at low altitudes, so it a) does not use any power from the engine, and b) does not heat the compressed air too much); the V-1710 used the variable-speed drive for the aux S/C.

The 2-stage S/Cs as installed on some (but important) RR engines was with both impellers being driven by the same shaft, via a 2-speed drive; both impellers were turning the same RPM. Huge advantage was the compactness and simplicity of the set-up - a major thing when someone wants to up-engine the existing aircraft type. That 2-stage system was adopted by both Jumo and DB for their (very late) 2-stage supercharged engines, that were driven via a 3-speed gearbox (Jumo), or via the variable-speed drive (DB).
RR went with the 3-speed drive for the post-war Griffon 100 series for the Spiteful/Seafang, to gain extra power down low.

The 2-stage R-2800 gave a lot of power at all altitudes, powering the heavy and draggy US fighters at around 400 mph, and at 440-450 mph by the late ww2. That means that it scores high as far as I'm concerned.



How much a fighter is effective is a sum of many factors; there is also a thing of 'horses for courses'.

The big & heavy F6F and F4U were designed around the heaviest and most powerful engines available, while also supposed to be good at low speed, with longer range than the previous designs. All of that drove the size and weight up, both of the things that will tone down the performance. The P-51 was a much smaller aircraft, powered initially by a V12 engine with a modest S/C, with next-gen aerodynamics and without the carrier suitability for the designers to take into account. Stick the modern V12 on it, and it becames an over-performer.
The P-47 didn't have the carrier requirement, but the R-2800, the associated turbo, big fuel tankage and 8 guns battery resulted with a fighter that was better above 25000 ft than the Navy birds. It was not much of a climber, though, due to the excessive weight.
F4U was of the performance similar to the Spitfire IX - not a mean feat considering the thin wing and light weight of the Spitfire. F6F was a bit worse. Both of the US fighters were also the much better carrier birds than the Spitfire/Seafire versions. F4U-4, with the much improved R-2800-18W, was comparable with the Spit XIV.



The A series -4 powered the XF4U; 1850 HP max.
The B series -8 powered the F4U-1; the -10 powered the F6F-3 and -5, as well as the P-61. The -8 and -10, as well as the 8W and 10W, were basically the same engines, apart fro the carb and some small bits & pieces.
The C series -18W powered the F4U-4; took part in ww2 in 1945.
The E series -32W powered the F4U-5, a post-war model; that engine was with two small superchargers (so-called 'sidewinder' layout) feeding together the engine-stage S/C.
'W' denotes water-alcohol injection.



Press on with development and testing - same as for any piece of kit that ups the state of art.


Military application of turbochargers predates the commercial application of turbochargers.
Indeed, fitting the turboes on the fighters, even the bespoke ones made around the turboes was not easy.

Ok thanks for clarifying, what are then the barriers to applying either the entire system or individual lessons and technical solutions from the P&W supercharger systems (either the multi speed or multi-stage or both) to the V-1710.

How large are both.
How wide specifically.
Can the two / multi-speed subsystem be isolated from the whole?
How heavy are they.
How much power do they require to run.

 

[Micetro]

No problem chaps, it comes from various Air Ministry Publications like pilot's notes, maintenance manuals and added to by pilot's autobiographies, plus current knowledge from research during restoration work. Collings own BR601 which is one of the early conversions from a MKV.

With regards to the MKVII/IXs not being seen with a Vokes filter, the Aboukir Filter is a very different looking thing, Vokes took it and refined it so that it could be standardized for incorporation into the lower cowl of all MKVIII/IX aircraft so you didn't have a specific lower cowl for Northern Europe vs dusty areas, it is just much better refined than those fitted to the MKVs. The Aboukir Filter was sporadically fitted to some machines in the Med/North African theatres but even the MKIXs used by Skalski's Circus weren't fitted with ANY form of filter so I wouldn't have wanted to be an Erk on that unit, they must have been swapping engines left, right and centre!

 

[MIflyer]

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

The reason the Martin B-26 had such a high survival rate was that the bomber units talked to the RAF and were told it was suicide flying around over Occupied Europe at 15,000 ft. They needed to change direction every five minutes or less, because that was how long it took the Germans to set up an ambush barrage. Change heading every five minutes or less and the chance of being hit went way down.

Interestingly enough, I have read of RAF Spitfire pilots escorting B-26's in the early days of their deployment in the ETO and it seems the bombers got lost a lot and had trouble finding the target. This is hardly surprising. If I had to change my heading every five minutes while flying I probably could not find my own house.

B-26's in the ETO carried four .50 cal package guns on the side but it seems they almost never did any strafing with them. I have read of B-26 pilots in the ETO using the package guns only twice. Once when they were directed to hit a concentration of German armor and then go down and strafe. The other time was when a B-26 pilot in formation saw a BF-109 make a pass at the formation and then zip by his airplane to the right. He was on the outer edge of the formation, dove after the 109, blew it out of the air with the package guns, and then pulled back into formation to hear the radio message, "Good Shooting." I mean, you talk about one very surprised Luftwaffe pilot that had to be!

So the B-26 in the ETO did almost no low level bombing and strafing (unlike the B-26's deployed to the Pacific early in the war), flew at around 15,000 ft zigging and zagging like crazy, typically did not hit heavily defended targets like factories and airfields, and usually had fighter escorts.

One USAAF fighter leader in the ETO I read of decided not to go back the States and instead took over a P-38 unit. He was fascinated with the Droop Snoot bombsight equipped P-38's and decided they could take over some bombing missions from the medium and heavy guys. So he had his P-38s equipped with bombs and led them straight and level with a Drrop Snoot P-38 over a Luftwaffe airfield in France. All seemed to be going well when ... BAM! The Germans hit them with a nice barrage of AA, not caring that these were fighters or bombers; they were just excellent targets.

 

[tomo pauk]

How large are both.
How wide specifically.
How heavy are they.

I don't have the weight breakdown of the S/C systems. The 2-stage R-1830s were about 150-200 lbs heavier than their 1-stage 2-speed siblings; on the R-2800s, difference was 100-150 lbs. On the V-1710 F series, about 200 lbs difference.
The impeller on the aux stage on the V-1710 was of 12.18in diameter, on the R-1830 was 11in, on the R-2800 was 13in. The p&W aux S/Cs were much more closely-coupled than the Allison system, just 13 in difference in length between the 1-stage and 2-stage R-2800s (at least on the B series of R-2800s, ie. the types mostly used in ww2) vs. 17-18in on the V-1710.

Can the two / multi-speed subsystem be isolated from the whole?

Probably It can.
RR adopted the 2-speed drive from Farman because their 2-speed drive was not satisfactory, while Packard adopted the Wright 2-speed drive for the V-1650 production. Granted, some engines might require more work than the other ones. Many engine went from 1-speed to 2-speed drives - Klimov V12ss, Mikulin V12s, Sakae, Zuisei, Ha 41 into 109, R-1820, R-1820, Jumo 210, G&R 14P/R, some Italian engines... The DB 600 adopted the hydraulic S/C drive as a part of development into the 601, while the Jumo 213 went from a 2-speed to a 3-speed S/C.
FWIW, Allison added the hydraulic drive to the basic V-1710 when they went with the 2-stage versions, so I'd imagin that adopting the other people's mechanical 2-speed drive should not be such a bugaboo.

How much power do they require to run.

At 20000 ft and at max power, it is at hundreds of HP, and just for the 1st/aux stage. The R-2800-8 or -10, that does 2000 BHP down low when the aux S/C is de-clutched, is making 1625 BHP at 22500 ft (rated power in high gear) - IOW, almost 400 HP difference.
(hence the appeal of the turbochargers)
Granted, a lot of that power loss is negated by a decent exhaust thrust, and the ram effect helps with the rated altitude, so the R-2800 in question will make the equivalent of perhaps ~1800 BHP at 25000 ft on the real-world F4U-1 or the F6F-3?

 

[MIflyer]

By the way, the early P-38's had a "fence" sticking up between the turbos and the cockpit. Turbos had been known to explode, especially at the highest altitudes, and the fence was designed to protect the pilot from the shrapnel. They fixed the problem by upping the speed of the V-1710's mechanical supercharger by changing the gear ratio and thus lowering how much boost the tubo had to provide above 30,000 ft or so.

 

[Steamed_Banana]

The reason the Martin B-26 had such a high survival rate was that the bomber units talked to the RAF and were told it was suicide flying around over Occupied Europe at 15,000 ft. They needed to change direction every five minutes or less, because that was how long it took the Germans to set up an ambush barrage. Change heading every five minutes or less and the chance of being hit went way down.

Interestingly enough, I have read of RAF Spitfire pilots escorting B-26's in the early days of their deployment in the ETO and it seems the bombers got lost a lot and had trouble finding the target. This is hardly surprising. If I had to change my heading every five minutes while flying I probably could not find my own house.

B-26's in the ETO carried four .50 cal package guns on the side but it seems they almost never did any strafing with them. I have read of B-26 pilots in the ETO using the package guns only twice. Once when they were directed to hit a concentration of German armor and then go down and strafe. The other time was when a B-26 pilot in formation saw a BF-109 make a pass at the formation and then zip by his airplane to the right. He was on the outer edge of the formation, dove after the 109, blew it out of the air with the package guns, and then pulled back into formation to hear the radio message, "Good Shooting." I mean, you talk about one very surprised Luftwaffe pilot that had to be!

So the B-26 in the ETO did almost no low level bombing and strafing (unlike the B-26's deployed to the Pacific early in the war), flew at around 15,000 ft zigging and zagging like crazy, typically did not hit heavily defended targets like factories and airfields, and usually had fighter escorts.

One USAAF fighter leader in the ETO I read of decided not to go back the States and instead took over a P-38 unit. He was fascinated with the Droop Snoot bombsight equipped P-38's and decided they could take over some bombing missions from the medium and heavy guys. So he had his P-38s equipped with bombs and led them straight and level with a Drrop Snoot P-38 over a Luftwaffe airfield in France. All seemed to be going well when ... BAM! The Germans hit them with a nice barrage of AA, not caring that these were fighters or bombers; they were just excellent targets.

The usual default is missions flying out of UK with 8th AF but I'm referring exclusively here to MTO and Pacific Theaters. In the Western Desert and Med Spitfires only escorted B-26s when they were flying very short range strikes, most of the time escorts were by P-40s or P-38s, later P-47s as they arrived in Theater.

In the Pacific it was similarly pretty much exclusively Kittyhawks and P-38s until the P-47s started arriving pretty late in the game, and then later the P-51s.

 

[Howard Gibson]

I think the two stage is maybe too far a leap for the US in time for early 1943, though I'd like to look a little closer at the R-2800 and R-2600

The Americans had working turbochargers. There was not all that much pressure to get fancy superchargers on R2800s.

High altitude carrier aircraft were not really required until the Germans showed up with FritzXs in 1943. Even so, the Royal Navy did not install two-stage Merlins in Seafires. Two-stage Griffon Seafires were post war.

 

[tomo pauk]

The Americans had working turbochargers. There was not all that much pressure to get fancy superchargers on R2800s.

Turbochargers were the Army thing.
US Navy both requested and funded the 2-stage superchargers' development at P&W and Wright.

High altitude carrier aircraft were not really required until the Germans showed up with FritzXs in 1943. Even so, the Royal Navy did not install two-stage Merlins in Seafires. Two-stage Griffon Seafires were post war.

Waiting for the enemy to came up with the better gear, so you can start improving your own gear is not how military procurement works if the respective ministries are worth their salt.

 

[tomo pauk]

I want to plunge a bit deeper into the wartime F4Us and F6F, as these are more confusing to me. Were the wartime production R-2800 as installed on these fighters both two stage and two-speed as I am reading, and was the two-stage supercharger efficient / effective? General consensus seems to be that these fighters are not as effective at altitude above 25,000' as a P-47 or a P-51 or a Spit IX etc.

I'm also unclear as to the timeline of various versions of the R-2800 in these fighters.

For anyone that has an interest in the US fighters, I'd suggest two books: 'America's hundred thousand' and 'Vee's for victory'. A seasoned enthusiast might spot a mistake or two, but still these rate very, very high IMO. The 'Vee's' also handily dispels the myth of the 400 mph XP-39; granted, that book paints the V-1710 in a better light than I think it is realistic.
For the gearheads, the 'The secret horsepower race' is the ticket, together with the Calum's website where many charts are displayed better than in the book, together with some errata.
The AEHS Home is another gold mine, even more so for the members paying the small yearly fee. On that site, the fairy tale of the Ford V-1650 is put to the bed.
https://wwiiaircraftperformance.com/wwiiaircraftperformance.org/index-modif.html - great site.