Why no heavier RAF machine gun calibres? (2 Viewers)

[tomo pauk]

In short a Spitfire I is a far better aircraft for the Battle of Britain than a Mythical Mustang with a Merlin III.

The P-51 with V-1710-39 (= an engine not as good as than the Merlin III) and at 8114 lbs was climbing to 15000 ft in 5.58 min, while the Spitfire I with the Rotol prop and sans the 73lb armor plate needed 5.4min.
Enough for the Spitfire to win the bar bet, but not enough of a difference to hang a hat to it.

Once both aircraft are at 15000 ft, the P-51 is faster by a good measure. We can also opt to fill just 85 imp gals and save (150-85) x 7.2 = 468 lbs from the P-51, in order to improve the RoC.
P-51 with full fuel load in service in the Group 12 can join the party above Group 11 territory, that will not go as smooth, if at all with the short-ranged and draggier fighters of the time. In service of the Group 11, it leaves more of a leeway wrt. mis-judging the German intents and flight paths, and allows for the fighters to chase the retreating LW aircraft over the channel.
Having the Merlin III-powered P-51 above Dunkirk would've also been great.

 

[Shortround6]

A 400 mph fighter in 1940, that weights 8100 lbs? Where do I sign?

To further this,
A P-51A with Allison engine had a gross weight of 8153lbs (close enough) BUT, this was with just over 100 US gallons of fuel.
For our hypothetical long range fighter the Early Mustangs could hold 1080 lbs of fuel in the internal tanks, not the 630 lbs in gross weight given, the 8153lb weight also is includes four .50 cal guns and ammo (378lbs Average of 310 rpg) adjust as needed/desired. Add external fuel tanks as anybody sees fit. Install what ever Merlin engine was available in 1940 (MK XII or XX) and see what people think. An extra 26lbs for the bomb/tank racks and the added drag, plane is just under 8400lbs (assuming the Merlin are a direct swap for the Allison, they are not, a British Merlin XX was about 1450lbs, about 120-130lbs heavier than the Allison used in the P-51A) ) even with 200lbs of fuel burned off and no drop tanks. So 1850lbs?
It will be fast, won't climb for crap. Don't dog fight, once it slows down it takes a long time to get back up to speed.

The Mustang was a wonderful airframe, but you needed more power to get the most out of it. Mustang Prototype first flew Oct 26th 1940 after about 2 weeks of ground testing/taxing.
Not much time for any lessons from the BoB to be incorporated.
And as far as climb goes, best case for even 1941 is a Merlin XX engine, Look the climb for a P-40F( test July 1942) to see how that went (8450lbs, time to 20,000ft 10.2 minutes, 2850rpm 48in/9lbs of boost).

 

[tomo pauk]

To further this,

Worthy of a thread of it's own

 

[Shortround6]

Enough for the Spitfire to win the bar bet, but not enough of a difference to hang a hat to it.

Unfortunately we run into the different test procedures. Brtish were using 2600rpm and 6lbs of boost (6.4 =43in?) for the entire climb, which is a reasonable procedure for climb even if it doesn't give the best numbers. Merlin III doesn't get to full throttle until 11,000ft and at power falls off the higher it goes (an extra 10% on the rpm will help keep the boost up for several thousand ft higher)
The US was using 3000rpm for the first 5 minutes and then throttling back to 2600rpm for the rest of the climb. This give the advantage to Allison at climbs to 13-15,000ft
Later in 1940 (just before the BoB) the British OK's the use of 2850 rpm for climbing and higher boost (?) when using 100 octane fuel.

We can also opt to fill just 85 imp gals and save (150-85) x 7.2 = 468 lbs from the P-51, in order to improve the RoC.

630lbs of fuel is the fuel carried in a P-51A for normal gross weight and at 7.2lbs per gallon that is 87.5Imp gal.
Please note that this was standard procedure for many US fighters during 1939-42. normal gross weight was NOT at max internal fuel. P-40s were figured at 120US gallons (99-100 Imp).

 

[Clayton Magnet]

Are we somehow back to the "Why didn't the silly British just use non-existent American tech from the future to win the BOB?" question?
My vote would be a fully fleshed out Spitfire Mk.III, with belt fed Hispano's.

 

[Reluctant Poster]

The P-51 with V-1710-39 (= an engine not as good as than the Merlin III) and at 8114 lbs was climbing to 15000 ft in 5.58 min, while the Spitfire I with the Rotol prop and sans the 73lb armor plate needed 5.4min.
Enough for the Spitfire to win the bar bet, but not enough of a difference to hang a hat to it.

Once both aircraft are at 15000 ft, the P-51 is faster by a good measure. We can also opt to fill just 85 imp gals and save (150-85) x 7.2 = 468 lbs from the P-51, in order to improve the RoC.
P-51 with full fuel load in service in the Group 12 can join the party above Group 11 territory, that will not go as smooth, if at all with the short-ranged and draggier fighters of the time. In service of the Group 11, it leaves more of a leeway wrt. mis-judging the German intents and flight paths, and allows for the fighters to chase the retreating LW aircraft over the channel.
Having the Merlin III-powered P-51 above Dunkirk would've also been great.

The V-1710-39 isn't as good as a Merlin III? That's pathetic considering it appears at least 2 years after the Merlin II which is a Merlin III with a different prop shaft. The Merlin XX is already in front line service before the -39 actually flies. The -39 entered combat at the same time as the Merlin 63.

 

[Shortround6]

The -39 entered combat at the same time as the Merlin 63.

You were doing pretty good up until this part.
First Merlin 63 in a production Spitfire (JF.274), wasn't delivered until Nov 1942.
-39 Allisons had been in combat on Dey 7th 1941. British were using them in NA in Jan 1942.
The Merlin 63 being the 4th two stage Merlin. Perhaps we can debate the combat debut of the Wellington VI ?

 

[MIflyer]

In short a Spitfire I is a far better aircraft for the Battle of Britain than a Mythical Mustang with a Merlin III.

The Spit had to climb fast because it was so short ranged. It could not afford to to be at 30,000 ft when the radar vectors came in.

Even without drop tanks Merlin Mustangs, with either V-1650-1 or V-1650-3, would have met the Luftwaffe over the coast of FRANCE. And so the interceptors would not have been at the continual disadvantage of having the 109's always above them, but rather the opposite.

 

[pbehn]

The Mustang Mk I and Spitfire Mk IX started being introduced in March April 1942, there were 6 squadrons of each at Dieppe in August 1942. To have Merlin engined Mustangs in the BoB you need o order them in early 1938, before any war was declared. They would not hav had the high speed low drag aerofoils and so would not have had the internal fuel capacity that the Mustang Mk I had. From late September the LW were sending in Jabo raids at 30,000ft, if the RAF had significant numbers of Allisson engined Mustang Mk Is these would have started sooner and RAF pilots would need a choice of aircraft. If this foresight about the way the world would develop was universal, why didnt the USAAF have Merlin engined P-51s in 1942, why not have jets flying in UK in 1939?

 

[PAT303]

A 400 mph fighter in 1940, that weights 8100 lbs? Where do I sign?

Mk III Spitfire fitted with a RM2SM Merlin engine hit 394 MPH on the 15th March 1940 running 100 octane fuel with a fixed pitched propeller. The Mk III had shortened wings to improve roll with strengthened main spar and fuselage, internal bullet proof windscreen, redesigned radiators, 100G main tank, retractable tail wheel, the forward landing gear rake increased by 2'' and the lower section fitted with small flaps to enclose the wheels and finally two cannons that didn't actually work but were the future, total weight 6700 lbs, the Mk III eclipsed everything in the air until the FW 190 appeared 2 years later, your welcome.

 

[PAT303]

The Spit had to climb fast because it was so short ranged. It could not afford to to be at 30,000 ft when the radar vectors came in.

Even without drop tanks Merlin Mustangs, with either V-1650-1 or V-1650-3, would have met the Luftwaffe over the coast of FRANCE. And so the interceptors would not have been at the continual disadvantage of having the 109's always above them, but rather the opposite.

I've already discussed this ad nauseum, put a 20G tank behind the Spits seat, problem solved. How well are your .50's working in 1940?

 

[PAT303]

Are we somehow back to the "Why didn't the silly British just use non-existent American tech from the future to win the BOB?" question?
My vote would be a fully fleshed out Spitfire Mk.III, with belt fed Hispano's.

Would the Mustang have become the aircraft it did let alone gone into production had the Mk III entered service?. The natural progression would have been Mk III with the two speed Merlin XX to what was the Mk VIII with two speed two stage Merlin 60 late 1941 so no need for the RAF to order obsolete American designs if the British industries get behind it's production. All the RAF need is for Portal to be left out of the decision making and let Joe Smith do his work.

 

[Alan Stevens]

Understood, but the USAF and USN considered the difference in fuel usage important.

It is important but we had a war to win.

Total mobilization nationwide.

 

[Alan Stevens]

Both using twice the fuel and providing a far larger target for the Germans to see and shoot at.

Size:
Not that much difference between P-47 and P-51
P-38 is larger but is a twin-engine fighter with its advantages.

 

[Alan Stevens]

• Lower fuel consumption allows a plane to fly further, which seems to have been an important consideration for escort fighters of the era.
• You still have to get the fuel to the air bases in England. Saying fuel consumption doesn't matter seems disrespectful to the thousands of men who died bringing supplies, including fuel, over the Atlantic. Though by the time the Mustang starts showing up in numbers the Battle of the Atlantic is practically over, but still.

I didn't say "fuel consumption doesn't matter." I questioned how much of a calculus there was for modern fighters which all contributed. The 4-engine bombers carried far more fuel and and the need for fuel is what it was.

Was there ever any initiative to replace P-47s and P-38s with P-51s?

Yes, there was an initiative to replace the P-47 Thunderbolts and P-38 Lightnings with P-51 Mustangs during World War II. However, this initiative faced resistance. For example, Lt. Gen. George C. Kenney, the commander of the Far East Air Forces, flatly refused the order to replace his P-38s and P-47s with P-51s, stating "No!".

The P-47 and P-38 were highly valued for their specific roles and capabilities, and many pilots and commanders preferred them over the P-51 in certain situations. The P-47, in particular, was known for its ruggedness and payload capacity, making it an excellent fighter-bomber.

 

[MiTasol]

Worthy of a thread of it's own

And all the shipping information seems worthy of a thread of its own to me. The information posted so far on that topic at least triples my knowledge of Liberty ships and all their kin and has been most enlightening.

 

[ThomasP]

re

It is important but we had a war to win.

Total mobilization nationwide.

1. True, but even the US supply chain was not infinite. Most people are not aware that the US used up ~1/3 of its readily accessible strategic resources (eg iron ore, oil, etc) as they were aware of in WWII. This was of very serious concern to the higher ups and strategic planners.

2. Also, the transport of the war materiel was not always assured. The War of the Atlantic was not really won until the end(?) of 1942.

3. By the end of 1944, the Allies were already pretty sure that the endo of the war was going to occur in 1945. They were so sure of this that they began training and selection of the occupation forces leadership (both civil and military) to the point where they were holding classes for the selected personnel.

Only with hindsight can we say (to a degree) concerns and decisions made based on fuel supply/usage did not matter.

A side aspect of the awareness of the coming end to the war was that when the Joint Fighter Conference took place the USAAF and USN were actually looking to future rationalization of the fighter production - eg what airframes should they continue in production if needed as opposed to what should they cut. Also, the Joint Fighter Conference was to help with deciding which airframes should they keep in service after the war - based on the performance, cost, and service experience of the different aircraft.

Deciding what qualities were desired in future designs was also part of the effort.

The fighter aircraft kept in service after the war is telling. The P-38 disappeared almost immediately. The P-47 was kept on in small numbers, mostly in the National Guard. The F4U and P-51 soldiered on through Korea.

It has been a long time since I read the Report on the Joint Fighter Conference, but IIRC the consensus was that the F4U Corsair and the P-51 Mustang were the top 2 in scoring.

Possibly someone else on the forum has access to a copy of the Report and can check?

 

[MiTasol]

Are we somehow back to the "Why didn't the silly British just use non-existent American tech from the future to win the BOB?" question?
My vote would be a fully fleshed out Spitfire Mk.III, with belt fed Hispano's.

IF the Hispano had been made reliable by then AND the belt feed system designed and perfected by then I would totally agree with Spitfire though I would go with the Mk V. I know too little about the Mk III to consider it. I thought it was the version with the C wing that was cancelled but I cannot think of any Mk IV Spitfires so maybe that was the cancelled one.

 

[PAT303]

IF the Hispano had been made reliable by then AND the belt feed system designed and perfected by then I would totally agree with Spitfire though I would go with the Mk V. I know too little about the Mk III to consider it. I thought it was the version with the C wing that was cancelled but I cannot think of any Mk IV Spitfires so maybe that was the cancelled one.

The Mk III was a total redesign of the Spitfire based on what was learnt from the Mk I/II, it was slated for production but the war started so the Mk II stayed in front line service. The Mk III was an exceptional aircraft, totally outclassing everything in the air in 1940/41 but still being armed with eight Browning .303's because like has already been posted numerous times none of the numerous .50 cal guns or the Hispano were anything near reliable.