Weight & Balance

Helicopter performance and handling depend critically on weight (how much) and CG (where). Helicopter CG envelopes are notably tighter than fixed-wing — there's less margin for error in loading. Out-of-CG operations don't merely degrade performance; they can produce a flight regime where the cyclic doesn't have enough authority to recover from a maneuver. Always compute weight and balance before flight — particularly with passengers, fuel loads, sling loads, or unusual cargo configurations.

Cabri G2 exterior diagram from the RFM showing the longitudinal datum reference and the arms from datum to each weight station — pilot, passenger, fuel tank, baggage compartment. Dimensions in inches/millimeters per the certification basis. — Cabri G2 datum and station arms (RFM). The datum is the reference point from which every load's "arm" is measured. Multiply load × arm to get its moment; sum moments and divide by total weight to find the CG.

The basic terms

Datum — an imaginary reference point from which all arms are measured. Specified in the POH; varies by aircraft (often the rotor mast centerline or a forward fuselage reference).
Arm — horizontal distance from the datum to a component or load. Forward of datum is sometimes negative; aft is positive (or vice versa, per POH convention).
Moment — weight × arm. Used to compute CG.
Center of gravity (CG) — the point where total weight effectively acts. Computed by summing all moments and dividing by total weight.
Basic empty weight — standard helicopter + optional equipment + unusable fuel + full operating fluids (including engine oil).
Operating empty weight — empty weight + pilot + crew baseline.
Maximum gross weight — POH limit for total weight. Two flavors: internal max gross (occupants, fuel, baggage) and external max gross (with sling load).

Computing W&B

Look up basic empty weight and arm (or moment) in the aircraft's most recent W&B sheet.
Add each load (pilot, passenger, fuel, baggage) with its weight and arm. Compute moment for each.
Sum total weight, sum total moment.
CG = total moment ÷ total weight.
Compare CG and total weight against the POH envelope chart. Both must be within limits.

Most flight schools provide a tabulated worksheet. Software (like ForeFlight or SkyVector W&B tools) automates this. Either way, the math takes 5 minutes and prevents the kind of mistake that doesn't fix itself in the air.

Cabri G2 weight-and-balance calculation worksheet (imperial units) from the RFM. Columns for weight (lb) and arm (in) and computed moment (lb-in) at each station; totals at the bottom; resulting CG location and within-envelope check. — Cabri G2 W&B calculation sheet — imperial units. Fill in weights at each station, multiply by arm to get moments, sum, divide moment by weight to get CG.

Cabri G2 weight-and-balance calculation worksheet (metric units) from the RFM. Same structure as the imperial sheet but with weight in kilograms, arm in millimeters, moment in kg-mm. The Cabri's European certification provides both unit systems. — Cabri G2 W&B calculation sheet — metric units. The Cabri is European-certified (EASA / JAR-27 / CS-27), so the RFM publishes both unit systems. Pick the one your operator uses; the math is identical.

The longitudinal CG envelope

The "envelope" is the region of weight + longitudinal CG combinations within which the aircraft is certified to operate. Outside the envelope, controllability and structural margins are no longer guaranteed.

Cabri G2 longitudinal CG envelope plot from the RFM. Vertical axis is gross weight; horizontal axis is longitudinal CG location. The envelope is a quadrilateral with a forward limit that shifts aft at higher weights and an aft limit that may shift forward at higher weights. — Cabri G2 longitudinal CG envelope (RFM). Total gross weight on the vertical axis, longitudinal CG on the horizontal. Your computed (weight, CG) point must land inside the quadrilateral. Some envelope edges have weight-dependent limits — the forward and aft CG limits can shift as weight changes.

Lateral CG — the often-forgotten axis

Most fixed-wing W&B focuses entirely on longitudinal CG because the airframe is symmetric and lateral loading is rarely an issue. Helicopters are different: occupants sit side-by-side near the rotor mast, fuel is often a single off-center tank, and side-mounted equipment (door-opening sensors, hoists, external cameras) shifts CG laterally. The lateral CG envelope is just as real as the longitudinal one.

Cabri G2 lateral CG envelope from the RFM. Vertical axis is gross weight; horizontal axis is lateral CG offset from the centerline (left negative, right positive). The envelope is narrower than longitudinal — most fuel and occupant positions produce small lateral offsets but they must still land inside the boundary. — Cabri G2 lateral CG envelope (RFM). Lateral offset from centerline on the horizontal axis, gross weight on the vertical. Solo flight with no front passenger, asymmetric fuel, and side-mounted equipment can each push the lateral CG; always verify it sits inside the envelope.

Forward CG — too much weight up front

Loading too far forward (heavy front passenger, light rear passenger, full nose baggage) shifts the CG forward.

Effects: Helicopter wants to pitch nose-down. Cyclic must be held aft to maintain attitude. In cruise, you may have less aft cyclic remaining than you'd like.
Risk: May not have enough aft cyclic authority to flare for landing. Excessive landing distance, possible inability to slow down before touchdown.
Fix: Move some weight aft (rear passenger, baggage repositioned).

Aft CG — too much weight in back

Loading too far aft (heavy rear passenger, light or no front passenger, baggage in the tail compartment) shifts CG aft.

Effects: Helicopter wants to pitch nose-up. Cyclic must be held forward to maintain attitude. In cruise, you may have less forward cyclic remaining.
Risk: May not have enough forward cyclic to lower the nose if a gust pitches you up. Risk of tail boom strike at high airspeed.
Fix: Move some weight forward (front passenger, repositioned baggage).

Aft CG is generally considered more dangerous than forward CG for helicopters because the recovery techniques (forward cyclic) are limited.

Underloading — solo flight ballast

Some helicopters (notably the Robinson R22 and R44) require a minimum weight or forward ballast for solo operations. The reason: an empty front seat shifts CG aft, putting the helicopter near or beyond the aft CG limit.

Without proper ballast, autorotation may not be achievable at desirable rotor RPM — the rotor may not autorotate properly. Robinson POH specifies seat ballast weights for solo flight. Use them.

Effects of overloading

Longer takeoff and landing distances
Reduced rate and angle of climb
Lower service ceiling
Reduced cruise speed and range (more induced power demanded)
Decreased maneuverability
Excessive structural loads — potentially exceeding airframe limits
Increased risk of retreating blade stall at high airspeed
Reduced VRS margin during slow flight

Overweight operation is illegal under FAR 91.9 and 91.13. It's also dangerous in proportion to how far over the limit you are. There's no margin past max gross weight.

Cabri G2 reduced-maximum-weight chart from the RFM. Maximum allowable gross weight on the vertical axis, density altitude on the horizontal axis. At higher DA the chart prescribes a reduced maximum weight to preserve OGE hover capability and adequate margins. — Cabri G2 reduced-weight chart (RFM). At higher density altitude, the maximum allowable gross weight is reduced below the placarded number to preserve adequate hover and climb performance. This chart turns the "high-DA penalty" into hard numbers you can plan against.