Before a single flight, a careful pilot answers two questions: is the aircraft too heavy, and is the load balanced? Getting either wrong is not a paperwork formality — an aircraft loaded outside its limits may refuse to climb, may be uncontrollable in pitch, or may be impossible to recover from a stall. Weight and balance is the simple arithmetic that keeps the machine inside the range the manufacturer flight-tested. This article walks through the quantities, a full worked loading table, the envelope, and what to do when the numbers fall outside it.
The Weight & Balance Calculator does this math for you — enter each station’s weight and arm and it sums the moments, finds the CG, and tells you whether the loaded point sits inside the envelope.
Why weight and balance matter
Two independent things can go wrong. Too much weight lengthens the takeoff roll, flattens the climb, raises the stall speed, and stresses the structure — on a hot day at a short strip an overloaded aircraft may simply fail to clear the trees. Bad balance is more insidious. The center of gravity (CG) is the point the aircraft balances about, and the tail’s job is to hold the nose where the pilot wants it. If the load puts the CG too far forward or too far aft, the elevator may not have enough authority to control pitch.
An aft CG is the classic killer: the aircraft becomes unstable, light and twitchy in pitch, and — critically — loses the natural nose-down tendency that helps a wing un-stall. An aft-CG stall or spin can be unrecoverable. A forward CG is more stable but nose-heavy: heavy elevator forces, a higher stall speed, and possibly not enough up-elevator left to flare for landing. Both extremes were flown to find the limits; staying between them is the pilot’s responsibility on every flight.
The three quantities: weight, arm, moment
All of weight and balance is built from three numbers per item of load:
| Quantity | What it is | Units |
|---|---|---|
| Weight | How heavy each item is — the aircraft itself, people, baggage, fuel | pounds (lb) |
| Arm | The horizontal distance from the datum to that item | inches (in) |
| Moment | Weight × arm — the turning effect about the datum | inch-pounds (in-lb) |
The datum is an arbitrary reference point the manufacturer picks — often the firewall, the nose, or even a point in space ahead of the aircraft. It does not matter where it is, only that every arm is measured from the same place. Each fixed location where load sits — front seats, rear seats, baggage area, each fuel tank — is called a station, and the Pilot’s Operating Handbook lists the arm for each one.
Finding the center of gravity
The CG is simply the weighted average position of all the load. You add up every weight and every moment, then divide:
Here is a complete loading table for a typical light single (numbers illustrative). Notice fuel is converted from gallons at 6 lb per gallon of avgas:
| Item | Weight (lb) | Arm (in) | Moment (in-lb) |
|---|---|---|---|
| Empty aircraft | 1,510 | 39.0 | 58,890 |
| Pilot + front passenger | 340 | 37.0 | 12,580 |
| Rear seat passengers | 170 | 73.0 | 12,410 |
| Baggage | 40 | 95.0 | 3,800 |
| Fuel (40 gal × 6 lb) | 240 | 48.0 | 11,520 |
| Totals | 2,300 | — | 99,200 |
So this aircraft is loaded to 2,300 lb with its CG 43.1 inches behind the datum. Those two numbers — weight and CG — are the loaded point we now check against the limits.
The CG envelope
The manufacturer publishes a CG envelope: a graph of weight (vertical axis) against CG position (horizontal axis), drawn as a four-sided box or polygon. Its boundaries are the forward CG limit (left edge), the aft CG limit (right edge), and the maximum gross weight (top edge). The loaded point must fall inside this box — both checks at once.
If our point at (43.1 in, 2,300 lb) sits between the forward and aft lines and at or below the gross-weight line, the load is legal and safe. The envelope often narrows at higher weights — the forward limit may move aft as you get heavier — which is exactly why you check the actual loaded point rather than relying on a single number.
The consequences map directly onto the edges. Push against the forward limit and the aircraft is nose-heavy: heavy elevator, higher stall speed, and possibly too little elevator to flare. Push against the aft limit and it is light and twitchy, with degraded stability and the very real risk that a stall or spin becomes unrecoverable.
Fixing an out-of-envelope load
When the point lands outside the box, you do not cancel the flight — you re-arrange it. Because the CG is a weighted average of position, moving weight is a lever you can pull:
- Move baggage. Shifting bags from an aft compartment to a forward one pulls the CG forward; the reverse pushes it aft.
- Swap seating. Putting the heavier passenger in the front seats instead of the rear moves the CG forward.
- Reduce weight. If you are over gross, the only fix is to off-load payload or carry less fuel.
- Watch fuel burn. Fuel weight changes in flight, so the CG moves as tanks empty — a load that is fine at takeoff can drift toward a limit later.
That last point deserves care. Because fuel sits at its own arm, burning it off shifts the CG along the line between the full-fuel and zero-fuel loading points. A flight that is in limits at takeoff may be out of limits on arrival, so prudent pilots check both the takeoff condition and the landing (or zero-fuel) condition. Run every loading scenario through the Weight & Balance Calculator before you fly — it does the moment arithmetic instantly and flags any point that strays outside the envelope, turning a column of figures into a clear go or no-go.
Frequently asked questions
What is the datum in weight and balance?
The datum is an arbitrary reference point chosen by the manufacturer, from which every arm (distance) is measured. It is often the firewall, the nose, or a point ahead of the nose, and it does not have to be on the aircraft. Its only job is to give a fixed zero so that every station has a consistent arm in inches.
How do you calculate center of gravity?
Multiply each item's weight by its arm to get its moment, add up all the weights and all the moments, then divide total moment by total weight. The result is the center of gravity (CG) in inches aft of the datum. You then check that this CG, at that total weight, falls inside the published envelope.
What is moment?
Moment is weight multiplied by arm (the distance from the datum). It expresses the turning effect of a load about the datum, measured in inch-pounds. Moments are what you sum to find the CG, because a single weight at the CG would produce the same total moment as all the individual loads combined.
What happens if the CG is too far aft?
An aft CG makes the aircraft longitudinally unstable and twitchy in pitch, reduces the elevator authority needed to lower the nose, and can make recovery from a stall or spin difficult or impossible. It is generally considered the more dangerous of the two limits because it removes the natural nose-down tendency that aids recovery.
What happens if the CG is too far forward?
A forward CG makes the aircraft nose-heavy: the elevator feels heavy, more up-elevator is needed to flare, stall speed rises, and at the extreme you may run out of elevator to raise the nose for landing. It is more stable than an aft CG but costs control authority and performance.
Does fuel burn change the CG?
Yes. As fuel is consumed the aircraft gets lighter and the CG shifts along the line between the takeoff and zero-fuel loading points, depending on where the tanks sit relative to the CG. A load that is in limits at takeoff can move toward or even past a limit later in the flight, so pilots check both takeoff and landing (or zero-fuel) conditions.
Can I be under max gross weight but still unsafe?
Yes. Weight and balance are two separate checks. You can be comfortably below maximum gross weight yet have the CG outside the forward or aft limit, which makes the aircraft hard to control even though it is not overloaded. Both the total weight and the CG position must be within limits.
How do I fix a load that is outside the envelope?
Redistribute the load: move baggage to a different compartment, swap which seats people occupy, shift heavy items forward or aft, or reduce fuel or payload to lower the weight. Because moving weight changes the CG, even small relocations can bring an out-of-limit point back inside the envelope.