Inline or radial

[Rick]

Interesting short discussion on inline vs radial engines. Did not know about the radial engine P38 idea

https://yarchive.net/mil/air_cooled.html

[sunday]

7 minutes ago, Rick said:

Interesting short discussion on inline vs radial engines. Did not know about the radial engine P38 idea

https://yarchive.net/mil/air_cooled.html

Could have been bit like the F5F or F7F. Or like this thing or this one.

Edited November 28, 2020 by sunday

[shep854]

P-61 Black Widow

[CaptLuke]

1 hour ago, shep854 said:

P-61 Black Widow

Nightfighters were often much larger aircraft; the P-61 was bigger and heavier than a B-25.  The F7F was more comparable in size, though still substantially heavier.

Mitsubishi Ki-83 and Kawasaki Ki-96 were also P-38 sized, radial engined, 1-2 seat fighters.

[Brian Kennedy]

15 hours ago, CaptLuke said:

Nightfighters were often much larger aircraft; the P-61 was bigger and heavier than a B-25.  The F7F was more comparable in size, though still substantially heavier.

Mitsubishi Ki-83 and Kawasaki Ki-96 were also P-38 sized, radial engined, 1-2 seat fighters.

My favorite https://en.m.wikipedia.org/wiki/Grumman_XF5F_Skyrocket

[DougRichards]

An interesting comparison of two aircraft that served side by side, albeit in different, but sometimes overlapping roles:  The Mosquito, powered by in-line (Merlin) and the Beaufighter powered by radials.

Apart from Merlins also being needed for Spitfires and Lancasters (and others of course) the speed and advantage of the Mosquito was notable, whilst the Beau was rugged and dependable, particularly in the low level roles in which it was used once the Mosquito took over night fighting.  Some torpedo carrying Mosquitoes were built, but more Torbeaus were used.  The Mosquito also had a much higher service ceiling.

[Yama]

CDB100620 is undoubtely correct in his argument about advantages of radials in ground attack or passenger aircraft applications. Though it must be noted that some very profilic ground attack aircraft used inline engines - Il-2, Ju-87 most notably.

However in fighters, argument is less clear-cut. Inline engined fighters remained successful and popular right up to end of war. Vulnerability of liquid cooling system didn't seem to have noticeable effect on their combat performance. Superchargers and turbochargers were just as vulnerable weak points in radial engines as they were in inline engines. Twin-row (or bigger) radials were also very complicated and expensive to manufacture. R-4360 Wasp Major proved completely uneconomical in commercial setting.

Finally, CDB100620 proved such a shady character that his integrity on almost any subject comes into question.

[DougRichards]

20 hours ago, CaptLuke said:

Nightfighters were often much larger aircraft; the P-61 was bigger and heavier than a B-25.  The F7F was more comparable in size, though still substantially heavier.

Mitsubishi Ki-83 and Kawasaki Ki-96 were also P-38 sized, radial engined, 1-2 seat fighters.

One of the competitors to the P-61 was the A-26 Invader, that at one stage was proposed as a nightfighter with radar.  This did not occur obviously, but the A-26 did serve in WW2, Korea and VN.

The P-61 was developed as the F-15 Reporter, a fairly high performance recon aircraft of the late 1940s.

[shep854]

The layout of the P-61 was what came to my mind.  There was an attempt to adapt the P-38 for night-fighting; the P-38M with a tiny radar operator's cockpit right behind the pilot and a radar pod under the nose:

----

For ground attack, I've seen mention that the P-40 was considered less vulnerable to ground fire, since the cooling systems were packed right under the engine, rather than spread out through the airframe.

[CaptLuke]

6 hours ago, DougRichards said:

An interesting comparison of two aircraft that served side by side, albeit in different, but sometimes overlapping roles:  The Mosquito, powered by in-line (Merlin) and the Beaufighter powered by radials.

Apart from Merlins also being needed for Spitfires and Lancasters (and others of course) the speed and advantage of the Mosquito was notable, whilst the Beau was rugged and dependable, particularly in the low level roles in which it was used once the Mosquito took over night fighting.  Some torpedo carrying Mosquitoes were built, but more Torbeaus were used.  The Mosquito also had a much higher service ceiling.

I'm not sure that's the best comparison due to the differences in the airframes.

For such a comparison you could also look to the Ki61/Ki100 conversion, LaGG 3 vs. LaGG 5, and, of course, the Hawker Tempest where you can see inline vs. radial in basically the same airframe and the same role.

• The Japanese greatly preferred the radial version which, to be fair, had a big advantage in horsepower
• The British experience seemed to be that the Sabre and Centaurus versions were very comparable but that the Centaurus powered version had an edge.  Nevertheless, they persisted with both lines of development so I assume they weren't seeing a big advantage either way.
  • There's an interesting comment ref the Tempest: "The weight of the heavier Centaurus engine (2,695 lb/1,222 kg versus 2,360 lb/1,070 kg) was offset by the absence of a heavy radiator unit, so that the Tempest II was only some 20 lb (9 kg) heavier overall."
• Like the Ki61/Ki100, the LaGG 3 (inline) to LaGG 5 (radial) was a huge improvement.

Edited November 29, 2020 by CaptLuke
Forgot the LaGGs first time through

[bojan]

A lot of La-5 improvement over LaGG-3 came not only from the engine, but from a frame and wings refinement.

[Markus Becker]

9 hours ago, DougRichards said:

Apart from Merlins also being needed for Spitfires and Lancasters (and others of course) the speed and advantage of the Mosquito was notable, whilst the Beau was rugged and dependable, particularly in the low level roles in which it was used once the Mosquito took over night fighting.  Some torpedo carrying Mosquitoes were built, but more Torbeaus were used.  The Mosquito also had a much higher service ceiling.

 

That's a matter of supercharging, not the type of engine. As to the question what engine is better, IMO any technical difference was too small to make a difference given that both inline and radials were widely used by most nations. 

[DB]

I think that as the number of cylinders increases, the radials simply get better from a packaging point of view. The step-change equivalent to "add another ring" for inlines is to go to W, Y W or H, and all of those are.... unpleasant for various reasons, and will generally present a step-change in cross section in comparison. You can't really put more cylinders in line (well, 8 exists), because crankshaft harmonics get more and more tricky as the shaft gets longer, same with the camshafts which rotate at twice the speed generally speaking.

You only have to look at the insane complexity of a Napier Sabre to see that it was always going to be tricky to make reliable, althopugh some of that was the sleeve valve design.

A bomber comparison would be the Lancaster B I versus the B II. One had Merlins, the other Bristol Hercules. Nominally similar powers, but the Hercules version had a lower ceiling and worse bomb-load (not unrelated!). Comparisons of the Merlin XX and the Hercules VI suggest that the latter should have improved performance, although that would depend entirely on how the two-speed superchargers were optimised.

[Stuart Galbraith]

Ironically the BII was the one with the oversize bomb bay.

The Hercules engine Halifax seemed to have better performance than the Merlin powered ones, though that may at least be in part losing the nose turret and swapping our the ultra craggy mid upper for a low drag example.

[Yama]

9 hours ago, bojan said:

A lot of La-5 improvement over LaGG-3 came not only from the engine, but from a frame and wings refinement.

Last two LaGG-3 series apparently were quite good performers. However by then most of the lines had been converted to La-5 already.

There were also examples of radial engined fighters switching to inline engines, such as P-40 and FW-190D et al.

[bojan]

Just now, Yama said:

Last two LaGG-3 series apparently were quite good performers...

IIRC they also got same refinements of the hull and wings as did La-5. Which would highlight the point that poor performances of original version was a problem of the aerodynamics, not engine. 

[EchoFiveMike]

Camshafts rotate at half crankshaft speed in 4 cycle engines.  Was there ever significant development of 2 cycle aircraft engines?  S/F....Ken M

[KV7]

There was. The Rolls Royce Crecy and Napier Nomad come to mind.

[DougRichards]

3 hours ago, EchoFiveMike said:

Camshafts rotate at half crankshaft speed in 4 cycle engines.  Was there ever significant development of 2 cycle aircraft engines?  S/F....Ken M

Only the https://en.wikipedia.org/wiki/Junkers_Jumo_205

But there was only ever 900 of those so 'significance' could be called into question.

then there was this:
https://en.wikipedia.org/wiki/Leyland_L60

Edited November 30, 2020 by DougRichards
additional information

[Rick]

Different airframes of course, but I thought the P47 and P51 were an interesting comparison.

[CaptLuke]

2 hours ago, Rick said:

Different airframes of course, but I thought the P47 and P51 were an interesting comparison.

And then there was the XP-47H, which used a 2,300 hp Chrysler XIV-2220-1 16-cylinder inverted-V engine in a P-47D-15-RE airframe, so (somewhat like the Tempest designers) Republic wasn't committed to radials so much as big, powerful engines.

[Yama]

3 hours ago, Rick said:

Different airframes of course, but I thought the P47 and P51 were an interesting comparison.

As effective as P-47 was, it was also like 70% more expensive than P-51. Really, USA was pretty much the only country which could afford to build thousands of very complicated fighters like P-47 and P-38.

[Stuart Galbraith]

Wasnt that something to do with USAAF requirements over airframe strength though? Something to do with being able to take stressloads that the British Air Ministry though somewhat unnecessary, which is why we were able to come up with something light like the Spitfire, and the US came up with the p47. Ok, so there is the P40, but even that aircraft, vastly underrated though it undoubtedly is, was not quite on the same level as a Spitfire or Me109.

Its interesting to note that the US only got the Mustang after the British Air Ministry wrote the specifications for it.  The difference is even more stark when you look at bombers, ie, Mosquito vs B25.

[Yama]

I'm not well-read on that area, but USAAF did seem to have some pretty weird requirements which ended up hobbling the performance. Certainly it is hard to understand why the most advanced country in aeronautics came up with uninspired slogs like P-35 and P-36.

That said, German airframe design standards actually had higher requirements for stressloads than US.

[Stuart Galbraith]

As far as bombers, thats at least in part because of the obsession with dive bombing. The desire of the German RLM to turn the HE177 into a divebomber has been much reported, but the same was true of the JU88. It was meant to be a schnellbomber, something akin to a Mosquito, but by the time they beefed it up and put divebrakes on it, it wasnt that much of an advance on a He111.

Fighters, im not sure how much I buy that. The Spitfire and the Me109 were very similar in performance, remarkably so when you consider the Germans were managing to carry heavy machine guns and even cannons before we regularly did. And there are several well known examples of Me109's coming unglued in service, in the F model and even later in the production as they turned to components made of wood. Maybe the Fw190 which was relatively un-maneuverable, except again, that was carrying a thumping great radial and several cannons around. So If they did indeed had standards similar to the Americans, they seem very creditably to have usually ignored them, at least as far as fighters were concerned.

Then there is the Japanese, who went yet another stage again when it came to lightness.