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Guest apadgett

How does FS9 calculate V-speeds?

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Hi,Does anyone know how FS9 calculates V-speeds? Does it use the figures in the aircraft.cfg files, or is it embedded in the AIR file?Thanks in advance,Andrew.

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FS doesn't calculate V speeds at all, I don't know exactly what you mean. The flight dynamics of a plane play a role here since the speed variable is part of the dynamics, but V speeds are no "core component" of the FDE nor can you extract them from some file in the first place without doing some computations and have a profound knowledge of aerodynamics.V speeds are determined in real life by computations and test flights and filled in tables.If you haven't got these tables for a specific airplane, you ain't got no V speeds. V speeds aren't taken out of the air, the tables are the one and only documentation for them. FS default planes usually have no V speed tables at all...Andreas

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Andreas pretty much summed it up... V speeds are a result of aircraft gross weight, ambient temperature, wind direction and velocity, wet or dry runway conditions and a host of other variables. Try a search for a program called TOPCAT It's not for the default aircraft but the manual is very good in explaining the calculation process.Rob

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Okay, perhaps my question should have been: are the tables that come in the aircraft documentation the only way we have of learning a plane's v speeds?But still, while we get to use the tables, and since v speeds aren't a stipulated part of the FDE, as you pointed out Andreas, so then must FS calculate the speeds that we call v speeds. Hence my question: does anyone know how FS calculates them?Thanks,Andrew.

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(Okay, perhaps my question should have been: are the tables that come in the aircraft documentation the only way we have of learning a plane's v speeds?)YES(But still, while we get to use the tables, and since v speeds aren't a stipulated part of the FDE, as you pointed out Andreas, so then must FS calculate the speeds that we call v speeds. Hence my question: does anyone know how FS calculates them?)FS cant calculate v speeds... sorry maybe I'm not quite understanding you??A basic explanation v1 = Aircraft has passed a point where an abort should only be made if the aircraft cannot fly vr = Safe rotation speed v2 = Climb out speed Maybe I'm wrong but I cant see how FS can factor for temps, pressure, derated thrust etc? Rob

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>Does anyone know how FS9 calculates V-speeds? Does it use the>figures in the aircraft.cfg files, or is it embedded in the>AIR file ?Andrew,the speeds of the simulated aircraft at specific flight conditions are output by the flight model (in other words flight physics model or simulation engine). This "hard-wired" flight model uses the data stored (and edited at will )in the aircraft.cfg- and .air-files to simulate a specific type of aircraft.V-speeds like Vr,Vs, Vs1, Vmca, Vx , Vy can be determined by the designer or user in flight testing the simulated aircraft measuring the speeds at appropriate flight conditions . They may or may not be equal to real life values, acording to the capability of the designer and/or limitation of the flight model. But if you fly the simulated plane properly you have to use the simulated speeds.I

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Hey Carl, Yeah I understand that diffrent temps etc affect the fs flight model as I calculate these for all my departures. I think the original question confused me a bit :) Rob

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I wrote above:This "hard-wired" flight model uses the data stored (and edited at will )in the aircraft.cfg- and .air-files to simulate a specific type of aircraft.I should have added: This data used by the flight model are 1.some (!) dimensions, weight and engine parameters, mostly but not exlusively in aircraft.cfg 2.dimensionless coefficients (derivatives), exclusively in .air-files. The latter may be derived from real life tables or computed by the FS tools FSEdit resp. Air Wrench, but also by costly professional programs. As well they may be tweaked manually (AAM, AirEd ) to obtain the desired handling characteristics and performance , which naturally includes some classes of V-speeds (classes see above). I point out that these coefficients take into account aircraft type-specific geometrical data which are not found as individual dimensional values in the .air-files ! Aircraft.cfg has such dimensions but they are used only by FSEdit to calculate the coefficients of the .air-files. They are not used directly by the flight model.Yes, it is complicated, but this is the way it is :-) CheersCarl

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