R-2800 for fighters: how would've you done it?

[Shortround6]

It took the USAAC almost half of war to throw the P-47 in combat, or a year after P-38 made it's mark on WW2. So I doubt that P-47 was such a necessity for USAAC.

Not all programs advanced at the same speed and it had nothing to do with the desires of the customer. Design work on the P-47 started several years later than the P-38. Design work on the Hawker Typhoon started in 1937 for example. Some of it has to do with the number of engineers and draftsmen a company has, how much new ground they are breaking in design work, unforeseen problems in development (Vultee Vanguard had tail surfaces enlarged twice as a result of flight testing) and other things. Please remember that in 1940 when the P-47 was ordered the actual serviceability of turbo aircraft was rather low. You had a number of companies working on the project. Republic for the airframe but the engine was Pratt&Whitney and was supplied to Republic as "government furnished equipment". The government contracted with P&W and paid them for the engines and then supplied them to the airframe manufacturers. GE was responsible for the Turbo. Again the Goverment contracted with GE and GE meet the government specs and shipped the completed turbos to who ever the government told them to. If Republic or P&W had a problem with the turbos design (or even quality control) they had to go through the government to get it changed or fixed.

I like the light F4U part
My idea would be a hull of F4U, with slightly smaller thiner wing (tailored for high speed, not for good CV performance), ca. 250 sqft, 250 gal of fuel.

You are not going to get much lighter than a F8F even if it is a later plane.

What is the war load or better yet what is the "useful load" you are intending for this fighter. The Navy said the useful of F4U-1 was in "fighter" condition was 2390lbs. 200lbs pilot, 1068lbs of gasoline (178gallons), 178lbs of oil, 767 lbs of armament ( guns, 1200 rounds of ammo and gun sight) and 177lbs of "equipment" (radio, navigation, Misc.). In "over load" condition it went to 3904lbs. Same pilot and equipment but fuel went to 363 gallons (2178lbs) oil went to 238lbs and armament went to 1111lbs (2350rounds of ammo. Please note that the aircraft is still "Clean", no external fuel or armament. Chopping even 150 gallons of fuel means you need a plane that can deal with a 1 1/2 ton useful load.

And R-2800s are thirsty, no matter what airframe you put them in or what supercharger you use. Not so bad at cruise speeds (aside from the drag) but at Military power a lot of excess fuel goes into the engine to act as an internal coolant (all high powered air-cooled engines do this). And, if you are going to use 2000hp, it takes more fuel than a 1500hp engine even if things were equal.

IIRC Vanguard already have had 200 (220?) gals of fuel.

That may be debatable. I know some sources actually say 240 gallons. But that doesn't add up. Empty weight of 5,235lb and a loaded weight of 7,100lbs and a max of 7384lbs. max load of 2149lbs. 240 gals of fuel is 1440lbs leaving 709lbs for pilot, oil and ammo if the empty weight is empty equipped. If it is not empty equipped than the weight of the guns and maybe the radios have to come out of the 709lbs (or less fuel?).
Vanguard may have been pushing the limits as it was. It was supposed to have some parts in common with the BT-13

Vultee BT-13 Valiant - Wikipedia, the free encyclopedia

In such a scenario, P-51 would not be needed (of course, NAA could've produced 'our' new fighter).

The radial engine fighter was never going to get down the drag level of the P-51 and so would never have it's range without carrying much more fuel.

 

[gjs238]

Originally Posted by tomo pauk
I like the light F4U part
My idea would be a hull of F4U, with slightly smaller thiner wing (tailored for high speed, not for good CV performance), ca. 250 sqft, 250 gal of fuel.

You are not going to get much lighter than a F8F even if it is a later plane.

I've long been interested in speculating about a USAAC non-turbocharged R-2800 powered fighter.
The timeframe would be much earlier than the F8F.
- It could be a non-turbo, smaller, simplified, scaled down version of the P-47.
- It could be a non-naval F4U or F6F. And by non-naval I don't mean removing the tailhook and installing non-folding wings. I mean a truly non-naval USAAC aircraft built to lighter specs.
- Or it could be an entirely separate, independent aircraft.

 

[Shortround6]

I've long been interested in speculating about a USAAC non-turbocharged R-2800 powered fighter.
The timeframe would be much earlier than the F8F.
- It could be a non-turbo, smaller, simplified, scaled down version of the P-47.
- It could be a non-naval F4U or F6F. And by non-naval I don't mean removing the tailhook and installing non-folding wings. I mean a truly non-naval USAAC aircraft built to lighter specs.
- Or it could be an entirely separate, independent aircraft.

The 3 main questions are;

How simplified? The Navy two stage instead of the turbo or the single stage two speed engine?

What is the weapons load? Armament of a F4F-3 or P-51B or more?

What range/endurance are you thinking of? At a low speed cruise the R-2800 in a B-26 could use 75 gallons at 15,000ft an hour but at a high speed cruise (below max continuous) it could almost double. Military power could be over 4 gallons a minute.

 

[tomo pauk]

Not all programs advanced at the same speed and it had nothing to do with the desires of the customer. Design work on the P-47 started several years later than the P-38. Design work on the Hawker Typhoon started in 1937 for example. Some of it has to do with the number of engineers and draftsmen a company has, how much new ground they are breaking in design work, unforeseen problems in development (Vultee Vanguard had tail surfaces enlarged twice as a result of flight testing) and other things. Please remember that in 1940 when the P-47 was ordered the actual serviceability of turbo aircraft was rather low. You had a number of companies working on the project. Republic for the airframe but the engine was Pratt&Whitney and was supplied to Republic as "government furnished equipment". The government contracted with P&W and paid them for the engines and then supplied them to the airframe manufacturers. GE was responsible for the Turbo. Again the Goverment contracted with GE and GE meet the government specs and shipped the completed turbos to who ever the government told them to. If Republic or P&W had a problem with the turbos design (or even quality control) they had to go through the government to get it changed or fixed.

Did not wanted to be to harsh @ USAAC; the intention was to point out that it took a lot of effort to put a state of art plane into combat.
The non-turboed, R-2800 engined fighter would've been easier to throw into combat.

You are not going to get much lighter than a F8F even if it is a later plane.

Of course - 'my' fighter would have more fuel, guns ammo on board, along with heavier engine than F8F, yet the deletion of CV stuff, along with lighter wing would mean it's lighter than F4U; perhaps 8000lbs empty weight

What is the war load or better yet what is the "useful load" you are intending for this fighter. The Navy said the useful of F4U-1 was in "fighter" condition was 2390lbs. 200lbs pilot, 1068lbs of gasoline (178gallons), 178lbs of oil, 767 lbs of armament ( guns, 1200 rounds of ammo and gun sight) and 177lbs of "equipment" (radio, navigation, Misc.). In "over load" condition it went to 3904lbs. Same pilot and equipment but fuel went to 363 gallons (2178lbs) oil went to 238lbs and armament went to 1111lbs (2350rounds of ammo. Please note that the aircraft is still "Clean", no external fuel or armament. Chopping even 150 gallons of fuel means you need a plane that can deal with a 1 1/2 ton useful load.

8000 empty, 200 lbs pilot, 1500 lbs of fuel (250 gals), 200 lbs of oil, 1110 of armament, 180 eqpt = 11190 lbs, or in between of F8F's 'loaded' max TO weights.

And R-2800s are thirsty, no matter what airframe you put them in or what supercharger you use. Not so bad at cruise speeds (aside from the drag) but at Military power a lot of excess fuel goes into the engine to act as an internal coolant (all high powered air-cooled engines do this). And, if you are going to use 2000hp, it takes more fuel than a 1500hp engine even if things were equal.

Agreed that Merlin gives one more range.
OTOH, a 'simple' fighter plane with great engine power, generous punch fuel quantity, tailored capable for 400-420 mph between 15-20K - that was not something USAAC have had in 1942.

That may be debatable. I know some sources actually say 240 gallons. But that doesn't add up. Empty weight of 5,235lb and a loaded weight of 7,100lbs and a max of 7384lbs. max load of 2149lbs. 240 gals of fuel is 1440lbs leaving 709lbs for pilot, oil and ammo if the empty weight is empty equipped. If it is not empty equipped than the weight of the guns and maybe the radios have to come out of the 709lbs (or less fuel?).
Vanguard may have been pushing the limits as it was. It was supposed to have some parts in common with the BT-13

Vultee BT-13 Valiant - Wikipedia, the free encyclopedia

Pushing, indeed
A license production of a good fighter would've been a better usage of Vultee assets.

The radial engine fighter was never going to get down the drag level of the P-51 and so would never have it's range without carrying much more fuel.

Already agreed - perhaps having a redesigned wing to accommodate 70-80 gals of fuel by 1944 (or to include it to the original specs? - a TOW increase by 500-600 lbs)? A water injection for the 2800 is available by '44, too - 1700 HP @ 20K, 1500 HP @ 25K.

 

[Rivet]

I believe my R-2800 would have sleeve valves allowing a greater brake mean effective pressure. This would probably have required the lawyers to license through Bristol Aviation. I'd have gone with a single-stage intake compressor and would have worked on a system of load requirement sensors for same.
Engine bearings double row front to rear with lubrication admittance to the engine at that point with a secondary admittance juncture at the heads. Pressure loss and direction of loss sensor in order to reduce effects of damage, this to maintain oil flow to a damaged engine until one is out of Dodge. A well regulated oil cooling system.

A system of investment casting for all engine parts, this including valve blanks.

This engine would have been in advanced prototype development at the time of your first call. Regards

 

[wuzak]

In the lat e1930s (1938 IIRC) George Mead of P&W went to England and had a look at the engines being developed. He was impressed by the Sabre, and when he got back to the US set out to design one. That would be the X-1800/XH-2600, the H-3130 and the H-3730.

What would have happened had Mead come back with the idea of licence production of the Sabre? Could it have made the Sabre reliable sooner?

I doubt a sleeve valve R-2800 would have appeared in time to do much for the war effort.

 

[Shortround6]

Of course - 'my' fighter would have more fuel, guns ammo on board, along with heavier engine than F8F, yet the deletion of CV stuff, along with lighter wing would mean it's lighter than F4U; perhaps 8000lbs empty weight

8000 empty, 200 lbs pilot, 1500 lbs of fuel (250 gals), 200 lbs of oil, 1110 of armament, 180 eqpt = 11190 lbs, or in between of F8F's 'loaded' max TO weights.

Well, you are saving about 900-1000lbs empty over a F4U or an F6F but you are 930lbs heavier than an F8F-1. Loaded clean you are 1804lbs heavier, 19%.

Now the question is which engine are you using? The two stage or or the single stage engine? The two stage engine has about 300hp more at 16,000ft than the single stage engine available in 1942-43 and about 400hp more at 22,500ft. Compared to the turbo at 25,000ft the single stage engine has 850 less horsepower.

Agreed that Merlin gives one more range.
OTOH, a 'simple' fighter plane with great engine power, generous punch fuel quantity, tailored capable for 400-420 mph between 15-20K - that was not something USAAC have had in 1942.

Again the question is using which engine. The -22W engine used in the F8F-1 was good for 1600hp at 16,000ft Military power (and 2100hp at take-off) compared to the 1600hp at 13,500ft of the "B" series engine ( and 2000hp take-off). That means it was good for about another 100hp from about 16,000ft up into the 20,000ft range, and that is without the water injection. The Water injection may have been good for around 250hp at sea level (guessing from a different model engine) and another 125-150hp at 16,000ft. In other words the F8F-1 that was good for 421mph at 19,700ft may have had an engine that was good for 1725-1750hp at 16,000ft, not the 1500hp or so that the earlier single stage engine would give. The 382mph at sea level, if done with water injection, was done with 350 more hp than the early single stage engine.

Already agreed - perhaps having a redesigned wing to accommodate 70-80 gals of fuel by 1944 (or to include it to the original specs? - a TOW increase by 500-600 lbs)? A water injection for the 2800 is available by '44, too - 1700 HP @ 20K, 1500 HP @ 25K.

It is just not the weight of the fuel but of the tankage and piping. F6F fuel system weighed 458lbs for 250 gallons, 3 fuselage tanks. Wing tanks weigh more in proportion to gallonage due to increased surface area of tanks to be covered in/made of selfsealing material.

Maybe you are planning on using the the two stage engine?

 

[Rivet]

Hmmm....That Bell fellow ran into a lot of problems attempting to utilize two-stage compressors in his p-39. Inter-stage drag effects/pressure buffering. Getting a single-stage unit run off the crankshaft to utilize its full potential would have been my goal until the long-term solution of multi-stage problems were reduced to a usable minimum. Regards

 

[Shortround6]

Hmmm....That Bell fellow ran into a lot of problems attempting to utilize two-stage compressors in his p-39. Inter-stage drag effects/pressure buffering. Getting a single-stage unit run off the crankshaft to utilize its full potential would have been my goal until the long-term solution of multi-stage problems were reduced to a usable minimum. Regards

Well, getting a single-stage unit up to it's full potential was actually quite a trick. By the end of the war they could do some rather amazing things with a single stage supercharger/compressor but it took a few years of work to get there.

Then there is the fact that for any given level of "technology" or knowledge there is a limit to how much of a pressure ratio you can get out of a single stage. The Merlin 61 needed to compress the surrounding air at 23,500ft 5.1 times in order to get the 12lbs of boost needed for rated power. This was far beyond the capability of any single stage compressor in 1941-2 and in fact was beyond the capability of any single stage compressor in use in 1945, lab test rig possibly excluded.
The two stage supercharger used in the F4U and F6F was operating within 1lb of boost of the Merlin 61 supercharger.

You also have the FACT that for a given level of compression, even 3 to 1, it takes less power and heats the intake charge air less if it is done in two stages and not one. It also rather hard to after cool a supercharger on a radial engine. It has been done but requires multiple after coolers, a nightmare of ducting or liquid coolant lines (or both)

 

[tomo pauk]

Well, you are saving about 900-1000lbs empty over a F4U or an F6F but you are 930lbs heavier than an F8F-1. Loaded clean you are 1804lbs heavier, 19%.

Now the question is which engine are you using? The two stage or or the single stage engine? The two stage engine has about 300hp more at 16,000ft than the single stage engine available in 1942-43 and about 400hp more at 22,500ft. Compared to the turbo at 25,000ft the single stage engine has 850 less horsepower.

...

It is just not the weight of the fuel but of the tankage and piping. F6F fuel system weighed 458lbs for 250 gallons, 3 fuselage tanks. Wing tanks weigh more in proportion to gallonage due to increased surface area of tanks to be covered in/made of selfsealing material.

Maybe you are planning on using the the two stage engine?

Sorry for not being clear - a two-stage engine is my favorite here.

The 120 gal fuel system of the P-39 weighted some 300 lbs, and in P-51B/C 320 lbs for 270 gals (wing + hull tanks) so for 70-80 gals in wings it's 150-200 lbs to add, plus fuel weight (420-480 lbs), the addition totaling 570-680 lbs.

 

[Shortround6]

I do not know if you have seen this but it has the weight breakdown for the F4U-1.

http://www.wwiiaircraftperformance.org/f4u/f4u-1-detail-specification.pdf

It may prove interesting. The wing of the F4U was rather heavy but apparently weight doesn't have a lot to do with speed. I don't know if the performance is test flight results or calculations but an extra 1500lbs was only worth 5mph at altitude but slowed climb to 20,000ft by almost 2 minutes.

 

[tomo pauk]

Was wondering where was that doc

The only way for the Fw-190 to evade both Hellcat Corsair (while on same altitude) was to climb away - not possible vs. a lightweigh 'F4U'?
I've proposed also the change of wing shape (making a wing slightly thinner) reduction of area, as an effort to reduce drag/increase speed.

 

[Shortround6]

The change in wing profile may help but one general rule of thumb was that 25% reduction in wing area increase top speed by about 3%. What it does to the stall speed is a lot different.

 

[davparlr]

I do not know if you have seen this but it has the weight breakdown for the F4U-1.

http://www.wwiiaircraftperformance.org/f4u/f4u-1-detail-specification.pdf

It may prove interesting. The wing of the F4U was rather heavy but apparently weight doesn't have a lot to do with speed. I don't know if the performance is test flight results or calculations but an extra 1500lbs was only worth 5mph at altitude but slowed climb to 20,000ft by almost 2 minutes.

Some comparisons of wing weights, mostly using America's Hundred Thousand. (aircraft type/wing area (sqft)/wing weight(lbs))

F4U 314 2121
F6F 334 2024
P-39 213 934
P-40 236 1003
P-47 300 1459
P-51 233 1066

It appears to me that maybe 1000 lbs could be saved just from a smaller, solely designed for land basing, wing.

I think a empty weight of 7000-7500 lbs would provide a very decent airframe, either a lightened up F4U or a toughened up P-66, with excellent performance even with the 1850 hp -4/5 engine (250 hp more than the Fw-190A-3) at all the necessary altitudes, although I know nothing about the engine altitude ratings. Certainly this is true for the '41 time frame.

 

[Shortround6]

The wing weight depends not only on it's size but the load it is supposed to support. I don't think you are going to get an R-2800 into the air with anything much smaller than a Mustang. The P-40 wing went from the 1003lbs you quote (on a P-40 no letter) to 1120-1130lbs on the E and up models. How much is due to the gun installation and how much is due to beefing up to handle the increase in gross weight from 7173lbs to 8300-8600lbs on the later models I don't know.

Some of the sea level HP advantage goes away if you use the 1850hp "A" series engine. Yes you have 250 more HP at sea level but at 16,000ft the difference is about 75hp. Military rating of the R-2800-5 was 1500hp at 14,000ft. One source says the early BMW 801 was good for 1380hp at 15,100ft. Without the BMW's fan cooling the R-2800 is going to have more drag. The F 190 A-3 used the "D" series engine with better performance. In fact above 18,000ft or so it may have had 5-15hp more hp than the 2000hp "B" series R-2800 with single stage supercharger. below that height the R-2800 has more power, in some cases (like sea level) 300 more HP.

This is the same problem that was brought up in the wright R-2600 threads. the R-2800 is a bit smaller but the radial installations were not as good as they were later in 1940-42. A Packard V-1650-1 was good for 1120hp at 18,500ft which doesn't sound like much compared to the radials but at 20,000ft it might be just 200hp behind the 1850hp R-2800. 1075hp (?) to 1275hp (?). Considering that a P-36 had 22% more drag than an early P-40 the power difference translates into not much of a speed difference.

And you have the fuel problem, flying the same speed as a V-12 powered fighter you are going to burn more fuel just because of drag. So you need more fuel to do the same mission. Once you start really stepping out and trying to use the power of the R-2800 instead of cruising it can get very thirsty indeed. The Fw 190 was not noted for long range and the BMW engine had higher compression and got a bit better fuel consumption for a given amount of power than the R-2800.

While a R-2800 might do very well at a low speed cruise military power (or take-off) can see them sucking down over 4 1/2 gallons a minute. At max cruise in lean mixture it was using close to 1 1/2 gallons a minute.

 

[davparlr]

The wing weight depends not only on it's size but the load it is supposed to support. I don't think you are going to get an R-2800 into the air with anything much smaller than a Mustang.

The Fw-190 had a wing area of 197 sqft and a similar size engine, maybe 150 lbs lighter. I don't see a problem here with wing area of 200-220 sqft.

Some of the sea level HP advantage goes away if you use the 1850hp "A" series engine. Yes you have 250 more HP at sea level but at 16,000ft the difference is about 75hp. Military rating of the R-2800-5 was 1500hp at 14,000ft. One source says the early BMW 801 was good for 1380hp at 15,100ft.

I don't have good engine data so I have to do the best I can with what I have. My reference, "American Combat Planes" by Ray Wagner, shows the XF4U-1, powered by the XR-2800-4 as generating 1850 hp at SL, and 1460 hp at 21,500 ft., and capable of 405 mph at an unknown altitude. First flight was May, 1940. Another reference by Wagner, "German Combat Planes", shows the Fw-190A-1 with the BMW 801C-1 engine producing 1600 hp at SL, and, with your data 1380 hp at 15,100 ft., is capable of max 388 mph at 18,000 ft. First Deliveries of the Fw-190A-1, was August, 1941. I have no performance data on the Fw-190A-2 with its new C-2 engine, but I suspect it was not much different. Unfortunately, I have no apples to apples comparison. However, it appears to me that a smaller, lighter, and smaller winged F4U type aircraft with an early R-2800, would be quite competitive with the Fw-190 with the C engine.

Without the BMW's fan cooling the R-2800 is going to have more drag.

It doesn't really seem to be noticeable.

The F 190 A-3 used the "D" series engine with better performance. In fact above 18,000ft or so it may have had 5-15hp more hp than the 2000hp "B" series R-2800 with single stage supercharger. below that height the R-2800 has more power, in some cases (like sea level) 300 more HP.

The D-2 engine in the Fw-190A-3 did not come available until 1942, when the R-2800-8 was becoming available. The D-2 generated 1738 hp at SL. Top speed was 420 mph at 21,000 ft. The R-2800-8 will produce 2000 hp at SL and 1800 hp to 17,500 ft, and 1650 hp to 1650 hp to 23,000 ft. Top speed of the F4U-1 was 417 mph at 20,000 ft. The performance of the Fw-190A-3 and the F4U-1 were pretty even. Now, take out 1000 lbs +, and reduce wing area to 30% from the F4U, and I think you would have to admit that the new plane would also be, at the least, competitive with the Fw-190. And since the Fw-190 has always been considered a state-of-the-art fighter in 1941-2, you would also have to admit the proposed aircraft would also be state-of-the-art.

So, if this plane could be fielded in 1941, the Brits would already have an answer for the Fw-190 when it appeared.

This is the same problem that was brought up in the wright R-2600 threads. the R-2800 is a bit smaller but the radial installations were not as good as they were later in 1940-42. A Packard V-1650-1 was good for 1120hp at 18,500ft which doesn't sound like much compared to the radials but at 20,000ft it might be just 200hp behind the 1850hp R-2800. 1075hp (?) to 1275hp (?). Considering that a P-36 had 22% more drag than an early P-40 the power difference translates into not much of a speed difference.

I think the Brits were having a problem with the radial Fw with their inline Spit V. Don't get me wrong, the Mustang was an amazing aerodynamically efficient aircraft with a very capable engine that drove the Fw to an inline engine. But, it wasn't there in 1941, nor was the Spit IX.

And you have the fuel problem,

This plane was not designed for long range escort missions, but rather to face the Luftwaffe (ala Spitfire) over France on even or better terms in 1941. And with 40-80 more gallons of gas than the Fw, would have reasonably good endurance.

 

[Shortround6]

you have a couple of problems with the comparison. The F4U prototype, if it actually carried guns, had one .30 and and one .50 in cowl and a single .50 in each wing. It was also a whole lot lighter than service planes. In fact it comes just about the numbers you want. 7505 lbs empty, 9375lbs normal gross and 10,500 max take-off. It's fuselage was also about 3 ft shorter than the F4U-1. This is part of the difference between a plane with the single stage engine and one with the two stage and inter coolers. (Granted they also moved most of the fuel from wing tanks into the fuselage). The Prototype had no armor or self sealing tanks. The Prototype, being a prototype, was fitted with a least two different R-2800s, there seems to be a fair amount of confusion as to the exact configuration at times.
The Americans also had an armament problem, I have no intention of getting into the .50cal Browning vs whatever here but the .50 cal and it's ammo were heavy. The guns and ammo for a P-40 (235rpg?) went 900lbs. The FW 190 guns went about 330lbs instead of 470 or so for six .50s and its ammo came up to about 430-330lbs or about the same as 1400 rounds of .50 cal ammo. Yjat is for 2000rounds of 7.9mm, 400 rounds of ammo for the Mg 151/20s and 120 rounds (+drums) for the MG/FFMs.

Neither the Spitfire or the Mustang were ever fitted with the 2 speed Merlin. It may make an interesting "what if". It does show that without a two stage supercharger the R-2800 fighter wasn't going to perform much better than what was already available.

While a long range escort fighter may not have been needed at the time the Spitfires barely had the range for what they were trying to do with them. It is one thing to cross the channel, it is another to make it past Paris, and yet even more just to make to the Rhine. Forget Berlin.

You also have the development problem, 6 two stage engines built in 1941, none in Dec 41 and Jan of 1942, and the 100th engine isn't delivered until some time in June. The "B" series single stage engine has 2 delivered in 1941 By P&W and and 2 by Ford, both are in the process of switching from "A" series to "B" series production, P&W delivers over 900 single stage "B"s in the first 3 months of 1942 and Ford delivers about 700 "A"s and 250 "B"s in those Months.

 

[Siegfried]

AN "A" series R-2800 went about 2270lbs with the single stage two speed supercharger. A "B" series engine with the same supercharger went about 2300lbs. A "B" series engine with two stage supercharger went about 2480lbs and a "B" series with single stage single speed supercharger (for use with turbo) went about 2265lbs. I have no data on weights of turbochargers or the weights of inter coolers for the turbo and two stage engines.

It's worth considering what might have been possible had the P-47 been equipped with the two stage mechanically driven supercharger rather than a turbo.
Altitude performance would likely barely have suffered while a large amount of space for fuel carriage would be liberated.

The BMW 801TJ is worth have a look at for the interesting way they packed the inter-coolers.

 

[Shortround6]

It's worth considering what might have been possible had the P-47 been equipped with the two stage mechanically driven supercharger rather than a turbo.
Altitude performance would likely barely have suffered while a large amount of space for fuel carriage would be liberated.

Well, if you consider having 350 less hp at 22,500ft and 500 less hp at 26,000 ft to be barely suffering. 75% of the power at 26,000ft. and that is for P-47B that never saw combat. The "C"s could hold 2000hp to 27,000t. If I am reading the graph right the 2 stage mechanically driven supercharger was giving 1400hp at 27,000ft. 42% more power does tend to cover a few sins in the weight and drag departments.

 

[Siegfried]

I think I agree with all the Shortround6 has said. The P-47 was a tour-de-force of high altitude performance. Its flat rated power up to 33k was unmatched from any WW2 fighter I know, except maybe the P-38. It would have been unwise to modify this program.

***
By the way, the stats look very close to the Fw-190, not all by accident. Think of the Fw-190 with the more powerful R2800 engine.

One thing that needs to be considered is that engines with two stage mechanical superchargers generated considerable Jet thrust at altitude
The Merlin about 300lbs and the bigger Jumo 213E about 440 lbs (200kg or kilopond, the correct unit for thrust or roughly 2000 Newtons).
At about 440mph (200 m/s) this is equal to 2000N x 200m/s = 400kW or 550hp. (Power = Force x Velocity).

The turbo-supercharger still comes out on top if service ceilings are looked at, and of course also generates some jet thrust, but the gap is quite a lot narrower than might
generally be supposed particularly for fast aircraft as opposed to bombers where jet thrust is more usefull than good cruise consumption.

In modern gas turbines the power is usually rated in ehp (equivalent shaft horse power) as opposed to shaft horse-power to take this factor into consideration.

The Germans were planning on a two stage mechanical supercharger for the BMW 801 (the 801F from memory) but machine tool shortages delayed
its production. The undoubted abillity of this engine to produce power and thurst in the thin low drag air of high altitude would in my estimation
(the 801F was to produce 2600hp) would have pushed the FW 190A10 (for which I believe it was to be installed) towards 460mph territory especially
since this engine was beginning to use MW-50 at the end of 1944.