Making better Italian aircraft, 1933~1945

[Howard Gibson]

Italy had a bad habit of shooting itself in the foot when it came to military development, from the shortsighted decision to nix inline engine development in 1933 to building tanks designed for the mountains of Sicily then using them in the deserts of Africa and the steppes of Russia.
While the tanks are outside the scope of this discussion, let's try and fix the aircraft development.

Some ideas to kickstart the discussion:

• Regia Aeronautica does not cancel all development of inline engines in 1933.
• Overall aircraft program requirements do not shift as much, resulting in the quicker introduction and production of aircraft.
• Reggiane successfully produces the Re 101~105 series of engines from 1937 to 1943, the Re 103 seeing widespread use on high-altitude interceptors such as the Ro.58 and Re.2005.
• The 16-cylinder Fiat AS.8 makes it into production by late 1941, primarily used by fighter aircraft such as the G.55 and C.205.
• The 18-cylinder Alfa Romeo 135 is designed for 87 octane off-the-bat, entering large scale production by 1938, the boosted 136 entering production in 1942.

Why can't the Italians just develop bigger radial engines? The Fiat G.50 used the Fiat A.74, which was slightly bigger than the Wright R1820 and the Pratt and Whitney R1830. These were not up to powering mid-WWII fighter aircraft.

The Italians also had problems with armament.

My understanding is that the Italians lacked the financial resources and infrastructure to develop a big war machine. When Mussolini announced that Italy would join Germany at war, king Victor Emmanuel III and Italian army staff tried to talk him out of it. The Italians built some nifty battleships. Maybe if they ditch naval warfare capability, they can build more advanced aircraft. Too bad for their forces in Africa.

 

[z42]

Why can't the Italians just develop bigger radial engines? The Fiat G.50 used the Fiat A.74, which was slightly bigger than the Wright R1820 and the Pratt and Whitney R1830. These were not up to powering mid-WWII fighter aircraft.

They had the Fiat A.80 and A.82 18-cylinder radials, neither of which was produced in particularly significant numbers. Those could have been decent, had they got them out the door in numbers a few years earlier?

My understanding is that the Italians lacked the financial resources and infrastructure to develop a big war machine. When Mussolini announced that Italy would join Germany at war, king Victor Emmanuel III and Italian army staff tried to talk him out of it. The Italians built some nifty battleships. Maybe if they ditch naval warfare capability, they can build more advanced aircraft. Too bad for their forces in Africa.

To an extent, but skills/materials/tools/etc. for building warships don't translate quickly or easily to aircraft.

The underlying problem might indeed be, as you say, that the Italian economy just didn't have that much muscle.

 

[tomo pauk]

Why can't the Italians just develop bigger radial engines? The Fiat G.50 used the Fiat A.74, which was slightly bigger than the Wright R1820 and the Pratt and Whitney R1830. These were not up to powering mid-WWII fighter aircraft.

Fiat's radials were god-awful lot. When you need 18 cylinders to make 1000-1200 HP on 87 oct fuel, it does not require a rocket scientist to tell that the engines are a that bad. Plus, 18 cyl engines don't come in cheap - important to note when the aircraft manufacture is lacking behind the needs.
The Piaggio radials were better, they needed 14 cylinders to get to 1000-1100 HP, and the 18 cyl types were good for 1350-1500 HP.
As noted before in the thread, Italian engines (bar prototypes) were not outfitted by 2- or variable-speed superchargers, let alone with 2-stage S/Cs - further limiting their power.

The Italians also had problems with armament.

Having 4 Breda HMGs already by 1940 on fighters would've put them in a much better position.
Buying the licence for the Oerlikon cannons by mid-1930s was probably not that expensive.

 

[Shortround6]

The Fiat G.50 used the Fiat A.74, which was slightly bigger than the Wright R1820 and the Pratt and Whitney R1830. These were not up to powering mid-WWII fighter aircraft.

The Fiat A.74 was around 590kg. The R-1830 went through several generations. The R-1830s that weighed close to 590kg and ran on 87 octane were good for..................surprise !! about 850hp at 5-8000ft and around 950-1000hp take-off. You want the 1000hp (at very low level) you need a the over 1400lbs(620kg) engines that run on 91/92 octane. Later R-1830s got to just about 1050 using 100 octane for takeoff. Later R-1830s gained another 30-40kg to get the two speed supercharger.

They had the Fiat A.80 and A.82 18-cylinder radials, neither of which was produced in particularly significant numbers. Those could have been decent, had they got them out the door in numbers a few years earlier?

These show the confusion and/or problems. It turns out that 18cylinder engines have bunch of vibration problems that 14 cylinder engines do not have. Increasing RPM really increases vibration problems. I am guessing the the A.82 was intended to solve some problem in the A.80. They used the same stroke and made the bore 2mm bigger. They kind of sandwiched the P & W R-2800 in displacement but.........................The A-80 was around 300kg lighter, something has to give and that was RPM. And the difference is not as bad as it appears at first glance.
The A.80 was supposed to make 1000hp at 13,500ft. The Early R-2800 made 1450hp (in high gear) at 13,500ft.
The A.82 was supposed to make 1250hp at 13,800ft. partially by being bit larger and partially by running faster, about 200rpm. It paid for it by being 120kg heavier (Still 160kg+ more than the R-2800A).

Having 4 Breda HMGs already by 1940 on fighters would've put them in a much better position.

Italians have got a real problem, The 12.7 has the weight of the American .50 cal without the firepower, either in the power of the cartridge or in the rate of fire.
The Italian 12.7mm has about 80 of the power of the American .50 cal but at the same weight for the guns. The Ammo is lighter.
The back up isn't good. The 7.7mm Breda-SAFAT was heavier than the Browings and fired slower.

Granted they needed something so using four 12.7s or two 12.7 + four 7.7s has merit. But it isn't going to be quite the firepower of an American plane using the same number of guns.

 

[tomo pauk]

They used the same stroke and made the bore 2mm bigger. They kind of sandwiched the P & W R-2800 in displacement but.........................The A-80 was around 300kg lighter, something has to give and that was RPM. And the difference is not as bad as it appears at first glance.
The A.80 was supposed to make 1000hp at 13,500ft. The Early R-2800 made 1450hp (in high gear) at 13,500ft.
The A.82 was supposed to make 1250hp at 13,800ft. partially by being bit larger and partially by running faster, about 200rpm. It paid for it by being 120kg heavier (Still 160kg+ more than the R-2800A).

See also the low-level power, that was supposed to be very important for the intended users (ie. the bomber aircraft). With 1100 HP, the A.80 is already much worse than the R-2600 of the late 1930s. Also takes more time and effort to make one (18 vs. 14 cyl), the price will also be higher (important if the country is not exactly rich).
Italians say that the A.82 was at ~770 kg, ie. about 20 kg heavier than the A.80.

The Fiat A.74 was around 590kg. The R-1830 went through several generations. The R-1830s that weighed close to 590kg and ran on 87 octane were good for..................surprise !! about 850hp at 5-8000ft and around 950-1000hp take-off. You want the 1000hp (at very low level) you need a the over 1400lbs(620kg) engines that run on 91/92 octane. Later R-1830s got to just about 1050 using 100 octane for takeoff. Later R-1830s gained another 30-40kg to get the two speed supercharger.

Power-to-weight ratio of an engine does not propel the aircraft. It is especially misleading with the radials of the day.
For a military A/C, a 500 lb engine of 500 HP ( 1hp/lb) is a worse choice than the 1250 lb engine doing 1000 HP (0.8 HP/lb). For all the good p/w ratio of the engine, and their small size, both G.50 and MC.200 were easily out-paced by the bigger Re.2000; nobody will say that Re.2000 was a miracle of aerodynamics.

1000 HP was the target for 12000-16000 ft by the late 1930s, not for the low altitudes, and that is for V12s. Competitive radials should be probably do at least 1100 HP at these altitudes (1200 is even better) due to their greater drag and lower exhaust thrust. The very small, light and reliable A.74, that was good for under 800 HP above 12000 ft, was out of it's depth come late 1930s (same as the best Mercury versions, that were actually making a bit better altitude power).

Italians have got a real problem, The 12.7 has the weight of the American .50 cal without the firepower, either in the power of the cartridge or in the rate of fire.
The Italian 12.7mm has about 80 of the power of the American .50 cal but at the same weight for the guns. The Ammo is lighter.
The back up isn't good. The 7.7mm Breda-SAFAT was heavier than the Browings and fired slower.

Italian HMGs fired faster until some time of late 1940? US HMGs were also with a bad bullet design until mid 1943? Reliability issues plagued the US MHG installations until 1942?
tl;dr: it was not all rainbows and unicorns in the .50 BMG land.

However, the job of the Italian HMGs is to kill enemy aircraft, not to win the bar bets against other people's weapons. Having 4 of them on the fighters is a darn sight better than having just two.
As for the Italian 7.7mm LMGs - the earlier these are banished from the 1st line combat aircraft, the better.

 

[Shortround6]

Power-to-weight ratio of an engine does not propel the aircraft. It is especially misleading with the radials of the day.
For a military A/C, a 500 lb engine of 500 HP ( 1hp/lb) is a worse choice than the 1250 lb engine doing 1000 HP (0.8 HP/lb). For all the good p/w ratio of the engine, and their small size, both G.50 and MC.200 were easily out-paced by the bigger Re.2000; nobody will say that Re.2000 was a miracle of aerodynamics.

Power to weight does not propel an aircraft, you are quite right. But if we are comparing aircraft engines then power to weight is a consideration, a better comparison than comparing power per liter. In car racing (or motorcycles or........) displacement is very important, but since none of the ground competition machines fly (fight gravity) weight of the engines is not really considered most of the time. The aircraft designer does not care if the engines he can chose from are 27 liters or 32 liters. What he cares about is if he requires 1000hp, how heavy is the engine and how big it is (width x height mostly) for him to figure out streamlining. Yes radials have problem compared to V-12s for streamlining.
It is up to the engine designer/s to figure out how to get the required power for the least weight, slow running with lots of displacement and light for size or fast running and less displacement for weight (this assumes equal fuel for both and near equal boost).

"nobody will say that Re.2000 was a miracle of aerodynamics."
Uh, Tomo have you looked at G.50 picture lately?

I strongly suspect French spies were putting something in the Italian's wine

1000 HP was the target for 12000-16000 ft by the late 1930s, not for the low altitudes, and that is for V12s. Competitive radials should be probably do at least 1100 HP at these altitudes (1200 is even better) due to their greater drag and lower exhaust thrust. The very small, light and reliable A.74, that was good for under 800 HP above 12000 ft, was out of it's depth come late 1930s (same as the best Mercury versions, that were actually making a bit better altitude power).

You are again, correct. The follow up engines to the A.74 failed. But things were not quite were they should have been for the Japanese either. While the Japanese were testing the two speed Sakae engine in the middle of 1941 The Single speed 950hp version powered bulk of the Japanese Army and Navy fighters through much of 1942. It was about 60kg lighter than the A.74 and about 80mm smaller in diameter.

See also the low-level power, that was supposed to be very important for the intended users (ie. the bomber aircraft). With 1100 HP, the A.80 is already much worse than the R-2600 of the late 1930s. Also takes more time and effort to make one (18 vs. 14 cyl), the price will also be higher (important if the country is not exactly rich).

Yes, low end power is important for bombers and transports. Wright cheated a little bit. Wright single speed R-2600s with 91 octane fuel were rated at 1600hp at 1500ft (457 meters) not even 2000 meters. This was military power. Max continuous was 1350hp at 5800ft (1750 meters), They needed the 2nd speed to get the military power rating of 1400hp at 10,000ft (3050 meters) Max continuous 1275hp at 11,500ft (3500 meters).
Fiat had fooled around with an A.76 engine which was supposed to be good for 1000hp at 4,000 meters but details are sketch in English language sources. Perhaps development was abandoned in order to concentrate on more powerful engines?

As for the Italian 7.7mm LMGs - the earlier these are banished from the 1st line combat aircraft, the better.

You may be right. The difference in weight between the 7.7mm and 12.7mm ammo is a lot less than the difference when comparing to .50 cal ammo.

 

[tomo pauk]

Power to weight does not propel an aircraft, you are quite right. But if we are comparing aircraft engines then power to weight is a consideration, a better comparison than comparing power per liter. In car racing (or motorcycles or........) displacement is very important, but since none of the ground competition machines fly (fight gravity) weight of the engines is not really considered most of the time. The aircraft designer does not care if the engines he can chose from are 27 liters or 32 liters. What he cares about is if he requires 1000hp, how heavy is the engine and how big it is (width x height mostly) for him to figure out streamlining.

The last sentence is what it is/was all about.
We can imagine a designer team of a fighter in the second half of 1930s figuring out that, in order to have the required firepower, speed, RoC, range/fuel etc. they need an engine "A" that makes 1000 HP at 4 or 5 km. The engine "B" that makes 800 HP at these altitudes is out of question, despite the engine "B" being smaller and lighter than the engine "A".

There was not enough of the engine "A" in Italy in the late 1930s.

"nobody will say that Re.2000 was a miracle of aerodynamics."
Uh, Tomo have you looked at G.50 picture lately?
I strongly suspect French spies were putting something in the Italian's wine

You are again, correct. The follow up engines to the A.74 failed. But things were not quite were they should have been for the Japanese either. While the Japanese were testing the two speed Sakae engine in the middle of 1941 The Single speed 950hp version powered bulk of the Japanese Army and Navy fighters through much of 1942. It was about 60kg lighter than the A.74 and about 80mm smaller in diameter.

Japanese at least have had a choice on what to power their fighters. They could've been cranking out fighters with 1250-1300 HP at altitude already by late 1941. Japanese were also increasing the size of the impellers on their engines, plus further improving the impellers, while also making the intakes less squished. Increased the allowed RPM, added 2-speed drives to the new engine versions, too. Already in 1943 the water-alcohol injection was available on some engines.
Japanese were at least installing the more powerful engines o their bombers in relatively big numbers.

There was no luxuries like that in Italy.

 

[z42]

There was not enough of the engine "A" in Italy in the late 1930s.

There was no luxuries like that in Italy.

Perhaps the Italians should have leapfrogged into jet engines..

On a slightly more serious note, were there any Italian jet R&D projects worth noting? Presumably they were aware of the potential, considering proximity to Germany and Switzerland (where a bunch of early pioneering work on industrial gas turbines was done).

 

[ThomasP]

They could have (I think) focused development on creating the first operational motorjet if they had followed up on the Caproni Campini N.1 concept, which first flew as a prototype in 1940.

"Caproni Campini N.1 - Wikipedia"

I do not know how well the idea of relying only on the jet thrust for propulsion would have worked out - the motorjet in the N.1 only produced 1600 lbf - but the basic idea when combined with a propeller was developed by the Soviets into the I-250 and Su-5 prototypes, both of which reached 500 mph.

I-250
"Mikoyan-Gurevich I-250 - Wikipedia"

Su-5 (I-107)
"Sukhoi Su-5 - Wikipedia"

 

[z42]

Ah, the Italian motorjet program, indeed. An interesting idea, but doesn't really get away from the need to develop a competitive piston engine. With my tongue in cheek comment above I meant jet as in turbojet.

 

[ThomasP]

Understood, but I figured the idea was worth mentioning re the thread subject as well.

I am not in any way an expert in jet engines, but based on what I do know about modern jet engine technology, the Italian boffins of the time could have developed a thermojet/motorjet system with about twice the thrust that they got out of the prototype, using about the same size piston engine and the materials available at the time. But they would have to develop a working knowledge of throttled duct mechanics - which there was no particular reason they could not have done as the basic physics concepts were already known - they had simply not been put together in the right way.

Maybe

 

[Shortround6]

The motojet, especially the Caproni, was the worst of both worlds (piston engine and turbine). It may have been clever in conception but the execution shows the problem and there was no way out.
The compressor stage is nowhere near efficient enough, 3 axial stages don't provide the compression ratio needed. Maybe with what we know now things could have been better.
State of compressor design even in mid WW II called for around 8 compressor stages to hit a 3.0 compression ratio.
Basically the Caproni used a 900hp engine to go about as fast in 1940 as a 750hp engine would drive a He 70 Blitz in 1932. (very similar wing area).
The jet engines being used at the end of WW II had compressors that took well over 900hp to drive.
The Caproni was sort of a ducted prop/fan with a 40ft duct it was trying to move air through, which is going to create a lot of drag. And size duct they used made a huge fuselage with a lot of drag on the outside.
In 1938-40 nobody knew any better and the men at Caproni were experimenting.

Soviet unit used smaller ducts

but it was not capable of flying the plane on it's own. It depended on the main engine and it's propeller to provide high speed air (ram air) to the system.
Soviet system used around 7.5 gal of fuel per minute which was a problem. That is just for the burner system in the motojet, You still needed to feed the main piston engine.

 

[ThomasP]

The 223 mph was achieved using 50% power. I do not know if they ever flight tested the N.1 at higher power settings, though the max speed would theoretically only have been around 315 mph(?), with a lot depending on the efficiency of the exhaust tube, the drag characteristics of the airframe, and the altitude at which the speeds were being recorded (I get the impression they did not test at higher altitudes than about 10,000 ft).

 

[ThomasP]

Hmm, I just ran across some interesting info. The Italian Air Ministry signed a contract with Campini in May 1934, and what became the N.1 was originally supposed to have made its first flight by 31 September 1936. Campini was teamed with Caproni for the manufacturing of the prototypes, but Caproni was too busy with already existing contracts to focus on the N.1 design. How much of the 3 year 11 month delay was due to Caproni I do not know. The highest altitude at which the N.1 was tested was 13,300 ft, which is the altitude at which the 223 mph at 50% power was recorded.

The Isotta Fraschini L.121 R.C.40 was a variant of the Asso XI R.C.40, rated at 900 (800?) BHP at 13,123 ft (4000 meters).

 

[tomo pauk]

The Isotta Fraschini L.121 R.C.40 was a variant of the Asso XI R.C.40, rated at 900 (800?) BHP at 13,123 ft (4000 meters).

The L.121 was indeed supposed to do 900 HP at 4000m.
One of the changes vs. the Asso was that 2350 rpm was the new limit for altitudes, vs. the 2250 for the Asso.



Hmm - stick the L.121 on the MC.200, make the darned canopy to be closed, and there is a 350 mph fighter? Italians being Italians, managed to install the decent V12 on the obsolete biplane, thus making the double self-deletion.

 

[Shortround6]

Well, The P-40 got around a 22% reduction in drag compared to the P-36.
Italians could have had sort of a home grown D.520.
L.121 being roughly equal to the HS 12Y in the D.520
Maybe the Italians can use water injection to make up for the 87 octane fuel?

 

[mack8]

The L.121 was indeed supposed to do 900 HP at 4000m.
One of the changes vs. the Asso was that 2350 rpm was the new limit for altitudes, vs. the 2250 for the Asso.

View attachment 807889

Hmm - stick the L.121 on the MC.200, make the darned canopy to be closed, and there is a 350 mph fighter? Italians being Italians, managed to install the decent V12 on the obsolete biplane, thus making the double self-deletion.

The good looking Macchi MC.204 was just that, they could have had it from the beginning.

On another note, what does that 1475 HP figure means in the graph above? I know it says theoretical ground level power or similar, but that's a lot of horses. Maybe a typo (intentional or not) and they meant 1075 or maybe 1175 HP?

 

[Shortround6]

On another note, what does that 1475 HP figure means in the graph above? I know it says theoretical ground level power or similar, but that's a lot of horses. Maybe a typo (intentional or not) and they meant 1075 or maybe 1175 HP?

You can find such figures for other engines in books written around 1940 (give or take). It is a reflection on the amount of air the supercharger could flow.
SO it is a hypothetical number than assumes A, the engine won't break and B, the fuel will allow enough boost to let the throttle be fully opened at sea level.
You can find figures of 870hp for a Kestrel XVI, 1365hp for a Peregrine, and 1500hp for Merlin II or Merlin X.

 

[TM06]

I do wonder if the Asso XI or L.121 might've been the best choice for an indigenous inline engine - the basic RC.40 was already quite solid for its weight class, not to mention that the Asso XI was around as early as 1934 (if my information is correct).
Maybe an upscaled version with 4 valves per cylinder, a 2-stage 2-speed supercharger and fuel injection? I'm not exactly privy on how to make a good aircraft engine but those seem like good places to start.

 

[bf109xxl]

I-250
"Mikoyan-Gurevich I-250 - Wikipedia"

Su-5 (I-107)
"Sukhoi Su-5 - Wikipedia"

Both planes were just useless ugly bastards and never fully functional fighters. They were of no use whatsoever, only dangerous to pilots.