Private Pilot Groundschool
Session 4
Weight & Balance, Aircraft Performance
(PHAK Chapters 9&10)
Weight & Balance
•
Increased weight requires more lift and power, and thereby
decreases available excess power for acceleration and climb
•
In order to be controllable, an aircraft must not only be within
the maximum allowed GROSS WEIGHT, but the balance
point, or CENTER OF GRAVITY must be within a specified
range, or CG ENVILOPE defined by A FORWARD LIMIT and
an AFT LIMIT.
•
An aircraft which is out of CG may be uncontrollable, and/or
unable to recover from a stall.
•
Aft CG will cause an airplne to be less stable about the lateral
axis
Calculating CG
•
To determine whether an aircraft is within the specified limits of
its CG envelope, the balance point must be calculated.
•
MOMENT is the weight of an object multiplied by it’s ARM or
distance from a reference point.
•
In order to find out if two weights balance, their moment must
me determined. Objects which have the same moment will have
the same effect on balance.
•
Weights forward of the reference point will have a negative
arm, and therefore a negative moment, whereas weights aft of
the reference point will have a positive arm and moment.
Calculating CG (continued)
•
To calculate CG, divide the TOTAL MOMENT by the TOTAL
WEIGHT.
•
The total moment is the sum of the moments of all objects in
the aircraft, and the aircraft itself. Objects with negative
moment will decrease this number.
•
The CG and total weight can be calculated in either a table or a
graph. Pilot’s Operating Handbooks will vary somewhat in their
presentation, but the overall information contained is the same.
•
Some manuals will give a graph of moment to weight,
eliminating the need to divide the moment by the weight. In
these cases, simply use the total weight and total moment to
determine if the aircraft is within weight and balance
limitations.
Aircraft Performance
•
In order to determine whether a flight can safely be completed, the
performance of an aircraft at the weights, altitudes, temperatures, and
airports expected on the flight must be calculated. Pilot’s Operating
Handbooks provide charts and data to calculate these.
•
Takeoff performance varies with aircraft weight, altitude, temperature,
runway surface condition, and wind Some manuals give this
information in table form, while others give it in chart form.
•
Cruise performance is dependent on altidude temperature, and aircraft
weight. However, the cruise speed derived from the information in the
POH must still be corrected for wind.
•
Landing performance is largely dependant on the same variables as
takeoff, however runway surface condition plays a larger role, as brakes
are used to slow the aircraft on landing.