On Tue, 2007-02-06 at 12:47 -0800, Tatsuhiro Nishioka wrote: > Dave, > > On Feb 5, 2007, at 8:35 PM, Dave Perry wrote: > > > I made > > an estimate from the 3D model as to approximately where the CG should > > be. The main wing should carry 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. > > I gave it a try and your configuration file seems very close to what > I want. It's a great help. > I was about to calculate the CG and some other parameters with a bit > more engineering way so I looked more deeply into the flight model > but hard to find the way to see the CG in yasim. your post saved me a > lot! > Plus, taking a look at your xml file told me that I mistakenly > settled the position of the main gears. > It should be -2.15 instead of -1.64 so your guess is right. And the > biggest mystery in my head was resolved. > > I calculated the position of CG with the equation obtained at: > http://www.paragonair.com/public/docs/FAA-Handbooks/8083-01_WnB/ > 8083-01_ch08.pdf > According to this document, the distance from the nose to the CG is > calculated as: > > CGoffset = D - (F*L) / W > > where D is the distance between the front wheel and the main wheel, F > is the weight of the front wheel, > L is the distance between the nose and the main wheel, and W is the > total weight of the aircraft. > Note: L and D are interchanged in your copy of the formula. I computed the sum of the moments over W to confirm this.
> I estimated the weight of the front wheel as 1/6 - 1/8 of the total > weight. > Then the CG is placed between 6.43 to 6.59 m behind the nose. The > nose is at 4.89 m in x-axis so the > position of the CG can be between -1.54 and -1.70 on x-axis. > I should have included all the results of the experiment. I had "good" stability and not unreasonable values for the effectiveness from about -1.5 to -1.7 m for the CGx. In the real AC there is a safe CG/weight envelope, so this all seem consistent. > I'm now trying the actual weight of Shinden (I was using the lighter > weight since Shinden was not stable at all) > I tried various CG point in between the positions above. -1.54 seems > a little bit front heavy and -1.70 looks just > a little bit rear heavy with the accurate mass since reseting > flightgear lifts the nose up. > > > > 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. > > 67 kts for the dirty stall is for A6M2 (sorry, I forgot to delete > these). > The one for Shinden should be a bit faster (probably around 75 - 85) > since its flight record says it landed at 100 or 120 kts. > I'm not pretty sure if it actually stall at this speed because > there's no such record as far as I know. (67 is very tempting > parameter to me though.) > By the way, the record says that it needed to put the elevator all > the way down at the full-flap to avoid the nose going down. > so the approach elevator in command-line yasim should be more than > 0.9, I guess. > > With a couple of test flights using the revised j7w.xml, I landed > Shinden at about 100 kts with three point landing with full-flap, > and 90 kts with a little bit aerodynamic landing (maybe I was lucky). > Again, thanks for this unique and interesting model. I really enjoyed experimenting with the config xml and was glad you found it helpful. I will likely misspell this, kombowa, Dave -- Dave Perry <[EMAIL PROTECTED]> ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier. Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
