Hi everybody, just a quick question regarding the zero fuel weight calculation along with the ZFWCG. Is it just me or does the one the MCDU calculates is off no matter how you load up the aircraft.If this is the case, I know how to get the Zero Fuel Weight, but does anybody know how to calculate the Zero Fuel Weight CG?
Thanks!!!
Why do you think it is off?
I was playing with it the other day and realized that it always is relatively constant because the passengers are usually evenly distributed on the plane. With only 40 people, you end up with 8 people way in the back which would never happen.
I was able to materially change the CG by simply distributing the passengers closer to the front. Also noticed this changes the trim as it should.
It feels off because no matter how much I load the airplane, the ZFW and CG always remain very low for me.
One of my most recent flights was starting for KSNA John Wayne up to CYYC Calgary, Alberta. I usually use simbrief to do the flight planning and all, so I get most of my numbers from there. The numbers I had was a ZFW of 140,351 lbs with a block fuel of 20,880 lbs. Now takeoff weight was at 160,903 lbs with passengers and cargo loaded up. So I input everything in the sim for fuel and cargo. However once all that is done the MCDU does not give me the proper ZFW or CG, and to confirm it, most of my V speeds never change. V1 is always 121, V2 is 122 with Vr being 126.
Unless I am doing something wrong, I feel like they are off. I am on the dev version, and I want to think that there is a bug within the aircraft because there is a note on the known bugs from the FBW team that says “Fuel consumption high, fuel prediction to low” making me think that maybe that is part of why the numbers are off in the MCDU, could be wrong on that theory however.
If you are using the developer version of the A32NX, the MSFS fuel and payload UI have been disabled. If you don’t load the airplane using the MCDU for passengers and the EFB (iPad) for fuel, you will start with about the same weight each time.
Please see https://docs.flybywiresim.com/fbw-a32nx/feature-guides/loading-fuel-weight/ for the correct loading procedure.
Awesome just what I was looking for then. Thank you so much! I have always loaded the fuel through the EFB but the passengers I would do it by the in game UI. I will do that for my next flight then
I think it’s off because it seems to be hardcoded in the W/B system. By default, according to the SimBrief airframe profile, the aircraft is set to have 174 pax maximum, with average weight of 104 kg each. And this is automatically split between passenger weight with their handcarry luggage and 20 kg of checked in baggage. Even if you change this in the airframe profile in SimBrief to let’s say 150 pax maximum and 90 kg average weight each. A32NX seems to ignore this, and instead takes 150 pax, with 104 kg each which includes 20 kg checked-in baggage.
It makes it less flexible, because I prefer to have my own cabin layout to have first class with less pax but more baggage weight in the cargo hold.
So everytime I fly with that configuration, the ZFW and ZFWCG is always off between the OFP brief and the actual weight calculated by A32NX. It can only match if I use a like for like 1:1 SimBrief airframe profile. Which I really don’t like since it fully maximises 3-3 seating configuration for the whole cabin like there’s no ticket classes.
This is correct. If you let your passengers board real time then you see how the CG slowly changes as the boarding starts from the rear seatrows. So if you check the CG halfway the boarding process it is way off!
Exactly that is what did not make sense to me. It was mainly because I always tried to load up the plane via the UI menu as I had no clue that they completely blocked it off and used their W/B in the MCDU so every time I added weight to the aircraft not noticing it did a reset to the original value, I would look at my ZFW and ZFWCG being so low thinking “wait that is not right?” Hopefully we get more flexibility regarding how PAX seat in your aircraft.
We are currently modeling one cabin layout. As I think you probably know, It is not a trivial matter to model other cabin layouts (if you want to do it right). It is not simply reducing the maximum seating capacity. The loading locations for each section of seats in a cabin layout must be specified in order to get the correct cg for a given cabin layout and passenger load. This also affects the operating empty weight of the airplane, which must also be taken into account.
We intend to offer additional loading flexibility in the future, including different passenger/baggage weights, but this also takes coordination with Navigraph in order to allow continued use of Simbrief with the capability. (Simbrief does not currently have the capability to separately specify the per passenger baggage weight.)