A340 FE part computed GW and CG
Thread Starter
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
A340 FE part computed GW and CG
FE WEIGHT COMPUTATION (BACKUP)
‐ When the aircraft is below 14 625 ft, and 255 kt :
GW = f(α, CAS, N1/EPR actual, CG from FE part, altitude)
‐ When the aircraft is above 14 625 ft, or 255 kt :
GW = TOGW – WFU
TOGW : Takeoff Gross Weight
WFU : Weight Fuel Used, acquired from the FADECs.
FE CENTER OF GRAVITY COMPUTATION (BACKUP/AFT CG WARNING)
The CG is computed from the position of the horizontal stabilizer, and is function of the N1/EPR,
Vc, ALT, MACH and GW from FE part.
‐ When the aircraft is below 14 625 ft, and 255 kt :
GW = f(α, CAS, N1/EPR actual, CG from FE part, altitude)
‐ When the aircraft is above 14 625 ft, or 255 kt :
GW = TOGW – WFU
TOGW : Takeoff Gross Weight
WFU : Weight Fuel Used, acquired from the FADECs.
FE CENTER OF GRAVITY COMPUTATION (BACKUP/AFT CG WARNING)
The CG is computed from the position of the horizontal stabilizer, and is function of the N1/EPR,
Vc, ALT, MACH and GW from FE part.
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
One of several ways to do it is by a process called 'iteration':
Step 1: Assume a CG position
Step 2: Compute Gross Weight
Step 3: Compute the horizontal stabilizer position for the computed GW and assumed CG
Step 4: Compare the computed to the actual position of the horizontal stabilizer.
- If the difference is less than a certain tolerance go to step 5, else -
- adjust assumed cg position and repeat steps 2, 3 and 4.
Step 5: Output GW and CG
Another method is interpolation:
Step 1: Compute GW and THS position for the CG on the forward limit
Step 2: Compute GW and THS position for the CG on the aft limit
Step 3: Interpolate GW and CG for the actual THS position
Step 1: Assume a CG position
Step 2: Compute Gross Weight
Step 3: Compute the horizontal stabilizer position for the computed GW and assumed CG
Step 4: Compare the computed to the actual position of the horizontal stabilizer.
- If the difference is less than a certain tolerance go to step 5, else -
- adjust assumed cg position and repeat steps 2, 3 and 4.
Step 5: Output GW and CG
Another method is interpolation:
Step 1: Compute GW and THS position for the CG on the forward limit
Step 2: Compute GW and THS position for the CG on the aft limit
Step 3: Interpolate GW and CG for the actual THS position
Last edited by HazelNuts39; 22nd Jun 2012 at 10:40. Reason: 2nd method
Join Date: Jan 2006
Location: Sussex, UK
Posts: 55
Likes: 0
Received 0 Likes
on
0 Posts
Omlette, anyone?
Don't forget you're not starting from a null value, during the pre-flight one enters ZWF/ZFCG, the FCMC uses the fuel load and the input value to spit out an initial value for the FG/FM to work with.
Once you've got a starting value then the boxes can apply their magic to get a value out of what the aircraft is doing aerodynamically, as described above.
Once you've got a starting value then the boxes can apply their magic to get a value out of what the aircraft is doing aerodynamically, as described above.
