WI: Wanked Spitfires?

[phx1138]

After reading this thread, I found myself agreeing with most of it, but still found one or two things omitted. Like the increased internal fuel possible, & the increased airframe stressing, this page suggests would be needed to achieve it. (With all respect, JustLeo's proposal, pictured below, while lovely, is just not on.)


Therefore, let me propose the idealized Spitfire. To start, cutdown fuselage and bubble (blister) canopy. Maximum internal fuel (if I have my math right) 262 gallons (forward fuselage 48 & 37 {lower/upper}, aft 48 & 33 {lower/upper}, 20 gal seat {from PR Spit; some said 29 in the linked thread, so anyone who can clear up the confusion, please do}, wing leading edges 18 &18 {port/starboard; based on PR Spit}, & 20 & 20 outboard {port/starboard; replacing gun bays}). Two Oerlikon FFs in wing roots. Two 12.7mm Brownings in cowl or cheeks (if practical). Four 12.7mm Brownings in OTL gearwells. (No outboard guns.) Wing modified with straight edge & outboard taper for simplicity, stressed to carry greater internal fuel & armament weight, plus two 75 gal teardrop (or "torpedo") wing drop tanks & one 120 gal teardrop (or "torpedo") belly tank. (Airframe generally stressed for higher weight than OTL 9500pd maximum.) Main gear struts stronger, possibly with additional fold to save space; main gearwheels somewhat smaller (& magnesium), to save weight & space; mounted to retract into OTL "twin" gun bays. Hollow-bladed prop (4 blades?). Merlin engine with SU-derived "fuel injector" at supercharger plus Mikulin-derived swirl inducer to reduce inlet charge temperature & supercharger drive losses. Date of introduction to be about September 1940, just missing the Battle of Britain.

Given the wing changes, is the amount of fuel in leading edges still practical?

Given this is the standard late 1940 Spit (Mark III? IV?), what influence does that have on RAF operations around the world? Does the long range butterfly away (or delay) long range P-47 or P-51 development? Does it offer the chance of reduced losses on USAAF missions?

Is there any prospect to build this aircraft in Canada?

Are there features that even this idealized Spitfire is lacking?

Am I beating a dead thread? ( )

 

[tomo pauk]

The 'flying AA battery and fuel tank' Spitfire probably will not fly well with Merlin of 1940, since it will be too heavy. Flying with full both rear tanks was straight & level. For the British needs, a mature drop tank installation plus a single 30-40 tank behind the pilot is feasible, useful and will not hamper the flying characteristics and performance much.
Granted, once the engine power is up by a considreable amout (talk Griffons, or 2-stage Merins), a major increase of weight due to major increase of internal fuel & armament is far easier to deal with.
Some other remarks:
Oerlikon (and Hispano) cannons can't be synchronised due to working principle - a reason why those either were installed outboard of the prop disc, or installed as prop gun (will not work with radials, plus as-designed Rolls Royce engines, V-1710, Sabre...). OTOH, having 4 HMGs installed instead of 8 LMGs (with proviso that British start mass production of the former) is a very good suggestion.
The shape of wing was not a reason for slow production of Spitfires, but the manufacturing process. Instead of whole ribs being stamped as singe pieces (like on Bf 109, P-36/40, Typhoon, Zero...), they were mostly built up from pieces (like on MC.200/202/205, Regianne or Fiat fighters). Same for fuselage formers & stringers. As a result of that, manufacturing hours skyrocketed (now we know why Germans quickly shelved the idea that Italian fighters are to be produced in Germany, and a partial reason why Italian fighters were produced in such low numbers).
Spitfire wing internals
Bf 109 wing internals

Change from float-carb to pressure carb does not just mean that negative G problems with fuel are dealt with, the better carb also can add up to 10 mph and service ceiling (per British tests). The Polikovskiy's swirl throttle, as found on wartime Mikulin engines and on late-war Klimov engines (VK-107 and rare -108s that never worked well) can help down low, especially if the engine has just 1 S/C speed tailored for higher altitudes, and fuel octane value is not reliably high. For improvement of power at all altitudes, people at RR need to streamline the air intake before the S/C - a thing that Hooker did 1st with Merlin XX with immediate results, like 20% increase of power vs. Merlin III or Merlin VIII. Combine that with a better carb, copy the exhausts from Bf 109D, improved streamlining of historical Spitfire III (= internal BP glass, covered main wheel wells, retractable & covered tail wheel) and there is a 400 mph Spitfire ready for the Adler Tag.

Bearing of the improved Spitfire on USAF bomber campaign will depend on a lot of factors, and Americans might felt hard pressed to match the SPitfire with thier own fighters. That might see a P-47 with actual drop tanks in service already by spring of 1943, and might yield with V-1650-1 powered P-51 instead of A-36.

 

[phx1138]

The 'flying AA battery and fuel tank' Spitfire probably will not fly well with Merlin of 1940, since it will be too heavy. Flying with full both rear tanks was straight & level. For the British needs, a mature drop tank installation plus a single 30-40 tank behind the pilot is feasible, useful and will not hamper the flying characteristics and performance much.

I imagined the aft tanks being used on climb-out & form up, & outbound, where Cg issues aren't critical. Too heavy to fly at all hadn't crossed my mind.

Candidly, I'd have deleted the forward fuselage tanks & moved the cockpit forward, but the benefit to ground handling isn't so significant, & the loss of range isn't worth it. (I'd love a nosewheel option...but I wouldn't expect one. )

I also have my doubts the 20gal outboard tanks are a good idea, given the effect on roll rate.

And thinking of roll rate, I'd also have metal-covered ailerons, slightly larger, but less deflection, like the late Spits.

Granted, once the engine power is up by a considreable amout (talk Griffons, or 2-stage Merins), a major increase of weight due to major increase of internal fuel & armament is far easier to deal with.

Care to push that forward? And offer ideas how it's possible? (IMO, Griffon Spits, while sexy as all hell, are pushing it before about '44. Also, the change is so big, they really ought to be renamed Spittoon, or something. They're not really Spitfires any more, IMO.)

Oerlikon (and Hispano) cannons can't be synchronised due to working principle

Somehow, I'd forgotten that...

having 4 HMGs installed instead of 8 LMGs (with proviso that British start mass production of the former) is a very good suggestion.

That's actually my original default idea. (I have a liking for a couple of cowl guns, just because. )

The shape of wing was not a reason for slow production of Spitfires, but the manufacturing process. Instead of whole ribs being stamped as singe pieces (like on Bf 109, P-36/40, Typhoon, Zero...), they were mostly built up from pieces

That was in the linked thread, & I managed to overlook it... Yeah, fix that early. Simplifying the wing isn't a bad idea in any case, IMO.

Change from float-carb to pressure carb does not just mean that negative G problems with fuel are dealt with, the better carb also can add up to 10 mph and service ceiling (per British tests).

I'd take either. Both is a definite plus.

The Polikovskiy's swirl throttle, as found on wartime Mikulin engines and on late-war Klimov engines (VK-107 and rare -108s that never worked well) can help down low, especially if the engine has just 1 S/C speed tailored for higher altitudes, and fuel octane value is not reliably high.

I like it for the improved efficiency, if nothing else.

For improvement of power at all altitudes, people at RR need to streamline the air intake before the S/C - a thing that Hooker did 1st with Merlin XX with immediate results, like 20% increase of power vs. Merlin III or Merlin VIII. Combine that with a better carb, copy the exhausts from Bf 109D, improved streamlining of historical Spitfire III (= internal BP glass, covered main wheel wells, retractable & covered tail wheel) and there is a 400 mph Spitfire ready for the Adler Tag.

Works for me. I'm thinking the airflow into the carb & less/no induced icing means no flow restriction there, too, for what difference it makes. (I personally would love an FI Merlin, but that seems to be asking a bit much for the Allies.)

Bearing of the improved Spitfire on USAF bomber campaign will depend on a lot of factors, and Americans might felt hard pressed to match the Spitfire with thier own fighters. That might see a P-47 with actual drop tanks in service already by spring of 1943, and might yield with V-1650-1 powered P-51 instead of A-36.

I'm wondering, given a LR escort-capable Spit before 1943, if the Brits even ask for the NA-73. (Presuming the *Spitfire's Merlin, or Griffon, powerplant keeps up with its weight.) If the new design pushes demand for the Griffon up, care to guess about the chances of a Griffon-powered NA-73 to start?

 

[tomo pauk]

...
Care to push that forward? And offer ideas how it's possible? (IMO, Griffon Spits, while sexy as all hell, are pushing it before about '44. Also, the change is so big, they really ought to be renamed Spittoon, or something. They're not really Spitfires any more, IMO.)

RR not making or cancelling the Exe, Peregrine and Vulture well before the ww2, and using the 'R' engine as base can certainly improve the Griffon timeline. Talk early 1942 for in-service 1-stage supercharged Griffon, and early 1943 the 2-stage S/Ced version. Pack the Spitfire with fuel, 2-stage Griffon in the nose and air war over Germany goes very bad for Luftwaffe.

I'm wondering, given a LR escort-capable Spit before 1943, if the Brits even ask for the NA-73. (Presuming the *Spitfire's Merlin, or Griffon, powerplant keeps up with its weight.) If the new design pushes demand for the Griffon up, care to guess about the chances of a Griffon-powered NA-73 to start?

NA-73 was a result of 1940 British requirement, that never called for long range escort; British were andamant in notion that escort fighter as a concept does not work, and BC and FC were supposed to fight their separate wars per RAF doctrine. It took them until mid-1944 to start modifying the Spitfires and Tempests for long range work, by what time LW was at back foot due to P-47s and P-51s.
The NA-73 might get the Griffon from RR in the UK? As-is, it will be already more than useful with what was made by Packard, just that it needs to be done.

 

[phx1138]

RR not making or cancelling the Exe, Peregrine and Vulture well before the ww2, and using the 'R' engine as base can certainly improve the Griffon timeline. Talk early 1942 for in-service 1-stage supercharged Griffon, and early 1943 the 2-stage S/Ced version. Pack the Spitfire with fuel, 2-stage Griffon in the nose and air war over Germany goes very bad for Luftwaffe.

I can definitely live with that. Even allowing the Griffon costs some fuel capacity for size & weight reasons (IIRC, it does), & allowing it burns more fuel, it's bad news for Luftwaffe. It makes me think the Ta-152 (or a better FW-190) as an answer has to happen sooner.

I maintain a new name is warranted.

NA-73 was a result of 1940 British requirement, that never called for long range escort; British were andamant in notion that escort fighter as a concept does not work, and BC and FC were supposed to fight their separate wars per RAF doctrine. It took them until mid-1944 to start modifying the Spitfires and Tempests for long range work, by what time LW was at back foot due to P-47s and P-51s.

Huh. So the "flying gas tank" option is effectively a non-starter, unless FC means to Rhubarb all the way to Berlin... Bugger.

The NA-73 might get the Griffon from RR in the UK? As-is, it will be already more than useful with what was made by Packard, just that it needs to be done.

Presuming the Griffon is advanced as described, a swap with the V1710 being trialled seems a reasonable outcome--providing *Spitfire production isn't already making the NA-73 moot, & providing the Spittoon isn't absorbing all Griffon production as it is.

 

[Helicon One]

How does the weight of a .50 Browning and ammo* compare with a .303? Given that upgunning the Brownings seems to be one of the first things AH talks about in relation to Spitfires, is there a significant weight penalty for doing so?

*I guess the obvious answer is 'it depends how much ammo you want it to carry'.

 

[phx1138]

How does the weight of a .50 Browning and ammo* compare with a .303? Given that upgunning the Brownings seems to be one of the first things AH talks about in relation to Spitfires, is there a significant weight penalty for doing so?

Without rereading the original thread, I can't say offhand. The .50s are bound to be a bit heavier, but there's only going to be 4 of them (perhaps 6), not 8, in each wing. (And that's presuming my cowl guns are non-starters. )

 

[tomo pauk]

How does the weight of a .50 Browning and ammo* compare with a .303? Given that upgunning the Brownings seems to be one of the first things AH talks about in relation to Spitfires, is there a significant weight penalty for doing so?

*I guess the obvious answer is 'it depends how much ammo you want it to carry'.

Single .50 BMG round was about 4.5-5 times heavier than the US .30-06; we can assume perhaps 5:1 weight ratio vs. .303.

Spitfires carried 300 rounds per gun during the BoB; for 8 LMGs it is 2400. One fifth of that is 480 rounds. Divide on 4 HMGs = 120 rd/gun.
The .50 BMG was firing at 600 rpg in 1940 and before (upped to 800 rpg by the end of 1940), that is half of what .303 Browning was making. So we'd need to add another 30 rd/gun (obviously 120 rds total) to equal the firing time of what Spitfires had in BoB.

Apart from the .50 BMG, the British could've taken a good look at different HMGs made by Vickers, the Breda-SAFAT 12.7mm that fired at 750 rd/min and used a bit lighter ammo (that is both good and bad), or perhaps see what the Belgians were doing pre-war - they have had on offering several their versions of the BMG that went between 1000 and 1200 rd/min.

About the cannons - do make a deal with Oerlikon ASAP. Hispano cannon was good, but it was a later development, that meant the RAF didn't have cannon-armed fighters in service en masse before 1941. Belt-fed cannons were not widely spread in RAF inventory before 1942.
So back to the Oerlikons. One suggestion is their FF(F), just make a deal for a round that fires ~100g shell with a bit extra propellant so the MV can go to ~700 m/s; buy big drums (75rd drum along with FF cannon was offered to the RAF well before the war, but pick the 90 rd drum instead); the deal must include belt feed for any cannon RAF buys from them. Belt-fed Oerlikon was offered to the RAF in early 1930s, nothing came from that. Advantage of the FF is that it was very light, at 25-28 kg it was lighter than HMGs.
Another proposal is the Oerlikon L (later FFL). Still not to heavy (lighter than the Hispano or the big Oerlikon S (later FFS)), a bit lower RoF than FF, but with higher MV. Japanese Navy bought it for their aircraft, and later developed the belt feed on their own.
Article by Tony Williams about that cannon.
The Oerlikon S was widely used, either in AA form (both from ships and ground), and was licence produced in France for their fighters from mid-1930s (one per fighter). I don't think this one is a sensible suggestion for arming the Spitfires, being the biggest and heaviest of the lot, with lowest RoF, and heaviest & bulkiest ammo.

 

[phx1138]

.50 BMG was firing at 600 rpg in 1940 and before (upped to 800 rpg by the end of 1940), that is half of what .303 Browning was making. So we'd need to add another 30 rd/gun (obviously 120 rds total) to equal the firing time of what Spitfires had in BoB.

Given the .50 hits quite a bit harder, IMO we could reasonably sacrifice some ammo; say, 10sec fire, versus 14 OTL? (IIRC, that was standard.)

That raises the obvious question: do we want a *Spitfire optimized against fighters, or bombers? Against fighters, 4xMG makes most sense; against bombers, 2x20mm (or even 4x). Mixing, 2xMG & 2x20mm in wings, seems a good compromise (tho I'm reminded what Colin Chapman thought of that ). (Can I return to the option of a pair of cowl or cheek MG, to make up the difference? Is that horse dead, yet? )

Belgians were doing pre-war - they have had on offering several their versions of the BMG that went between 1000 and 1200 rd/min.

That IMO improves the MG against fighter targets, but demands a consummate increase in ammo load... If this site is correct, 670 rounds of .50 BMG would weigh in the range of 77kg. That doesn't seem outrageous, given a leading edge or outboard wing fuel tank would be 60-65kg of fuel (plus the tank weight).

IMO, the short-barrelled Oerlikon FF is the ideal cannon choice: available, reliable, & less draggy compared to the longer-barrelled Hissos.

 

[Cryhavoc101]

First of all lets not throw the baby out with the bath water

Before we consider the Spitfire as a LR Escort fighter lets remember that its job and one it did admirably was to prove the adage that the 'bomber will always get through' a lie.

In order to do that it needed to be able to take off climb rapidly, have an armament suitable to remind the Luftwaffe of the error of their ways - rinse and repeat several times a day.

Jacking it up with 4 large heavy autocannon (27kgs for the FF) and doubling the fuel will very likely 'ruin it' as an interceptor until later in the war when engine power rapidly increases.

A Mk2 Browning .303 weighed 10 KGs - 350 round of .303+link also weighed 10 KGs - so an 8 gun outfit = 160 KGs

It also fired at 1150 RPM x 8 = 9200 RPM or about 150 rounds a second

A brace of 4 x 27 KG FF (108 KGs) plus ammo - which I understand to be about 12 x the weight of 303 ammo - so A lot more than the original 160 kgs - a 60 round drum is likely to be the largest at the time and I have no clue how that would be installed in a Spitfire wing and it would only give about 7 seconds of 'get some' with a combined ROF of 2080 RPM or 35 RPS but then that was the same issue with the HS404 at the time.

I am not convinced that 50 cal is the answer either - its also 27 KGs (AN/M2 light aircraft version) and the ammo and link is about 3 x heavier than .303 and link so again the 4 guns and ammo is going to be as heavy if not heavier than the 4 guns on the original

Its ROF is about 800 RPM so a combined ROF of a 4 gun fit is about 2800 RPM or 47 RPS

Being a closed bolt short recoil gun it does lend itself to being a synchronised cowl gun (which the RAF seemed to have abandoned in the 30's and I have never discovered why?)

Now that all being said the job of the Spitfire and Hurricane was ultimately to intercept and destroy/dissuade enemy bombers - and nothing says 'fuck off back to whence you came and never darken our doorstep again' to a twin engine bomber like 20mm rounds do relative to .303

So lets entertain the idea that pre war experimentation which had already established that 4 x 303 and later 8 x 303 was not enough to down a twin engine bomber of the day with a 2 second burst are taken even further and we see the RAF reaching the full overwhelming conclusion that a cannon is needed and see the FF cannon as available by the late 30s and begin to address the problem head on in order to reliably down bombers.

Now the problems remain with the fitting - and for the Spitfire with it thin wing - the issue is exacerbated by the problems of keeping the outer gun in each wing from freezing (one of the reasons why most cannon armed WW2 Spits only had 2 Cannon - 1 in each wing as hot air from the Engine could not be reliably rooted to the outer cannon) - The European Air war being fought at somewhat more rarefied altitudes than other theatres.

Now for the Hurricane with its chunky wing - not so much an issue - 4 x FF guns with 60 round drums (enclosed with a bulge) is just about doable and as engine power increases - that could be increased to 6 guns!

For the Chad Spit I propose 1 gun per wing as inboard as possible and then I entertained the idea of having 2 Browning AN/M2 cowl guns - but where?

There is no room for them (Fuel tanks, oil tanks and supercharger annoyingly in the way) and they would have to be near the engine for the mechanical synchronisation to enable them to shoot through the prop.

So we are back to the wings.

So in 1940 its either a pair of FFs and 2 AN/M2 or a pair of FFs and 4 M2 Browning 303s (which is very close to what happened) all wing mounted.

I have tried to find the dimensions of the FF over the HS404 - but it may be possible that the FF is smaller and that the heating issues might be solvable earlier or the gun being available earlier results in an effective earlier resolving???

 

[Crowbar Six]

There is a good reason to go to a .50 cal in that it has better penetration than a .303 and also has a bigger payload for incendiary/high explosives. .50 ball will do more damage to an aircraft structure than a rifle caliber projectile but if you substitute .50 API it becomes more than capable of making some pilots day truly miserable.. So opting for 4 or 6 .50 cal MG's may well make more sense than 8 or 12 .303 caliber machine guns.

When there are practical 20mm or 30mm cannon then it makes sense to trade up to cannon over machine guns.

 

[King Augeas]

First of all lets not throw the baby out with the bath water

Before we consider the Spitfire as a LR Escort fighter lets remember that its job and one it did admirably was to prove the adage that the 'bomber will always get through' a lie.

In order to do that it needed to be able to take off climb rapidly, have an armament suitable to remind the Luftwaffe of the error of their ways - rinse and repeat several times a day.

Yeah performance and interception times are key - better to have adequate firepower when and where you need it, than have your quad 20mm bomber-whacker lumbering 2000' below the action. So heavier armament is nice, but watch the weight.

 

[phx1138]

Before we consider the Spitfire as a LR Escort fighter lets remember that its job and one it did admirably was to prove the adage that the 'bomber will always get through' a lie.

In order to do that it needed to be able to take off climb rapidly, have an armament suitable to remind the Luftwaffe of the error of their ways - rinse and repeat several times a day.

Yeah performance and interception times are key - better to have adequate firepower when and where you need it, than have your quad 20mm bomber-whacker lumbering 2000' below the action. So heavier armament is nice, but watch the weight.

For the earlier Marks, yes. For this notional Mark III*, appearing after the Battle of Britain, less so.

Jacking it up with 4 large heavy autocannon (27kgs for the FF)

I wouldn't go that far until the Griffon is standard, sometime in late '43 or early '44.

I am not convinced that 50 cal is the answer either

IMO, it's the best available compromise between the .303 & the 20mm.

So lets entertain the idea that pre war experimentation which had already established that 4 x 303 and later 8 x 303 was not enough to down a twin engine bomber

Perhaps instead rely on the BoB experience to prove it?

I entertained the idea of having 2 Browning AN/M2 cowl guns - but where?

There is no room for them (Fuel tanks, oil tanks and supercharger annoyingly in the way) and they would have to be near the engine for the mechanical synchronisation to enable them to shoot through the prop.

I don't suppose the forward fuselage tank(s) could be removed? I've imagined one under the cockpit; was there space for more than the 20gal (or so) of the PR Spits? The supercharger...I imagine that could be relocated (couldn't it?).

So in 1940 its either a pair of FFs and 2 AN/M2

As noted upthread (slightly), I tend toward the 4xM2 until later.

 

[tomo pauk]

...
IMO, the short-barrelled Oerlikon FF is the ideal cannon choice: available, reliable, & less draggy compared to the longer-barrelled Hissos.

Not just that. You can have two Oerlikon FF cannons for the weight of single Hispano or Oerlikon S.

Jacking it up with 4 large heavy autocannon (27kgs for the FF) and doubling the fuel will very likely 'ruin it' as an interceptor until later in the war when engine power rapidly increases.

FF was light and small.

A Mk2 Browning .303 weighed 10 KGs - 350 round of .303+link also weighed 10 KGs - so an 8 gun outfit = 160 KGs
It also fired at 1150 RPM x 8 = 9200 RPM or about 150 rounds a second

The 8 .303 battery was a very good choice when the decision was made.

A brace of 4 x 27 KG FF (108 KGs) plus ammo - which I understand to be about 12 x the weight of 303 ammo - so A lot more than the original 160 kgs - a 60 round drum is likely to be the largest at the time and I have no clue how that would be installed in a Spitfire wing and it would only give about 7 seconds of 'get some' with a combined ROF of 2080 RPM or 35 RPS but then that was the same issue with the HS404 at the time.

Pre war, Oerlikon was offering 90 rd drums; RAF was offered with 75 rd drum for Spitfire before ww2 ('Spitfire - the history' by Morgan & Shacklady, pg. 61). The ammo for FF (and FFL) was more slender than for the S. Germans used 100 rd box in their experimental 'cannon bird' He 112 during the Spanich civil war. Then there is possibility for belt feed.
Unfortunately, RAF didn't put much emphasis on cannons until they saw French and Germans installing the cannons on their fighters.
On the other hand, both Spitfires and Hurricanes with mixed batteries would've worked fine in 1940 (eg. 2 cannon + 4 LMGs), with much improved firepower and without much decrease of performance.

I am not convinced that 50 cal is the answer either - its also 27 KGs (AN/M2 light aircraft version) and the ammo and link is about 3 x heavier than .303 and link so again the 4 guns and ammo is going to be as heavy if not heavier than the 4 guns on the original
Its ROF is about 800 RPM so a combined ROF of a 4 gun fit is about 2800 RPM or 47 RPS

The RoF of the .50 BMG when RAF was shopping for new armament was 600 rd/min; Americans upped the RoF by some time of mid-late 1940.

Being a closed bolt short recoil gun it does lend itself to being a synchronised cowl gun (which the RAF seemed to have abandoned in the 30's and I have never discovered why?)

.50 BMG was synchronised in many aircraft (P-39, early P-40s, some P-36s and P-43s, Mustang I and A-36). On the other hand, I can't recall any MG that was synchronised with Merlin in the nose.

So lets entertain the idea that pre war experimentation which had already established that 4 x 303 and later 8 x 303 was not enough to down a twin engine bomber of the day with a 2 second burst are taken even further and we see the RAF reaching the full overwhelming conclusion that a cannon is needed and see the FF cannon as available by the late 30s and begin to address the problem head on in order to reliably down bombers.

Now the problems remain with the fitting - and for the Spitfire with it thin wing - the issue is exacerbated by the problems of keeping the outer gun in each wing from freezing (one of the reasons why most cannon armed WW2 Spits only had 2 Cannon - 1 in each wing as hot air from the Engine could not be reliably rooted to the outer cannon) - The European Air war being fought at somewhat more rarefied altitudes than other theatres.

Thin wing of the spitfire allower for big Hispano with it's big ammo to be instaled, sometimes 4 per aircraft. Ergo, the small FF with it's slender ammo will have even easier time to fit. But yes, it might be a good idea to keep the numbers of cannon to 2 per A/C until the heating is resolved in satisfactory manner.

For the Chad Spit I propose 1 gun per wing as inboard as possible and then I entertained the idea of having 2 Browning AN/M2 cowl guns - but where?
There is no room for them (Fuel tanks, oil tanks and supercharger annoyingly in the way) and they would have to be near the engine for the mechanical synchronisation to enable them to shoot through the prop.

Yes, front fuselage was packed with crucial items so a fuselage armament is going to induce some big rework - better keep it as-is.
Fuselage is the best place for fuel tanks anyway.

So we are back to the wings.
So in 1940 its either a pair of FFs and 2 AN/M2 or a pair of FFs and 4 M2 Browning 303s (which is very close to what happened) all wing mounted.

Agreed.

I have tried to find the dimensions of the FF over the HS404 - but it may be possible that the FF is smaller and that the heating issues might be solvable earlier or the gun being available earlier results in an effective earlier resolving???

Having the cannons available pre-war might lend to fixing the heating problems in a timely manner. For example, a good deal of waste heat emanating from coolers was used to heat the gun bays on the later Spitfires, like the Mk.IX (the heating system that used exhaust gasses to heat the guns was abandoned).

 

[Cryhavoc101]

There is a good reason to go to a .50 cal in that it has better penetration than a .303 and also has a bigger payload for incendiary/high explosives. .50 ball will do more damage to an aircraft structure than a rifle caliber projectile but if you substitute .50 API it becomes more than capable of making some pilots day truly miserable.. So opting for 4 or 6 .50 cal MG's may well make more sense than 8 or 12 .303 caliber machine guns.

When there are practical 20mm or 30mm cannon then it makes sense to trade up to cannon over machine guns.

Problem is the 'lighter' AN/M2 is only really available in 1940 onwards and so the RAF would have even less time to debug issues than with the FF or HS404

Also when I say lighter - the gun is nearly 3 x the weight (27 kgs) of a Mk 2 Browning (10 kgs) and the ammo is also 3x the weight of 303 ammo - and its ROF is substantially slower 800 RPM verses 1150 RPM.

And if as the OP has suggested the RAF get the FF pre war then this weapon is 27 kilos - the same weight as the later 'lighter' AN/M2 50 cal - so why would they go 50 cal?

The RAF concluded that the weight penalty of the 50 cal did not over weigh any damage increase per hit over 303 while the same was not true of the cannon which retained its effectiveness beyond both 303 and 50 cal effectvie range and if they did go to the FF pre war then I cannot see the 50 cal being a starter on British built aircraft.

The Americans managed to muddle through with the AN/M2 50 cal but everyone else moved to Cannon pretty much as soon as they could

The Americans would have moved to cannon if they had managed to get them to work reliably - and its a good job the Japanese did not armour their aircraft and install self sealing baffles in their tanks (mind you I can see the Zero being a pig if they had)

In the equation Bullet mass and effect + ROF + weight - going to cannon made a lot more sense

Unfortunately 3 other parts of the equation are getting it to fit + reliability + ammo supply

In 1940 and before 20mm cannon on aircraft are pretty much limited to 60 round drums - and this is where the Mk2 Browning and AN/M2 have an advantage in that they already have a belt feed allowing a large number of rounds to be carried and they worked reliably.

OTL the major 'players' struggled with this equation - as we are here it seems.

 

[phx1138]

Not just that. You can have two Oerlikon FF cannons for the weight of single Hispano or Oerlikon S.

True, but IMO, there's an issue of space, both for the cannon & the ammo/feed, especially if we're adding an outboard wing tank. I'm not a fan of the "distributed" guns, so if possible, I'd like to keep them in one gunbay: 2x12.7 or 1x12.7 & 1x20mm/side. (I wouldn't howl about a 12.7mm inboard, nearer the wing root, each side...)

Pre war, Oerlikon was offering 90 rd drums; RAF was offered with 75 rd drum for Spitfire before ww2 ...Then there is possibility for belt feed.

I much prefer belt feeds, for simplicity & weight: I don't see the drum adding a benefit, & it makes packaging more complicated & difficult.

.50 BMG was synchronised in many aircraft (P-39, early P-40s, some P-36s and P-43s, Mustang I and A-36). On the other hand, I can't recall any MG that was synchronised with Merlin in the nose.

Here's another idea: what about a "beard" mounting, instead? If there's no room (or clearance) in the cowl, tuck them underneath. (Think of the proposal for the A-36/P-51 prototype, like this: )

a good deal of waste heat emanating from coolers

That reminds me: could the Spit (or others) have used buried rads & boundary layer scoops, rather than external scoops?

 

[Cryhavoc101]

on Cowl guns

Here is a P40 IIB Note the position of the 2 Cowl mounted 50 cals (numbered as 4) - also note the large ammo hoppers (numbered as 6 - including the spent cases chute)

And then note how busy the area is in the Spitfire - no room for a pair of synchronised AN/M2 and ammo hoppers

 

[tomo pauk]

Here's another idea: what about a "beard" mounting, instead? If there's no room (or clearance) in the cowl, tuck them underneath. (Think of the proposal for the A-36/P-51 prototype, like this:View attachment 546514 )

Where the Mustang I and A-36 (not just prototype) have had 'beard' gus & ammo, Spitfire had oil tank.

That reminds me: could the Spit (or others) have used buried rads & boundary layer scoops, rather than external scoops?

Spitfire (and Bf 109, for example) used half-burried radiators; external scoops were used on many Soviet and Italian fighters. Also on on P-51 series (granted with each iteration they were improved (4 times during the ww2)). The wing position does not favor sticking out the boundary layer spliter/scoop on Spitfire or Bf 109, since the U/C legs will hit it when retracting?
The radiator drag of Spitfire probably went too high once the Griffons and 2-stage Merlins were being introduced, it was manageable with early Merlins.
OTOH - perhaps redesigning the wing leading edge so the radiators can be installed there is easier to pull off? Or - have the oil cooler instaled under the prop, just in front of the oil tank?
Or - do a radiator like the Italians did it with when going from MC.200 to MC.202, and from G.50 to G.55, so the U/C legs are not in the way? Obviously, the drop tanks must go under the wings now.

 

[Crowbar Six]

Problem is the 'lighter' AN/M2 is only really available in 1940 onwards and so the RAF would have even less time to debug issues than with the FF or HS404

Also when I say lighter - the gun is nearly 3 x the weight (27 kgs) of a Mk 2 Browning (10 kgs) and the ammo is also 3x the weight of 303 ammo - and its ROF is substantially slower 800 RPM verses 1150 RPM.

And if as the OP has suggested the RAF get the FF pre war then this weapon is 27 kilos - the same weight as the later 'lighter' AN/M2 50 cal - so why would they go 50 cal?

The RAF concluded that the weight penalty of the 50 cal did not over weigh any damage increase per hit over 303 while the same was not true of the cannon which retained its effectiveness beyond both 303 and 50 cal effectvie range and if they did go to the FF pre war then I cannot see the 50 cal being a starter on British built aircraft.

The Americans managed to muddle through with the AN/M2 50 cal but everyone else moved to Cannon pretty much as soon as they could

The Americans would have moved to cannon if they had managed to get them to work reliably - and its a good job the Japanese did not armour their aircraft and install self sealing baffles in their tanks (mind you I can see the Zero being a pig if they had)

In the equation Bullet mass and effect + ROF + weight - going to cannon made a lot more sense

Unfortunately 3 other parts of the equation are getting it to fit + reliability + ammo supply

In 1940 and before 20mm cannon on aircraft are pretty much limited to 60 round drums - and this is where the Mk2 Browning and AN/M2 have an advantage in that they already have a belt feed allowing a large number of rounds to be carried and they worked reliably.

OTL the major 'players' struggled with this equation - as we are here it seems.

If the RAF had opted for the 50 cal then they would have spent the time and effort they used on the .303 to get a 50 cal AN/M2 earlier

 

[phx1138]

Where the Mustang I and A-36 (not just prototype) have had 'beard' gus & ammo, Spitfire had oil tank.

Had, but wouldn't have to have, since oil doesn't much care.

Spitfire (and Bf 109, for example) used half-burried radiators...wing position does not favor sticking out the boundary layer spliter/scoop on Spitfire or Bf 109, since the U/C legs will hit it when retracting?

If you have to avoid hitting the rad in any event...

perhaps redesigning the wing leading edge so the radiators can be installed there is easier to pull off? Or - have the oil cooler instaled under the prop, just in front of the oil tank?

I like the idea of a leading edge inlet. It shouldn't need the whole front redesigned, & not a big deal anyhow, considering we're re-engineering the wing for fuel tanks & gear mounts. The problem arises in conflict with the leading edge fuel tanks...

And if we're trying to find space for beard guns, putting the oil cooler under the chin could be problematic...unless you can squeeze it between them.