American purchase programs, alternatives and reality, 1937-43 (1 Viewer)

[Shortround6]

AAF was favoring the V-1710 one time, and most of the companies were trying to make the new fighters around that engine. Seems like the system worked.

Yes and no. I am not sure the Allison was really favored or if the Allison was the only liquid cooled engine that was close to being available?
The Continental (AAC) XX-1430, Lycoming O-1230, P&W X-1800 were still on the test stands and not flying. P&W shut down the liquid cooled engine program/s on their own.
Lycoming turned the flat 12 into a 24 cylinder H engine to get enough power (Vultee XP-54s 2nd choice) and figuring out who was funding the Continental/army project gets murky over the years. Somebody ( the AAF and the Defense Plant Corporation funded a new aircraft engine plant for Continental in Muskegon, Michigan that cost $5 million) paid for a factory to make V-1430s that finally built V-1650 Merlins when the V-1430 program was finally killed off. Early development (mid 30s) was sort of shared between the Army and Continental, but Continental was less willing to do unfunded work for the Army than Allison so by 1939 Allison was much further ahead but also was much deeper in the whole with unpaid bills.
But this whole saga took over 10 years (?) so there was lots of time for things to go back and forth.

There is no doubt that USAAF and Allies would've been better without the Tornado and hi-per engines' fiasco.

No doubt about that.

FWIW, they were earlier than Allison with a working 2-stage S/C.
Any quantifiable measure of how really good/bad were the GE superchargers from the 1930s? When did the companies decided they are better on their own wrt. the superchargers?

Which 2-stage supercharger? The Army was buying GE turbos and sticking them in B-17s in 1938?
It seems (Wright production records) that Wright built 11 two stage mechanical supercharged R-2600s before Allison built a mechanical 2 stage supercharger.
Curtiss XP-37 flew in April 1937 with a turbo.

Finding information on the GE superchargers is difficult. It also seems that at times it was a group effort. GE provided the impellers and some technical help but some of the engine makers built the supercharger bodies themselves. So who was in charge of the inlet and the outlet? Whose fault was bad results?
A lot of the mid 30s Wright and P&W engines had critical altitudes of under 3000 meters and with US 87 octane fuel (not British 87 octane) they could not run very high boost anyway so poor efficiency was somewhat hidden.

Probably better than the number of the V-1710-powered aircraft in the same time?

Wright wins but not by much. Allsion built 48 V-1710s in 1939. In part for Bell and the Airacudas.

The big radials, at least in the USA, were also making better power. A thing that, together with preference towards the V-1710, meant that two were needed on the P-38 - and now all the savings in drag, weight and price disappear.

Timing is everything.
We can look at the test results and see the difference in drag on a P-36 (R-1830 engine) and early P-40 and look at the power used or estimated from dyno cards at altitude.
As mentioned, the two speed Curtiss engines shift out of low gear very soon (as did the 2 speed R-1830s) so 1-200 hp disappears very quickly once you get over 10,000ft.
we can also look at the theoretical flat plate areas of the F4U-1D and the P-38J and the F6F-3. The P-38J is neatly sandwiched in between the two R-2800 powered navy fighters. P-47 is better. R-2600 had a bit more frontal area than the R-2800 so a lot depends on cowling.
The drag and exhaust thrust shifted back and forth in just a few years.

 

[tomo pauk]

Yes and no. I am not sure the Allison was really favored or if the Allison was the only liquid cooled engine that was close to being available?

Seems like that, at least for the future P-38 and P-39, that Allison was not just favored, but specified. FWIW:

A similar proposal for a single-engined fighter was issued at the same time, Circular Proposal X-609, in response to which the Bell P-39 Airacobra was designed.[15]​ Both proposals required liquid-cooled Allison V-1710 engines with turbosuperchargers and gave extra points for tricycle landing gear.

Which 2-stage supercharger? The Army was buying GE turbos and sticking them in B-17s in 1938?
It seems (Wright production records) that Wright built 11 two stage mechanical supercharged R-2600s before Allison built a mechanical 2 stage supercharger.
Curtiss XP-37 flew in April 1937 with a turbo.

Wright's 2-stage supercharger.

Wright wins but not by much. Allsion built 48 V-1710s in 1939. In part for Bell and the Airacudas.

Wright wins also in 1940, with 1925 R-2600s vs. 1149 V-1710s. Or about 3/4s more.

We can look at the test results and see the difference in drag on a P-36 (R-1830 engine) and early P-40 and look at the power used or estimated from dyno cards at altitude.
As mentioned, the two speed Curtiss engines shift out of low gear very soon (as did the 2 speed R-1830s) so 1-200 hp disappears very quickly once you get over 10,000ft.

We can also take a look at the difference in speed between the Bf 110C and A-20B. The later was faster, on early R-2600s, and despite having the bulky, bomber fuselage. Or, vs. a 'gunned' Mosquito, where the difference was negligible, despite the Merlin 20s being in theory the far better engines than the R-2600s for the fast aircraft (and a far, far better engine than the C series V-1710s), and the Mosquito being that streamlined in total.

we can also look at the theoretical flat plate areas of the F4U-1D and the P-38J and the F6F-3. The P-38J is neatly sandwiched in between the two R-2800 powered navy fighters. P-47 is better. R-2600 had a bit more frontal area than the R-2800 so a lot depends on cowling.
The drag and exhaust thrust shifted back and forth in just a few years.

A fighter designed around a big radial that has no turbo and it is not a Navy aircraft can be lighter, smaller and less draggy than either of the three (P-47, F4U, F6F). There is no need for the 18% thick wing, there is no need for a 334 sq ft wing, either. No oversized fuselage needed, no need to pay for the folding wing penalty.
It is not like the Americans didn't tested the ways to make the radial engine installation better, from the fan cooling to the individual exhaust stacks. Apply the gained knowledge.
Granted, the Army preference for turbo avoids need to perfect the exhaust stacks since the exhaust is used to turn the turbo, as we know.

 

[Shortround6]

Seems like that, at least for the future P-38 and P-39, that Allison was not just favored, but specified.

Again, things depend on timing.
The development of the -1430 engine started in 1932 but the first complete 12 cylinder engine was not run until 1938 as a flat 12. By the Start of 1938 Allison ad built and run 14 V-1710 engines. It looked like Allison was going to get a production engine into service before Continental/AAF engine. And the Lycoming was even further behind.
If the AAF wanted liquid cooled engines in 1939/40/41 it was the Allison or nothing no matter what the AAF thought of the technical merits of the different engines.
The AAF and the Defense Plant Corporation were not offering to fund a 2nd Allison plant or a major expansion of the first Allison factory in 1940-41.

Wright's 2-stage supercharger.

Wright's first two stage R-2600 may have been completed in May of 1941 and the 9th in May of 1942. P&W built their 5th production R-2800 (single stage) in March of 1940. The two stage Wright was late.

We can also take a look at the difference in speed between the Bf 110C and A-20B. The later was faster, on early R-2600s, and despite having the bulky, bomber fuselage. Or, vs. a 'gunned' Mosquito, where the difference was negligible, despite the Merlin 20s being in theory the far better engines than the R-2600s for the fast aircraft (and a far, far better engine than the C series V-1710s), and the Mosquito being that streamlined in total.

the high powered radials could be a bit better. An early A-20 with R-2600 engines was about 10-15mph faster than a 110C. It also weighed about 50% more than 110C. It also took almost 20% more time to reach 20,000ft. The A-20s were fast but the R-2600 engines peaked low, unless you added weight and bulk with the two stage supercharger.

It is not like the Americans didn't tested the ways to make the radial engine installation better, from the fan cooling to the individual exhaust stacks. Apply the gained knowledge.
Granted, the Army preference for turbo avoids need to perfect the exhaust stacks since the exhaust is used to turn the turbo, as we know.

yes, the US were testing all kinds of things and yes they applied that knowledge. The problem is tooling up for a new fighter (or more than one) when you don't know if the experiments are actually going to work. In some "what If's" we know that the experiments will work. But a more "historical what if" the decision makers do not have that benefit.
The P-40D/E was ordered in the summer of 1940 with first delivery almost a year later. Would an R-2600 powered fighter have been significantly better than a P-40D/E in the summer of 1941 using a single stage/two speed supercharger?
And if somebody designed a fighter to fly in 1941 with enough space in the airframe for 1943 engine how good would it have been?

 

[tomo pauk]

Again, things depend on timing.
The development of the -1430 engine started in 1932 but the first complete 12 cylinder engine was not run until 1938 as a flat 12. By the Start of 1938 Allison ad built and run 14 V-1710 engines. It looked like Allison was going to get a production engine into service before Continental/AAF engine. And the Lycoming was even further behind.
If the AAF wanted liquid cooled engines in 1939/40/41 it was the Allison or nothing no matter what the AAF thought of the technical merits of the different engines.

That is if they wanted the liquid cooled engines. My idea is that they should've been requiring power and availability.

Wright's first two stage R-2600 may have been completed in May of 1941 and the 9th in May of 1942. P&W built their 5th production R-2800 (single stage) in March of 1940. The two stage Wright was late.

Vs. the P&W 2-stage R-2800, yes, it was running late. Vs. a 2-stage V-1710, it was running earlier as a working engine.

the high powered radials could be a bit better. An early A-20 with R-2600 engines was about 10-15mph faster than a 110C. It also weighed about 50% more than 110C. It also took almost 20% more time to reach 20,000ft. The A-20s were fast but the R-2600 engines peaked low, unless you added weight and bulk with the two stage supercharger.

There was no instance where the 2-stage S/C didn't add the bulk and weight. People were willing to pay that price, in order to get better power. The ones that were unwilling to go with a 2-stage S/C were the ones in the wrong.

yes, the US were testing all kinds of things and yes they applied that knowledge. The problem is tooling up for a new fighter (or more than one) when you don't know if the experiments are actually going to work. In some "what If's" we know that the experiments will work. But a more "historical what if" the decision makers do not have that benefit.

People that were doing the experimenting and testing didn't just went their merry way after the testing. They were doing the test reports, so other people can put the test results into a working hardware. Americans knew that the individual exhaust stacks were adding 13-18 mph to a radial-engined fighter when they tested the XP-41 in Spring of 1940. The historical decision makers - both in institutions and in companies - were aware of the benefit, unfortunately it took the people until ~1943 to put the crucial info in the use.

The P-40D/E was ordered in the summer of 1940 with first delivery almost a year later. Would an R-2600 powered fighter have been significantly better than a P-40D/E in the summer of 1941 using a single stage/two speed supercharger?

We don't need to use the 1600 HP R-2600 in 1941. We can use the 1850 HP R-2800, and the 2000 HP R-2800 already in early 1942.
The case of P-40E shows the folly of a weak engine being required to power a fighter armed with 6 heavy MGs and their ammo, a lot of fuel and a lot of protection. There is no oomph.

And if somebody designed a fighter to fly in 1941 with enough space in the airframe for 1943 engine how good would it have been?

It would've been excellent. The engine of 1943 will be of similar weight and bulk as that of 1941, while offering better power and thrust.

 

[Shortround6]

That is if they wanted the liquid cooled engines. My idea is that they should've been requiring power and availability.

The liquid cooled engines, on average, did have a significate advantage in drag. The difference in power, at least in American engines tended to be closer around 4-5000 meters.
Allison had some problem getting going in the power race. Not bad in 1939/40 but then it stagnated due to supercharger problems.
US production capacity for the big radials was under construction in 1940-41-42. Production of branch and license plants only really started to kick in 1942.
As mentioned,
the 1600hp Wright had 1400hp at 11,500
The 1850hp P&W had 1500hp at 14,000ft
The 2000hp P&W had 1600hp at 13,500ft.
If you want to fight at 20,000ft (6000m) and above the single stage large American radials are not the answer.

For comparison the early BMW 801 was giving 1600hp at sea level (old source) and 1380hp at 15,100ft.
the later BMW 801 had 1700hp at sea level and 1440hp at 18,700ft.

In 1940 the Merlin XX was making 1120hp at 18,500ft.
The V-1710-C15 was not bad at a snapshot in time (spring of 1940?) and Allison was working on the -39 engine in spring/summer of 1940 and getting orders for thousands of engines in 1940, for delivery in 1941/42. Wright and P&W were not going to do any better, orders in 1940 are going to be delivered in 1941/42. and what are the Germans going to be building in 1942? Japanese are a total unknown in 1940.

What is unknown is how much the Tornado fiasco costs Wright and America in delayed development/production of the R-2600.
The 1700hp Wright R-2600 was built, except for prototypes, in a brand new plant in Cincinnati. How much that could have been speeded up is subject to question.

Vs. the P&W 2-stage R-2800, yes, it was running late. Vs. a 2-stage V-1710, it was running earlier as a working engine.

Some of this depends on how good the 2 stage superchargers/engines were. The P&W 2 stage R-1830 was not really that good. It was better than the single stage R-1830 but that was a low bar.
It was within a few % of the 2 speed engines in Zero and Ki-43 in power at altitude. (around 6000 meters)
Engine in F4U-1 was good for 1650hp at 22,500ft. Good but not really great. Supercharger could deliver a pressure ratio of just over 4 to 1. Single stage supercharger in the Merlin 47 could deliver a 3.8 to 1 pressure ratio and the 2 stage supercharger in the Merlin 61 could deliver a 5.4 pressure ratio.
Allison had screwed up their early 2 stage attempts and with the failure to get a working intercooler the later versions failed to get the desired results.

There was no instance where the 2-stage S/C didn't add the bulk and weight. People were willing to pay that price, in order to get better power. The ones that were unwilling to go with a 2-stage S/C were the ones in the wrong.

In general you are right. In practice it is not so clear cut. Germans got 1300hp at 4800 meters out of DB 601E and 1355hp at 5700 meters out of the DB 605A and then 1200hp at 8000 meters with the DB 605 AS. These are without power boosting systems.
You also need either high PN fuel or good intercoolers (or both) to get the best results from 2 stage superchargers.

People that were doing the experimenting and testing didn't just went their merry way after the testing. They were doing the test reports, so other people can put the test results into a working hardware. Americans knew that the individual exhaust stacks were adding 13-18 mph to a radial-engined fighter when they tested the XP-41 in Spring of 1940. The historical decision makers - both in institutions and in companies - were aware of the benefit, unfortunately it took the people until ~1943 to put the crucial info in the use.

I don't know why it took so long to use exhaust thrust on radial engines. You are correct that the testing was done in 1940 and results took a while (A-20s and B-25s got the stacks before fighters?). What is strange is that it took a while for other nations to also use it, like the Japanese. British had a very hard time because their engines were built different (exhaust ports were on the front of the cylinders and doing a 180 degree turn was not easy). Of course for some reason even getting the exhaust nozzles right on V-12s was hard for some people.

We don't need to use the 1600 HP R-2600 in 1941. We can use the 1850 HP R-2800, and the 2000 HP R-2800 already in early 1942.

Kind of covered above. The US doesn't know what the Japanese are planning and against the Germans the single stage radials don't offer the performance at altitude that they wanted. Sort of American Fw 190 except the cowling won't be as good without the fan. In 1941 the British are shipping P-39s to Russia and P-40s to Africa because they don't work at high altitudes. Building fighters with large radials that don't offer much more critical altitude than the existing V-12 fighters is not going to find much favor.
I found this report.

https://www.aahs-online.org/pubs/journals/files/271055.pdf

Late 1940 and early 1941 they were looking at a stretched P-39 to hold a two stage Allison AND house the IV-1430 Continental.
This is before the P-40D even flies and before a Tomahawk fires it's guns in anger.
Curtiss had come up with XP-53 in the fall of 1940 (P-40 fuselage and tail with a new wing and the IV-1430 Continental engine) and then the P-60 series which started with either a turbo Allison or the Packard built Merlin. The entire program failed but for the single stage radial fighter idea to work the AAF had to change it's mind about what is wanted.
It is a combination of technical and air power theory.
We know that the US fighters of 1942 pretty much sucked. Mostly due to low power and too much weight. Allison made some improvements during 1942 but the USAAC resisted using combat power for months despite Allisons urging and reports from the British. Allison also didn't go the easy route and design a lager diameter supercharger and a two speed drove to make sort of an American Merlin XX. They tried to jump to the two stage supercharger with a variable drive. Just about all of the American projects were for higher altitude planes.
It is not until the US has been flying combat in 1942 and 1943 that the need for low altitude planes really shows up.
The US could have built the planes that You want, Tomo, but the USAAF didn't want them and the question here is how well would they have performed? You are quite right, they don't have to be as big as F6F, unless you want to stuff the high altitude supercharger/intercoolers in later.
Need for six .50s is questionable but the actual need for 400rpg is even more questionable. Just going 300rpg saves about 180lbs adjust as needed.
Now with the big radials fuel becomes an issue. Army may not need 250 US gallons of an F6F but 150-160 US gallons (600 liters) internal is not going to work even for the 1600hp Wright.
It may be possible to build sort of an American La-7 earlier but we need to solve the armament problem, three .50s weight more than two 20mm ShVAK cannon and US may not be satisfied with under 20 seconds of firing time. Americans are going to want more instruments/radios. Protection for pilot and fuel?
Figure out the intended load to help figure out the size/weight of this hypothetical fighter.

The case of P-40E shows the folly of a weak engine being required to power a fighter armed with 6 heavy MGs and their ammo, a lot of fuel and a lot of protection. There is no oomph.

True, the failure of the first attempt to use 9.60 supercharger gears and raise the FTH to 15,000/15,500ft in Dec 1941 PLUS the failure to use WEP settings of some sort for most of 1942
really hurt things. Or the failure to really look at the P-40 and figure out how to lighten it. Taking the electric starter/battery and one fuel tank out were real evidence of desperation (or being cheap) rather than serious effort. The Fuel was needed. Under 600 liters is only excessive if compared to very short range planes like Spitfires and 109s.
What is the desired (needed) firing time for the guns, not what sounds cool or whatever the 1940-41 word was.

 

[tomo pauk]

The liquid cooled engines, on average, did have a significate advantage in drag. The difference in power, at least in American engines tended to be closer around 4-5000 meters.
Allison had some problem getting going in the power race. Not bad in 1939/40 but then it stagnated due to supercharger problems.
US production capacity for the big radials was under construction in 1940-41-42. Production of branch and license plants only really started to kick in 1942.
As mentioned,
the 1600hp Wright had 1400hp at 11,500
The 1850hp P&W had 1500hp at 14,000ft
The 2000hp P&W had 1600hp at 13,500ft.

Having heaps more of power was a tested and true way to cancel out the additional drag. It was also a way to have all-singling all-dancing fighters (ie. can strap a lot more firepower and protection before the negative impact of that is really felt).

If you want to fight at 20,000ft (6000m) and above the single stage large American radials are not the answer.

Americans were investing in turboes (Army) and 2-stage superchargers (Navy), so we have that covered.

For comparison the early BMW 801 was giving 1600hp at sea level (old source) and 1380hp at 15,100ft.
the later BMW 801 had 1700hp at sea level and 1440hp at 18,700ft.

In 1940 the Merlin XX was making 1120hp at 18,500ft.
The V-1710-C15 was not bad at a snapshot in time (spring of 1940?) and Allison was working on the -39 engine in spring/summer of 1940 and getting orders for thousands of engines in 1940, for delivery in 1941/42. Wright and P&W were not going to do any better, orders in 1940 are going to be delivered in 1941/42. and what are the Germans going to be building in 1942? Japanese are a total unknown in 1940.

Germans in 1942 will certainly build engines - be these V12s or radials - that provide far better power than it were the DB 610A, V-1710-33 or the -39. The R-2600 and R-2800 stand far better chances to equal or beat these new engines than a 1710 cu in engine, providing the similar level of supercharging.
The C-15 was making in mid-1940 the similar power that the Db 601A was doing in late 1938, or the Merlin II in 1937.

Some of this depends on how good the 2 stage superchargers/engines were. The P&W 2 stage R-1830 was not really that good. It was better than the single stage R-1830 but that was a low bar.
It was within a few % of the 2 speed engines in Zero and Ki-43 in power at altitude. (around 6000 meters)
Engine in F4U-1 was good for 1650hp at 22,500ft. Good but not really great. Supercharger could deliver a pressure ratio of just over 4 to 1. Single stage supercharger in the Merlin 47 could deliver a 3.8 to 1 pressure ratio and the 2 stage supercharger in the Merlin 61 could deliver a 5.4 pressure ratio

The earlier the Navy moves away and up from the R-1830, the better. Much better.
If you think that R-2800-8 was only good, than the BMW 801 was outright bad. A R-2800-8 in a non-Navy fighter, lighter, with a thinner and smaller wing, would've been simply awesome in 1942-44. For all altitudes, and with enough fuel, for very long ranges.
If the fighter is made around the -4, the earlier engine model, even better since it is earlier.

Kind of covered above. The US doesn't know what the Japanese are planning and against the Germans the single stage radials don't offer the performance at altitude that they wanted. Sort of American Fw 190 except the cowling won't be as good without the fan.

As above - Americans were planing to much improve their supercharging, that, despite some hiccups, did provide their aircraft with high power at high altitudes. There is no need that we cancel these developments in this what-if.
As for the fighters powered by big radials, the American '9/10s of Fw-190' is a far better suggestion than an American '9/10s of Spitfire II'.

The US could have built the planes that You want, Tomo, but the USAAF didn't want them and the question here is how well would they have performed? You are quite right, they don't have to be as big as F6F, unless you want to stuff the high altitude supercharger/intercoolers in later.
Need for six .50s is questionable but the actual need for 400rpg is even more questionable. Just going 300rpg saves about 180lbs adjust as needed.
Now with the big radials fuel becomes an issue. Army may not need 250 US gallons of an F6F but 150-160 US gallons (600 liters) internal is not going to work even for the 1600hp Wright.
It may be possible to build sort of an American La-7 earlier but we need to solve the armament problem, three .50s weight more than two 20mm ShVAK cannon and US may not be satisfied with under 20 seconds of firing time. Americans are going to want more instruments/radios. Protection for pilot and fuel?
Figure out the intended load to help figure out the size/weight of this hypothetical fighter.

Army badly wanted a fighter armed with heavy firepower, that included the 37mm gun, and a turboed engine. If the V-1710 was not stipulated, Lockheed can take the 1600 HP R-2600 into consideration, making basically a 'P-47 minus', with the 37mm guns under the wings (that will quickly be replaced by 6 HMGs for production). Protection for pilot and fuel, the earlier the better. 250-300 gals of fuel when s-s tanks are in. Drop tanks.
Add the newer engines - both R-2600 and R-2800 are in play - as these are available. A singe-fuselage aircraft will be faster to make than the P-38, and will be devoid of many problems the P-38 had as a twin (the tunnel between the fuselage and nacelles that made the compressibility issues as bad as they were, the low rate of roll due to having high weight away from centreline, the need to service two engines and two turboes, blind spots). Once Bell flops with the Aircuda, the might get the contract for more of Lockheed fighters.
The plan B is something with a 1-stage engine, sized like the F4F, but as a low-wing aircraft. 250 gals of fuel without the s-s tanks, or 200 with, + drop tanks.

Navy - go with big radials ASAP. The best is the 2-stage R-2800, other will do, too.

 

[Shortround6]

Germans in 1942 will certainly build engines - be these V12s or radials - that provide far better power than it were the DB 610A, V-1710-33 or the -39. The R-2600 and R-2800 stand far better chances to equal or beat these new engines than a 1710 cu in engine, providing the similar level of supercharging.
The C-15 was making in mid-1940 the similar power that the Db 601A was doing in late 1938, or the Merlin II in 1937.

There are several things in here. The C-15 had problems. The main was the reduction gear. It was not designed to handle higher powers. The C-15 was not quite as bad as it is portrayed.
Not as good as the Merlin (either II or III) but it made 1040hp at 4360 meters and 1090hp at 4023 meters. In comparison to the early Merlins it was allowed to make 1040hp for take off compared to 880hp. Early DB 601s were rated a 3700 meters and later 4000 meters and some got up to 4500meters.
In regards to the highlighted section. The Air cooled engines had problems with the supercharging, or rather the limit was not the superchargers but cooling. The engines had pretty maxed out the engine cooling and any attempts to use higher boost either didn't go anywhere or only a small increase. The 1700hp Wright R-2600 maxed out at 45.5in boost but only in high gear. That is about 7.7lbs of boost. It didn't get better until the 1900hp version came along with new crankcase, crankshaft and new heads and cylinders with much better cooling.
Allisons, once they get to the end of 1941, stand up to about 13lbs of boost fairly well and some people claim 20lbs of boost. Problem here is that while the engine will stand up to it the supercharger cannot supply high boost very high off the ground. The late 9.60 geared Allisons would do 13.3lbs of boost at 9500ft for 1410hp. Turbo P-38 engines finally got up to 1600hp using 15lbs of boost. The engine will stand up to the power (assuming the radiator/s will) but the superchargers cannon provide the air.
You can beat that power with the large radials but you need a much heavier engine. Things moved back forth over the years and the margin was rarely stationary for a large number of months.
It might suit the US to make more smaller planes in 1941-42-early 1943 than fewer larger planes. By late 1943 the size of the airplanes doesn't matter so much. The US industry can supply large numbers of large aircraft.

The earlier the Navy moves away and up from the R-1830, the better. Much better.
If you think that R-2800-8 was only good, than the BMW 801 was outright bad. A R-2800-8 in a non-Navy fighter, lighter, with a thinner and smaller wing, would've been simply awesome in 1942-44. For all altitudes, and with enough fuel, for very long ranges.
If the fighter is made around the -4, the earlier engine model, even better since it is earlier.

The R-2800 was very good engine, the two stage supercharger was not so good, or perhaps, it was good for it's time. P&W was pouring a lot of effort into the R-2800 and into the R-4360. The R-1830 was neglected. It did get some trickle down technology in 1944 that allowed it to make 1350hp.
As an example of changing technology, the single stage R-1820s put in the FM-2 Wildcats made 1000hp at 17,000ft compared to the 1040hp at 18,400-19,000ft from the two stage 1830s. The 9 cylinder radial installation was about 400lbs lighter. That is difference 3-4 years could make in the US.

The US leaned heavily into water injection to use more boost in the radials. The two stage radials already were using intercoolers and larger intercoolers get to point of diminishing returns fairly soon. R-2800s were known for smoky exhaust when running hard. When using water injection, the carbs reduced fuel flow by around 1 US gallon per minute. Without water injection the engine/s were using extra fuel as cooling agent.

As far as scaling things down (or up) if we look at the F6F and decide we can make do with 100 US gallons fuel less that can mean 600lbs less fuel. 190lbs less for the smaller protected tank. It can also mean around 20-22 sq ft less wing area to keep the same wing loading and we might be able to shrink the wing by another 4 sq ft because of the lighter wing (about 6lbs per sq ft). This works in reverse if we try to scale up an existing aircraft (adding fuel to a FW 190 or La-7).

 

[tomo pauk]

The Air cooled engines had problems with the supercharging, or rather the limit was not the superchargers but cooling. The engines had pretty maxed out the engine cooling and any attempts to use higher boost either didn't go anywhere or only a small increase. The 1700hp Wright R-2600 maxed out at 45.5in boost but only in high gear. That is about 7.7lbs of boost. It didn't get better until the 1900hp version came along with new crankcase, crankshaft and new heads and cylinders with much better cooling.

That is the thing - the big radials were, well, big. Being big meant they can produce a lot of power without needing huge boost.
Seems like the turboed R-2800s (and the R-1830s before them) were not having any cooling problems at high altitudes.

Allisons, once they get to the end of 1941, stand up to about 13lbs of boost fairly well and some people claim 20lbs of boost. Problem here is that while the engine will stand up to it the supercharger cannot supply high boost very high off the ground. The late 9.60 geared Allisons would do 13.3lbs of boost at 9500ft for 1410hp. Turbo P-38 engines finally got up to 1600hp using 15lbs of boost. The engine will stand up to the power (assuming the radiator/s will) but the superchargers cannon provide the air.

You can beat that power with the large radials but you need a much heavier engine. Things moved back forth over the years and the margin was rarely stationary for a large number of months.

I'm trying to find the way to have that level of power at altitude available by 1940 (and more by 1941, more still by 1942). The V-1710 will not cut it. The big radials will, and it will be cheaper in weight, drag and money than to go with two V-1710s per a fighter.

It might suit the US to make more smaller planes in 1941-42-early 1943 than fewer larger planes. By late 1943 the size of the airplanes doesn't matter so much. The US industry can supply large numbers of large aircraft.

Yes, definitely better aircraft are needed.

As far as scaling things down (or up) if we look at the F6F and decide we can make do with 100 US gallons fuel less that can mean 600lbs less fuel. 190lbs less for the smaller protected tank. It can also mean around 20-22 sq ft less wing area to keep the same wing loading and we might be able to shrink the wing by another 4 sq ft because of the lighter wing (about 6lbs per sq ft). This works in reverse if we try to scale up an existing aircraft (adding fuel to a FW 190 or La-7).

Works for me.
Depending on the engine chosen, type of supercharger, role of aircraft (is it to be fully navalized, or it is Army aircraft), fuel and firepower requirement, we might wing up with a aircraft as small as the P-40, or as big as the Sea Fury. Going turbocharged puts us to the P-47 territory, even if the R-2600 is used initially.
I'm not sure that Americans will go the 'European Continental' path, that favored big engines on as small airframes as possible, thus producing the small aircraft that were successful, like the Fw 190 or the La-5/-7, as well as the aircraft that never panned out, like the I-185.

 

[Shortround6]

I'm trying to find the way to have that level of power at altitude available by 1940 (and more by 1941, more still by 1942). The V-1710 will not cut it. The big radials will, and it will be cheaper in weight, drag and money than to go with two V-1710s per a fighter.

The V-1710 will not give the power you want in 1940 or 1941. 1942 is iffy, like when in 1942 and how.
Unfortunately, in 1940 there isn't a good alternative. Back in May of 1939 that was reason for the order of the P-40. It was not what the army wanted. It was what they could get that was low risk. They had a very good chance of getting what they ordered in numbers in 1940.
Alternative engines that might have worked in 1940 would be
Wright R-1820 with two speed supercharger.
Wright R-1820 with turbo?
Wright R-2600 with two speed supercharger.
Wright R-2600 with turbo (first flown in fall of 1940 and they had cooling problems)
P&W R-1830 with two speed supercharger (initial production in 1940)
P&W R-1830 with two stage supercharger (only 96 built in 1940)
P&W R-1830 with turbo
P&W R-2180 with two stage supercharger (none actually built)
P&W R-2180 with Turbo (none built?) (proposed P-44 engine)

basic problem was getting any engine that offered around 1000-1100hp at 15,000-18,000ft that would fit into an under 8,000lb fighter.
The F4F and P-43 just made it at around 7500lbs (depends on fuel)
Turns out the P-43 had some problems, some would have been fairly easy (but would add weight) and one needed some development with technology. Apparently, the P-43s were not equipped with turbo regulators that would manage the waste gate as the plane climbed and dived or not manage it well requiring the pilot to do so. Not sure what the P-38s were doing but in 1940 and 1941 there were a lot more P-43s in service. Pilots having to manage the turbo in combat added a lot to the pilot's workload and failure could lead to a turbo failure (turbo over-speeds and explodes). The 4 engine bombers had fight engineers to manage the turbos and climbed and dove a lot slower. What the sole turbo A-20 did I don't know. Obviously the AAC solve the turbo regulator problem but it took a while. The first version turned out not work well as it tended freeze.
P&W offered an R-2180 with either a 2 speed or a 2 stage supercharger. Details are unclear, 1150hp at 17,500ft is not good for such a large engine but a weight gain of around 150-180lbs does not sound right for just a two speed drive to an existing supercharger.
R-2180 used the same size cylinders as the R-2800 and putting that engine into service might delay or reduce the number of R-2800s in 1941/42.
My objection to the R-2600 solution is that is only good for around 1150-1200hp at 17,500 and it is a really big engine (over 1900lbs and over 54in in diameter). Great bomber engine with 1600hp to get you off the ground. Not so good for trying to fight at even 15,000-20,000ft. Props on the A-20s were 11ft 3in in diameter (2ft bigger than the prop on an f4F-3) but perhaps a fighter could have used a smaller diameter propeller?
In 1941 the US could drop in the 1700hp version fairly easily and incorporate exhaust thrust at the same time but as noted before, the gain in performance is not great.

As a check on Performance the Japanese Ki-100 with an engine that gave 1250hp at 19,030 ft was good for about 360mph at 19,685ft.
An R-2600 powered plane may offer some advantages over the Allison powered planes but not a lot under 15,000ft an very little vs a Merlin XX powered plane.
Perhaps the Ki-100 radial conversion could have been done better but extra power over the Ki-61 did not offer much.

That is the thing - the big radials were, well, big. Being big meant they can produce a lot of power without needing huge boost.
Seems like the turboed R-2800s (and the R-1830s before them) were not having any cooling problems at high altitudes.

Extra power got eaten up fairly quickly, Granted the F6F was huge but at low level it's 2000hp didn't offer much advantage over the P-40 with the Allison with 1150hp. A lot depends on exact height, the 2000hp disappears at much over 1000ft, depends on RAM. But a smaller radial powered plane (1600hp) still has a power to drag problem.
P&W was using smaller cylinders which cooled a bit better in general. Then we have to figure out the amount of cooling fin area on each cylinder and the effectiveness and the baffling and the cowling. Much of this is not available to most of us.
But.
R-2800 155 cu/in per cylinder and at 2000hp 111hp per cylinder.
R-2600 185 cu/in per cylinder and at 1600hp 114hp per cylinder.
R-1830 130 cu.in per cylinder and at 1200hp 86hp per cylinder.
Cooling is also affected by the volume of the cylinder vs the external surface and here bigger cylinders have more volume (heat) to surface area ratio.
With turbo engines trying to make high power at high altitudes in thinner air means you need more cooling air (volume of air) for the same cooling. yes the colder temperatures help but if the air at 25,000ft is only 71% as dense as it is at 15,000ft and you need almost 30% more air for the same cooling. Adjust for temperature but you still a lot more air flowing over the engine.
With engine we also have the problem of the temperature of intake air. If the temperature of the intake air for combustion goes up 100 degrees the peak temperature in the cylinders goes up 100 degrees and the temperature of the exhaust also goes up 100 degrees. With a less than optimum supercharger set up and a less than optimum intercooler we can also wind up with over-heating problems. Quick solution is to cut holes in the cowl to try to cool everything off. Longer solution (and lower drag) is to try to make the compressors more efficient (heat the intake air less) or design a better intercooler.
I don't know what the Problem with Turbo R-2600 was but Wright was buying the turbos from GE and had no control over them. Wright was designing the 1700hp R-2600 with a bit better cooling. I don't know who was responsible for the intercooler. I don't know if there problems with cowl and baffling. Wright certainly ran into a lot trouble with the R-3350 cowls but not much with B-25s and Baltimores but they didn't fly at high altitudes.

How much the R-2800 program can be speeded up is questionable. It took about 3 3/4years (for the 1850hp engine) which was pretty much standard for the US.
That is from start of project to making several dozens of engines per month. Even the P&W R-2000 took over 3 years and it not a big change from the R-1830.

As mentioned early there were several engines in development in 1937-40 that were canceled and several more that should have been so a lot of aircraft design teams wasted a lot of time working on prototypes that were either cancelled or had to be reworked with substitute engines. Not helped by the Army trying to push the state of the art. Asking for 500mph fighters in 1939/40 instead of 450mph fighters? They didn't have the wind tunnel results to do that and none of the proposed designs came close.

 

[tomo pauk]

The V-1710 will not give the power you want in 1940 or 1941. 1942 is iffy, like when in 1942 and how.
Unfortunately, in 1940 there isn't a good alternative. Back in May of 1939 that was reason for the order of the P-40. It was not what the army wanted. It was what they could get that was low risk. They had a very good chance of getting what they ordered in numbers in 1940.
Alternative engines that might have worked in 1940 would be
Wright R-1820 with two speed supercharger.
Wright R-1820 with turbo?
Wright R-2600 with two speed supercharger.
Wright R-2600 with turbo (first flown in fall of 1940 and they had cooling problems)
P&W R-1830 with two speed supercharger (initial production in 1940)
P&W R-1830 with two stage supercharger (only 96 built in 1940)
P&W R-1830 with turbo
P&W R-2180 with two stage supercharger (none actually built)
P&W R-2180 with Turbo (none built?) (proposed P-44 engine)

Thank you for the list.
IMO, the big radials should've been the 1st priority engines for the fighters, the V-1710 as the second priority, and the small radials as the 3rd priority (2nd priority for the Navy). Also, 1940 is not the only year that is important to the Americans, and P-40 is not a priority even for the British. There is no need to be saddled with the engine that gives 1000 HP on a good day, even if is a better engine than the small radials.
A fighter powered by a turboed R-2600 can be flown as early as the one with the turboed V-1710, ie at least by 1937-38, if the AAF is specifying it. Let's say, they put the tender for such a fighter instead of the V-1710 turboed fighters. Have a few companies sink their teeth in it - Republic (instead of the P-43), Lockheed (instea dof the P-38 and the big fighter project that never took flight), Bell (instead of Airacuda and Airacobra), Curtiss (instead of XP-37). One or two will be duds, one or two will have the potential.

basic problem was getting any engine that offered around 1000-1100hp at 15,000-18,000ft that would fit into an under 8,000lb fighter.
The F4F and P-43 just made it at around 7500lbs (depends on fuel)
Turns out the P-43 had some problems, some would have been fairly easy (but would add weight) and one needed some development with technology. Apparently, the P-43s were not equipped with turbo regulators that would manage the waste gate as the plane climbed and dived or not manage it well requiring the pilot to do so. Not sure what the P-38s were doing but in 1940 and 1941 there were a lot more P-43s in service. Pilots having to manage the turbo in combat added a lot to the pilot's workload and failure could lead to a turbo failure (turbo over-speeds and explodes). The 4 engine bombers had fight engineers to manage the turbos and climbed and dove a lot slower. What the sole turbo A-20 did I don't know. Obviously the AAC solve the turbo regulator problem but it took a while. The first version turned out not work well as it tended freeze.

The pilot will have far less to take care of in a 1-engined fighter with the turboed engine, than on a 2-engined A/C with turboed engines. Adding the turbo regulator on a 1600-2000 HP fighter is a rounding error wrt. the weight increase.
An engine that does 1000 HP at 15000 ft will not be necessarily the engine that does 1100 HP at 18000 ft.

My objection to the R-2600 solution is that is only good for around 1150-1200hp at 17,500 and it is a really big engine (over 1900lbs and over 54in in diameter). Great bomber engine with 1600hp to get you off the ground. Not so good for trying to fight at even 15,000-20,000ft. Props on the A-20s were 11ft 3in in diameter (2ft bigger than the prop on an f4F-3) but perhaps a fighter could have used a smaller diameter propeller?

The 'no free lunch' rule applies as ever. If the customers don't like the R-2600, up-engine the fighter with the R-2800 when available - do I really need to repeat this ad nauseam?
The P-40A to K and the P-39D to K were also bad at fighting above 15000 ft, so we lose nothing in that regard.

As a check on Performance the Japanese Ki-100 with an engine that gave 1250hp at 19,030 ft was good for about 360mph at 19,685ft.
An R-2600 powered plane may offer some advantages over the Allison powered planes but not a lot under 15,000ft an very little vs a Merlin XX powered plane.
Perhaps the Ki-100 radial conversion could have been done better but extra power over the Ki-61 did not offer much.

Ki 61 was a fighter with a thick wing (16%), the outdated wing profile (same series as on the Bf 109), and a big wing for the power installed. Top speed was better as altitude increased, and the RoC was much better.
The R-2600 powered plane will offer a factory-certified power of 1600-1700 HP down low, no need for the pilots and mechanics to gamble lives and machines with overboosting attempts. Same fighter will be easy to up-engine to 1850-2000 HP.
Merlin XX powered plane was not available for the Americans until into 1942 (never for the USN), while the Hurricane was meh even with it come 1941. If the USN went with the big radials big time, they would've been fielding the R-2800-powered Naval fighters by the time of Pearl Harbor, or at least by the very early 1942. Much better thing than to have the B-26s, or to fiddle with the XF5F and XP-50.

How much the R-2800 program can be speeded up is questionable. It took about 3 3/4years (for the 1850hp engine) which was pretty much standard for the US.
That is from start of project to making several dozens of engines per month. Even the P&W R-2000 took over 3 years and it not a big change from the R-1830.

P&W might've probably been able to shave a couple of months if the R-2180 was not in development?
But all of my musings with engines' applications assume no change to the basic engine availability, makes the math easier.

As mentioned early there were several engines in development in 1937-40 that were canceled and several more that should have been so a lot of aircraft design teams wasted a lot of time working on prototypes that were either cancelled or had to be reworked with substitute engines. Not helped by the Army trying to push the state of the art. Asking for 500mph fighters in 1939/40 instead of 450mph fighters? They didn't have the wind tunnel results to do that and none of the proposed designs came close.

Pushing forward the state of art was the basic route, lest your competition and enemy might've gotten the upper hand. Granted, if the aims are too ambitious, the end result might be just the waste of time and resources, so having several companies competing was a good thing to do. Same for having the plan B - sorta low-tech approach that can at least give the number required, even if it does not make the over-performers.

Army (and Navy) will do good when they acknowledge that power, reliability and availability of aero engine trump the metrics like shaving that extra inch from the engine height, or 'lets' make the engine as small as possible'. One bad engine design can kill several aircraft designs, or at least make them be too late.
Navy was far more realistic here; however, they did allow that their in-service fighters have no power advantage vs. the Axis aircraft, until later in the war. Fighters' high weight and high drag, not followed by the engine power, were one of the contributing factors for several of US carriers and other warships being sunk, in an inopportune time.

 

[Shortround6]

Thank you for the list.
IMO, the big radials should've been the 1st priority engines for the fighters, the V-1710 as the second priority, and the small radials as the 3rd priority (2nd priority for the Navy). Also, 1940 is not the only year that is important to the Americans, and P-40 is not a priority even for the British. There is no need to be saddled with the engine that gives 1000 HP on a good day, even if is a better engine than the small radials.
A fighter powered by a turboed R-2600 can be flown as early as the one with the turboed V-1710, ie at least by 1937-38, if the AAF is specifying it. Let's say, they put the tender for such a fighter instead of the V-1710 turboed fighters. Have a few companies sink their teeth in it - Republic (instead of the P-43), Lockheed (instea dof the P-38 and the big fighter project that never took flight), Bell (instead of Airacuda and Airacobra), Curtiss (instead of XP-37). One or two will be duds, one or two will have the potential.

A lot of this is timing and we have the advantage of seeing what did not work. So lets look at the Army fighter history.
The P-40 "design" started in early 1938. The Army had a design competition for new fighters that was suppose to happen in 1938.
The P-40 was based on the P-36 which dates back the 1935 pursuit competition which was postponed due to Curtiss being the only competitor that that show up with a working aircraft. Trial was postponed to April 1936 where Curtiss and Seversky show up but neither meet the performance goals (Curtiss is on it's 3rd different engine) and Seversky is given a contract for 77 airplanes in June 1936. Same month that Hawker got a contract for 600 planes. A big part of Seversky's win was due to price. Army was not convinced of Seversky's ability to deliver the aircraft according to schedule and gave Curtiss in July for 3 P-36 aircraft with the 4th engine (P&W R-1830). These show up in March/April of 1937.
Now the test Hawk 75 aircraft, still owned by Curtiss gets turned into the XP-37 with a turbo Allison but we are getting ahead.
July 1937 sees Curtiss get a contract for 210 P-36s. The P-35s are running late in delivery and let's face it, the P-35 with it's 850hp at 8000ft P&W R-1830-9 engine was not scaring anybody in Europe.
Back tracking to 1936 when Curtiss started design studies for Allison with turbo installed in a Hawk 75 airframe. Army issues a contract Feb 16th,1937 for the prototype, 5 months ahead of the P-36 production order. Testing started in July 1937. Things are busy at Curtiss in 1937. The 4th production P-36 is pulled from the production like to become the XP-42 with the extended prop shaft R-1830 engine and the long streamline nose. The 10th airframe is pulled to become the XP-40 with the Allison engine.
The XP-37 showed both Curtiss and the Army what not to do but it had potential when it actually worked. 340mph at 20,000ft and 330mph at 25,000ft. Curtiss gets a contract for 13 YP-37s in Dec 1938 but these are too late for the 1938 pursuit trial (which took place in Jan 1939) and the YP-37 was more of concept in progress when it did show up, with a number of restrictions on maneuvers. 12 of them showed in Nov/Dec 1939. Potential showed with a claimed 346mph at 25,000ft but this may have been with the original power level which was later de rated.
The XP-42 showed up in March 1939 and had cooling troubles to start and showed little or no performance gains over the standard P-36A/c aircraft.
The Army was looking for a large increase in performance in future fighters, They were looking for performance at 25,000ft (XP-39 with turbo).
In the spring of 1939 the Army estimated that a turbo equipped aircraft was 2 years away from entering squadron service. BUT all of the experimental engines that the army was looking at or funding were expected to use turbos.

The Army June 1939 design competition for Fiscal year 1940 (and later) aircraft did not favor any radial engines, Favorites included

P&W X-1800 watercooled 24-cylinder H-block of 2,240 cu in (later 2600) with sleeve valves. Think Sabre stood on it's side. Planned at times for 6 different aircraft. P&W had a change in management and canceled in Oct 1940. Planned production was not until 1942. This shows the time scale for some these projects.
Pratt & Whitney XH-3130, Big brother, enlarged to 3730cu/in while still in the planning stage. 2900hp planed with 100/100 fuel. Complete 24 cylinder engine never built and canceled at the same time as the smaller engine.
Continental IV-1430, this was supposed to offer 1600hp at 25,000ft in most of it's many variations.
Lycoming O-1230 of the 1930s was now too small to be useful even if it ran right. Lycoming simple stacked two together and used a common propeller and supercharger for the
Lycoming XH-2470 which found a little bit of interest from the navy. This one actually flew.
Wright R-2160 Tornado we have been over this thing already but it was included in planned 1941 funding, at least for development.
What is absent from the Army proposals is any air cooled engines or at least any that scored well in the proposals.

The pilot will have far less to take care of in a 1-engined fighter with the turboed engine, than on a 2-engined A/C with turboed engines. Adding the turbo regulator on a 1600-2000 HP fighter is a rounding error wrt. the weight increase.

Yes, a single is less that twin. The problem with the turbo regulator is not the weight but the fact that they either didn't exist or didn't work. Much like the early American aircraft didn't have boost regulators or boost limiters and the pilots were expected to manage the boost limit of the engine while in combat. Many Allison pilots over boosted by accident and still made it home. Engine's live may have been shortened. Radials are not going to as forgiving. Things got a lot better in late 1942 and early 43.

An engine that does 1000 HP at 15000 ft will not be necessarily the engine that does 1100 HP at 18000 ft.

True, I was just trying to cover a span for possible engines.

The 'no free lunch' rule applies as ever. If the customers don't like the R-2600, up-engine the fighter with the R-2800 when available - do I really need to repeat this ad nauseam?

Actually, you do need to repeat because there was a significant difference between the R-2600 and the R-2800. F6F aside there is not just a difference in the engines but there is a difference in the needed propellers, the size/weight of the exhaust systems, fuel system, etc. The smaller the initial airframe the harder it is to swap the engines and I keep saying, if you design for the R-2800 to begin with you have and oversized airframe for best performance with the R-2600.

The P-40A to K and the P-39D to K were also bad at fighting above 15000 ft, so we lose nothing in that regard.

Very true but Allisons failure to get the 9.60 gears to work is not a good justification for another low altitude engine. Especially one that uses more fuel for the same performance.

Ki 61 was a fighter with a thick wing (16%), the outdated wing profile (same series as on the Bf 109), and a big wing for the power installed. Top speed was better as altitude increased, and the RoC was much better.

Just using it as a sort of yardstick. What kind of performance can we expect from a "standard" Radial engine fighter of 1939-41 technology. Not a P-51 with a radial engine.
Try Ki-44 if you want. 1320hp at 17,225ft for 376mph. Granted the Ki-44 did not use exhaust thrust very well but it was a small airframe with light armament, and 485 liters of internal fuel doesn't get you very far with large engines.
R-2600 is a rather thirsty engine. It is not bad when throttled way back, but it is capable of using around 3 gal a minute at high throttle settings.
If you want an R-2600 powered fighter to have even the same range as a P-40 you need more fuel.
In 1939 you don't know where you will wind up fighting and the P-39 did not get it's self sealing tanks until 1940/41. It's short range was problem in the Pacific and the drop tank was short of crutch. Ideally the Hypothetical R-2600 fighter doesn't fall in the same trap.

The R-2600 powered plane will offer a factory-certified power of 1600-1700 HP down low, no need for the pilots and mechanics to gamble lives and machines with overboosting attempts.

Kind of covered above. The factory certified 1600hp power limit was at 1000ft on a 59 degree standard day. Things were a bit better with the 1700hp version. Granted this low alitdue limit does mean that the pilots can't get into much trouble in low gear as the engine simply can't provide much more boost. High gear may be another story.

Same fighter will be easy to up-engine to 1850-2000 HP.

Covered above, Using the same prop for both 1600hp and 2000hp is not a good idea. Depending on state of the art in prop design you may need longer landing gear.

P&W might've probably been able to shave a couple of months if the R-2180 was not in development?

maybe but probably not. P&W built about 30 R-2180s total so there was little if any production tooling.
It took P&W about 2 years to go from initial design/planning to first test engine, design changed from a 2600 cubic engine to the 2800 when P&W learned about Wrights 2600 and P&W wanted to beat Wright. The R-2180 may have given them a head start in cylinder design, just use 18 instead of 14.

Army (and Navy) will do good when they acknowledge that power, reliability and availability of aero engine trump the metrics like shaving that extra inch from the engine height, or 'lets' make the engine as small as possible'. One bad engine design can kill several aircraft designs, or at least make them be too late.

Navy was far more realistic here; however, they did allow that their in-service fighters have no power advantage vs. the Axis aircraft, until later in the war. Fighters' high weight and high drag, not followed by the engine power, were one of the contributing factors for several of US carriers and other warships being sunk, in an inopportune time.

As shown by the list above, the best was often the enemy of good. None of the Army's favored engines of 1939/40 ever powered an aircraft in active service. And 3 not favored air cooled radials powered many WW II and post war combat aircraft.
If you want a fighter plane for 1940/41 to be going into production, it had to have been in development in 1938/39 with 1939 aerodynamics and construction and you have to get the Army to overcome their liquied cooled engine bias. Army wanted air cooled engines for ground attack (no shot out radiators) but they didn't like them for other things. For the B-17 and B-24s they didn't have a lot of choice. They didn't have any liquid cooled engines ready to go (be built) except for the Allison and with the Allison slated for most/all of the 1940/41/42 fighters there weren't any to spare for bombers.
We should note that the Army was wrong in May 1939, the Turbos were not 2 years away from service use in fighters, they were 3 years away. The early P-38s and P-43s had trouble as did some early P-47s and several experimental aircraft were lost due to turbo troubles.

 

[Elan Vital]

A lot of this is timing and we have the advantage of seeing what did not work. So lets look at the Army fighter history.
The P-40 "design" started in early 1938. The Army had a design competition for new fighters that was suppose to happen in 1938.
The P-40 was based on the P-36 which dates back the 1935 pursuit competition which was postponed due to Curtiss being the only competitor that that show up with a working aircraft. Trial was postponed to April 1936 where Curtiss and Seversky show up but neither meet the performance goals (Curtiss is on it's 3rd different engine) and Seversky is given a contract for 77 airplanes in June 1936. Same month that Hawker got a contract for 600 planes. A big part of Seversky's win was due to price. Army was not convinced of Seversky's ability to deliver the aircraft according to schedule and gave Curtiss in July for 3 P-36 aircraft with the 4th engine (P&W R-1830). These show up in March/April of 1937.
Now the test Hawk 75 aircraft, still owned by Curtiss gets turned into the XP-37 with a turbo Allison but we are getting ahead.
July 1937 sees Curtiss get a contract for 210 P-36s. The P-35s are running late in delivery and let's face it, the P-35 with it's 850hp at 8000ft P&W R-1830-9 engine was not scaring anybody in Europe.
Back tracking to 1936 when Curtiss started design studies for Allison with turbo installed in a Hawk 75 airframe. Army issues a contract Feb 16th,1937 for the prototype, 5 months ahead of the P-36 production order. Testing started in July 1937. Things are busy at Curtiss in 1937. The 4th production P-36 is pulled from the production like to become the XP-42 with the extended prop shaft R-1830 engine and the long streamline nose. The 10th airframe is pulled to become the XP-40 with the Allison engine.
The XP-37 showed both Curtiss and the Army what not to do but it had potential when it actually worked. 340mph at 20,000ft and 330mph at 25,000ft. Curtiss gets a contract for 13 YP-37s in Dec 1938 but these are too late for the 1938 pursuit trial (which took place in Jan 1939) and the YP-37 was more of concept in progress when it did show up, with a number of restrictions on maneuvers. 12 of them showed in Nov/Dec 1939. Potential showed with a claimed 346mph at 25,000ft but this may have been with the original power level which was later de rated.
The XP-42 showed up in March 1939 and had cooling troubles to start and showed little or no performance gains over the standard P-36A/c aircraft.
The Army was looking for a large increase in performance in future fighters, They were looking for performance at 25,000ft (XP-39 with turbo).
In the spring of 1939 the Army estimated that a turbo equipped aircraft was 2 years away from entering squadron service. BUT all of the experimental engines that the army was looking at or funding were expected to use turbos.

The Army June 1939 design competition for Fiscal year 1940 (and later) aircraft did not favor any radial engines, Favorites included

P&W X-1800 watercooled 24-cylinder H-block of 2,240 cu in (later 2600) with sleeve valves. Think Sabre stood on it's side. Planned at times for 6 different aircraft. P&W had a change in management and canceled in Oct 1940. Planned production was not until 1942. This shows the time scale for some these projects.
Pratt & Whitney XH-3130, Big brother, enlarged to 3730cu/in while still in the planning stage. 2900hp planed with 100/100 fuel. Complete 24 cylinder engine never built and canceled at the same time as the smaller engine.
Continental IV-1430, this was supposed to offer 1600hp at 25,000ft in most of it's many variations.
Lycoming O-1230 of the 1930s was now too small to be useful even if it ran right. Lycoming simple stacked two together and used a common propeller and supercharger for the
Lycoming XH-2470 which found a little bit of interest from the navy. This one actually flew.
Wright R-2160 Tornado we have been over this thing already but it was included in planned 1941 funding, at least for development.
What is absent from the Army proposals is any air cooled engines or at least any that scored well in the proposals.

Yes, a single is less that twin. The problem with the turbo regulator is not the weight but the fact that they either didn't exist or didn't work. Much like the early American aircraft didn't have boost regulators or boost limiters and the pilots were expected to manage the boost limit of the engine while in combat. Many Allison pilots over boosted by accident and still made it home. Engine's live may have been shortened. Radials are not going to as forgiving. Things got a lot better in late 1942 and early 43.

True, I was just trying to cover a span for possible engines.

Actually, you do need to repeat because there was a significant difference between the R-2600 and the R-2800. F6F aside there is not just a difference in the engines but there is a difference in the needed propellers, the size/weight of the exhaust systems, fuel system, etc. The smaller the initial airframe the harder it is to swap the engines and I keep saying, if you design for the R-2800 to begin with you have and oversized airframe for best performance with the R-2600.


Very true but Allisons failure to get the 9.60 gears to work is not a good justification for another low altitude engine. Especially one that uses more fuel for the same performance.

Just using it as a sort of yardstick. What kind of performance can we expect from a "standard" Radial engine fighter of 1939-41 technology. Not a P-51 with a radial engine.
Try Ki-44 if you want. 1320hp at 17,225ft for 376mph. Granted the Ki-44 did not use exhaust thrust very well but it was a small airframe with light armament, and 485 liters of internal fuel doesn't get you very far with large engines.
R-2600 is a rather thirsty engine. It is not bad when throttled way back, but it is capable of using around 3 gal a minute at high throttle settings.
If you want an R-2600 powered fighter to have even the same range as a P-40 you need more fuel.
In 1939 you don't know where you will wind up fighting and the P-39 did not get it's self sealing tanks until 1940/41. It's short range was problem in the Pacific and the drop tank was short of crutch. Ideally the Hypothetical R-2600 fighter doesn't fall in the same trap.

Kind of covered above. The factory certified 1600hp power limit was at 1000ft on a 59 degree standard day. Things were a bit better with the 1700hp version. Granted this low alitdue limit does mean that the pilots can't get into much trouble in low gear as the engine simply can't provide much more boost. High gear may be another story.

Covered above, Using the same prop for both 1600hp and 2000hp is not a good idea. Depending on state of the art in prop design you may need longer landing gear.

maybe but probably not. P&W built about 30 R-2180s total so there was little if any production tooling.
It took P&W about 2 years to go from initial design/planning to first test engine, design changed from a 2600 cubic engine to the 2800 when P&W learned about Wrights 2600 and P&W wanted to beat Wright. The R-2180 may have given them a head start in cylinder design, just use 18 instead of 14.


As shown by the list above, the best was often the enemy of good. None of the Army's favored engines of 1939/40 ever powered an aircraft in active service. And 3 not favored air cooled radials powered many WW II and post war combat aircraft.
If you want a fighter plane for 1940/41 to be going into production, it had to have been in development in 1938/39 with 1939 aerodynamics and construction and you have to get the Army to overcome their liquied cooled engine bias. Army wanted air cooled engines for ground attack (no shot out radiators) but they didn't like them for other things. For the B-17 and B-24s they didn't have a lot of choice. They didn't have any liquid cooled engines ready to go (be built) except for the Allison and with the Allison slated for most/all of the 1940/41/42 fighters there weren't any to spare for bombers.
We should note that the Army was wrong in May 1939, the Turbos were not 2 years away from service use in fighters, they were 3 years away. The early P-38s and P-43s had trouble as did some early P-47s and several experimental aircraft were lost due to turbo troubles.

After it was found turbos were 2 years away, was there any attempt to step up development of superchargers for Allisons or air-cooled engines?

 

[tomo pauk]

<snip>

I do appreciate the replies.
My stance is still the same: American fighters should've been designed around and for big radial engines as the 1st priority once these engines are in development. Americans have the industrial might, money, fuel, raw materials, suitable know-how, and security from the outside threat and to make that happen.
Everything else should be the plan B, or even plan C.

 

[Shortround6]

After it was found turbos were 2 years away, was there any attempt to step up development of superchargers for Allisons or air-cooled engines?

It doesn't seem so but there was a separation between Army and Navy.
The Army wanted turbos and had been playing with them for around 10 years or more in 1939.
The Navy had not used/tested any turbos and went for the mechanical two stage superchargers from P&W.
The Navy had no use for liquid cooled engines. Too many officers making discissions in the late 30s had flown behind Liberty engines in the 20s and had forced landings due to coolant leaks. With the navy flying over water that was an important consideration although things were getting better in the 1930s as were many other things.
Allison was asked to use the highest gear ratio on the supercharger that would work in 1938/39 and that turned out to be the 8.77/8.8 one that let the engine make 1040hp at 14,200ft.
Not as good as the Merlin but better than just about anything else in 1938/39.
P&W announced the two stage R-1830 in Feb 1938 but how well it worked is subject to question. Two stage engines in early 1939 seem to be rated at 1050hp at 17,500ft and the engines in the F4F Wildcats were rated at 1000hp at 19,000ft. It took a while for P&W to sort things out. A lot of rumbling in the ductwork at part throttle.

Turbos were attractive to the AAC as theory seem to say that they could set the engine up to run at sea level and then use the turbo to keep the air pressure at the intake of the carb the same as sea level all the way to 20-25,000ft. This assumes they could use an intercooler to keep the temperature under 100 degrees F at the entrance to the carb.
In 1938-40 using 92-100 octane gas this was a real problem with heat from the superchargers.
The two speed R-2600 engine as mentioned was rated at 1400hp at 11,500ft with 100 octane fuel. If the engine was running on 91 octane it could make 1400hp at 10,000ft. Trying to use more boost at higher than 10,000ft would push the engine into knocking and/or detonation. R-2600 used about 6lbs of boost max. But the higher the plane flies the more the supercharger heats the air to keep the 6lbs of boost and you are forced to reduce the boost to keep the chances of detonation down. If you had tried to either spin the existing supercharger faster or used a larger supercharger to get more boost to go higher you would have run into the detonation limit.

Each engine and supercharger has somewhat different detonation limits.

Everything was changing very fast in the late 30s and 1940/41.
The A-S Tiger that was mentioned in another thread and powered the early Whitley bombers was the first engine to use a two speed supercharger, once it got off the runway it never used more than 1 lb of boost (engine strength limit?).
Until you had good fuel how good your supercharger was didn't matter much or it was hard to figure out if the supercharger was any good. Once the engine and fuel would work with 5-6lbs of boost it was easier to tell how good the supercharger was (efficiency).

100/130 fuel allowed for not only more boost at low altitude it allowed for more boost at higher altitudes where the supercharger heated the air more. Poor wording, if you just increase the gear ratio of the supercharger for more power at high altitude the supercharger will heat the air more at all altitudes. P&W uses intercoolers even on the R-1830 engine.
RR with Hooker managed to build better superchargers that gave good pressure at higher altitudes and didn't need intercoolers. RR also used a lower compression in the cylinders and could use a little more boost before they hit detonation. But this hurt fuel economy.

 

[tomo pauk]

Allison was asked to use the highest gear ratio on the supercharger that would work in 1938/39 and that turned out to be the 8.77/8.8 one that let the engine make 1040hp at 14,200ft.
Not as good as the Merlin but better than just about anything else in 1938/39.

The V-1710-33 was not in service use in 1939, let alone in 1938.
Even taking for granted the book performance figures that it was supposed to offer in 1940 - when it became available - comparing it with the engines of 1938-39 looks very off. It is like saying that BMW 801D of early 1943 was better than the Allied engines of mid 1941 - yes, we know it was better, but it is a wrong comparison to make in the 1st place.
By Summer-Autumn of 1940 - when the -33 was available - Merlin gotten it's 3rd/4th supercharger upgrade (the -33 was even under the original Merlin from two years before), and the Germans were introducing the DB 601N (it was not a perfectly reliable engine, but neither it was the -33), the 601A is with the improved S/C, and it was allowed for the increase of RPM above the rated altitude.

 

[Shortround6]

I do appreciate the replies.
My stance is still the same: American fighters should've been designed around and for big radial engines as the 1st priority once these engines are in development. Americans have the industrial might, money, fuel, raw materials, suitable know-how, and security from the outside threat and to make that happen.
Everything else should be the plan B, or even plan C.

You may be right.
The Americans were trying to skip the intermediate/safe step and jump to the advanced step. They may have thought they had time. They weren't alone.
British had all sorts of plans for aircraft powered by the Sabre and Vulture engines and even the early Centaurus in 1938/39. They had as many or more plans than for using the Hercules. Obviously many of these plans came to nothing with war starting and planes made now were better than planes that would not show up for 3-4 years.
The 100/130 fuel also meant that they could get more power of existing engines and the pressure to build new engines to make big power with 87-100 octane fuel was much reduced.

1940 showed the Americans that while they had more time than Britian had (let alone France) some of the "advanced" engines would not show up in time. P&W figured they could make a good 200hp radial in a lot less time than trying to build an H 24 sleeve valve 2300hp engine.
P&W also started work on the 2100hp C series R-2800 in May of 1940 and started work on the 28 cylinder R-4360 the month after they stopped the sleeve valve engines. Still a gamble but one they were more familiar with.

But the R-2800 itself was unknown quantity in late 19398 or early 1939 when design work would have to start.
XP-39 first flew in April of 1938, granted they redesigned it a bit to take out the turbo-charger but they only built 13 of them in 1940, 10 of them in Dec.
They ordered 13 YP-43s in May of 1939, first one was delivered in Sept 1940 and the last in April 1941 although that might have been quicker without trying to make the EP-106s for Sweden.
I don't think we want to involve Brewster in this project
Grumman managed to build 103 F4Fs in 1940 but the F4F project dates back into late 1937.

the R-2600 was first used in the Boeing Clippers starting in the May/June of 1938 and these were single speed engines rated at 1500hp for take-off (2300rpm) and 1200hp max continuous (2100rpm) at 5400ft in the first 6 planes. Which took until late 1939 to build. The second group of six was started in 1940 with the first completed in early 1941 with uprated engines. By Aug of 1940 the Clippers had completed 200 trans-Atlantic crossings in addition to Pacific flights. Demands for spare engines was?

 

[Shortround6]

The V-1710-33 was not in service use in 1939, let alone in 1938.
Even taking for granted the book performance figures that it was supposed to offer in 1940 - when it became available - comparing it with the engines of 1938-39 looks very off. It is like saying that BMW 801D of early 1943 was better than the Allied engines of mid 1941 - yes, we know it was better, but it is a wrong comparison to make in the 1st place.
By Summer-Autumn of 1940 - when the -33 was available - Merlin gotten it's 3rd/4th supercharger upgrade (the -33 was even under the original Merlin from two years before), and the Germans were introducing the DB 601N (it was not a perfectly reliable engine, but neither it was the -33), the 601A is with the improved S/C, and it was allowed for the increase of RPM above the rated altitude.

You may be right but Allison was working on the 8.77 gears in late 1937. They thought they could get 1150hp at 9000ft. With a change in carburetor and a different inlet elbow they could get the rated power at 10,500ft to 11,000ft. It was that started the Curtiss proposal of sticking such an engine into a P-36 airframe in March of 1938.
Things were evolving, Curtiss thought that the engine could make 1050hp at 2950rpm at 15,000ft with ram air. The OK was given to proceed in July 1938 with first flight in Oct 1938. using the XV-1710-19 (C13) engine which was giving 1090hp at 10,000ft (no ram?) at the time.
Except that the engine used in the Jan 1939 pursuit competition was not the same engine as was installed 3/4 months before. The carb inlet scoop was changed, the exhausts were changed to give both lower back pressure to the engine and add some measure or exhaust thrust. This was followed by Ron Hazen and some of the staff at Allision coming up with modified impeller and supercharger and arriving (so the story goes) the morning of the competition with just enough time to install the new parts before the the XP-40 had to fly in the competition.
There may be some confusion as to whether the first 134 P-40s were ordered with the -19 engines and the rest with -33 engine or if the -19 engines ever showed up in quantity by the time it came to make deliveries The -19 was supposed to make 1090hp for take off and 960hp at 2600rpm "normal".
The -33 engine was able to make 1040hp at 14200 or 14300ft, part of the "problems" with the -33 was when the AAC wanted 1090hp anywhere from sea level to 13,200ft. An extra 50hp may not sound like much but it may have been enough to push things over the edge coupled with the already mentions flawed test stand.
Lets also remember that the Allison was tested at 150 hours, not 100 hours. The Merlin XX when tested to US standards passed the 100 hour mark but failed before reaching 150 hours but was "passed" because the failures were minor and time was important.

And we are discussing what was ordered in 1939. Complaining that the engines ordered in 1939 were not as good as engines beginning delivered in the fall of 1940 by Britian and German is kind of mixed message.
Both RR and DB were building hundreds of engines a month in 1939. Allison was building a couple of engines a month in 1939. They were still building the factory.

Going to the R-2600 may not have given you what you are looking for. The R-2600 is kind of heavy for the amount of Power it gives at altitude.

 

[tomo pauk]

And we are discussing what was ordered in 1939.

No. I've never said when the better Merlins or DBs were ordered.
I don't find it neither amusing nor informative that you are trying to compare the V-1710-33 (with the most favorable power ratings possible) of mid/late 1940 with the engines that were older than it by a year or two, just so the -33 can look better than it actually was.

Complaining that the engines ordered in 1939 were not as good as engines beginning delivered in the fall of 1940 by Britian and German is kind of mixed message.

It was what was delivered that mattered. Both RR and DB delivered the engines better than the -33 in the time the -33 was in service.

Both RR and DB were building hundreds of engines a month in 1939. Allison was building a couple of engines a month in 1939. They were still building the factory.

That was neither DBs nor RRs fault.

 

[Shortround6]

No. I've never said when the better Merlins or DBs were ordered.
I don't find it neither amusing nor informative that you are trying to compare the V-1710-33 (with the most favorable power ratings possible) of mid/late 1940 with the engines that were older than it by a year or two, just so the -33 can look better than it actually was.



It was what was delivered that mattered. Both RR and DB delivered the engines better than the -33 in the time the -33 was in service.



That was neither DBs nor RRs fault.

I am sorry you feel that way. It was not my intention to deceive.

The V-1710-33 was outdated in 1941. It was less outdated in 1940 or perhaps it goes by month. It was not the equal of the Merlin III let alone the Merlin XII. Merlin XX was totally different.
The real problem for the P-40 was the weight. Once they stuck in armor and self-sealing tanks the P-40B was about 50lbs lighter than Hurricane IIB with 12 guns. Or about 600lbs heavier than Hurricane I with all the stuff added during the BoB.
I am cheating a bit, I am using the Weight for the P-40B with 120 US gallons of fuel instead of full internal fuel.
A P-40B was about 1600lbs heavier than 109E-3.
A V-1710-33 was not very far off from a DB 601A in the fall of 1940. 1020ps at 4500 meters is not that far off from the Allison.
The DB 601N was a lot better than the Allison. One report says that 36 (?) 109Es had the 601E in July 1940. Same source says another report on January 22nd 1941 lists 112 109Es and 5 109Fs with DB 601s in service. How many were out of service (repairs?) or lost by that date?
Things did not better for the P-40, with no increase in power (Allisons fault) the P-40C gained about 150lbs over the P-40B. 7500lbs was way too much for a 1090hp engine regardless of critical height.
The Power plant weight was supposed to be 2589lbs for the P-40C with only 1352-1357lbs being the engine itself.

Unless the US can figure out how to make lighter fighters they need to build really big engines. Now the problem is getting engines that make big power at 20,000ft, not big power at 1-3,000ft.
Next problem is fitting in enough fuel for the really big engines.

 

[z42]

Perhaps Americans should have done what has often been suggested in the various what-if threads about the European powers, that is, instead of tripping over themselves with various exotic concepts (Hyper program etc), make a big (~40L?) V-12?