Re: [Jsbsim-devel] Normal (& abnormal?) accelerations

 Re: [Jsbsim-devel] Normal (& abnormal?) accelerations From: Jon S. Berndt - 2007-12-07 14:17:54 > I'm not sure what you mean by Nz, but here are some equations > > a_z (acceleration in the z-body axis) = (Z_T - D sin \aplha - L cos > \alpha + g m \cos \phi \cos \theta)/gm > > a_n (output from an accelerometer at the c.g. but oriented in the > negative z axis) = (- Z_T + D sin \alpha + L cos \alpha )/gm > > a_n_i (output from a normal accelerometer displaced from the aircraft > c.g.) = a_n - [(pr + \dot{q}) l_x > + (qr + \dot{p}) l_y - (q^2 + p^2)l_z]/g > > > As you can see, none of these definitions match the load factor > equation except for a_n when angle of attack is small. > > Lee Yes. The middle equation is the one I'm concerned about, as far as its implementation and *use* in JSBSim and/or aircraft. My first post in this thread explains that. I think I've come to a conclusion about what is needed. This is based on my recollection of how the F-16 FLCS works with regard to the use of normal acceleration, what I have seen in plot traces from JSBSim, and by looking at the code and aircraft definitions over the past few days. I plan to create two new properties named accelerations/load-factor accelerations/Nz The first is in wind axes, the second, body, both would be based at the CG - that is, they won't include rotational effects (omega terms) at the pilot location. As I recall, the F-16 FLCS expects Nz, and sums it with -1, to get a zero-based value. This is now being done wrong in the F16.xml file. This is all still open for discussion. Comments? Jon 

 [Jsbsim-devel] Normal (& abnormal?) accelerations From: Lee Duke - 2007-12-07 13:43:04 I'm not sure what you mean by Nz, but here are some equations a_z (acceleration in the z-body axis) = (Z_T - D sin \aplha - L cos \alpha + g m \cos \phi \cos \theta)/gm a_n (output from an accelerometer at the c.g. but oriented in the negative z axis) = (- Z_T + D sin \alpha + L cos \alpha )/gm a_n_i (output from a normal accelerometer displaced from the aircraft c.g.) = a_n - [(pr + \dot{q}) l_x + (qr + \dot{p}) l_y - (q^2 + p^2)l_z]/g As you can see, none of these definitions match the load factor equation except for a_n when angle of attack is small. Lee 
 Re: [Jsbsim-devel] Normal (& abnormal?) accelerations From: Jon S. Berndt - 2007-12-07 14:17:54 > I'm not sure what you mean by Nz, but here are some equations > > a_z (acceleration in the z-body axis) = (Z_T - D sin \aplha - L cos > \alpha + g m \cos \phi \cos \theta)/gm > > a_n (output from an accelerometer at the c.g. but oriented in the > negative z axis) = (- Z_T + D sin \alpha + L cos \alpha )/gm > > a_n_i (output from a normal accelerometer displaced from the aircraft > c.g.) = a_n - [(pr + \dot{q}) l_x > + (qr + \dot{p}) l_y - (q^2 + p^2)l_z]/g > > > As you can see, none of these definitions match the load factor > equation except for a_n when angle of attack is small. > > Lee Yes. The middle equation is the one I'm concerned about, as far as its implementation and *use* in JSBSim and/or aircraft. My first post in this thread explains that. I think I've come to a conclusion about what is needed. This is based on my recollection of how the F-16 FLCS works with regard to the use of normal acceleration, what I have seen in plot traces from JSBSim, and by looking at the code and aircraft definitions over the past few days. I plan to create two new properties named accelerations/load-factor accelerations/Nz The first is in wind axes, the second, body, both would be based at the CG - that is, they won't include rotational effects (omega terms) at the pilot location. As I recall, the F-16 FLCS expects Nz, and sums it with -1, to get a zero-based value. This is now being done wrong in the F16.xml file. This is all still open for discussion. Comments? Jon 
 Re: [Jsbsim-devel] Normal (& abnormal?) accelerations From: Tony Peden - 2007-12-07 14:47:58 In my mind, Nz= az/g and Nz=a_n iff the accelerometer is mounted parallel to the body z. -----Original Message----- From: jsbsim-devel-bounces@... [mailto:jsbsim-devel-bounces@...] On Behalf Of Lee Duke Sent: Friday, December 07, 2007 5:33 AM To: JSBSim development issues Cc: Agostino De Marco; Jon S. Berndt Subject: [Jsbsim-devel] Normal (& abnormal?) accelerations I'm not sure what you mean by Nz, but here are some equations a_z (acceleration in the z-body axis) = (Z_T - D sin \aplha - L cos \alpha + g m \cos \phi \cos \theta)/gm a_n (output from an accelerometer at the c.g. but oriented in the negative z axis) = (- Z_T + D sin \alpha + L cos \alpha )/gm a_n_i (output from a normal accelerometer displaced from the aircraft c.g.) = a_n - [(pr + \dot{q}) l_x + (qr + \dot{p}) l_y - (q^2 + p^2)l_z]/g As you can see, none of these definitions match the load factor equation except for a_n when angle of attack is small. Lee ------------------------------------------------------------------------- SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Jsbsim-devel mailing list Jsbsim-devel@... https://lists.sourceforge.net/lists/listinfo/jsbsim-devel _______________________________________________ The JSBSim Flight Dynamics Model project http://www.JSBSim.org _______________________________________________