Matching Moment of Inertia in OpenRocket

Slide with OpenRocket diagram and steps for matching CG and moment of inertia: 1. Measure empty rocket mass and center of gravity location; 2. Measure empty rocket longitudinal moment of inertia using Bifilar pendulum; 3. Create basic OpenRocket file (only need external features and parachutes); 4. Override individual component masses to zero; 5. Create two mass objects with zero thickness, a diameter equal to the rocket airframe, and a mass of half the measured rocket mass; 6; Evenly space the mass objects from the measured CG by the measured radius of gyration r = sqrt(I / M) — Image by Drew Nickel.

I found this method in the OpenRocket Facebook group. The image and description are credited to Drew Nickel.

Pro-tip for more accurate dynamic stability analysis in OpenRocket: measure your rocket’s moment of inertia directly with a Bifilar pendulum, override each component’s mass to zero, and use two mass objects that together equal the weight of the rocket evenly spaced from the measured cg to match the measured longitudinal moment of inertia and center of mass of your rocket. Video tutorial on using the Bifilar pendulum: [1]

Updated YouTube link provided by Ezra Christensen: