A Wilder Wildcat

[tomo pauk]

The British engine designers suffered from the need to focus on quick improvements to existing designs and thus the next generation was paused and then restarted in fits and starts. With an extra 2 years of peace the British would have had jet aircraft and even the Royal Navy would have had proper fighters.

The 1st sentence is probably only true for RR. Other engine companies made a lot of own goals well before we can blame the wartime urgency.

Napier, after it's domination in the 1920s, entered the 1930s without a competitive engine and stayed there for the whole decade. They were also sold a pup with the sleeve valve story.
They Bristol company was of opinion that having multiple separate designs to cover 850-1050 HP bracket was a good idea, that was not the case. After dominating the radial engine market in 1920s, under leadership of Fedden, they spent most of the 1930s in order to have sleeve valve engines to work (again, as preferred by Fedden), meaning that there was no high power radial in mass use by the time ww2 started.
A-S went nowhere with their big radials, that were well behind the curve a few years before ww2 started.
De Havilland was mostly making engines that could trace their lineage to the ww1, and was without a high power design in the works, like ever.
Neither of these companies ever made a competitive supercharger for a long time for the in-service engines. Even Bristol, that set the altitude world records in the 1930s with 2-stage supercharged Pegasus.

At the end of the day, all of that left RR with Merlin to save the day.

If we want the RAF flying jet-engined fighters, having A.A. Griffith not po-pooing Whittle's work would've helped immensely.

added: Wrt. 'quick improvements' on the wartime British engines - Merlin was relatively quickly improved with the 20 series, that was soo good that it powered the most important British bombers; also, the introduction of 2-stage S/C for the Merlin helped to make one of the best - if not the best - engines of ww2.

 

[alspug]

I agree that the Merlin was the best engine of WW2 for numerous reasons. The first is that it's potential for improvment saw it go from 1030hp to 2060hp and remain in a small package able to be streamilned.

It powered several of the best aircraft of WW2 with the Spitfire, Mustang, Mosquito, Lancaster showing the variety of aircraft using it.
The other claim to fame for the Merlin goes by the name Meteor and powered several tanks.

All in all it was literally Britains best hope and it fullfilled it's role wonderfully.

The Wildcat as discussed here is really a proto hellcat with a wildcat name. It is a good idea and proposal but it is better to start with a clean sheet in order to get the performance desired. No suitable engine exists and any better engine is literally the starting point for a new design. Sure model it after the Wildcat but fundamentally it has little beide the camopaint and rivet style in common.

The more I read about engine design in the interwar years the more I understand how jealously guarding ideas slowed down development and caused more harm than good.

 

[tomo pauk]

I agree that the Merlin was the best engine of WW2 for numerous reasons. The first is that it's potential for improvment saw it go from 1030hp to 2060hp and remain in a small package able to be streamilned.
It powered several of the best aircraft of WW2 with the Spitfire, Mustang, Mosquito, Lancaster showing the variety of aircraft using it.
The other claim to fame for the Merlin goes by the name Meteor and powered several tanks.
All in all it was literally Britains best hope and it fullfilled it's role wonderfully.

I'll drink to that.

The Wildcat as discussed here is really a proto hellcat with a wildcat name. It is a good idea and proposal but it is better to start with a clean sheet in order to get the performance desired. No suitable engine exists and any better engine is literally the starting point for a new design. Sure model it after the Wildcat but fundamentally it has little beide the camopaint and rivet style in common.

Yes, pretty much a new design is needed.

The more I read about engine design in the interwar years the more I understand how jealously guarding ideas slowed down development and caused more harm than good.

Cooperation between engine manufacturers and intended cross-pollination was an exception indeed. That engine development was about as high-tech as it gets didn't helped, either. Sometimes it took a lot of time for the top people in engine company A to came to the terms that the top engineers in the engine company B were actually better in something.
In Germany for example, there was no streamlined process of siphoning out the lessons learned between the companies (like DB adopting chrome-coated valves a full year after BMW did it, or DB being too late with central oil feed to the crankshaft - unlike the Jumo or BMW). But German engine development was a sorry saga on their own.

At least the British were smart enough to see Bristol help out Napier with sleeve valves so Sabre became workable by late 1942/43.

 

[DougM]

I think what actually happened is the better option. Get the existing Wildcat into production, get folks trained on it, get it into the fight ASAP. Then sit back take the l reasons learned by GB and the limited amount the US had and start with basicly a clean sheet and make a replacement for the Wildcat that can be built fast and got into the war in a very short time.
This way we get something now and a better aircraft later. As they say perfect is the enemy of good enough. And while the Wildcat could have been better, the truth is it is highly unlikely that an improved Wildcat could have been avai in numbers at the same time the Wildcat was. And it is also doubtful that this improved Wildcat would have been as good as the Hellcat.

 

[Reggieperrin]

R-1830 was featuring in many of the late 1930s designs for them,
…..
The R-1830 probably saw a lot less of development during ww2.

This doesn’t seem very likely, tbh. An engine very widely used in many front-line aircraft is going to get a ton of development effort. Personally I think it just didn’t get exactly the kind of development effort needed to suit popular alt-hist scenarios such as this one.

• The air force sighted on durable power for multi-engined bombers and transports, and were obsessed with turbos - so their push had limited relevance for e.g. wildcat
• The navy did want powerful single-engines but had significant constraints posed by the need for reliable deployment in limited numbers far away from servicing facilities and lots of overwater flying. So they couldn’t just push for max power at the cost of e.g. 50-hour rebuild times.
• The usual struggle of development engineering vs production engineering was even more of an issue when the USA was spooling up from 2-3 factories and hundreds of engines per year to dozens of factories and tens of thousands of engines/year - this must have soaked up tremendous engineering resources

IMO better supercharger knowledge is what they really needed to get more useable power, as by 1940 both engines had implemented almost a decade of mechanical improvement plus 100 octane fuel. The low hanging fruit was all gathered.
Without that (or similar tech jumps such as the water injection you mentioned) it’s just shuffling around different packages of broadly equivalent engine technology in the hope of getting a better outcome, which is unlikely to achieve much without going up a size category in engine & aircraft.

 

[tomo pauk]

This doesn’t seem very likely, tbh.

What doesn't seem very likely? Sentence A:
R-1830 was featuring in many of the late 1930s designs for them,
or sentence B:
The R-1830 probably saw a lot less of development during ww2.

Or both sentences?

 

[Draconis]

I think what actually happened is the better option. Get the existing Wildcat into production, get folks trained on it, get it into the fight ASAP. Then sit back take the l reasons learned by GB and the limited amount the US had and start with basicly a clean sheet and make a replacement for the Wildcat that can be built fast and got into the war in a very short time.
This way we get something now and a better aircraft later. As they say perfect is the enemy of good enough. And while the Wildcat could have been better, the truth is it is highly unlikely that an improved Wildcat could have been avai in numbers at the same time the Wildcat was. And it is also doubtful that this improved Wildcat would have been as good as the Hellcat.

Yes. What would have been more beneficial is if Grumman could have put the R-2800 powered Hellcat into production earlier. What could have possibly sped up the development process? Not originally designing the XF6F for the Wright R-2600 but going with the P&W R-2800 right from the start? Was the R-2800 available in mid to late 1942 for Grumman to mass produce the F6F?

 

[tomo pauk]

Yes. What would have been more beneficial is if Grumman could have put the R-2800 powered Hellcat into production earlier. What could have possibly sped up the development process? Not originally designing the XF6F for the Wright R-2600 but going with the P&W R-2800 right from the start? Was the R-2800 available in mid to late 1942 for Grumman to mass produce the F6F?

(my bold)

Both Hellcat and Corsair used the 2-stage supercharged R-2800s. The 1st flight of the XF4U-1, powered by then-novel XR-2800-4, happened on 29th May 1940. The -4s were manufactured in minuscule numbers, however - less than a handful, and possibly only two or three?.
P&W delivered grand total of 6 (six) 2-stage R-2800s in 1941, 1st month that saw more than 20 of these engines was April 1942 (none in January, for example). Real mass production of 2-stage S/Ced R-2800s hit the stride by June 1942, with 1st triple digits production of these engines.

The 2-stage S/Ced R-2600 was running late, 1st examples saw actual flying in early 1942, by what time P&W's equivalent R-2800s were offering not just 15-20% more power, but were in actual production. So despite the lower number (2600 vs. 2800) that might suggest otherwise, P&W sorted their fighter-focused engines earlier.

Unfortunately, unless we settle for lesser versions of the R-2800s, we will not be getting the Hellcat (or Corsair) equivalent ready for Midway. Such the "Hellcat minus" fighter was mooted by Grumman, and the project was serious enough that it 'earned' it's own data sheet by the USN.
Engine stipulated for the -4 Hellcat was the 1-stage supercharged R-2800-27, top speed of almost 360 mph was expected - quite a turn-down with the normal Hellcat making 380-390 mph, but still better than the F4F-4. We will still be out-climbed by Zero, FWIW.
Mass production of the -27 and the like (2000 HP down low) was very good already by Jan 1942, that saw 220 such engines produced by P&W, and even 36 by Ford.

tl;dr - perhaps the best bet is to have XF4U-1 keep it's outside form as-is, accept the fact that the -4 engine is some 7-8% less powerful than the -8 and -10 (and of course have P&W series producing these), and have it produced by late 1941?

 

[Belisarius II]

I realize that the Hellcat was much different than the Wildcat, but unless I am mistaken it was designed originally starting from the concept of an upgraded Wildcat and ultimately turned. Into a new aircraft.
Much as the Super Hornet was supposed to be an upgraded Hornet and then basically turned Into a new aircraft that just looked like the older aircraft and then only superficially.

And having various engines and various aircraft using them being build on different manufacturing facilities has its advantages. If a weakness shows up then you have other engines and or air raft to take the place. Plus using different parts and materials also helps.
The US was powerful enough that it could afford to lose a bit in efficiency. But as long as the plants are all working at full speed and as long as you have to set up different part supplies because of coming from multiple plants and going to multiple locations say Carriers in the pacific vs England or what ever. You are not losing enough efficiency to worry about.

The Hellcat was always intended as a follow-on aircraft, not an upgrade of the Wildcat. From the start Grumman gave the F6F a different project number and sold it to the navy that way. The F4F was Grumman Model 33 and the F6F was Model 50. Saying it was an improvement of the F4F has caused a lot of confusion to aviation buffs over the years. The F6F was always intended to have the most powerful engine available at the time, that's why they wanted the Wright R-2600 and ended up taking the PW R-2800. With the same design philosophy of using the most powerful engine available Grumman believed the R-2600 powered F4F would have a top speed of 320 mph, with better acceleration, and rate of climb, a big improvement over its OTL performance. The F6F was designed to accommodate ether a later model Wright R-2600 or the new PW R-2800. The navy had already seen the amazing speed of the F4U-1A using the PW R-2800 so it was only natural that they'd want it for the F6F as well.

Yes, your right the U.S. had a lot of excess capacity leading up to WWII. However, what's so amazing about the U.S. aviation industry is it really started at a low point. Although there were many aircraft companies none of them had ever filled very large aircraft orders. Much of that capacity literally had to start from almost nothing. The Great Depression had left major sectors of the industrial base idol along with high unemployment. Defense orders started to take up some of that slack. The auto industry had the capacity to build large numbers of high-powered aircraft engines and the construction industry could literally build factories. Machine shops found themselves building all kinds of weapons, and equipment they never dreamed they would be producing.

The F/A-18E/F/G model Super Hornets are a different story. After a number of major failures in trying to build the next generation of naval aircraft Congress was in no mood to fund new projects. Using some navy ingenuity, they borrowed a page from 19th Century ship building where a small part of an old warship was incorporated into a new one which the navy said was the old ship just with a few repairs. In this way Congress didn't have to authorize new construction and the navy got new ships. By selling the Super Hornet as a simple upgrade like the F/A-18C was an upgrade of the A model Congress wasn't authorizing a new aircraft, but the navy was getting a whole new fighter. The Super Hornet has as much in common with the Hornet as the F6F had with the F4F. You can see the lineage, but they have little else in common.

 

[tomo pauk]

By selling the Super Hornet as a simple upgrade like the F/A-18C was an upgrade of the A model Congress wasn't authorizing a new aircraft, but the navy was getting a whole new fighter. The Super Hornet has as much in common with the Hornet as the F6F had with the F4F. You can see the lineage, but they have little else in common.

Apart from the gauges/instruments, radios and guns, there was probably no other part that was shared between the two Grumman fighters.
Similar was the story with 'normal' Merlin Mustangs and ligthweight Mustangs, the later being a whole new aircraft, yet keeping the P-51 nomenclature.

Legacy Hornet at least served a kinda/sorta parts donor for the Super Bug 'giving' it the front and rear fuselage sections, M61 installation, and very likely the cockpit canopy. Also some parts of the cokpit? But yes, it will take probably 90% of new parts to make a Super Hornet, if we we consider the F414 as a separate type vs. the F404, as well as new electronics.

 

[Belisarius II]

I agree that the Merlin was the best engine of WW2 for numerous reasons. The first is that it's potential for improvment saw it go from 1030hp to 2060hp and remain in a small package able to be streamilned.

It powered several of the best aircraft of WW2 with the Spitfire, Mustang, Mosquito, Lancaster showing the variety of aircraft using it.
The other claim to fame for the Merlin goes by the name Meteor and powered several tanks.

All in all it was literally Britains best hope and it fullfilled it's role wonderfully.

The Wildcat as discussed here is really a proto hellcat with a wildcat name. It is a good idea and proposal but it is better to start with a clean sheet in order to get the performance desired. No suitable engine exists and any better engine is literally the starting point for a new design. Sure model it after the Wildcat but fundamentally it has little beide the camopaint and rivet style in common.

The more I read about engine design in the interwar years the more I understand how jealously guarding ideas slowed down development and caused more harm than good.

I agree with your assessment of the Merlin engine being the most important aircraft engine of WWII followed by the PW R-2800. At the time Grumman was requesting the Wright R-2600 the F4F was practically a clean sheet design. The prototype for the F4F could accommodate the R-2600 engine without redesigning the front section. The questions involved greater torque requiring a higher vertical stabilizer, and larger propeller needing a lower wing, and different landing gear. Many aircraft in WWII went through similar redesign work. If the first designs of the F4F were inferior to the F2A Buffalo, the Grumman fighter needed all the power it could get.

 

[tomo pauk]

The prototype for the F4F could accommodate the R-2600 engine without redesigning the front section.

This is very interesting. Care to elaborate?

 

[Belisarius II]

Yes. What would have been more beneficial is if Grumman could have put the R-2800 powered Hellcat into production earlier. What could have possibly sped up the development process? Not originally designing the XF6F for the Wright R-2600 but going with the P&W R-2800 right from the start? Was the R-2800 available in mid to late 1942 for Grumman to mass produce the F6F?

No time was lost by putting an R-2600 in the first test model. The F6F was designed from the beginning to accommodate the R-2800. The R-2800 was becoming more available in early 1942. It's not like the F6F could've been in production in 1941. Their production date was October 1942 and it's hard to imagine a much earlier date. The F4F-4 was left holding the line as the primary navy/marine fighter till early 1943 when squadrons began converting to F6F-3 & F4U-1A models.

 

[Belisarius II]

This is very interesting. Care to elaborate?

That's exactly what the Grumman engineers said when they made the request. The Bureau of Aeronautics never refuted that. What they did say was that the increased weight would change the center of gravity, it would need a larger propeller so the landing gear would have to change. They also feared the heavier F4F would have a higher landing speed. I would also guess the increased torque would demand a higher vertical stabilizer like the FM-1/2 needed. I think it would've been well worth it to have a more powerful F4F Wildcat from 1940-43. With some weight saving measures even a 9,000 lbs. Wildcat could operate off of CVE's.

 

[mack8]

Unfortunately, unless we settle for lesser versions of the R-2800s, we will not be getting the Hellcat (or Corsair) equivalent ready for Midway. Such the "Hellcat minus" fighter was mooted by Grumman, and the project was serious enough that it 'earned' it's own data sheet by the USN.

I can't seem to be able to see or download the XF6F-4 data sheet, could you repost it if possible? Thanks.

 

[tomo pauk]

I can't seem to be able to see or download the XF6F-4 data sheet, could you repost it if possible? Thanks.

This link should be working:
https://web.archive.org/web/2022020...om/SAC/XF6F-4_(Land)_PD_-_November_1_1942.pdf

That's exactly what the Grumman engineers said when they made the request. The Bureau of Aeronautics never refuted that. What they did say was that the increased weight would change the center of gravity, it would need a larger propeller so the landing gear would have to change. They also feared the heavier F4F would have a higher landing speed. I would also guess the increased torque would demand a higher vertical stabilizer like the FM-1/2 needed. I think it would've been well worth it to have a more powerful F4F Wildcat from 1940-43. With some weight saving measures even a 9,000 lbs. Wildcat could operate off of CVE's.

If I'm reading this right: it was an opinion of the people from Grumman that R-2600 would've fitted easily on the Wildcat, and not that the R-2600 was an actual, working fit to the F4F prototype ever?

 

[Belisarius II]

This link should be working:
https://web.archive.org/web/2022020...om/SAC/XF6F-4_(Land)_PD_-_November_1_1942.pdf



If I'm reading this right: it was an opinion of the people from Grumman that R-2600 would've fitted easily on the Wildcat, and not that the R-2600 was an actual, working fit to the F4F prototype ever?

If I understand you correctly, you're suggesting between February 1938 & February 1940 the prototype aircraft couldn't have been rebuilt to take the power of the R-2600? The prototype was rebuilt several times while Grumman was trying to compete with the F2A Buffalo. Respectfully that's what a prototype is used for. The great fighters of WWII were built around their engine, the engine wasn't picked to fit the protype. General Motors had little trouble building the FM-2 version with a more powerful engine, and new tail section. It was still able to use the same wing and landing gear of the F4F-4. In 1938 Grumman wanted to exploit the power of the R-2600 and could modify the airframe with little trouble, after all they had 2 years to do it in.

The issues you raise about the turbo charging are more relevant. High altitude performance would depend on what Wright had available in 1940-41. General Electric led the way in WWII with its Superturbochargers, perhaps they could've helped out in improving the high-altitude performance of the R-2600 like they had on the Wright R-1820 engines on the B-17. It's not like this was an insoluble problem.

 

[tomo pauk]

If I understand you correctly, you're suggesting between February 1938 & February 1940 the prototype aircraft couldn't have been rebuilt to take the power of the R-2600? The prototype was rebuilt several times while Grumman was trying to compete with the F2A Buffalo. Respectfully that's what a prototype is used for. The great fighters of WWII were built around their engine, the engine wasn't picked to fit the protype. General Motors had little trouble building the FM-2 version with a more powerful engine, and new tail section. It was still able to use the same wing and landing gear of the F4F-4.

It is not the power I have problems with re-building the Wildcat prototype, it is the weight spiralling up severely due to the jump from the initial 1-stage 1-speed S/C R-1830-SCG the XF4-2 used. That engine was 1370 lbs, and was replaced with the 2-speed 2-stage S/Ced R-1830-76 (weight 1565 lbs) for the F4F-3. For comparison sake, the R-2600 as used on most of A-20s, with 1600 HP, weighted 1950 lbs.
The 10 ft prop (314-315 lbs) will not cut it, will need at least the 11.3ft prop like the A-20 used - 400 lbs?
(the FM-2 used a 394 lb prop)
Oil system (30 lbs on the -3, 35 lbs on the -4, since it was supposed to use drop tanks) will not cut it, half of the oil system for the A-20 = 172 lbs (for 344 lbs total); the FM-2 went with 99 lb heavy oil system. Oil itself on the -3 was at ~70-80 lbs, we gonna need 100 just to cater for greater power?
Engine bearers, firewall - perhaps another 100 lbs?
So after we're past the firewall, weight is up by ~550 lbs, or about extra 10% of the empty weight.
Extra fuel tankage (140-ish US gals will not cut it anymore, 200 just might?) = 360 lbs + another 100 lbs for the self-sealing fuel tanks (it was 233 lbs for the fuel system on the -3, more on -4).
Sturdier U/C, since the old, 351 lb unit will not do - another 50-100lbs (FM-2 U/C was at 442 lbs). New U/C will need longer legs and wider tires, too.
We didn't added any ballast to the tail yet, and we didn't increased the tail yet.

If we don't touch anything else, we're at a 1000 lbs greater weight for a clean and fueled 'Chad Wildcat', ie. at 8500-8600 lbs instead of at 7560 lbs (full ammo for 4 HMGS, full fuel, still no folding wings). Now we enter the problem of aircraft not being able to match the same G limit as the -3 did since the strength (and also the weight) of the structural elements remained the same. We also don't meed the stalling speed requirements that -3 meat easily, since the wing loading just went up by 15%. Both of the problems are made worse with desire to have the folding wings and an extra pair of MGs for the next version of the Chad Wildcat.

FM-2 was powered by a lighter engine than the engine on the F4F-3 or -4 (1400 lbs with accesories for the R-1820-56), that meant the FM-2 weighted as much as the F4F-3 despite the FM-2 having the heavier, folding wings. Increase in power was modest, 1360 HP vs. 1200.

I agree that the fighters were designed around the engine. Problem with the F4F was that it was designed around a relatively small and light engine.

In 1938 Grumman wanted to exploit the power of the R-2600 and could modify the airframe with little trouble, after all they had 2 years to do it in.

Would they be better advised to modify the XF4F-2 to have the R-2600, or that they make a bespoke aircraft with the R-2600 in the nose?

The issues you raise about the turbo charging are more relevant. High altitude performance would depend on what Wright had available in 1940-41. General Electric led the way in WWII with its Superturbochargers, perhaps they could've helped out in improving the high-altitude performance of the R-2600 like they had on the Wright R-1820 engines on the B-17. It's not like this was an insoluble problem.

For their own reasons, USN was never really sold on turbochargers. They did support (not just in wording, but also monetarily) the work at P&W to make the 2-stage supercharging a viable tech; I assume that they also supported the similar work at Wright, that was later than P&W by many months in that regard.
A fighter that also has the turbocharger required to supply the compressed air at 20000+ ft for the R-2600 will add both weight and drag penalty, so again I'd say we're better off with a bespoke design.

 

[mack8]

It is not the power I have problems with re-building the Wildcat prototype, it is the weight spiralling up severely due to the jump from the initial 1-stage 1-speed S/C R-1830-SCG the XF4-2 used. That engine was 1370 lbs, and was replaced with the 2-speed 2-stage S/Ced R-1830-76 (weight 1565 lbs) for the F4F-3. For comparison sake, the R-2600 as used on most of A-20s, with 1600 HP, weighted 1950 lbs.
The 10 ft prop (314-315 lbs) will not cut it, will need at least the 11.3ft prop like the A-20 used - 400 lbs?
(the FM-2 used a 394 lb prop)
Oil system (30 lbs on the -3, 35 lbs on the -4, since it was supposed to use drop tanks) will not cut it, half of the oil system for the A-20 = 172 lbs (for 344 lbs total); the FM-2 went with 99 lb heavy oil system. Oil itself on the -3 was at ~70-80 lbs, we gonna need 100 just to cater for greater power?
Engine bearers, firewall - perhaps another 100 lbs?
So after we're past the firewall, weight is up by ~550 lbs, or about extra 10% of the empty weight.
Extra fuel tankage (140-ish US gals will not cut it anymore, 200 just might?) = 360 lbs + another 100 lbs for the self-sealing fuel tanks (it was 233 lbs for the fuel system on the -3, more on -4).
Sturdier U/C, since the old, 351 lb unit will not do - another 50-100lbs (FM-2 U/C was at 442 lbs). New U/C will need longer legs and wider tires, too.
We didn't added any ballast to the tail yet, and we didn't increased the tail yet.

If we don't touch anything else, we're at a 1000 lbs greater weight for a clean and fueled 'Chad Wildcat', ie. at 8500-8600 lbs instead of at 7560 lbs (full ammo for 4 HMGS, full fuel, still no folding wings). Now we enter the problem of aircraft not being able to match the same G limit as the -3 did since the strength (and also the weight) of the structural elements remained the same. We also don't meed the stalling speed requirements that -3 meat easily, since the wing loading just went up by 15%. Both of the problems are made worse with desire to have the folding wings and an extra pair of MGs for the next version of the Chad Wildcat.

FM-2 was powered by a lighter engine than the engine on the F4F-3 or -4 (1400 lbs with accesories for the R-1820-56), that meant the FM-2 weighted as much as the F4F-3 despite the FM-2 having the heavier, folding wings. Increase in power was modest, 1360 HP vs. 1200.

I agree that the fighters were designed around the engine. Problem with the F4F was that it was designed around a relatively small and light engine.


Would they be better advised to modify the XF4F-2 to have the R-2600, or that they make a bespoke aircraft with the R-2600 in the nose?



For their own reasons, USN was never really sold on turbochargers. They did support (not just in wording, but also monetarily) the work at P&W to make the 2-stage supercharging a viable tech; I assume that they also supported the similar work at Wright, that was later than P&W by many months in that regard.
A fighter that also has the turbocharger required to supply the compressed air at 20000+ ft for the R-2600 will add both weight and drag penalty, so again I'd say we're better off with a bespoke design.

Great overview of implications of the R-2600 on F4F.

Do you think the 1400HP R-2180 would work without having to drastically redesign the aircraft, so the F4F remains recognizable? I'm taking a cue from the A6M where they did sucessfully fitted the Kinsei instead of Sakae. I'm imagining it as having the bigger tail from FM-2, the rear fuselage tank at least doubled in size to cater for higher fuel consumption, maybe drop tanks, and generally shifting things around in the rear fuselage to compensate for the heavier engine. If the performance for this ALT F4F-4 remains around the same level as F4F-3 (330 mph, 3000 ft/min climb) that is still a significant plus over the OTL capabilities.

Fitting the F4F with the R-2600 looks to be like fitting the Zero with a Kasei, ie not going to work without a new airframe. The R-2600 fighter was the XF6F-1 which i think proves the point.

As a general comment, fwiw my alternate pre-war Grumman/USN timeline is this:

XF5F and XP-50 cancelled, total waste of time.

Instead the design resources are used to bring forward by about a year the TBF to summer 1940, because imo they first need the TBF to replace the absymal TBD before needing better fighters. So that means the VT squadrons have TBFs by Midway. Without better torpedos they still hit squat, but at least they are not completely massacred as in OTL. They still take say at least half the OTL losses though.

Then the R-2600 XF6F-1 is brought forward a year too, so summer 1941. Probably means first units are equipped with it by late 1942, ie roughly the same time as F4U-1. If necessary the first series would be good enough with a 2-speed SC R-2600 only, or a similar R-2800 if the switch still happens after the first couple prototypes. (same applies to a TL getting the F4U ready earlier btw, 2-speed R-2800 would be good enough initially).

Finally for the purpose of this thread (otherwise probably not in the timeline), by cancelling the XP-50, design resources are used to get the R-2180 F4F-4 ready in spring 1941, with subsequent timeline roughly same as OTL. PW also has to not waste time on the R-2000 and concentrate on improving the R-2180, presumably the USN would want the 2-stage SC on it. Like above, if necessary the first series would still be good enough with a 2-speed SC.

 

[tomo pauk]

Do you think the 1400HP R-2180 would work without having to drastically redesign the aircraft, so the F4F remains recognizable? I'm taking a cue from the A6M where they did sucessfully fitted the Kinsei instead of Sakae. I'm imagining it as having the bigger tail from FM-2, the rear fuselage tank at least doubled in size to cater for higher fuel consumption, maybe drop tanks, and generally shifting things around in the rear fuselage to compensate for the heavier engine. If the performance for this ALT F4F-4 remains around the same level as F4F-3 (330 mph, 3000 ft/min climb) that is still a significant plus over the OTL capabilities.

Weights data that I was able to collect give ~1650 lbs for the 1-speed S/Ced R-2180s (100 oct fuel, 1400 HP), ~1750 lbs for the 2-speed S/Ced version that was never manufactured (both with 1-stage S/C), and 1810 lbs for the 2-stage 2-speed version (again never produced; 1400 HP on 100 oct). The 1750 lb version was supposed to turn 2600 rpm and make 1500 HP (this is very, very close to what the Ha 109 was good for, FWIW), others were at 2500 rpm.
All these max power figures are for low altitudes; the 1-speed S/Ced versions were low-altitude types.

Will any of these fit on the F4F? The better and the heavier the version, the harder will be to fit it. If we want the lightest so 1-stage, 1-speed, 2500 rpm max), yet tuned for altitudes 13000-15000 ft at least, we'd be probably getting ~1200 HP there (almost mimics the Ha 41), or about 100 extra when compared with what the F4F-3 and -4 already had. Enough of difference to bother? You'd be the judge, as Paul Harrell was saying, expecially since the original engine on the F4F-3 was a bit better as altitude increased further.
Going with the best option wrt. the power at all altitudes, the 2-stage 2-speed version is the best fit, with probably 1250 HP at 18000 ft (assuming the same S/C tech level as on the F4F-3's engines), although the 1750 lb version mentioned above will be close to it there due to it's extra 100 rpm.

tl;dr - the more power we want, the greater the weight penalty will be had, and also greater increase of structural weight will be needed

Fitting the F4F with the R-2600 looks to be like fitting the Zero with a Kasei, ie not going to work without a new airframe. The R-2600 fighter was the XF6F-1 which i think proves the point.
<snip>
XF5F and XP-50 cancelled, total waste of time.

Bingo! for the whole quoted passage.

Instead the design resources are used to bring forward by about a year the TBF to summer 1940, because imo they first need the TBF to replace the absymal TBD before needing better fighters. So that means the VT squadrons have TBFs by Midway. Without better torpedos they still hit squat, but at least they are not completely massacred as in OTL. They still take say at least half the OTL losses though.

Then the R-2600 XF6F-1 is brought forward a year too, so summer 1941. Probably means first units are equipped with it by late 1942, ie roughly the same time as F4U-1. If necessary the first series would be good enough with a 2-speed SC R-2600 only, or a similar R-2800 if the switch still happens after the first couple prototypes. (same applies to a TL getting the F4U ready earlier btw, 2-speed R-2800 would be good enough initially).

Works for me.
I'm okay with the another alternative scenario - a conservative fighter designed around a big radial is made instead of the XF5F/XP-50 with TBF going on as-is; the big fighter gives the hard time to the Zeroes so the overall USN losses are lower (ie. losses the fighters, dive bombers and torpedo bombers suffered).
The X5F5 1st flew on April 1st 1940, the XP-50 on 18th February, so there is a good chance that a big fighter is making a lot's of flights as a prototype by second half of 1940 instead, with early 1941 seeing the pre-series examples in test phase, and tooling up for series production through the best part of 1941.

I'd again agree with the early F4U, even with an imperfect R-2800 in the nose.