Why so few single engine Hercules applications?

[Koopernic]

Developments in poppet valves negated the need for sleeve valves. This includes sodium cooled valves and some of the new materials such as nimonic 75 and other new materials for the valve seats and valves themselves.

The reintroduction of rotating reciprocating sleeves with poppet valves has been considered. The sleeves movements reduces friction and fuel burn of the piston.

 

[Admiral Beez]

Developments in poppet valves negated the need for sleeve valves.

All the other companies making radial engines, from Armstrong, P&W, Wright, Shvetsov, Fiat, Nakajima, Gnome-Rhône and BMW, etc. understood this. Why didn't Bristol get the memo that the science had canceled their idea?

The sleeves movements reduces friction and fuel burn of the piston.

Why would one want reduced fuel burn? Do you mean the risk of melting a hole into the piston or carbon buildup?

 

[Koopernic]

Very few two strokes now, they cant pass emission regs. When I was racing a friend of mine had a Yamaha RD 250 tuned by a specialist, took out the liner and introduced a new one with ports all over the place, it was slightly more powerful than what the guy already had (a race tuned road bike) But it didn't last more than a meeting which is about 20- 30 miles. The bigger you make the ports the more the piston and especially the rings want to go inside them.

All the other companies making radial engines, from Armstrong, P&W, Wright, Shvetsov, Fiat, Nakajima, Gnome-Rhône and BMW, etc. understood this. Why didn't Bristol get the memo that the science had canceled their idea?
Why would one want reduced fuel burn? Do you mean the risk of melting a hole into the piston or carbon buildup?

Sleave valves are more knock resistant for fuels under about 87.

Harry Ricardo (proponent of sleeve valves and if enormous reputation) and Fedden were related. Perhaps it gets down to that.

I've seen papers on introducing sleeves for anti friction purposes. The sleeve probably maintains hydrodynamic oil when pistons are stopped at top and bottom dead centre or prevents stiction. There may also have been ceramic cylinder liner involved.

From the wiki article on sleeve valves:
"Another concept, the Rotating Liner Engine has been developed, where the wear and friction benefit of the sleeve valve is exploited in a conventional engine layout. A friction reduction of the order of 40 % has been reported for a Heavy Duty diesel.
The same company can also supply somewhat larger engines for use in military drones, portable generators and equipment such as lawn mowers.[20] These are "multi fuel" insofar as they can be configured to run on gasoline, kerosene, including aircraft fuels, and diesel oil.
Owing to the impossibility to use conventional poppet valves in opposed-piston engines, American company Pinnacle Engines also promotes a sleeve-valve layout in its 4-stroke opposed-piston engine developments. Variable valve timing was also proposed in a 3-cylinder 1.5L development from Pinnacle Engines, but as of December 2016 there are not so many details available for the general public."

 

[fastmongrel]

Very interesting, thanks. Your description reminds me of the OHV motorcycle engines of the 1920s with open valve springs, sometimes clothespin type.

What of the Armstrong radials? I know they had their own failures.

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The Tiger crankshaft was lightly built and didn't have a centre crank bearing, as a result it couldn't handle the revs and had vibration problems. 1250lbs for a 33 litre 14 cylinder engine was never going to handle the boost or revs.

There was nothing wrong with Armstrong Siddeleys small engines, the 350hp Cheetah had a service life of 1200hours. According to my Dad they never failed as long as the oil temperature was kept out of the red zone.

 

[Admiral Beez]

The Tiger crankshaft was lightly built and didn't have a centre crank bearing, as a result it couldn't handle the revs and had vibration problems. 1250lbs for a 33 litre 14 cylinder engine was never going to handle the boost or revs.

Why didn't Armstrong-Siddeley add a centre crank bearing? I think I can answer that. In 1928 Armstrong merged with Vickers (and acquired Supermarine) to create Vickers-Armstrong. This new conglomerate then sold off Armstrong's aero engine, which became Armstrong Siddeley.

Vickers-Armstrong then declined to use their former division's engines; with no post-merger designed Vickers or Supermarine radial-powered aircraft using Armstrong-Siddeley engines. And then in 1935, A-S merged with Hawker Aviation, but still no update of the Tiger was made so that Hawker-Siddeley aircraft could use their own in-house radial. There is one exception I can think of, the Avro Anson of 1935, then a division of Hawker-Siddeley used the company's Cheetah radial - I bet that took some rows at the boardroom table to make happen. With the exception of offshore licensed copies, every Bristol radial-powered aircraft I can think of used a Bristol engine. Clearly Armstrong-Siddeley's engine division was starved of funding and engineering resources. Look at their work on the Cougar, a seemingly strong contender for 1935, but not in 1945.

Finally during the postwar period H-S aircraft began using in house engines, notably the Sapphire in the Gloster Javelin and early Hawker Hunters.

 

[Koopernic]

Small gasoline 2 strokes use crankcase compression to force air through the cylinders. All 2 stroke diesels that I am aware of use superchargers to achieve the same effect. Note that pure turbochargers don't work as you can't start the engine. Detroit Diesels use a turbocharger in series with a mechanical supercharger. The big EMD engines use a combination unit that operates mechanically at low loads with a overriding clutch that lets the turbo take over when it has enough energy. All GM 2 strokes (DD and EMD and Cleveland Diesel) only have exhaust valves. The intake ports are uncovered by the pistons ( no sleeves). The opposed piston engines (Junkers, Fairbanks Morse, Deltic) take this a step further by eliminating valves all together. One piston controls the inlet while the opposite one controls the exhaust.
Diesels also have an advantage in that the scavenging air necessary for 2 strokes doesn't waste fuel as it does for a carburetor engine.
This is a long winded way of saying that Diesels dont have have total loss oil systems.

Spark Ignition engines need to operate at a lambda 1 (or stoichiometric air fuel ratio) of close to (14.2 parts air to 1 part fuel) to get reliable ignition. Compression Ignition Diesels are far less restrictive in lambda so control is simply by adjusting fuel flow. In a 2 stroke SI engine it's hard to get lambda 1 with direct injection because the actual oxygen in the cylinder is unknown due to mixing with exhaust. However nowadays a lambda probe can be used to measure the exhaust and adjust accurately.

The Rolls Royce Crecy was a 2 stroke sleeve valve with a prechamber for the spark plug where good lambda was maintained, this ignited the main chamber.

 

[bdefen]

Did all these gears turn in an oil bath?

Don't know. I imagine at least a deluge of oil spray, if not a bath. I'm sure one our our learned engine colleagues on this thread knows.

 

[Admiral Beez]

Don't know. I imagine at least a deluge of oil spray, if not a bath. I'm sure one our our learned engine colleagues on this thread knows.

You'd want a thin oil or watchmaker's grease I would think, otherwise you'd gum up all those wheels, especially in cold climes.

Here are the oil pathways, see top right, second down for "Intermittent Feed to Supercharger Gears & Bearings". Perhaps this also lubricates the timing gears or wheels?

Images from Bristol Hercules 264

 

[bdefen]

You'd want a thin oil or watchmaker's grease I would think, otherwise you'd gum up all those wheels, especially in cold climes.

Here are the oil pathways, see top right, second down for "Intermittent Feed to Supercharger Gears & Bearings". Perhaps this also lubricates the timing gears or wheels?

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Images from Bristol Hercules 264

In that diagram, there is a red oil pathway shown inside a sleeve crankshaft (the uppermost red oil path moving from the front rearwards). There is going to be one of these sleeve crankshafts for each cylinder. (or perhaps each pair of cylinders) My guess is that the multiple gears in that area are bathed in oil under pressure, and using that pressure, each hollow crankshaft shaft delivers oil rearward to the moving sleeve at the cylinder. The oil is either scavenged back to the oil pump, or, in keeping with these engines prodigious oil consumption, it's ultimately into the cylinder, and out the exhaust.

Respectfully, I don't think there would be any separate delicate watchmaker's oil for these sleeve crankshaft gears. All would use the same oil as the rest of the engine. I don't disagree that cold startup temperatures could be a complication for these engines and those gearsets. Again, IMHO. I'll watch for correction. Thanks for the discussion.

 

[Simon Thomas]

Respectfully, I don't think there would be any separate delicate watchmaker's oil for these sleeve crankshaft gears. All would use the same oil as the rest of the engine. I don't disagree that cold startup temperatures could be a complication for these engines and those gearsets. Again, IMHO. I'll watch for correction. Thanks for the discussion.

Something Fedden deliberately designed into his engines to be able to operate quickly after starting. Many of the Pegasus/Mercury/Hercules had a minimum oil temperature for takeoff of 5°C.

 

[fastmongrel]

The sleeve valve engines used a special oil made by iirc Shell. It was designed to resist the film of oil lubricating the sleeve and transferring heat breaking down.

Radials use more oil than an equivalent inline but the Bristol sleeve valve engines generally used slightly less oil per hp than the equivalent US engines. It would be interesting to see if the Lancaster MkII needed bigger oil tanks than the Merlin engined MkI and MkIII

Edit: the oil was Shell Aeroshell 100U

 

[fastmongrel]

Found this on the website of key.aero

A good few years ago I knew the last Rolls Royce inservice support engineer officially charged with supporting the Bristol Sleeve valves. He told the same story relating to oil and limited spare availability but added the following;-
The really significant retirement of the Bristol sleeve valve fleet was pretty advanced in the early 70's so demand for the Shell oil ceased. Because the oil was deemed necessary for the safe operation of the engine and there were still a few operators (mainly Noratlas and Bristol Freighter) determined to continue, Rolls Royce (& Snecma) brokered a deal whereby Shell would still produce the oil to special order but only with a commitment to buy a minimum quantity. Right into the mid 80's he organised several operator syndicate purchases which enabled some of these types to linger on, providing commercial/military service into the late 80's, early 90's.

When I asked about the private Sea Fury operators in the 70's & 80's he was less than complimentary about their attitude. They refused to accept the Rolls Royce instructions, declined invitation to join oil purchasing syndicates, and preferred to believe rumours that other oils would work just as well. The gotcha was that an engine filled with an alternate oil which would appear to being doing fine but was liable to very, very rapid deterioration and would inevitably destroy the engine, leading frequently to the loss of aircraft and sometimes the pilot. Of course when this happened the operators would always blame the engine and arrogantly never admit their wilful neglect of the manufacturers directives.

It's a great shame that the ignorance of a few has left a perceived poor reputation on what was a magnificent piece of engineering.

 

[bdefen]

Found this on the website of key.aero

A good few years ago I knew the last Rolls Royce inservice support engineer officially charged with supporting the Bristol Sleeve valves. He told the same story relating to oil and limited spare availability but added the following;-
The really significant retirement of the Bristol sleeve valve fleet was pretty advanced in the early 70's so demand for the Shell oil ceased. Because the oil was deemed necessary for the safe operation of the engine and there were still a few operators (mainly Noratlas and Bristol Freighter) determined to continue, Rolls Royce (& Snecma) brokered a deal whereby Shell would still produce the oil to special order but only with a commitment to buy a minimum quantity. Right into the mid 80's he organised several operator syndicate purchases which enabled some of these types to linger on, providing commercial/military service into the late 80's, early 90's.

When I asked about the private Sea Fury operators in the 70's & 80's he was less than complimentary about their attitude. They refused to accept the Rolls Royce instructions, declined invitation to join oil purchasing syndicates, and preferred to believe rumours that other oils would work just as well. The gotcha was that an engine filled with an alternate oil which would appear to being doing fine but was liable to very, very rapid deterioration and would inevitably destroy the engine, leading frequently to the loss of aircraft and sometimes the pilot. Of course when this happened the operators would always blame the engine and arrogantly never admit their wilful neglect of the manufacturers directives.

It's a great shame that the ignorance of a few has left a perceived poor reputation on what was a magnificent piece of engineering.

I use full synthetic in my cars and motorcycle. I don't know whether synthetic oils are used in aircraft application. I wonder if modern synthetics would show the same resistance to breakdown and deterioration as the once-specified Shell 100U?

 

[Simon Thomas]

Synthetic aviation oil for air cooled piston engines was tried by Mobil, and it was not a success.
Mobil AV-1 Under Attack

 

[cammerjeff]

You cannot just run Modern Synthetic oils in engines that were designed to use older Mineral based oils. Even in cars you are running the risk of bearing or ring failure, sometimes just seals that fail either because of a certain additive or lack of that additive.

Any engine designed in the last 20 years (probably 30 years) should have no issue with synthetic oils. But older designs were not tested for them. In fact if you do run synthetic oil in a 1980's or older engine, you are performing a durability test for the oil company at your expense. Just a story about our local car club in the 1990's, several members started running full synthetic oil in their Pontiac V8 engines, a short while later the rear seals started leaking, followed shortly by lower main bering issues.

I just can not imagine doing it with a car, let alone an aircraft.

 

[bdefen]

You cannot just run Modern Synthetic oils in engines that were designed to use older Mineral based oils. Even in cars you are running the risk of bearing or ring failure, sometimes just seals that fail either because of a certain additive or lack of that additive.

Any engine designed in the last 20 years (probably 30 years) should have no issue with synthetic oils. But older designs were not tested for them. In fact if you do run synthetic oil in a 1980's or older engine, you are performing a durability test for the oil company at your expense. Just a story about our local car club in the 1990's, several members started running full synthetic oil in their Pontiac V8 engines, a short while later the rear seals started leaking, followed shortly by lower main bering issues.

I just can not imagine doing it with a car, let alone an aircraft.

My bike is a 2013 BMW R1200 GSW. Castrol 4T Synthetic specified for use. Used since new. No issues. Cars - 2020 Toyota Tacoma - synthetic blend or full synthetic recommended; 2016 Ford Edge - synthetic blend or full synthetic recommended. Just keep it out of older engines, right?

 

[Admiral Beez]

You cannot just run Modern Synthetic oils in engines that were designed to use older Mineral based oils. Even in cars you are running the risk of bearing or ring failure, sometimes just seals that fail either because of a certain additive or lack of that additive.

Any engine designed in the last 20 years (probably 30 years) should have no issue with synthetic oils. But older designs were not tested for them. In fact if you do run synthetic oil in a 1980's or older engine, you are performing a durability test for the oil company at your expense. Just a story about our local car club in the 1990's, several members started running full synthetic oil in their Pontiac V8 engines, a short while later the rear seals started leaking, followed shortly by lower main bering issues.

I just can not imagine doing it with a car, let alone an aircraft.

And in vintage motorcycles synthetic oil can cause clutch slippage.

 

[fastmongrel]

And in vintage motorcycles synthetic oil can cause clutch slippage.

doesnt smell as nice as Castrol R either

 

[pbehn]

doesnt smell as nice as Castrol R either

In my years of teenage stupidity I bought a Norton 500SS just because it was running Castrol R, I used to enjoy the lights changing to red.

 

[Admiral Beez]

doesnt smell as nice as Castrol R either

Some good history here Castrol R - Motor Sport Magazine