WesWorld

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Originally posted by Red Admiral

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But take a look here: http://members.xoom.alice.it/_XOOM/mc72/mc72.htm and you'll see it's closer to 4m.

That is the same internal view I have, just that mine is larger and a lot more clear in the book I have. The engine finishes just forwards of the aft float pylon. The AS.5 was an extremely compact engine, its only 680mm high with 4.5sq ft frontal area.

No, it doesn't: the engine itself may end at the aft float pylon, but the supercharger and the carburetors clearly extend past the pylon and end just before the cockpit.

Being "extremely compact" doesn't say anything about it's length, and if it's already extremely compact, it's unlikely that it's going to be able to be shrunk any more without expanding in other dimensions.

Also, as shown in the second link I posted, your engine picture is missing the big bank of carburetors that was behind the supercharger. ie, increasing it's length.

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Originally posted by Brockpaine

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Originally posted by Hrolf Hakonson
The contra-rotating props, however, are more of a stretch, as no production designs used them until 1945 or later.

Was that because of the war interfering, though, or were there other reasons?

Mostly that it wasn't a problem that needed to be solved: unless you were trying to squeeze an oversized engine into an existing airframe, it was easier and cheaper to use a large prop and longer landing gear (or inverted gull wings, like on the Corsair).

The Fiat A.60 Ciclone engine arose from the AS.6 racing engine that had powered the Macchi C.72 to victory in the 1932 Schneider Trophy race. SuperAero gave Fiat a contract in 1933 to develop the technology used in the engine and to research applications for it on the new engines that were currently being designed. Fiat went away and started by redesigning the engine itself, in which they were helped by Ing. Gabrelli who wanted a powerplant for the monoplane fighter that was on his drawing board. With the close interface between engine and airframe design teams, a number of changes occurred to make the engine more suitable. The length was the most problematic, being around 3m long. It was hoped to reduce this by placing the supercharger underneath the engine. As a result, the layout was changed to a flat-24 to better accommodate the change. The other large change was in the valves to improve their volumetric efficiency. The simple poppet valves were vibrating far too much at the high engine speeds employed so a desmodromic position-action system was developed instead. The valves were more difficult to construct, needing fine tolerancing, but were considerably superior to the old poppet valves. Sleeve valves were also considered after reading Ricardo's work form the UK but it was decided that there was too much risk and the desmodromic valves were a safer choice for the required improvement. The completed engine first ran in prototype form in late 1934 with mixed results, it was to be earl 1936 before a satisfactory standard of reliability and power had been reached.

Specification;
Type: 24-cylinder supercharged liquid-cooled flat engine
Bore: 138mm (5.4")
Stroke: 140mm (5.5")
Displacement: 50.26L (3067cu in)
Length: 3.0m (118")
Width: 1.17m (45.6")
Height: 0.86m (33.9")
Dry Weight: 1200kg (2640lb)

Valvetrain: Double overhead camshaft with two inlet and two sodium cooled exhaust desmodromic valves per cylinder
Supercharger: Single stage, three speed centrifugal type
Fuel system: Eight row updraft carburettor
Fuel type: 87 octane
Oil system: Dry sump with one pressure and two scavenge pumps.
Cooling system: Liquid-cooled with a mixture of 70% water and 30% ethylene glycol, pressurized

Power Output:
2540hp (1894kW) at 2000m (6560ft) at 3300rpm
2140hp (1596kW) at 5000m (16400ft) at 3300rpm
1940hp (1446kW) at 7600m (25000ft) at 3300rpm
Specific power: 18.84 kW/L (0.41hp/ cu in)
Compression ratio: 7.0 : 1 with 87-octane fuel
Power to weight ratio : 1.58kW / kg (0.96hp/lb)

Couple issues:

First, the power/weight ratio - A ratio of 1.05 hp/lb is out of line for even period + 5 years production engines. Closest thing I can find is the Napier Sabre, which won't really be production-ready until 1943 or so (that's when the bugs really get fixed). The V-3420 has a ratio of 1.0 and it's available in about 1941. Reduce the max power output to get a ratio of 1.0 for the 1936 version and I'll be still.

Second, fuel injection - Which Italian engines used this? Historically it was fairly rare outside of German engines, with some American engines adopting it late in the WWII period.


I assume the reason for going to a flat 12 is so the next generation can go to an H layout, because otherwise it seems to not be helping (compared to a Merlin II, the Fiat engine here is shorter (by about 7") but wider (by about 16 inches))

The AS.6 itself weighs 930kg as the racing engine. To come up with the 1100kg weight of the A.60 I scaled from the R->Griffon which weighed 774 and 900kg respectively. This gave a weight of 1080kg which I rounded up to 1100kg for simplicity.

Power is calculated from similar BMEP values to the Merlin I/II which gives 1030hp at 16000ft. BMEP = power * 960 / displacement * rpm = 12.2bar for the Merlin, 12.3 for this engine.

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No, it doesn't: the engine itself may end at the aft float pylon, but the supercharger and the carburetors clearly extend past the pylon and end just before the cockpit.

Have a look where the exhausts end. That is where the engine block stops, then after that is the gearing, supercharger and carburettors which is about 14% the length of the overall length. The length of the engine blocks and gears is 74%. You can then do some scaling off the external views and the carbs do end just forward of the aft float pylon giving a length of around 3m.

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And yet adding a ventral turret and replacing 2 8mm MG with 12.7mm MG was considered totally unrealistic.

I wouldn't say totally unrealistic, but the extra armament isn't needed at the moment. Until it is shown to be needed theres no point in carrying the extra weight around. Extra power is always needed.

Exellent Power/weight ratio comes from the AS.6 engine itself which managed 1.51hp/lb, quite an achievement. This has been reduced by 33%, which is quite a lot. The improvement compared to other engines is because the power is generated at low level, there is far less power loss from the supercharger so the engine itself can produce more power. At a similar altitude that other single stage engines are supercharged to, it produces 2140hp which gives a power/weight of 0.88hp/lb which is quite normal for the period.

No petrol engines using direct fuel injection, but plenty of diesels. The method was considered for the AS.6 when they were having bad carburation problems but these were solved another way. Direct fuel injection is a more complete solution to the problem.

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I assume the reason for going to a flat 12 is so the next generation can go to an H layout

Not at all, because of the problems gearing all the shafts together. Developing this engine to 1943/44 Merlin levels of power gives over 4000hp. Increasing this to over 8000hp would give massive problems converting it into thrust. The flat layout just gives more space to work with because of the bottom mounted supercharger. I also wanted to mount a gun firing through the propeller axis which would be impossible if the V-24 layout was retained.



A picture of the engine on a test rig. (actually its a Fiat A.38, V-16 inverted Vee with bottom mounted supercharger and contra-rotating props from 1939)

Some bits and pieces of information here.

RA,

Simple question- was the AS.6 ever used in a regular service aircraft ? Was that use in 1941 or earlier?

Hypothetical developements of a racing engine are not the same.

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Simple question- was the AS.6 ever used in a regular service aircraft ?

No

Neither was the Rolls-Royce R, then RR created the Griffon along similar lines.

So the agreement as I understand it is that Piston engine plane development is 3 years ahead "standard" and 5 years ahead "bleeding edge" based on OTL regular service aircraft.

There has been additional considerations for Italy, with some extra flex room with limited-production hand built engines, and with a-historically large (for the time) displacement engines with +5 year HP/Weight ratios from smaller engines.

So, as I understand it, the hypothetical AS.60 is based on an engine that never was in a regular production aircraft. Further, the AS.60 expands that engine, changes it's arrangements, adds technology the original base AS.6 engine never used, for a resulting output about +7 years advanced.

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Originally posted by Red Admiral
Exellent Power/weight ratio comes from the AS.6 engine itself which managed 1.51hp/lb, quite an achievement. This has been reduced by 33%, which is quite a lot. The improvement compared to other engines is because the power is generated at low level, there is far less power loss from the supercharger so the engine itself can produce more power. At a similar altitude that other single stage engines are supercharged to, it produces 2140hp which gives a power/weight of 0.88hp/lb which is quite normal for the period.

1.51 hp/lb is nothing special for a racing engine, though. See the DB-601R, for example, which could produce up to 2300hp on a little over 600 kg, or the Rolls Royce R, at up to 2780 hp out of 774 kg. It's good, but not great.

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No petrol engines using direct fuel injection, but plenty of diesels. The method was considered for the AS.6 when they were having bad carburation problems but these were solved another way. Direct fuel injection is a more complete solution to the problem.

I agree it's a more complete solution, but for Italy it's a completely a-historical one. Given that the AS.6's problems with carburetors were solved, and more difficult problems (like, say, the R-4360) solved, it seems a reach

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I assume the reason for going to a flat 12 is so the next generation can go to an H layout

Not at all, because of the problems gearing all the shafts together. Developing this engine to 1943/44 Merlin levels of power gives over 4000hp. Increasing this to over 8000hp would give massive problems converting it into thrust. The flat layout just gives more space to work with because of the bottom mounted supercharger. I also wanted to mount a gun firing through the propeller axis which would be impossible if the V-24 layout was retained.



A picture of the engine on a test rig. (actually its a Fiat A.38, V-16 inverted Vee with bottom mounted supercharger and contra-rotating props from 1939)

Some bits and pieces of information here.

I wasn't expecting an H-48, I was expecting an H-24, allowing for a much shorter length. An H-48, I agree, would be a recipe for problems.

In that case, no fuel injection as its not needed - I just liked the completeness of the solution, and a bit heavier. 1200kg gives more interchangeability with the Isotta-Fraschini W1518 as well.

Comparing sheer power output is a bad measure between engines as it overlooks the variation in capacity. For each engine you can draw a graph of pressure against volume for the 4-stroke cycle, which gives a continuous loop. The area inside the loop is the mean effective pressure, which does not depend on capacity. The BMEP for this engine is around the same as the Merlin I and DB 601, the power increase comes from this being larger, which is represented in the extra weight and size.

In the summer of 1935, Ing. Giuseppe Gabrielli, head of the 2nd division of the technical office, conceived a new fighter around the Fiat A.60 engine being tested : the G.50

By August the calculations were complete, allowing the project to proceed to aerodynamic testing in the wind tunnel of the Turin Polytechnic and to begin the drawing phase. At this stage, the G.50 wing had a 23 sq. m. area and an unusual structure based on a single tubular spar which Gabrielli had patented several years earlier. Armament comprised three 13.2mm Scotti machine guns in the outer wings and on an engine mount. A top speed of 750km/h was estimated. In October a redesign was initiated after the proposed A.60 had put on weight, the wing area was increased to 30 sq. m. and redesigned as a four piece assembly comprising two half wings with removable tips, offering great construction and transport advantages. In November, Fiat was asked to build three G.50 prototypes, with the additional requirement of an engine mounted 20mm cannon. The first prototype, MM.491 first flew on 4th April 1936 and immediately showed it's good performance and flying characteristics.

Serie II
Year: 1936 Crew: 1 Engine: 1 * 2540hp Fiat A.60 Ciclone RC.20/50/76 3v
Wing Span: 35ft Length: 36ft Wing Area: 312sq ft
Empty Weight: 8287lb Max Weight: 9460lb
Max Speed:
449mph@25000ft
429mph@16000ft
411mph@6000ft

Ceiling: 42,000ft
Climb Rate: 4452fpm Wing Loading: 30lb/sq ft
Armament: 5 x 13.2mm Scotti, four in wings and one engine mounted with 500rpg

Serie I are the pre-production prototypes, Serie II are fighters with 13.2mm machine guns, Serie III are interceptors with 4 x 20mm Oerlikon FFL with 60rpg drums

Now that is WAY to advanced. No fighter capable of 450mph entered service anywhere before 1945. The P-51B (440mph) only entered service in 1943. You're talking about Ta-152/P-51H performance here, not something that was seen in 1936.

The closest historical plane I could find was the Hawker Typhoon. Similar power, size, and an early entry date (1941). Performance: 405mph, 34,000 service ceiling, rate of climb 2,600fpm.

It's irrelevant Fox, unless there is something RA hasn't said, the AS.60 engine is not a valid engine as it is not even based on a historical regular service engine in the proper time frame.

The difference is mostly due to the altitude which significantly reduces the drag. At the same altitude of other period ac, the speed drops considerably. Its simply the result of having a lot of power available and a relatively clean airframe. Going fast brings a whole host of other problems, which'll start to come apparent when the prototypes start crashing into the ground during diving tests - something that'll delay the in service date to around 1939-40.

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even based on a historical regular service engine in the proper time frame.

Sabre I is making more specific power in 1938, and then again in 1940 with the boost to 2240hp. V-3420 has even larger displacement, makes more power, makes more specific power, and is available in 1939. Similar with the Merlin X and XX that make higher specific power around 1939/40

V-3420 had a run of 150 engines and never actually saw regular service.

The 1938 Saber I was the prototype and was also not a production engine.

Why even bring them up? The litmus test is regular service.

The easiest source for me to check is Wiki - The Napier Saber II did see service with the Typhoon, but various problems, including with the engine appear to have delayed service until about 1942. tThe Napier Saber IIC was 2,240hp and about 2360lbs, but an H block. Its interesting that its competition was the RR Vulture- an unsuccessful bolted together engine.

Wiki also indicates the Merlin II was delivered in 1938, and gives the Merlin X, as fielded in the Halifax I at 1,280hp and a dry weight of about 1,375. But this was never bolted together. Instead, they developed a new engine.

There are plenty of powerful historical engines- including assembled engine such as the DB 606 (which entered service in 1942 ? ) available to rebrand.

I'm not sure what the problem is? Its not a real engine, therefore it wouldn't work seems a strange argument considering that hardly any of our SS designs are real designs. The Sabre is relatively easy to fix ahead of historically. The problem there was that Napier lacked the manufacturing capability for precise machining of the sleeve valves and when coupled with very sloppy quality control, the engines tended to overheat and seize very easily. Most of the Vulture problems could be solved by designing the crank/con rod joint as per radial design, by adopting a V-12 type design it was under far too much stress. Then again, when it was cancelled the problems had been fixed.

I did intend something like the DB606/610 but rather simpler. Simply two engines mounted side by side and only joined with a common gearbox/drive to the propellor shaft. It'll be wider, but avoids most of the problems with the DB606/610 series (most notably the burning).

What's the problem? There are NO production aircraft in the next five years with anywhere near that performance. That plane is around 9 years ahead of time, and remember that most of aircraft development in the 40s was due to WWII.

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Originally posted by Red Admiral
I'm not sure what the problem is?

This is, of course, my opinion:

I do not think it is necessarily the performance, rather what generates that performance- the engine.

The problem is the general agreement that regular service engines up to 3 years in advance are the standard, and 5 years in advance are the absolute limit of technology. It is a simple limiter that can be followed by everyone.

When if in June, 1936, the G-1B stops using the "Avia Hercules II", and starts using the "Minerva Atlas" with 1650hp, I can point to the June 1941 introduction of the 1650 hp Bristol Hercules VI in the Beaufighter VIF (I think I've got that right) as the +5 year engine that allows that. Though I am trying to move to a greater mix of +4s and +3s for reliability reasons.

"Sabre is relatively easy to fix ahead of historically"
That may be very true...and I concede you are far better equipped to make that call.

But that quick fix did not actually happen, and there were planes designed for engines that never did pan out. This is the advantage of requiring production aircraft for the benchmark- by and large the engines were working by then.


As a related issue, I do not want to sound like I am demanding everyone only use rebranded copies of historical engines.

One, it most certainly isn't my place to do that.

Second, while I happen to use historic engines, that is not really the agreement as I understand.

Lastly, I do think there should be room to talk and have some variance, 'storyline' in other words.

If an engines history says it was ready for production but the plant was overrun by Germans, or things were too critical to switch, thats a good case to allow use in my opinion. Likewise if you want a slightly larger 40L instead of a 36L at the same P/W, I would guess you could explain that and it would be excepted. I happen to think your big 51L (?) radial last year pushed beyond that, but there really wasn't much discussion as I recall.

I don't have a problem with non-historical engines, heck I even use them. As long as they are similar in performance to historical ones, it should be fine, but once you start introducing engines way better than historical ones, then you have a problem.

Sure the problems for the Sabre and other similar engines could have been fixed earlier, but humans will err and there is that law by the name of "Murphy's Law"... Something WILL go wrong, someone WILL mess up, and beurocrats WILL ax a promising system.

It's as simple as that. Heck if someone had listened to Babbage, there would have been computers during the Civil War.