On Mon, 2002-11-11 at 15:12, Andy Ross wrote: > Curtis L. Olson wrote: > > Cruising in the 747-yasim at 18,000' (altitude holding me steady) and > > with throttle adjusted so I'm stable at 490 kts, I'm seeing a -3 > > degree pitch down (/orientation/pitch-deg) > > > > This looks odd from an external view standpoint. It seems like we'd > > want a slight amount of positive alpha, but I couldn't find alpha in > > the property tree? > > The angle of attack property is available as /velocities/alpha-deg. > No, I don't know why it's under velocities, either. :) > > One thing to point out is that FL180 is a very low cruise altitude, > and 490 knots indicated (you are quoting IAS off the HUD, right?) is a > very high indicated airspeed. At this speed, the aircraft will be > producing significantly more lift than it would at a normal cruise > altitude of FL360. In order to keep the lift at 1G, the nose needs to > point down more.
FYI: 490 KIAS is way too fast for most big jets under *any* circumstances. > > Remember also that angle of attack is an arbitrary number. Zero AoA > is almost never the same as the AoA of zero lift. In YASim's case, > zero AoA is defined as the X axis direction. The point of zero lift > depends on several factors, most importantly including the camber and > incidence of the wing. > > So basically, you have the plane in an unusual flight environment. > Real planes are almost never flying this fast at this altitude; > they'll be at ~300 KIAS or so and using the extra available thrust for > climbing. I really don't know what attitude real jet would have under > these conditions. You can try playing with the "camber" attribute of > the main wing (which defines the zero-AoA lift of the wing). If you > reduce it, you'll get less lift at low angles of attack and thus > require less nose-down attitude to get the same lift. This can have > nasty interactions with the drag computation, though. > > I can at least say that YASim solves for a cruise AoA as part of > initialization and prints it along with the rest of the report. In > the solution cruise environment, it is flying with a slightly positive > AoA: something like 2-3 degrees if I remember correctly. > > Andy > > -- > Andrew J. Ross NextBus Information Systems > Senior Software Engineer Emeryville, CA > [EMAIL PROTECTED] http://www.nextbus.com > "Men go crazy in conflagrations. They only get better one by one." > - Sting (misquoted) > > > _______________________________________________ > Flightgear-devel mailing list > [EMAIL PROTECTED] > http://mail.flightgear.org/mailman/listinfo/flightgear-devel -- Tony Peden [EMAIL PROTECTED] We all know Linux is great ... it does infinite loops in 5 seconds. -- attributed to Linus Torvalds _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
