Alfa Romeo 136 R.C.25

[Burmese Bandit]

While researching engines which might have been used by the Axis to design a better fighter and/or bomber in WWII my attention was caught by this Italian engine, which, according to the Wiki (not that I trust it 100%, but it's much more often right than wrong!) says -

"...At the time of its first running in 1938 and 1939 it was the most powerful radial engine in the world, generating just less than 1492 kW (2000 hp) on 100-octane fuel."

Although the 135 in question is then described as having "...Power output:1177 kW (1600 hp) at Take Off, 1030 kW (1400 CV) at 3200m..." Wiki goes on to say that a variant, the Alfa Romeo 136 R.C.25, had a power output of

"...Power output:1765 kW (2400 hp) at 0m, 1360 kW (1850 CV) at 2500m..."

TWO THOUSAND FOUR HUNDRED HORSEPOWER AT SEA LEVEL????

If that was true, and it was produced in the very early years of the war, why wasn't it used as the primary engine for thw Wurger - especially the ground attack version???

Did this engine have reliability problems, or production problems, or was it just a case of German Technical Jealousy???

I have searched this forum and the net, but i have not been able to come up with the answers to those questions.

Which is why I am asking the very knowledgeable members of these forums - could someone enlighten me on the history and fate of this (on paper at least) world-beating engine of its time?

 

[red admiral]

I'm not sure when the 136 itself was produced but the 135 is from around 1938/39.

There were a few initial problems with the 135, mostly relating to the cam ring breaking, but reliability was otherwise good. The Germans did some harsh reliability tests against the BMW 801 and found the 135 to be much better. Its a little bit wider than the 801 but shorter and lighter.

 

[Burmese Bandit]

AHA! Thanks, Red Admiral...

So then, it is as I suspect...the old GERMAN JEALOUSY monster rears its head again...

Who can tell me more? I am intending to resurrect my old 'could you have desiged a better warbird' thread around this engine, and I would like more input before I do so.

 

[b0ned0me]

I can't add much more than you have already found, but I have myself been intrigued by that engine - if for no other reason than it seems to be based on a licence-built Bristol Pegasus 'doubled', which indicates what Fedden might have been able to achieve if he hadn't bought into Ricardo quite so whole-heartedley.

I have to say I'm a bit suspicious of that 2400hp number. Not to disrespect the Italians, but could Alfa Romeo really volume-produce an engine early-war that would match a late-war R-3350? Only 150 of these engines were made, and my feeling is that getting an 18-cylinder four-valve radial to 2400hp for testing might have been doable, but achieving the same on a mass-produced engine with standard-issue fuel would be another matter. If that were the case, then the 2400 hp from the 136rc25 would be like the 2200hp from the early Napier Sabre - available from the test bed and the workshop, but not from the factory.

[edited to correct stupid typo]

 

[Burmese Bandit]

Good point, and by the way - excellent first post! Welcome to the Forums!

 

[sibboh]

Hi everyone.
Alfa Romeo 136 was only a project. I think it was projected after 1940 but before 1943. I'm not sure. But surely not before 1940. Alfa Romeo 135 used 87 octane fuels. But with 100 octane fuels it reached 2000 CV (the same as PS, CH etc... but not like HP: 1 CV = 0,9863 hp. So 2000 cv = circa 1970 hp). But at the beginning of WWII Italy hadn't 100 octane fuels for the Regia Aeronautica. Probably during the war the 100 octane fuels became more available. Even if the majority of engines ran with 87 and 92 octane fuels. Another thing is the supercharger boost. The 135 supercharger produced less preassure than that of the Alfa 128 (an evoluted Alfa Romeo version of the Bristol Pegasus). But probably the 135 supercharger was better than that of Alfa 126 (a lesser evoluted version of the Bristol Pegasus, respect to 128). Infact if 135 have used the 128 supercharger it has reached sizeable more power. Probably Alfa Romeo, when they resolved the 135 problems, projected the 136: an evoluted version of the 135. With a better supercharger and 100 octane fuels.
Italians had weak supercharger (like those of Fiat A.80 and A.74), but the 128 had good performances.
But Alfa 136 didn't ever run.
Probably there are more infos in this publication (but it's very difficult to find it): "Marina Bonifazio, Eleonora Canetta, Elvira Ruocco: Archivio Storico Alfa Romeo, Volume II, 1998, Fiat Auto S.p.A. Editore (Press), Torino"
I'm trying to find it.

 

[krieghund]

Here's the specs on the Alfa 135, this is from my copy of Wilkinson's "Aircraft Engines of the World" printed 1941

 

[sibboh]

Sorry. There is a mistake. Stroke is 165 mm (6.50 in). Infact Alfa 135 originate from two Bristol Mercury IV. Alfa had a license to build Mercury and Pegasus from Bristol in 1932.
Displacement was 49,722 l. I'll post some bibliography.

 

[sibboh]

Two images from the book: Oscar Marchi (author), 1980, "Aeronautica militare. Museo storico. Catalogo MOTORI", Pàtron Editore (Publisher)

 

[razor1uk]

Cool Alfa Romeo, whilst I can't speak or read Italian, I can guesstimate some of what is written. Might there be a chance for a translation of the pictured text just above?

 

[sibboh]

This is the translation:
Manufacturer: ALFA ROMEO, Societa Anonima, Milano
Designer: Engineer H.C. Giustino Cattaneo (1881-1973)

Description: 18-cylinder two-star, with compressor and gear, obtained by coupling two derivatives from the Bristol Mercury (designer AH Roy Fedden) engine produced under license by Alfa Romeo
Cooling: air
Bore: 146 mm
Stroke: 165 mm
Displacement: 49,722 dm3
Distribution: overhead valves, four per cylinder arranged with slightly inclined axis control valve pushrod
Geometric compression ratio: 6.3
Power supply: with aspirated carburetors
Supercharger: centrifugal single-stage and one speed with controlled dispensing by an automatic limiter
Ignition: double with four rnagnets
Reduction Gear: epicyclic conical (bevel) gear
Max power: 1410 cv (1390 hp) at 3200 meters of altitude
Speed of revolution: 2400 rpm
Dry Weight: 990 kg
Specific weight: kg/cv 0.702
Specific power per unit of displacement: CV/liter 28.36
Year of construction: 1934-1937
Production: in small series
Installs: Caproni Ca135, Ca169, Ca325 - Fiat G12 - CantZ1018 - SIAI SM90 and SM82 (only center)

The famous engineer Cattaneo, during the brief period spent as a technical director at Alfa Romeo Avio engines, after started the chain of production for the 126, he began to study two engines: the Alfa 130RC38, a derivative from Mercury who died prior to the approval , and a high power engine, the Alfa 135RC32, designed as a double star obtained with the coupling of two derivatives of the same Mercury. The Mercury, already mass-produced without great success, was born before the Pegasus and it appeared pretty much the same all over, including details, but it was sized with a stroke of the piston of an inch lower than that of its derivative Pegasus.
This implied a diameter of dimensions of the front of only 130.7 cm, exactly ten less than the Pegasus-126 and derivatives, and thus a lower surface of beyond what had been 15%. In addition to this it should be noted that the weight was also lower by about 10%, while the performance of the most advanced versions made by Bristol were made equal to those of the bigger Pegasus. Alfa instead, perhaps for lack of demand, gave no following to the Mercury in addition to the failed attempt of 130. Cattaneo, using the valuable potential capacities of Mercury, he conceived an engine as unpredictable as the 135 engine with a long history that deserves to be known.
Since the birth were many hopes pinned on this engine, on paper had all the qualities to succeed, "the" engine long awaited by our Air Force. It was exhibited at the Air Show in Milan in 1937 in an aura of mystery doing good impression, it was a major engine in all respects, aesthetically valuable. It was a pre-built, but in 1943 it was not yet sufficiently developed. In conclusion an engine failure, as its derivative 136 remained on paper and the experimental 138RC23/65 incorporating the idea of Cattaneo with the coupling of two 126, or with their derivatives, and a superb two-speed compressor with the power rated altitude at 6500 meters. Even the subtype 135RC45 few examples were built, and flew with the wonderful CantZ1015.
The "135" also aroused admiration only to watch it: a beautiful machinery. This led even the rumors about requests made by the Germans to have the supply or construction license. But two facts are enough to show that these were only rumors: the events that accompanied the life of the few copies produced and the existence of a much better engine, and equivalent characteristics, mass production line, the BMW801.

 

[razor1uk]

Gratsi Sibboh I wasn't expecting so quick a reply, mille-gratsia

 

[Civettone]

Sibboh, have you been able to locate that publication on Alfa Romeo?


Kris

 

[sibboh]

No, unfortunately. I did not have time to go looking for him.

 

[Tollmar]

I can add this one as publication on Alfa Romeo 135, but in italian too :
Alfa Romeo 135 Lo Splendido Propulsore Che Poteva Essere (Italian Edition): Alessandro Colace: 9781470965297: Amazon.com: Books

 

[msxyz]

There is a beautiful specimen of a AR 135 at the Alfa museum in Arese, in pristine conditions. For a photo, look up in the Italian Wikipedia. Another one rusted, missing several parts turned out for scrap several years ago but I don't know its fate. I have the publication Tollmar linked but it looks like the hastily done work of an amateur. Not only the print quality of bad, but the text contain several ortographic errors.

 

[dogsbody]

I have always felt that Bristol's missed out developing a good powerful engine by not joining two Peggys together. It seems like an easy solution to get to the 2000hp range. While the Hercules and Centaurus engines were great engines, they did take a while to develop the needed power.



Chris

 

[msxyz]

View from the compressor of an early (1937) AR 135 prototype preserved at the Milan Science museum. The plaque on the wall state that had a maximum power of 1550HP at 2400 rpm.

Another AR 135 in bad shape and missing several parts. Source unknown.

As for why Bristol didn't develop further the Pegaus, I think it had to do with several factors:
-Diameter: the Pegasus was one of the radials with the largest front area. The sleeve valve mechanism in development allowed to design slightly shorter pots with the same stroke.
-Complexity: the Pegasus was one of the few radials produced in quantities with four valves per cylinder; the rear valves were used for intake, the front for exhaust. An odd arrangement, maybe designed to keep the 'hot' part of the head on the front of the engine, but the exhaust piping arrangement was generally more complex and probably blocked some of the airflow around the heads as well. Routing of the exhaust gases on the Alfa 135 was done via a large diameter collector ring which probably would have been partially exposed outside the engine nacelle (as it was done already in some Italian designs using the AR 125/26). The valve push-rod mechanism was also quite complex and the coil springs were still exposed and cooled by air instead of oil, unlike the other modern, two valve designs.
-Growth potential: the Pegasus used a long stroke (190mm) which resulted in a high linear speed of the piston (15 m/s at 2400 rpm). The Italian engineer Giustino Cattaneo (the same who designed some of the best Isotta Fraschini engines/cars) reduced the stroke to 165mm to create the AR 135 and Bristol did the same with their 'Mercury' engine.
-Opportunity: Alfa Romeo and Bristol had a long partnership to develop the Pegasus and its derivatives; the Italian introduced several improvements and simplifications over the basic design which were relayed back to Bristol to be incorporated in their designs as well. After Italy and UK relations deteriorated, the partnership was essentially ended and this, among other things, prevented Italy from obtaining sleeve valve engine designs (talks were already underway).

Note that while radial engines seem to be the epitome of modular engine designs, adding pots or adding another bank is never as easy as it sounds.

 

[Shortround6]

Just look at the trouble Wright had when they shortened the stroke on the Cyclone 15mm and tried to use two rows of cylinders to make the R-3350. Russians took 4 tries to get to about the same end point from the same start.

 

[razor1uk]

Every change of a design weather intended or needed by necessity, sometimes just converting a design from imperial to metric systems, will introduce a change that will have a different affect upon a the end effect of that 'production' made design.
Countering these differences once you know them and is the hard part, finding and identifying each one; when, where and how it manifest under what variation of possible conditions, that Is the harder part that has and is performed in pre-hindsighted evaluations and theorising and in hindsight redesign.