Glider Weight & Balance Guide

1. Why weight and balance matters in gliders

A glider can only be operated safely if both total weight and center of gravity are within the limits defined by the manufacturer. The maximum take-off mass alone is not enough. A loading condition may be below the weight limit and still place the center of gravity outside the permitted range.

Center of gravity affects longitudinal stability, elevator forces, trim, stall behavior and overall handling. In gliding, it also has a direct impact on performance. A glider with an unfavorable CG may require more trim or control input, which can increase drag and reduce efficiency.

2. Required documents

A reliable calculation starts with the official documents for the specific glider. Generic values or data from a similar aircraft should not be used for actual flight preparation.

3. What must be included?

All masses that affect weight or moment must be included. In gliders, pilot weight, passenger weight, water ballast, trim weights, batteries and oxygen equipment can be particularly important.

• pilot including parachute
• passenger or rear-seat pilot
• water ballast
• trim ballast or removable weights
• batteries and oxygen equipment
• additional equipment, logger, FLARM or radio changes
• removed or replaced components

4. Reference plane, arm and moment

For each glider, the manufacturer defines a reference plane. The arms of the individual loading positions refer to this reference plane and are provided in the flight manual, weighing report or other approved aircraft documents.

Pilots normally do not measure these arms themselves. The values for seats, ballast tanks, batteries or equipment positions must come from the aircraft documentation.

The moment of a loading position is calculated from its weight and arm. The sum of all moments and the total weight are then used to determine the center of gravity.

5. Step-by-step calculation

Depending on the flight manual, the calculation may use arms or pre-calculated moment values. The principle remains the same:

The result must be compared with the allowable CG range or with the CG chart of the specific glider.

6. Water ballast and center of gravity

Water ballast increases total weight and may also influence the center of gravity, depending on tank position and arm. In some gliders the ballast is close to the CG, while in others its effect is more noticeable.

In addition to CG limits, the maximum permitted take-off mass must be checked. A loading condition may be correct in CG but still exceed the allowable weight.

7. Reading a CG diagram

A CG diagram shows whether a combination of total weight and center of gravity is within the permitted envelope. The allowable range may change with weight, so it is not always sufficient to look at a single CG value.

8. Optimum CG range and glide performance

Many gliders have a range within the permitted CG limits where they fly particularly well. This is often perceived as an optimum CG range. It is not a separate approval and never allows operation outside the official limits.

A favorable CG position can reduce trim drag and make the glider feel more balanced. Depending on aircraft type and flight conditions, a small change in CG position can improve the glide ratio by more than one point.

The purpose is not to push the CG toward a limit, but to operate safely within the manufacturer’s envelope and, where possible, near a range that gives balanced handling and efficient flight.

9. Example calculation

The following example is simplified and demonstrates the method only. It does not replace the data of a specific glider.

Total weight: 448 kg
Total moment: 160.72 kgm

The calculated CG is 0.359 m in this example. Whether this is permitted depends on the official limits of the specific glider.

10. Gliding club operations and shared aircraft

In gliding clubs, the same aircraft may be flown by many pilots with very different body weights. A two-seat glider may also be used for training, trial flights or cross-country flying with changing front and rear seat loading.

A standardized and simple weight and balance workflow helps reduce errors. Aircraft-specific data should not have to be re-entered manually for every flight if a verified profile is available.

11. Practice Tip: TrimCalc app and QR-code profiles

TrimCalc supports aircraft profiles, local storage, QR-code import and QR-code export. It runs directly in the browser and can also be installed as a web app.

13. Common mistakes

• using a profile from a similar but not identical glider
• using outdated weighing data after equipment changes
• confusing meters and millimeters
• forgetting parachute weight
• using estimated pilot weight instead of realistic loading
• not including water ballast
• forgetting trim ballast
• ignoring oxygen equipment or batteries
• not accounting for removed equipment
• checking CG but not maximum take-off mass
• using shared profiles without comparing them with the aircraft documents

15. References and important notes

The official documents of the specific glider are always authoritative:

• flight manual
• current weighing report
• equipment list
• manufacturer information on CG limits and mass limits
• club procedures, if based on official aircraft data