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Joe L

Cruise Speeds - 0.81 mach overspeed?

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Cruising on LNAV / VNAV at 34000, 200k lbs gross weight. STD temps (-52 deg SAT). The Delta PW overwing exits 757-200.Cruise is set at 0.80 in the CDU/FMC. On a planned RTE.Barber pole and red line on the speed tape occurs at about 0.81 mach. Your manual lists mmo at 0.84 mach (other non sim 757 sites list 0.86 BTW)This makes a std 0.80 cruise look as if right at the red line.Furthermore, I go to SPD | ALT HOLD | LNAV |CMD and enter 0.82 mach just to see what happens, overspeed warnings etc. AC will not exceed 0.806 mach no matter what (going on 15 minutes with no accel).EICAS shows CRZ, Reference/Target EPR green carrot and MAXIMUM EPR amberline show 1.52, but engines / EPR Pointer will not go above 1.41.If I go back into VNAV and select enter and exec 0.82 as my speed it reflects in the ADI Speed tape (although well over the red line), but magneta TARGET EPR stays at 1.41, and again, no acceleration at all. Selecting a lower speed will result in deceleration.Shouldn't 0.82 mach in these conditions be attainable?Joe Lorenc

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noted and added to the list to be looked at.Has anyone else experienced this?

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Steven please Skype me and look for BUG 463 in the bug traker.Cyrille de LattreAsus P4P800/PIV 3 Ghz/2 Giga DDRAMATI X800 GT 256 MegWin XP SP2 / FS9.1 PSS Beta tester

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Although, Joe, could you confirm this is with the new interim fix, or the release set? Cyrille de LattreAsus P4P800/PIV 3 Ghz/2 Giga DDRAMATI X800 GT 256 MegWin XP SP2 / FS9.1 PSS Beta tester

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QUOTE:Although, Joe, could you confirm this is with the new interim fix, or the release set?This was with the interim fix downloaded about 10 or so hours ago.Thx for the rapid looks.Joe Lorenc

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Yep, i saw this last night on my KEWR-KORD run with the updated installer. Still a very pleasant flight :)-Paul

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hello folks,yup, got the same problem. At FL350 can only still cruise at M.78. Higher than M.79 or so, is overspeed... But i

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Great picture!:-)The graphics quality is superb. I think this should please the majority of users.Unfortunately for the "systems purists", RR engine data shown in the picture is very inaccurate for that flight condition.:-(..anyway I guess this won't be a concern for most users as well.Tom

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>Great picture!:-)>>The graphics quality is superb. I think this should please the>majority of users.>Unfortunately for the "systems purists", RR engine data shown>in the picture is very inaccurate for that flight>condition.:-(..anyway I guess this won't be a concern for most>users as well.>>Tom>*screenshots are like 800-1mb in size*Hi Tom!I may be doing something wrong in that screenshot, as I just simmed it up to altitude, and here is another that I didn't just sim on up, the MFDs are set the way they are to be similar to ATA Airlines 757s. I'm just messing around with the airplanes, and not using any checklists, manuals etc, just the common knowledge one has from using the PSS/PMDG/Dreamfleet Big Boeings.http://img371.imageshack.us/img371/5989/b752panelcw4.jpgPaul

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>Great picture!:-)>>The graphics quality is superb. I think this should please the>majority of users.>Unfortunately for the "systems purists", RR engine data shown>in the picture is very inaccurate for that flight>condition.:-(..anyway I guess this won't be a concern for most>users as well.>>Tom>I'm curious to know how the data is inaccurate for that flight condition. Not being a trained engineer or trained pilot I can't tell from a glance whether engine parameters are correct or not, but if they aren't that could well be a bug that needs reporting.

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Paul,Still most engine numbers are not correct...I can give you the right figures if you want. As an example, N3 value is right out of bounds...and N2/N3 digital values do not show decimal places in the real bird.Tom

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Well, after being modelling the RB211 535E4 for 8 months, I think I know a bit about what are the proper numbers for different flight conditions..:-) As for being a bug, I wouldn't call it so, just something that visually is not as real as it gets, but that probably wouldn't affect the flight conditions.Tom

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TomI'm not an engineer either - but I have several thousand hours on RR engines on a very different aircraft [similar 2 engines but max M=1.?]. - So purely for my interest, very grateful if you could summarise what the various relationships should be in an aircraft such as the 757 in the cruise.Best WishesJohn Rooum

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John,My pleasure:-)Just to avoid boring people I'll give you some rough numbers for "standard" cruise values from 35 to 39 k feet.M80, for the RR211 535E4 :EEC EPR limit (amber bug) - 1.79 (two engines on)EPR CRZ (green bug and digits) - 1.75Nominal EPR range (white pointer and digits) around 1.60-1.65, but can vary depending on winds.N1 - 84.5 to 87.5EGT - 530-600 (with strong tailwinds could be 650+)N2 - 76-83 N3 - 79-84FFlow 1.6 ton = 3.52 k pounds Regards,Tom

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Seems to be an issue even with the final release version. I can't exceed 0.807 mach at FL330. Can anybody confirm?Rainer

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Tom,How are winds going to affect cruise engine performance? The aircraft is flying along relative to a moving body of air. For a given flight condition (mach, altitude, TAT) the engine performance will be the same, regardless of wind. Wind only affects ground speed and track.Kevin

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Kevin,I was refering to nominal EPR cruise values, average M80 and ground speed of aprox 460 knots, for an aircraft weighting 190-210 K lbs. Headwinds would require a bit of higher EPR to maintain ground speed, and vice versa.Tom

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Tom,No, when you cruise you maintain a Mach number, not a ground speed. All the performance charts and the FMC are set up that way. Tail wind will not affect EGT either, apart from on the ground during an engine start.Kevin

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I'm getting the same thing. This needs to to be fixed. The plane should be able to acheive the VMo of .86M at FL350 at standard day temp. One more thing to ask....where is the ILS tuner that is supposed to be on the center pedestal just aft of the throttles? Do you have the normal NAV1 radio programmed to accept ILS localizer frequencies? In the real plane the ILS frequency and inbound course is set in a receiver that is on the center pedestal. Just curious. Execellent aircraft.

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Kevin,""No, when you cruise you maintain a Mach number, not a ground speed.""Of course, but as a result of the need to follow a flight plan.Airliners use Cost Index calcs for each flight phase (clb,crz,etc). One of the vars employed is time of flight, which depends totally on ground speed, which is affected by winds. The FMC computer determines the best Mach needed at any time to comply with the CI entered, and command the engines towards that number, BUT as a consequence, not a cause. What is primary important is Time of flight (=ground speed) and Fuel flow supervision (among others). ""Tail wind will not affect EGT either, apart from on the ground during an engine start.""This is something that you won't find in the books for sure :-)Tom

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Seeing overspeed above .810 with the "Final" release here also.Steve Park

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I have fixed this myself just by changing the max_mach to 0.86 under Reference Speeds in the aircraft.cfg files. Once done everything seems fine.I have not updated to the latest version, yet, but it seems from what others have said it was still not fixed.Joe Lorenc

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