On Monday 15 August 2011 11:18:53 Gary Neely wrote: > Looks like a great start. The first thing I would do before anything > else is make sure your CG is positioned reasonably. In your SF-25, the > CG is much too far back; given the forward-swept wings, it looks to be > about a meter behind MAC: > > E:\FlightGear projects\sf25b>yasim sf25b-yasim.xml > Solution results: Iterations: 1292 > Drag Coefficient: 10.955851 > Lift Ratio: 291.677826 > Cruise AoA: 1.469686 > Tail Incidence: 2.793443 > Approach Elevator: -0.014301 > CG: x:-0.900, y:-0.000, z:0.284 > > Inertia tensor : 1831.357, -0.000, 78.171 > [kg*m^2] -0.000, 2075.542, 0.000 > Origo at CG 78.171, 0.000, 3856.738 > > The command-line YASim solver is showing CG at x=-0.9, well behind the > wing's root chord position at x="-0.371".
I took a look at the YASim solver today, first comparing the Inertial tensor with the inertias coming out of aeromatic. Not too far apart, but the 2 yasim aircraft I looked at were both 50% higher than the aeromatic numbers. Then I took a look at the -g switch and was rather shocked at the curves yasim generates. It generates CL, CD and L/D. My plot software computes force as (lift^2+drag^2)^0.5. Lift and drag are perpendicular by definition so this gives the total force in the lift/drag plane. I made 3 plots with Tat's A6M2 and Helijah's Katana and Gloster-Meteor models: http://www.jentronics.com/fgfs/temp/yasim/yasim-A6M2.png http://www.jentronics.com/fgfs/temp/yasim/yasim-katana.png http://www.jentronics.com/fgfs/temp/yasim/yasim-glostermeteor.png And then I loaded some data I had from a NACA 4 digit 0015 airfoil into the same plot definition: http://www.jentronics.com/fgfs/temp/yasim/naca0015.png I was pretty shocked to see the YASim charts drag numbers all seem to fall off at stall. This is counterintuitive to me, I expect drag to increase at stall, that is what keeps the speed low during the stall. Also, the lift/drag (L/D) ratio is actually the tangent of the angle the aerodynamic force is acting in. On the real airfoil it rapidly approaches 0 after the stall because the force is acting nearly parallel to the free stream velocity and drag dominates the ratio. This seems not to be the case with the YASim models. Thanks, Ron ------------------------------------------------------------------------------ uberSVN's rich system and user administration capabilities and model configuration take the hassle out of deploying and managing Subversion and the tools developers use with it. Learn more about uberSVN and get a free download at: http://p.sf.net/sfu/wandisco-dev2dev _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
