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Guest Fabio Miguez

Need some aerodynamics help

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Hi team.I am working on an accurate flight model for my A-4 cockpit project.I started with Lewis Magruders very cool FS98 model, converted it to FS2002 then changed all the good stuff like wing area, sweep, root chord etc.Next up was fuel tank locations and sizes.The problem I now have is this:Up to about 220KIAS the thing flies really well, and achieves an approach speed which is correct by the flight manual. BUT above 220KIAS the thing oscillates in pitch something terrible! It does not get any worse, it's like there is a pitch up which is seriously over damped or something!I have tried moving the static CoG around, and also changing the loaded fuel quantities, but to no avail :(HELP!Sean.Sean GalbraithBizarreWorks,Specialists in Obscure and Bizarre Sim Development http://homepages.paradise.net.nz/seang1/

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Open the a/c CFG and scroll down to the section ";Moments of Inertia". Find the parameter "empty_weight_pitch_MOI" and increase the value of this entry to above 12,000, save the change and go fly your A-4. If necessary, continue increasing the pitch MOI by 2000 to 5000 until the aircraft is free of pitch oscillations at all airspeeds up to Vmo. The pitch stability parameter ( found in the CFG file under [flight_tuning] and in the .air file under section 1101 ) and the pitch MOI are interrelated, an increase in pitch stability will require a corresponding increase in pitch MOI. Remember to reload the a/c or restart FS2002 after each CFG file change. With a little tweaking and flight testing this is one flight dynamics problem that is easy to solve.

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Hey Sean.Donna covered the MOI parameter, which should have the answer for your problem. But I think it is worth saying that the aerodynamic engine of FS is not flawless, and therefore you may need to tweak the geometry parameters. A lot of good AIR files out there do not represent the real plane when it comes to many numbers, such as wing area, horizontal stabilizer area, incidence, and so on. Some planes out there even have 0 for the horizontal stab area!It is not always the case, but I just thought you should know about this.Also, with a program called AirEd it is possible to edit parts of the AIR file that Microsoft's FSEdit does not.

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