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such as radios, batteries, flight instruments, or airframe
repairs, can have an effect on the center of gravity position.
Aviation maintenance technicians must record
any changes in the weight and balance data in the
GFM/POH or glider airframe logbook. Weight and balance
placards in the cockpit must also be updated.
PROBLEMS ASSOCIATED WITH CG
FORWARD OF FORWARD LIMIT
If the center of gravity is within limits, pitch attitude
control stays within acceptable limits. However, if the
glider is loaded so the CG is forward of the forward
limit, handling will be compromised. Nose heaviness
will make it difficult to raise the nose on takeoff and
considerable back pressure on the control stick will be
required to control the pitch attitude. Stalls will occur at
higher than normal airspeeds and will be followed by a
rapid nose-down pitch tendency. Restoring a normal
flight attitude during stall recoveries will take longer.
The landing flare will be more difficult than normal, or
perhaps even impossible, due to nose heaviness.
Inability to flare could result in a hard nose-first landing.
The following are the most common reasons for CG
forward of forward limit.
• Pilot weight exceeds the maximum permitted
pilot weight.
• Seat or nose ballast weights are installed but are
not required due to the weight of the pilot.
PROBLEMS ASSOCIATED WITH CG
AFT OF AFT LIMIT
If the glider is loaded so the CG location is behind the
aft limit, handling is compromised. The glider is said
to be tail-heavy. Tail heaviness can make pitch control
of the glider difficult or even impossible.
When the glider is tail-heavy recovering from a stall
may be difficult or impossible. When the stall occurs,
the tail-heavy loading tends to make the glider nose
continue to pitch upward, increasing angle of attack
and complicating stall recovery. In extreme cases,
recovery from stall or spin may be difficult or even
impossible.
The following are the most common reasons for flight
with CG located behind permissible limits.
• Pilot weight is less than the specified minimum
pilot seat weight and trim ballast weights necessary
for the lightweight pilot are not installed in
the glider prior to flight.
• Tailwheel dolly is still attached, far aft on the
tailboom of the glider.
• Foreign matter or debris (water, ice, mud, sand,
and nests) has accumulated in the aft fuselage of
5-12
the glider and was not discovered and removed
prior to flight.
• A heavy, non-approved tailwheel or tail skid was
installed on the aft tailboom of the glider.
• Improper repair of the aft fuselage of the glider
resulted in an increase in aft weight of the fuselage
that was not recorded in the glider airframe
logbook, or not reflected in cockpit placards, or
both.
SAMPLE WEIGHT AND BALANCE
PROBLEMS
Some glider manufacturers provide weight and balance
information in a graphic presentation. A well-designed
graph provides a convenient way to determine whether
the glider is within weight and balance limitations.
In Figure 5-17, the chart indicates that the minimum
weight for the front seat pilot is 125 pounds, and that
the maximum is 250 pounds. It also indicates that the
maximum rear seat pilot weight is 225 pounds. If each
pilot weighs 150 pounds, the intersection of pilot
weights falls within the envelope and the glider load is
within the envelope and is safe for flight. If each pilot
weights 225 pounds, the rear seat maximum load is
exceeded, and the glider load is outside the envelope
and not safe for flight.
DETERMINING CG WITHOUT
LOADING CHARTS
The CG position can also be determined by calculation
using the following formulas:
Weight multiplied by Arm equals Moment
Weight x Arm = Moment
Total Moment divided by Total weight equals CG
position in inches aft of the reference datum.
Total Moment • Total Weight = CG
The computational method involves the application of
basic math functions. The following is an example of
the computational method.
Given:
Maximum Gross Weight....................1,100 lb.
Empty Weight.......................................600 lb.
Center-of-Gravity Range..........14.8 – 18.6 in.
Front Seat Occupant.............................180 lb.
Rear Seat Occupant..............................200 lb.
Figure 5-17. Graphic presentation of weight and balance envelope.
5-13
To determine the loaded weight and CG, follow these
steps.
Step 1—List the empty weight of the glider and the
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Glider Flying Handbook(50)
