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Re: [Jsbsim-devel] Datcom and coefficient conversion
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From: Alan T. <ajt...@v-...> - 2014-12-15 14:45:34
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JSBSim will accept stability axis (CL,CD,CM) or body axis (CX,CN,CM) data in the longitudinal axes, and Datcom gives both sets of outputs. The lateral axes are the problem, as Datcom outputs only stability axis data and JSBSim accepts only body axis data. The solution is simple – just apply the body to stability axis transformation to the Datcom derivatives and use these for your JSBSim input. I do this with a simple spreadsheet. See this document, page 37. http://contrails.iit.edu/DigitalCollection/1964/FDLTDR64-070.pdf Alan From: Elias Tarasov Sent: Monday, December 15, 2014 1:46 PM To: jsb...@li... Subject: [Jsbsim-devel] Datcom and coefficient conversion Hello! Situation: Datcom produces coefficients in the stability axis system. JSBSim requires it to be in a body or a wind axes. Since body differs from stabilty only at the AoA, it seems rationally to convert stability to body. The way to convert (assumption): 1. Get coefficients from <Airplane_Name>.out file, produced by Datcom. 2. Evaluate respective force or moment. 3. Convert F or M into Body axis. 4. Evaluate coefficients form the F or M that now in a body system. Is that way correct? Or there are some other ways do exist? The problem i have encountered: Since for instance F = qbar * S* C, then qbar is an obvious vector. qbar = (1/2)*density*V^2. So: 1. When we do a step №2 and evaluate the Force wrt to Stability axis do we have to express V as a vector wrt to Stability? 2. When we do a step №4 and evaluate the coefficients wrt to Body axis do we have to express V as a vector wrt to Body? These 2 questions seems an obvious, but since in Datcom we cannot input Beta, and don't have it in an output file, that means we can't get or calculate the components of V and therefore can't get qbar wrt Body or Stability axes. Cannot find the solution at Stevens and Lewis and Datcom User Manual. Can anybody point how to solve that problem? Thanks a lot and best regards. -------------------------------------------------------------------------------- ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk -------------------------------------------------------------------------------- _______________________________________________ Jsbsim-devel mailing list Jsb...@li... https://lists.sourceforge.net/lists/listinfo/jsbsim-devel _______________________________________________ The JSBSim Flight Dynamics Model project http://www.JSBSim.org _______________________________________________ |