744 Cruise Phase - Loss of Airspeed/Altitude

[opherben 0]

Hello Darren,aircraft performance at the end of the day boils down to weight, thrust, aerodynamics, atmosphere. Regarding acceleration, a good indicator would be thrust to weight ratio. At spec takeoff std day, for your A320 I figured twice 50,000 Lb thrust and 215,775 weight, T/W is 0.232, and for B744, median engine, 62,100 times 4, weight 875,000 Lb, T/W is 0.284, namely ~20% difference. Also please note that climb and cruise mach is the same for the B744, meaning drag characteristics there are good.If any flight circumstance resulted in a sudden loss of 30-40 KIAS, that aircraft would not pass certification. Did that for a living.>HI Opher>I would not be so sure about the excess thrust at crz power.>On the A320 if we are climbing at max weight to say 36000' it>will take at least 3 mins to go from .76 to around .79 level>at 36000.>The amount of excess thrust is small and the window for speed>control small also.>The 76 is a pretty highly powered aeroplane and imagine its>pretty good.>Any 400 drivers around to talk about the aeroplane accel>ability at crz thrust but given it is only at crz rating>wouldnt imagine it to be to high?>Especially if you let the speed bleed back by 30-40 kts.>Darren

[Guest Darren Howie]

I guess one thing we dont have to worry about in the real world though are 40kt swings in wind speed at high alt unlike FS9.I think that is the primary cause of the problem.You have real life performance specs with unreal wind changes.Speed fluctuations at altitude of as little as 5 kts give enough turbulence to require seating of cabin crew.So god knows what a swing of 40kts would be like!!!CheersDarren

[opherben 0]

Concur, assuming you meant God.

[jeffhunter 0]

:-erks

[Chaos81 110]

>Concur, assuming you meant God.And what if he didn't?

[opherben 0]

Then I do not concur.>>Concur, assuming you meant God.>>And what if he didn't?

[B777ER 2,486]

I have tried two flights from JFK to EHAM and both ended about an hour later with stalls and crashes. The FP was set correctly like I have done numerous other times with the 744 of PMDG. LNAV and VNAV set and weights were within operating limits. Was at the recommended altitude of FL350. ASV was running and I monitored NO significant wind shifts. Air temp remained steady at -20C. I have done these routes many times and the only change has been the update to the 744. PMDG needs to look at this and suddenly people are crashing and stalling useing the same bloody programs as before with the only change being the update.

[B777ER 2,486]

Could PMDG comment on this problem. I know I just suddenly did not become an idiot unable to fly the plane or did I?

[Guest Stanner1953]

Gentlemen;After reading all of the posts I think I have a solution. It seems you are experiencing a weight/altitude problem. In heavy aircraft you must burn of a specific amount of fuel weight before attempting to go to the next altitude. Depending on the payload weight, this can take a long time. If you do not do this, you will encounter problems at the higher altitudes, since the nose of the plane will continue to pitch up to counter the loss of speed. When the pitch reaches a certain angle, you will lose control of the aircraft.Try climbing slowly, say at 1200 fpm and leveling off at various altitudes to burn off some fuel before trying to go to the next altitude. I have had this problem with the default B777 and the default B747. I then read the solution in the PC Aviator magazine.Stanner

[opherben 0]

Your suggestion is not in line with proper aircraft operation. Instead of using Aspirin to cure cancer pain, aircraft characteristics should be set to more closely reflect the real thing. BTW I have not noticed this item on the SP list, but to me it seems that there now are better excess thrust and fuel consumption.>Gentlemen;>After reading all of the posts I think I have a solution. It>seems you are experiencing a weight/altitude problem. In>heavy aircraft you must burn of a specific amount of fuel>weight before attempting to go to the next altitude. >Depending on the payload weight, this can take a long time. >If you do not do this, you will encounter problems at the>higher altitudes, since the nose of the plane will continue to>pitch up to counter the loss of speed. When the pitch reaches>a certain angle, you will lose control of the aircraft.>>Try climbing slowly, say at 1200 fpm and leveling off at>various altitudes to burn off some fuel before trying to go to>the next altitude. >>I have had this problem with the default B777 and the default>B747. I then read the solution in the PC Aviator magazine.>>Stanner

[Guest hankaaron]

>HiI have also experienced this problem. But I have two exceptions to your case:1. I do not have active sky installed.2. Problem only occurs when using 15 minute update in FS9 option.I notice that FS9 does not include actual winds aloft data from "Live Weather" option. But it could be that during one of the updates, dummy/corrupt wind data is temporarily imported into the flight model. I noticed how wind data went haywire after manually entering wind aloft and then going back to 15 minute update. The FMC in the Queen did not handle this transistion well (you can duplicate this by manually setting a value for wind intensity and heading. The FMC will reflect the manual setting fairly well. But when check the option to go back to 15 min update, the FMC not settle immediately back to zero and the aircraft will react negatively).hankaaron.>>I have searched though the forum and come accross a couple of>instances where my query was raised previously but I was>hoping someone might be able to update me on the latest advice>re a solution.>>I absolutely love the PMDG 744 and it is now firmly>established as my aircaft of choice however whenever I attempt>a long haul route - usually, but not always over an ocean ->1/3 to 1/2 way through the flight the aircraft will start to>gradually bleed airspeed. After a short while when the IAS>has reduced below something like 190 knots I start losing>altitude and then get into an almost irrecoverable nose high>attitude.>>I am using ASVE and having looked on their forum have>unchecked all VAS options as suggested but I am still having>the same problem with every flight I try to make.>>I really hope someone can help as the problem is ruining my>enjoyment of which, in all other regards, is a super add-on.>>Thanks>Graeme