Prepavol calculates an aircraft's total mass and centre of gravity from the data in its profile, and shows the result in a chart with the centre of gravity envelope. The calculation is used in three places: the aircraft calculator, the flight file (“Navigation” menu) and the performance page.
Filling in the aircraft profile
The calculation is only possible if the aircraft profile (aircraft edit page, “Mass & Balance / Performance” section) is filled in. It requires permission to edit aircraft.
“Masses and moment arms” block
- “Empty weight (kg)” and “Empty mass arm (m)”;
- “Front seats arm (m)”, “Rear seats arm (m)” and “Baggage arm (m)”;
- “Fuel arm (m)”, shown only if the aircraft has fuel;
- “Front seats”, optional: leave empty for the default value, or enter 1 for a tandem aircraft.
The stations are fixed: front, rear, baggage and fuel (and ballast for a glider). Each has a single arm. All rear seats share the same arm.
“Centre of gravity envelope” block
- “Minimum mass”, “Intermediate mass” and “Maximum mass” (in kg);
- “Minimum moment”, “Intermediate moment” and “Maximum moment”: despite the word “moment”, these three values are centre of gravity positions in metres (forward and aft limits at each mass step).
“Performance” block: “Fuel tank (L)”, “Fuel density” (0.72 by default) and “Maximum take-off weight (kg)”. A glider has no tank, density or fuel arm, but a “Max water ballast (kg)” and a “Water ballast arm (m)”.
As long as the empty weight is not filled in, the page shows a message asking you to fill in the aircraft's weight and balance in its profile first, with a “Configure profile” button.
The calculator
There is no “Weight and balance” entry in the menu. It is reached from the aircraft profile, with the “Weight & balance calculator” button.
Enter the “Front pilot (kg)” (80 by default), the “Rear pilot (kg)” if the aircraft has at least two seats, the “Fuel (L)”, the “Baggage (kg)” and, for a glider, the “Water ballast (kg)”. The calculator shows:
- the total mass and the maximum allowed mass with the available margin;
- the centre of gravity in metres: total moment divided by total mass;
- the verdict “Within envelope” or “Out of envelope!” (in red), and the chart.
For a helicopter, only the longitudinal centre of gravity is calculated: check the lateral balance in the flight manual. Calculation for a balloon is not supported.
Reading the chart
The chart plots the centre of gravity on the horizontal axis (in metres) and the mass on the vertical axis (in kg). The “Envelope” curve draws the limits from the profile, and the “Center of Gravity” point is green inside the envelope and red outside. The chart only appears if the envelope's “Minimum mass” is filled in.
In the flight file
In the “Navigation” page, the “Front seat (kg)”, “Rear seat (kg)”, “Fuel (L)” and “Baggage (kg)” fields feed the calculation. Masses are filled in from the “Crew and passengers” block (with an “Optimise seating” button). The “Manual mass entry” box lets you type them in directly.
- The “Generate briefing” button stays disabled until the departure, arrival, aircraft, front mass and fuel are filled in, or if a mass field is invalid.
- A field turns red if the value exceeds the calculated maximum (“Max: N kg” indication), provided the maximum take-off weight is filled in.
- The chart is inserted in the file's PDF, “Summary & balance” block. In case of excess, the PDF shows a warning that the maximum mass is exceeded with the value and the excess, and the summary states “Within the CG envelope” or “OUTSIDE THE CG ENVELOPE”.
- Only active aircraft that have performance data are offered.
An “Out of envelope!” result does not prevent generating the file: only invalid fields block the button. Do not depart on the strength of a generated file without checking the result.
Passenger book
The “Passenger book” (/passengers/registry/, with permission to manage passengers) records frequent passengers and their weight. The weight is validated from 1 to 400 kg. Occupants have a “Front” or “Rear” seat, and weights are added up per row. A weight is only used with the person's consent.
Frequently asked questions
Where do I find the weight and balance calculator?
Open the aircraft profile (aircraft menu), “Mass & Balance / Performance” section, then the “Weight & balance calculator” button. There is no dedicated entry in the side menu.
Why is the chart not shown?
The chart requires the envelope's “Minimum mass” to be filled in on the aircraft profile, in addition to the empty weight and the arms.
Are the three “Moment” values of the envelope really moments?
No. Despite the label, they are centre of gravity positions in metres: the forward and aft limits at the minimum, intermediate and maximum mass.
Does Prepavol calculate the lateral balance of a helicopter?
No, only the longitudinal centre of gravity is calculated. A message invites you to check the lateral balance in the flight manual.