Lesson 14: Weight And Balance

Importance Of Weight And Balance

• Forward CG

• Increases tail down force which increases effective weight (real weight + tail down force)

• All parameters of aircraft performance will decrease except maximum power off glide distance.

Importance Of Weight And Balance

• Forward CG

• Take off and landing distance and stall speed will increase, cruising speed and rate of climb will decrease.

• Control pressures for pitch changes will be greater.

• Pitch trim nose up

• Most dangerous part of flight with forward CG is landing (ground effect).

Importance Of Weight And Balance

• Aft CG

• Decreases the need for tail down force so effective weight is less.

• Control changes for pitch changes will be light.

• Pitch stability will be poor.

• Stall speed decreases.

Importance Of Weight And Balance

• Aft CG

• All performance parameters improve, except maximum power off glide distance.

• Most dangerous part of flight with aft CG occurs in slow flight (stall/spin may lead to flat spin).

Importance Of Weight And Balance

• Who has the final responsibility for accurate, up-to-date aircraft empty weight and Balance?

Importance Of Weight And Balance

• Who has the final responsibility for accurate, up-to-date aircraft empty weight and Balance?

Pilot

Importance Of Weight And Balance

• Any time equipment is added or removed, or any repair or alteration is made, this change must be recorded in the weight and balance information.

• Weight and balance information used by the pilot must be kept up to date.

• Done by maintenance technician.

• Referenced by the pilot for weight and balance calculations.

Terminology

• Arm – The horizontal distance of any object from the datum. Expressed in inches and may be – or +.

• Center of Gravity - The point at which the nose and tail moments are of equal magnitude (CG).

• Datum – An imaginary vertical line from which all horizontal measurements are made or indicated.

Terminology

• Moment – A rotational force caused by a weight acting on an arm. The product of the weight multiplied by the arm.

Weight X Arm = Moment

W X A = M

Determining the CG

Determining the CG

• Moment Index

• Loading graph is used to determine the moment index

• Advantage: No multiplication.

• Disadvantage: Shows only the loaded CG.

Figure 16-14 Loading graph

Figure 16-15

Terminology

• Ballast – Weight used to obtain a favorable center of gravity location. It is often made of lead. It may be movable or permanent and must be marked as such.

TOTAL WEIGHT X DISTANCE NEEDED TO SHIFT BP

ARM OF BALLAST – ARM OF NEW BP

Figure 16-25 (Temporary Ballast)

Figure 16-26 (Shifting Weight)

Weight And Balance Changes

• An A&P maintenance technician will have to find the new empty weight and empty weight center of gravity after an alteration to the aircraft has been performed.