Aircraft Technical Manual
Jabiru Aircraft
Pty Ltd
J120, J160, J170, J200/J400, J230/J430, J250/J450 Variants
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ISSUE
1
2
3
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5
Dated: 29th October 2014
Issued By: AS
Page: 55 of 298
5.16 Special Inspections
– Weighing (all J-Series)
Required Tools:
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Chocks
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Calibrated scales (x3)
-
Square or Plumb-bob
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String and Tape
Parts and Material:
N/A
Type of Maintenance:
Line Maintenance
Level of Certification:
L1, L2 or LAME (Owner, A&P or LSA Repairman / Maintenance)
5.16.1.1 Scale Locations
For weighing three scales are used; one under each main wheel and one under the nose wheel.
5.16.1.2 Procedure
1. Position the aircraft on the scales on a level surface, preferably one that positions can be marked
on to, in the configuration to be weighed.
2. Chock the main wheels and make sure the brake is released. (If the chocks are of significant
weight their weight will need to be subtracted from the relevant scale readings).
3. Level the aircraft using technique in Section 4.2.4. If the nose needs to be raised place packers
under the nose wheel. If the nose needs to be lowered pack under main wheels or deflate nose
wheel. (Remember to re-inflate to operating pressure before use)
4. Using a square or a plumb bob mark the wheel centres on to the floor or scale surface. Both
sides of the nose wheel axle must be marked to eliminate any error if it isn’t exactly straight.
5. Again using a plumb bob or a level, mark the wing leading edge onto the floor. Mark these points
at a position outboard of the main wheels.
6. Take the wheel weights. When the wheel weights are being taken there must be nil wind blowing
on the aircraft. Due to the light nature of the Jabiru even a small breeze can cause significant
weight transfer and consequentially C of G errors. In addition, door must be shut, flaps in the UP
position and any items not part of the standard equipment of the aircraft removed.
7. Using a string line or similar mark the wing leading edge on the floor under the aircraft. Normally
using tape to fix a string line between the points marked earlier is the best method.
8. Measure the horizontal for/aft distance for each wheel (both sides of nose wheel) to the wing
leading edge. Note that the two readings for the nose wheel are averaged.
9. All distances aft of the datum are considered positive and all distances forward of the datum are
negative. See Figure 16. Note that while the arrangement shown assumes that the wing leading
edge is the aircraft datum, for some Jabiru models the datum is displaced a fixed amount forward
of the leading edge. For these models the measurements taken must be adjusted to readings
relative to the datum. For example,
-
The datum is 1403mm forward of the wing leading edge
-
Measurements have found that the nose wheel is 400mm forward of the wing leading edge
and the main wheels 400mm aft.
-
Corrected to reference the datum, these measurements become 1003mm aft of the datum
for the nose wheel and 1803mm aft for the main wheels.
10. Always weigh and measure the aircraft at least twice and average the results. If one weighing
gives results that are significantly different from the other
– typically the aircraft weight should not
be different by more than 2kg and the calculated CG position within 5mm
– then weigh the
aircraft a third time to get a better match. Discard the anomalous results. If the third weighing is
also different then there is most likely a procedure or equipment issue and the weighing must be
postponed until this issue has been corrected.
11. Due to the light weight of the aircraft, the scales used must have an accuracy of at least +/-0.5kg
and distances must be measured to /-1mm to ensure accurate results.
