Aircraft Performance
Calculate total weight, CG position, and moment across all four phases of flight — Zero Fuel, Ramp, Takeoff, and Landing. Visual 2D CG envelope diagram, maneuvering speed at actual weight, MZFW check, fuel by volume, and FAA standard passenger weights.
Enter weights, fuel loads, and CG limits — all phases of flight computed instantly
Usage Guide
Five steps from your POH to a verified weight and balance.
Click Cessna 172S or PA-28-181 to populate all stations, fuel tanks, CG limits, envelope points, and VA instantly. Set your weight unit (lb/kg), volume unit (US gal, Imp gal, or litres), and fuel type — the density converts automatically. Use your aircraft's actual current weight and balance record, never the POH example.
Enter fuel in your preferred volume unit — weight calculates automatically at the selected fuel density. Toggle FAA standard passenger weights (190 lb summer / 195 lb winter) or enter actual weights. Baggage rows show compartment limits — a red border warns if the limit is exceeded independently of total weight.
The phase summary shows Zero Fuel, Ramp, Takeoff, and Landing weight and CG — each independently checked against the envelope. Enter ground burn (taxi fuel) and flight burn separately. The 2D envelope diagram plots all four points so you can see the CG travel path through the envelope during the entire flight.
VA at actual takeoff and landing weight is computed automatically — it is always lower than the published VA at max gross weight. Check the MZFW box if your aircraft has a zero fuel weight limit. Confirm all four phase rows in the summary table show a green ✓ before departure — any red phase is a go/no-go issue that must be resolved by adjusting fuel, seat assignments, or load.
Foundational Knowledge
Weight and balance is one of the four preflight legal requirements. Exceeding either limit is not a performance issue — it is a loss-of-control risk.
Every pound above the maximum gross weight increases stall speed, extends takeoff roll, degrades climb performance, and increases structural loads on every manoeuvre. The aircraft's structural certification is based on maximum gross weight — operating overweight means load factors may exceed structural limits during normal turbulence.
Maximum gross weight is the highest weight at which the aircraft is certified to fly. It is fixed by the type certificate. No emergency, convenience, or scheduling pressure justifies exceeding it. Many small GA aircraft have useful loads of under 1,000 lb — full fuel plus four adults often exceeds this.
An out-of-balance aircraft can be within weight limits but completely uncontrollable. Aft CG is particularly dangerous: as CG moves aft, the aircraft becomes less stable in pitch. The pilot must apply increasing forward stick force to prevent pitch-up. At extreme aft CG, the aircraft may be impossible to recover from a stall because the elevator cannot generate sufficient nose-down moment.
Forward CG limits exist because elevator authority limits the ability to rotate on takeoff and flare for landing. An extremely forward CG may prevent the aircraft from lifting off within the available runway length.
The imaginary vertical reference plane chosen by the manufacturer. All arm measurements are taken from the datum. Defined in the Type Certificate Data Sheet. Datums vary by aircraft — some use the firewall, some use the leading edge of the wing, some use a point forward of the nose.
The horizontal distance in inches (or metres) from the datum to the point where a load acts. Published for each station in the POH. Arms aft of the datum are positive. Arms forward of the datum are negative.
Weight × Arm. Represents the rotational tendency of a load about the datum. Total moment = sum of all individual moments. Dividing total moment by total weight gives the CG arm position.
Total moment divided by a constant (often 100 or 1000) to reduce the size of numbers for manual calculation. Some POHs use moment/100 in their loading graphs. Always check the index used before reading charts. This calculator supports ×1, ÷100, and ÷1000.
The graph of permissible weight versus CG arm combinations. Any point inside is permissible. Must be satisfied at all four phases: Zero Fuel, Ramp, Takeoff, and Landing. The 2D diagram in this calculator plots all four points simultaneously.
Maximum gross weight minus basic empty weight. Represents the total capacity for fuel, crew, passengers, and baggage. Full fuel plus four adults often exceeds useful load — a critical planning constraint.
The maximum permissible weight with zero fuel loaded. Where published, the zero fuel weight must not exceed MZFW even if total weight with fuel is below MTOW. Common in twins and light jets where wing bending loads at zero fuel are the structural limiting factor.
Published at maximum gross weight only. At lighter weights VA is lower: VA_actual = VA_max × √(actual weight ÷ max gross weight). Always use the weight-corrected VA — operating at the published VA figure at a reduced weight can still overstress the airframe with full control deflection.
CG Effects on Handling
CG position directly changes the feel, stability, and safety margins of every aircraft. This is not about comfort — it is about controllability.
Aft CG accident record: Aft CG exceedances have been responsible for numerous fatal accidents worldwide, including loss of control after stall from which recovery was impossible. The most dangerous characteristic of aft CG is that the aircraft may handle well during cruise but become unrecoverable at lower speeds. Never operate with an aft CG exceedance.
Common Questions
Weight and balance in aviation refers to the process of calculating the total weight of an aircraft and the position of its centre of gravity (CG) before flight. Weight affects performance — a heavier aircraft requires more runway to take off, climbs more slowly, and burns more fuel. Balance (CG position) affects stability and control — if the CG is too far forward, the aircraft requires excessive elevator back-pressure and may not be able to rotate on takeoff or flare to land; if the CG is too far aft, the aircraft becomes progressively less stable and eventually uncontrollable in pitch. Both the maximum weight limit and the CG envelope are published in the Pilot Operating Handbook (POH) and must not be exceeded on any flight.
Centre of gravity is calculated using the moment method: CG = Total Moment ÷ Total Weight. For each item (aircraft empty weight, fuel, each occupant, baggage), multiply the weight by its arm — the horizontal distance from the datum to the point where that load acts. The sum of all these products is the total moment. Divide total moment by total weight to get the CG arm in inches (or metres) from the datum. Compare the resulting CG to the forward and aft CG limits published in the POH for the current total weight. If the CG falls outside the envelope at any point during the flight — including at landing weight after fuel burn — the flight must not proceed.
The datum is an imaginary vertical reference plane chosen by the manufacturer, from which all arm measurements are taken. Common datum positions include the firewall, the leading edge of the wing, the nose of the aircraft, or an arbitrary point forward of the nose. All arms in the aircraft's weight and balance documentation are measured from this datum. Distances aft of the datum are positive; distances forward of the datum are negative (for datums located behind the nose). The datum itself is defined in the aircraft's Type Certificate Data Sheet (TCDS) and the Pilot Operating Handbook.
An arm is the horizontal distance from the aircraft datum to the point where a given load acts, measured in inches or metres. The arm of the pilot's seat, for example, is the horizontal distance from the datum to the pilot's seat position. Arms for standard loading stations (pilot, front passenger, rear seats, baggage) are published in the POH weight and balance section. For fuel, the arm is the horizontal distance from the datum to the centre of the fuel tank. Some aircraft have two fuel tanks (left and right wing) and the arm for each may differ slightly.
A moment is the product of weight multiplied by arm. It represents the rotational tendency of a load about the datum. Moment = Weight × Arm. The unit is inch-pounds (in-lb) or pound-inches when using imperial measurements, or kilogram-metres (kg-m) in metric systems. Some manufacturers divide all moments by 1000 or another factor (the moment index) to keep the numbers manageable. Total moment is the sum of all individual moments. Dividing total moment by total weight gives the CG arm.
Operating outside the CG envelope is illegal and dangerous. If the CG is too far forward (forward of the forward limit), the aircraft requires excessive nose-up elevator trim to maintain level flight, may not be able to rotate on takeoff, and the elevator may not have sufficient authority to flare for landing. In extreme cases, the aircraft may pitch down uncontrollably. If the CG is too far aft (beyond the aft limit), the aircraft becomes progressively less stable. The stick-force-per-g decreases, making it easy to overstress the airframe inadvertently. At extreme aft CG positions, the aircraft may be impossible to recover from a stall or unusual attitude. Aft CG exceedances have been responsible for numerous fatal accidents.
As fuel burns during flight, the total weight decreases and the CG position shifts. The direction and magnitude of the shift depends on the arm of the fuel tank relative to the aircraft CG. If the fuel arm is forward of the CG, burning fuel moves the CG aft. If the fuel arm is aft of the CG, burning fuel moves the CG forward. A correct weight and balance calculation checks the CG position at takeoff weight (maximum fuel) and at landing weight (minimum fuel after the planned flight). The CG must remain within the envelope at all fuel states — both the takeoff and landing conditions should be plotted on the envelope.
The CG envelope is a graph published in the POH that defines the range of CG positions that are permissible at each gross weight. The horizontal axis shows CG position (arm in inches from datum). The vertical axis shows gross weight. The envelope is typically a four-sided or irregular polygon: it narrows at low weights (allowing a smaller CG range) and may have a different shape at high weights. The forward CG limit is usually determined by elevator authority for landing. The aft CG limit is set by longitudinal stability requirements. Any CG and weight combination that plots inside the envelope is permissible. Any combination outside is prohibited.
Maximum ramp weight (also called maximum taxi weight) is the maximum allowable weight during ground operations, including engine start, taxi, and run-up. Maximum takeoff weight (MTOW) is the maximum weight at which the aircraft may begin the takeoff roll. The difference between ramp weight and MTOW accounts for fuel burned during taxi and run-up — typically 10–30 lb for piston aircraft. Many smaller GA aircraft have identical ramp and takeoff weight limits. For Part 25 transport category aircraft, the distinction is operationally important because structural limits differ between ground and flight loads.
Useful load is the difference between the maximum gross weight and the basic empty weight of the aircraft. It represents the total payload available for fuel, pilot, passengers, and baggage. Useful load = MTOW − Basic Empty Weight. A typical 4-seat single-engine piston aircraft has a useful load of approximately 900–1200 lb. Filling the fuel tanks to maximum capacity and carrying four adult passengers simultaneously often exceeds the useful load — a common preflight planning challenge. Pilots must balance fuel range against passenger and baggage loads, often requiring trade-offs between fuel load and passenger weight.