RR Merlin, Vulture and 2,000hp+ engines


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4 June 2006
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A question arising from a post on another board, if RR are allowed to abandon the Vulture in August 1939 when IIRC they asked to do so , how does that leave the Merlin 60 series engines given the supercharger was from the Vulture design – how quickly could a supercharger have been developed for the Merlin if no Vulture?

If RR had decided to build a 2000hp+ engine from scratch rather than trying to combine two Peregrines and succeeded in getting a reliable engine by end of say 1940 what does that do for the need for the Merlin 60 series?
The answer to the first question would seem to be "exactly where they were or possibly just a little later", as dropping the Vulture would have allowed more concentration on Merlin improvement. The alternative possibility feeds into your second question. I suspect the answer there is (a) RR Griffon (which IIRC was the Schneider R engine dusted off and modernised) and (b) it gets complex, because what's implied there is a much earlier change to Griffon Spitfires at least.

I suspect the 2-stage 2-speed Merlin would have soldiered on, in part to keep production lines of badly needed aircraft flowing and in part because redesigning and retooling for a substantially different engine isn't always as easy or as possible as it was for the Spitfire. I don't know, for example, whether the Mosquito would have taken too kindly to it, if only because the engine required bigger and bigger props to absorb all the power, and fuselage clearance problems (at least) might eventually have got in the way. OTOH a Griffon Lancaster running 2000hp up to high altitudes might have proven a more difficult 'catch' for a German night fighter, with overall lower losses across the night-bomber campaign.

I seem to recall that the Peregrine itself wasn't without problems, so what on earth possessed RR to try to bolt two of them together is beyond me. The Westland Whirlwind really needed the Merlin, but a Whirlwhind redrawn big enough to take the Merlin essentially becomes a Dehavilland Hornet...
I suspect that Hooker, who conceived the 2-stage supercharger would have realised that the Vulture impellor and diffuser would have the right capacity after the analysis of what was required for the Merlin had been compeleted. This enabled the experimental shop to use the supercharger rig to demonstrate feasibility very quickly. The rig power source was a large electric motor with a drive offtake at each end... it could be used to power two tests simultaneously or in this case a Merlin and a Vulture supercharger. Hooker had a sheet metal duct made from the outlet of one to the inlet of the other to show it worked and then left it to Rubbra to get the Main Engine Design Office to scheme out a compact version for the actual production. If the Vulture had not existed no doubt they would have scaled up the Merlin one to suit and machined out the required parts. Hooker had introduced non-dimensional analysis which for the first time meant all the supercharger tests could be plotted on the same graph even if from Vulture, Peregrine, Merlin or a special.... this meant a skelton supercharger could be drawn and then scaled to give the right size for the job. A really good craftsman could then 'carve' an accurate form for copy milling a metal example. The use of non-dimensional clusters meant that the Eagle II used an advanced Merlin rig design and also the Dart turoprop was scaled from the Merlin supercharger family.
Here is a good photo of the Vulture in a airplane.


  • Vulture.jpg
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johnbr... super pic of Vulture. Rubbra's R-R Piston Engines - A Designer Remembers has a good chapter on the Vulture and gives a good indication of how the connecting rod issues could have been solved if the pressures on Merlin development had not been so high. there is a fascinating comment on possible further development which involved Merlinising the engine rather than continue with Kestrel technology. This included Merlin sized cylinders which could be done as there was sufficient space to 'drop' a larger piston into the existing crankshaft geometry... now there's a thought!
I don't think that is a Vulture. To me that looks like an Exe, the cylinder heads are individual, round and finned.
whoops... I had downloaded it to look at later...on zooming in I can see the cooling air guides round the cylinder... which makes this a picture of the Fairey Battle installation which RR used as a pretty reliable taxi during the war.

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