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From: Roman G. <rgr...@ho...> - 2001-09-10 07:03:08
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Thanx Tony for your reply but I try to make F16 XML file and what to better understand following values: RegisterVariable(FG_LBARH, " h-tail arm " ); RegisterVariable(FG_LBARV, " v-tail arm " ); RegisterVariable(FG_HTAILAREA, " h-tail area " ); RegisterVariable(FG_VTAILAREA, " v-tail area " ); RegisterVariable(FG_VBARH, " h-tail volume " ); RegisterVariable(FG_VBARV, " v-tail volume " ); Could you please explain what is arm and volume and how it can be calculated Sorry for my lamely question Thanx in advance Bye ----- Original Message ----- From: "Tony Peden" <ap...@ea...> To: <fli...@li...> Sent: Saturday, September 08, 2001 3:11 AM Subject: Re: [Flightgear-flightmodel] New properties in c172.xml > On Friday 07 September 2001 05:01 am, you wrote: > > > Thanx Tony for your reply > > > but could you please explain what does this values mean? > > > > > > > They are parameters needed for tail-off aero models. If you don't use: > > > > FG_LBARH > > > > FG_LBARV > > > > FG_HTAILAREA > > > > FG_VTAILAREA > > > > FG_VBARH > > > > FG_VBARV > > > > > > > > in any of your coefficients then you need not supply values for these. > > > > Could you restate what tail-off aero is, too, while you answer Roman's > > question? > > For an aircraft like the c172, the pitching moment sum is primarily composed > of contributions from the wing, fuselage, thrust and horizontal tail. So I > can write: > Cm = Cmwing + Cmbody + Cmthrust + Cmhtail > The primary sources of lift are: > CL = CLwing + CLbody + CLhtail > That lift from the tail is generally the largest contributor to tail pitching > moment (there will be a relatively small Cmo from the tail): > Cmhtail = -lh / cbar * CLhtail > where lh is the distance from the aero reference point to the MAC of the > horizontal tail. Note the minus sign, positve tail lift produces negative or > nose down pitching moment. > > OK, so now if I derive Cmhtail offline and separate out the elevator effects > so that I've got: > Cmhtail = Cmstabilizer + Cmde > Then realize that the stabilizer is fixed relative to the body in the case > of the c172, I can combine some terms and reduce the amount of data I need in > the config file: > Cm = Cmwbh + Cmthrust + Cmde > where > Cmwbh = Cmwing + Cmbody + Cmstabilizer > A similar sort of reasoning can be followed for the lift equation: > CL = CLwbh + CLde > > That's a tail-on model. > > On the other hand, if I wanted to take a little more fundamental approach I > can build an aero model that always calculates the tail pitching moment from > the tail lift. Many people like this approach because it preserves the > physical relationship that we know must exist between the tail lift and its > contribution to the total aircraft pitching moment. Also, if you design an > airplane, you pretty much have to look at it this way so that you can make > good choices regarding the tail airfoil section and planform. > > The downside to a tail-off model is that it can be harder to make changes to > the model data to get the simulation to match flight. How much harder > depends on both what you can measure on board and how you go about > reducing the flight data down into something that can be applied to the > simulation. > > A similar sort of approach can be applied to the vertical tail (though my > understanding is that tail-off vertical models are even harder to get right) > > Does that help? > > > > > > > > > Jon > > > > > > _______________________________________________ > > Flightgear-flightmodel mailing list > > Fli...@li... > > https://lists.sourceforge.net/lists/listinfo/flightgear-flightmodel > > -- > Tony Peden > ap...@ea... > We all know Linux is great ... it does infinite loops in 5 seconds. > -- attributed to Linus Torvalds > > _______________________________________________ > Flightgear-flightmodel mailing list > Fli...@li... > https://lists.sourceforge.net/lists/listinfo/flightgear-flightmodel > |