Axial Bowstrings · Tools

Arrow Stability Calculator

FOC tells you where an arrow balances. It cannot tell you how that arrow will fly, because it contains no aerodynamics at all — swap a field point for an equal-weight broadhead and FOC barely moves. This calculates the centre of pressure from your actual vane and broadhead geometry, so you can see the stability your FOC number is hiding.

Shaft

Shaft type

Length in

OD in

GPI

Nock throat to end of shaft, not including the point — the ATA/AMO convention.

Front end

Head

Ferrule len in

Blades in flight

Cut dia in

Blade length in

Blades in flight. A mechanical that stays closed should be 0 — that is why it flies like a field point.

Head weight gr

Insert gr

Back end

Vane / feather

Length in

Height in

Grains ea

Count

Nock gr

Wrap gr

Trailing edge from nock throat, in

Flight

Arrow speed fps Angle of attack for CP, degrees

Centre of pressure moves forward as yaw increases, so a stability figure is meaningless without stating the angle. 4° is the convention used throughout Axial's research.

What your broadhead actually costs you

—

Equal-weight field point

—% FOAC

FOC—

Static margin—

Settles by—

Your head

—% FOAC

FOC—

Static margin—

Settles by—

—

Total weight

— gr

FOC

— %

FOAC

— %

Settles by

— yd

Where the steering force comes from

Component	Share of steering	Acts at	Effect

Anything acting behind the balance point steers the arrow straight. Anything acting ahead of it steers the arrow off course — that is what broadhead blades do.

Fletching that restores this broadhead

—

Fletching	Count	FOAC	Settles	Added gr	Restores

Flight behaviour

Measure	Value	Meaning

Shaft

Front end

Back end

Flight

—

Equal-weight field point

Your head

Where the steering force comes from

Fletching that restores this broadhead

Flight behaviour

Notes on your components