German engines used 87 octane fuels too.
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
It is very hard to compare superchargers in this way. Superchargers can be measured in airflow (pounds of air per minute), Pressure ratio ( how much they compress the incoming air) and efficiency (what percentage of the power used to drive the supercharger is actually compressing the air).
When looking at engine charts you are looking at a complete engine system that has to take into account the strength of the engine (blowing cylinders off is not a good thing), the fuel used (only so much boost can be used with certain fuels) AND the desired characteristics of the engine in question.
as an example the British Mercury radial could make 830hp for take off and 890hp at 1800 meters using a 7.0:1 gear drive on the supercharger (using about 914mm) , great for a flying boat or seaplane. Change the gear ratio to 9.4:1 and high level power went to 840hp at 4250 meters but take-off fell to 725hp. (using just over 1000mm) Same supercharger intake, impeller and housing/diffuser. Much better for a fighter or light bomber.
At 4250meters the Mercury supercharger was compressing the air 2.27 times and lets face it, the Mercury supercharger wasn't exactly the latest and greatest.
Just about anybody could design a supercharger with a pressure ratio of over 2 to 1 in the 30s and by the late 30s 2.3-2.8 was fairly common. The two big problems where getting the engine to stand up to it and getting fuel that allowed you to use a boost pressure of over 4-6lbs, 38-42 absolute or the metric equivalent.
Italian radial engines were rather light for their size ( in some cases very light) which leads to suspicions of a lack of structural strength to tolerate higher RPM or over boosting.
Lack of planning in 1939-34 (or later) is a bit understandable, the fuel situation changed dramatically. France was another country that got caught with engines that were fine with 80 octane fuel, OK with 87 octane but near hopeless with 100 octane or higher. The basic engines were not strong enough to stand up to higher boost pressures with out either major redesign or starting over.
Both the Piaggio P.XI and the Fiat A.80 were homologated in 1937. So there was not an Italian radial in the class of 1000 hp first. In late 1939 were homologated both the 1500 hp Piaggio P.XII and the 1600 hp Alfa Romeo 135 (which was never ready for operational use, but complied the approval tests), so...1) Example please.
146.2) Number of the page please.
@Shortround6: could you give me any example about rather light or very light italian engines? And other engines (US, UK, Germany...) for comparison. So i can understand.
Dogwalker said:Both the Piaggio P.XI and the Fiat A.80 were homologated in 1937. So there was not an Italian radial in the class of 1000 hp first. In late 1939 were homologated both the 1500 hp Piaggio P.XII and the 1600 hp Alfa Romeo 135 (which was never ready for operational use, but complied the approval tests), so...
146.
The Fiat A 74 was a 31.2 liter engine that went about 1257lbs.
The Piaggio P.XI was a 38.6 liter engine that went about 1433lbs.
Italians had the:
Alfa 135 = 48.2 liters at about 2094lbs
Fiat A 80 = 45.7 liters at about 1625lbs
Fiat A82 = 47.1 liters at about 1910lbs
Piaggio P.XII =53 liters at about 1874lbs
On a weight to displacement ratio the Italian engines were on the light side. Figures are pretty much From Wilkinson's "Aircraft engines of the World" and may not agree with Italian sources.
Fiat A80 engine was about the same displacement as the P&W R-2800 and yet weighed about 70% as much. Something had to give?
In the span 1937-1940, on the DB600-601 and on the Merlin, we see mostly the tevelopement from prototypes to mass production (and, on the Merlin, those to adapt it to the 100 octane gasoline). The R-1830 had surely an evolution, but that's part of an evolution started in 1932. That's similar to the evolution of the Alfa Romeo 125-128 series (basically the same engine) from 650 to more than 950 hp. Moreover, the evolution of the Alfa was done mantaining the same gasoline, while the later modification on the R-1830, as your chart show, were meant to use a different fuel (it's true hat the power output of the r-1830 grew up even with 87 octane gasoline, but much less). In Italy, there would be useless to design an engine to run on 100 octane fuel (let alone 130). In wartime, a mass produced 100 octane italian engine simply would not have flown due to the lack of fuel. An evolution similar to that of R-1830 there would have been if it had been completed the A.76. but it was dropped in 1940 not so much because it was impossible to get, but because, with just over 1000 hp (similar to R-1830-SC3-G, which worked with 87 octane gasoline), in 1940, With the licence production of the DB601 already obtained, the next generation of fighter already ordered with it (and the Alfa Romeo 135 already homologated for 1600 hp max, if someone would want to present a radial engined fighter anyway), the engine would have been born already obsolete. It was the very same concept of "lightweight engine for fighters" to be obsolete and to have been replaced by that of "powerful engine for fighters".I thought you did not understand what I meant. I'm sorry that I have not explained well. I thought I had explained it well. Subsequent interventions Shortround6 (04-28-2013 04:28 AM) and wuzak (04-28-2013 06:13 AM) made me think that.
When i speak about "lack of improvements", i want to tell about improvement of a single engine type (for example: Merlin improvements, R-1830 impreovements, etc... during the years). But i don't want to tell about improvement in the whole industrial production. For me another engine is another engine. Piaggio P.XIX was a P.XI improvement, as the P.XI was a G-R 14Krs improvement. Certainly P.XII was a P.XI derivative. But this is another thing, for me. I'm italian and i have to translate my thoughts.
I hope I have explained it well now.
A questo punto mi chiedo io se sappia leggere tu l'italiano. Quella nota dice chiaramente che la leva che comanda la sovrapressione è inutile sopra i 2000 metri, ed è perciò impossibile ottenere una sovrapressione, perché il controllo automatico (che deve garantire gli 821 mm hg), da quella quota in poi ha già aperto la valvola a farfalla più di quanto la leva possa fare.The controversial part says:
"NOTA - La sovrapressione d'alimentazione è sempre ottenibile durante i decolli effettuati a quota zero oppure ad altitudini che non meritano grande considerazione agli effetti della diversa pressione atmosferica esistente fra tali quote e la stessa quota zero.
Durante i decolli effettuati a quote superiori alla predetta, il valore di sovrapressione scenderà, sino a raggiungere, durante decolli effettuati da un altipiano (p es. 2000 m.}, la pressione normale d'alimentazione assicurata automaticamente dal compressore.
Decollando da quest'ultima quota presa in considerazione, la sovrapressione non sarà possibile ottenerla, poichè la farfalla del compressore — a motore funzionante a pieni gas — si aprirà automaticamente per un certo angolo che sarà sempre maggiore da quello ottenibile manovrando la leva di sovrapressione a quota zero o di non molto superiore. In quest'ultimo caso perciò il comando del congegno di sovrapressione, atto ad ottenere la maggior apertura della farfalla durante il decollo, si renderà inutile poichè la leva 187 si sposterebbe a « folle » senza imprimere l'ulteriore apertura a mano della farfalla."
TRANSLATION:
"NOTE - The supply pressure is always obtainable during takeoffs made at zero or at altitudes that do not deserve great consideration to the effects of different atmospheric pressure existing between these altitudes and the same zero level.
During takeoffs made at higher altitudes to the aforesaid, the value of pressure drop, to reach, during take-offs made by a plateau (for example, 2000 m), the normal pressure power ensured automatically by the compressor.
Taking off from the latter altitude taken into account, the overboosting will not be possible to obtain it, because the throttle of the supercharger - with the engine running at full gas - will open automatically to a certain angle that will always be greater than that obtainable by manipulating the overboosting lever at zero altitude or not much higher. In the latter case, therefore, the control of the overboosting device, able to get wider throttle opening during takeoff, it will be useless because the lever 187 would move to "neutral" without giving further handmade throttle opening."
I told (05-10-2013 04:04 PM): "I see only a problem about takeoff in plateaus up to 2000 m. But takeoff, not overboost at altitude. The power chart tell me other."
And infact the manual at page 146 tell only about takeoff. At this point I think that you are not Italian.
In the span 1937-1940, on the DB600-601 and on the Merlin, we see mostly the tevelopement from prototypes to mass production (and, on the Merlin, those to adapt it to the 100 octane gasoline). The R-1830 had surely an evolution, but that's part of an evolution started in 1932. That's similar to the evolution of the Alfa Romeo 125-128 series (basically the same engine) from 650 to more than 950 hp. Moreover, the evolution of the Alfa was done mantaining the same gasoline, while the later modification on the R-1830, as your chart show, were meant to use a different fuel (it's true hat the power output of the r-1830 grew up even with 87 octane gasoline, but much less). In Italy, there would be useless to design an engine to run on 100 octane fuel (let alone 130). In wartime, a mass produced 100 octane italian engine simply would not have flown due to the lack of fuel. An evolution similar to that of R-1830 there would have been if it had been completed the A.76. but it was dropped in 1940 not so much because it was impossible to get, but because, with just over 1000 hp (similar to R-1830-SC3-G, which worked with 87 octane gasoline), in 1940, With the licence production of the DB601 already obtained, the next generation of fighter already ordered with it (and the Alfa Romeo 135 already homologated for 1600 hp max, if someone would want to present a radial engined fighter anyway), the engine would have been born already obsolete. It was the very same concept of "lightweight engine for fighters" to be obsolete and to have been replaced by that of "powerful engine for fighters".
A questo punto mi chiedo io se sappia leggere tu l'italiano. Quella nota dice chiaramente che la leva che comanda la sovrapressione è inutile sopra i 2000 metri, ed è perciò impossibile ottenere una sovrapressione, perché il controllo automatico (che deve garantire gli 821 mm hg), da quella quota in poi ha già aperto la valvola a farfalla più di quanto la leva possa fare.
at this point I wonder if you can read Italian. That note says clearly that the lever controlling the overpressure is useless over 2000m, and is therefore impossible to obtain an overboost, since the automatic control of pressure (which maintains the 822 mm hg), from that altitude onwards, has already opened the intake valve of the supercharger more than the lever can do.
So I asked to you if there are listed, on the manual, other systems to obtain an overboost, since the only one mentioned is useless above 2000m.
Note that do not seems to me that, on the manual, the overboost being allowed in any other flying condition than the takeoff.
Now i post a comparison chart between Fiat A.74 and different R-1830 ( -9, -11, -13, -35 ) versions between 1936 and 1940.
We see the R-1830 improvement. And its boost improvement.
There are some problems with different data versions. But I hope it is understood the meaning of my speech.
E io ti ho chiesto se, oltre all'attivazione di quella leva, inutile oltre i 2000m, il manuale prevedesse altri modi di ottenere una sovrapressione. A me non pare. Quindi devo arguirne che la sovrapressione non è ottenibile sopra i 2000m, almeno finchè i comandi del compressore non vengano modificati. Il fatto che lo stesso manuale non preveda l'uso di una sovrapressione in altre condizioni che non siano il decollo, spiegherebbe poi il perchè di questo arrangiamento (in teoria, il compressore è in grado di offrire una sovrapressione, anche se sempre meno spinta, fino alla quota di ristabilimento meno un metro), dato che è ben difficile ipotizzare, in Italia, o in Europa, da parte di un aereo equipaggiato con un Asso XI, un decollo da oltre 1000m di altezza (non parliamo nemmeno di 2000m).Per la seconda parte si parla di decollo. Specificamente decollo.
Thank you for the work.
The R-1830 does show improvement due to higher rpm and better fuel (higher boost pressure). It also shows the weight gain.
We do have "Chicken or the egg" question here. I hope that translates.
If the Italians cannot get better than 87 octane fuel there is no sense building heavy crankshafts and heavy crankcases ( and heavy cylinder bolts) to hold high cylinder pressures. Without the heavy construction you can't raise the power even if you get the fuel.
Going the high RPM route (road) has a problem too. The stress on the crankshaft, crankcase and reciprocating parts goes up with the square of the speed. 10% increase in rpm is 21 % more stress. You also have 21% more friction so crankshaft HP is a smaller fraction of the fuel burned in the cylinders. You do make more power but the engine is less efficient for fuel economy. You also make more heat so you need better finning (more fins, closer spaced and longer). Better finning can limited by foundry techniques. Both American and British companies going from cast heads to forged when the currant casting techniques could not give the desired fins (at an acceptable scrap rate). Sometimes they could switch back when better casting techniques were developed, sometimes they could not.
It does no good to design a very advanced engine if you cannot make it in quantity.
Italian engine designers were not backward, they had to design for the fuel available or likely to be available and had to design engines that could be made, in quantity, using the technology available in Italy. At times the British and Americans could not make each others engines (air cooled) because of difference in HOW they were made.
Sorry, but there is not possible parallel. The possibility to reach 2400 rpm, and even 2590rpm, is clearly stated in the manual. We know how to rev up the engine, and there is not a single statement, in the manual, about the fact thath the throttle doesn't work once reached, say, 2200 rpm. So we have to assume that it works at least until 2590rpm.You're right there is nothing in the text. Only the graphs of powers. In fact not only those though.
The manual also tells us on p. 25 that the speed of rotation of the motor is the maximum of 2400 rpm, and that great (for not more than 30 ") is 2590. The takeoff (obtainable power for no more than 3 ') is obtained at only 2140 rpm. Other powers (normal to the ground and at altitude) at 2250 rpm. Then throughout the manual does not talk about it anymore. What are the conditions in which you can use 2400 rpm or 2590 rpm? Does it mean that they were not obtainable certain rpm?
However early versions of the Merlin already had a high pressure and rpm, but using 87 octane fuel.
And the various italian engine projects and prototypes, some powerful, after 1940 didn't have the same high rpm and the same high boost of the first Merlin. So there was much leeway. Even without the 100 octane fuel.