FIAT A.S.8 ENGINE.

[jerryw]

The Fiat A.S.8 engine was designed and developed in Italy during the early years of WW2 but was not intended for combat use. Its function was to capture the outright air-speed record installed in a specially built aircraft known as the CS15.
The A.S.8 was a V-16 design with individual cylinders and 45 deg. between the banks. Bore and stroke were 140 X 140mm giving a swept volume of 34.5 litres.
As with the 24 cylinder A.S.6 seaplane engine, the A.S.8 was designed to turn counter-rotating propellers.
Info on the internal arrangements of this engine is hard to find. Did this engine have two, side-by-side crankshafts each driving a propeller or was it a conventional V-16; if so, then the reduction gears at the front must have been of unusual design?
Any information welcomed.

 

[red admiral]

CMASA CS.15

 

[jerryw]

Thank you Red Admiral but can you provide any proof of what you say? One of the patents filed by FIAT SPA clearly shows a 16-cylinder engine with two side-by side crankshafts.
Also, if it did have just one crank, how did they provide the drive for the two propellers?

 

[kool kitty89]

For the props it should be similar to what those used with the Griffon, R-2800, and R-4360 etc. were equipped with on various projects durring WWII and post-war. (XB-35, YP-60, Seafang, etc) I believe were geared to be operated by a single shaft.

 

[red admiral]

I'm pretty sure from the arrangement of the A.38 engine which was based on the AS.8. This was definitely an inline V-16 and also had contra-rotating propellers. The drawing of the installation of the AS.8 above also looks like an inline V16. The contra-rotating propeller has a single input which drives the rear propeller. Then there is a gearing system (could just be a simple bevel gear) that moves the drive to the opposite direction of rotation driving the forward propeller.

Do you have a link to that patent? I had a quick search but couldn't find anything like it.

 

[jerryw]

The only reference I have to the Fiat A.S.8 that gives some description of the internals is by Coggi (Italian text). I've had this translated - the account is a bit vague and is not accompanied by any drawings.
The patent is GB 360,167 which can be downloaded free from the Espacenet site.
Drawing attached shows basic layout of the A.S.6 (two 12-cylinder engines in tandem) and the A.S.8(?) (two straight-8 engines, side-by-side)

 

[red admiral]

Thanks for that. Its quite an interesting arrangement. Have you any idea why the compressor casing is shaped so strangely?

 

[jerryw]

Never mind the compresser shape, Rear Admiral - we are still waiting for you to substantiate your claim that this engine had only one crankshaft!

If you can't prove it, remove it!!

 

[red admiral]

I don't have a great deal of information on the AS.8 to give a definite answer one way or the other. If the angle between the banks is 45° as in post #1 then I'd guess that its a conventional V16 as this is a nice balance angle for the arrangement and the angle between the banks in the patent drawing is not 45°

 

[kool kitty89]

Looks to be about 30° in the patent.

 

[The Red Baron]

The Fiat A.S.8 engine was designed and developed in Italy during the early years of WW2 but was not intended for combat use. Its function was to capture the outright air-speed record installed in a specially built aircraft known as the CS15.
The A.S.8 was a V-16 design with individual cylinders and 45 deg. between the banks. Bore and stroke were 140 X 140mm giving a swept volume of 34.5 litres.
As with the 24 cylinder A.S.6 seaplane engine, the A.S.8 was designed to turn counter-rotating propellers.
Info on the internal arrangements of this engine is hard to find. Did this engine have two, side-by-side crankshafts each driving a propeller or was it a conventional V-16; if so, then the reduction gears at the front must have been of unusual design?
Any information welcomed.

Salve, sono Italiano non parlo Inglese,
per caso mi sono imbattuto sul Vostro Forum e vedo che cercate info sul Fiat AS8

vi allego la scheda tecnica tratto dal libro "Aereonautica Italiana museo storico catalogo motori"

Buona lettura

Saluti

 

[Marcogrifo]

Salve, sono Italiano non parlo Inglese,
per caso mi sono imbattuto sul Vostro Forum e vedo che cercate info sul Fiat AS8

vi allego la scheda tecnica tratto dal libro "Aereonautica Italiana museo storico catalogo motori"

Buona lettura

Saluti

Ciao Red Baron,
benvenuto
Grazie per quello che hai postato, è molto interessante e praticamente sconosciuto per me
Cercherò di tradurre l'articolo in inglese meglio che posso, per poi inserirlo nella discussione.

Ciao

For other people: Red Baron doesn't speak english well, so I'm going to translate for him the pages he posted and put them here as soon as possible (and the best I can ).

Cheers

 

[jerryw]

Ciao Marcogrifo,

Thank you for your offer to translate the Italian language posts.

These pages posted by "Red Baron" are very helpful. The little drawing of the crankshaft seems to indicate that there is only one in the engine rather than two as indicated in the patent filed by FIAT.

What we need now is a drawing to show the gears involved in transmitting the power to the two contra-rotating propellers. From the outside of the engine, it looks as if it is a very symmetrical arrangement.

 

[The Red Baron]

Salve Marcogrifo,

speravo di trovare qualcuno che parlava italiano, così da poter tradurre il tutto!

anche io sono superappassionato di aerei , motori e tutto ciò che è scienza e tecnica

peccato che con l'inglese ho sempre avuto seri problemi, in realtà ne ho anche con l'italiano!

La scheda tecnica del Fiat AS8, l'ho presa dal manuale dei motori dell'aereonautica militare, al museo di "Vigna di Valle" vicino Bracciano RM

nel manuale ci sono descritti un centinaio di motori, anche a reazione tipo il J79 del' F104

al museo sono esposti anche vari motori tra cui il Fiat AS6 dell'idrovolante da corsa Macchi Castoldi MC72,
un vero spettacolo!!!

Ciao,

 

[The Red Baron]

Salve Jerryw,

se non ho capito male state cercando i meccanismi interni di trasmissione degli alberi controrotanti.

vi posto quelli del AS6 che equipaggiava il macchi MC72, sono uguali a quelli del AS8

spero di esservi stato utile
ciao,

 

[Vincenzo]

Ti do il benvenuto The Red Baron lascio il lavoro di traduzione a Marcogrifo che pure io con l'inglese so negato (ma pure con l'italiano in effetti), spero vivamente che posterai i dati dei motori in uso nella regia aeronautica in questa sezione.

ciao e buon forum

(in ~english)
The Red Baron welcome, i left translater work to Marcogrifo, my english is bad (for true too my italian) i hope that you'll post the other info on engine of Regia Aeronautica (italian RAF)

 

[Marcogrifo]

OK, translation is ready

But before few words from the author:

First of all, I'd say I apologize in advance for every term or sentence may have a weird sound: I tried to do my best here but technical English is sometimes a nightmare for me (and nontechnical too ).
The translation is intentionally almost literal.

So, here we go:

Page 115

AS8 engine technical specifications
---------------------------------

Type: special engine for record plane, 16V at 45 degrees with supercharger and reduction gear for coaxial counter-rotating propellers

Cooling: liquid

Bore: 140 mm

Stroke: 140 mm

Displacement: 34.482 dm3

Mixture distribution system: four over-head valves each cylinder two overhead camshafts for each row

Compression ratio: 6.5

Fuel supply: depression carburetors

Compressor: centrifugal one stage

Reduction gear: with double output for coaxial counter-rotating propellers rate 1:1.666

Ignition: double with four magnetos

Max power: 2250 CV* approx. at sea level, 3200 RPM

Dry weight: 790 kg

Specific weight: 0.35 kg/CV

Power/displacement rate: 65.25 CV/liter

Year of manufacture: 1939-40

Quantity: unknown (few items)

Aircraft of destination: Fiat-CMASA CS15


* note CV = Cavallo Vapore (Horsepower); 1 CV = 0.99 Hp approx.

---------------------------------------------------------------------------------

During spring of 1939 germans - in few days and by means of two different aircraft -
broke the all-time speed record held by italian MC72 racer powered by Fiat AS6 engine.
So Fiat, in agreement with italian government, decided to build a new machine in order
to reconquer the losted world record: eng. Manlio Stiavelli was charged with aircraft
development and prof. Antonio Fessia with new engine.

The new engine was a V16, an unusual layout (even if engine of that kind were built
since 1918 but with considerably less power) for the intended high power output: this
choice was due mainly to the special duty required for the engine but also for making full
use of the great know-how Fiat had gained in those years.

The engine was built with the minimal cross-section, even less than that of AS6.
The V16 configuration had already been took in account in 1929 by eng. Zerbi during his
preliminary study on a 2300 CV engine, as requested by ministry, but was rejected at
that time because of the predicted unreliability of the needed eight-crank shaft for the
given cylinders displacement (45-50 liters); and more, the excessive size of cylinders would
have leaded to greater cross-section of the engine and unsatisfacfory speed range.
In 1939 most things were changed but the eight-crank shaft still was a trouble in a
powerful engine (more than 2000 CV for the new engine against 1400-1500 CV for the
AS6)(see figure at page 116 bottom: layout scheme for AS8 engine's crankshaft).

Page 116

The AS8 engine was greatly derived from AS6, so it had almost the same cylinders size
(bore for AS8's cylinders was only 2 millimeters more than AS6's), and consequently
pistons, rods, valves etc, and the fuel system was very similar to the latter; on
the other hand the pressure supplied from supercharger system was slightly less than in
AS6.
In order to minimize torsional vibrations in the long crankshaft all actuators of auxiliary
devices (fuel system, magnetos, pumps, etc.) were placed near the power train output.
The torque reaction was minimized adopting counter-rotating propellers, but, in a
different way from AS6, there was only one crankshaft and it drove the two propellers by
means of a special reduction gear.
At the beginning of 1940 the engine was already on the test-bench, showing great
power of endurance and reliability, which was unusual thing for such powerful device at
that time. The engine ran safe and easy for tens of hours at high speed without failures
and, though it was rated for a max power of about 2000 CV, it supplied up to 2500 CV
for periods. At 3200 RPM, 2250 CV the mean effective pressure was 18.35 kg/cm2
against a value of 16.8 for the AS6 at 3100 CV.
In conclusion AS8 was an outstanding engine, the best ever built in Italy in all times, the
only one that could beat the AS6.
Unfortunately, at the outbreak of the war development of the new record plane was
stopped and so the fine tuning of AS8 was never completed and it hadn't the chance to
show its great value in flight.

Cheers

 

[jerryw]

Marcogrifo,

Well done. Your translation of the text from the "Aereonautica etc" book is very good.

We still need two things: 1/ now that we know the A.S.8 had only ONE crankshaft, what sort of con-rods were used, fork-and-blade or articulated?
2/ What was the gear arrangement used to split the power to the two propellers?

For this we will need a sectional drawing of the motor. In the past I have tried to contact FIAT in Torino and the museum at Vigna di Valle, near Rome where the A.S.8 engine is kept. No luck at all!

 

[Marcogrifo]

Thanks Jerry for your kind words

Yes, I'd like to know more about this engine too.
According to the text on that book seems it had the potential to evolving in a serious competitor of Daimler-Benz's and Rolls-Royce's but its fate was sealed by its ill-fated born...

Cheers

 

[The Red Baron]

saluti