Hello,

I just purchased this aircraft and WOW, it was beyond my expectations.

Anyways, I'm having trouble finding out the CG% value on the "TAKEOFF" page of the FMC.  I've tried looking on FS9's Fuel/Load Manager and the ACE but it doesn't show the CG%.

Would anyone care to shed some light on this?

I have FSX and there is no CG% there either. I use 27% as found on the second Takeoff Ref Page. I dont have any problems.

Ok,
I found a neat calculator that should fix your CG Problem.
http://www.eflite.com/software/wb_demos/301/1063/

https://scontent-b-lga.xx.fbcdn.net/hphotos-prn2/1185628_10151868650987764_2082179378_n.jpg

this is the actual 757-200 load sheet in real life, and math is heavily used

you need to know the balance ARM  figures.

Hi, the CG of airliners ( with tapered wings ) is called the CG of MAC
Mean Aerodynamic Chord. factory like Boeing establiswhes a datum line. the pitch axis of the aircraft. Then using a mathematical formula, they define the leading edge of MAC and the trailing edge of MAC of an equivalent straight wing. Then the factory defines a Neutral Point on that chord, They build a safety Margin in front of the NP - 5 to 15% of the MAC chord.
Then the factory establishes the empty weight CG, they also provide CG for various fuel load. - the CG creeps forward as the fuel burns in the wing tanks because of the shape.

The operator is responsible to load the aircraft within the CG of MAC
as established by the factory. i.e. from 12.5 to 35% of MAC

A low static margin from the NP, will make the aircraft tail heavy and susceptible to stall.
To much static margin  will make the aircraft nose heavy, reduces the effectiveness of the stab, and promotes very hard landing with a risk of stall at TO>

The factory provides all her numbers in the flight manual.

Happy flying ;D

Raymond   Boeing or nothing
KFLL  South florida

Dal, if you still want to determine the CG of MAC for your loaded aircraft, follow my guideline, it is pretty easy, you need a little time to do it. The formula is in the internet.  Google " CG of MAC "

First find the chord of MAC for the airplane you are working with.
Use a Boeing graphic to find the lenght of wing panels, position of stab
for calculation. blow up the graphic and scale measure the distances.

Next the datum line, go to the aircraft.cfg find 'ref_datum_position"
the numbers could be 0.0, in such case Microsoft in its definition of the file says 0.0 is equal to the front edge of the leading edge of the wing.
Each weight added sits a a distance from the datum line ( the arm)
watch also the lateral distance to load equal on each side. You could fly with a low wing.
Work the moment of each item.  and including the aircraft empty weight
moment and the distance to the datum. Fuel !
remember that the weight of passenger varies with country of departure and season.
add up all the moments + or minus / total weight of aircraft.
this will give you the CG. Transfer it to the MAC chord and see if you are within the range.
I dont do that !
I rather fly !
This is what I do. take the 57, add your payload. Make the cargo a little light at the back. Take a little over 9000lbs of fuel - your expected landing fuel - the reserve.
Take off and come back to land. In full landing config at the treshold at the proper Vref speed, the attitude of the plane should be 1 or 2 degrees nose up. Your CG is set right. If not, move cargo weight until you get it.
Recently I though my 67 when landing, the nose wheel was coming down a little too quick, I added 300 lbs in my bulk cargo at the back'
Now I get 2 to 3 seconds before the nose come down.

Dal, Happy flying  ;)

Raymond   boeing or nothing
KFLL   South Florida  

It might also be of interest that the airliners' 757 fly with a CG of Mac around 26 or 27. Both AA and Delta fly domestic around these numbers.
The CG is with one decimal like 26.8
The CI is around 56 -60.
Then there is a section of the impact is the CI was 0 or 300.
I cannot speak of International flights - I have none for the 57.

Raymond    Boeing or nothing
KFLL   South Florida

Forget all the calculations concerning center of gravity because the CS752 is not sophisticated enough to recognize any changes. Just use 30 all the time and you will be alright.

Michael Cubine

If you install v-one for the CS757, it will provide spoken v-speeds, spoken flaps, slats and spoilers, and CofG.

Also, the default FSX load manager can provide a CofG % indication (from memory, so do please check: count lines from top down to your present CofG, and divide this by 32, then x100).

I completed an immaculate flight in my CS752 tonight, VNAV and LNAV from start to finish. Brilliant!

DAL191 wrote on Oct 24^th, 2013 at 1:04pm:

Forget all the calculations concerning center of gravity because the CS752 is not sophisticated enough to recognize any changes. Just use 30 all the time and you will be alright.

That's what I do, and it works fine every time. ;) ;D

My friends ! If I read this correctly, you are saying that the weight and balance of the aircraft.cfg is baloney and you overide it in the FMC.

My 757 is reading the aircraft.cfg,  :P  :P  and all my planes.

This is how I tune my airplanes, in the aircraft.cfg.
And they fly great !

Raymond   Boeing or nothing
KFLL   South Florida

Blover wrote on Oct 25^th, 2013 at 2:48am:

My friends ! If I read this correctly, you are saying that the weight and balance of the aircraft.cfg is baloney and you overide it in the FMC. Raymond   Boeing or nothing KFLL   South Florida

Raymond
It is not baloney in the RW but this is not the real world. I don't think I would put 10 or 90 in the CG but 30 will handle it every time.
Michael Cubine

Michael, I just did my test flight from KJAX to KMIA under these conditions.  First I did not touch the payload of my 57, because it is perfect as is.
When I did my preflight in the FMC, I keyed in a CG of 39%
Then I pulled my genuine flight manual to set my stab trim,
at my weight of 160.0 , 39% CG is 2.0. I set it for 25% - roughly where I fly.   at 3.5.  The take off was normal at V2.

In flight my angle of attack was normal- under 2 deg.

I landed on RW 9, in a light crosswing. Vref30 was 118kts. I added 2kts for Vref30  120.

Over the treshold, 2 deg of nose up.  After touch down, a good delay of 3 sec and the nose wheel was lightly down. Like it is always.

The 39% does not do anything except to show the aircraft pop up with a rear CG. The 57 flies with the weight & balance of the aircraft.cfg.
not with the FMC number.

If the 39 was active , my airplane would have taken off at 100kts with a stab trim at 3.5 instead of the required 2.0 at a 39% CG<

It is a game Michael, not RW, but honest CS does a great job.
This little flight now. Real weather. some IFR patches, Miami open but clouds over me. A little turbulence close to the clouds.  Pretty good.
To get the weather, I look out my windows!   :)

Raymond    Boeing or nothing
KFLL   South Florida

Blover wrote on Oct 26^th, 2013 at 2:46am:

I just did my test flight from KJAX to KMIA under these conditions.  First I did not touch the payload of my 57, because it is perfect as is. Raymond    Boeing or nothing KFLL   South Florida

Raymond
What fuel, number of passengers, and cargo weight are you using?
Thank you
Michael Cubine

Michael, you are early on the apron !

Payload is 23,150 - 119 pax and 5300lbs of cargo.
This being a 37 minutes flight, I took on 10500lbs of fuel.
10000, in the wings.

In aircraft.cfg I did my own weight and balance, I load my pax in section.

My CRZ was FL190,  CI 60  distance 279, I also benefited with a northern wind of around 30 - 32kts all the way , GS around 425

My rate of dsc in the GS under 1000 was -600 -700, very stable in landing cfg at Vref30 120  8-) Boeing says to come in over the treshold with 1 or 2 degress nose up. It is my only goal when I tune my CG.

At the end of a flight, I normally land with 9000lbs of fuel after a straight in approach. My reserve. Not in this flight.

Raymond   Boeing or nothing
KFLL   South Florida

To close the subject, let me add a comment.

The first section of every flight plan is called   TPS
Takeoff Performance System.

1. Header is time and date of flight, type of aircraft, assumed weather at time of TO, weight at the gate, TO and fuel on board.

2. Thrust and Vspeed for each rw - up to 5.
this section includes the flap setting, the stab setting, N1, AC on , and maxTO for setting. Also gives the TO CG.- shift back with the pitch. Slat and flap retract speed and min speed maneuverring

3. Then there is an airport analysis, RW lenght, slope, obtructions, considerations for NI setting and flap for each runway.

4. Last there is a summary of the weight and balance - which is supported by the actual load closeout.
Last minute changes, added cargo + or - pax, is given to the crew and the impact on the flight.

Ballast fuel - if present, is part of the payload and cannot be used
The crew must placard the fuel pump for that tank.

Flying these planes is a serious business !! :)

Happy Flying !

Raymond   Boeing or nothing
KFLL   South florida

Good morning pilots, I have been flying the cs757 for about 3 years now, i have my own Simpit i created. https://scontent-a-lga.xx.fbcdn.net/hphotos-ash3/t1/1623728_10152243528507764_282661923_n.jpg


I have taught myself CG load and balance, and have edited the CS757 aircraft.cfg to reflect the load station data of the real 757-200.

Know that the empty cg of a 757-200 is 23%

I will start with the basics on the fundamentals before i go into the actual math involved in determining your planes CG% or %mach can also be called.

All Center of gravity is based upon the starting point which we call DATUM.


DATUM is refered as the starting point of the line which the manufacturer determined for each plane they make, and for the B752 that line starts 159 inches infront of the nose.

You draw that line linear from that point to the start of a small window of balance which we call MAC. which is mostly located at the wings ( center Of plane)


So you start with your Datum and a line is drawn from there to the start of the MAC and measure that distance in inches. , the start of the MAC line we call LEMAC or leading edge MAC. and for the

B752 LEMAC is @ 991.9 inches from the datum. The mac line starts from there and is 199.7 inches long,. we refer MAC as 199.7 inches.

So drawing that line from Datum to the LEMAC point and if you add up the point of LEMAC 991.9 + your mac 199.7 = 1191.6

0% mac is 991.9 inches. where it starts, 100% mac is 1191.6 inches.

Here is a image of what we are talking about, I illustrated where the datum line starts and where lemac is and 0 - 100 % MAC.

https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-frc1/t1/1897682_10152267102412764_1274097834_n.jpg

https://scontent-b-lga.xx.fbcdn.net/hphotos-ash3/t1/1511702_10152267256717764_650951074_n.jpg

Between 0%MAC and 100% MAC is the window of CG we need the plane to be balanced. But that isnt the balance point. Per aircraft each is different based on Weight and

placement of Objects forward and aft of the LEMAC line. For instance, For the B752 The CG window envelope is 7% - 39% CG and that depends on your Gross Weight.

This can be found in the 757 - 200 weight and balance handbook.

Finaly, where the Cg is located within that window is called BALANCE ARM or the distance from CG% to datum. measured in inches.

ARM is measured by balance point when the airplane is at DRY OPERATIING WEIGHT or EMPTY WEIGHT, and changes from aircraft to aircraft because of seating configurations

forward and Aft Lemac. I found out that per the 757-200 my Virtual Airlines Flies is called.  75X PER seating specification that can hold 184 PAX.

The Balance Arm or distance from datum to the EMPTY WEIGHT CG is 1037.8 inches. This is How you determine your planes EMPTY CG%

````````````distance aft of LEMAC
`` cg%mac = ___________________
```````````````````` MAC


Distance aft OF LEMAC is easy to figure out now, if our LEMAC is 991.9 inches and the balance arm is 1038.7 inches. we take 1038.7 -991.9 = 46.8 inches.

````````46.8
CG%=____________ = 23.43%
```````1.997

if you just had your CG% and needed your ARM ( to compute DOI )

~~~~~~~~~~~~~~~~~~%MAC
Balance Arm = LEMAC + ( ----------------× MAC )
~~~~~~~~~~~~~~~~~~ 100

SO

``````````````` 23.43%
ARM = 991.7 + ( ----------------- x MAC ) = 1038.68971 or 1038.7
`````````````````100

Next is Computing the planes Dry Operating Index empty weight.

Formula for this is for the B752

DOI = Weight x (Arm - 1037.8) + 50
````````````````75000

Since balance arm is 1037.8 that zeros out the equation and you add 50. so our DOI is 50.

refer to the actual LOAD SHEET

https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-prn2/t1/1911821_10152267389852764_65201268_n.jpg



and finally go to your aircraft.cfg and go to the following section, copy and paste the new data.
This will give you a fully loaded 184 pax 757 with 9200 cargo . As well as an Empty CG of 23%  to match the 757x

[WEIGHT_AND_BALANCE]
max_gross_weight = 256000 // (pounds)
empty_weight = 127520 // (pounds)
reference_datum_position = 2.3, 0, 0 // (feet) distance from FlightSim Reference position: (1/4 chord, centerline, waterline)
empty_weight_CG_position = 2.5, 0, 0 // (feet) longitudinal, lateral, vertical distance from specified datum

max_number_of_stations =12

station_load.0 ="460, 70, 0, 0, Flight Crew"
station_load.1 ="920, 0, 0, 0, Cabin Crew"
;Moments of Inertia
empty_weight_pitch_MOI = 7040000
empty_weight_roll_MOI = 1960000
empty_weight_yaw_MOI = 7500000
empty_weight_coupled_MOI = 1000
station_load.2=4550, 25, 1, 0, F/C Row 1-7
station_load.3=11900, 14, 1, 0, E/C ECON Row 20-30
station_load.4=9450, -13, 0, 0, ECON Row 31-39
station_load.5=6300, -33, 0, 0, ECON Row 40-45
station_load.6=888, 25, -1, -2, FWD Cargo Bay 1
station_load.7=0, 12, -1, -2, FWD Cargo Bay 2
station_load.8=8318, -12, -1, -2, AFT Cargo Bay 3
station_load.9=0, -25, -1, -2, AFT Cargo Bay 4
station_load.10=1975, 0, 0, 0, OPERATIONAL ITEMS
station_load.11=0, 0, 0, 0, ADDITIONAL WEIGHT

Ok so testing this Mod,
Your ZFW CG % will be 30%
Your TOW CG % is now 29% and using the fmc will give trim value around 5.0 up.

Thank you all for watching any questions please dont hesitate to ask.

DAL191 wrote on Oct 24<sup>th</sup>, 2013 at 1:04pm:

Forget all the calculations concerning center of gravity because the CS752 is not sophisticated enough to recognize any changes. Just use 30 all the time and you will be alright. Michael Cubine

The CS-B752 follows the rules that FSX has defined. If you never change your passenger count, cargo weight or destination, you always end up with the same CG, thus the same everything always.

As a test, change your cargo to the front cargo bays only. Input '30' in the FMS for your CG, set your trim units as suggested. When you rotate, the aircraft will require more stick back and feel sluggish and less responsive.
Setting '30' as Micahael has suggested, will not always work.

I have investigated the CG and weights for 2 months now. I understand more now than I ever though I would.

I have created an Excel spreadsheet that will show CG as well as fuel requirements for the B752.

Don't under estimate this aircraft! It is actually works as it should!

SEAN ZARELLA wrote on Oct 1<sup>st</sup>, 2013 at 9:23pm:

this is the actual 757-200 load sheet in real life, and math is heavily used you need to know the balance ARM  figures.

thanks man helped me a lot.