Aircraft weight and payload question

[Jackpilot]

Problem is that it's empty, just the squares.

B737-800 Steve Reyling is used.

Same for me, I double checked and the CG entry is empty, using 737-700 Opensky and S.Reyling 700.
It is an important data and no pertinent data to figure it.
FS9 fuel and payload window shows where the CG is on a rough little scale.
How to interpret it in % is a mystery to me.

[fweinrebe]

FS9 fuel and payload window shows where the CG is on a rough little scale.
How to interpret it in % is a mystery to me.

That little scale shows you your MAC% although it doesn't say what it is. The more back it is the greater the Mac%. Because it is expressed as a percentage relative to the forward MAC limit. See the glossary item MAC.

And oops the formulae below was mixed up, but I corrected it.

[Jackpilot]

Well, I can follow that...BUT where can I get those numbers (except the gross weight)
for the simulated airplane.
JP

[fweinrebe]

I made a little example, hope it is clear. I can't still figure out where the AFT MAC setting comes from.

From aircraft.cfg:

[WEIGHT_AND_BALANCE]
station_load.0 =  "170.0,     80.0,  -2.0,    0.0, Pilot"                  //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.1 =  "170.0,     80.0,   2.0,    0.0, Co-Pilot"               //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.2 =  "1250.0,    60.0,   0.0,    0.0, Crew"                   //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.3 =  "5200.0 ,   22.0,   0.0,    0.0, First Class"            //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.4 =  "11549.0 ,  11.0,   0.0,    0.0, Business Class"         //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.5 =  "15305.0 , -22.0,   0.0,    0.0, Coach 1-16"             //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.6 =  "15305.0 , -38.5,   0.0,    0.0, Coach 16-29"            //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.7 =  "6000.0 ,   47.0,   0.0,    0.0, Forward Cargo"          //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.8 =  "45000.0 , -67.0,   0.0,    0.0, Aft Cargo"              //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
max_gross_weight = 656000                     // (pounds)
empty_weight     = 314000                      // (pounds)

[airplane_geometry]
wing_root_chord         = 42.0                  //Feet
wing_pos_apex_lon       = 15.0                  //Feet, longitudinal distance from reference point, negative going aft

Now an example using the above weights and arms:

Moment = Weight x Arm

                      Weight (lbs)      Arm (ft)        Moment (Lb*Ft)
Pilot                 170                80             13600
Co-Pilot              170                80             13600
Crew                  1250               60             75000
First Class           5200               22            114400
Business Class        11549              11            127039
Coach 1-16            15305             -22           -336710
Coach 16-29           15305             -38.5         -589242.5
Forward Cargo         6000               47            282000
Aft Cargo             45000             -67          -3015000

TOTAL:                99949                         -3315313.5

PAYLOAD               99949   (PILOTS, CREW, PAX and FREIGHT)
EMPTY WEIGHT         314000   (empty_weight in [WEIGHT_AND_BALANCE])
ZERO FUEL WEIGHT     413949   (PAYLOAD + ZERO FUEL WEIGHT) 
FUEL WEIGHT          250000   (WEIGHT OF THE FUEL)

Here are the data needed to calculate the MAC%:

GROSS WEIGHT 663949 (WEIGHT OF AIRCRAFT BEFORE TAXIING)
TOTAL MOMENT -3315313.5 (MOMEMENT)
AFT MAC LIMIT 42.0 (wing_root_chord in [airplane_geometry])
FWD MAC LIMIT ??.?? (DO NOT KNOW WHERE THIS IS YET ???)

During a search I discovered this Take-Off & Landing Performance Calculation Tool: TopCat. TOPCAT Home page. It calculates the MAC% for you.

[Michael Carter]

That's why they pay dispatchers to do this stuff!

All you need to know is the %MAC from the dispatcher and look up the TO trim setting.

[AchillesP]

Hi to all,

I can tell you how I procced with this problem.

1.) I start at parking position, with changing the payload and the fuel load depending the flight I want.

2.) I configure the flight route to FMC.

3.) At init ref page I inform the weights.

4.) The CG% is always 22 at me. I press the LSK to be reseted and I have only the squares.

5.) I open pmcheckfile and I type the offset 2EF8 8 getting the CG%.

6.) I enter the valve to pm cg% and I get the trim which I configure to aircraft.

With this way, I always can rotare the plane at VRotate speed and not before or after.

* I will build a small program today or later tommorow to read the aircraft weights, the CG% and the trim value. It will be for free. So it will really easy to run this proggram and get the values you want.

[fweinrebe]

Achilles,

thks for that one. That is a great solution.

At least I had lots of fun learning about the MAC% calculations. At least now I can calculate the missing FWD MAC LIMIT if the AFT MAC LIMIT is indeed the same as the wing_root_chord in [airplane_geometry].

Maybe TasKing or you can write a Gauge to show the CG%? That will be really cheating. No dispatchers needed thank you.

[AchillesP]

Ok,

I uploaded a program I made. It is calling payload manager.

Works via fsuipc and wideclient. Reads the data from Fs and also the CG%.

http://www.mycockpit.org/forums/down...do=file&id=310

Options
Aircraft type
Flight number
Tail number
Airline name
Max Gross weight
Basic operating weight
Payload
Zero fuel load
Fuel weight
Total weight
CG%
CG% Fwd
CG$ Aft
Trim indicator as value.
Overload Warning.

If someone have any new ideas to add to this program just post it.

[carlos hermida]

Thanks, any chance to use it with KG ?

[Jackpilot]

Kg.....? what's that...(lol)