Weight and Balance for the JS3 / JS MD3

The JS3 (also marketed as the JS MD3) is a highperformance singleengine aircraft used for training, touring, and lightsport operations. Proper weightandbalance management is essential for safety, fuel efficiency, and compliance with the aircrafts flight manual. This page explains the fundamentals, provides the data you need, and walks you through the calculation steps.

Why Weight and Balance Matter

• Center of Gravity (CG) limits The CG must stay within the prescribed envelope to guarantee controllability and structural integrity.
• Takeoff and landing performance Excess weight reduces climb rate, extends runway distance, and may increase stall speed.
• Fuel consumption A wellbalanced aircraft uses less fuel because the wings generate lift more efficiently.
• Regulatory compliance Many jurisdictions require a documented weightandbalance report before flight.

Basic Definitions

Basic Empty Weight (BEW) The weight of the aircraft with all permanently installed equipment, unusable fuel, full oil, and all fluids required for operation.

Moment The product of weight and its arm (distance from a reference datum). Moment = Weight Arm.

Center of Gravity (CG) The point where the total moment divided by the total weight equals the arm of the CG.

JS3 / JS MD3 Reference Data

The arm values are measured from the aircrafts datum, which is located at the firewall forward edge.

CG Limits

The JS3s allowable CG range is expressed as a forward limit of 85in and an aft limit of 115in. The corresponding envelope can be visualized on a weightvsCG graph. Staying within this envelope ensures that the aircraft remains controllable throughout all phases of flight.

StepbyStep Calculation Example

Assume the following loading configuration:

• Pilot: 185lb (front seat)
• Passenger: 160lb (rear seat)
• Fuel: 30gal (180lb) measured from the fuel gauge
• Baggage: 60lb (placed behind the rear seat)

1. List each item with its weight and arm

2. Calculate moments

Multiply each weight by its arm:

• BEW Moment = 1,400 95.0 = 133,000lbin
• Pilot Moment = 185 73.5 = 13,597.5lbin
• Passenger Moment = 160 97.5 = 15,600lbin
• Fuel Moment = 180 84.5 = 15,210lbin
• Oil Moment = 12 95.0 = 1,140lbin
• Baggage Moment = 60 115.0 = 6,900lbin

3. Sum weights and moments

Total Weight = 1,400 + 185 + 160 + 180 + 12 + 60 = 1,997lb

Total Moment = 133,000 + 13,597.5 + 15,600 + 15,210 + 1,140 + 6,900 = 185,447.5lbin

4. Determine the CG

CG (in) = Total Moment Total Weight = 185,447.5 1,997 92.8in

This CG lies comfortably within the 85in115in envelope.

Practical Tips for Pilots

• Weigh the aircraft at least once a year, or after any major modification.
• Keep a load sheet in the cockpit; fill it out before each flight.
• When loading baggage, place heavy items as close to the datum as possible.
• Burning fuel moves the CG aft. For long flights, verify that the aft CG after fuel burn will still be within limits.
• Use a portable load calculator or a spreadsheet to speed up the process.

Common Errors to Avoid

1. Assuming the empty weight is the same for every aircraft manufacturing tolerances can create differences of 15lb.
2. Neglecting the weight of optional equipment (e.g., GPS, extra seats, or a fireextinguisher).
3. Using the wrong arm for a specific item; always reference the aircrafts Pilots Operating Handbook (POH).
4. Rounding moments too early keep at least one decimal place until the final CG is computed.

Resources

For deeper study, consult the following documents:

• JS3 Pilots Operating Handbook (PDF)
• FAA AC 434C Aircraft Weight and Balance
• AOPA WeightandBalance Training Modules

Summary

Accurate weightandbalance calculations are a nonnegotiable part of operating the JS3 / JS MD3 safely. By understanding the definitions, using the aircraftspecific data, and following a systematic calculation process, pilots can ensure that every flight begins within the approved CG envelope. Regular checks, careful loading, and awareness of how fuel consumption affects balance will keep the aircraft performing as designed and reduce the risk of mishaps.