Kevin J
Banned
Does any one know why the Centaurus took so long to get into production? Could a Double Mercury or Double Pegasus have been developed faster?
Delays in Bristol Centaurus service entry
- Thread starter Kevin J
- Start date
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Shortround6
Major General
In part because Bristol fired Roy Fedden in Oct of 1942. In part because it was put on hold while they got the Hercules straightened out.
To build a Double Mercury or Double Pegasus would require dumping the whole sleeve valve line of engines.
This doubling of engines is not quite as easy as it seems, It took the Russians 4 tries to go from a licence built R-1820 to a service 18 cylinder engine.
The Wright R-3350 it self went through a total redesign before in went into production B-29s and it was actually far from ready for service. It could also be viewed as an R-2600 with two extra cylinders per row, easy right
To build a Double Mercury or Double Pegasus would require dumping the whole sleeve valve line of engines.
This doubling of engines is not quite as easy as it seems, It took the Russians 4 tries to go from a licence built R-1820 to a service 18 cylinder engine.
The Wright R-3350 it self went through a total redesign before in went into production B-29s and it was actually far from ready for service. It could also be viewed as an R-2600 with two extra cylinders per row, easy right
- Thread starter
- #3
Kevin J
Banned
Would it have been quicker and easier for Bristol to only have done a twin Aquila, the Taurus, rather than building the Perseus, Hercules and Centaurus? Would it have been better to have built a double Mercury and a double Pegasus? Your thoughts are welcome. What was the advantage of the sleeve valve?In part because Bristol fired Roy Fedden in Oct of 1942. In part because it was put on hold while they got the Hercules straightened out.
To build a Double Mercury or Double Pegasus would require dumping the whole sleeve valve line of engines.
This doubling of engines is not quite as easy as it seems, It took the Russians 4 tries to go from a licence built R-1820 to a service 18 cylinder engine.
The Wright R-3350 it self went through a total redesign before in went into production B-29s and it was actually far from ready for service. It could also be viewed as an R-2600 with two extra cylinders per row, easy right
swampyankee
Chief Master Sergeant
- 4,002
- Jun 25, 2013
Despite the advantages of four-valve heads, I believe there were no production multi-row radials with 4-valve heads, possibly because arranging for the actuation of the valves was excessively complex.
I tend to think that Fedden got a "sleeve-valve" bug in his ear, and gave up on development of high-power density poppet valve engines for no particularly valid reason. Sleeve valves were actually quite difficult to make, requiring precision machining of thin cylinders and specific storage (they would distort to the point of being unusable were they stored horizontally); they also required a complex mechanism to drive them (look at the mechanism to drive the sleeves in a Centaurus).
Sleeve valves offered somewhat better volumetric efficiency and avoided "hot spots" from the exhaust valve, reducing the tendency to detonation and allowing higher effective compression ratios. I tend to think that history and contemporary aircraft engines showed those hypothetical advantages to be somewhat illusory. It's hard to see any particular advantage of the sleeve-valve radials in comparison to their poppet-valve contemporaries.
I tend to think that Fedden got a "sleeve-valve" bug in his ear, and gave up on development of high-power density poppet valve engines for no particularly valid reason. Sleeve valves were actually quite difficult to make, requiring precision machining of thin cylinders and specific storage (they would distort to the point of being unusable were they stored horizontally); they also required a complex mechanism to drive them (look at the mechanism to drive the sleeves in a Centaurus).
Sleeve valves offered somewhat better volumetric efficiency and avoided "hot spots" from the exhaust valve, reducing the tendency to detonation and allowing higher effective compression ratios. I tend to think that history and contemporary aircraft engines showed those hypothetical advantages to be somewhat illusory. It's hard to see any particular advantage of the sleeve-valve radials in comparison to their poppet-valve contemporaries.
Admiral Beez
Major
Isn't the Taurus already the twin Aquila you propose?
The Hercules and Centaurus were war-winning engines, just need to make them earlier and faster. Unless a double Mercury or Pegasus could have been produced earlier and faster, I'd say stick with the the sleeve valves. By the time the Hercules is in production Bristol is a world leader in the type.
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Admiral Beez
Major
Good thing he didn't become focused on diesels.
swampyankee
Chief Master Sergeant
- 4,002
- Jun 25, 2013
I agree: by this time, it's far too late for Bristol to change direction and start active development on new poppet-valve engines; they'd have to make that decision in 1937 or, the latest, 1938 to be able to produce high-power density poppet valve engines in time for service in WW2.
Reluctant Poster
Tech Sergeant
- 1,624
- Dec 6, 2006
The only double row 4 valve radial I am aware of is the Alfa Romeo 135 but that never entered service
Shortround6
Major General
The Aquela was a 9 cylinder single row engine. 950 cu in/15.6 liters
The Taurus was a 14 cylinder two row engine. It's cylinders used and extra 1/4 in of stroke. 1550 cu in 25.4 L
A two row Aquela (18 cylinders) would have been 1900 cu in, 31.15L
An 18 Cylinder Taurus (two rows of 9 cylinders) would have been 1993 cu in/ 32.7L
The Hercules was 14 cylinders, 2360 cu in/38.7 L
The Aquela and the Taurus were both too small to warrant any further development. And more than likely, too expensive for the power they provided.
fastmongrel
1st Sergeant
When Sleeve valves became the greatest thing since sliced bread fuel was approximately 50 to 60 octane and Sodium cooled exhaust valves, High pressure superchargers and leaded 100 octane were science fiction. The sleeve valve in 1925 probably was better but by 1935 the gap was closing fast and by 1940 was non existent.
Sleeve valves might have had their day if Tetra Ethyl Lead had never been invented.
Sleeve valves might have had their day if Tetra Ethyl Lead had never been invented.
Or it may be like Betamax verus VHS. If Napier were using poppet valves and Rolls Royce building sleeve valves the Hurricane and Spitfire may have flown with a sleeve valve engine. The RR Eagle came after the Griffon and was basically the same layout as a Sabre without the issues.
swampyankee
Chief Master Sergeant
- 4,002
- Jun 25, 2013
It's hard to tell if the RR Eagle would have had the same problems as the Sabre, as it never went into production. I suspect that it also gained from Napier's and Bristols' experience with sleeve valves, which would have been available by the simple method of poaching staff from either company.
Admiral Beez
Major
If Armstrong-Siddeley had figured out how to get their Tiger performance and reliability up Bristol might have been pushed to fall back onto poppets.
Shortround6
Major General
Armstrong-Siddeley needed a new engine.
You need a new crankshaft with a main bearing between the two rows of cylinders, which means a new crankcase. You need a lot more fin area on the cylinders. You need a lot more fin area on the heads. Much closer spacing and deeper. It would help to use a bit more angle between the valves? Might want to think about changing the spark plug location?
The Tiger was about 1300lbs with the two speed supercharger and was a 1,996 cu in (32.7L)engine.
Without starting over it was too lightly built to stand up to a lot of power and it was too small to compete with the Bigger engines.
The Gnome-Rhone 14K also had no center bearing but at 2360 cu in (38.7L) it's larger displacement meant that much more power and yet it still wasn't enough.
Bristol could match the Tiger pretty much with the Pegasus.
You need a new crankshaft with a main bearing between the two rows of cylinders, which means a new crankcase. You need a lot more fin area on the cylinders. You need a lot more fin area on the heads. Much closer spacing and deeper. It would help to use a bit more angle between the valves? Might want to think about changing the spark plug location?
The Tiger was about 1300lbs with the two speed supercharger and was a 1,996 cu in (32.7L)engine.
Without starting over it was too lightly built to stand up to a lot of power and it was too small to compete with the Bigger engines.
The Gnome-Rhone 14K also had no center bearing but at 2360 cu in (38.7L) it's larger displacement meant that much more power and yet it still wasn't enough.
Bristol could match the Tiger pretty much with the Pegasus.
Admiral Beez
Major
Well sure, if given the funding Armstrong-Siddeley would have designed the Tiger's successor, much of it from scratch. It would likely be the UK's largest poppet valve radial.
It'll need a name, maybe call it the Lion if Napier doesn't protest. Doesn't need to be a cat, other predators apply.
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fastmongrel
1st Sergeant
Armstrong Siddeley built 37,200 Cheetah radial engines that powered nearly all the twin engine training and light transport aircraft used by Britain and the Empire. It's a dull boring thing but no twin engine trainers means no multi engine bomber aircraft crews.
Armstrong Siddeley did work on the dog series of radial engines and later the ASX turbine engine but neither ever got close to production.
The Cheetah engine is not as sexy as the big 1,000hp plus engines but it did just as much for the war effort.
Armstrong Siddeley did work on the dog series of radial engines and later the ASX turbine engine but neither ever got close to production.
The Cheetah engine is not as sexy as the big 1,000hp plus engines but it did just as much for the war effort.
fastmongrel
1st Sergeant
Armstrong Siddeley built a 9 cylinder radial called the Cougar after the war but there was no market for it so it never sold.
Armstrong Siddeley Cougar - Wikipedia
Admiral Beez
Major
Very interesting.
The third British radial producer, Pobjoy made some interesting small, even micro-sized poppet valve radials, like their widely used Niagara.
My favourite application is the Short S.31 half scale Short Sterling - I wonder how fast it flew with four 95 hp radials!
Pobjoy also dabbled in sleeve valve engines, including the onboard generator motors for the Short Shetland. Though with unfortunate results....
"The unit consisted of a flat-six sleeve-valve air-cooled petrol engine driving the generator. This was installed inboard on the aircraft, and due to the incorrect closure of the cooling ducts the engine overheated and the resulting fire destroyed the prototype Shetland."
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