RAF Preference for in line engines vs radials in WW2
Most RAF aircraft seem to have used in line engines in WW2, the Spitfire, Hurricane, Lancaster are a few examples of this
The USAF still used radials in many of their types however, the P47, B17 and B29 etc, curious as to why this was |
Been written about over the years.
How did we get to here from there ? Here being WW2, and there being the first petrol engine manufactured that would predate winged aviation. |
Probably because in-line had a smaller frontal area, so less drag and were developed from the racing engines used in the likes of Schneider cup racers such as the S6.
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In-line engines were water cooled - they had less frontal area, but had complex cooling systems and could be taken out by a single hit on the cooling system. Some of that drag advantage was given back due to the need for big radiators, plus you couldn't run them very long on the ground prior to takeoff without overheating.
Radial engines had more frontal area, but were air cooled so no plumbing, radiator, etc. and were far more tolerant of battle damage. Radial engined aircraft were preferred for ground attack due to the better tolerance to damage from ground fire, and since cooling airflow was provided by the turning prop, they didn't generally overheat sitting on the ground waiting to takeoff. |
Originally Posted by stilton
(Post 11335516)
Most RAF aircraft seem to have used in line engines in WW2, the Spitfire, Hurricane, Lancaster are a few examples of this
The USAF still used radials in many of their types however, the P47, B17 and B29 etc, curious as to why this was Most versions of the Wellington Most versions of the Beaufighter (the merlin powered version was a dog) The most successful version of the Halifax Stirling Sunderland Anson Lysander Beaufort Most versions of the Master Martinet Botha Gladiator Albemarle Swordfish Albacore One version of the Tempest Harrow Bombay Most of the USAAF Fighters did use in-line engines P-38 P-39 P-40 P-51 P-63 The US use of Radials Would have been because that was what powered most of their civil airliners in the pre war period. The British civil market was a cottage industry in comparison. |
Originally Posted by MAINJAFAD
(Post 11335543)
A Lot of RAF/FAA British Aircraft in WWII didn't use In-line Engines,
Most versions of the Wellington Most versions of the Beaufighter (the merlin powered version was a dog) The most successful version of the Halifax Stirling Sunderland Anson Lysander Beaufort Most versions of the Master Martinet Botha Gladiator Albemarle Swordfish Albacore One version of the Tempest Harrow Bombay Most of the USAAF Fighters did use in-line engines P-38 P-39 P-40 P-51 P-63 The US use of Radials Would have been because that was what powered most of their civil airliners in the pre war period. The British civil market was a cottage industry in comparison. Thats a very interesting comparison and the historical perspective you provided was just what I was looking for |
Greg's Airplanes and Automobiles - YouTube
This guy has a plethora of content that deals with your question. Bit nerdy in places, but worth a shufti. |
Originally Posted by MAINJAFAD
(Post 11335543)
A Lot of RAF/FAA British Aircraft in WWII didn't use In-line Engines,
Most versions of the Wellington Most versions of the Beaufighter (the merlin powered version was a dog) The most successful version of the Halifax Stirling Sunderland Anson Lysander Beaufort Most versions of the Master Martinet Botha Gladiator Albemarle Swordfish Albacore One version of the Tempest Harrow Bombay Most of the USAAF Fighters did use in-line engines P-38 P-39 P-40 P-51 P-63 The US use of Radials Would have been because that was what powered most of their civil airliners in the pre war period. The British civil market was a cottage industry in comparison. |
The Secret Horsepower Race by Calum Douglas answers all the possible questions about the engine configuration choice of the British, American, and German manufacturer and is well worth a read. BMW for instance were basically told by the RLM to start building radials despite having no experience and started off by licence building some P&W models.
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Originally Posted by tdracer
(Post 11335535)
In-line engines were water cooled - they had less frontal area, but had complex cooling systems and could be taken out by a single hit on the cooling system. Some of that drag advantage was given back due to the need for big radiators, plus you couldn't run them very long on the ground prior to takeoff without overheating.
Radial engines had more frontal area, but were air cooled so no plumbing, radiator, etc. and were far more tolerant of battle damage. Radial engined aircraft were preferred for ground attack due to the better tolerance to damage from ground fire, and since cooling airflow was provided by the turning prop, they didn't generally overheat sitting on the ground waiting to takeoff. The P51 with clever ducting actually produced thrust from the big radiator bulge on the undersde, not a lot, but more than enough to offset it's drag. A site well worth a visit and read through. https://enginehistory.org/ |
Nobody has mentioned availability yet. When designing a new aircraft type, you go to your (preferred) engine supplier(s) and see what they've got on the shelf/drawing board and how this fits your needs. Wright and P&W had a lot of radial types available or could produce them in sufficient numbers. RR had the Merlin available and could produce these in sufficient numbers. Other types may not have fitted the design as well as these did.
(I know that I am over-simplifying this... but it helps to get the point across. Nobody ever sat down and decided to only have radial engined fighters in the US and inline engined fighters in the UK, so the original question is also very much simplified, as already shown above.) |
And yet the USN fighters such as the Corsair,Wildcat, Hellcat, Bearcat and Tigercat all used radials. Were radials more reliable than in-line engines for over-sea ops?.
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Originally Posted by Jhieminga
(Post 11335744)
Nobody has mentioned availability yet. When designing a new aircraft type, you go to your (preferred) engine supplier(s) and see what they've got on the shelf/drawing board and how this fits your needs. Wright and P&W had a lot of radial types available or could produce them in sufficient numbers. RR had the Merlin available and could produce these in sufficient numbers. Other types may not have fitted the design as well as these did.
(I know that I am over-symplifying this... but it helps to get the point across. Nobody ever sat down and decided to only have radial engined fighters in the US and inline engined fighters in the UK, so the original question is also very much symplified, as already shown above.) I know there are lots of arguments for and against. |
A quick search brought up the Hurricane Mk VII Radial Hurricane with a Bristol Hercules installed
It says it flew with 320 squadron, but I can't find any other information. Another link on a modelers' site said it was a trial only Not that the hurricane was an attractive aircraft, but in this configuration it's an aircraft only a mother could love |
Originally Posted by Sue Vêtements
(Post 11335918)
A quick search brought up the Hurricane Mk VII Radial Hurricane with a Bristol Hercules installed
It says it flew with 320 squadron, but I can't find any other information. Another link on a modelers' site said it was a trial only Not that the hurricane was an attractive aircraft, but in this configuration it's an aircraft only a mother could love |
Originally Posted by MPN11
(Post 11335943)
The Radial Hurricane is bad enough. A Radial Spitfire would be an abomination! And a bet a modeller somewhere has done that!
A radial would indeed turn it into a complete abomination. |
Originally Posted by Sue Vêtements
(Post 11335918)
A quick search brought up the Hurricane Mk VII Radial Hurricane with a Bristol Hercules installed
It says it flew with 320 squadron, but I can't find any other information. Another link on a modelers' site said it was a trial only Not that the hurricane was an attractive aircraft, but in this configuration it's an aircraft only a mother could love |
Originally Posted by VictorGolf
(Post 11335746)
And yet the USN fighters such as the Corsair,Wildcat, Hellcat, Bearcat and Tigercat all used radials. Were radials more reliable than in-line engines for over-sea ops?.
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Perhaps we couldn't build a decent fighter radial? Seems the only radials were for bombers.
Or perhaps it could be argued the inline was superior. P51? |
Originally Posted by NutLoose
(Post 11335735)
The P51 with clever ducting actually produced thrust from the big radiator bulge on the undersde, not a lot, but more than enough to offset it's drag.
Minimizing the frontal area (and resultant drag) of a big radial engine was non-trivial, but there were several highly successful designs that did that and gave the resultant fighter aircraft impressive top speed. To name just a few: F6F Hellcat F4U Corsair P-47 Thunderbolt Japanese A6M Zero |
Minimizing the frontal area (and resultant drag) of a big radial engine was non-trivial, but there were several highly successful designs that did that and gave the resultant fighter aircraft impressive top speed. To name just a few: F6F Hellcat F4U Corsair P-47 Thunderbolt Japanese A6M Zero |
I concur with Jheiminga, in that available or proposed engines would be called up in a new design and the airframe is built around it and the other key requirements of the contract. Significant modifications could then be assessed for a different engine type but would ultimately proven by flight test.
As stated above, some engine/airframe combinations were much more successful: the Hercules powered Halifax and Beaufighter than the Merlin-powered versions, for instance. The Hawker Tempest flew with both the Napier Sabre (Mk.V) and Bristol Centaurus(II) and both were extremely capable. |
Originally Posted by Bing
(Post 11335689)
The Secret Horsepower Race by Calum Douglas answers all the possible questions about the engine configuration choice of the British, American, and German manufacturer and is well worth a read. BMW for instance were basically told by the RLM to start building radials despite having no experience and started off by licence building some P&W models.
“..the company, acting under pressure from the Air Ministry, bought the aero-engine division of the bankrupt Cosmos Engineering Company based in the Bristol suburb of Fishponds, to form the nucleus of a new aero-engine operation..” https://en.m.wikipedia.org/wiki/Bris...oplane_Company |
I seem to remember reading about RR scuppering work on other engine types on the basis that all resources should go towards improving the Merlin. I believe one casualty was an engine by Napier.
Anilv |
In-line engines were water cooled - they had less frontal area, but had complex cooling systems and could be taken out by a single hit on the cooling system. Some of that drag advantage was given back due to the need for big radiators, plus you couldn't run them very long on the ground prior to takeoff without overheating. Radial engines had more frontal area, but were air cooled so no plumbing, radiator, etc. and were far more tolerant of battle damage. Radial engined aircraft were preferred for ground attack due to the better tolerance to damage from ground fire, and since cooling airflow was provided by the turning prop, they didn't generally overheat sitting on the ground waiting to takeoff. A quick search brought up the Hurricane Mk VII Radial Hurricane with a Bristol Hercules installed It says it flew with 320 squadron, but I can't find any other information |
Originally Posted by megan
(Post 11336309)
One of the major problems with the B-29 during WWII was overheating during the taxi for take off, such that there was a CHT limit laid down for commencing the take off run, reach that and it was back to dispersal, take off was commenced with the cooling flaps fully open and the flight engineer with an eye on the CHT's progressively closed them while barreling down the runway. They learnt that maintenance of the cooling baffles around the cylinders was critical. Certainly could take battle damage though, reports of radials making it home with cylinders missing, as in shot off, not misfiring.I think someone is having a leg pull with that site. 320 never flew fighters, they flew Fokker T.VIII, Anson, Hudson and B-25.
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Originally Posted by Anilv
(Post 11336280)
I seem to remember reading about RR scuppering work on other engine types on the basis that all resources should go towards improving the Merlin. I believe one casualty was an engine by Napier.
The engine they DID abandon despite it's evident potential was the 26litre V12 2-stroke Crecy - an engine that could have delivered a Spitfire limited only by Mcrit (~500mph) with 3,000bhp plus 1200lbs of direct exhaust thrust being a very realistic possibility. But the Crecy was mainly abandoned simply because jets were already in development that offered even better performance. Of course Napier spent pretty well 100% of their effort tinkering with the potentially superb but flawed Sabre. The shear amount of time and effort dissipated in their tinkering was a serious issue at a time when war-survival needs demanded efficient use of all resources. There was a point when they were threatened with compulsory nationalisation and being handed to Rolls Royce (who were a "trusted pair of hands") if they didn't get their act together. But I digress. On the point of the original question - in the limit a liquid-cooled engine can always be run at higher specific power outputs than an air-cooled one because of the finer control over the thermal dynamics of the internals. High-power air-cooled engines need to have wider fits and clearances when cold to allow for the poorer control of running temperatures, which is one of the reasons why they often belch so much smoke (burned oil) during start-up and warm-up compared to liquid-cooled ones £0.02 supplied, PDR |
I think also it was due to industrial history. Rolls-Royce built inline engines. Bristol built radials. In the US, it was really only Allison that built inlines. Wright and Pratt & Whitney built radials and were good at it. Wartime exigency, you use the engines and technology you have, rather than trying to re-invent the wheel. Witness the RR Vulture and Napier Sabre developmental problems. You just develop the ones you have as much as you can, while concentrating on the next gen ie turbojet.
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I'm surprised nobody mentioned the Sea Fury. It had a radial.
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Maybe the U.S. found Rolls Royce's license fees to high?
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Originally Posted by Chu Chu
(Post 11336726)
Maybe the U.S. found Rolls Royce's license fees to high?
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Originally Posted by megan
(Post 11336309)
One of the major problems with the B-29 during WWII was overheating during the taxi for take off, such that there was a CHT limit laid down for commencing the take off run, reach that and it was back to dispersal, take off was commenced with the cooling flaps fully open and the flight engineer with an eye on the CHT's progressively closed them while barreling down the runway. They learnt that maintenance of the cooling baffles around the cylinders was critical. Certainly could take battle damage though, reports of radials making it home with cylinders missing, as in shot off, not misfiring.
Having race air-cooled engines, one trick to keep air-cooled engines from overheating was to run them intentionally fuel rich - the extra fuel that can't burn acts to keep the peak temps down (rather counter-intuitive to run more fuel to cool the engine but it works). Of course that has an adverse effect on range... |
Originally Posted by tdracer
(Post 11336772)
The big problem with the B-29 engine was that it was a four-row radial (I believe the first ever attempt at a four-row radial) and cooling the back row was very problematic - especially as you note when there wasn't a lot of airflow through the engine.
Having race air-cooled engines, one trick to keep air-cooled engines from overheating was to run them intentionally fuel rich - the extra fuel that can't burn acts to keep the peak temps down (rather counter-intuitive to run more fuel to cool the engine but it works). Of course that has an adverse effect on range... Fading memories of seeing/hearing a couple of AFRES KC-97s passing over the UK in the mid-70s, fantastic sound! |
Originally Posted by vegassun
(Post 11336596)
I'm surprised nobody mentioned the Sea Fury. It had a radial.
PDR |
Originally Posted by treadigraph
(Post 11336792)
The B-29 used the Wright R3350 which is a two row 18 cylinder engine; as you say the rear row initially proved hard to cool. The B-29 was then developed into the B-50 and C-97, both of which used the P&W R4360 with four rows and 28 cylinders - the "corncob". Also problematic in keeping the backmost rows cool. Did any other four row radial engines see production?
Fading memories of seeing/hearing a couple of AFRES KC-97s passing over the UK in the mid-70s, fantastic sound! I’m guessing these engine cooling issues were also a factor in the B29’s noticeable shallow, almost flat climb angle after takeoff Best forward speed for cooling ? |
B36's featured production, 4-row P&W R4360.
It was also used in Boeing 377, B50, C97, and the Flying Boxcar. It was terribly maintenance intensive in all of them. But, yes, production 4-row radials existed, even, briefly, in civilian service. |
Originally Posted by tdracer
(Post 11336772)
Having race air-cooled engines, one trick to keep air-cooled engines from overheating was to run them intentionally fuel rich - the extra fuel that can't burn acts to keep the peak temps down (rather counter-intuitive to run more fuel to cool the engine but it works). Of course that has an adverse effect on range...
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Originally Posted by tdracer
(Post 11336772)
The big problem with ... cooling the back row was very problematic - especially as you note when there wasn't a lot of airflow through the engine.
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Originally Posted by treadigraph
(Post 11336792)
The B-29 used the Wright R3350 which is a two row 18 cylinder engine; as you say the rear row initially proved hard to cool. The B-29 was then developed into the B-50 and C-97, both of which used the P&W R4360 with four rows and 28 cylinders - the "corncob". Also problematic in keeping the backmost rows cool. Did any other four row radial engines see production?
I visited an air museum last year that had a B-29 on display (sort of the crown jewel of their collection). It had the four row R4360 engines (one engine was sitting on a display stand next to the aircraft) - I mistakenly assumed that was the typical configuration. :( At any rate, cooling the back row(s) on a big radial engine proved problematic, a problem big, water-cooled engines don't have. |
Originally Posted by tdracer
(Post 11337347)
Yea, I stand corrected - apparently most B-29s (and all earlier build) had the two row R3350 engine, with the Pratt R4360 coming along later.
I visited an air museum last year that had a B-29 on display (sort of the crown jewel of their collection). It had the four row R4360 engines (one engine was sitting on a display stand next to the aircraft) - I mistakenly assumed that was the typical configuration. :( At any rate, cooling the back row(s) on a big radial engine proved problematic, a problem big, water-cooled engines don't have. |
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