British escort fighter--what might it have been like?

[wuzak]

The P-51H was noted as being extremely fast and fast climbing (it had a climb rate faster than the later Griffon Spitfires and the Spiteful).

Did it really?

At 90inHg MAP (~+30psi boost) could climb better than the Spitfire XIV with +18psi boost. And it could at 80inHG MAP (+25psi boost).

It was, however, quite a bit slower at 67inHG (+18psi boost).

Can't find climbing performance for a XIV with +21psi or +25psi boost at the moment - only level speeds.

The Griffon 65 had ~500hp more up to 7,00ft (~20% more) when using +25psi against +18psi boost. And about 400hp more in FS gear from ~13,00ft to 20,000ft.

I should think that the Spitfire XIV with +25psi would be a very fast climber.

 

[GrauGeist]

The F8F was also a late-war lightweight fighter, which, like the P-51H, was adapted to circumstances learned during the war, which led to their development.

These aircraft were not an epiphany, they were a result of trial and error.

We have the luxury of sitting back and looking at the war three quarters of a century later and saying, "well, if this could have been done five years earlier..." - but the brightest minds at the time worked with what they knew and what they had on hand.

 

[tomo pauk]

And in 1940 what constitutes long range? The British don't have ANY 4 engine bombers or at least no operational squadron. Even with escorts Whitleys are not what is needed in daylight. Without a new bomber you are going to be escorting Wellingtons with Pegasus engines. How far are the long raids going to be? The Ruhr?
even with escorts the Hampden is a lost cause in daylight.

Wellington I is just fine as a long-range bomber, 1200 miles with 4500 lb (max bombs case), or 1805 with 2750 lb (max fuel case, without going for auxiliary/bomb bay? tanks) . Hampden have had greater practical ceiling than the Welligton, it will do 1800 miles with 2000 lb of bombs. With a 1750 lb torpedo and 2x500 lb bombs under wing, it will still do 1540 miles (yes, I have a hunch that bombs will be a better tool to hit a ground target...).

If there is A/C with a short range in the RAF's inventory, that will not be their bombers.

I keep arguing here that long range escort fighter planes require technology superior to that of the enemy. All else being equal, the short range defending fighters will be slightly faster, will have much better acceleration, rate of climb and maneuverability. They can sacrifice a bit of reduced weight, for better armament. The escort fighters will dive more quickly.

In WWII, the Germans failed to issue high octane fuel and two stage superchargers to their front line squadrons, and none of their aircraft had laminar flow wings.

Germans certainly were issuing the high-octane fuel to their frontline squadron, vast majority of Fw 190s used that. Laminar-flow wings are not be-all end-all thing.
Short range defending fighter of 1943-45 will have 4x 20mm cannons sticking out (or what have you), contributing both to the drag and weight. A LR offensive fighter will do with 4 HMGs neatly tucked in the wing. Extra fuselage tankage adds nothing to the drag of an A/C.

If the British are to convert a Spitfire to a long range fighter, they must assume it will have reduced performance. The Spitfire_IX was about equal to an Fw190 at most altitudes. The long range Spitfire would be inferior at any altitude below 25,000ft. British bombers did not operate above 20,000ft. American bombers operated at altitudes that suited the two stage superchargers used by their fighters.

Especially the British are aware of performance disadvantage the Spitfire Vc had vs. the Va, due to the much increased weight and drag of the cannons. They know they can reduce weapon of the LR fighter in order to compensate for extra weight of fuel, and they know that German fighters have ever the greater drag and weight penalty due to their increased guns' firepower.
Crucially, British know that they have Luftwaffe out-numbered once LW turns east, let alone once Americans join the party.

Having 300 vs. enemy's 150 fighters, even if the own fighters have 5% performance disadvantage, is not something that any military planer worth his salt would've discarded, especially when accounting for hundreds of gun-toting bombers Allies have.
These planers should also know that German short-range fighters can't easily concentrated because they are, well, short-ranged.

Significantly, in 1943, North American and Supermarine upgraded their aircraft. North American added two machine guns, they strengthed their wings, they added a bubble canopy, and they enlarged fuel tanks. The P-51D was slower than the older P-15Bs and Cs, but they had a longer range. The superior allied technology assured that they were effective at long range.

P-51B have had the same internal fuel tankage as the P-51D, bar the 1st series of the Bs. The D was equally fast as the B, since it have had less draggy wing racks - 4 mph speed loss vs. 12 mph on the A, B and C.

 

[BarnOwlLover]

The F8F was also a late-war lightweight fighter, which, like the P-51H, was adapted to circumstances learned during the war, which led to their development.

These aircraft were not an epiphany, they were a result of trial and error.

We have the luxury of sitting back and looking at the war three quarters of a century later and saying, "well, if this could have been done five years earlier..." - but the brightest minds at the time worked with what they knew and what they had on hand.

My problem with that statement is that Ed Schmund knew that the P-51 was overweight and way overbuilt as early as 1942. That's why he went to Supermarine to study the Spitfire V and IX, in 1942. The result was the lightweight Mustang program and ultimately the P-51H, which I'd argue possibly should've been re-designated by reviving the XP-78 designation initially assigned to the P-51B, given that while the B was able to use most of the tooling that the earlier Allison powered versions did, the lw Mustangs and the P-51H had little in common with the other Merlin powered models.

It's obvious that most USAAF and USN aircraft of World War II were overbuilt due to obsolescent load standards that didn't align with what everyone else was doing. Even Britain's big-boys, the Hawker Typhoon and Tempest, were built to the same basic load standards that the Merlin Spitfires were, and even the Griffon Spitfires were built to those same basic standards. That's why even with a Griffon, the Spitfire 14 weighed nearly 1500 lbs than a P-51D in the same condition (clean gross weight of about 7900 lbs vs 9200 lbs). Yes, the Spitfire 14 carried a lot less fuel, was shorter ranged and a draggier airframe, but that lighter weight meant a lot in terms of handling, agility and climb rate. And I also know that I'll probably get told that making an interceptor (Spitfire) vs an escort fighter (Mustang) is like comparing chalk and cheese as far as duty and abilities--horses for courses.

But the P-51H showed that you could make a fighter that could do both, even if it didn't have the latest and greatest from Rolls-Royce as far as the Griffon (even the XP-51F with the same engine as a P-51D was significantly faster than the D or the Spitfire 14, and also climbed faster than either aircraft).

I'm willing to even say that fitting a Griffon to even a dedicated high performance Mustang fighter would likely be a detriment. The Griffon, though no longer or wider than a Merlin, was still significantly taller, and was significantly heavier. Not to mention probably more fuel thirsty in a single engine fighter.

 

[BarnOwlLover]

I do also feel that it's worth pointing out that from what I read that the longer-ranged late war IJA/IJN fighters still adhered to the low speed flight theories of their fore-bearers as far as achieving long range. A Ki-84 had up to a 1000+ mile range on internal fuel, but that was with a 175mph cruse speed. If it was pushed to P-51-like cruse speeds (280-300+mph), fuel economy would probably take a huge hit vs the Mustang.

 

[PAT303]

I do also feel that it's worth pointing out that from what I read that the longer-ranged late war IJA/IJN fighters still adhered to the low speed flight theories of their fore-bearers as far as achieving long range. A Ki-84 had up to a 1000+ mile range on internal fuel, but that was with a 175mph cruse speed. If it was pushed to P-51-like cruse speeds (280-300+mph), fuel economy would probably take a huge hit vs the Mustang.

I've posted this very statement numerous times, the Japanese planes had extreme range but the technique they used to achieve it would not have worked over defended airspace.

 

[Howard Gibson]

My problem with that statement is that Ed Schmund knew that the P-51 was overweight and way overbuilt as early as 1942. That's why he went to Supermarine to study the Spitfire V and IX, in 1942. The result was the lightweight Mustang program and ultimately the P-51H, which I'd argue possibly should've been re-designated by reviving the XP-78 designation initially assigned to the P-51B, given that while the B was able to use most of the tooling that the earlier Allison powered versions did, the lw Mustangs and the P-51H had little in common with the other Merlin powered models.

It's obvious that most USAAF and USN aircraft of World War II were overbuilt due to obsolescent load standards that didn't align with what everyone else was doing. Even Britain's big-boys, the Hawker Typhoon and Tempest, were built to the same basic load standards that the Merlin Spitfires were, and even the Griffon Spitfires were built to those same basic standards. That's why even with a Griffon, the Spitfire 14 weighed nearly 1500 lbs than a P-51D in the same condition (clean gross weight of about 7900 lbs vs 9200 lbs). Yes, the Spitfire 14 carried a lot less fuel, was shorter ranged and a draggier airframe, but that lighter weight meant a lot in terms of handling, agility and climb rate. And I also know that I'll probably get told that making an interceptor (Spitfire) vs an escort fighter (Mustang) is like comparing chalk and cheese as far as duty and abilities--horses for courses.

But the P-51H showed that you could make a fighter that could do both, even if it didn't have the latest and greatest from Rolls-Royce as far as the Griffon (even the XP-51F with the same engine as a P-51D was significantly faster than the D or the Spitfire 14, and also climbed faster than either aircraft).

I'm willing to even say that fitting a Griffon to even a dedicated high performance Mustang fighter would likely be a detriment. The Griffon, though no longer or wider than a Merlin, was still significantly taller, and was significantly heavier. Not to mention probably more fuel thirsty in a single engine fighter.

As Wuzak points out above, P-51Hs were using 90"Hg to achieve their high performance. This means they were using 150 octane fuel, and water injection. Spitfires did not have water injection, but they could use the 150 octane gas.

I would expect a P-51H on plain 100/130 octane gasoline to be somewhat faster than a P-51D.

 

[BarnOwlLover]

As far as "small" escort fighters, there was the Yak-9D and -9DD, which had ranges up to 850 and 1450 miles respectively. Granted, this was possible because they packed the wings full of fuel (Yakovlev fighters, like most Soviet fighters, had nose mounted armament) since the Soviets didn't really use drop tanks, and the Soviet fighters didn't do well at altitude. But it shows maybe what was possible if the Mustang was able to stay at the same weight and such as the NA-73X and Mustang I (most US aircraft, P-51s included until the XP-51F/G and the P-51H, were overbuilt by British standards) while adopting the Merlin and could grow it's range a bit.

 

[tomo pauk]

As far as "small" escort fighters, there was the Yak-9D and -9DD, which had ranges up to 850 and 1450 miles respectively. Granted, this was possible because they packed the wings full of fuel (Yakovlev fighters, like most Soviet fighters, had nose mounted armament)

Yak-9DD was the one with a big fuselage tank, made possible due to relocation of the cockpit 40 cm aft. That, combined with wing tanks (carry-over from the Yak-1), small size and modest power, made it very rangy aircraft.
It also made it climb slow, and turn worse than other Yak-9s, since there was no substantial increase in power.

But it shows maybe what was possible if the Mustang was able to stay at the same weight and such as the NA-73X and Mustang I (most US aircraft, P-51s included until the XP-51F/G and the P-51H, were overbuilt by British standards) while adopting the Merlin and could grow it's range a bit.

Even the Mustang I was heavier than the Yak-9DD. Under 7500 lbs for the -9DD, more than 8100 lbs for the Mustang I; gross weights for both.
Mustang was a bigger A/C than the Yak-9 series, greater size usually means greater weight.

 

[BarnOwlLover]

One, I do wonder why the Soviets didn't think of using drop tanks? They'd get the range without hampering the aircraft's handling on full internal fuel. Impressive that they could pack that much fuel in a plane smaller than a Spitfire, but IMO not entirely practical.

And two, the Mustang I may've been fairly big compared to the Spitfire by 1942 standards, but if it maintained that weight in the Merlin powered variants (which were half a ton heavier, due to structural reinforcements), it would've probably been more maneuverable and maybe a bit faster. It certainly would've climbed better.

In fairness, the Mustang I's weight compared to the Spitfire prompted the lightweight Mustangs, but that was one, due to different build standards (IMO, USAAF/USN load standards were overly conservative and IMO somewhat archaic--the Hawker Tempest was not much smaller than a P-47, but much lighter, even if you take the big turbo out of the P-47), and even then the Mustang I (and P-51 through P-51D/K) was over 3 feet longer than a single stage Merlin Spitfire, and over 2 feet longer than a two stage Merlin Spitfire. Overall Mustang dimensions were comparable to the Spitfire XIV with a two stage Griffon (and even then was several hundred pounds lighter in terms of max clean fully equipped weight than a Merlin Mustang).

 

[tomo pauk]

One, I do wonder why the Soviets didn't think of using drop tanks? They'd get the range without hampering the aircraft's handling on full internal fuel. Impressive that they could pack that much fuel in a plane smaller than a Spitfire, but IMO not entirely practical.

Wrt. the Soviet being hesitant to use drop tanks often - I don't know the reason. The way they stuffed so much of fuel in a small A/C was totally practical, but idea was 'backstabbed' by not installing a better engine - the mass-produced VK 105 was behind the curve already by 1942 for crying out loud.

And two, the Mustang I may've been fairly big compared to the Spitfire by 1942 standards, but if it maintained that weight in the Merlin powered variants (which were half a ton heavier, due to structural reinforcements), it would've probably been more maneuverable and maybe a bit faster. It certainly would've climbed better.

Mustang's wing was the size of Spitfire's. Both were much bigger than the Yaks or Bf 109. Even the Fw 190 was smaller than Mustang or Spitfire. Weight of the Merlin Mustangs went up for god reasons.

 

[BarnOwlLover]

IMO, only good reason the Merlin Mustangs gained weight was the two stage Merlin was about 300 lbs heavier than a single stage one or an Allison. The development of the lightweight Mustangs IMO is proof that Schmued knew that the P-51 was overbuilt. Not to mention that even when armed the XP-51F and G models were lighter than the NA-73X, and still had decent range on internal fuel (not as good as the B/C/D/K or even H, but still way better than a normal spec Spitfire).

Even the Rolls-Royce FTB Mustang with a Merlin was a good deal lighter than a normal Merlin P-51 (max take off weight estimated at 8950 lbs for the Merlin version). Granted, aside from the wings and (initally) tail unit, which were standard P-51 components, most everything else was new and built to British engineering specs. In the end, aside from both Merlin and Griffon powered mock ups (the Griffon version weighed IIRC about the same as a normal Merlin P-51 clean for reference), none ever flew. It should be noted that the fighter version seemingly was intended to be armed with at least a 20mm cannon firing though the prop spinner and probably multiple other wing mounted .50 MGs or 20mm cannons.

And in the end, the Mustang tail was to be discarded for a modified Hawker Tempest tail.

BTW, all the info about the FTB did come from a Key Aero article. Though I was able for some reason to view it on another computer, it's paywalled when I try and look it up on my laptop.

EDIT: Found non-paywalled article:

SECRET PROJECTS:Rolls-Royce’s own fighter concept

The involvement of Rolls-Royce’s Hucknall plant in fitting the North American P-51 Mustang with its Merlin engine...

www.key.aero

 

[Shortround6]

Yak 9 had a 184 sq ft wing.
The YAK 9D increased the fuel capacity from 440 to 650 L.
At some point they started using metal spars instead of wood and this is what allowed them more room in the wing to fit the fuel tanks.
The Yak 9DD got a further modified wing and allowed for 845 liters of full.

However there were several problems. The hoped for engines ( the B-106 and M-107) were not working and they had to keep the existing M-105 engines. To compensate for the heavier fuel load they reduced the armament to a single 20mm ShVAK cannon. No cowl machine guns. Better instruments were fitted (like a radio compass) and they installed US built SCR-174N radios and larger oxygen bottles. More to long rang fighters than just stuffing more fuel in them

BTW the Russian source says the new radios were good for a two way range of 93 miles (150km) at 1000metes altitude and could receive at 186 miles (300km) at an altitude at 23,000ft (7,000 meters).

 

[Shortround6]

IMO, only good reason the Merlin Mustangs gained weight was the two stage Merlin was about 300 lbs heavier than a single stage one or an Allison.

I don't have the weights for the Allison powered Mustangs but the P-51B&C used a cooling system about 360lbs heavier than P-40 (Ks) and propeller about 45lbs heavier (late model P-40s used heavier propellers than the E and Fs)

A P-51B was about 440lbs heavier than P-51A at "basic" weight. That includes trapped fluids, four .50 cal guns (no ammo) and things like gun sight a flares.
Apparently they already took a few things out of the P-51A or some weights got shifted. Empty weight (which still included coolant) was about a 555lb difference.

 

[wuzak]

IMO, only good reason the Merlin Mustangs gained weight was the two stage Merlin was about 300 lbs heavier than a single stage one or an Allison. The development of the lightweight Mustangs IMO is proof that Schmued knew that the P-51 was overbuilt. Not to mention that even when armed the XP-51F and G models were lighter than the NA-73X, and still had decent range on internal fuel (not as good as the B/C/D/K or even H, but still way better than a normal spec Spitfire).

Even the Rolls-Royce FTB Mustang with a Merlin was a good deal lighter than a normal Merlin P-51 (max take off weight estimated at 8950 lbs for the Merlin version). Granted, aside from the wings and (initally) tail unit, which were standard P-51 components, most everything else was new and built to British engineering specs. In the end, aside from both Merlin and Griffon powered mock ups (the Griffon version weighed IIRC about the same as a normal Merlin P-51 clean for reference), none ever flew. It should be noted that the fighter version seemingly was intended to be armed with at least a 20mm cannon firing though the prop spinner and probably multiple other wing mounted .50 MGs or 20mm cannons.

And in the end, the Mustang tail was to be discarded for a modified Hawker Tempest tail.

BTW, all the info about the FTB did come from a Key Aero article. Though I was able for some reason to view it on another computer, it's paywalled when I try and look it up on my laptop.

EDIT: Found non-paywalled article:

SECRET PROJECTS:Rolls-Royce’s own fighter concept

The involvement of Rolls-Royce’s Hucknall plant in fitting the North American P-51 Mustang with its Merlin engine...

www.key.aero

From what I recall, the FTB was only ever going to use the Griffon.

 

[BarnOwlLover]

Article I linked to elsewhere (SECRET PROJECTS:Rolls-Royce’s own fighter concept) says that the mock up was fitted with a Merlin (no two-stage Griffon was available).

Here's the paragraph from said article (in case it gets paywalled again):

"The original private venture project was called the Fighter Aircraft Proposal (Hucknall PV) and work on it really got going in January 1943. The new fuselage was designed to take a 2,500hp two-stage Griffon 61 unit which would give an all-up weight of 9,400lb (4,264kg) but, since it was unlikely that this engine would be ready at the same time as the airframe, a Merlin 61 giving almost 2,000hp would be used for initial testing; this gave an estimated all-up weight of 8,950lb (4,060kg). A set of Rotol contra-rotating propellers of 11ft (3.35m) diameter and a teardrop-shape canopy would be fitted. The planned armament was a 20mm cannon firing through the propeller spinner, while there would be full armour protection and bulletproof fuel tanks. Major alterations to the engine brought changes to the propeller reduction gear and, of course, the introduction of the connecting shaft running through a trough in the cockpit floor between the pilot's feet."

And here's a document talking about the proposal (with the hoped for Griffon engine):

Mustang Variants

Hi folks, A new thread for and unknown, secret or rare North American P-51 Mustang variants. I'll start off by including what may have been the ultimate Mustang: This was supposedly a proposal that North American had come up with in case the war had continued. As you can see, it had...

www.secretprojects.co.uk

Sadly, no range figures exist, though they do give expected fuel capacities. I don't know how much that'll help in terms of a sub-9000 lb all up/MTO Merlin single seater in terms of performance, also given that normal (clean or interceptor/air superiority) TO weight would be a lot less.