1937-45: Doubling down on the 2-engined 'day fighters'

[tomo pauk]

Everyone and his brother knows that I'm not a fan of 2-engined day fighters for the period of interest (mostly because their advantages were often short-lived - if not dubious - while representing a big drain on the resources), so this is me playing the devil's advocate: making the case for the beligerents to make even more of them. Whether by making a lot more of historical examples, or producing the alternative designs (these can be either the designs that became eventually stillborn, or something else that is plausible for a nation/company to make).
I have no quarrels that twins later make a name for themselves as recons, NFs, ground attakc aircraft etc, but the 1st rand foremost role is that of the day fighter.
Note that something else will need to be axed, with the benefit of hindsight.

For example, Gloster makes the F.9/37 around the Merlins (note that I'm not talking about the later 'Rapier' design) from the get go, for the role of the heavily armed bomber-buster; being halfway house between the Whirly (fine, but without much of the 'stretch') and Beaufighter (good in many roles, but lets keep it away from the enemy's best fighters), it might do well as a day fighter. I'm willing to sacrifice the Defiant and the whole turret fighter idea in order to get the ball started.

 

[Admiral Beez]

If we swapped out all (or some) the Spitfires and Hurricanes in 1939-40 with something equal to the P-38G of 1943, then sure. There's nothing inherently wrong with twin-engined fighters, provided they keep or exceed the power-to-weight ratio, high wing loading, top speed and rate of climb of the opposing single-engined fighters. Any deficits in low speed agility should be made up with advantages in top speed and heavier armament.

The Mk.2 Spitfire of 1939-40 had a 1,175 horsepower Merlin XII engine. So, let's put two of these into a single-seat P-38 equivalent, with the best British superchargers then available. As it was, we did not see the British put two Merlins into an operational single-seat fighter until the postwar DH Hornet. I'd stay away from the Westland Welkin high altitude interceptor concept - we need the ability to mix with Bf 109s and Fw 190s. Maybe we should start here:


View: https://www.youtube.com/watch?v=F2tOq0qmNXI

 

[Zmauky]

Yes, actually when we count then P-38, Whirlwind, Fw 189V1 and F5F are the only pure (one crew) fighters, either interceptors or long range.

The Bf 110 is a Zerstörer, a concept in which Willy 'cheated' because he did not include a bomb bay, so instead of a multirole, he became a fighter, but I would say at least 1/4 too big for that role. Its successor, the Me 210, was supposed to be a replacement for a long-range fighter, but also for a Ju 87, so it certainly wasn't a pure fighter (but at least it had a bomb bay like a real Zerstörer)
All the others - and I will include the French Potez 630, the Polish Wilk, the American F5F, the Yugoslav Zmaj R-1, the Dutch Fokker DXXI, the Russian Moskalev, and I'm sure I've forgotten some of them, were with (too) weak engines. I would say that instead of a premium engine, they went for a number (to be competitive with single engines fighters powers). And here I agree with Admiral Beez. The problem is that with two smaller (weaker) engines, you can't get a small and light enough construction to compete with premium single engined fighters (especially if you add another crew member). Although the British almost succeeded with the Whirlwind (and maybe the FW 189 would have if it had not become a two-seater and had received a DB 601 or at least a Jumo 211). Only with the first engine league do we get to the F7F, P-61 and Hornet.

 

[special ed]

You mean Fokker D.XXIII - it was a push pull.

 

[Reluctant Poster]

If we swapped out all (or some) the Spitfires and Hurricanes in 1939-40 with something equal to the P-38G of 1943, then sure. There's nothing inherently wrong with twin-engined fighters, provided they keep or exceed the power-to-weight ratio, high wing loading, top speed and rate of climb of the opposing single-engined fighters. Any deficits in low speed agility should be made up with advantages in top speed and heavier armament.

View attachment 796230

The Mk.2 Spitfire of 1939-40 had a 1,175 horsepower Merlin XII engine. So, let's put two of these into a single-seat P-38 equivalent, with the best British superchargers then available. As it was, we did not see the British put two Merlins into an operational single-seat fighter until the postwar DH Hornet. I'd stay away from the Westland Welkin high altitude interceptor concept - we need the ability to mix with Bf 109s and Fw 190s. Maybe we should start here:


View: https://www.youtube.com/watch?v=F2tOq0qmNXI%5B/URL

twice as many engines required with associated maintenance necessary for what benefits?

 

[Zmauky]

Uh, clumsy fingers, yes of course push-pull D XIII.

Benefits of a pure twin-engine fighter - well, for the class with the currently strongest available engines (Merlin, DB 601/5, Allison V-1710 ect) heavier weapons (and more ammunition) as a rule at a significantly larger operating radius is certainly a justified reason. Not that, say, benefits of the FW 189 wasn't discussed in several threads.

And let's not get into the discussion now about the P-51B/D and P-47N we know when they appeared (late) and there weren't enough strong engines for them earlier anyway.

Another solution is the "type" Whirlwind, i.e. a very small airframe just enough for second class of engine. Benefits - for practically the same area of the wing, approx. 40% hp more you have approximately the same performance ( vs Spitfire I) and significantly stronger armament 4x20 vs 8x7.7, and the use of engines that are not needed elsewhere.
This type would be interesting for the big players to take advantage of the production capacity of engines that are not in the first league. (the problem with Whirlwind was that there was no well-established production, although RR could have transferred the tools or even the production line of the older kestrel to a smaller manufacturer?). The F5F/P-50 had a problem with the R-1535 (which Pratt & Whitney is putting out of production).
This type of small two-engined aircraft could also be interesting for small players, but they all went for "multirole" two-seaters, and for that, as a rule, they were equipped with rather weak engines or oversized constructions (like the Fokker G I).
Admittedly, it would be nice to see what performance the refined single-seat variants of the PZL.48 Lampart or Bre 690 would have.

 

[yulzari]

The Westland Whirlwind gives a good model for the high power twin single seat fighter. With the Peregrine you were using a better Kestrel which was a known success already. With the Merlin, at the time of design, you were looking at a private venture engine of unknown quality. With the Peregrine you got a 1,00bhp fighter in 1940, with a developed Peregrine you would be getting a 2,000bhp fighter in 1942, with early Merlin's the same but in 1941 and with later Merlins 3,000bhp in 1943 and 4,000 in 1945. Compared to the OTL big engines you use no more cylinders and less complexity. With the economies of scale of Merlin production and the AH production and design resources used IOTL for the Vulture and Sabre it would probably be cheaper and easier to use twin Merlins and certainly easier to maintain and familiar to more mechanics.

There is a whole deep well appointed and centrally heated/air conditioned rabbit hole to be gone down in the whole Whirlwind 'what if' which I am not going down in this post.

 

[Shortround6]

I'm willing to sacrifice the Defiant and the whole turret fighter idea in order to get the ball started.

But you can't get rid of the turret fighter!!!
Without Defiants you have no replacement for the
HAWKER DEMON

Obviously a 182mph two seat fighter is vastly superior to a 220mph single seat fighter using the same engine so the formula should be repeated with the new 1000hp engine.

Back on point. the twin engine single seat fighter has a rather narrow niche or perhaps two paths. 2 small engines to keep cost down (but still more expensive than a single engine fighter) or using two full size engines for an expensive but very capable airplane. But if you can only afford say 60% of them compared to single engine fighters using the same engines?

British used somewhat crappy accounting on the Whirlwind. They should not have been comparing it to the Spitfire but rather to the Hawker Tornado/Typhoon. Granted there were overlaps or differences in timing, much like the Americans with the F5F program and the F4U program.

The small twin works (?) when compared to the next generation big engine, not the current generation big engine. And it you are bit too small then the whole thing falls apart.

Beaufighter is another side track. Not quite what was wanted but rather what they thought they could get fast. And the promised performance was thwarted by faulty wind tunnel data, the promised 370mph speed would have needed rockets. But it could be built using some Beaufort tooling for early delivery.................except the promised Hercules engines weren't showing up in time.

 

[ThomasP]

re

There is a whole deep well appointed and centrally heated/air conditioned rabbit hole to be gone down in the whole Whirlwind 'what if' which I am not going down in this post.

Good one! I am going to (unashamedly) steal this phrase and figure out how to occasionally intersperse it among my explanations to my friends as to why I am researching certain seemingly strange (to them) subjects that somehow allows tracing of important information to some other subject that they have an interest in.

 

[tomo pauk]

The Westland Whirlwind gives a good model for the high power twin single seat fighter. With the Peregrine you were using a better Kestrel which was a known success already. With the Merlin, at the time of design, you were looking at a private venture engine of unknown quality. With the Peregrine you got a 1,00bhp fighter in 1940, with a developed Peregrine you would be getting a 2,000bhp fighter in 1942, with early Merlin's the same but in 1941 and with later Merlins 3,000bhp in 1943 and 4,000 in 1945.

I'm not sure what was the 1000 HP Whirlwind - on 87 oct fuel, it was actually 2x885 = 1770 HP, and on the 100 octane it was 2 x ~1000 HP = 2000 HP, already in 1940.

A 'big Whirlwind' that mimics the size of the Fw 187, powered at 1st by 745 HP Kestrels, and later with Merlins should've been a very useful aircraft IMO.

 

[yulzari]

I'm not sure what was the 1000 HP Whirlwind - on 87 oct fuel, it was actually 2x885 = 1770 HP, and on the 100 octane it was 2 x ~1000 HP = 2000 HP, already in 1940.

A 'big Whirlwind' that mimics the size of the Fw 187, powered at 1st by 745 HP Kestrels, and later with Merlins should've been a very useful aircraft IMO.

Finger trouble. Yes quite so.

 

[ThomasP]

For the Germans, to me the obvious example would be the Fw 187 - if developed further with DB601 and 605s. In the real timeline it might have been a waste of resources due to the strategic situation, but for this what-if it probably has the best twin-engine potential for the Luftwaffe.

 

[tomo pauk]

For the Germans, to me the obvious example would be the Fw 187 - if developed further with DB601 and 605s. In the real timeline it might have been a waste of resources due to the strategic situation, but for this what-if it probably has the best twin-engine potential for the Luftwaffe.

Going by the real timeline, any and every Nazi German or Axis waeapon was a waste of resources, since they lost the war anyway

Fw 187 option allows for a few things to happen that, while cannot outright war the war on their own, can make things more difficult to the Allies. Like it's long range (useful againt the UK, Soviet union and in MTO), ability to carry heavy firepower and still perform at high altitudes (yes, it will need these DB engines to do it), or ability to double as a fast bomber that has long range (being better in that regard than the Fw 190 or the Bf 110, let alone the Ju 88). Already with the Jumo 210G engines it should be an useful combat aircraft, can use the HS 12 engines (even the versions like the legacy -31 or the Ydrs offer ~25% more power at altitude than the 210G, while not being too heavy), can use the Jumo 211 engines for the theaters like Soviet Union or MTO.

In order to have the Fw 187, I'd make less Bf 110s (no outright cancellation, since the spirit of this thread is to make even more 2-engined day fighters), no Do 215, less Ju 87s and 88s. Less, if no Hs 129, since German and Vichy resources are better spent on production of HS 12 engines or the German V12s than on the G&R 14M.
No Me 210s and 410, and perhaps even less Bf 109s, since the DB 187-s will be better suited to play defense of the Reich due to their better ability to carry heavy guns' firepower.

 

[TM06]

Japan is an interesting case because they have two of the most compelling reasons for a twin-engined fighter: long range requirements and a desperate need of Interceptors. The Ki-45 and J1N were decent but not nearly enough to pose a genuine threat to the vast swathes of American heavy bombers.
Fortunately, there were two aircraft in particular that could pick up that slack - the Ki-46-III and the Ki-96. The Ki-46-III was a good bit faster than the Ki-96 (390 mph to the Ki-96's 370 mph) but the Ki-96 climbed much better (16.6 m/s to the Ki-46-III's 7.5 m/s) and both of them wield a quite heavy armament package of 2 x 20 mm cannons + 1 x 37 mm cannon (obliquely mounted Schräge Musik style for the Ki-46).
The biggest draw of these two in my opinion is that they don't use the volatile Homare or Ha-43, they use the highly reliable and widely produced Kinsei (specifically the Kinsei 62 making 1,500 hp).
Had the requirement for the Ki-96 not randomly shift back to a two-seat fighter, it absolutely would have entered mass production and would likely have been a strong weapon against the bomber horde.

 

[tomo pauk]

The Ha 41/109 family of engines was criminally under-used by the Japanese. Stick these two on a fighter size of Ki-46 already by 1941 (1942 for the 109), and there is a performer that can also carry a heavy firepower. Don't over-do the internal fuel tankage - use the drop tanks to provide the required range, while making sure that internal tanks are of the self-sealing type.

Americans - someone (Douglas? Curtiss? NAA?) make a simple fighter with two V-1710s on the wings, with the idea that two 37mm cannons are carried in the nose, as per USAAC wishes and blessings. Switch these for 6-8 HMGs, perhaps even install the turbos later - might be easier to do on a classic twin, than to retrofit that on a 1-engined job.

 

[SaparotRob]

With great gooey gobs o' gratitude to T Bolt

 

[TM06]

The Ha 41/109 family of engines was criminally under-used by the Japanese. Stick these two on a fighter size of Ki-46 already by 1941 (1942 for the 109), and there is a performer that can also carry a heavy firepower. Don't over-do the internal fuel tankage - use the drop tanks to provide the required range, while making sure that internal tanks are of the self-sealing type.

One has to wonder how different the designs would be had Nakajima focused on the Ha 41 family instead of the Homare. The Homare was a good engine when it worked, but actually getting it to work was a different matter. The Ha 219 likely could have been fielded much earlier if the Homare wasn't prioritized, maybe even in decent numbers by 1944.
The Ki-83 was already a monster with the Ha 43 engine, imagine the performance had it been fitted with a properly developed Ha 219.

 

[tomo pauk]

One has to wonder how different the designs would be had Nakajima focused on the Ha 41 family instead of the Homare.

Nakajima should've focused on the Ha 41 instead of the Sakae, IMO. Expecting from a 1000-1100 HP engine to perform miracles when the other people are moving towards the 1500-2000 HP types was directly from la-la-land.
Ha 109 never gotten the water-alcohol injection (good for another 15-20 HP at low and mid altitudes), and it's installation never gotten the individual exhausts (can add another 15 mph on a fighter). Ha 109 with a 2-stage S/C would've been sweet.

The Homare was a good engine when it worked, but actually getting it to work was a different matter. The Ha 219 likely could have been fielded much earlier if the Homare wasn't prioritized, maybe even in decent numbers by 1944.

My understanding is that Homare was good if/when the maintenance was good, fuel was at least as specified (ie. 91 or 92 oct), etc. AT least the US experiences were as such. Expecting from a highly-strung Japanese engine that perform at 'book specs' during the harsh realities of the last 12 months of Japanese war (includes shortage of nickel for the valves) will be asking too much IMO.

The Ki-83 was already a monster with the Ha 43 engine, imagine the performance had it been fitted with a properly developed Ha 219.

Ha 43 was flown with advanced superchargers in play, hence the high performance of the aircraft powered by it. Nakajima will need to do kick themselves out from the 1-stage superchargers land 1st, in order to compete with Mitsubishi (as well as against P&W and Packard/RR).

 

[TM06]

Nakajima should've focused on the Ha 41 instead of the Sakae, IMO. Expecting from a 1000-1100 HP engine to perform miracles when the other people are moving towards the 1500-2000 HP types was directly from la-la-land.
Ha 109 never gotten the water-alcohol injection (good for another 15-20 HP at low and mid altitudes), and it's installation never gotten the individual exhausts (can add another 15 mph on a fighter). Ha 109 with a 2-stage S/C would've been sweet.

The Sakae completely slipped my mind, my bad.
I was more referring to the potential increased development time of the 18 cylinder Ha 219 rather than expecting the 14 cylinder 41/109 to compete with the bigger 18 cylinder engines directly. As far as I know, the 219 was based on the 41 platform so my thinking was to prioritize its development over the Homare as they might've been able to get it into production faster that way. The way I see it the 219 had a higher ceiling of potential than the Homare, the Homare was kneecapped by its tiny size and extremely stringent build requirements. The larger 219 would've had more room to mature into a genuinely excellent engine.
From what I've been able to glean, the 219's problems could've been solved in a relatively timely matter if it had been made earlier in the war, but that's merely conjecture on my part.

Ha 43 was flown with advanced superchargers in play, hence the high performance of the aircraft powered by it. Nakajima will need to do kick themselves out from the 1-stage superchargers land 1st, in order to compete with Mitsubishi (as well as against P&W and Packard/RR).

The 219 was fitted with a pretty good turbocharger in its two actual installations - the Ki-87 and Ki-94-II. From what I understand, the Ki-87 only encountered turbo problems due to its installation being too tight. The Ki-94-II didn't fly, but its turbo was placed much further back and likely wouldn't have suffered from the same problems.
Twin-engined aircraft having much more space to work with means the turbo wouldn't have to be tucked in so snugly.
However it might be possible that they would have mated the 219 with a more conventional 2-stage supercharger with enough development time - ditching the turbo for the practicality of a 2-stage perhaps?

 

[GreenKnight121]

Only with the first engine league do we get to the F7F, P-61 and Hornet.

The P-61 was a heavy night-fighter with a 2-3 man crew (pilot, radar operator, optional gunner).
To dispense with the gunner the dorsal 4 x .50 mg turret would be locked to fire directly forward.

Perhaps you meant the P-82 Twin Mustang?