Center of Gravity calculated by Fuel Planner is illogic

[AMJBecker 0]

I am trying to understand, how the Fuel Planner calculates the Center of Gravity.

Comparing the COG calculated by the Fuel Planner for an empty aircraft, i.e. ZFW = BOW, which results in %MAC of 27,2%, with the COG for the full amount of passengers, but no cargo and no fuel, resulting in %MAC of 21,9%, I'm getting confused. A lower %MAC means that the more passengers are on board, the more forward is the CG. I would expect the contrary, because there are more seats behind the 25% MAC line than before that line, isn't it?

See the following screenshots

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Other Load and Trim Sheets, as can be found in the Airbus Flight Crew Operation Manual, Part 2, Chapter 1.40, also suggest a shift of the COG towards the back with a growing number of PAX.

[DaveCT2003 2553]

8 minutes ago, AMJBecker said:

I am trying to understand, how the Fuel Planner calculates the Center of Gravity.

Comparing the COG calculated by the Fuel Planner for an empty aircraft, i.e. ZFW = BOW, which results in %MAC of 27,2%, with the COG for the full amount of passengers, but no cargo and no fuel, resulting in %MAC of 21,9%, I'm getting confused. A lower %MAC means that the more passengers are on board, the more forward is the CG. I would expect the contrary, because there are more seats behind the 25% MAC line than before that line, isn't it?

See the following screenshots

 

 

 

 

I believe the answer is the Inner Trim tank... and how we set that value internal in the code when you move the CoG.

 

https://images.app.goo.gl/eSoc3qoNoVhar5tR9

[AMJBecker 0]

I am not yet familiar with the A330. But does the A319 also have such a trim tank?

[DaveCT2003 2553]

11 minutes ago, AMJBecker said:

I am not yet familiar with the A330. But does the A319 also have such a trim tank?

 

Ah, okay, sorry.  You didn't specify which of our 8 aircraft you were asking about, and I assumed it was the A330 because of it being A330 Release day!

 

Part of the problem here maybe that you don't have our most up to date Fuel Planner, which was delivered with the A330 today and will soon (hopefully late next week) be delivered to you via the A318/A319 update we're working on.

 

That said... the other part of the problem is that you can't adjust Trim on an empty aircraft (ours or real world), at least without manually adding ballast to the actual aircraft.   Without PAX, Cargo, Fuel (to a limited extent on the A319) or ballast, the aircraft weight distribution and therefore trim is static.  When I do this in the updated Fuel planner, nothing changes, which is how it should be.

 

I hope I understood and answered your question my friend.  Please let me know.

 

 

[AMJBecker 0]

Another example, where I cannot find an explanation: looking at the index units for fuel in the Airbus Load and Trim Sheet, they are all negative and for a high fuel amount growing substantially, meaning that the COG is expected to move forward. But the Fuel Planner shows an increasing %MAC for high amounts of fuel. See following screenshot:

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[AMJBecker 0]

Oh, good news! The one for the A330 release, I mean. I'm very excited!

 

I will continue my understanding work with the new Fuel Planner. I'll see. Thanks Dave

[masterhawk 799]

The CG positions of the A32S series is Buggy.

It’s one of the items I want to correct myself since long time.

But currently I had my focus on A330 development.