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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.


#21 gary76

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Posted 16 June 2021 - 09:55

There is a very good published by the Rolls Royce Heritage Trust on this engine, titled "The Rolls Royce Crecy". It is an excellent book written by people who were involved not only in the design but in the testing of this interesting engine. If it had not been for the singular concentration on the Merlin engine it would have perhaps developed further. Circumstances perhaps. 

If you also read "Secret Horsepower Race" by Callum Douglas is outlines (to me!) the divergent paths the Germans made with the number of engines they made during the Second World War and the consequent loss of concentration on solving both engine design and manufacturing problems.

Two-Strokes, sleeve valves and pre-combustion chambers are always a interesting subject with me and dread the day that the electric motor pales all the scientific and engineering knowledge we have learnt and enjoyed into insignificance.

 

Gary



#22 Lee Nicolle

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Posted 27 June 2021 - 06:53

Having read books about Merlin powered planes from the English during WW2 then in more recent times about the US made radials of the same period I honestly think the radial for aircraft only is by far the better thing for all larger planes. Though maybe not for fighters. Though all fighters have been jets since the end of WW2!

After hearing a few Merlins in various uses they are quite underwhelming. Though in  a plane ofcourse a different scenario.



#23 Allan Lupton

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Posted 29 June 2021 - 11:52

After hearing a few Merlins in various uses they are quite underwhelming. Though in  a plane ofcourse a different scenario.

I'm not sure what non-aeroplane uses you mean but many of the "Merlin-powered" cars are really Meteor-powered. That plus an exhaust system leads to a noise that is very different from (say) a Spitfire.

 

Back to the Crecy the claims made were chiefly based on the single-cylinder test unit factored up for number and size of cylinders etc .I can say that I was told by former RR people, in a position to know, but of course that's hearsay rather than evidence now.

They did claim 1700 h.p. from the 12-cylinder engine they made and tested, which wasn't a lot different from some of the late Merlins.

 



#24 mariner

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Posted 03 July 2021 - 12:41

There is an intersting page here about the ultimate US radial the P&W R -4360. It was very powerful and helped the  B 36 climb to 50,000 ft which is , I think, a piston record. However it was somewhat complex and even the USAF had trouble keeping all six running in B 36.

 

BTW I have never heard of silver being used in bearings before but it was in R 4360.

 

http://www.enginehis...60/r-4360.shtml

 

The installaton on teh B 36 was very complicated and  its issues were many! 

 

https://ww2aircraft....acemaker.52056/


Edited by mariner, 03 July 2021 - 12:46.


#25 Bikr7549

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Posted 03 July 2021 - 16:07

There is an intersting page here about the ultimate US radial the P&W R -4360. It was very powerful and helped the  B 36 climb to 50,000 ft which is , I think, a piston record. However it was somewhat complex and even the USAF had trouble keeping all six running in B 36.

 

BTW I have never heard of silver being used in bearings before but it was in R 4360.

 

 

 

Allison used silver in the bearings for their engines starting in the mid 1930s. They also sold bearing sets containing silver to other aircraft engine manufacturers during WW2-the Packard built Merlins, as well as P&W used them. The bearing surface used a silver plating along with lead plating. Unfortunately I do not have any details on the manufacturing process, such as how much silver was used.



#26 gruntguru

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Posted 04 July 2021 - 02:37

BTW I have never heard of silver being used in bearings before but it was in R 4360.

Many GE EMD locomotive engines had silver lined wrist pins. Probably related to the absence of load reversal in 2 stroke engine wrist pins ie boundary lubrication.



#27 Kelpiecross

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Posted 04 July 2021 - 05:02

There is an intersting page here about the ultimate US radial the P&W R -4360. It was very powerful and helped the  B 36 climb to 50,000 ft which is , I think, a piston record. However it was somewhat complex and even the USAF had trouble keeping all six running in B 36.

 

BTW I have never heard of silver being used in bearings before but it was in R 4360.

 

http://www.enginehis...60/r-4360.shtml

 

The installaton on teh B 36 was very complicated and  its issues were many! 

 

https://ww2aircraft....acemaker.52056/

 

 The B36 was not really totally piston-powered  - it had "four burning".    



#28 Kelpiecross

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Posted 04 July 2021 - 05:06

  Besides the point a little - but some racing two-stroke motorbikes (in the good old days) had the entire head made from silver - because of its heat conductivity.  Silver is not really all  that expensive.    



#29 GreenMachine

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Posted 04 July 2021 - 06:04

 The B36 was not really totally piston-powered  - it had "four burning".    

 

Yes, the initial production run were totally piston-powered. 

 

When the later B36D arrived with the addition of 'four burning', the earlier models were upgraded by adding the jet engines.



#30 Kelpiecross

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Posted 04 July 2021 - 06:21

Yes, the initial production run were totally piston-powered. 

 

When the later B36D arrived with the addition of 'four burning', the earlier models were upgraded by adding the jet engines.

 

 Beside the point as ever - but the 4360 was a four row radial  - there were single,  two and four row radials - but no three row radials. 



#31 Wuzak

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Posted 04 July 2021 - 08:17

 Beside the point as ever - but the 4360 was a four row radial  - there were single,  two and four row radials - but no three row radials. 

 

I present to you the Armstrong Siddeley Deerhound.

 

It didn't get to production, but it did fly.



#32 Wuzak

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Posted 04 July 2021 - 08:25

There is an intersting page here about the ultimate US radial the P&W R -4360. It was very powerful and helped the  B 36 climb to 50,000 ft which is , I think, a piston record. However it was somewhat complex and even the USAF had trouble keeping all six running in B 36.

 

Not sure that the B-36 could reach 50,000ft on piston engines alone.



#33 mariner

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Posted 04 July 2021 - 09:30

The B 36 couldn't reach 0ver 50,000 ft nornally but one did reach 55,000 ft during nuclear bomb test sampling. It had to use the jet engines to climb there but they flamed out at the 55,000 ft leaving the piston engines doing the job!



#34 GreenMachine

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Posted 04 July 2021 - 09:49

 

 The B36 was not really totally piston-powered  - it had "four burning".    

 

 Beside the point as ever - but the 4360 was a four row radial  - there were single,  two and four row radials - but no three row radials. 

 

:confused:  Your point was that it had jet engines - the first ones did not.  Not sure what the rest of that reply is about though, who is talking about three row radials?

 

Not sure that the B-36 could reach 50,000ft on piston engines alone.

 

What I have seen is pretty vague.  Jets were used for takeoff and dash to and from target, they were not it seems used for cruise as they were too thirsty. 

 

But whether they were used for the last stages of climb, or whether they used cruise-climb to gain altitude as fuel was burned off, isn't clear to me.  There is reference to a climb to 55,000ft over the target, that surely would have needed the jet engines.


Edited by GreenMachine, 04 July 2021 - 09:51.


#35 desmo

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Posted 04 July 2021 - 15:33

  Besides the point a little - but some racing two-stroke motorbikes (in the good old days) had the entire head made from silver - because of its heat conductivity.  Silver is not really all  that expensive.    

I don't see any possible advantage there, to make the cooling fins smaller to save weight? Silver is massively denser than Al-alloy, I don't think even that would work out.



#36 Greg Locock

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Posted 04 July 2021 - 23:02

The solar car was very weight sensitive, we seriously considered silver wiring as a cost effective weight reduction.



#37 Kelpiecross

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Posted 06 July 2021 - 05:29

 

 

 

 

:confused:  Your point was that it had jet engines - the first ones did not.  Not sure what the rest of that reply is about though, who is talking about three row radials?

 

 

What I have seen is pretty vague.  Jets were used for takeoff and dash to and from target, they were not it seems used for cruise as they were too thirsty. 

 

But whether they were used for the last stages of climb, or whether they used cruise-climb to gain altitude as fuel was burned off, isn't clear to me.  There is reference to a climb to 55,000ft over the target, that surely would have needed the jet engines.

 

 

 Three-row radials were not relevant to the B36 - I just thought it was interesting that there were no three-row radials. 



#38 Kelpiecross

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Posted 06 July 2021 - 05:36

I don't see any possible advantage there, to make the cooling fins smaller to save weight? Silver is massively denser than Al-alloy, I don't think even that would work out.

 

 I know silver heads were tried - I don't know how successful they were.  Racing air cooled two-strokes engines get desperately hot  - silver  with is great heat conductivity was thought  to be a solution.  I think the problem of overheating was partly solved by water cooling.   



#39 MatsNorway

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Posted 08 July 2021 - 21:19

Does a water cooled engine beat a air cooled engine for the same weight total when you include the radiator and more?

 

Those Singer 911 cars have 500hp from an air cooled engine now. Co designed with Williams engineering and the original Air cooled engine designer for Porsche.


Edited by MatsNorway, 08 July 2021 - 21:21.