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RAF Preference for in line engines vs radials in WW2

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RAF Preference for in line engines vs radials in WW2

Old 22nd Nov 2022, 23:06
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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
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Old 22nd Nov 2022, 23:17
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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.







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Old 22nd Nov 2022, 23:43
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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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Old 22nd Nov 2022, 23:53
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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.
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Old 23rd Nov 2022, 00:22
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Originally Posted by stilton View Post
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
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.
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Old 23rd Nov 2022, 05:55
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Originally Posted by MAINJAFAD View Post
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
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Old 23rd Nov 2022, 06:06
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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.
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Old 23rd Nov 2022, 08:19
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Originally Posted by MAINJAFAD View Post
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.
You forgot the MK II Lanc old boy.
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Old 23rd Nov 2022, 09:10
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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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Old 23rd Nov 2022, 10:11
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Originally Posted by tdracer View Post
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 original S6 racers pumped the coolant through the leading edges of the wings for cooling IIRC

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/
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Old 23rd Nov 2022, 10:20
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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.)

Last edited by Jhieminga; 24th Nov 2022 at 09:25. Reason: silly typos
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Old 23rd Nov 2022, 10:21
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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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Old 23rd Nov 2022, 11:05
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Originally Posted by Jhieminga View Post
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.)
Without wanting to open a can of worms, I was always led to believe that the reason most US aircraft ( civil and military) pre and indeed post war used air cooled engines, was to do with the superior weight/power ratio.
I know there are lots of arguments for and against.
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Old 23rd Nov 2022, 14:49
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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
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Old 23rd Nov 2022, 15:28
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Originally Posted by Sue VÍtements View Post
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
The Radial Hurricane is bad enough. A Radial Spitfire would be an abomination! And a bet a modeller somewhere has done that!
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Old 23rd Nov 2022, 15:45
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Originally Posted by MPN11 View Post
The Radial Hurricane is bad enough. A Radial Spitfire would be an abomination! And a bet a modeller somewhere has done that!
My late uncle flew both the Spitfire and the Hurricane during the war. His view was that the Hurricane was a far more capable aeroplane, and that the only reason the Spitfire got so much more attention was because it looked so much prettier. I've had the good fortune to fly a Spitfire H.F.IXe for a very short time and, apart from the unbelievable handling (particularly the roll response) the stand out memory is looking out over that beautiful elliptical wing when rolling around The Needles at the west end of the Isle of Wight. Of all the different types I've flown, or flown in, over 40 odd years, that short flight is the one that stands out.

A radial would indeed turn it into a complete abomination.
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Old 23rd Nov 2022, 16:23
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Originally Posted by Sue VÍtements View Post
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
I think you will find that this is based on a design concept only and that no Hurricane was built, never mind entered service, with a radial engine. Note the url of the modelling website! http://www.airwar1946.nl/index.htm
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Old 23rd Nov 2022, 17:22
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Originally Posted by VictorGolf View Post
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?.
A US Navy admiral is reputed to have pointed out that they didn't have air cooled submarines.
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Old 23rd Nov 2022, 19:28
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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?
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Old 23rd Nov 2022, 19:46
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Originally Posted by NutLoose View Post
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.
That sort of depends on who you believe. While it's often claimed that the Mustang radiator had a net thrust gain, most knowledgeable analysis I've seen suggest that - at best - it was thrust/drag neutral and under most conditions it created some net drag (although not much). That being said it was a brilliant design that minimized the drag penalty of the cooling system.

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
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