The bifilar pendulum is a torsional pendulum that can be used to experimentally measure the mass moment of inertia of a test object. A typical application is to measure mass moment of inertia of aircraft, especially small unmanned air vehicles (UAV). This model corresponds to the one discussed in the following article:
Jardin, M., Mueller, E., "Optimized Measurements of Unmanned Air Vehicle Mass Moment of Inertia with a Bifilar Pendulum," Journal of Aircraft, Vol. 46, No. 3, May-June 2009, pp. 763-775.
This paper was also presented at the AIAA GNC Conference in 2007:
Jardin, M., Mueller, E., "Optimized Measurements of UAV Mass Moment of Inertia with a Bifilar Pendulum," AIAA-2007-6822, AIAA GNC Conference, Hilton Head, SC, Aug. 20-23, 2007.