FMS speed and fuel calculations

[Guest zth]

Could a PMDG developer please provide support and respond to the above questions, it would be highly appreciated. Thanks in advance.Regards,Zoltan Hegedus

[CF104 0]

Hello Zoltan,I can't help with 1 or 2 but in regards to the GEN OFF BUS, they work as the real 737 does. The lights only tell what position the gen. breaker is in through relaxed contacts in the GB. It doesn't matter if the engine is running or not. I believe that tripping the GCU as well as a Gen. fault will remove power from the relaxed contacts of the GB and turn off the light. I'm doing this from memory without the benefit of my manuals (at home now) so if anyone has differing info, please post.Cheers,JohnBoeing 727/737 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[Guest zth]

Hello John,Thanks for the information: I'm definitely going to look into this more thoroughly, as I have always known the lights to function identically as the APU GEN OFF BUS lights do (their simulated operation is "correct" in this sense): when the APU is available to supply power, the lights illuminate and indicate the gen drive can be brought online: otherwise the lights are extingiushed. I can only recall seeing similar operation of the engine gen off bus lights as per this sequence, thus AFAIK they should be extinguished if the generator drives are not available to supply power (which doesn't happen), but then again I may be wrong so I'm definitely going to run through the 737 training material one more time to see what I can find: I take if from your post that this operation is modeled correctly, so if I'm wrong please forgive my continued explanation: it is because I have always known that the lights should extinguish when the source is not available.Thanks alot for your insights, much appreciated.Greetings,Zoltan

[Qavion 19]

"The blue GEN OFF Bus Light comes on when the engine generator control breaker (GCB) is open. The power for the GEN OFF BUS light #2 comes from the DC Bus 2. The GEN OFF BUS light #1 gets power from the DC Bus 1. Power also comes from the battery bus when the master dim/test switch is in the BRT postion. The light gets a ground through the auxiliary contacts of its generator control breaker. The light goes off when the GCB closes."It's basically a light switch circuit. Power (Master Dim/Test) + switch (GCB contacts) + light (GEN OFF BUS) ;-)Cheers.Ian.

[Guest zth]

Hello all,Since SU2, I've continuesly run into several small issues when using the PMDG 737 NG, and I'd like to clear them up. So let's get started:#1: Fuel calculation done by the FMS. During my flights, I plan with a reserve fuel of approx. 2000 kg, which includes holding and alternate fuel as well. Upon completing preflight in the CDU, I find that the display shows a predicted fuel amount at destination to be 1-1.2 t less than the planned (and actual) amount (e.g. 900 kg), and this initiates the INSUFFICIENT FUEL message to appear. Once airborne - following the vertical profile planned and entered in the FMC prior to flight - the FMC will correctly display the estimated fuel at the destination, and this value is rather precise. What is causing the strange deviation from correct calculation during preflight? (perhaps the prediction of taxi fuel before takeoff?)#1: 737-700 FMC takeoff speed calculations. We had a discussion about this prior to SU2 release, and the developers acknowledged the problem for updating. I am running SU3, and on every flight with the -700 model, I am consistently getting low calculations for v1 and vR speeds: v2 speeds are usually correct on the other hand. The reference I am comparing the data to is the actual QRH of a -700 aircraft, and so I am wondering what might be causing the offset? Is this a limitation of the flight model? The offset of the v1 and vR speeds is usually about 5-6 kts. #3: ENG GEN OFF BUS lights. I seem to recall some discussion about the Generator OFF BUS lights recently, but not in regard to my problem. I reported this way before SU1, but it was never really acknowledged, or confirmed AFAIK. The problem is that even when the engines are off, their respective GEN OFF BUS lights remain illuminated. It looks strange with engines off, that the ENG GEN OFF BUS lights are illuminated as if they were available but offline, yet the engines are off, along with their respective generator drives. Could this problem be fixed? Or is there an explanation to this behaviour that would prove it is correct?Let me just pressure again that these are REALLY small issues, and I am wondering if they are issues at all, or it's just my incorrect understanding of some items. So any enlightening or feedback would be greatly appreciated!Best wishes,Zoltan Hegedus