Sandia National Laboratories has finished testing a full-scale mock unit representing the aerodynamic characteristics of the B61-12 gravity bomb in a wind tunnel. The tests on the mock-up were done to establish the configuration that will deliver the necessary spin motion of the bomb during freefall and are an important milestone in the Life Extension Program to deliver a new version of the aging system.
The B61 must spin during flight — spin that is controlled by a combination of rocket motors and canted fins on the tail. Engineers determined from flight tests in the 1990s that plumes from the rocket motors worked against the fin performance, counteracting the torque from the motors and reducing the vehicle spin rate. Sandia engineers termed that phenomenon "counter torque."
The complex test required a wind tunnel big enough for a full-size mock B61. Most wind tunnel tests use models smaller than the actual flight hardware, but the physics of the B61 rocket motors cannot be replicated on a reduced scale. Researchers determined that the test uncovered a previously uncharacterized physical phenomenon that they believe arises because of the unusual shape of the rocket motors and from other features.
The Sandia team revised the remainder of the wind tunnel tests to provide fresh data to unravel the complex physics of the behavior observed at near-sonic flow conditions. The improved understanding will inform the design of the B61-12 and provide an additional technical basis for the well-characterized performance of the versions of the B61 in the current U.S. stockpile.