What is the CG envelope?

The CG envelope is a graph published in the aircraft’s POH that shows all approved combinations of gross weight and center of gravity location. Any loading that places the aircraft’s weight/CG point outside this boundary is outside the aircraft’s certified limits.

Can an aircraft be within weight limits but outside CG limits?

Yes — and this is a common source of dangerous loadings. An aircraft loaded with heavy baggage in the aft compartment and light passengers in the front seats may be within its weight limit but aft of its CG limit.

What does "aft CG" feel like in flight?

An aft CG makes the aircraft pitch-sensitive and reduces longitudinal stability. In a stall, an aft CG can make recovery more difficult or impossible. The aircraft may feel "light on the nose" and require forward pressure to maintain level flight.

What does "forward CG" feel like in flight?

A forward CG makes the aircraft nose-heavy. It may require excessive back pressure to rotate on takeoff and to flare on landing. In extreme cases, the elevator may not be powerful enough to hold the nose up at slow speeds.

Why does the envelope shape change with weight?

The forward CG limit typically moves aft at higher weights because the aircraft needs more elevator authority to rotate at higher speeds. The exact shape depends on the aircraft’s aerodynamic design and is determined by the manufacturer through flight testing.

CG Envelope Checker

Plot your aircraft's weight and CG on the approved envelope chart. Enter values manually or arrive from the Weight & Balance Calculator.

Last reviewed: July 2026

Aircraft

Weight (lbs)

CG / Arm (in)

Condition

Cessna 172S Skyhawk SP CG Envelope

Source: Cessna 172S POH, Revision 4 (2006), Part No. 172SPHBUS-00

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Why the CG Envelope Matters

The CG envelope is not just a regulatory requirement — it reflects real aerodynamic limits. The forward CG limit is set by the elevator's ability to rotate the aircraft on takeoff and flare on landing. The aft CG limit is set by the aircraft's longitudinal stability — beyond the aft limit, the aircraft may become uncontrollable in a stall.

A loading that is within weight limits but outside CG limits is just as dangerous as an overloaded aircraft. The FAA treats both as airworthiness violations under 14 CFR 91.9.

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This result is for educational and planning purposes only. Always verify against the current approved weight and balance data for your specific aircraft. Read our full Safety Disclaimer.

Frequently Asked Questions

The CG Envelope in Depth

The center-of-gravity envelope is the graphical region, published in your aircraft flight manual, that shows every combination of weight and CG position the aircraft is certified to fly within. Plotting your computed loading against this envelope is the visual confirmation that a weight-and-balance calculation is legal: if the point falls inside the shaded area, the load is approved; if it falls outside, it is not. This calculator places your loading on that envelope so the result is unmistakable.

The envelope is not a simple box. Its forward and aft CG limits often change with weight, narrowing at higher weights where structural and stability margins are tightest. Understanding the shape of the envelope explains why a load that is fine at a light weight can become illegal as weight increases, and why the safest loadings sit comfortably inside the region rather than hugging an edge.

Step-by-Step: How the Calculation Works

To use the envelope, you first compute total weight and CG exactly as in a standard weight-and-balance calculation, summing moments and dividing by weight. The resulting single point — weight on one axis, CG on the other — is then plotted against the certified boundary. The calculator draws both the envelope and your point so you can see not only whether you pass but how much margin you have.

Because the forward and aft limits vary with weight, the check must be made at the correct weight, not against a single fixed CG range. A thorough analysis plots at least two points: the takeoff loading and the projected landing loading after fuel burn. If a straight line between those points stays entirely inside the envelope, the aircraft remains legal throughout the flight.

More Worked Examples

Example 1 — Comfortably inside

A computed loading of 2,150 lb at a CG of 42 inches plots well within an envelope whose limits at that weight run from about 39 to 47 inches. The point sits near the middle, giving generous margin on both sides and predictable handling.

Example 2 — Near the aft edge at high weight

At the maximum gross weight of 2,550 lb the aft limit may tighten to 46 inches. A rear-heavy load computing to a CG of 46.5 inches now plots just outside the envelope even though the same CG was legal at a lighter weight, showing why the check must be made at the actual weight.

Pilot Decision-Making Context

Reading the envelope turns abstract numbers into an intuitive picture of safety margin. A point near the center means the aircraft will handle as the test pilots found it, while a point pressed against the aft limit warns of reduced stability and a lighter, more sensitive feel in pitch. Experienced pilots deliberately aim for loadings inside the envelope with room to spare, treating the boundary as a hard edge they never plan to touch.

The envelope also guides how to fix a bad loading. If your point falls aft of the limit, moving weight forward — baggage to a forward compartment, a passenger to a front seat — walks the point back into the region. Seeing the plot makes the size and direction of the needed change obvious rather than a matter of trial and error.

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