WI The Rolls Royce Vulture is a success

[fastmongrel]

We probably all know the story of the RR Vulture and the fact that it was initially unreliable and was discontinued just as RR were getting the problems sorted. Rolls-Royce Vulture - Wikipedia, the free encyclopedia

If the Vulture had been successful from the beginning or RR had the time and resources to throw at it and develop it with cylinders heads and superchargers like the Merlin could it have been a major engine in WWII. Just by doing some sums on the back of an envelope a 42 litre Vulture giving the same power per litre as a Merlin 60 series is going to give approx 2,300hp in 1943.

I like the idea of squadrons of Hawker Tornadoes Hawker Tornado - Wikipedia, the free encyclopediaand there reliable Vulture 60 engines blasting there way across Europe. High altitude versions operating as long range fighters and low level fighter/bombers with cropped impellors tearing up the German army. The Avro Manchester Avro Manchester - Wikipedia, the free encyclopedia could be the RAFs premiere twin engine daylight medium bomber and long range coastal command aircraft. The Lancaster (similar in size to the real life Lincoln) with its 4 high altitude Vultures would be a difficult target for a LW night fighter to catch.

Okay forget about the above stream of fantasy how could a reliable and powerful Vulture help the allies what aircraft could have used a 2,000 to 2,300hp X 24 engine. I am thinking anything that used a PW 2800 wouldnt be too much of a problem and obviously anything that used a Napier Sabre.

 

[wuzak]

An interesting idea, which has been touched on in other threads.

I calculate that a Vulture with the same Brake Mean Effective Pressure (BMEP) as a Merlin XX on 100 octane fuel (ie 1480hp @ 3000rpm) would make 2210hp @ 2250 rpm (max permissable rpm of the Vulture in operations). If we then allow the maximum design rpm of 3200 rpm we have 2480hp - RRHT tells me that the Vulture was tested at 2500hp several times before it was cancelled.

So, 2500hp may have been possible in 1942 - providing that engine could remain reliable.

A two stage Merlin 76 series was rated at 1710hp @ 3000rpm at full throttle height using PN130 fuel. This is about 1943/1944. Plugging the BMEP from that into the Vulture results in 2865hp @ 3200 rpm.

In late 1943 a Merlin 66 with PN150 fuel was capable of 2000hp @ 3000rpm @ 2000ft. That equates to 3350hp @ 3200rpm in the Vulture.

In late 1944/early 1945 the RM.17SM was rated at 2200hp @ 3000rpm, this equating to 3690hp @ 3200rpm in the Vulture.

Now, if RR were getting 2500hp from the Vulture in 1942, they may have considered increasing the bore to the same as the Merlin. This would raise the engine from 2592cid/42.47l to 3023cid/49.54l. With the increased capacity and using the BMEP from the Merlin 76 would give 3345hp, the BMEP from the 66 would give 3910hp, and with the rated BMEP of the RM.17SM and the increased bore the power would be 4300hp! All at 3200rpm.

This all theorises that the BMEPs could be achieved in the Vulture, and that it would be reliable under those circumstances. As the Vulture used the same combustion chamber shape as all but the earliest of the Merlins, one would assume that the boost pressures and compression ratios required for these performances would be possible in the Vulture.

 

[wuzak]

As for where a reliable Vulture could have been used, I think anywhere that a big radial was used. The only problem would be where the CoG is moved too far forward, due to the extra length of the Vulture compared with the radial.

If we are saying reliability had been achieved earlier the Vulture may have been used for the Wellington. Though it would be twice the power of the existing engine, so may have been too powerful for the airframe.

One that stands out as a candidate is the Short Stirling. The Vulture as it was historically was more powerful than the Hercules II in the Stirling (even at its reduced ratings), and may have helped with the low ceiling of the aircraft.

So, anything fitted with a Hercules could be considered. Or a P&W R-2800, Wright R-2600 or R-3350. Th eVulture was smaller in diameter than each of those, so it would fit up to the same bulkhead. If a QEC was made using an annular radiator, and containing all oil coolers, air intakes, etc, it could be a bolt up fit.

I also imagine that if the Vulture was reliable and successful by 1941 it may have been considered as an alternative for the R-3350 in the B-29. It certainly would have matched the R-3350 for takeoff power by then, if not for altitude capability (without a turbo). Enter the 60-series Vulture....

 

[wuzak]

FWIW, a muture Vulture late in the war could have been comapred to the R-4360 used in the F2G and after the war in the B-50. By 1944 3000hp should have been well within the capability of the Vulture, probably more. This is the same power that the R-4360 in the F2G had. The Vulture was also about 9in shorter, smaller in diameter, and some 1400lbs lighter (so of which would be used for teh cooling system). The Vulture would have had a new reduction (epicyclic) gear system if it had continued, saving a further 150-200lbs.

 

[davebender]

The RR Vulture engine might have been perfected but I think your time frame for 2,300 reliable hp is optimistic.

In any case I think it would come down to a competition between the RR Vulture and the similiarly powerful Napier Sabre engine. Only one of these engines would enter mass production during WWII.

 

[Tartle]

The problem with the Sabre was its unreliability that made the Vulture look incredibly good! Seriously, Rod Banks talks of the cost of the Sabre being 4 to 5 times the cost of a merlin per hp. (And Bristol Hercules being twice 'Merli' per hp). The Vulture was almost there, in terms of integrity when it was cancelled to relaese resources for the Merlin; also the Manchester was turning out to be not a good idea as single-engined performance was not adequate, so the 4-engines were inevitable. Another way of approaching potential performance of Vulture is to assume all the technology going into the Merlin and Griffon (and back into Merlins) is put into the Vulture ... we could then plot a curve that ratio'd the power and power/weight to derive target performance for the Vulture.. maybe I'll do that later on...

 

[fastmongrel]

The RR Vulture engine might have been perfected but I think your time frame for 2,300 reliable hp is optimistic.

In any case I think it would come down to a competition between the RR Vulture and the similiarly powerful Napier Sabre engine. Only one of these engines would enter mass production during WWII.

I got to 2,300 hp simply by dividing 1,500 by 27 and multiplying by 42. The Merlin 60 series engines were reliably giving 1,500 hp approx by mid 42 so I think a 42 liter 2,300 hp Vulture using the same technology as the Merlin is doable 6 months or so later.

What got me thinking of the Vulture was a thread on different engines for the B 29. The idea that came to me whilst out on my mountain bike was what if the RAF saw the B 29 specs in early 41 and decided they liked it but didnt like the R3350 engines and wanted an equivalent British engine. In this timeline Bristol are struggling to produce enough Hercules and the tempremental Sabre has been canned because the Vulture has been such a success. Rolls Royce use the experience to build a super Vulture (a bit like they used Merlin experience on the Griffon) with 24 Merlin sized cylinders and a 3 stage blower to give 54 litres of high altitude engine. Maybe the USAAF would use a Packard super Vulture on there B29 follow up because of the problems of the big Wright engine.

 

[Shortround6]

When comparing some of these engines, especially for bomber use, you might want to compare the cruise power or 30min/1 hour ratings vs the 5 min or WEP power settings. or take-off power vs WEP settings.

The P&W R-2800 in it's bomber versions single stage two speed supercharger was good for a mere 2000hp for take off but it was good for 1450hp at 13,000ft until the fuel ran out, it wasn't economical or a normal "cruise" setting but the engine would do it.
A Centaurus MK IV was good for 1850hp at 14,250 ft for 30 minutes or so.

While the air-cooled radials didn't have the peak power of the liquid cooled engines the difference between the the take-off power and max continuous and cruise power settings was some what less than the drop in power for the liquid cooled engines.

It could also take one to two years (or more?) to switch engines in a major aircraft program. BY the time you know you are having troubles and they WON'T be fixed quickly. The production lines are in place and material allocations have been made. A new installation has to made and tested (so you know you are not jumping from the frying pan into the fire) and then both the engine factory and the aircraft factory have to retool, or another airframe with lower priority has it's engines 'borrowed' and so on.

 

[wuzak]

The RR Vulture engine might have been perfected but I think your time frame for 2,300 reliable hp is optimistic.

In any case I think it would come down to a competition between the RR Vulture and the similiarly powerful Napier Sabre engine. Only one of these engines would enter mass production during WWII.

I don't think so.

The Vulture's problems were almost completely sorted by 1941. The cancellation came due to needing to put the resources into other projects - chiefly the Merlin and Griffon.

In 1941 the Vulture V was rated for takeoff at about 1800hp at 2850rpm with +6psi boost. The boost was kept low, and the rpm reduced due to reliability concerns. With the reliability fixed the rpm could be taken back up to the design maximum of 3200rpm, and RR could add more boost. By 1941 the Merlin had already gone to +12psi, and in 1942 the 60 series were cleared for +15 and then +18 by 1943. This was only possible with testing and strengthening of components to cope. If the Vulture had continued then it would have gone through teh same development cycle, resources permitting.

If the Vulture was being used in several production types, instead of just the Manchester, the consideration to discontinue it would have been more difficult.

 

[wuzak]

I got to 2,300 hp simply by dividing 1,500 by 27 and multiplying by 42. The Merlin 60 series engines were reliably giving 1,500 hp approx by mid 42 so I think a 42 liter 2,300 hp Vulture using the same technology as the Merlin is doable 6 months or so later.

While using hp/l is ok, I think using BMEP is better. That can also account for differences in rpm as well as capacity. The Merlin XX was rated at 1480hp @ 3000rpm by then, which equates to, as I have said above, 2480hp @ 3200rpm for the Vulture. And we know this is in the ball park as to what is possible by 1942, as the Vulture had tested to 2500hp by the time of its cancellation. The XX, like the Vulture at that time, was a single stage two speed supercharged engine.

What got me thinking of the Vulture was a thread on different engines for the B 29. The idea that came to me whilst out on my mountain bike was what if the RAF saw the B 29 specs in early 41 and decided they liked it but didnt like the R3350 engines and wanted an equivalent British engine. In this timeline Bristol are struggling to produce enough Hercules and the tempremental Sabre has been canned because the Vulture has been such a success. Rolls Royce use the experience to build a super Vulture (a bit like they used Merlin experience on the Griffon) with 24 Merlin sized cylinders and a 3 stage blower to give 54 litres of high altitude engine. Maybe the USAAF would use a Packard super Vulture on there B29 follow up because of the problems of the big Wright engine.

It would be logical for the RAF to desire to use one of their own engines, and they did tend to favour liquid cooled engines. If they had been brought on board the B-29 development in 1941 the engines they would have considered possible would be a developed version of the Vulture, the Sabre, which still held for them great promise, and the Bristol Centaurus. The Bristol Hercules would have been considered underpowered for the duty.

I don't think a Vulture with bore and stroke the same as the Merlin would have been designed - as it would grow the size of the engine, and the extra capacity would not really be necessary. I could see the Merlin bore being used, as the bore spacing between the Vulture and Merlin were nearly the same. That would give 5.4in bore x 5.5in stroke for 3023cid/49.54l. That should give more than enough power.

I also wonder if RR's objections to turbochargers would be suspended for such a project. Two B-seroes turbochargers would be required, as they were for the B-29, or a single C-series would suffice.

 

[wuzak]

When comparing some of these engines, especially for bomber use, you might want to compare the cruise power or 30min/1 hour ratings vs the 5 min or WEP power settings. or take-off power vs WEP settings.

True, but we don't always have those numbers for comparison.

The P&W R-2800 in it's bomber versions single stage two speed supercharger was good for a mere 2000hp for take off but it was good for 1450hp at 13,000ft until the fuel ran out, it wasn't economical or a normal "cruise" setting but the engine would do it.
A Centaurus MK IV was good for 1850hp at 14,250 ft for 30 minutes or so.

These are for normal supercharged engines. What would they be for turbocharged engines? The R-3350s in the B-29 had it sea level ratings all the way up to 25k-30k ft. A Centaurus, for example, would surely have more power at altitude in a turbocharged appliation due to teh supercharger not having to work as hard. Maybe closer to 2000hp?

While the air-cooled radials didn't have the peak power of the liquid cooled engines the difference between the the take-off power and max continuous and cruise power settings was some what less than the drop in power for the liquid cooled engines.

Look at the Allison V-1710 111/113 used for the P-38L. According to Vees for Victory takeoff power was 1500hp, WEP was 1600hp and military power (which would be a 30 minute rating) was 1425hp.

Another chart shows, for a P-40/P-40B/P-40C with a V-1719-33 take-off power of 1040hp, military rating of 1040hp @14,300ft, normal rated power 930hp @ 2600rpm @ 12,800ft, max cruising power (75% of normal) of 697hp @ 2280rpm @ 12,800ft, and preferred cruisng power of either 60% or 67% or normal power (568hp or 623hp).

How does that compare with the air cooled engines?

Take-off power is as important, or maybe more so, than cruise power. It is the difference between taking off comfortably or not.

If we size or liquid cooled engine to give the required cruise power we can then expect that the takeoff and maximum power will be much more than the air-cooled engine.

It could also take one to two years (or more?) to switch engines in a major aircraft program. BY the time you know you are having troubles and they WON'T be fixed quickly. The production lines are in place and material allocations have been made. A new installation has to made and tested (so you know you are not jumping from the frying pan into the fire) and then both the engine factory and the aircraft factory have to retool, or another airframe with lower priority has it's engines 'borrowed' and so on.

Fastmongrel was suggesting that the British be involved in the B-29 program from early on (1941). In that situation the alternative British engines have QECs designed around them and are throughly tested before they are sent to the US for installation of the RAF B-29 prototypes (1943). It also must be noted that the R-3350 installation could be unbolted and the V-3420 bolted up in its place. The airframe was not altered in any way. A similar situation could have been engineered for a Vulture/Sabre/Centaurus version.

 

[fastmongrel]

I also wonder if RR's objections to turbochargers would be suspended for such a project. Two B-seroes turbochargers would be required, as they were for the B-29, or a single C-series would suffice.

I thought RR preferred supercharging for fighters but had turbo charging in mind for high altitude bombers. Prototypes were built but RR never had the resources nor the demand from the RAF to take the project any further. I dont think RR had any particular objection to the turbo they just thought a well designed engine driven blower could do most things needed. Possibly more a "we know engine blowers so lets stick with what we know for the timebeing"

 

[fastmongrel]

Fastmongrel was suggesting that the British be involved in the B-29 program from early on (1941). In that situation the alternative British engines have QECs designed around them and are throughly tested before they are sent to the US for installation of the RAF B-29 prototypes (1943). It also must be noted that the R-3350 installation could be unbolted and the V-3420 bolted up in its place. The airframe was not altered in any way. A similar situation could have been engineered for a Vulture/Sabre/Centaurus version.

Exactly my thoughts though I didnt realise the B 29 could have a V-3420 bolted in place I thought it was a different model that had the V engine.

 

[Shortround6]

[

True, but we don't always have those numbers for comparison.

perhaps not easily available but some of the numbers are available.

These are for normal supercharged engines. What would they be for turbocharged engines? The R-3350s in the B-29 had it sea level ratings all the way up to 25k-30k ft. A Centaurus, for example, would surely have more power at altitude in a turbocharged appliation due to teh supercharger not having to work as hard. Maybe closer to 2000hp?

Use the low blower rating instead of high blower. 1600hp for a R-2800, 2000hp for a R-3350, 2095hp for a Centaurus IV, later ones did better.

Look at the Allison V-1710 111/113 used for the P-38L. According to Vees for Victory takeoff power was 1500hp, WEP was 1600hp and military power (which would be a 30 minute rating) was 1425hp.

See. this for a page from the flight manual.

http://www.zenoswarbirdvideos.com/Images/P-38/38SEFC.gif

1100hp for max continuous, no time limit, like the American radial power figures I gave.

Another chart shows, for a P-40/P-40B/P-40C with a V-1719-33 take-off power of 1040hp, military rating of 1040hp @14,300ft, normal rated power 930hp @ 2600rpm @ 12,800ft, max cruising power (75% of normal) of 697hp @ 2280rpm @ 12,800ft, and preferred cruisng power of either 60% or 67% or normal power (568hp or 623hp).

How does that compare with the air cooled engines?

http://www.zenoswarbirdvideos.com/Images/B-17/17SEFC.pdf

Take off 1200hp, military the same, 1000hp Max continuous (normal rated) and 750hp max cruise.

I would note that while the take of power of the Allison went up 44% between those two models and the max combat power went up 54% (granted the early engine didn't have a WEP rating) the max continuous or normal rating only went up 7.5%.

A Merlin 130 was rated at 1645hp for take off using 18lbs of boost, it was rated at 1830hp military at 20lbs of boost using 100/130 fuel and 2020hp using 25lbs boost and 100/150 fuel. "normal" rating was 1410hp and max cruise was 1250hp. all hp ratings are in low gear.

A Centaurus V was rated at 2500hp for take off using 8.5lbs of boost. 2520hp max or military at 2700rpm at 1000ft, 2,150hp normal at 2400rpm at 3,000ft and 1725hp cruising at 2400rpm at 9000ft. Granted this engine might be a bit late for this time period.

Take-off power is as important, or maybe more so, than cruise power. It is the difference between taking off comfortably or not.

True but in many of these "what ifs" the comparisons are made on take off power or max power and not all engines offered the same cruise or climb power as a percentage of their take-off power or max power.

 

[Shortround6]

I thought RR preferred supercharging for fighters but had turbo charging in mind for high altitude bombers. Prototypes were built but RR never had the resources nor the demand from the RAF to take the project any further. I dont think RR had any particular objection to the turbo they just thought a well designed engine driven blower could do most things needed. Possibly more a "we know engine blowers so lets stick with what we know for the timebeing"

Rolls-Royce also liked the idea of using the thrust from the exhaust which is very hard to do with a turbo charged engine. It is pretty much one or the other.

 

[wuzak]

Exactly my thoughts though I didnt realise the B 29 could have a V-3420 bolted in place I thought it was a different model that had the V engine.

It was designated XB-39. The V-3420 was mounted in a QEC module designed by Fisher Body Division (GM) to fit to a firewall designed for the R-3350. The V-3420 program was delayed over the years due to cancellations and reinstatements, some difficulty in getting approved for flight status, and then Fisher's eforts were diverted to the XP-75. The QEC module was designed around a new GE supercharger, which had a two stage compressor allowing a critical altitude of 40,000ft, but when testing they were unreliable. And they also would not be in production in time for the B-29 program. The V-3420s fitted to the XB-39 were, therefore, altitude rated units. The XB-39 was nearly 50mph faster than the B-29.

The V-3420 QEC had all oil and engine coolant radiators fitted, so no modifications to the airframe were necessary.

In contrast, the XB-38, a modified B-17E, required leading edge radiators to be installed in the wing leading edge, meaning a far bigger changeover problem.

 

[wuzak]

[

perhaps not easily available but some of the numbers are available.





Use the low blower rating instead of high blower. 1600hp for a R-2800, 2000hp for a R-3350, 2095hp for a Centaurus IV, later ones did better.






See. this for a page from the flight manual.

http://www.zenoswarbirdvideos.com/Images/P-38/38SEFC.gif

1100hp for max continuous, no time limit, like the American radial power figures I gave.


http://www.zenoswarbirdvideos.com/Images/B-17/17SEFC.pdf

Take off 1200hp, military the same, 1000hp Max continuous (normal rated) and 750hp max cruise.

I would note that while the take of power of the Allison went up 44% between those two models and the max combat power went up 54% (granted the early engine didn't have a WEP rating) the max continuous or normal rating only went up 7.5%.

A Merlin 130 was rated at 1645hp for take off using 18lbs of boost, it was rated at 1830hp military at 20lbs of boost using 100/130 fuel and 2020hp using 25lbs boost and 100/150 fuel. "normal" rating was 1410hp and max cruise was 1250hp. all hp ratings are in low gear.

A Centaurus V was rated at 2500hp for take off using 8.5lbs of boost. 2520hp max or military at 2700rpm at 1000ft, 2,150hp normal at 2400rpm at 3,000ft and 1725hp cruising at 2400rpm at 9000ft. Granted this engine might be a bit late for this time period.





True but in many of these "what ifs" the comparisons are made on take off power or max power and not all engines offered the same cruise or climb power as a percentage of their take-off power or max power.

The fuel ratings PN115/150 is for lean/rich mixtures. If I understand it correctly, air cooled engines could only run rich, whereas liquid cooled engines could run lean as well. This may explain the ability of the, generally, smaller liquid cooled engines to have maximum powers as much as or greater than the radials.

Now, if we size a liquid cooled replacement for the R-3350s based on cruise powers I we would certainly have the bonus of much higher tak-off and maximum powers. I would also say that it would not require a 3350 cubic inch liquid cooled engine to do this, and something about 2500-2800 cubic inches, like the Vulture, should be about right.

There is also the effect the changeover has on drag.

 

[Shortround6]

The fuel ratings PN115/150 is for lean/rich mixtures. If I understand it correctly, air cooled engines could only run rich, whereas liquid cooled engines could run lean as well. This may explain the ability of the, generally, smaller liquid cooled engines to have maximum powers as much as or greater than the radials.

Air cooled engines were perfectly capable of running lean in cruise settings. The liquid cooled engines needed to run rich for the higher power settings just like the aircooled engines, please look at the charts provided.

The Allison was good for 795hp max cruise with lean mixture. The ability of the smaller liquid cooled engines to have maximum powers as much as or greater than the radials, had to do with the liquid cooling both providing a more uniform cooling preventing hot spots and detonation and with the coolant providing a heat sink of sorts. You had to heat all the coolant and cooling system up to a certain point before the engine would would over heat. The aircooled engine just had the cooling fins and would over heat much quicker. At rich mixture settings some of the fuel was being used as a coolant and was not being burned.

 

[tyrodtom]

The more hp you make the more heat a engine produces. Liquid coolant is more efficient at removing heat than air. Liquid cooled engines can make more hp for their displacement because they can remove the excess heat from the combustion chamber area, better than a air cooled engine.

You lean out a mixture for economy, not power. A aircooled engine can be leaned out too, but since a lean mixture runs hotter, it may be limited in how lean it can go by it's ability to cool.

 

[davebender]

I don't think that works.

Increasing hp places more stress on bearings, pistons, valves, lubrication system, cooling system etc. Increase hp enough and the old technology is no longer adequate. You need to develop new technology just as Daimler-Benz had to when the DB601 / DB605 engine was pushed to 1,475 hp. RR engineers will develop technical solutions but that will take time and money.