FIAT A74 RC38 performance

Discussion in 'Engines' started by greybeard, Mar 8, 2012.

  1. greybeard

    greybeard Member

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    Please I would ask for help finding data about other power outputs than emergency/take-off ones about italian engine FIAT A74 RC38. I mean "max continuous" and "cruise" with related RPM and MAP, if available.

    Thanks in advance,
    GB
     
  2. Vincenzo

    Vincenzo Active Member

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    just thinking, i.e. not looking somewhere, i do not remember have never read time limit for the official power of 840 cv, maybe this are max continuous?
     
  3. greybeard

    greybeard Member

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    I don't think so. Seemingly, max continuous power was 740 CV and 840 was the famous "+100", probably meaning horsepower increase, just for take-off/emergency. Unfortunately, all sources repeate from decades same incomplete data.
     
  4. Vincenzo

    Vincenzo Active Member

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    secondo il manuale del G-50 Bis a pagina 100, "la potenza normale sviluppata dal motore.... alla quota di mt 3800 con la pressione di alimentazione di 790 m/m Hg ed a 2400 giri al minuto è di 840 cv" " a quota 0 la potenza è di 740 cv" (pagina 101 stesso regime del motore). il +100 è permesso solo nei decolli, nei casi in cui è strettamente necessario (nel manuale del C.200 VII serie è specificato comunque non più di 3 minuti). Da tenere presente che i giri massimi per il motore sono 2500+20 e questi sono i giri indicati per i voli a velocità massima, ma specificati di durata limitata/brevi periodi (secondo il manuale), quindi il motore può dare di più dei 840 cv della potenza di omologazione, se è proporzionale ai giri, 882 cv.
     
  5. greybeard

    greybeard Member

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    Grazie per le preziose informazioni.

    Piero Vergnano, nel suo "I caccia FIAT 1930-1945", da come potenza massima 870 CV a 2520 giri/min per un massimo di 3 minuti.

    Devo interpretare i 740 CV a 2400 giri/min e 790 mm Hg come massima potenza continua a quota zero?

    Conosci anche un regime inferiore, tipo di crociera economica e la relativa potenza e pressione di alimentazione?

    Grazie ancora e buonanotte.
     
  6. Vincenzo

    Vincenzo Active Member

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    per quanto riguarda i regimi di crociera il manuale del 50 Bis indica di mettere il motore sui 2200 giri e la pressione a 650 mm (il tutto è consigliato per una quota di 6 km) con la possibilità di variare la pressione secondo le circostanze e le necessità fra i 500 e i 790 mm. il manuale del 200 VII serie consiglia una crociera economica a 2100 giri e 590 mm (quota 5 km), per la crociera veloce 2400 giri e 700 mm (stesse indicazioni sono presenti anche sul manuale delle serie I/V). Sfortunatamente non sono indicate le potenze espresse a tali regimi.
    per i 740 ritengo di si, come avevo detto io non ho mai trovato limiti di tempo riguardo la potenza di omologazione del A74
     
  7. greybeard

    greybeard Member

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    Grazie ancora, Vincenzo.

    Saluti.
     
  8. Vincenzo

    Vincenzo Active Member

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    pardon, backing to english, in the Vergnano book there is the altitude for the 870 cv power?
     
  9. Denniss

    Denniss Active Member

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    I have an excerpt of an unknown book stating some data about italian aircraft engines. Powers for the A.74 RC38 are given as:
    2400 rpm, 740 hp at sea level and 840 hp at 3800m (normal output)
    2520 rpm, 870 hp at sea level (take-off rating)

    Book states performance figures are tested in altitude chamber, I don't know if the given values are really hp or metric PS (I assume Italy did not use imperial hp).
     
  10. greybeard

    greybeard Member

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    Vergnano's book doesn't give altitude for 870 CV power, but I think it's meant at sea level, as mentioned by Denniss.

    Power outputs are all in metric unit of measure, CV=Cavalli Vapore, each equal to 75 kgm/s. Often british sources neglect conversion, which is 1CV=0.986 HP (1HP=550 lbft/s). Curiously, german PS, initially wasn't quite the same, being expressed in lbft/s too and different for various regions.

    GB
     
  11. Vincenzo

    Vincenzo Active Member

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    so 870 cv probably was a 2520 rpm and +100, it's all proportional, 740 cv at 2400 rpm, 790 mm hg, +5% for rpm (37 cv) and +12,6% (93 cv) for presure = 870 cv
     
  12. Tzaw1

    Tzaw1 Member

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  13. Vincenzo

    Vincenzo Active Member

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    very good

    "condizioni d'emergenza" is only for twin engined on one engine
     
  14. greybeard

    greybeard Member

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    I think what posted by Tzaw answered to all questions!

    Thanks Tzaw, that site you linked is great!

    S!
    GB
     
  15. Vincenzo

    Vincenzo Active Member

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    but it's strange that the engine give same power at 2400 rpm and 2520 rpm also if a bit higher altitude
     
  16. greybeard

    greybeard Member

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    Sorry, I can't see where is same power for the two different RPM. I read 870 CV for the 2520 RPM and 740 CV at 2400 RPM (becoming 840 CV at same RPM at 3800 m).

    GB
     
  17. Vincenzo

    Vincenzo Active Member

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    see caratteristiche di omologazione and volo orizzontale a velocità massima
     
  18. greybeard

    greybeard Member

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    I think it's matter of dynamic pressure. I mean, power of "caratteristiche di omologazione" is probably got at dynamometer (banco prova motori) whilst that in flight takes in account (it's anyway a computed one, not measured, obviously) further raise in rated altitude (quota di ristabilimento) due to speed of air that becomes pressure into intake manifold. This allows to get same 840 CV "static" at 3800 m, at 4300 m, still with same MAP. Can't explain the higher RPM.
     
  19. Vincenzo

    Vincenzo Active Member

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    so we are agree, too me thinked that altitude difference can be from difference like your explanation, it's strange, maybe a mistake in the compilation of manual
     
  20. greybeard

    greybeard Member

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    The "ram" air effect is ascertained; I mean, that's routine for that category of aircraft engines. About the 2520 RPM, I don't think that could be an error (those documents were approved by fascist government, which was no soft about mistakes! lol), since also G50bis manual mentions at page 122 to get velocità massima at 2500 RPM and not 2400. Simply, I'm unable to explain.

    Ciao,
    GB
     
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