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. 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
