Performance & Limitations - B: Weight & Balance

Question 1

Define the following:

• Empty weight
• Gross weight
• Useful load
• Arm
• Moment
• Center of gravity
• Datum

Answer 1

Empty weight—The weight of the airframe, engines, all permanently installed equipment, and unusable fuel. Depending on the FARs under which the aircraft was certificated, either the undrainable oil or full reservoir of oil is included.

Gross weight—The maximum allowable weight of both the airplane and its contents.

Useful load—The weight of the pilot, copilot, passengers, baggage, usable fuel and drainable oil.

Arm—The horizontal distance in inches from the reference datum line to the center of gravity of the item.

Moment—The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches.

Center of gravity—The point about which an aircraft would balance if it were possible to suspend it at that point. Expressed in inches from datum.

Datum—An imaginary vertical plane or line from which all measurements of arm are taken. Established by the manufacturer.

Question 2

What basic equation is used in all weight and balance problems to find the center of gravity location of an airplane and/or its components?

Answer 2

Weight x Arm = Moment
By rearrangement of this equation to the forms:
Weight = Moment ÷ Arm
With any two known values, the third value can be found.
Remember: W A M
(Weight x Arm = Moment)

Question 3

What performance characteristics will be adversely affected when an aircraft has been overloaded?

Answer 3

a. Higher takeoff speed.
b. Longer takeoff run.
c. Reduced rate and angle of climb.
d. Lower maximum altitude.
e. Shorter range.
f. Reduced cruising speed.
g. Reduced maneuverability.
h. Higher stalling speed.
i. Higher landing speed.
j. Longer landing roll.
k. Excessive weight on the nosewheel.

Question 4

What effect does a forward center of gravity have on an aircraft’s flight characteristics?

Answer 4

Higher stall speed—stalling angle of attack is reached at a higher speed due to increased wing loading.

Slower cruise speed—increased drag; greater angle of attack is required to maintain altitude.

More stable—the center of gravity is farther forward from the center of pressure which increases longitudinal stability.

Greater back elevator pressure required—longer takeoff roll; higher approach speeds and problems with landing flare.

Question 5

What effect does a rearward center of gravity have on an aircraft’s flight characteristics?

Answer 5

Lower stall speed—less wing loading.

Higher cruise speed—reduced drag from elevator; smaller angle of attack is required to maintain altitude.

Less stable—stall and spin recovery more difficult; the center of gravity is closer to the center of pressure, causing longitudinal instability.

Question 6

What are the standard weights assumed for the following when calculating weight and balance problems?

• Gasoline
• Oil
• Water

Answer 6

Gasoline 6 lbs/U.S. gal
Oil 7.5 lbs/U.S. gal
Water 8.35 lbs/U.S. gal

Question 7

The rental aircraft you normally fly has just returned from the avionics shop with newer, lighter-weight avionics. When reviewing the aircraft weight and balance record, you don’t see an A&P entry reflecting this change. Is this normal? Why?

Answer 7

No. Changes of fixed equipment may have a major effect upon the weight of the aircraft. Many aircraft are overloaded by the installation of extra radios or instruments. Fortunately, the replacement of older, heavy electronic equipment with newer, lighter types results in a weight reduction. This weight change, however helpful, can cause the CG to shift, which must be computed and annotated in the weight and balance record. It is the responsibility of the A&P mechanic or technician making any repair or alteration to know the weight and location of these changes, and to compute the CG and record the new empty weight and empty weight center of gravity (EWCG) in the aircraft weight and balance record.