> Hi, > > I agree with Norman. As long as control system is of concern, it is much > better to use normalized units.
Control law block diagrams I have seen take stick input in pounds force (pilot inputs) and output in degrees to actuators. I've never seen one that output control commands to an aerosurface actuator in a range from 0 to 1. Have you? > > surface deflections in degrees, and for good reason: it's natural, it's > > physical. From the point of view of JSBSim, "normalized" aerosurface > > Degrees are not natural, nor physical. We may argude that *radians* > might be natural, but *not* degrees. By "natural" I mean that it's: the most commonly seen angular command unit for aerosurfaces, that it's what is used by the rendering routines to rotate 3D objects, that it completely specifies the commanded angular position without the need for a range (a range of 0 to 1 by itself specifies nothing without the definition of what the maximum is - there is no standard here for that), and much aero data is non-dimensionalised using degrees (or radians, see below). So, sorry, but based on the above description, for this application, yes, degrees are "natural". > This would lead us to another class of problems, what system of > measurements is used? (I'm used to SI system) or > what about input (I mean stick, pedals positions...)? > Should the input be expressed in "natural" or normalized units? I've said several times that we expect INPUTS in a range from zero to 1. We can process the inputs to arrive at a force unit to match the FCS block diagram. Note that for JSBSim we are also changing the config file format. When the next major version of JSBSim is released (early next year) supporting the new configuration file format, many items will now take a UNIT="" attribute, allowing aircraft to be defined in different unit systems. > And about FDM itself, aerodata to be used are not unified... I have seen > some using degrees as a control surface deflections units, and others > using radians. What would you choose as a "natural"? True, I've seen both. JSBSim has used both, and we accept both, but "normalized" units are anything but normal - you have to provide a range for it to mean anything, and as far as I can tell, there is no standard here. It's defined on a per-aircraft basis. And, as I have pointed out above, for aerosurfaces it requires an intermediate conversion twice. Jon _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
