Hello James, > [I assume Thomas will reply anyway, but I want to check I have this > right (from using the PMDG 757/767/777s which are supposed to be just > about the most accurate systems models out there)]
> On the FMC, one of the pages is THRUST LIM (actually there's a couple). > This is where you select TO/GA, CLB and CRZ power (as EPR values). Well, at least on the B757/B767s (other Boeings might have different configurations) the thrust limit is set on a seperate "Thrust Mode Select Panel", which has the Buttons "TO/GA", "CLB" + "1" + "2", "CON" and "CRZ" and a little selector for Assumed Temperature reduced takeoff thrust settings. The only thing thrust reference that can be selected via the FMC is the "assumed temperature" for take off thrust (on the TAKEOFF REF page). Our B757 and B767 (and I am almost certain that all B757/B767) don't have a "THRUST LIM" page on the FMC. Maybe this is for B777 only. > I am > assuming (hopefully Thomas will correct me) that the auto-throttle picks > the 'limit' based on these settings. TO/GA, btw is Take Off / Go Around > thrust. It warrants a button of it's own (on the center pedestal, behind > the throttles, I think) that activates this power setting (presumably > one less thing to worry about when the crew is busy enough...) This is correct (The G/A Buttons are at the Throttles, just below your thumbs) > > For an automatic take-off, the procedure in the PMDG manuals I have is > roughly as follows: > (have the various LNAV / VNAV modes armed, and the auto-throttle > enabled on the MCP) > manually advance the throttles to start the take off roll (while > holding the bakes as required etc) > at 80% N1, engage TO/GA thrust (button in real life, Ctrl-Alt-F12 > in Fly! 2, I think it's Ctrl-Shift-G in FS2k2) If you want to do a autothrottle takeoff in real life, you first have to select TO thrust mode (on ground automatically selected after at least one flight director is switched on). To actually set T/O thrust you would have to select "EPR" mode on the MCP, which will engage the autothrottle and command it to go to the selected thrust limit (in this case takeoff thrust). > > from this point on, the auto throttle should maintain the specified > take-off thrust setting Actually (to go into details), once T/O thrust is reached, the autothrottle will go to "THR HLD" mode and it won't touch the throttles anymore. This is to prevent any thrust reductions due to autothrottle malfunctions during takeoff. So "THR HLD" basically means, that the autothrottle disengages the throttles and goes to armed state until a new mode is selected. > > Note the point here is to use a de-rated take-off EPR to save expensive > engine maintenance, as far as I can remember. When doing a manual take > off, I habitually bang the throttle slider on my joystick (which has a > very ligth feel anyway) right up to the stop. This is bad on all kinds > of levels .. the engine's N1 and EGT regularly go 'red', for example. In the real aircraft there are "Engine Limiters", which prevent such a thing. Firewalling the throttles will give you Max. T/O thrust (=GA thrust) without exceeding any limits (at least for a few minutes) > >> * FLCH is the most common Mode for climb/descents. In this mode the > > Thank you for this description. This is very helpful. > Yeah, I really need to start using it more in Fly! 2 .... it makes a lot > more sense now. I really wish I could find a joystick with a > servo-throttle, since without it a THR HLD mode is rather hard to > simulate. Come to think of, this probably explains why my descents in > Fly! are always way too fast (err ... i.e rate of decent is too > small) ... my throttle is still at some flight setting, so as soon at > the auto-throttle goes from IDLE -> THR HLD, it's going to jump right > back up. Since non-servo throttles are rather more common in the amateur world of flight simulation, the simulations should all simulate the "airbus" way of doing this. On an Airbus, if the autothrottle reduces thrust you have to "catch" the new thrust setting with your throttles to get your manual throttles back. > > One thing I'm noticing ... a modern jet auto[pilot | throttle] really > works better when it has an FMC to talk too :-) Absolutly. We use LNAV and VNAV (FMC Guidance) almost all the time except for final approach. But an FMC is not easy to simulate correctly. On our full flight simulators the FMC is not simulated (wich would be really cheap), instead the real FMC ($$$) hardware is installed. thomas > > H&H > James _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
