Alternatives to the historical P-38 Lightning?

[Shortround6]

So basically, we're reinventing the P-47

Not quite

The Wright R-2600 never took to turbo charging very well. granted they only tried a few times.

There was also sort of a hole in GE turbo line up. the B series turbos worked with 800-1400hp engines, later ones do better with late model P-38s. but they operated 3-4,000rpm higher rpm than the early versions.

The C-series started at 1800hp to 2200hp. The early Wright R-2600s made 1500-1600hp. You don't have the required air flow from the B- series turbo. You might be able to restrict the C Series to lower air flow but the C series turbo was about 100lbs heavier than a B series. You are going to need 33% more cooling air for the intercooler for a 1600hp engine than for a 1200hp engine. If you cut the rated altitude down from 25,000ft to 20,000ft you can use a smaller intercooler and less airflow.

Until 1940 comes the .50 machine guns were only good for 600rpm (and in testing often that didn't work) and we have a lot of airplane and powerplant tied up for only four .50 cal guns.

 

[Reluctant Poster]

Ya know, it's amazing the thought process when decisions like this are made. I would think the generator would weigh about 40 pounds and cost about $150.00 in 1941 dollars. When you're trying to get the maximum amount of performance out of an aircraft, you'll have folks looking at doing anything to reduce weight. 40 pounds can be huge, especially when developing a fighter. Multiply that $150 generator cost by say 1000 units and you're looking at $150,000 in 1941 dollars which equates to $2.7 million in today's dollars. During a time when you're trying to build a high performance aircraft almost by committee and having to deal with a budget office that is still watching depression era dollars, I could see how this decision could be made. It would take operational experience as well as open purse strings to rectify this.

The one of the biggest cause of losses for B17 and 24s were engine fires so in the spring of 1943 the USAAF removed the nacelle extinguishers as part of a weight reduction program. in December 1943 the B24s got theirs back while the B17 waited until the summer of 1944. The other feature I believe was deleted was the emergency oil back up tank for the propeller feathering system. It was rare for a bomber to make it back with an unfeathered prop. With thinking like that for big expensive bombers with big expensive crews I think the P38 pilots should have been grateful that they at least got an engine driven generator instead of a wind driven one.

 

[wuzak]

The R-2600 was never built for a motor-cannon through the hub (that I'm aware of) and the 37mm cannot be synchronized so the wing roots are out.

There is going to be a great amount of difficulty getting a motor-cannon through the hub on an R-2600, or any other radial, for that matter, unless the reduction gearbox is remotely mounted (like the P-39).

 

[wuzak]

Well, this might have done the trick. Same time frame as P-38.

View attachment 659015View attachment 659016

A no-nonsense fighter with two non-turbo* V-1710s in 'classic' layout (ie. along the lines of Whirlwind, Type 327, Fw-187 and later DH Hornet) might've been a valuable asset. We'd probably have 370+ mph at 15000 ft even with the -33 engines if the aircraft's size is kept modest, at least when looking at what Ro.58 or Whirly were capable for.
(P-38D and E were doing ~375 mph, but at 20000 ft)

*yes, USAAC/AAF was hell bent on the idea that new fighters have to have turbochargers

The Type 324 and 327 were quite a bit smaller than the P-38.

If it was being built in the IS I would think the 6 x 20mm cannon would have been replaced with 2 x 37mm cannon, because these have a flat trajectory all the way to the end of the barrel, and possibly 2 or 4 0.50" hmgs in the outer wings.

The Type 327, as proposed, had the exhaust ducted through and exiting at the rear of the nacelle. The projected power of the Merlin XX at the time was similar to the V-1710, 1,265hp @ 9,500ft and 1,145hp @ 16,750ft.

A turbo may have been able to be fitted at the rear of the nacelle, like the installation of teh XP-67.

McDonnell XP-67 Moonbat

The final McDonnell design, the McDonnell XP-67 "Bat" or "Moonbat", was powered by a pair of engines in wing-mounted nacelles with 4-bladed propellers in a tractor configuration. However, the design was quite ambitious; the design team tried to maintain a true airfoil section through the center...

ww2aircraft.net

 

[Thumpalumpacus]

There is going to be a great amount of difficulty getting a motor-cannon through the hub on an R-2600, or any other radial, for that matter, unless the reduction gearbox is remotely mounted (like the P-39).

What could go wrong?

 

[GrauGeist]

The only radial engined fighter that had a nose-cannon, that I can think of, is the Piaggio P.119 - and it was able to mount a 20mm cannon in the nose, because the radial engine was mounted mid-ship (a la P-39).
By virtue of a radial engine's design, there is literally no way to mount a motor cannon in it's centerline.

 

[tomo pauk]

Here's my attempt. Although the trouble is that CP.608 specifically called for a Twin-Engine interceptor so this would have to be in response to 609 (which led to the P-39). The other roadblock I'm running into is getting the proper armament fitted. I just can't find a way to fit 20mms much less a 37mm. The R-2600 was never built for a motor-cannon through the hub (that I'm aware of) and the 37mm cannot be synchronized so the wing roots are out.

Such a fighter, made around a big radial engine, turbo installation and a lot of fuel is ought to have a big wing, talk 280-300 sq ft. 20mm will have no problems to be fit in the wings, while 37mm can go in the pods.

So basically, we're reinventing the P-47

Something in-between the XP-44 and XP-47B.
Main advantage is the earlier availability, 1st flight in early 1939 and series production by early 1941, instead of 1st flight in mid 1941 and series production in early 1942.

The only radial engined fighter that had a nose-cannon, that I can think of, is the Piaggio P.119 - and it was able to mount a 20mm cannon in the nose, because the radial engine was mounted mid-ship (a la P-39).
By virtue of a radial engine's design, there is literally no way to mount a motor cannon in it's centerline.

No need for nose cannon here.

 

[EverKing]

So basically, we're reinventing the P-47

Something less than a P-47. But more than the P-43. As I was drawing it I certainly saw the resemblance—but something else was creeping in there too as I was trying to find clever packaging solutions: this almost seems as American FW-190.

 

[EverKing]

There is going to be a great amount of difficulty getting a motor-cannon through the hub on an R-2600, or any other radial, for that matter, unless the reduction gearbox is remotely mounted (like the P-39).

Yes, which is why I ruled it out.

I think what we've discovered in this discussion was that there really wasn't a single engined radial solution to the Circular Proposals in question. Unless we get really goofy and go for something along the lines of the XP-52/59.

I may try a conventional twin R-2600 design though.

 

[GrauGeist]

The Bell XF-52/59 was not all that unreasonable as a design, as the Swedes had a comparable design with the SAAB J-21.
Which, by the way, transitioned from a piston-powered type, to a jet-powered type (J-21R).

The problem the the USAAC's proposal, was timing. At that point in time, they were wanting an aircraft to fill a role that current engines were hard-pressed to deliver. This is why many air forces were exploring twin engined fighters (true fighters, not "heavy fighters") like SNCASE's SE.100, Fokker's G.I, Focke-Wulf's Fw187 and Grumman's XF5F/XP-50.

 

[Shortround6]

I may try a conventional twin R-2600 design though.

The 1600hp R-2600 was rated for 1600hp at 1,000ft on 91 octane fuel and 1,500ft on 100 octane fuel in low gear.
In high gear the engine was good for 1400hp at 10,000ft on 91 octane fuel and 11,500ft on 100 octane fuel.

A R-2600 was the same diameter as an R-3350.

The R-2600 doesn't seem like a good candidate for a fighter engine, either single or twin.

 

[Thumpalumpacus]

The Bell XF-52/59 was not all that unreasonable as a design, as the Swedes had a comparable design with the SAAB J-21.
Which, by the way, transitioned from a piston-powered type, to a jet-powered type (J-21R).

The problem the the USAAC's proposal, was timing. At that point in time, they were wanting an aircraft to fill a role that current engines were hard-pressed to deliver. This is why many air forces were exploring twin engined fighters (true fighters, not "heavy fighters") like SNCASE's SE.100, Fokker's G.I, Focke-Wulf's Fw187 and Grumman's XF5F/XP-50.

Out of curiosity only, do you reckon the P-38 a "fighter" or a "heavy fighter"?

 

[GrauGeist]

Out of curiosity only, do you reckon the P-38 a "fighter" or a "heavy fighter"?

Being a single-seater, I've always felt the P-38 fits into the fighter category perfectly. It is perhaps one of the largest of the twin-engined fighters, but it delivered on the USAAC's request for a twin-engine interceptor, and then some.

 

[tomo pauk]

The 1600hp R-2600 was rated for 1600hp at 1,000ft on 91 octane fuel and 1,500ft on 100 octane fuel in low gear.
In high gear the engine was good for 1400hp at 10,000ft on 91 octane fuel and 11,500ft on 100 octane fuel.

A R-2600 was the same diameter as an R-3350.

The R-2600 doesn't seem like a good candidate for a fighter engine, either single or twin.

R-2600 will need all the turbo help it can get. Even the 1750 HP and the later 1900 HP versions, in order to be competitive against the axis best.
It is/was probably too bad that the 2-stage R-2600 was a bit late in coming (even if it was much earlier than the 2-stage V-1710); it was also 'Navy engine', that can complicate things for the Army before Pearl Harbor.

A fighter designed around a R-2600 should be able to switch to the R-2800...

 

[Shortround6]

Even the 1750 HP and the later 1900 HP versions, in order to be competitive against the axis best.
It is/was probably too bad that the 2-stage R-2600 was a bit late in coming (even if it was much earlier than the 2-stage V-1710); it was also 'Navy engine', that can complicate things for the Army before Pearl Harbor.

Curtiss records show 9 (?) two stage R-2600-10 engines built between 5/41 and 5/42.
they had a take-off rating of 1700hp. Page/s I am looking don't show altitude rating/s.
dry weight of engine was 2215lbs. It looks like most were installed (or planned to be installed in) a variety of TBFs and TBMs although one PB2Y-4 engine flying boat may have had them.

there was also a single R-2600-14 built in Aug 1943, with an 1800hp rating (?) for the XF7F but since the plane was a twin?

and then there were two R-2600-16 (?) built 12/41- 4/42. This was the engine for the F6F-1 Hellcat. This was rated at 1700hp for take-off. Dry weight was 2127lbs.
Grumman Aircraft since 1929 claims that the engine gave 1380hr at 21,500ft.

There were no 1900hp R-2600 engines before 1943 no matter what kind of supercharger/s. And fewer than 20 were built before July.

A fighter designed around a R-2600 should be able to switch to the R-2800...

Should be able to switch and it should switch, just a soon as possible.
The window of opportunity for the R-2600 powered fighter is very short, a few months? Which basically means airframe makers know the R-2800 powered version would be a better choice before either version actually gets in the air. The R-2800 Hellcat flew 34 days after the R-2600 powered plane and Grumman had estimated that the R-2800 version would have much higher performance.

If you want to try for a single stage supercharger the 1700hp version doesn't start to show up until June of 1941 for production models. In June of 1941 the R-2800 "A" (1850hp) hits 100 engines a month. The single stage 1700hp R-2600 is going to stay a 1700hp engine until 1943. The P & W R-2800 goes to a 2000hp engine in Jan 1942 with over 400 engines built.

The only window of opportunity for the R-2600 is for the 1600hp version in 1940 and early 1941.

The 1850hp P & W engine (early B-26) at altitude makes 100hp (1500hp) more 2,500ft higher up (14,000ft instead of 11,500ft)
The 2000hp P & W engine makes 1600HP at 13,500ft in Jan 1942.

The R-2600 is a bit lighter but is actually a few inches bigger in diameter.
The 1600hp R-2600 runs at 2400rpm.
The 1700hp R-2600 runs at 2500rpm
The 1850hp R-2800 runs at 2600rpm
The 2000hp R-2800 runs at 2700rpm.

 

[gordonm1]

I read this question and just thought of what played out in history. There wasn't an "easy button" to press and replace the P38 so they built a second factory to build more Mustangs and tried to get Curtiss to build P47's. The USA having three great Army fighters and several good Navy fighters was a good thing (for USA). Have a good Memorial Day all.

 

[wuzak]

Could the P-38 have been built as a conventional twin, with turbocharged V-1710s, but with the turbochargers mounted in the fuselage, similar to what was proposed for the Curtiss XP-71?

Would such an arrangement lose more due to complexity than it would gain?

 

[Thumpalumpacus]

Could the P-38 have been built as a conventional twin, with turbocharged V-1710s, but with the turbochargers mounted in the fuselage, similar to what was proposed for the Curtiss XP-71?

Would such an arrangement lose more due to complexity than it would gain?

That's a lot of ducting. Wouldn't that requirement some enlargement to the design?

 

[wuzak]

That's a lot of ducting. Wouldn't that requirement some enlargement to the design?

Not sure. It depends on how big the fuselage is, I guess.

It is a lot of ducting, but, perhaps, not much more than the actual P-38.

 

[Thumpalumpacus]

Not sure. It depends on how bigsg the fuselage is, I guess.

It is a lot of ducting, but, perhaps, not much more than the actual P-38.

The -38 had its turbochargers in the booms. Wouldn't ducting that into the centerline enlarge the central nacelle, and cramp the interior part of the wings?