Weight and balance
One
of the responsibilities a pilot in command of an aircraft has during preflight
preparations is the computation of the aircraft’s weight and balance.
Manufacturers
of all aircraft specify their maximum gross weight. The following example indicates how an
aircraft with a maximum gross weight of 3,000 pounds can be loaded:
Basic
empty weight of the aircraft is 1,600 pounds, including undrainable
fuel and oil.
Accessories
added to aircraft — extra radios, air-conditioning — equals 100 pounds in the
sample aircraft.
Ten
quarts of drainable oil at seven-and-a-half pounds per gallon equals 17.75
pounds. To this point the basic empty
weight of the aircraft is 1717.75 pounds.
The
pilot has options as to how much fuel, passengers, and baggage he can put in
the aircraft up to the maximum allowable gross weight of 3,000 pounds.
Three
passengers will accompany the pilot on this trip. (The Federal Aviation Administration
specifies a standard person’s weight to be 170 pounds; however actual weights
should always be used when available).
The three passengers and the pilot weigh in at 680 pounds. Altogether, they are carrying 100 pounds of
baggage.
At
this point in the loading the pilot has 502.25 pounds available for fuel.
If the aircraft has a usable fuel capacity of
72 gallons, the total fuel load could be as much as 432 pounds, with aviation
gas weighing six pounds per gallon.
The
aircraft would still be more than 70 pounds under the maximum gross weight
allowed for safe operations. If the
passengers weigh more than the standard 170 pounds per person, or if the
baggage is much more than only 100 pounds, then the fuel load, baggage load, or
number of passengers would have to be decreased to keep the gross loaded weight
under the maximum allowable gross weight of the aircraft.
Loading
an aircraft beyond its maximum gross weight can result in adverse performance
from the aircraft. The stalling speed of
the aircraft is increased.
The
loads imposed on the landing gear and tires may be beyond a safe margin.
The
wings are supporting a greater weight than they were designed to support,
possibly causing damage to the structure.
Another
important aspect of the loading of the aircraft is where in the aircraft the
weight is distributed. This is known as
balance.
The
center of gravity of an aircraft is a point at which the aircraft would balance
if it were possible to suspend the aircraft from that point.
An
aircraft loaded outside its loading envelope, either too far forward or too far
aft of the limits, will not perform in a normal way.
The
stalling speed will be adversely affected, and the handling qualities of the
aircraft may be degraded to the point of making the aircraft
uncontrollable.
The
stalling speed will be adversely affected, and the handling qualities of the
aircraft may be degraded to the point of making the aircraft uncontrollable.
In
large cargo or passenger aircraft, loadmasters or dispatchers compute the
weight and balance of an aircraft prior to flight.
These
figures are made available to the pilots of the aircraft and the flight
engineer in order for the pilots to compute take off and landing distances,
fuel loads, and other important data, including best rate of climb speeds.
Some
aircraft have maximum zero fuel weights.
This is the maximum weight of the aircraft with the fuel tanks
empty.
This
maximum zero fuel weight is important due to the twisting moment exerted on the
wings by a heavy fuselage. Because fuel tanks are located in the wings and contribute
to the structural strength of the wings, the load-bearing capacity of the wings
at touchdown is reduced when there is no fuel in the tanks.