On Monday 21 February 2011 17:41:10 Jack Mermod wrote: > I wasn't planning to get into an argument over the 777-200, but yes it > does have an unrealistic FDM. > > See here: > > http://img219.imageshack.us/img219/891/picture5mj.png > > > Are you telling me this is realistic too? > > Check Six, > Jack
Generally a picture is worth a thousand words, but here, not so much. What is it, exactly, you are troubled by? Coefficient of Lift (Cl) is the Lift force divided by dynamic pressure and wing area.[1] For the 777-200 FDM lets say we require 602,320 lbf of lift (this is near max weight, btw) and we'll assume we're flying about 300 knots. So: Cl = ((−602320lbf)/((0.5*(300knot)^2*0.00278slug/ft3)*427.8m2)) ~= -0.367 Negative, because we're inverted... Thin airfoil theory suggests the Cl curve is about alpha*2pi + alpha0 where alpha is the angle of attack in radians and alpha0 is the Cl at alpha=0. [2] So: alpha = (Cl - alpha0)/2pi If we assume alpha0 is around 0.333 (probably an over estimation) we get alpha = -0.7/2pi = -0.114 radians or -6.4 degrees. An alpha of -6.4 probably wouldn't stall the airfoil. Also, transport class aircraft must be rated to at least -1 g [3] So, inverted level flight in the 777-200 doesn't sound impossible. Near the ground and under a bridge... Foolhardy, perhaps, but not physically impossible. Oh, and ground effect will lower the required angle of attack required below about 200 feet also. 200 feet being the wingspan of this aircraft. Thanks, Ron [1] http://www.aerospaceweb.org/question/aerodynamics/q0078.shtml [2] http://www.aerospaceweb.org/question/aerodynamics/q0136.shtml [3] http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=a1b09ee39e3a8d0190f1bcf462436936&rgn=div5&view=text&node=14:1.0.1.3.11&idno=14#14:1.0.1.3.11.3.164.9 ------------------------------------------------------------------------------ Index, Search & Analyze Logs and other IT data in Real-Time with Splunk Collect, index and harness all the fast moving IT data generated by your applications, servers and devices whether physical, virtual or in the cloud. Deliver compliance at lower cost and gain new business insights. Free Software Download: http://p.sf.net/sfu/splunk-dev2dev _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
