Jabiru SP/UL – Weight and Balance

This is an example of how to complete the J120C Load and trim sheet. Remember to use the figures for the specific aircraft which you are flying.

To complete this example you will need;

– Copy of your Aircrafts Load and Trim
– Your Aircrafts POH (Weights)
– a Ruler and a Pen

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For this example we will use the following figures;

Pilot 90 KG
PAX front 65 KG
Fuel 70 LT (SG 0,72 = 50,0 KG)
MTOW 500 KG
BEM 285 KG
Empty Trim Index (CG) 48 (Empty Weight * Empty Arm) / 1000

STEP 1 – MTOW

Firstly, before going through the effort of using the trim sheet it is always advisable to add up your load to ensure that it does not exceed the aircraft MTOW. (However the trim sheet will show this)

BEM 285 KG
Pilot 90 KG
PAX front 65 KG
Fuel 70 LT (SG 0,72 = 50 KG)
TOTAL (RAMP) 498 KG
MTOW 500 KG

From the above we determine that the aircraft is within MTOW, however we still need to ensure that the CG is within limits.


STEP 2 – AIRCRAFT INDEX

In this step we will enter at the aircraft index as per our calculation above it’s 48, from here we will draw a line vertically down to intercept the first slanted lines representing the crew index.

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STEP 3 – CREW INDEX

In this step we draw a horizontal line along the crew index units, crossing 1 diagonal per 10KG of crew. In our example 15,5 lines across, we then draw a vertical line down to intersect the baggage index. Since we have no baggage in our example we will move straight down to the fuel index units.

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STEP 4 – FUEL INDEX

In this step we will move 1 diagonal across for each 10L of fuel that we have onboard. In our example 70L. (Remember this is litres, not Kilograms so there is no need to convert using SG). We then draw a vertical line from this point down through the envelope.

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STEP 5 – EMPTY WEIGHT

In this step we enter the graph from the right at the first ladder representing aircraft empty weight. As per our example our empty weight is 285KG, from here we draw a horizontal line to intercept the crew ladder.

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STEP 6 – CREW LADDER

In this step we will follow the crew ladder down one line per 10KG of crew member. As per our example this is 155kg so we will move down 15,5 lines. We are not carrying any baggage so we can move from the baggage line directly across to the fuel ladder.

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STEP 7 – FUEL LADDER

In this step we will move down the fuel ladder 1 bar for every 10L of fuel. Again not that this is litres not KG so there is no need to convert. From the bottom of the fuel line we draw a line horizontally through the envelope to see where the two lines will cross. As can be seen below the aircraft is within the envelope.

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STEP 8 – EMPTY WEIGHT

This is always a good step to take to ensure that the aircraft will be within the envelope for the entree trip regardless of how much fuel you have remaining.

Complete the steps above again but use 0 as your fuel quantity. See where the lines intercept, if they are still within the CG we have ascertained that the aircraft will remain within CG for all expected weights during this flight.

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STEP 9 – FURTHER CONSIDERATIONS

Looking at the table in step 8, whether the empty mass trim index falls within the envelope is questionable and it would be a good idea to check your figures. However in the example above the empty index used is quite low and therefore effected the final result. Working with extreme accuracy on these graphs is very important.

It is considered that many students will start their training on the J120 so for pilots not familiar with the terms above, the envelope referred to is the red polygon as depicted below. The aircrafts final centre of gravity must always be within this envelope for any flight condition to ensure that the aircraft will perform as per specifications. (Vx / Vy / Vma and structural integrity)

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Don’t forget to check the aircrafts TORR against TORA at your airfield at the density altitude expected on the day.