Hello ,
E.B. Refers on the different methods used by JSBSim and YASim. Unfortunately there a lot of false statements floating around how X-Plane, MSFS, JSBSim or YASim works and it seems to me that E.B. felt on such.
I wish to point out:
-X-Plane does make use of the so called "blade element theory". Each surface of an aircraft (as an example a wing) is break down into several elements which their number can be specified. For getting the needed coefficients it considers a whole lot of datas, and makes use of table-datas and looking at fixed values like ratios as well. At the end, step three, all forces are built up by summing up for the entire aircraft to get the aerodynamic behavior. Engines are simulated quite detailed.
-JSBsim as well build up the coefficients to get the aerodynamic behavior. Each force or moment is defined by a specifiation which can be a mathematical function, a value
or a Table-look-up, but the aircraft is seen as whole unit and not broken into smaller elements as in X-Plane. But as I understood Jon S. Berndt JSBSim would also allow to break a surface into several elements. (?)
The fact that JSBSim aircraft doesn't take the ground surfaces into account is a problem on FlightGear/SimGear's side and not on JSBSim. JSBSim offers all needed things, just FlightGear/SimGear doesn't use them. Engines are simulated quite realistic, but maybe not very detailed.
-With YASim, we have to seperate between helis and fixed-wings.
On Fixed-wings the aircraft is broken only in its main elements: Fuselage and wings. A wing is just a single element, you can't specify any airfoil on it, and the coefficients which can be specified by the user are quite abstract. Engine simulation is quite poor, so YASim as whole can't be much compared with X-Plane, and a fdm made with has to be tweaked a lot to come close to the real counterpart.
The YASim-heli-fdm is indeed using the "Blade-Element-Theory", but just for the rotors. So the rotors are break up into several elements, and their number can be specified. Real airfoils datas can be applied to the rotor blades like in X-Plane. It has more values to tune than X-Plane. Unfortunately there is no engine simulation and no vortex simulation.
And there is of course the sliding-on-ground-bug.
MSFS: MSFS does use look-up-tables for some more complicated stuff like AoA, Mach and ground effects, Downwash and engines. This doesn't surprise me much as MSFS started very early and the home computers at this time wasn't able to deal with a different simulation processes like Blade Element Theory.
Facts and conclusion:
X-Plane does make use of Look-up-Tables and fixed values as well- the difference to other models is that they break down each surface into smaller elements before.
YASim-fixed-wing can't be much compared with X-Plane's methods.
YASim-heli are using the same method only for the rotors as X-Plane.
JSBSim allows different methods to get the needed coefficients- Look-up-tables are just one possible method among others.
-->JSBsim seems to be quite more flexible as it allows different methods, so JSBSim isn't outdated.
The realism-factor is specified by the developers who uses any of those fdm and not necessarily by the fdm itself: Garbage in- Garbage out. Just with creating a file with Aeromatic or the Blender-Yasim-script doesn't make the aerodynamic behavior of an aircraft in FGFS already realistic.
In fact both fdm needs a lot of real life datas like Windtunnel datas, airfoil numbers and pilot flight reports. It is naive to think that Aeromatic or the Blender-Yasim-script creates realistic fdms out-of the-box!
It is a only rough approximation that will require much tweaking before you get a result that approaches realism.
Sources:
http://download.microsoft.com/download/1/7/8/17808bed-9b1e-4542-90a6-4c1d8af27fae/Aircraft_Sim_Tech_Zyskowski.pdfhttp://jsbsim.sourceforge.net/JSBSimFlyer.pdfhttp://www.x-plane.com/pg_Inside_X-Plane.htmlhttp://wiki.flightgear.org/YASim