All the Bristol Jupiter/pegasus engine family and its related Gnome and Rhone, AlfaRomeo and Piaggio derivatives are very badly modellized. Same for the Mercury family (very strange entries there!). For the Gnome 14 and variants it's even worse.
I have suceeded to get the original documentation of these engines from the French Air Museum Documentation Center, and some more technical material from the Flight archive of the period, and with the help of George1991 who got Rumanian original data for the K14 we are trying to put some order in these emd files.
The most obvious mistakes are:
1) First of all using uncorrect datas from wikipedia or other web sources (copying mistakes is probably the most popular activity on the web) - this is not new, the English language "specialized" publications of the seventies are at the origine of quite a number of these long-lasting mistakes. With teh present situation we are flooded by these mistaken data, and it is really compulsory to try to go to original constructor data or to datas published by official sources of the period concerned for technicians/mechanics/pilots
2) The basic rpm ("point fixe", 'idle speed engine run") generally used seems to have been based upon....modern car vehicle engines than upon real historical data - it is way too low (between 200-400 rpm usually) while in reality it was quite high (around 800 rpm for the 9 cyl, around 1200 rpm and more for the 14cyl).
3) Another main mistake is a lack of understanding that flaot carburators were the most frequently used and that all float carburators do not behave similarly under negative Gs.. This comes from a lack of knowledge on the differences between various carburators: the Zenith (and Claudel) float carburators, the Stromberg ("Zenith Stromberg") float carburator but behaving to some extent like the later "shelling hole carburator, above when used in duplex installation) and the much later out of the period Bendix-Stromberg pressure carburator, not speaking of the early SU updraught "float type" carburator, suction carburator and other variants.
4) Another source of mistake is the engine power data entries in the emd - a confusion between the various types of power definitions :
Nominal Power ("Puissance nominale") - continuous power under standard conditions of utilizations (altitude, rpm, temperature)
Theoretical output at sea level ("equivalent de puissance") ("potenza ideale") (Theoretical power at sea level) - power on groundm at sea level, without compressor, with full throttle and at nimnal rpm regime
Power at take off (Puissance au decollage")
Take off power ("Rated power") - the maximum power permitted for a limited period of time during the take off of the aircraft (generally a 1 to 5 minutes period)
Maximal Power (Puissance Maximale)
Maximum Continuous Rated power ("METO - "Maximum Except Take OFF" power) - the highest power that can be maintained/ allowed continuously.
WEP power - power obtained after injection of a chemical additive, for a shor period of time
Cruising flight power - 75% of take off power at 90% of maximum rpm
Economical cruising flight power - 65% of take off power
The Il2 game engine uses formulas to calculate the power outpout from the data entered in the emd file - for instance maximal continuous rated power is generally around 1.3 the nominal power at sea level. The boost power (the over 100% throttle, not the WEP) can be used to simualte take off extra power (but most often 1 value of 103% will be better in accordance with hiostorical reality than a value of 110%) and so on....
Interesting these formulas do not use the ATA manifold entries but calculate manifold entries on teh basis of the real critical entries, the rpm regimes at various heights/power - If one include an ATA rpm relationship in the emd file, to compell the game engine to use a given power curve, one msut be very careful, and in practice, as a result, this will be a mistake more often than not......
Take also as a rule of thumb that in the absence of compressor power output decreases by 10% with every 1000m of atitude
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Topic: Cant Z.506B (Read 43485 times)
