The P-38 with radial engines? A slightly different X-608 proposal.

[Draconis]

Here is an excerpt from http://www.warbirdsresourcegroup.org/URG/p38_design.html website page.

"Specifications called for a maximum airspeed of at least 360 mph (580 km/h) at altitude, and a climb to 20,000 ft (6,100 m) within six minutes; the toughest set of specifications USAAC had presented to that date. The unbuilt Vultee XP1015 was designed to the same requirement, but was not advanced enough to merit further investigation. A similar single-engine proposal was issued at the same time: Circular Proposal X-609, in response to which the Bell P-39 Airacobra was designed. Both proposals required liquid-cooled Allison V-1710 engines with turbo-superchargers and both gave extra points for tricycle landing gear."

I haven't been able to find a copy of the original circular proposal X-608 document so lets assume the above description is accurate for our purposes.

What if Kelsey and Saville had not made the Allison engine a requirement for the X-608? That is for the twin engine design. This would allow the aircraft companies to choose whatever domestic produced engine, inline or radial they deemed best for their design. Turbocharging would still be a requirement.

Lockheed might have been happier with these conditions. Their previous experience was with radial engine designs. What would Kelly Johnson have come up with using the P&W R-1830? There were turbocharged versions as were used in the P-43. Or the Wright R-1820 similar as in the B-17? Using the wider nacelles radial engines required it would have been possible to fit the landing gear, turbocharger and intercooler, and the oil cooler within the engine nacelle with careful design. This would result in a plane without the need for twin fuselage booms. More of a conventional layout. Would Lockheed have gone with their signature twin fin and rudder?
What might the other aircraft companies have designed under this alternate X-608 proposal?

Something like this using the R-1820s or R- 1830s?

Or what if somebody went for the P&W R-2800? Were these engines available in 1938 or 1939 with turbocharging? Then there might have been something resembling this airplane with similar or better performance in a lighter, single seat design.

I think that requirement for only the Allison V-1710 in OTLs' circular proposal X-608 stifled a lot of potential opportunity. In hindsight a mistake. I wonder why they insisted on that requirement?

 

[Canuck Wingnut]

The Grumman F5F springs to mind as a twin-radial-engine single-seat fighter under development in the US at approximately the same time; turbocharging it would be a lot of development work, but primarily on the engine rather than the airframe side. It was also proposed to the USAAF as the XP-50 and they did look into it- although they much preferred the P-38. I wonder if turbochargers for Pratt and Whitney's radials being available in '38 would have made a difference there?

 

[Draconis]

The Grumman F5F springs to mind as a twin-radial-engine single-seat fighter under development in the US at approximately the same time; turbocharging it would be a lot of development work, but primarily on the engine rather than the airframe side. It was also proposed to the USAAF as the XP-50 and they did look into it- although they much preferred the P-38. I wonder if turbochargers for Pratt and Whitney's radials being available in '38 would have made a difference there?

The Wright R-1820 engine with turbocharging were being installed in B-17s in 1938. That's one possible radial engine for the X-608 proposal. I'm not sure exactly when turbocharged versions of P&W R-1830 became available.

 

[marathag]

Here is what Curtiss was doing in 1935

The Model 76, or XA-14. Underpowered, and a revamp as the Y1A-18 with R-1820s of 850hp really didn't help with speed, and USAAC moved on to the Douglas DB-7, with the new R-2600
General characteristics

• Crew: 2
• Length: 40 ft 6 in (12.34 m)
• Wingspan: 59 ft 6 in (18.14 m)
• Height: 11 ft 0 in (3.35 m)
• Wing area: 530 sq ft (49 m2)
• Empty weight: 8,875 lb (4,026 kg)
• Gross weight: 11,656 lb (5,287 kg)
• Powerplant: 2 × Wright R-1670-5 14-cylinder two-row air-cooled radial piston engines, 775 hp (578 kW) each
• Propellers: 2-bladed two-position variable-pitch propellers

Performance

• Maximum speed: 243 mph (391 km/h, 211 kn) at sea level
• Cruise speed: 222 mph (357 km/h, 193 kn)
• Service ceiling: 28,000 ft (8,500 m)
• Rate of climb: 1,690 ft/min (8.6 m/s)

Armament

• 4 × 0.30 in (7.62 mm) M1919 Browning machine guns forward-firing
• 1 × 0.30 in (7.62 mm) machine-gun on a flexible mount in the rear cockpit
• 650 lb (290 kg) bombs in an internal bomb-bay

 

[Peg Leg Pom]

Here is what Curtiss was doing in 1935

The Model 76, or XA-14. Underpowered, and a revamp as the Y1A-18 with R-1820s of 850hp really didn't help with speed, and USAAC moved on to the Douglas DB-7, with the new R-2600
General characteristics

• Crew: 2
• Length: 40 ft 6 in (12.34 m)
• Wingspan: 59 ft 6 in (18.14 m)
• Height: 11 ft 0 in (3.35 m)
• Wing area: 530 sq ft (49 m2)
• Empty weight: 8,875 lb (4,026 kg)
• Gross weight: 11,656 lb (5,287 kg)
• Powerplant: 2 × Wright R-1670-5 14-cylinder two-row air-cooled radial piston engines, 775 hp (578 kW) each
• Propellers: 2-bladed two-position variable-pitch propellers

Performance

• Maximum speed: 243 mph (391 km/h, 211 kn) at sea level
• Cruise speed: 222 mph (357 km/h, 193 kn)
• Service ceiling: 28,000 ft (8,500 m)
• Rate of climb: 1,690 ft/min (8.6 m/s)

Armament

• 4 × 0.30 in (7.62 mm) M1919 Browning machine guns forward-firing
• 1 × 0.30 in (7.62 mm) machine-gun on a flexible mount in the rear cockpit
• 650 lb (290 kg) bombs in an internal bomb-bay

For 1935 that's not bad, with further development it could have been quite useful in the first couple of years of WWII. That does assume that the aircraft flew as well as it looks like it should.

 

[Driftless]

Here is what Curtiss was doing in 1935

The Model 76, or XA-14. Underpowered, and a revamp as the Y1A-18 with R-1820s of 850hp really didn't help with speed, and USAAC moved on to the Douglas DB-7, with the new R-2600
General characteristics

• Crew: 2
• Length: 40 ft 6 in (12.34 m)
• Wingspan: 59 ft 6 in (18.14 m)
• Height: 11 ft 0 in (3.35 m)
• Wing area: 530 sq ft (49 m2)
• Empty weight: 8,875 lb (4,026 kg)
• Gross weight: 11,656 lb (5,287 kg)
• Powerplant: 2 × Wright R-1670-5 14-cylinder two-row air-cooled radial piston engines, 775 hp (578 kW) each
• Propellers: 2-bladed two-position variable-pitch propellers

Performance

• Maximum speed: 243 mph (391 km/h, 211 kn) at sea level
• Cruise speed: 222 mph (357 km/h, 193 kn)
• Service ceiling: 28,000 ft (8,500 m)
• Rate of climb: 1,690 ft/min (8.6 m/s)

Armament

• 4 × 0.30 in (7.62 mm) M1919 Browning machine guns forward-firing
• 1 × 0.30 in (7.62 mm) machine-gun on a flexible mount in the rear cockpit
• 650 lb (290 kg) bombs in an internal bomb-bay

To go with the thin wing/fat wing discussions from other recent threads, that one has to be pretty "fat", which couldn't help the speed much, I'd guess.

 

[Driftless]

Several of Lockheed's advanced designs from the late 20s to early 30s were single engine radial powered craft: the Sirius, Altair, Orion, etc. The later twin engined small passenger-cargo jobs were radials too. However, none were Kelly Johnson designs though.

As much as I love the OTL P-38 and its relatives, the idea of a Kelly Johnson designed fighter, configured like the F7F Tigercat has an appeal. As noted above, with carefully designed engine nacelles, you probably could fit the turbosupercharger plumbing AND landing gear, plus have room for nose mounted weaponry, even starting in the late thirties. (Grumman's slow progress on the F5F, before it morphed into the F7F largely could be laid on the much higher demand and much higher priority Grumman had for the single engined Wildcat, Hellcat, even Bearcat, and the Avenger. There just wasn't time to give and resources available for working the kinks out of a carrier capable F5F, IMO)

 

[marathag]

To go with the thin wing/fat wing discussions from other recent threads, that one has to be pretty "fat", which couldn't help the speed much, I'd guess.

haven't found that ingo, but thick enough for the bomblets in the wings, that the US flirted with in the late '30s
Pretty, though...

Squint and you can see the KI-46 Dinah there

 

[Peg Leg Pom]

haven't found that ingo, but thick enough for the bomblets in the wings, that the US flirted with in the late '30s
Pretty, though...
View attachment 744902

Squint and you can see the KI-46 Dinah there

I was thinking more a Battle with two Mercury Engines instead of a single Merlin.

 

[Driftless]

haven't found that ingo, but thick enough for the bomblets in the wings, that the US flirted with in the late '30s
Pretty, though...
View attachment 744902

Squint and you can see the KI-46 Dinah there

Exactly - it sure looks like the real goods. Give that plane different engines and wing and it should have had a longer service life. Even the stodgy single engine Shrike variants hung around till early 1942, before they got recycled.

 

[Driftless]

Questions for the radial P-38 analog. I'm assuming it gets the full aerodynamic press (flush riveting, mockups going through the NACA windtunnels (ala Everkings version), maybe even some type of aerodynamic prop spinner(Japanese or FW-190 style) , reduction of as much parasitic drag as possible, etc). Did the US do some form of forced air fan works to prevent radial engine overheating in hot climates?

Give it the OTL P-38 gun package as a starter? Or swap in the Madsen 23mm, even with the performance caveats that always seem to dog it - at least it worked.

I'm also assuming a single pilot and no additional crew member in the early versions. Perhaps an additonal seat can be added for later training or night-fighter versions.

Handed engines?

What would be the basic expected combat radius? (full fuel tanks, full ammunition load, no bombs, pilot, radios, armor plating)

 

[Paul_Sussex]

The Dinah possibly gives a good basis for performance? A two seater aircraft good for 375mph on twin 1040hp engines. So shrink the airframe, install two Twin Wasps and stick four .50s in the nose - could be approaching early Lightning performance.

 

[alspug]

The P-38 was that intersection between gifted airframe designer and excellent engines. The Allison engines had as much if not more capability than the Merlin but somehow got missed in the mix. The P-38 could have had a pair of big radials in closely fitted fairings and been just as succesful it would however not meet the same visual apeal.

 

[tomo pauk]

I think that requirement for only the Allison V-1710 in OTLs' circular proposal X-608 stifled a lot of potential opportunity. In hindsight a mistake. I wonder why they insisted on that requirement?

Wisdom of the day stipulated that at very high altitudes, like the 25000 ft was back then, and at high power settings ('normal' occurrence with fighter A/C) the radial engines will be harder to cool than the liquid-cooled types. Radials 'fought back' with ever-increasing finning area.

Or what if somebody went for the P&W R-2800? Were these engines available in 1938 or 1939 with turbocharging? Then there might have been something resembling this airplane with similar or better performance in a lighter, single seat design.

The R-2800 was not in production until early 1941. It was 1st flown in mid-1940.
However - the Wright R-2600 powered the Boeing 314 Clipper prototype in mid-1938. So my idea is that Lockheed makes a fighter around a single R-2600 with a turbocharger behind the cockpit, and then do a switch to the R-2800 by 1941. Bingo - an early P-47.
(I've copied the engine-swap idea from the Hellcat's history; granted, there was no turboes involved there, bar one prototype)

 

[tomo pauk]

The P-38 was that intersection between gifted airframe designer and excellent engines. The Allison engines had as much if not more capability than the Merlin but somehow got missed in the mix. The P-38 could have had a pair of big radials in closely fitted fairings and been just as succesful it would however not meet the same visual apeal.

P-38 engine choice was probably least of it's concern. A list of problems unrelated to the engine choice:
- opting for a twin-boom layout by Lockhedd (= slower to make than a classic, will cost and weight more, less useful internal volume, distinctive shape for enemy to indentify, blind spots due to the booms)
- compressibility issues
- insufficient capacity of original intercoolers
- appalling heating until too late
- choice of just one generator per A/C
- slow rate of roll until 1944
- utterly complicated cockpit vs. other US fighters

 

[Draconis]

Wisdom of the day stipulated that at very high altitudes, like the 25000 ft was back then, and at high power settings ('normal' occurrence with fighter A/C) the radial engines will be harder to cool than the liquid-cooled types. Radials 'fought back' with ever-increasing finning area.



The R-2800 was not in production until early 1941. It was 1st flown in mid-1940.
However - the Wright R-2600 powered the Boeing 314 Clipper prototype in mid-1938. So my idea is that Lockheed makes a fighter around a single R-2600 with a turbocharger behind the cockpit, and then do a switch to the R-2800 by 1941. Bingo - an early P-47.
(I've copied the engine-swap idea from the Hellcat's history;grated there was no turboes involved there, bar one prototype)

Well, if the Allison V-1710 only requirement was also relaxed for the single engine X-609 proposal then something along those lines may have occurred. A further improved P-43 Lancer might have worked if Seversky/Republic had started earlier on its design.

 

[tomo pauk]

Well, if the Allison V-1710 only requirement was also relaxed for the single engine X-609 proposal then something along those lines may have occurred. A further improved P-43 Lancer might have worked if Seversky/Republic had started earlier on its design.

Big radial (R-2600, quickly followed by R-2800) in the nose, turbo behind the pilot - too bad that such a layout didn't materialized already by Spring of 1940. Eg. by USAAC saying to Seversky/Republic by early 1939: Okay, the YP-43 concept is valid, but we want even more performance than it will be possible with 1200 HP, and will wait a few months until you get the design's estimates; obviously, this also skips the paper-only XP-44, and the Allison-engined XP-47A that remained as a mock-up.
Or - K. Johnson supposedly wanted one 1500 HP engine for the new fighter, but settled for two 1000 HP ones since the 1500 HP engine was not available; in this case, he picks the R-2600 and goes from there.

The V-1710-powered fighter of the layout like the P-43 (engine->cockpit->turbo) should've also worked far better than the too small and complicated XP-39.

 

[Draconis]

P-38 engine choice was probably least of it's concern. A list of problems unrelated to the engine choice:
- opting for a twin-boom layout by Lockhedd (= slower to make than a classic, will cost and weight more, less useful internal volume, distinctive shape for enemy to indentify, blind spots due to the booms)
- compressibility issues
- insufficient capacity of original intercoolers
- appalling heating until too late
- choice of just one generator per A/C
- slow rate of roll until 1944
- utterly complicated cockpit vs. other US fighters

Those are all very good points. Lockheed (and not only Lockheed) using radial engines instead could alleviate some of those problems.

I think the basic layout would be different. No twin booms needed for fitting equipment. Would Lockheed use different NACA designs? Without having the central nacelle and boom design the effects of compressibility will be different. Would this lead to a higher critical Mach number? Would the worse element of "compressibility tuck" be avoided? Maybe, but all these new fighters will face compressibility problems in one form or other. I think a change to the OTLs' P-38 is more likely to improve rather then worsen it. Speculative I know.

Fitting box type intercoolers similar as were used in the B-17 into the engine nacelles with a cowl flap to control the airflow will give a more effective and better controlled intercooling.

The cockpit heating simply requires some intelligent design work. This item is not so dependent on engine type.

Adding the weight and complexity of a second generator should be done only if necessary. If the airplanes are using Hydromatic propellers instead of Curtis Electric then losing the electric power won't feather the propellers. But at that time they'd likely be Curtis Electric propellers.

For sure boosting the roll rate at high speed was a big improvement. This is not really dependent on the engine choice but it was certainly needed. Either by hydraulic boost of the aileron control rod linkages or deflection tabs on the trailing edge of the ailerons as was done with the F6F. The sooner the better.

Lockheed did lag somewhat in cockpit ergonomics. But there was an awful lot to cram into one cockpit. The engine controls for one example were complex. The P-47 had a simpler one lever control for its engine. Was that because it used the R-2800? Were turbocharged radial engines easier to fit with a simpler throttle set up then an inline engine?

I'm thinking that using radial engines possibly would have solved some of the P-38s' problems. Using the Wright R-2600 would add a bit more weight then the Allison even accounting for no coolant radiators but would provide a few hundred more HP each side too.

 

[Draconis]

haven't found that ingo, but thick enough for the bomblets in the wings, that the US flirted with in the late '30s
Pretty, though...
View attachment 744902

Squint and you can see the KI-46 Dinah there

Split second aircraft recognition is tough enough without squinting thank you very much.

Does look a bit like the Dinah though. The kind with the original nose.

 

[tomo pauk]

I think the basic layout would be different. No twin booms needed for fitting equipment. Would Lockheed use different NACA designs? Without having the central nacelle and boom design the effects of compressibility will be different. Would this lead to a higher critical Mach number? Would the worse element of "compressibility tuck" be avoided? Maybe, but all these new fighters will face compressibility problems in one form or other. I think a change to the OTLs' P-38 is more likely to improve rather then worsen it. Speculative I know.

There 'tunnel' between the pod and nacelle was speeding up the airflow above and under the inner wing section, leading to the Mach tuck, even if the NACA 23016 (ie. 16% thickness to chord ratio) was not that thick a profile. If the 'no P-38' is still a 2-engined A/C, perhaps the issue will repeat even if the radial engine is not used; going with one-engined design removes that issue all together.
One way to avoid the 'tunnel' problem is to have nacelle hang down, and pod/fuselage to be above the wing (ie. like the DH Hornet had), so the tunnel does not form. Again, a thing that has no bearing on engine type. Same as intercooler type chosen.
A 2-engined aircraft with tons of metal many feet from the centreline will not be rolling as good as the 1-engined fighter.

Lockheed did lag somewhat in cockpit ergonomics. But there was an awful lot to cram into one cockpit. The engine controls for one example were complex. The P-47 had a simpler one lever control for its engine. Was that because it used the R-2800? Were turbocharged radial engines easier to fit with a simpler throttle set up then an inline engine?

Pilot of a P-38 have had two of everything - powerplant-wise - vs. what the pilot of a P-47 had - gauges, levers, and probably emergency lights, plus two liquid cooling systems with their gauges. Some of the gauges and levers were also tossed hap-haphazardly on the P-38.
The assessment of the WAllied fighter types notes, in 1944, that P-38 had the worst layout of the stuff in the cockpit, while the F6F was rated as the best ('Report from the Joint fighter conference' via 'America's hundred thousands' book).

I thinking that using radial engines possibly would have solved some of the P-38s' problems. Using the Wright R-2600 would add a bit more weight then the Allison even accounting for no coolant radiators but would provide a few hundred more HP each side too.

Needs to account for the greater fuel capacity now required, too. We'd probably end up with a fighter sized like the F7F?
Another possible engine is the R-2180A, if we still want a twin?