On Thu, 2007-02-01 at 13:43 -0800, Tatsuhiro Nishioka wrote: > I hope many people fly it and tell me how to improve the stability > without doing this. I know it's supposed to be a bit unstable but > it's too unstable without > this workaround. Hi Tat,
Thanks for this great addition! I took a look at the j7w Shindon including the j7w.xml yasim configuration. Did you know there is a command line yasim in $FG_ROOT/bin that allows you to get a lot of feedback from a trial config xml file like j7w.xml w/o running fgfs? After a flight in the Shindon, I was fairly certain that the CG (center of gravity) was too far forward. This required you to use an effectiveness of 3.5 on the cannard. And you did get the desired increase in stability. So I made an estimate from the 3D model as to approximately where the CG should be. The main wing should cary most of the weight, so since the wing is swept, I tried to change the ballast to move the CG to about x = -1.7 m (yours is at x = -0.666), or approximately at the leading edge root. This allowed me to reduce the cannard effectiveness to 1.5. Also, from your data, I see that the power off dirty stall is 67 knots, so I used that in the approach configuration (yasim assumes that the approach speed is the dirty stall speed). This allows a slower stall and better short field landings with approach at 85 knots. I flew from KSFO to KHLF and landed and turned off before the tower with little braking. Bert Rutan's Long-EZ, etc. were designed so the cannard stalls first. This is true for your model of the j7w also. I moved the x coordinate of the main gear aft for the duration of this experiment to assure the AC sat with the nose gear on the ground as I moved the CG back and forth. Give this config a try. -- Dave Perry
j7w.xml
Description: application/xml
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