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rgamurot

FL CH activating automatically

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While climbing out of WSSS, I had a lot of trouble keeping my speed up. I tried to use the VS to manage my speed but the autopilot constantly forced FL CH to activate. Is this supposed to happen? Is there a way to override it aside from cutting the A/P?Also, it took me almost and hour and a half to climb from takeoff to T/C at FL330 as I could only climb at 200fpm. I noticed the temperature was very high. Is this what affected the engine performance?Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

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High temp might, but your experience sounds more like you were not getting takeoff and climb power, or you were very heavy.. are you sure autothrottle was active and you had TOGA? I assume you were flying the 747, what was your takeoff gross weight? Max is 775,000.

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I always use TOGA for takeoff and also my weight was about 342 tonnes (750,000lbs) which is well below the MTOW. In fact, with the high assumed temp I calculated (48C) I ended up hitting VR earlier than I should have. After, the engines switched to CLB 1 on schedule but even at CLB I didn't get enough power. I had to switch the THRUST LIM to CON just to get as much thrust as possible. Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

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I came back to correct my stated MTOW..you're correct, at 750klb you should make it o FL350 in 21 min (conincindenly I'm running climb tests). Where did you find 48C? That's 108F, which is a hot day in Phoenix where at least two carriers fly 744s so it's thin but should fly. Can you reproduce the problem?

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48C is the assumed temp I used for takeoff, not the ambient temp. I got it from a performance calculator someone recommended a while ago. http://topcat.ofplan.net/ I think what happened was that with the combination of the high temp at higher altitudes and the low pressure system caused the air to become too warm and thin for the engines to operate efficiently. Now that I'm over Australia, the temperature dropped a bit and the pressure is higher. The engines are still working a little harder than usual but the more the temp drops, the better the performance is.Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

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Ryan,Were you using a weather programming addon?...maybe this created the abnormal condidtions (HIGH TEMPS AT ALTITUDE) you encountered...I stopped using them a while back as they did create several abnomalies.I now keep things simple (yeah - I'm stupid) & use the FS9 WX menu to create three WX areas (just like we did in PS13?) using downloaded real world wind & temp charts at the foll altitudes:Surface (incl DEP ARPT WX)5000100180240300340390450Now it's all set up & saved as a flight I seem to get fairly realistic results, taking less than 10 min to set up the WX for a particular flight. It gives me an average wind/temp at each alt...so its not a precise science, even in the ITCZ the temps at altitude (above FL340) are never too extreme when studying real world wind/temp data.It's one less addon running in the background.Steve B

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I agree with suspecting the "assumed temperature." If ambient is anything below 30C then no adjustment is required (the engines are flat rated at that level - according to what I've read). If the ambient is above 30C then the assumed temperature is just what you might expect it to be out on the runway... generally just a few degrees warmer due to all the pavement. It is not realistic to have elevated temperatures like that once airborne where you should experience true ambient.I do use an add-on with few problems.. Active Sky. There are tweaks necessary to ensure smooth wind and pressure transitions but I don't consider them complicated.

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Assumed temperature is used to de-rate the engines by a specific amount instead of using a pre-set de-rate (ex. TO-1=5%, TO-2=15%). This way you can have the engines provide just enough thrust to get off the runway comfortably. For example, when I left Seattle earlier, the ambient temperature was about 16C but I used and assumed temperature of 38C to reduce the amount of thrust the engines provide. This way, I would be able to lift off the runway with about 2000ft left. Also, in the ITVV Virgin 747-400 they had an ambient of +10C and used I think +44C. It was somewhere in the 40s.As for the weather, I too use AS6.5. I guess it may have been an anomaly in the Singapore area. But considering there was also a very bad storm in the area, maybe I was just a really bad day for flying. In another forum, I remember reading this one post from someone:"high temperature affects performance (including climb rate). Last summer it was hot enough in Warsaw that flying schools were forced to close for July. Authorities have issued the ban for flying students not allowing them any operations. Even licenced pilots were limited in their operations (I am speaking about EPBC and GA aircraft)."Who knows.Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

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Thanks, I learned something.Our temps aloft over Texas in the summer are routinely 30F above standard where I fly (14,000 - 17,000), and an extra inch or two of manifold pressure is needed to maintain desired power. Normally aspirated engines really suffer. I know Lake Taho CA at about 6,000 has density altitudes on the surface higher than the service ceilings for most non-turbo GA aircraft during the summer days. Same basic physics applies to fanjets.But, I agree with you in that something else was going on to experience what you did... doesn't the delimit only apply during takeoff thence the N1 is limited by the climb limit?

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>But, I agree with you in that something else was going on to>experience what you did... doesn't the delimit only apply>during takeoff thence the N1 is limited by the climb limit?Yes, assumed temp is only active while you are in the D-TO thrust mode. When the aircraft switches to (for me) CLB 1, the assumed temp is deleted and the N1 limits return to normal. So when not even switching to CON gives you enough thrust to maintain speed in level flight at FL140, something is really up.Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

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