Advanced French Fighters vs 1942/1943 contemporaries (4 Viewers)

[ThomasP]

re the MiG-3

The MiG-3 carried a lot of fuel for its size - initial production had 640L (169 USgal), while later production had 530L (140 USgal).

In my notes I have it without SSFT, but receiving an exhaust based purging system on the production line beginning in mid-41 - with the exhaust gases/exhaust pressure being used to reduce/replace the available O2 in the fuel tanks.

Does anyone know if the MiG-3 was ever fitted with SSFT?

 

[Shortround6]

Who says you want a B-25? How about a slimmer French equivalent of the A-20 That might actually be a lot better.

I am using the B-25 as a sort of generic stand-in. Not a standout at any one thing but pretty good at a number of things.

B-25C-D operated at around 33,000lbs and offered much more that 24-25,000lb Amiot 351/354 or the 25,000lb LeO 451could offer.
The French bombers could offer either bomb load or range but not a lot of either at the same time. Aside the 20mm gun on top the other defensive armament sucked. Not much better than WW I. Economical cruising speeds of around 220-230mph so high speed dashes are possible but further restrict bombload/range.
They did very well for under 1200hp engines but game had passed them by without major updating/changes.

French had a love of small, cheap aircraft. That or a major bribe in the purchase of 700-800hp radial engines.
The French bought 5 different prototypes and service designs of 2-3 man aircraft powered by the GR-14M engines. Including a carrier-based torpedo bomber.
They also bought one prototype of a 4 engined medium bomber using 4 of the small engines. They decided not to buy it when the war broke out in Sept 1939 to avoid complicating the production problem since they already had two twin engine medium bombers.
They were also looking at several multi seat aircraft powered by two 500hp V-12 Renault engines.
Small is not always good but it seemed to be a religion in the French Aeronautic industry/Air Ministry. Price per plane, not price for capability.

French had trouble (low powered engines) making a decent medium bomber. Trying for French A-20 is possible
The Bloch 175 B3 used a slightly enlarged bomb bay over the Bloch 174 but this required a lot of redesign to space the wing spars out by 15%.
Plane could hold three 441lb bombs, four 220lb or eight 110lb bombs. Range at 85% power with three 441lb bombs was 993 miles.
Max speed with GR 14N 48/49 engines was 335mph at 17,000ft.
Normal weight was 17,170lbs

 

[Shortround6]

re the MiG-3

The MiG-3 carried a lot of fuel for its size - initial production had 640L (169 USgal), while later production had 530L (140 USgal).

In my notes I have it without SSFT, but receiving an exhaust based purging system on the production line beginning in mid-41 - with the exhaust gases/exhaust pressure being used to reduce/replace the available O2 in the fuel tanks.

Does anyone know if the MiG-3 was ever fitted with SSFT?

This system was used on a number of Soviet aircraft.
some books say the Mig-1/3 had tough cord fabric helping protect the fuel tanks. No mention is made of coating/treatment although some sort of glue (?) would seem to have been used.
Mig-3 production stopped pretty much in Dec 1941, with about 30 built in 1942 from left over parts. While the Soviets continued to use them in 1942 and into 1943 in some areas I doubt there was much of a refit program going on and any Soviet aircraft that were fitted with western style self-sealing fuel tanks got them much later than Dec 1941/Jan 1942.

 

[Shortround6]

There is no such thing as a free lunch. If people want a do-all Soviet fighter, the relatively light M-105 engine will not cut it.

Very true but one reason for this Soviet sidetrack is some people keep bring up the soviet fighters with their 600kg 1260/1180hp engines to say how well French fighters would do once they replace the 490kg 1100-100hp (or lower) HS engines with the ??? kg H-S 12Z of 1200-1600hp at ????? altitude.
Soviets did use their "fighters" for lots of things that maybe they shouldn't have if they had more of the proper type aircraft.

Nobody is asking them to repeal the laws of physics. The MiG-3 with two cannons was made in small series.

It was, how effective it really was is unknown. More effective yes, but one 20mm ShVAK weighs as much as two ShKAS and one UB put together. Ammo weight is unknown.
Also unknown (by me anyway) is the firing rate when synchronized by most of these guns. The UB is often credited with 800rpm firing through the prop disk. The ShKAS is credited at 700-800rpm through the hub (or in wing?) The 1800rpm ShKAS may have been good for 1500rpm firing through the prop? Less?
LA-5 didn't have any good options.
LA-5/7 didn't get 3 guns until they got the lighter B-20 guns.
French 20mm gun was about 60kg without the drum. French could have/would have had belt feed had the war gone on. Now add 5-8kg for the belt feed system.

t is a darned fighter. Do not even think on the bombs and ground-attack rockets on a fighter before you have at least the air parity.

Assumes you have decent ground attack planes. Which, without major changes, the French do not have.

Yes, the drop tanks need to be of useful size, preferably so that drop tankage equals the internal tankage.

Well, they almost got that one right with the two 97-100 liter fuel tanks on the I-16 to help the 255l internal fuel. Also used (?) on the I-153
Now do the Soviets standardize or use bespoke drop tanks for each fighter
Soviets need to do a number of other things on their fighters before they worry about drop tanks. Mig-3s didn't even have a fuel gauge.
French standard of equipment (instruments and radios) could have/would have been higher in 1941/42.
Worring about blind flying may be important before worrying about 3-5 hour flights.

The Do-217 was a cheeky way to get a lot from just two engines invested in.

Yes, another case it not sidelining the DB 603 for several years. A 1600-1750hp DB 603 powered Do 217 would have been a bit tougher opponent in 1941-42.

French have a real problem, They are not going to get a 1600-1700hp version of the HS 12Z for years or without a major change in the engine. (still years), The GR 14R was almost vapor ware in 1940. What they could have done in 1941-42 debatable.
One problem for French engine development is that 1940 100 octane fuel is not going to be a magic wand. The US and British had not standardized yet. Are the French going to get 100/100 or 100/115 or 100/130 fuel? British for most of 1940 didn't know they had 100/130 fuel, it was 100/115+, they didn't have a way to measure it.
For engine development how much cylinder pressure you are making affects how strong you make the parts. Adding 100/130 fuel to engines designed to use lower octane fuel and boosting the pressure is going to lead to a lot of broken parts/engines or a lot of cooked engines (not enough cooling). French can get there. But some of the development work done in 1940 may need to be redone.
R-2800 is a case in point. The B-series engines were developed to make 2000hp on 100/100 fuel. They never made more that 2000hp on 100/130 fuel unless they got water injection.

 

[Airborne2001]

French Fw 187 would've been just the ticket. Or the French Ki-45, but as a bomber. The tactical bomber need to be small and zippy.
The Mosquito with the G&R 14R engines would've been just fine.

Actually, France did have a rather strong heavy fighter/ground attack project in the works with the CAPRA R40:

View: https://www.facebook.com/groups/2219850264895329/posts/3711865475693793/

Sadly, the mockup got destroyed during the Battle of France, and the whole project died with the armistice.

 

[bf109xxl]

Does anyone know if the MiG-3 was ever fitted with SSFT?

There are some discrepancies in the sources - some state that even the first production MiG-1 was equipped with self-sealing fuel tanks (the "Anazot" sponge), but then, for some reason, they state that SSFTs first appeared on the improved MiG-3 in March 1941 (serial numbers 2107 and 2115). Later, an engine-exhaust inerting system was installed.

 

[ThomasP]

re "Anazot" foam

Interesting. I am familiar with the material type, but was not aware that it was used during WWII.

For anyone interested, it is usually classed as a resin based 'explosion-suppressant reticulated foam'. The foam has a void space ratio of around 90-95%, so using it inside the tank only decreases the fuel capacity by 5-10%.

Similar materials are used in many of today's aircraft in the form of foam inserts that fit in the fuel tank spaces, acting as a slosh preventer and as 'ullage' protection - with the term 'ullage' (in this case) meaning what would otherwise be air space in the fuel tanks that could explode due to the fuel vapor to air ratio present when hit by AP, tracer, incendiary, and explosive rounds. The foam structure is meant to prevent the rapid spread of the flame front, which in effect often prevents an explosion.

It should be noted, however, that "Anazot' type foam does not prevent fuel leakage, although it will reduce the loss rate.

 

[Steamed_Banana]

Gentlemen, I believe you are wrong on the P-40 engines, though these things are tricky so I want to tread carefully. This is what I have:

Allison V-1710-33 / C-15
P-40 / P-40B / P-40C / Hawk 81 / Tomahawk types

Full throttle height is shown as:

1040 hp at 2800 rpm and 37.2" Hg manifold pressure @ 14,500' . [no date]
1040 hp at 3000 rpm and 40" Hg manifold pressure @ 13,600' (5 minute rating) [A second document dated 5 Sep 1941]

This shows military power peaking at 14,300'

This translated to an effective "critical altitude" of about 18,500 ft / 17,000 ft for level flight, (somewhat lower for climbing). Obviously this does vary by temperature and atmospheric conditions, fuel used, and possibly manifold pressure. Top speed for P-40B is shown as 352 mph with 1090 hp and 3,000 rpm @ 15,000' (Apr 26 1941)

Max cruise is at 12,500' and 12,000' respectively for the two documents.

These Hawk 81 types with the C-15 engines were used by both AVG and (eventually, as higher octane fuel became available) various British and Commonwealth squadrons including 3 RAAF and 112 RAF at unofficial / overboost "War Emergency" power settings of up to 56" Hg. It was just riskier for the engine with the C-15 as it was not specifically strengthened for this.

Allison V-1710-39 / F3R
P-40D / P-40E / Hawk 87 / Early Kittyhawk type

Full throttle height is 2600 RPM and 38.5 " Hg @ 12,000' [flight manual Feb 25 1943, revised April 10, 1943]

This shows military power peaking at 11,800'

This translated to an effective "critical altitude" variously indicated as 15,000 or 16,000', above which performance falls off steeply.

Allison V-1710-73 / F4R
P-40K (and some refurbished P-40E) Hawk 87 Allison (mid-run)

Full throttle height is shown as 1150 hp at 3,000 rpm and 44.2" Hg manifold pressure @ 11,800'. (15 minute rating) [Dec 18 1942, revised Apr 25 1944]
War Emergency Power is shown as 1550 hp at 3,000 rpm and 60" Hg manifold pressure @ Sea Level
Another document shows 1,000 hp at 2600 rpm and 37" Hg manifold pressure at @10,500' and
@ 1,150 hp at 3,000 rpm and 42" Hg at 12,000 ft [ June 25 1942]

This is usually translated as a critical altitude of ~ 15,000 or 14,800 as shown for maximum cruise altitude here. Sometimes it's reported as 16,000 ft, above which performance falls of steeply.

Allison V-1710-81/ -99 / F20R
P-40M and P-40N, Hawk 87 Allison (late)

Full throttle height is shown as 1125 hp at 3,000 rpm and 44.2" Hg manifold pressure @ 17,000 ft (with ram) and 15,000 ft (no ram)
WEP is shown as 1480 hp at 3,000 rpm and 57" Hg @10,000 ft. [Dec 18, 1942]

Maximum cruise is at 16,600 ft.
The nominal critical altitude for P-40M and N depends on the load and weight but is usually shown at about 17-18,000 ft, and they still had decent performance up to about 20,000 ft

I don't know if there was an actual difference is just weight, the impellers are the same size until you get to the P-40M and N types with F20R etc., possibly the slight difference (?) in the supercharger gear ratio C-15 / -33 or the reduction gear (?) but critical altitude is shown consistently as higher. I'd show much more here but alas

WW2AircraftPerformance seems to be down again.

I have impellers at:

9.5" for V-1710-33 with an 8.77:1 ratio
9.5" for V-1710-39 F3R (8.80:1 ratio)
9.5" for V-1710-73 (8.80:1 ratio)
9.5" for V-1710-81 (9.6:1 ratio)

 

[Steamed_Banana]

This is the document I have showing military power altitudes for the various Allison V-1710 types (attached). It is dated 1 Jan 1949.

I believe, therefore, that the P-40B and C ('Tomahawk') types actually had an effective critical altitude of about 3-4,000' higher than that of the P-40D, E and K (early to mid run 'Kittyhawk') types, which made a big difference in application for each type. P-40D, E and K had better performance down near Sea Level, and could be safely boosted more, with official WEP settings at various times during the war ranging from 54", 57" Hg for E and 60" for K.

But the 'Tomahawk' types had better altitude performance and almost double the rate of climb at normal loaded weights (which obviously varied widely).

So for the French, who would be receiving Tomahawk types initially and earlier, would have the type better suited for their circumstances in many respects. In North Africa, Tomahawk IIA and IIB types proved a match for Bf 109E4-E7 on several occasions, which resulted in the accelerated deployment of the 109F

Unfortunately Curtiss did go the other direction with the Kittyhawk types making them a bit less ideal for fighter supremacy against German or (later model) Italian fighters due to their reduced effective ceiling.

This was somewhat corrected with the P-40M and N, but these were not really used much for air superiority in the MTO, (M were a little bit by the British). Instead the Merlin powered F/L types were preferred, due mainly to their much improved altitude performance (which meant effectively a 7-8,000' higher performance ceiling than a P-40D, E or K)

 

[Steamed_Banana]

I am using the B-25 as a sort of generic stand-in. Not a standout at any one thing but pretty good at a number of things.

B-25C-D operated at around 33,000lbs and offered much more that 24-25,000lb Amiot 351/354 or the 25,000lb LeO 451could offer.
The French bombers could offer either bomb load or range but not a lot of either at the same time. Aside the 20mm gun on top the other defensive armament sucked. Not much better than WW I. Economical cruising speeds of around 220-230mph so high speed dashes are possible but further restrict bombload/range.

Hold on a minute here.

I'm going to focus intially on the Leo 451 since it has somewhat of a combat history, notably in the British-Vichy war in 1941. Leo 451 had superior range to any version of the B-25 as far as I'm aware, what I see is 1,800 miles for the LeO 451 vs 1,350 - 1,500 miles for the B-25. I am of course, aware that these vary by loadout and use of space, specific variant, cruise speed etc.. The Leo 451 also seems to potentially carry a larger bomb load (noted with the same caveats).

Leo 451 was also ~30 mph faster than the B-25 (308 mph vs 270-285 mph for B-25C)

The Amoit 354 also seems to have better speed (300 mph), range, and equivalent bomb load to the B-25, though it barely got into combat so it's hard to say for sure how it really worked in a combat situation. On paper however, it looks fairly competitive in many respects.

But more importantly, I think you are also forgetting that with regard to the French types, there are built and operational in May or June of 1940. The first combat deployment of the B-25 that I am aware of was in April of 1942. So you are comparing quite different eras of the war here. By the standards of 1940, both Leo 451 and Amoit 354 are quite well protected. The Leo 451 has self sealing fuel tanks and some armor, a 20mm dorsal cannon and 2 x 7.5mm machine guns.

In 1940, the US was flying these for medium bombers. Top speed 216 mph, range 900 miles, armament 3 x .30 caliber machine guns, 2,000 lb normal bomb load. No armor or self-sealing fuel tanks.

The older Marin B-10 was still being manufactured for export through 1940, and was still being flown by the US in two bomber and one reconnaissance squadron in 1940. Top speed 213 mph, range 1,200 miles, guns 3 x .30 cal, bomb load 2,200 lbs.

The only really competitive twin engined bomber designs the US had in 1940 was in fact the DB-7 / A-20, and the Martin 167 Maryland, both of which the French had been among the very first to order.

Early DB-7 was fast (308 mph) but quite short ranged and it too lacked armor or self sealing tanks, weapons consisted of 2-4 forward firing machine guns and 2 defensive .30 caliber guns.

The Maryland was also fast, had much better range, but was similarly armed. Early versions did not have self-sealing tanks.


It is a valid question as to whether A) the French can build bigger engines than the 1060 hp Gnome Rhone 14Ns they built on these bombers. (Conceivably, with 1,200 hp engines instead of 1,060 hp performance would have been fairly extraordinary), and whether they could develop good power turrets. But it is notable that the A-20 did not have a power turret until the much improved G variant which arrived in combat squadrons in late 1943. So maybe power turrets aren't necessary if your aircraft are fast enough.

But we can indeed observe that the French have nothing like the R-2600 either ready to go or in development in 1940. That is the open question here that I see. Given 2 years either I suspect they can import US or British engines or develop something improved, though the latter is debatable. Gnome Rhone 14 and HS 12Y were near the end of their development potential. Precisely how near is hard to say. The Swiss got the 12Y engine, based entirely on French specs I believe, up to roughly 1,300 hp. That could carry one of these very well designed planes into 1942 IMO. Hispano Suiza was experimenting with multi-speed superchargers for the 12Y and 12Z going back to 1938, though I don't know how far they got with this. The Soviets managed to produce a two speed supercharger for the VK-105 / M-105.

I think it's quite clear that Japanese fighters like the A6M were still quite competitive well into 1943 and none of them had 1,300 hp up to that point.

They did very well for under 1200hp engines but game had passed them by without major updating/changes.

French had a love of small, cheap aircraft. That or a major bribe in the purchase of 700-800hp radial engines.
The French bought 5 different prototypes and service designs of 2-3 man aircraft powered by the GR-14M engines. Including a carrier-based torpedo bomber.
They also bought one prototype of a 4 engined medium bomber using 4 of the small engines. They decided not to buy it when the war broke out in Sept 1939 to avoid complicating the production problem since they already had two twin engine medium bombers.
They were also looking at several multi seat aircraft powered by two 500hp V-12 Renault engines.
Small is not always good but it seemed to be a religion in the French Aeronautic industry/Air Ministry. Price per plane, not price for capability.

I observe that there are advantages to smaller aircraft, though the Leo 451 isn't particularly small. It's a bit larger than the A-20, just eyeballing 1/72 scale models on my shelf. If you want small look at something like the Japanese Ki-48.

French had trouble (low powered engines) making a decent medium bomber. Trying for French A-20 is possible
The Bloch 175 B3 used a slightly enlarged bomb bay over the Bloch 174 but this required a lot of redesign to space the wing spars out by 15%.
Plane could hold three 441lb bombs, four 220lb or eight 110lb bombs. Range at 85% power with three 441lb bombs was 993 miles.
Max speed with GR 14N 48/49 engines was 335mph at 17,000ft.
Normal weight was 17,170lbs

So far as I know Bloch 170-174 series was used almost entirely as a reconnaissance aircraft, and seemed quite successful in that role (330 mph and a cruising speed of 290 mph was quite good for 1940) but it probably did have potential as a bomber, especially with a little further development.

 

[tomo pauk]

I believe, therefore, that the P-40B and C ('Tomahawk') types actually had an effective critical altitude of about 3-4,000' higher than that of the P-40D, E and K (early to mid run 'Kittyhawk') types, which made a big difference in application for each type. P-40D, E and K had better performance down near Sea Level, and could be safely boosted more, with official WEP settings at various times during the war ranging from 54", 57" Hg for E and 60" for K.

Thanl you for the effort to find and post the data.

As before, term 'critical altitude' is not giving the data we need. Would we rather have the Merlin III with critical altitude of 16250 ft (on 87 oct fuel), or the same engine with the rated altitude at 9000 ft (100 oct fuel)?
What mattered was what kind of power at desired altitude. Both -39 and -33 (and the similar engines, with the S/C drive of 8.8:1) will do the same power above ~14500 ft (without the ram effect). The -33 will do a bit better under that altitude because it was allowed for a somewhat greater boost.

The reason why the P-40E was such a dog was due to it porking out, with all of the HMGs & their ammo, protection, structural reinforcements etc, while the engine power above 10000 ft was still firmly in the 1939 land when compared with what the European best had. See the Spitfire II as a bit less problematic example, that despite the better engine it was not as zippy as the Mk.1. Or, see how the Spitfire V would've fared if we put the Merlin III in the nose, with as high-octane fuel as available.

 

[Shortround6]

Allison V-1710-73 / F4R
P-40K (and some refurbished P-40E) Hawk 87 Allison (mid-run)

Full throttle height is shown as 1150 hp at 3,000 rpm and 44.2" Hg manifold pressure @ 11,800'. (15 minute rating) [Dec 18 1942, revised Apr 25 1944]

And if you follow the 14,000ft altitude line up to the power line you get about 1060hp at between 39 and 40 inches. 14,500ft gives you about 1040hp at just under 39in
Going down to the 13,000ft line you get just under 1090hp.
The C-15 and -33 engines were originally supposed to give 1040hp at 14,300ft.
Army then wanted 1090hp at 13,200ft which is pretty much on track for the supercharger's capability. Trouble is when they tried for a 150hr test at the higher rating they broke the engine several times. In part due to a defective test stand (not discovered until later). Allison had to rebuild 277 engines at Allisons expense and the in-service engines were operated at lower power ratings (like a max rpm of 2770rpm) until the engines could be rebuilt/replaced. British engines (ex French) built in 1941 (?) may not have been rebuilt. Later engines got the beefed up parts.
The chart for the -73 shows this rather well. Also shows, not quite so clearly, that the engine was good for very close to the 1490hp at 4,300ft and the 1580hp at 2,500ft.
As I said early, they changed the intake manifolds and the backfire screens at times during this progression so exact manifold pressures are a little off.
Critical altitude is the altitude at which the supercharger can no longer supply the desired pressure. If you change the power you want and chose a new max pressure level you can pick any altitude you want as long as the power/pressure falls on that line. Going the other way I could pick 900hp at 18,000ft with 34in and maybe I could do that with 87 octane gas. Adjust the carb to fully open at 18,000ft and I have new 18,000ft critical altitude

All of the WEP settings fall under the highest line on the power chart. The supercharger can only flow so much air.
The Chart is for Zero RAM so adjust higher as needed for high speed level flight.

Some of the engine charts are mistaken. They put the no RAM numbers in the RAM columns.
But Full RAM only happens at high speed in level flight. If you are climbing 180mph you get a lot less RAM than you get at 360mph. Not 1/2, an awful lot less.

 

[Steamed_Banana]

Sure. but the bottom line is that the P-40C seemed to have a higher practical performance ceiling than the D / E / K, no matter how you slice it.

 

[Elan Vital]

Is there a power curve for the V-1710-33 online by the way? I'm curious how the curve compared to the Szydlowski-supercharged HS-12Ys, mostly whether the Szydlowski S-C reduced the power gap at certain altitudes in spite of an inherently weaker engine.

Something that has not been discussed much is whether the British would have sent the Tizard mission to the French in the same way they did to the Americans OTL. While less desperate with the French Metropole in the fight, they could still find valuable to share important technology to allow engineers on both sides of the Channel to progress faster. The ongoing plans to exchange aero equipment would suggest this would have been the case.

The 352 mph (566 kph) given for the P-40B would make it still competitive and valuable from October 1940 onwards when the first deliveries were expected. This is slightly or significantly superior to D520, VG 33 and Bloch 155 fighters which are the best French fighters as of that date, and remains comparable to the 12Y-51-powered D523s (about 570 kph) that may come online from July 1940 onwards or a bit later. It is only with the 12Y-51 VG 36 (October 1940) and Allison V-1710 C-15 VG 32 (December 1940) that the French get a substantially faster production fighter.

To be clear, the HS-12Z fighters, production D-55X series (of which the first 200 are powered by the 12Y-51), VG 50 and the Bloch 157 are all firmly 1941 designs at least, both considering the production schedules for older types and the time needed to switch production lines and complete development of the new airframes and engines (which were only at the prototype stage in June 1940). Some documents only anticipate some early prod/pre-production 12Z for late 1940, and mayyybe the D520 types beyond serial number 780 get produced before the end of the year (that's the serial number cutoff after which the 12Z D524 is meant to be made) but that's about it. That leaves a momentary period where the German Bf-190F has a clearer speed advantage over the VG 36 and VG 32 which would achieve about 590 kph, but at least the French caught up with and slightly outperformed the Bf 109E during the year.

The French negociated substantial deliveries of American engines with some slated to go to French airframes, including the R-2600 for bombers and the V-1710 C-15 and, per Cuny and Danel, possibly F3Rs down the line for the VG 32 and VG 50 fighters respectively (VG 50 being the Allison-powered equivalent to the VG 39 Bis/VG 40). The V-1710 C-15 already provided a non-negligible power advantage over the HS 12Y-51, depending on the power curve and availability of the Szydlowski-supercharged version, and the F3R provided a genuine advantage alongside the 12Z series.

There was a somewhat implicit division of labor with bombers as the Martin 167s and 187s on order and the DB-7s fill an intermediate role between the Breguet 693s and Bloch 175s (evolving with more powerful engines) on the lower end and the LeO and Amiot bomber on the slightly higher end. By 1940, France didn't really have any known aircraft projects in that niche and I suspect this was deliberate to focus on other types.

 

[tomo pauk]

Is there a power curve for the V-1710-33 online by the way?

On this site, the specific doc is here. Original chart is in the 'Vee's for victory' book.

Something that has not been discussed much is whether the British would have sent the Tizard mission to the French in the same way they did to the Americans OTL. While less desperate with the French Metropole in the fight, they could still find valuable to share important technology to allow engineers on both sides of the Channel to progress faster. The ongoing plans to exchange aero equipment would suggest this would have been the case.

Shoveling the supercharger section of the 14R 4/5 through the Bristol's throat would've helped the Hercules a good deal.
Perhaps an interesting thing would've been the adoption of the S-P swirl throttle for the newer radials, like the Hercules and 14R.

With France still fighting, there will be no invasion panic, the knock on effects might've included the adoption of the Spitfire III, the 6pdr, as well as the faster introduction and improvements of the Hispano cannon. Far less of the light tanks made in the UK, so more of the better tanks might've been produced. British gunners would've appreciated the early adoption of the more advanced AP shots, as well as the HE shells for their small guns, like the 2pdr and 6pdr. Perhaps an earlier introduction of a decent 75-76mm gun on the British tanks? Even if it is just a version of the French 75.
No pressing need for the 25 pdr to became an impromptu AT gun, so more shells can rain on the German positions.
Hispano engine might've received the 2-speed drive; after all, RR settled for the Farman's design for their engines. The 2-stage S/Cs would've also been nice to have. French tankers would've welcomed the multi-crew turrets.

The French negociated substantial deliveries of American engines with some slated to go to French airframes, including the R-2600 for bombers and the V-1710 C-15 and, per Cuny and Danel, possibly F3Rs down the line for the VG 32 and VG 50 fighters respectively (VG 50 being the Allison-powered equivalent to the VG 39 Bis/VG 40). The V-1710 C-15 already provided a non-negligible power advantage over the HS 12Y-51, depending on the power curve and availability of the Szydlowski-supercharged version, and the F3R provided a genuine advantage alongside the 12Z series.

French might also count on the -39 engine to be shipped by some time of Spring of 1941. Should get them an equivalent of the MC.202 when installed on the French fighters.

 

[Shortround6]

Hold on a minute here.

I'm going to focus intially on the Leo 451 since it has somewhat of a combat history, notably in the British-Vichy war in 1941. Leo 451 had superior range to any version of the B-25 as far as I'm aware, what I see is 1,800 miles for the LeO 451 vs 1,350 - 1,500 miles for the B-25. I am of course, aware that these vary by loadout and use of space, specific variant, cruise speed etc.. The Leo 451 also seems to potentially carry a larger bomb load (noted with the same caveats).

My source is a very old book in English and could well be wrong. Somewhere in this thread I believe there are some French sources.
However, Wiki is total BS for some things.
My old book for the LeO 451 says 1430miles with an 1100lb bomb load. Doesn't say what ferry range is. It does give bomb loads with 220 imp gal. 398 Imp gal, 530 imp gal and 712 Imp gals ( the 1100lb load)
Yes it was possible to put two 1100lb bombs and five 441lb bombs in the LeO 451 but that was with the 220 imp gal fuel load, You aren't going very far with that.
Most B-25s are credited with 1350-1500 mile ranges with a 3000-3200lb bomb load.
So lets compare apples to apples.

Leo 451 was also ~30 mph faster than the B-25 (308 mph vs 270-285 mph for B-25C)

True but again lets compare like to like.
Early B-25s (the first 40) had crap for guns and no armor and no protected tanks. But they were fast, 322mph?
The next 40 (B-25As) got armor, four of the wing tanks were protected (at the cost of 222 gal of fuel) and still had crap for guns, It was possible to fit a 412 gal tank in the bomb bay which came in handy a bit later.
the next 120 were the B-25B, 1st delivery was in Aug 1941 and about 50 of these were completed before Dec 7th and the rest after, however, back in Oct 1940 NA had gotten a contract for 863 B-25Cs, in Feb 1941 they got a contract for 1200 B-25Ds (basically Cs built at the new Kansas City factory. The First C flew on 9 Nov 1941 and the first D flew in Dec, first delivery's were about 2 months later.
The B-25Bs were the first with the top and bottom turrets which started to slowing down. The C & Ds got extra fuel tanks in the wings to bring wing tankage up to 974 US gallons in protected tanks. If you have a B-25C that can only do 270mph it needs a tune up and fresh plugs.

But more importantly, I think you are also forgetting that with regard to the French types, there are built and operational in May or June of 1940. The first combat deployment of the B-25 that I am aware of was in April of 1942.

Covered above.

In 1940, the US was flying these for medium bombers. Top speed 216 mph, range 900 miles, armament 3 x .30 caliber machine guns, 2,000 lb normal bomb load. No armor or self-sealing fuel tanks.

Hold on a minute here.
B-18s started to be delivered in 1937 (anybody want to see what the French were getting into service in 1937?_
Last one was completed in 1939, The B-18A with the shark nose, the last 38 (?) were completed to an amended contract as...............................

But we can indeed observe that the French have nothing like the R-2600 either ready to go or in development in 1940. That is the open question here that I see.

B-23

First flight July 27th 1939, the last of the 38 planes were delivered in sept 1940. All with R-2600 engines (granted the A model and not the B models used in the B-25s)
top speed was 282mph, guns sucked but the bomb bay would hold 4000lbs of bombs (Wiki lies). Range with 4000lb bomb load is listed as 1400 miles but (?). No armor and no protection. Requirement for the B-25 and B-26 had been issued 6 months before the prototype B-23 flew which explains the lack of further production orders.

The Swiss got the 12Y engine, based entirely on French specs I believe, up to roughly 1,300 hp.

That is not the generally accepted story although "based entirely on French Specs" could subject to interpretation.
One story is that it took until 1943 for the Swiss to get acceptable reliability from the 12Y-51 (several crashed aircraft) at 1030hp at 3250 meters (93 (octane fuel?)
The Saurer YS-2 made 1300hp or more for take-off but it got 4 valve heads, direct fuel injection, a new crankshaft and gained around 160-170kg.

If you want small look at something like the Japanese Ki-48.

It was a waste of resources and labor..............and crew.
4 men to deliver a 660lb bomb load?
Yes it is faster than Blenheim and it is better than Blenheim.....................................................................how?

So far as I know Bloch 170-174 series was used almost entirely as a reconnaissance aircraft, and seemed quite successful in that role (330 mph and a cruising speed of 290 mph was quite good for 1940) but it probably did have potential as a bomber, especially with a little further development.

They built about 23 of the bomber version with the larger bomb bay but in the chaotic situation in France the number that made it to French combat units was smaller, around 200 other airframes were in various stages of completion and another 200 (?) had component parts produced. There were a number of developments which show that it was one of the better French airframes. An attempt to use P&W R-1830 was made although the lower powered engines and same direction rotation cost about 40mph. Shortage of GR 14N engines force at least planes to be built.
The Bloch 175 was judged suitable as an operational trainer by the Luftwaffe and an order for the completion of 200 airplanes was given. From Oct 1940 to June 1941 56 planes were competed but then an order came to strip out all the engines, cowling, propellers, oil coolers and wiring and send them to a Messerschmitt factory. Then they tried to use spare HS 12Y engines. This took so long the Germans basicly gave up (march of 1942). Post war the French built about 80 torpedo bombers for the Aeronavale. Production ended in1950.

 

[Shortround6]

Sure. but the bottom line is that the P-40C seemed to have a higher practical performance ceiling than the D / E / K, no matter how you slice it.

We have explained several times that is weight difference between the planes, nothing to do with the engines or supercharger.
Put 1200lbs of lead in a P-40C and see how well it flys at high altitude.

 

[Shortround6]

. Far less of the light tanks made in the UK, so more of the better tanks might've been produced

The little light tanks were already out of production and work on the Tetrarch light tank wound up taking up huge amount of resources for 100-177 actual tanks. The need for a 'bespoke' engine that was not used in anything else (except the Harry Hopkins) was a loss of engineer hours.
UK tank design/production was an absolute mess. With 6 different 2pdr armed tanks needing 5 different engines (and a slightly fewer number of transmissions) all needing development and testing and modification the little 6 ton light tanks were the least of the British problems. Build another 100-150 VIC with Besa guns and send them off to Abyssinia, Syria, Malasia and Borneo. Cost might have been 40-50 of the bigger tanks? A small, tiny drop in the bottom corner of the huge bucket that was the waste of the Covenanter program.

 

[Steamed_Banana]

Hold on a minute here.

My source is a very old book in English and could well be wrong. Somewhere in this thread I believe there are some French sources.
However, Wiki is total BS for some things.
My old book for the LeO 451 says 1430miles with an 1100lb bomb load. Doesn't say what ferry range is. It does give bomb loads with 220 imp gal. 398 Imp gal, 530 imp gal and 712 Imp gals ( the 1100lb load)
Yes it was possible to put two 1100lb bombs and five 441lb bombs in the LeO 451 but that was with the 220 imp gal fuel load, You aren't going very far with that.
Most B-25s are credited with 1350-1500 mile ranges with a 3000-3200lb bomb load.
So lets compare apples to apples.

True but again lets compare like to like.
Early B-25s (the first 40) had crap for guns and no armor and no protected tanks. But they were fast, 322mph?
The next 40 (B-25As) got armor, four of the wing tanks were protected (at the cost of 222 gal of fuel) and still had crap for guns, It was possible to fit a 412 gal tank in the bomb bay which came in handy a bit later.
the next 120 were the B-25B, 1st delivery was in Aug 1941 and about 50 of these were completed before Dec 7th and the rest after, however, back in Oct 1940 NA had gotten a contract for 863 B-25Cs, in Feb 1941 they got a contract for 1200 B-25Ds (basically Cs built at the new Kansas City factory. The First C flew on 9 Nov 1941 and the first D flew in Dec, first delivery's were about 2 months later.
The B-25Bs were the first with the top and bottom turrets which started to slowing down. The C & Ds got extra fuel tanks in the wings to bring wing tankage up to 974 US gallons in protected tanks. If you have a B-25C that can only do 270mph it needs a tune up and fresh plugs.


Covered above.

Hold on a minute here.
B-18s started to be delivered in 1937 (anybody want to see what the French were getting into service in 1937?_
Last one was completed in 1939, The B-18A with the shark nose, the last 38 (?) were completed to an amended contract as...............................

B-23
View attachment 896100
First flight July 27th 1939, the last of the 38 planes were delivered in sept 1940. All with R-2600 engines (granted the A model and not the B models used in the B-25s)
top speed was 282mph, guns sucked but the bomb bay would hold 4000lbs of bombs (Wiki lies). Range with 4000lb bomb load is listed as 1400 miles but (?). No armor and no protection. Requirement for the B-25 and B-26 had been issued 6 months before the prototype B-23 flew which explains the lack of further production orders.

That is not the generally accepted story although "based entirely on French Specs" could subject to interpretation.
One story is that it took until 1943 for the Swiss to get acceptable reliability from the 12Y-51 (several crashed aircraft) at 1030hp at 3250 meters (93 (octane fuel?)
The Saurer YS-2 made 1300hp or more for take-off but it got 4 valve heads, direct fuel injection, a new crankshaft and gained around 160-170kg.

It was a waste of resources and labor..............and crew.
4 men to deliver a 660lb bomb load?
Yes it is faster than Blenheim and it is better than Blenheim.....................................................................how?

They built about 23 of the bomber version with the larger bomb bay but in the chaotic situation in France the number that made it to French combat units was smaller, around 200 other airframes were in various stages of completion and another 200 (?) had component parts produced. There were a number of developments which show that it was one of the better French airframes. An attempt to use P&W R-1830 was made although the lower powered engines and same direction rotation cost about 40mph. Shortage of GR 14N engines force at least planes to be built.
The Bloch 175 was judged suitable as an operational trainer by the Luftwaffe and an order for the completion of 200 airplanes was given. From Oct 1940 to June 1941 56 planes were competed but then an order came to strip out all the engines, cowling, propellers, oil coolers and wiring and send them to a Messerschmitt factory. Then they tried to use spare HS 12Y engines. This took so long the Germans basicly gave up (march of 1942). Post war the French built about 80 torpedo bombers for the Aeronavale. Production ended in1950.

LeO 451s were carrying more ordinance than 1,100 lbs in Syria. I'll post some examples later.

B-23 was little more than a prototype, and was clearly inferior to the Leo 451.

Leo 451 had a 20mm cannon for defense, armor and self sealing fuel tanks, and made 300 mph with all that on board, in mid 1940.

The first B-25s went into action in the Pacific in April 1942, do you know of any earlier deployments?

France has 10 times the population and equivalently larger arms industry than Switzerland, not to mention they were already working on the 12Y/Z series in 1940 so I'm confident they could achieve the same results as the Swiss but sooner.

The Ki-48 had a vastly superior operational history to the Blenheim and was still being used successfully on the front line against US and British Forces well into 1943. It's better in the sense that far fewer were shot down per mission, it was more accurate bomber, and it caused more harm to Allied targets than the Blenheim did to Axis targets. It's objectively inaccurate to claim that the Ki-48 was a waste of resources, labor and / or crew.

It wasn't a perfect bomber but those are pretty rare in the real world.

 

[Steamed_Banana]

We have explained several times that is weight difference between the planes, nothing to do with the engines or supercharger.
Put 1200lbs of lead in a P-40C and see how well it flys at high altitude.

I'm not yet convinced that is actually the case, but even if it is, the fact remains, the P-40B/C was a better fit for the needs of the French in 1940-41