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