FIAT A.30 RA - 800 HP engine?

[tomo pauk]

Yes, everybody will say: nope, 600 HP. However, the data plate from 1939 says otherwise:



So I've took the CSI approach, and tried to take a look at Italian manuals to comfirm or refute this. So far I've bagged only the manual for the Fiat CR.32 fighter, where it says that 'international power' was 600 CV @ 2750 rpm, while 2890 rpm was allowed with 'pieno gas', or, roughly, 'full throttle'. Unfortunately, the power on that rpm is not stated.
(for example, the 'international power' of the Merlin III was stated at 900 HP @ 2600 rpm at 12250 ft, vs. 'maximum power' of 1030 HP @3000 rpm at 16250 ft, obviously on 87 oct)



I'd appreciate feedback on this

 

[WJPearce]

Aeronuatica Militare Museo Storico Catalogo Motori by Oscar Marchi states for the A.30 RA BIS:
600 CV at 0 meters and 2,600 rpm
550 CV at 2,750 meters and 2,750 rpm
700 CV at 0 meters and 2,750 rpm for five minutes

However, the attached FIAT promotional photo states 600-880 cav for the A.30 R.

I'm not sure how different the engines were. I think the "R" stood for riduttore de giri (gear reduction) and the "A" for alta quota (high altitude).

 

[Graeme]

From Jane's....

 

[tomo pauk]

Thank you, people

 

[Bretoal2]

I can't imagine how a 24 liters (1470 ci ) engine without supercharger could provide 800 hp !

550 hp at 2750 rpm gives a BMEP about 110 psi (correct for naturally aspirated engine) , but 800 hp at 2890 rpm would be 150 psi or more...

Obviously, last figure is wrong.

 

[tomo pauk]

Thank you. Those funky Soviets stated that A.30 was with supercharger.

 

[Bretoal2]

Obviously, no supercharger ! Otherwise the engine would have been named A 30 RC xx ( R = riduttore /geared , C = compressore / supercharged, and xx = rated altitude, in thousands meters).

 

[Shortround6]

An un-supercharged Kestrel was good for 635hp at sea level at 2900rpm from 1297 cu in (21.25 L) BMEP of 133.7 ?

Moderately supercharged Kestrel was good for 730hp at 5,250 ft at 2900rpm and using 2 5/8lbs of boost. BMEP of 153.5 ?

edit, changed BMEP due to using wrong formula

 

[Bretoal2]

An un-supercharged Kestrel was good for 635hp at sea level at 2900rpm from 1297 cu in (21.25 L) BMEP of 66.85 ?

Moderately supercharged Kestrel was good for 730hp at 5,250 ft at 2900rpm and using 2 5/8lbs of boost. BMEP of 76.8 ?

BMEP = 792.000 x hp / (displacement x rpm).

So 635 hp at 2900 rpm from 1297 cu i gives 133 psi BMEP.

And 730 hp with boost is no use in this post, as Fiat A30 was naturally aspirated.

 

[Hardrada55]

Where does the Fiat A.33 engine fit in? Is it just a supercharged A.30? 700hp@2600rpm@3500m.

 

[tomo pauk]

Seems like compettition for the Kestrel of 1934?

 

[Bretoal2]

From "Aerosphere" (1939), Fiat A-33 RC 35 is said to be "practically identical with the A-30 R design except that the compression ratio was dropped from 8:1 to 6:1, and a supercharger turning 9,48 times crankshaft speed maintained a rated output ot 700 hp at 2600 m up to an altitude of 3500 FEET - Consumption 0.60 lb of fuel per hp-hr, and weight 1.102 lb".

Re-read my post #7 and you will instantly understand that the 3500 feet rated altitude is a print error for 3500 meters.

Regards,

Alain

 

[kool kitty89]

On the note of BMEP, it's significant that the Fiat A.30 used a proprietary ethanol blend for its fuel. (nominally 55% gasoline, 23% ethanol and 22% benzol; the latter should be a mixture of mostly benzene, toluene, and xylenes)

Ethanol/gasoline fuel blends in the range of 20-40% ethanol can have significant effects on BMEP, but more importantly on BTE (brake thermal efficiency) as well, with a corresponding increase in power output. (this without otherwise changing the engine's RPM or compression)
BTE increases of 15% in this blending range are quite plausible and would make the 800 CV or HP figures plausible as well. The A.30A's compression ratio of 8:1 should also be higher than that of a Kestrel (even an un-supercharged one), which should also result in an increase in BTE, so comparing the power output of the unsupercharged Kestrel at 635 HP at 2900 rpm and 1297 CI displacement, with the A.30's displacement of 1470 CI and 2890 RPM, 800 hp would represent an efficiency increase of 11.54%, though if this is 800 CV and not HP, it would thus equate to 789 HP and thus represent an improvement of 10.0%, which seems quite realistic.

Additionally, with this 10% improvement in brake thermal efficiency, and accounting for ethanol's energy content of 68.2% of that of aviation gasoline, the specific fuel consumption on a mass basis (ie lb/hp/hr) would actually improve slightly with around 98.1% the fuel consumption of conventional aviation gasoline.
(this ignoring the potential impact of the benzol content; this would be similar to any aviation fuel with significant aromatic content, like was common in British use though not so much in US usage during WWII; there's also the issue of ethanol or methanol blends more dramatically improving combustion efficiency of aromatics due to the inherently sootier/more incomplete combustion of aromatics, but that could only help here, and likely also had a significant impact on the Methanol/Benzol/acetone blend used with the Rolls Royce R)

 

[Bretoal2]

I think that the manufacturer FIAT knew its engine much better than any Russian author...

So here is the engine plate.

We read that maximum power is 600 hp at 2600 rpm on the ground, and 550 hp at 2750 rpm at 3,000 m. (exactly what Jane's says).

We also see that the normal engine fuel is a blend of gasoline, alcohol and benzol in the proportions given above.

But I don't believe what KoolKitty says about the increase in energy power provided by this blend. Rather, I believe that this special fuel only allowed engine to operate at an abnormally high compression ratio (8:1), whereas many mid-1930s engines were limited to 5.5 or 6:1 with normal fuel (octane between 73 and 87).

And, I repeat, I do not understand how an UNsupercharged engine could perform at 3,000 m. 33% more power than on ground.

In summary, I remain convinced that the 800 hp is an urban legend... or a typo. In both cases, from a suspicious source !

 

[Shortround6]

The problem with alcohol as a fuel is that it needs different amount of air.
Ethanol has about 62% of the BTUs per pound that gasoline does.
Ethanol has a 9.00 Stoichiometric Air Fuel Ratio. So you need about 50% more Ethanol per pound of air.
The Higher compression used may be a result of the higher "octane" rating of the blend. They had already set up the engine to use this blend for performance reasons. Not to stretch gasoline supplies.
Alcohol was rather popular in the 1920s and 30s for racing cars and record setting aircraft and racing planes.

My own beliefs are that the Italians knew what they were doing with Fiat A.30 and the 23% ethanol fuel. They set up the engine to take advantage of the fuel. There was no trick to unlock more power with a slightly different blend.

I will note that there were a number of WW I and later engines that were set up to use only part throttle at take-off/low alludes even without superchargers and only made full power at higher altitudes were the throttles could be fully opened. Many engines were not allowed to use full rpm for take-off.
Just like the data plate. Take-off was done at 2600rpm but power at altitude was at 2750rpm.

Kestrel engines were built with 6.0 compression ratio when supercharged and 7.0 compression ratio supercharged. Unsupercharged Kestrels in 1938 were good for 560hp 2375rpm fpr take-off, 585hp at 2500rpm "international" rating and a mere 635hp at 2900rpm at sea level. 13% increase in power for a 22% increase in RPM? piston ring drag/friction much have been a a bitch.

A lot of inconsistencies on both sides.

 

[Bretoal2]

The problem with alcohol as a fuel is that it needs different amount of air.
Ethanol has about 62% of the BTUs per pound that gasoline does.
Ethanol has a 9.00 Stoichiometric Air Fuel Ratio. So you need about 50% more Ethanol per pound of air.
The Higher compression used may be a result of the higher "octane" rating of the blend. They had already set up the engine to use this blend for performance reasons. Not to stretch gasoline supplies.
Alcohol was rather popular in the 1920s and 30s for racing cars and record setting aircraft and racing planes.

My own beliefs are that the Italians knew what they were doing with Fiat A.30 and the 23% ethanol fuel. They set up the engine to take advantage of the fuel. There was no trick to unlock more power with a slightly different blend.

I will note that there were a number of WW I and later engines that were set up to use only part throttle at take-off/low alludes even without superchargers and only made full power at higher altitudes were the throttles could be fully opened. Many engines were not allowed to use full rpm for take-off.
Just like the data plate. Take-off was done at 2600rpm but power at altitude was at 2750rpm.

Kestrel engines were built with 6.0 compression ratio when supercharged and 7.0 compression ratio supercharged. Unsupercharged Kestrels in 1938 were good for 560hp 2375rpm fpr take-off, 585hp at 2500rpm "international" rating and a mere 635hp at 2900rpm at sea level. 13% increase in power for a 22% increase in RPM? piston ring drag/friction much have been a a bitch.

A lot of inconsistencies on both sides.

About data plate, don't forget this engine had a fixed pitch propeller. So, higher rpm when airplane has gained speed is normal.

And yes, I wonder if this Fiat A.30 RA was able to sustain full throttle operation at sea level - I think the answer is NO, in fact ! This would explain why the loss of power at 3.000 m. in this normally aspirated engine is only 50 hp..

 

[Simon Thomas]

Charts below are from:
C. A. 133
MINISTERO DELL'AERONAUTICA
ISTRUZIONI PER L'USO DEI MOTORI FIAT A 30 RA E A 30 RA bis
5a EDIZIONE
FIAT

Appears that 800 hp was a short term power.
The manual has two permissible fuels - the petrol/alcohol/benzene brew and 94 octane. It notes that the octane rating is from the "30 series single cylinder".
The A 30 RA bis differed from the A 30 RA in that it had the bearings upgraded to lead bronze (from white metal) after motor no A 300154 RA/9510), as well as other minor improvements.
I found it surprising that the A 30 RA was still using castor oil. The manual is the 5th edition published in 1936.

I also found from another source that the propeller was a ground adjustable, rather than a true fixed pitch.

 

[Bretoal2]

And yes, I wonder if this Fiat A.30 RA was able to sustain full throttle operation at sea level - I think the answer is NO, in fact ! This would explain why the loss of power at 3.000 m. in this normally aspirated engine is only 50 hp..

Exactly what I said.

Fixed pitch (or ground ajustable - i.e. non adjustable in flight) is not suited for running at full rpm BOTH on ground and rated altitude.

And probably the high CR of engine (8:1) doesn't allow it, neither.

Next Fiat 30-series engine (A-33 RC35) had a supercharger and a reduced CR.

 

[Shortround6]

And probably the high CR of engine (8:1) doesn't allow it, neither.

Actually high compression ratio was common way of compensating for lack of supercharger.
However it required, for safety sake, special gated throttles to prevent the pilot/s from fulling opening the throttle at low altitude which would wreck the the engine.
Germans were doing this in WW I. One engine/airplane had three slots in the throttle and the throttle handle was moved to the appropriate slot/gate as the aircraft climbed and descended, Plane was a 2 seater (?) and didn't climb/dive like a single seater. It allowed for high compression with the low octane fuel of the time but full throttle was only at high altitudes.

 

[tomo pauk]

Actually high compression ratio was common way of compensating for lack of supercharger.
However it required, for safety sake, special gated throttles to prevent the pilot/s from fulling opening the throttle at low altitude which would wreck the the engine.
Germans were doing this in WW I. One engine/airplane had three slots in the throttle and the throttle handle was moved to the appropriate slot/gate as the aircraft climbed and descended, Plane was a 2 seater (?) and didn't climb/dive like a single seater. It allowed for high compression with the low octane fuel of the time but full throttle was only at high altitudes.

The BMW IIIa was with the 'triple throttle'. Used also on one of the versions of the fighter Fokker D.VII.