Andy Ross <[EMAIL PROTECTED]> said: > Jim Wilson wrote: > > Think I saw something that was maybe at a fixed weight. Not the full > > Flight manual table. When I get home I'll look for it. But I was > > suprised at the data. At lower altitudes it was over 4000fpm and was > > at least 2000fpm up to and over 30000ft. Finally dropped off to about > > 400fpm at 40000ft, reaching 0 somewhere around 43000ft. > > I found this X-Plane site: > > http://webpages.charter.net/rtpete/html/747.html > > Which agrees with you for the most part: > > > ROC Rate Of Climb > > [...] > > Above 10,000 ft to Cruise Flight Level FL > > * 2200fpm from 10,000 - 20,000ft @ 280 - 340kts > > * 2000 - 1500fpm from 20,000 - 26,000ft > > * 1500 - 400fpm from 26,000 - 35,000 ft depending on weight
Yes I've seen that, which is why the other table suprised me, it's numbers were generally higher. Showing the 747-400 capable of climbing up to 43000ft and cruising at 40,000ft. > But note the speed: 280-340 knots (it doesn't say indicated or true, > sadly). That's much higher than the 230 knots that I was flying last > night. I think what's happening is that for the initial climb out, > the aircraft wants to be in a high-AoA attitude; otherwise you'd have > a liftoff speed of 300+ knots and the wheels would incinerate. Once > off the ground, the 250 knot speed limit is still on the back side of > the power curve. If the autopilot is engaged there, the aircraft will > get stuck on the back side, and never find the high-efficiency climb > regime at lower AoA. > > Try this (since I'm at work and can't): trim for 250 knots only up to > 10000 feet, and then push the nose down and accelerate to something > like 300 before engaging the autopilot again (or better yet, trim for > 300 knots and don't engage the autopilot at all). See if the climb > performance in the flight levels improves. I've run many tests on that theory, and trying to find the right way. Even stepping up a couple thousand feet at a time keeping the pitch very gradual and the airspeed up it still dies out in the mid 20kft range. Can you commit that air temperature fix? That sounds like it might be important. If the air is too thin for the altitude, that AoA margin could be very small indeed. Best, Jim _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
