The Rolls Royce Vulture enters service.

If the Whirlwind became the standard RAF fighter, due to the Merlin issues not being solved, Rolls Royce would be mass producing Peregrines. For heavy bombers the Peregrine lacks capacity so the step up for Rolls Royce would be the Vulture. By the time its issues were solved it was abandoned. At the same time the Sabre was far from perfect.

So, were the Rolls Royce Vulture to enter service in time, what uses might it have seen? IOTL it powered the Manchester,Tornado and Firebrand. Sabre Mosquito? USA production by Packard for the B24 and P47?

I'd imagine if Merlin weren't available, another powerful engine for a singe-engined fighter would have the highest priority, so I'd say the Tornado all the way. Bombers would be using the Hercules. Maybe we'd have seen a Vulture-powered Mustang eventually, though obviously adapting the Mustang from the Allison would have required a much more massive redesign than the historical Allison->Merlin transition.

And if the Vulture would have been successful, I wonder if it would have sucked the air out from the Sabre project.

Rolls Royce always had the Buzzard/ Type R/ Griffon lineage on the back burner.

The Vulture weighed around 2400lbs (?)


Hawker Henley used as a test bed.
A nice article can be found here.
Rolls-Royce Vulture X-24 Aircraft Engine

Included is an installation diagram with measurements, This is not a small engine.

A P-47 powered by the Vulture would be interesting. The reduced BSFC of the liquid cooled Vulture would mean that it would need less of the drop tanks that it didn't have. The higher power would make heavy takeoffs easier.
It would never work, as R-R was short staffed already and it would take quite a bit of work to shoe-horn the engine, radiators and ducting into the airframe.

As a side note, has anyone got the engineering/drafting staff numbers for the likes of Bristol, R-R, P&W, Napier, Wright, Allison from say 1935 to 1945? From reading "Fedden", it seems as though Bristol didn't have many staff, and those they had were working seriously long hours.

Simon Thomas said:

A P-47 powered by the Vulture would be interesting. The reduced BSFC of the liquid cooled Vulture would mean that it would need less of the drop tanks that it didn't have. The higher power would make heavy takeoffs easier.

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Was the reduced BSFC theoretical or proven?
An R-2800 in a P-47 could go down to around 0.45lb/hp/hr in cruise. That is down low, at 25,000ft and doing just under 300mph it may have been 0.525lb/hp/hr.
An old book claims the Vulture II could do 0.48lb/hp/hr but it does not say,
1 At what altitude (like high or low gear in the supercharger)
2 what level of power,
3, Lean or rich, assuming lean to even get close to 0.50lb/hp/hr

Air cooled engines could certainly suck down the fuel at high power but at cruising powers the actual difference between air cooled and liquied cooled may have only been a few hundreds of pound per hour.
When the Vulture make more than 2000hp ???

Simon Thomas said:

the engineering/drafting staff numbers for the likes of Bristol, R-R, P&W, Napier, Wright, Allison from say 1935 to 1945?

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Varied tremendously for each company all through the years mentioned. Some of the American companies expanded their engineering departments many times over from pre war to height of war years. I am sure the British expanded a number of times also. The Americans just had a larger population to draw from. They also had 1938-41 to start steering young men into engineering/technical schools before they started drafting them into the military.

Shortround6 said:

Air cooled engines could certainly suck down the fuel at high power but at cruising powers the actual difference between air cooled and liquied cooled may have only been a few hundreds of pound per hour.

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Why? I would guess an equivalent air cooled engine would need a richer mixture to avoid detonation due to higher cylinder head temps, but surely someone has actually researched the issue? How big was the difference between an inline and air cooled engine at full power?

z42 said:

Why? I would guess an equivalent air cooled engine would need a richer mixture to avoid detonation due to higher cylinder head temps, but surely someone has actually researched the issue? How big was the difference between an inline and air cooled engine at full power?

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At cruising the engines (both types) are running at lower rpm and much less boost and making around 1/2 the heat (assuming that the R-2800 in making 800-1200hp at cruise instead of 2000hp) so the engine can handle the heat without additional fuel. Early P-47 engine chart.


Notice that to go from 1200hpto 1625hp (33% increase) requires double the amount of fuel (100% increase) but in the range of power covered by auto-lean (A.L.) the specific fuel consumption is not much different than liquid cooled engine. In fact it might be better. The R-2800s of the time were using 6.65 to 1 compression ratio. This limited the ability to use high boost with a given fuel but may have given slightly better SFC. Allisons used 6.7 to 1, RR used 6.0 to 1.
Just like maximum power being the most, SPC was often listed as the best SPC they got in testing and NOT at max power or anywhere near it for either liquid cooled or air cooled engines. We need to check what the specs really said.

Now at full power the R-2800 in the P-47 had an SFC of 0.825 so it is more than likely that just about anybody's liquid cooled engine could beat it at high power.

I was just thinking that myself.

I calculated the Vulture II BSFC at MS around 8000' (~1240 hp) at max continuous weak (2600 rpm & +2 psi) of 0.476 lb/hp.hr Based on Manchester flight manual Para 27. and Neil Stirling's performance charts on this forum. The same charts have the TO power of the Vulture RV2SM on 100 octane at 2100 hp.

The R-2800-21 BSFC's from the above chart are: (assuming avgas at 6 lb/gallon, not strictly correct due to density variation but commonly used and so adequate for comparison)
At comparable power figures, the liquid cooled BSFC is 91% of the air cooled BSFC.

Rutan's Voyager went with liquid cooled versions of air cooled Continentals, as they needed every bit of efficiency they could get.

Charts for a different R-2800. This one is for -8 as used in the Corsair and although it doesn't say so I believe it is for the -8W with water injection as the reduction in fuel consumption at War Emergency makes no sense otherwise.



Note that in high gear making 1650hp in military power the engine exceeds 1 lb/hp/hr. only slightly but it does
however at 570hp in low gear at low altitude it gets 0.442 lb/hp/hr
At 1070hp at 10,000ft it gets 0.465 lb/hp/hr

Different supercharger set ups, slightly different supercharger gears, different inlets (I believe the F4U could route the intake air into the main supercharger by passing the aux supercharger, the F6F could not do that?) compared to the P-47.

Please note the different rpms/ boost levels and fuel burns at the different altitudes with the aux supercharger in neutral, low gear and high gear. It took over 275hp to drive the aux supercharger in high gear and that has to be payed for by SFC.
These charts help explain why the F4U was not going to work as a long range escort over Germany. At higher speed cruises the turbo engine was going to give better fuel consumption for an R-2800 powered aircraft.

The question for the Vulture trying to replace in the R-2800 in the P-47 is will the engine perform at 25,000ft and above?
Perhaps Hooker could have worked his magic and come up with a two stage supercharger but now you have to drive the 2 stage supercharger and you will not get the same SFC as a single stage engine. Or even a single stage engine in high gear.
Or perhaps you figure out how to match the Vulture engine to the turbo sitting in the rear fuselage?

SFC is nowhere near as easy as it looks at first glance.

z42 said:

Maybe we'd have seen a Vulture-powered Mustang eventually, though obviously adapting the Mustang from the Allison would have required a much more massive redesign than the historical Allison->Merlin transition.

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Not likely - if anything, the absence of the V-1650 would have most likely seen the V-1710 improved for higher altitude service as well as moving several inline projects from the back burner to accelerated development, like Allison's V-3420 or even Continental's I-1430.

GrauGeist said:

Not likely - if anything, the absence of the V-1650 would have most likely seen the V-1710 improved for higher altitude service as well as moving several inline projects from the back burner to accelerated development, like Allison's V-3420 or even Continental's I-1430.

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Maybe mating the Vulture to the Mustang would have been a bit too much, yes. Though I'm suspicious if any of the above projects would have been ready to serve in volume during the war. So in that case maybe the Mustang would have lived out it's WWII service as a decent upgrade to the P-40, but not the spectacular success it historically became with the Merlin?

In either case, the lack of the Merlin would have massive implications for the force structure on the Western front, hard to see any really good options for single engined fighters until Vulture and/or Griffon arrive on the scene. Then again, while it's perhaps poor form to criticize the underlying premises of these what-if scenarios, I'm finding it difficult to imagine RR not being able to successfully field what is in many ways a plain and boring V-12 (Merlin), but OTOH succeeding with a much more complex X-24 engine.

z42 said:

Maybe mating the Vulture to the Mustang would have been a bit too much, yes.

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Yes, take the Vulture out to sea, far out, and push it overboard.
The Vulture was 2450lbs,
the Allison was under 1400lbs,
the Merlin in the Mustang was about 1700-1715lbs.
A two stage Griffon was under 2100lbs.
An R-2800 out of an F4U was about 2450lbs and it doesn't need radiators and coolant.