Zero Fuel Weight moment

[FSXstudent]

hi pilots,

Can someone tell me why zero fuel weight moment is being computed for each flight. ZFW I get it, its there to protect wing root twisting or so... but moment....???? is it to check that front wheel weight is within limits on the ground or what ? :rolleyes:

[mutt]

If you dont have it, how are you going to calculate your takeoff CG?

Mutt

[Speedbird0390]

ZFW will give you the weight of the aircraft with no fuel. From here, you then add your, reserves, flight fuel etc to get your TOW. Then you can subtract your Flight fuel to find your LW.

[FSXstudent]

Matt,

Of course you don't need zfw to compute t/o weight. Good example is any small aircraft which has no such zfw requirement yet t/o weight and moment is easily obtained. Now, once again all I want to know is what is the significance of zero fuel moment. At no point will the plane fly without fuel so what if moment comes up outside of the envelope ?

[Meikleour]

FSXstudent:the ZFW moment is the starting point about which the loaded fuel moment is applied to derive the take-off index which in turn relates to stabiliser trim setting and also to confirm that the aircraft is loaded within it's certified limits.

[mutt]

Of course you don't need zfw to compute t/o weight. OK, you might not need it in a Cessna 172, but with longer aircraft cabins with multiple loading configurations, what starting point would you suggest we use to calculate takeoff CG?

For the aircraft that i fly, if the ZFW CG is within limits, then you cannot put it out of limits by adding fuel. So for us the ZFW, Moment and CG is extremely important.

Mutt

[Kennytheking]

FSXstudent,

mutt is correct when he says it is a starting point for the final calculations. Remember that you never know how much fuel you will be landing with, whilst it is unlikely(but has happened) that you will land with no fuel, it is not uncommon for a 570 ton A380 to land with 7 tons of fuel. Therefore, it is imperative that the GC be within range for any and all fuel states, including empty.

There are further factors, such as ZFW & ZFWCG comes from load control and has very little to do with the pilots......I don't load the plane.....I just need to know what the end result is. In the same vein, load control don't want to be bothered about how the fuel is loaded.....they simply want a range to keep the CG within so they can get on with their job.

If we divert, it is easy to calculate the TO CG as the ZFWCG is unchanged(although one could argue that some of the catering has shifted to the toilets).

[minigundiplomat]

If you don't calculate or plot your ZFW, how do you know you haven't exceeded the parmeters of the data manual?

In 99% of cases it is going to be fine, but calculating it and plotting it helps avoid the 1% of times when it is exceeded.

[Vittorio.Perotti]

Apparently there is some misunderstanding in the interpretation of MZFW and ZFW : in fact MZFW is a certified weight, and basically is a weight that cannot be exceeded by nothing else than fuel.

ZFW is not a certified weight ; it can be translated as something as ‘dry weight’ or ‘equipped weight’ and is just the weight of a/c, baggages, pilot and passengers but with empty tanks … just before filling it with fuel.

Therefore, you need to know the ZFW in order to know the TOW (which is the ‘loaded weight’ ) , and to verify if it is below the MTOW (which is a ‘certified’ weight) – just add the weigth of the fuel to the ZFW.

Before filling the a/c with fuel, you need as well to know the ‘dry aircraft ’ CG position (in other words: the ‘dry aircraft’ moment) so that, adding fuel, you will be able to verify that the TO CG position (or ‘moment’) is inside the TO GC (or moment) envelope.

Most of the small general aviation aircraft do not have a MZFW - it means that you can mix whatever combination of fuel, pilots and baggages until you remain below the MTOW and inside the TO CG envelope.
Vittorio

[Tinstaafl]

If you don't know ZFW moment, how do you know that when you're forced to use those last few kilograms of fuel, that the aircraft will still be within CG limits? Sure we *plan* not to use every last drop, but every drop is there in case it's needed. You're wrong to say that we never, or will never, use that fuel. Remember the Gimli glider? Or the Azores glider?

[Tinstaafl]

I should add that fuel-as-ballast is an exception to what I wrote above. It's not really 'fuel' for the purpose (ie there for burning) but just another type of ballast. Theoretically you could pour lead fishing weights into the fuel tank to achieve the same effect but, of course, that's not practical. I've used fuel as ballast too. Damn glad I had when I happened to get ramped by CASA one day and was given a 'please explain' about the plane's CG being outside the envelope at ZFW. Wasn't far out, but that was the point of the ballast fuel.