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Senin, 14 Juli 2025

Maintenance Practice kelas XII AP, Kompetensi : Aircraft Weight and Balance

 

Aircraft Weight and Balance


Upon Completion of Training, You will be able to : 

1. Understand to determine Empty Weight Center of Gravity (EWCG)
2. Understand A/C Weighing
3. Describe Weighing and Balancing 

The purpose of Weight and Balance control :  

1. Primary is Safety  
2. Secondary is to achieve the efficieny during flight.

- The c.g. (center of gravity) of aircraft must be determined. Aircraft have a tendency to gain weight (accumulation of dirt, greases, etc), for thus reason periodic a/c weighing are desirable; usually weighed when originally certificated or after making major alterations.
- Maximum Weight : The maximum authorized weight of the a/c and all of its equipment as specified in the Type Certificate Data Sheets (TCDS)
- CG : The point at which an Airplane would Balance. Its distance from the reference datum is found by dividing the total moment by the total weight of the airplane.
- Empty Weight : The weight of the airframe. engines, and all items of operating equipment that have fixed locations and are permanently installed in the aircraft.

Theory of Weight and Balance.

The level that is in equilibrium or balance when it rests on the fulcrum in a level position. 


The distance of any object from the fulcrum is called the lever arm, multiplied by the weight of the object is its turning effect about the fulcrum (known as the Moment)
An a/c is balanced if it remains level from an imaginary point; this point is the location of its ideal c.g.


The removal or addition of equipment changes the a/c empty weight and the c.cg the useful load is affected.
- Datum is an imaginary vertical plane from all horizontal measurement for balance purpose, with the a/c in level flight attitude.
There is no fixed rule for the location of the datum, in few cases it is located a certain distance forward of the nose section a/c.

The arm is the horizontal distance, measured in inches exactly in the datum (0).
(+) indicates a distance aft of the datum and (-) minus a distance forward of the datum.
Moment is the product of a weight multiplied by arm.
- The moment of an item about the datum is obtained by multiplying the weight of the item by its horizontal distance from the datum
.

- Maximum weight is the maximum authorized weight of the a/c and its contents, which the a/c is to be flown.
- Empty weight of an a/c includes all operating equipment that has a fixed location and is actually installed in the a/c (weight of the airframe, powerplant, reqiured equipment, optional or special equipment; fixed ballast, hydraulic fluid, and residual fuel and oil). 
- Useful load is determined by subtracting the empty weight from the maximum allowable gross weight (consist of maximum oil, fuel, passengers, baggage, crew member). 
- Empty Weight Center of Gravity (EWCG) is teh c.g. of an a/c in its empty weight condition. 
- EWCG Range is an allowable variation of travel within the c.g. limits.
- Operating Center of Gravity Range is the distance between the forward and rearward c.g. limits (a/c specification or TCDS). 
- Mean Aerodynamic Chord is the mean average chord of the wing.
- The location of the MAC in ralation to the datum is given in teh a/c specification or type certificate data sheet. 

Picture : The location of the MAC 


H : Distance from the datum to the EWCG (170)
X : Distance from the datum to the MAC leading edge (150)
C : Length of MAC (80 inch)

Picture : c.g. in % of MAC

- A/C Leveling Means is a reference points are provided for leveling the a/c on the ground. (Place a spirit level at designated points on the a/c; special leveling scales built in structure with a plumb bob to level the a/c longitudinally and laterally). 
- Zero fuel weight is teh maximum allowable weight of a loaded a/c without fuel.
Weighing Procedure :
1. Drain fuel until indication reads zero or empty.
2. The position of flight control surfaces (zero) : hydraulic reservoirs and systems should be filled, drinking and washing water reservoirs and lavatory tanks should be drained, constant speed drive oil tanks should be filled.
3. All the items included in the certificated empty weight are installed in proper locations.
4. Removed all covers protective and all doors, windows in their normal position (closed).
5. Properly calibrate, zero and use the weighing scales.
6. Level the a/c position if possible, espcecially along the longitudinal axis.











Rebalancing of Control Surfaces. 

Balancing of control surfaces are given in the manufacturer's service and overhaul manuals for the specific a/c. When an a/c is repainted, control surface that is out of balance is unstable and does not remain in a streamlined position during normal flight. Rebalancing a control surface concerns both STATIC and DYNAMIC balance.

STATIC BALANCE
Is the tendency of an object to remain stationary when supported from its own CG.
There are two ways in which a control surface may be out of static balance : Underbalance and Overbalance.


UNDERBALANCE.
When a control surface is mounted on a balance stand, a downward travel of the trailing edge below the horizontal position indicates underbalance. 



These signs show the need for more or less weight in the correct area to achieve a balanced control surface. 
A tail-heavy condition (static underbalance) causes undersirable flight performance and is not usually allowed.


DYNAMIC BALANCE
Is that condition in a rotating body wherein all rotating forces are balanced within themselves so that no vibration is produced while the body is in motion. 


REBALANCING PROCEDURES




REBALANCING PROCEDURES




Rebalancing Methods.
Balancing (rebalancing) control surfaces are in use by the various manufacturers of a/c. The most common are the : 
1. Calculation method,
2. Scale method, and
3. The balance beam method.


1. Calculation Methods.
Advantage over the other methods in that it can be performed without removing the surface from teh a/c. The weight of the material from the repair area and the weight of the materials used to accomplish, Subtract the weight removed from the weight added to get the resulting net gain in the maount added to the surface. 








2. Scale Methods.
The scale method of balancing a control surface requires the use of a scale that is graduated in hundredths of a pound. A support stand and balancing jigs for the surface are also required (requires the removal of the control surface from the a/c).

3. Balance Beam Methods.
This method requires that a specialized tool be locally fabricated. The manufacturer's maintenance manual provides specific instructions and dimensioins to fabricate the tool. Placed on level supports, the weight required to balance the surface is established by moving the sliding weight on the beam. The maintenance manual indicates where the balance point should be. If the surface is found to be out of tolerance, the manual explains where to place weight to bring it into tolerance.

Refernce : 
1. FAA HANDBOOK
2. GMF Aeroasia

NEXT COMPETENCE IS AC HANDLING AND STORAGE ...


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