LECTURE 4BALANCE, STABILITY AND

CENTRE OF GRAVITY

MASS AND BALANCE

BALANCESTABILITY

CENTRE OF

GRAVITY

WEIGHT

INTRODUCTION : RELATIONSHIP

INTRODUCTIONAs weight change, it affect the aircraft stability and balance.

Stability is the condition of being stable.

Balance refer to the location of centre of gravity (CG).

If we can’t guarantee the aircraft stability and balance, we’ll have trouble to operate the aircraft.

THEORY OF LEVERTo balance the lever, the weight must

be distributed so that the turning effect is the same on one side of the fulcrum.

Balance

Refer to CG

Important for Aircraft

Stability Ensure Flight safety

1. What is CG?2. How important CG is?3. Where is CG location?4. When aircraft CG

move away?5. Who can control CG?

4H 1W CREATION

The center of gravity is a point at which an airplane would balance if it were suspended at that point.

WHAT IS CG?

How to Balance Aircraft?

CG LocationLateral

(From A/c front view)

Longitudinal(From A/c side

view)

Figure:Aircraft

Axis

CG LocationThe prime concern of airplane balancing is

the fore and aft location of the CG along the longitudinal axis.

1. Where is Fore?

2. Where is aft?

Draw on note!

CG LocationLocation of the CG with reference to the

lateral axis is also important.

Center of gravity

CG Location ShiftedLateral balance is relatively easy to

control and longitudinal balance is more critical.

The center of gravity is not necessarily a fixed point.a) Location depends on the distribution of

weight.b) As variable load items are shifted or

expended, there is a resultant shift in CG location.

EXAMPLE

• As we move, CG also move. • Still remember what is CG?

• How can you relate with aircraft situation?IN 5 MINUTES, I WANT EACH OF YOU

TO GIVE EXAMPLE OF CG WHICH CAN BE RELATED WITH AIRCRAFT

SITIUATION / CONDITION.

INDIVIDUAL TASK : CLASS

What are the variables that can affect weight and CG?

Luggage Fuel

Instrument

Passenger

& CrewAffect Lateral CG

Affect Longitudinal CG

CG Importance

• As the results, CG location shifted (move).• Thus, thus the A/C have will pitch up.• Can cause the A/C stall.

CG Importance

• This cause the A/c lose lateral balance.• One side of the wing is much more heavy.• This cause difficulties for pilot to control.• This unbalance create aircraft instability

Continue. . . The pilot should realize that if the CG of

an airplane is displaced too far forward on the longitudinal axis, a nose-heavy condition will result.

Conversely, if the CG is displaced too far aft on the longitudinal axis, a tail-heavy condition will result.

It is possible that an unfavorable location of the CG could produce such an unstable condition that the pilot could not control the airplane.

Forward Center of Gravity

Nose become Heavy – Problems controlling and raising the

nose – Inability to flare for landing

Acts as more weight – More stable ( base on basic

principle. The more the weight, the more stable an object)

– Decreased PerformanceHigher stall speeds

Aft Center of GravityTail become Heavy

– Light control forces– Easy to over-control and overstress

Reduced capability to recover from stalls and spins– Can not lower nose– Flat spin: nearly impossible to recover

Decreased stability– Difficult to right itself after

maneuvering/turbulence

WHO CAN CONTROL CG?

PILOTGROUND

TECHNICIAN

• Ensure Luggage weight• Calculate Luggage loading• Monitor fuel weight

• Ensure Luggage weight• Communicate with Pilot

Terminology & Definition

Terminology & Definition Datum Imaginary vertical plane or line from which

all measurements of arm are taken. Established by manufacturer. Everything (moment arms, CG range) measured from this point.

Arm The distance from the datum to any

component part of the airplane, or any object loaded on the airplane. (+) denotes aft of datum, (-) denotes forward of datum

Terminology & Definition Station Location in the airplane identified by a number

designating its distance in inches from the datum.Moment Product of the weight of an item multiplied by its

arm.

Moment = Weight (Load) x Arm Distance

Exercise 1 : Calculate Moments

Exercise 2 : Calculate Moments

Exercise 3 : Calculate moments

After receiving your Private Pilot Certificate, you decide to

take your family on sight-seeing flight around Grand Forks.

If your mom weighs 150 lbs and sits it the co-pilot seat, your

dad is 200 lbs, your sister is 115lbs and you weigh 130 lbs:

How much fuel can you bring? Calculate moments.

Given: MZFW = 800lbsMTOW = 775lbsMLW = 1090 lbs