Custom Engineering · Platform and Payload Customization

Weight and Balance Assessment

Weight and balance is done per configuration, in writing, and re-done whenever anything changes. It is cheap to do and expensive to skip.

3 of 10Method note

Overview

Build a mass table with a moment arm for every item, and keep it with the configuration record.
Check lateral and vertical as well as longitudinal; offset or high-mounted payloads cause different problems.
Include the mount, cabling, fasteners and any counterweight in the table — these are the usual omissions.
Re-verify after any payload, battery or mount change, and record the result rather than relying on memory.

Two numbers, and the second is the dangerous one

A weight and balance assessment produces two results and they are not equally forgiving. The first is whether the total mass is within what the aircraft can carry and still complete the mission. The second is whether that mass sits within the centre-of-gravity envelope. A configuration can pass the first and fail the second, and failing the second is more dangerous because the symptom appears in flight rather than on the ground.

The reason is control authority. An aircraft has a finite amount of authority to hold attitude and to correct disturbances. A load outside the intended envelope consumes some of that authority simply to hold attitude, leaving less to correct a gust or to recover. The aircraft may fly perfectly right up to the moment it needs the margin the load has already spent.

So the assessment must be done with the actual load, in the actual container, in the actual mounting position. A representative estimate is not sufficient, and the difference between an estimate and a measurement is exactly where these problems live.

How we establish it

Total mass is measured, not estimated. Weigh the loaded container at the loading point. Where contents vary trip to trip, weigh each trip or define a documented standard load and confirm it is being followed. A scale at the loading point removes an assumption from every flight.

Centre of gravity is the harder one. Where the platform publishes a mounting position and an envelope, and the container is standardised with a documented empty centre of gravity, it is a calculation. Where either is missing, it becomes a measurement. Where the load can move — liquid, granular, slung — the assessment has more than one answer and has to cover the range of positions the load can occupy.

Free liquid surface is the classic case and the reason baffles exist in tanks. A partly filled tank changes its centre of gravity as the aircraft manoeuvres, and the dynamic behaviour is worse than the static one. If your load can move, say so at the requirement stage, because it changes the assessment from a single number into a range.

What happens when it fails

If total mass is over, the options are to reduce the load, to split it, or to remove something else — and the honest answer is usually the first or second. Carrying more than the allowable payload is not a marginal decision; it is a decision to operate outside the tested envelope, and it affects handling, endurance and structural margin at the same time.

If the centre of gravity is out of envelope, the answer is usually to reposition the load or redistribute the contents, and that is usually cheap. Where it is not possible — a load that must hang from a specific point, for instance — the configuration needs engineering attention rather than a waiver.

The two interact, and this is where assessors go wrong. Reducing mass moves the centre of gravity. Repositioning changes drag. Re-run the assessment after any change rather than assuming that a change which improves one figure leaves the other untouched.

Turning it into routine

The assessment should be a documented step before flight rather than a design exercise done once. Loads change, containers wear, hardware is replaced and contents vary. A two-minute check with a scale and a documented container is what keeps the design assumption true on the two-hundredth flight.

The minimum routine is: weigh the loaded container, confirm the loading position matches the documented one, confirm the securing is engaged, and record the figures. Where the same container and load are used repeatedly this collapses into a confirmation that nothing has changed, but it should remain a named checklist item rather than an assumption.

Record keeping is what makes it worth doing. A log of loaded mass and configuration per flight turns an incident into a diagnosable event and a slow drift into a visible trend. Our cargo box and load securing note covers the physical side, and the log is what makes it auditable.

Commissioning an assessment

For a standard platform with a standard container inside the published envelope, the assessment is a procedure the operator runs — we can supply the worksheets and the routine. For anything else, it is engineering work and it should include a flight test.

Send the platform, container, load mass and dimensions, mounting position and any variability in the load. We will confirm whether the configuration sits inside the envelope and, where it does not, what would need to change.

Contact our engineering team, and see flight test scheduling for how the airborne validation is arranged where the configuration has not been flown before.