Chasing the elusive FIAT A.82 high power radial

[msxyz]

When the Italians entered ww2 they had a bunch of low power radials to power their latest designs but they soon switched to local produced copies of German designs of inline V12s.

While it's widely known that the Italian industry was hampered by the lack of high octane fuel (all they had in quantity was an 87 octane fuel comparable to B7) and lack of high quality steels (though they successfully employed several zinc / magnesium and aluminum alloys in their engines because these light metals could be mined locally) there were many designs of high power (>1000hp) radials at various stages in 1940. One of these design was the FIAT A.82, a follow up of the 18 cylinder FIAT A.80. The FIAT A.82 was never employed operationally, if not in a handful of FIAT BR.20Bis light bombers and in a few prototypes.FIAT soon switched to produce locally the DB605 under the name of FIAT RA1050 "Tifone". That's the story so far...

My interest in the FIAT A.82 was renewed when I happened to acquire a promotional brochure, dated September 1937, from FIAT Aviazione where the A.82 is explicitly mentioned as the 'hottest' new engine from FIAT producing 1500HP. Here are a few shots of the brochure:

The brochure is bilingual (Italian - French) since French was the 'international' language at the time in Europe so it makes sense that a promotional flyer aimed at some aircraft manufacturer around the world would be written in French as well (today it would be English). At the bottom left, the date of the document, 30/9/1937 , the XV nearby indicates it was the 15th year since the advent of fascism.

In the second page there are two nice shots of the FIAT A.80; on the third page a short recap of the principal characteristics of the radial engines manufactured by FIAT.

The interesting part is in the bottom half: "1500 cavalli" reads the title "sono quelli forniti dal nuovissimo motore FIAT A 82 RC" (these are the horsepowers provided by the newest engine)

The text goes on to explain that thanks to new castings techniques FIAT was able to increase the radiating surface (fins) of the cylinders and head, lowering the temperature and in turns allowing higher powers to be achieved and it also mention something about better lubrication of the valves heads.

The small text in Italic then concludes: "It is not possible, due to explicit prohibition of the Ministry of Aviation, to reveal any other detail about this cutting edge engine which is currently in development by FIAT industries."

I was quite amazed to learnt that already in 1937 the design of the A.82 was complete. I thought that, at the time, only Alfa Romeo was far ahead with their AR 135 engine. Italy entered war only in May 1940, so what happened in those two and a half years since this brochure was printed? Imagine if FIAT was able to deliver, by 1940, a 1500HP engine. At any rate, after this revelation, I set out to find if there were otehr documents around about this elusive and mysterious engine... and I was able to find a complete service/operating manual (or rather the scans). I will post some extracts here at a later time, if anybody is interested.

 

[msxyz]

Second part:

This booklet is titled "Manuale d'uso", so it would loosely translate as "user manual". It contains both instruction on how to operate the engine and how to service it.

The date on the booklet is November 1943 although this seems to be a second edition of sort, the first print being dated August 1942

The first pages contain a detailed description of the engine specs and performance. Let's review them:

The A.82 is an 18 cylinders radial engine, with bore and stroke of 140 x 170 mm (5 mm longer than the A.80) for a total displacement of 47.1 liters. Weight including accessories is stated to be 870 Kg. On page 7 there is a detailed description, with weight, of the accessories. Their total weight is 46 Kg, so it follows that the net weight of the engine is 824 Kg.

The second half of page 5 and page 6 contains the detailed specs of the engine (power, rated altitude, manifold pressure [absolute, in mm Hg], specific fuel consumption). Here's a summary:

Max power at altitude: 1250 Hp - Alt: 4200 m - Rpm: 2300 - Manifold: 850 mm Hg - SFC: 280 gr/CVh
Max power at sea level: 1090 Hp - Alt: 0 m - Rpm 2300 - Manifold: 850 mm Hg - SFC: not stated

The A.82 engine still employs a single stage, single speed centrifugal supercharger spinning 8.6 times faster than the crankshaft.

Take off power (time limited): 1400 Hp - Alt: 0 m - Rpm 2400 - Manifold 1040 mm Hg - SFC: 330 gr/Cvh

It's interesting to note that there is a foot note regarding take off and military power: It says: "Ottenuti usando combustibile normale con numero di ottano 87; usando invece combustibile B4 con numero di ottano 90 si può avere al decollo 1500CV" - Translated, it says: "Obtained using normal fuel with an octane number of 87; by using instead B4 fuel with octane number 90 it's possible to achieve 1500HP". This is interesting because it tells to us something about how the Italians measured Octane number. The Germans considered their B4 fuel to be 87 octanes; the Italians, instead, rated it 90 (though I've seen other Italian engines service manuals rating it even higher, at 91-92). Italian fuel was truly worse compared to what was available at the time to Germans and Japanese and, on top of that, it didn't contain a lot of antiknock addictive. The standard formulation was distilled gasoline + 0.08% in volume of Ethyl which was a mixture of TEL + Bromoethane. By contrast, in Italy in the '30s, there was already available a special gasoline for sports cars, called 'Dynamin', which was composed of 49% distilled gasoline, 30% Benzol (a distillate of coal tar rich in BTX aromatics), 20% anydrous alchool and 1% ricin oil. It's octane rating was 95-100 so, at least in theory, the Italians knew how to make a better fuel. Too bad they used it for sports cars and not for the war effort

The rest of the claimed specs are the following:

'Economic cruise' setting: 750 Hp - Alt: 5500 m - Rpm 2000 - Manifold : 575 mm Hg - SFC: 240 gr/Cvh
'Fast cruise' setting: 1100 Hp - Alt: 5500 m - Rpm 2300 - Manifold: 770 mm Hg - SFC: 260 gr/Cvh
'Emergency rating': 1400 Hp - Alt: 4000m - Rpm 2400 - Manifold: 1040 mm Hg - SFC: 330 gr/Cvh

Last, at the bottom of page 7, there are the valve and ignition timing:

Intake opens 9°48' before top dead center and closes 68°52' after bottom dead center
Exhaust opens 67° before bottom dead center and closes 21° after top dead center (a lot of overlap, it seems)
Ignition timing was fixed at 26° before top dead center

That's all for the moment. If anybody is interested in more info, drop a few lines here and I will answer the best I can. The manual is also full of interesting drawings of the engine and of its parts.

 

[Hardrada55]

Thank you for this information. I find the World War 2 Italian aircraft engines interesting, but confusing at times. I know that on one of my lists, I had the Fiat A80 as an 18 cylinder engine and the A82 as a 14 cylinder engine. The very number of radial engine projects produced by Fiat, Alfa Romeo and Piaggio is hard to keep straight. In the English language sources there always seems to be typographical errors and other mistakes. It seems like if the Italians had concentrated on any one of the Fiat A82 or the Alfa Romeo 135 or the Piaggio XII engines, they might have been able to develop a very powerful and reliable large double row engine in time to make an impact on fighting in WW2.

 

[msxyz]

The A.82 is definitively a 18 cylinder engine; FIAT also planned to introduce an upgraded version of the A.74 in the form of the A.76. According to the tidbits of info I have, the A.76 had the same bore and stroke of the A.82, so possibly it could have been just a scaled down version of the larger engine.

The Italians backtracked on their decision to concentrate on radial engines possibly after seeing the latest development of the Germans and British. With the war looming and no updated designs of their own (if one exclude the exotic Isotta Fraschini air cooled V12) they had no other option than buying a license from Mercedes.

In addition to that, the Italians were handicapped by the sanctions decreed by the Society of Nations after the African colonial wars. Take fuel for example: in Italy there were plenty of good scientists specialized in organic chemistry (for example Giulio Natta, who is considered the father of modern plastics) and there were plans to synthesize fuel even before the war, , from methane or alcohols (which were sources available even to the sanction stricken Italy) but WW2 happened simply too early to set this plan in motion.

Italy also lacked many raw materials; for steel and coal it relied heavily on Germany; this is also reflected in the Italian engine designs which contain a lot of lightweight alloys (elektron was extensively used in aircraft engine castings) but are generally weaker and cannot scale well in power even using better fuel. When Alfa Romeo obtained the license to manufacture the DB601 in 1940, it took them more than one year to adapt the engine to local manufacturing techniques and materials. The result was an engine which was somehow not as powerful but still possessed good reliability and even solved some quirks of the original design.

 

[Hardrada55]

Do you have any information or details about the horsepower and altitudes for the Fiat A.76 engine? I have it as having a displacement of 33.404 litres (2037ci). Too bad they couldn't make the Fiat A.38 work or successfully update the 900 cv Isotta Fraschini Asso L.121 RC40 to the L.122 RC 50 of 1000cv.

 

[msxyz]

Sorry I haven't. I can only speculate that the power curve would be similar to that of the A.82RC42 given the similarities. Italian designs always used a single stage, single speed supercharger except for a few prototypes for high altitude research (these engines would have the postfix "/2V" added after the altitude code).

The Isotta Fraschini engines were too old to be updated in addition to being too bulky. Piping for 18 cylinders in a W configuration must have been a nightmare, too! German designs at the time were the best that could be used also because, using direct injection of gasoline, the vaporization of fuel directly inside the combustion chamber lowered the air temperature, thus with the same low octane fuel it was possible to rise pressure and compression ratio without incurring in knock (same with GDI engines today: that can go up to 14:1 while most cars with indirect injection cannot go over 11:1).

 

[msxyz]

Sorry, double post

 

[greybeard]

The Germans considered their B4 fuel to be 87 octanes

I saw B4 stated as 87-90 octane in some documents. As you know, there are generally two octane numbers stated for aviation fuels: first in weak mixture condition, second in rich mixture (e.g.: 100/130, 115/145).

 

[camman]

I saw B4 stated as 87-90 octane in some documents. As you know, there are generally two octane numbers stated for aviation fuels: first in weak mixture condition, second in rich mixture (e.g.: 100/130, 115/145).

From what I've heard, the lower number in the 100/130 octane rating system corresponds to the numbers achieved using the octane rating system that the Germans used and the 87-90 part just is an indication of variance in the quality of B4 gasoline.

 

[bdefen]

Interesting discussion on aircraft motor fuels. Modern auto racing fuels include toluene in some mixtures. Any use of toluene in WW2 aero engine fuels?

 

[msxyz]

Interesting discussion on aircraft motor fuels. Modern auto racing fuels include toluene in some mixtures. Any use of toluene in WW2 aero engine fuels?

From coal tar it's possible to obtain a mix of BTX aromatics (Benzene, Toluene, Xylene). These aromatics have very good anti-knock properties, better than iso-octane itself, and they were indeed used in conjunction with gasoline, as I also mentioned in my first post. The so called 'Benzole' was such a mix obtained either as a by-product of coke gas production or by processing coal tar.

But, at least in the case of Toluene, alone or in too high concentrations, it would make a poor aviation fuel. It's a thick fluid, which doesn't evaporate as readily as gasoline, especially at low temperatures. Formula 1 cars of the '80s, during the turbo craze, used toluene as fuel but it was pre-heated before being injected.

 

[Piper106]

From coal tar it's possible to obtain a mix of BTX aromatics (Benzene, Toluene, Xylene). These aromatics have very good anti-knock properties, better than iso-octane itself, and they were indeed used in conjunction with gasoline, as I also mentioned in my first post.
.

As far as I know all of the combatant nations would have liked to put more toluene in aviation fuel, but nearly all the toluene available was needed as raw material for trinitrotoluene (TNT).

 

[Shortround6]

Race car fuel (or even record setting/racing aircraft fuel) makes poor aircraft fuel.

Knock resistance is just one aspect.
Most aviation fuel is blended to give 18,500-18,800 Btus of energy per pound.
The use of alcohols or high amounts of aromatics will reduce the BTUs per pound and give less power per pound of fuel burned. It may give more power per minute by burning more fuel.
Alcohols for example have roughly 1/2 the BTUs per pound so a plane that needs 5,000lb of fuel to fly a certain distance at a certain speed would need 10,000lbs of alcohol to do the same flight, which cuts into performance and weapons load.
Start throwing in vaporization problems at low temperatures or different vapor pressures (fuel evaporates quicker at low air pressure) and stability problems (fuel stored in 55 gal drums for months) and most of the alternative fuels and/or racing fuels get impractical in service real quick.

 

[msxyz]

Alcohols like ethanol or methanol are cheap to manufacture but 1) have much lower energy content 2) they have higher freeze temperatures 3) don't vaporize as easily. In addition to that, light alcohols don't mix very well with gasoline because one has affinity for water (polar) molecules, the other for oils. Pure anhydrous ethanol can be mixed with gasoline in small quantities to increase octane rating (up to around 10% without resorting to additives like in modern 'E' fuels) but with cold the two substances separates. Butanol would be a better substitute, but it's expensive to produce.

Gasoline, for all its shortcomings, is a very convenient fuel for reciprocating aircraft engines:
1) high energy content per weight
2) very low freeze temperature
3) easily vaporizes even at low temperatures

Unfortunately, gasoline obtained via distillation from crude oil can vary a lot in its anti knock properties because its a complex mixture of hydrocarbons sharing a similar boiling point (hence the distillation process cannot separate them effectively). Typical octane rating for raw distilled gasoline could go from 40 to 70. Even synthetic gasoline, depending on the manufacturing method, can be quite low on octane. I remember reading a post war report on German C3 synthetic fuel and the base gasoline obtained from their Bergius process had a rating of around 70. Good for a car/truck engine back in the day, but not near good enough for an aircraft engine. Thus the Germans added a lot of aromatics, Xylene and Toluene mostly, which were obtained again from coal/coke. And even then, they still had to add lead tetra ethyl to bring it to around 96. On the bright side, sulfur content was very low, even lower than today strict standards, so it was good for the environment

Jokes aside, it has to be remembered that, for the wartime effort, you want your strategic materials to be readily available, in quantity, and cheap enough (and possibly, the sources must be replaceable, in case some of them are no longer available). The cracking process to manufacture better gasoline with higher octane/aromatics content was quite well known at the time in chemistry circles, unfortunately for Germany: 1) it is more energy intensive 2) it takes more crude oil to obtain the same amount of finished product. Bergius process on the other side is very efficient, over 90% of the Carbon gets turned into useful gasoline, and it works with a variety of readily available coals.