Why use TrimCalc?
Free for private pilots and flying clubs
TrimCalc is free for private pilots and flying clubs. Companies, commercial operators and aircraft rental businesses are asked to make an appropriate donation.
Donations support socially disadvantaged children. They are used for charitable projects through Lions-Hilfswerk Köln-Rheinbrücke e. V.
1. What is aircraft centre of gravity?
The centre of gravity, or CG, is the point at which the total mass of the aircraft can be considered to act. For weight-and-balance purposes, each individual mass is combined with its distance from a manufacturer-defined datum. This distance is called the station arm.
Multiplying mass by station arm gives a moment. The aircraft CG is found by dividing the total moment by total mass.
2. Why weight and balance matters
CG position affects longitudinal stability, control forces, trim, take-off performance, climb, stall behaviour and landing. A forward CG commonly increases stability and control forces. An aft CG reduces the stability margin and can make handling critical if the approved limit is exceeded.
Forward CG
Usually higher control forces, more trim drag and potentially longer take-off distance.
Favourable CG
Appropriate stability and control forces with reduced unnecessary trim drag.
Aft CG
Lower stability margin and potentially critical low-speed and pitch behaviour.
3. TrimCalc in practice
TrimCalc provides an immediate and straightforward weight-and-balance calculation. Aircraft-specific data are saved once as a profile. Before flight, only the current crew, fuel, baggage and other variable loads need to be entered.
- calculate CG and total mass immediately
- enter main and wing fuel separately
- display wing loading
- save profiles for several aircraft
- share profiles by file or QR code
- use saved profiles offline
- operate the app in English, German or French
4. Datum and station arm
The datum is defined by the manufacturer. It may be ahead of the nose, at the firewall, at the wing leading edge or at another specified point. The station arm is the distance between a load and that datum.
Station arms must come from the official documents for the individual aircraft. They must not be estimated or copied from another aircraft merely because it is the same model.
5. Formula and moments
Calculate the moment for every loading station:
Add all moments and divide by total mass:
The result must then be checked against the approved loading envelope and maximum permitted mass.
6. Which data are required?
| Data item | Source | Note |
|---|---|---|
| Empty mass | Weighing report | Update after reweighing or significant modification. |
| Empty-mass CG | Weighing report | Check unit and sign convention. |
| Crew and passengers | Current loading | Use the correct seat station arms. |
| Fuel | Flight manual and current quantity | Use the specified density and tank stations. |
| Baggage | Current loading | Aft baggage compartments can have a large CG effect. |
| Additional equipment | Equipment list / weighing report | Installations and removals must be reflected. |
| CG limits | Flight manual | Forward and aft limits may depend on mass. |
| Maximum take-off mass | Flight manual | Must be checked in addition to CG. |
7. Worked example
This simplified example demonstrates the method only and is not aircraft data.
| Item | Mass | Station arm | Moment |
|---|---|---|---|
| Empty aircraft | 640 kg | 0.720 m | 460.80 kgm |
| Pilot and passenger | 160 kg | 0.450 m | 72.00 kgm |
| Fuel | 90 kg | 0.820 m | 73.80 kgm |
| Baggage | 25 kg | 1.450 m | 36.25 kgm |
Total mass: 915 kg
Total moment: 642.85 kgm
Whether 0.703 m is approved depends entirely on the loading envelope for the individual aircraft.
8. Understanding the loading envelope
For many powered aircraft, the permitted forward and aft CG limits vary with total mass. The loading envelope therefore combines both values. A loading condition is approved only if the calculated point lies inside the envelope and all other mass limits are respected.
9. Fuel and CG movement
Fuel changes both total mass and CG. The direction and amount of movement depend on tank location. On some aircraft the CG moves forward as fuel is burned; on others it moves aft.
The departure condition may therefore be insufficient on its own. Where required, calculate the condition after fuel burn and at landing as well.
10. Passengers, baggage and additional equipment
Passenger seating and baggage stations can move CG substantially. An aft baggage compartment can reach the aft limit even when the aircraft remains below maximum take-off mass.
Oxygen bottles, batteries and installed equipment must also be included. After installation, removal, repair or reweighing, the saved aircraft profile should be checked and updated.
11. CG position and fuel consumption
A forward CG commonly requires the tailplane to produce a greater balancing force. This increases aerodynamic load and trim drag.
A favourable CG position within the approved envelope can reduce trim drag and therefore reduce fuel consumption. This is an efficiency benefit, not a reason to approach or exceed the aft limit.
12. Flying clubs, flight schools and rental aircraft
In club, school and rental operation, crew, passengers, baggage and fuel quantities change frequently. Weight and balance therefore has to be recalculated regularly.
TrimCalc saves one profile per aircraft. A QR code can be placed in the cockpit or with the aircraft documents. After scanning, users only need to enter the current loading.
13. Profiles, files and QR codes
Profiles can be exported, sent by email or messenger and imported on another device. They can also be displayed as QR codes and scanned directly with TrimCalc.
Every imported or community profile must be verified against the official documents for the individual aircraft before use.
Open a file with TrimCalc15. Common weight-and-balance errors
- using the wrong aircraft profile
- copying data from another aircraft of the same type
- mixing units or sign conventions
- estimating crew mass inaccurately
- forgetting a passenger or baggage item
- using the wrong fuel quantity or density
- combining tanks that have different station arms
- failing to update installed equipment
- checking CG but not maximum take-off mass
- failing to check the condition after fuel burn
- using a shared profile without verification
16. Frequently asked questions
How do you calculate aircraft centre of gravity?
Add all moments and divide the sum by total mass. Each moment equals mass multiplied by station arm.
Which values does TrimCalc need?
TrimCalc needs the aircraft-specific masses, station arms, CG limits and the current loading with crew, fuel and baggage.
Is TrimCalc free?
TrimCalc is free for private pilots and flying clubs. Companies, commercial operators and rental businesses are asked to make an appropriate donation. Donations support socially disadvantaged children.
Does TrimCalc work offline?
Yes. Once installed as a web app, TrimCalc can be used without an internet connection.
How does fuel affect CG?
The effect depends on tank position. CG may move forward or aft as fuel is burned.
Can CG position reduce fuel consumption?
Yes. A favourable CG inside the approved envelope can reduce trim drag and fuel consumption.
Does TrimCalc replace the flight manual?
No. The flight manual, weighing report, equipment list and official documents for the individual aircraft always remain authoritative.
When should an aircraft profile be updated?
After reweighing, repairs, modifications, equipment changes or any alteration to permanently installed masses.
More TrimCalc pages
Glider Weight and Balance · Schwerpunkt Flugzeug · Masse et centrage avion · Open a file with TrimCalc