Hi chaps!

 

There is probably a very simple explanation for this, but when I was setting up the startup functions for the PMDG737ngx 800 earlier I realised that if I set the passenger numbers to zero, cargo to zero and fuel to zero, the FMC displayed the ZFW as 45.8 (45,800 lbs). To me this would represent the all-up weight of the aircraft itself with no fuel and no payload. However I noticed that the gross weight was shown as 91.3 (91,300 lbs).

 

I must have missed something so can someone please explain it to me?  I cannot see why there is a difference between zero fuel weight and gross weight, when there is no fuel loaded and no payload.

 

Cheers all.

 

Dennis

 

 

ZFW is a limit, a fixed value.  It is the max weight allowed after adding the empty weight and the payload.

I think I have figured out your issue. The max fuel a 737-800 can take is 20891Kgs, and this is around 46000lbs. Do you by any chance have the "Unlimited Fuel" option selected within FSX? If you do then it may have kept the weight at full fuel, giving you your 45000lbs ZFW, but a 91000lbs GW.

 

-Alexander

Just so everyone is clear on the terms...

 

ZFW= Zero fuel weight. It's not a fixed value, it represents the aircraft DOW + payload.

 

DOW= Dry operating weight, akin to gross weight of airplane with nothing in it. This is a fixed number.

 

MZFW= Max ZFW, this is also a fixed number based on aircraft payload capability.

 

MTOW=Max Take Off Weight, fixed number based on aircraft performance limits. All weights including payload and fuel are considered.

 

MLW= Max Landing weight, fixed number based on aircraft performance

 

 

737-800 weights are as follows, via TOPCAT

 

DOW 91,7400 lb

MZFW 136,000 lb

MTOW 174200 lb

MLW 146300 lb

 

ZFW is variable, but can be no less than DOW and no greater than MZFW. If your numbers show anything else, there is something wrong or you are looking at one number in kilograms. 

Guys, thanks very much for your replies.

 

Alex, your explanation seems very reasonable.  Could you tell me how to check in FSX how to get to 'unlimited fuel' to change that, please?

 

Cheers,

 

Dennis

Sorted!!!

 

 

Thanks to Alexander. Just went to aircraft - realism settings - check 'unlimited fuel' and it all made sense. Thats one problem out of the way, Cheers!

 

Dennis