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time may require re-weighing to keep the basic empty weight and
center of gravity current. The frequency of weighing is determined by
the operator. All changes to the basic empty weight and center of
gravity are the responsibility of the operator. Refer to Section 8 for
specific servicing procedures.
1. Preparation:
a. Inflate tires to recommended operating pressures.
b. Service brake reservoir.
c. Drain fuel system.
d. Service engine oil.
e. Move crew seats to the most forward position.
f. Raise flaps to the fully retracted position.
g. Place all control surfaces in neutral position.
h. Verify equipment installation and location by comparison to
equipment list.
2. Leveling:
a. Level longitudinally with a spirit level placed on the pilot door
sill and laterally with of a spirit level placed across the door
sills. Alternately, level airplane by sighting the forward and aft
tool holes along waterline 95.9.
b. Place scales under each wheel (minimum scale capacity, 500
pounds nose, 1000 pounds each main).
c. Deflate the nose tire and/or shim underneath scales as
required to properly center the bubble in the level.
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Supplements SR20
3. Weighing:
a. With the airplane level, doors closed, and brakes released,
record the weight shown on each scale. Deduct the tare, if
any, from each reading.
4. Measuring:
a. Obtain measurement ‘x’ by measuring horizontally along the
airplane center line (BL 0) from a line stretched between the
main wheel centers to a plumb bob dropped from the forward
side of the firewall (FS 100). Add 100 to this measurement to
obtain left and right weighing point arm (dimension ‘A’).
Typically, dimension ‘A’ will be in the neighborhood of 157.5.
b. Obtain measurement ‘y’ by measuring horizontally and
parallel to the airplane centerline (BL 0), from center of
nosewheel axle, left side, to a plumb bob dropped from the
line stretched between the main wheel centers. Repeat on
right side and average the measurements. Subtract this
measurement from dimension ‘A’ to obtain the nosewheel
weighing point arm (dimension ‘B’).
5. Determine and record the moment for each of the main and nose
gear weighing points using the following formula:
Moment = Net Weight x Arm
6. Calculate and record the as-weighed weight and moment by
totaling the appropriate columns.
7. Determine and record the as-weighed C.G. in inches aft of datum
using the following formula:
C.G. = Total Moment / Total Weight
8. Add or subtract any items not included in the as-weighed condition
to determine the empty condition. Application of the above C.G.
formula will determine the C.G for this condition.
9. Add the correction for engine oil (15 lb at FS 78.4), if the airplane
was weighed with oil drained. Add the correction for unusable fuel
(15.0 lb at FS 154.9) to determine the Basic Empty Weight and
Moment. Calculate and record the Basic Empty Weight C.G. by
applying the above C.G. formula.
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Cirrus Design Section 9
SR20 Supplements
10. Record the new weight and C.G. values on the Weight and
Balance Record.
The above procedure determines the airplane Basic Empty Weight,
moment, and center of gravity in inches aft of datum. C.G. can also be
expressed in terms of its location as a percentage of the airplane
Mean Aerodynamic Cord (MAC) using the following formula:
C.G. % MAC = 100 x (C.G. Inches – LEMAC) / MAC
Where:
LEMAC = 133.1
MAC = 47.7
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Supplements SR20
Center of Gravity Limits
The charts below depict the airplane center-of-gravity envelope in
terms of inches aft of the reference datum and as a percentage of the
Mean Aerodynamic Cord (MAC). The relationship between the two is
detailed in the weighing instructions.
FS 148.1
2100 lb
FS 148.1
3050 lb
FS 139.1
2700 lb
FS 140.7
3050 lb
FS 137.8
2100 lb
2000
2050
2100
2150
2200
2250
2300
2350
2400
2450
2500
2550
2600
2650
2700
2750
2800
2850
2900
2950
3000
3050
3100
136 137 138 139 140 141 142 143 144 145 146 147 148 149 150
C.G. - Inches Aft of Datum
Weight - Pounds
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Cirrus Design Section 9
　
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