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Rolls Royce Crecy - The Most Advanced Piston Aero Engine Never Made


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#1 MatsNorway

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Posted 01 June 2021 - 11:46

 

Impressive engine, quite the complicated design. I find it interesting how they focus on power Pr. litre over power Pr kg.


Edited by MatsNorway, 01 June 2021 - 11:48.


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#2 mariner

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Posted 01 June 2021 - 12:32

The Crecy was certainly impressive but by the end of WW2 air cooled radials form the US builders had reached nearly 3000 bhp and didn't need the water radiator systems.

s

Tony Rudd tells in his book "It was fun" that despite all RR's engineering  they couldn't persuade even BOAC to use water cooled engines in long haul pasenger planes.

 

The US radials  were also very complex with lots of fuel efficiency things like exhaust turbos geared the  prop. drive. 

 

There is an interesting discussion to be had about the different demands of fighter and bomber engines. For fighters power and bhp/lb are paramount. For bombers ( and long haul passenger ) planes fuel economy is everything as in a 6-10 hr flight an extra lb in engine weight pays of if you can save 3 lb of fulel and  so fly further or carry more bombs.



#3 desmo

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Posted 01 June 2021 - 14:18

I've never understood the power per displacement fascination. Power per unit of cost, fuel use, or weight make good sense; power per displacement unit is arbitrary to the point of near meaninglessness in an engineering sense. It only becomes important when stupid, artificial constraints are applied.



#4 Nathan

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Posted 01 June 2021 - 14:23

I hope this becomes a runaway conversation..



#5 mariner

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Posted 01 June 2021 - 16:10

going back into Tony Rudd's book he helped develop the Merlin as head of reliabilty analysis in WW2. He openly admits the early merlin's weren't that reliable, having to upset his RR bosses by siding with Air Marshal Tedder who complained of too many failures endangering his pilots!

 

The Merlin was a much smaller displacement than  the MB rival. 27 litres vs 44 litres I think. It relied on very high boost pressures , useful experience for the v 16 BRM of course.

 

The secret to getitng back home safe in a Merlin-engined bomber was apparently  lots of prop pitch to load up the  engine then lots of boost to get power at low revs. This boosted BMEP and cut  wear rates Rudd used to have to persuade the pilots in his RR engine handling courses to let the engine sound laboured all the time.



#6 Canuck

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Posted 01 June 2021 - 20:43

It would be interesting to build up a scaled-down version of the V-twin (as he sits looking at his motorcycle...)



#7 gruntguru

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Posted 01 June 2021 - 21:14

The secret to getitng back home safe in a Merlin-engined bomber was apparently  lots of prop pitch to load up the  engine then lots of boost to get power at low revs. This boosted BMEP and cut  wear rates Rudd used to have to persuade the pilots in his RR engine handling courses to let the engine sound laboured all the time.

Fuel economy was the main benefit of the low rpm, high MAP operation.



#8 gruntguru

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Posted 01 June 2021 - 21:19

It would be interesting to build up a scaled-down version of the V-twin (as he sits looking at his motorcycle...)

Like this you mean?

https://www.youtube....h?v=H70OqfF0AWY

https://www.youtube....h?v=OTlulIkMNqg



#9 GreenMachine

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Posted 01 June 2021 - 22:13

going back into Tony Rudd's book he helped develop the Merlin as head of reliabilty analysis in WW2. He openly admits the early merlin's weren't that reliable, having to upset his RR bosses by siding with Air Marshal Tedder who complained of too many failures endangering his pilots!

 

The Merlin was a much smaller displacement than  the MB rival. 27 litres vs 44 litres I think. It relied on very high boost pressures , useful experience for the v 16 BRM of course.

 

The secret to getitng back home safe in a Merlin-engined bomber was apparently  lots of prop pitch to load up the  engine then lots of boost to get power at low revs. This boosted BMEP and cut  wear rates Rudd used to have to persuade the pilots in his RR engine handling courses to let the engine sound laboured all the time.

 

I think (IIRC) Henshaw reports something similar in his 'Sigh for a Merlin', concerning his job doing acceptance testing.

 

Lindberg did a similar job re fuel economy with USAAF in the SWPA, and recounted in his 'Wartime Journals' how it transformed the range of the fighters there.  I must check the details ...



#10 Wuzak

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Posted 02 June 2021 - 06:40

The Merlin was a much smaller displacement than  the MB rival. 27 litres vs 44 litres I think. It relied on very high boost pressures , useful experience for the v 16 BRM of course.

 

The rival for the Merlin at the beginning of the war was the DB 601 at 33.9L. The DB 601 was similar in weight to the single stage, single speed Merlin.

 

The DB 605 was a development of the DB 601 with bigger bores, taking displacement out to 35.7L. The weight was equivalent to a 2 stage Merlin.

 

The DB 603 design was started before the war (it was used to power the Mercedes-Benz T80 record car), but didn't get into production until late in the war. It had a capacity of 4.5L and weighed about the same as a 2 stage Griffon (36.7L), but had less power.

 

The Allison V-1710 was 28L.

 

By the end of the war the Merlin boost for cruise settings was higher than the maximum boost at the beginning of the war.



#11 Wuzak

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Posted 02 June 2021 - 06:48

The Crecy was certainly impressive but by the end of WW2 air cooled radials form the US builders had reached nearly 3000 bhp and didn't need the water radiator systems.

 

The R-2800 was capable of 2,800hp for short periods, but required ADI and a lot of boost to do it.

 

The R-3350 wasn't capable of 3,000hp without power recovery turbines. I think it could get ~ 2,700hp without.

 

The R-4360 was the first genuine 3,000hp engine, mainly because of its size (71.5L). It was not a favourite for airliners either, having 28 cylinders.



#12 Allan Lupton

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Posted 02 June 2021 - 11:05

I've never understood the power per displacement fascination. Power per unit of cost, fuel use, or weight make good sense; power per displacement unit is arbitrary to the point of near meaninglessness in an engineering sense. It only becomes important when stupid, artificial constraints are applied.

Yes, for aeroplane powerplants the cost of power in terms of price, weight and fuel useage are what matters. The power per unit displacement is more of a motor racing concept as for most of the 115 years of Grand Prix racing there has been an engine displacement limit.

However I would not agree that it is meaningless in any sense, as it is an indication of how hard the machine is being worked.



#13 Canuck

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Posted 02 June 2021 - 20:53

Yes, for aeroplane powerplants the cost of power in terms of price, weight and fuel useage are what matters. The power per unit displacement is more of a motor racing concept as for most of the 115 years of Grand Prix racing there has been an engine displacement limit.

However I would not agree that it is meaningless in any sense, as it is an indication of how hard the machine is being worked.

Or how efficient it is.



#14 Canuck

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Posted 02 June 2021 - 20:56

Not quite what I was thinking. Cool idea there, but I prefer the Millyard with it's 5-litre twin that actually has 10,000+ miles on it now. Admittedly it's really only aircraft engine from the pistons up, but that build is really quite something. Inspiring in it's own way.

 

What I was (very casually and not very deeply) thinking was physically scaling down the Crecy concept with sleeve valves and compound supercharging for a more modest V-twin displacement.



#15 desmo

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Posted 03 June 2021 - 01:43

That bike is silly, but in the best way. I was particularly impressed by the scratch-made carburetors for some reason, and the 'eyeballed' crank counterweights  :D  Good enough for 900 rpm, which would be a fine idle speed on a normal engine,



#16 Canuck

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Posted 03 June 2021 - 14:16

I would like to be more silly in the best way but the inner critic always gets the best of me. That's a special kind of freedom he's got there.



#17 gruntguru

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Posted 03 June 2021 - 21:10

That bike is silly, but in the best way. I was particularly impressed by the scratch-made carburetors for some reason, and the 'eyeballed' crank counterweights  :D  Good enough for 900 rpm, which would be a fine idle speed on a normal engine,

One of those wonderful machines that make no sense. I'd love to ride it - once or twice would be enough to absorb all that eccentricity then I'd be done. The owner is a master craftsman and an absolute nutter. Great that we are not all built the same isn't it?



#18 MatsNorway

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Posted 05 June 2021 - 00:02

Is no one going to comment on that prechamber? I smiled seeing it, same principle/idea too.



#19 GreenMachine

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Posted 05 June 2021 - 01:00

Yes.  Nothing new under the sun! 



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#20 Wuzak

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Posted 06 June 2021 - 03:58

An animation of the Crecy's sleeve valve mechanism

 

https://youtu.be/gweaCBaSmfk


Edited by Wuzak, 06 June 2021 - 03:59.