Loading, Mass and Balance for Spray Operations
Weight and balance fundamentals
Every helicopter has a maximum gross weight, an empty weight with equipment list, and a center of gravity (CG) envelope. Loads include crew, fuel, spray product and the spray system itself. The CG must remain inside the envelope from takeoff through landing, and the load changes as product is released, so the worst case may be at the start or the end of the run.
Concepts you must know
Understand how to compute the moment (weight × arm) and total CG. Know the difference between maximum takeoff weight and maximum landing weight where applicable. Understand the effect of the spray tank position and the dump valve on CG travel. Know fuel burn changes CG as fuel is consumed. Understand that the hopper is usually near the CG, but boom and nozzle installations add arms of their own. Know the loading limits of the spray system and the effect of product density on volume versus mass.
Traps
Questions often ask for the CG after product release, not before. Another trap: mixing liters and kilograms; product density matters. Watch for the assumption that a full tank is always the critical case, when an empty tank with full fuel and aft crew may be worse. Also watch for the empty-weight change after equipment modification, which invalidates old calculations.
Rule of thumb
Compute CG at three points: loaded takeoff, mid-run, and end of run. If all three are inside the envelope, the flight is legal. If any is outside, change the load distribution before flight.
Worked example: Empty weight 1,200 kg at arm 2.50 m gives 3,000 kg·m. Add 200 kg crew at 1.80 m (360), 150 kg fuel at 2.60 m (390), and 300 kg product at 2.45 m (735). Total weight 1,850 kg; total moment 4,485 kg·m; CG = 4,485 / 1,850 ≈ 2.42 m. Check that 2.42 m lies inside the envelope for 1,850 kg, and repeat with the product released.