Six degree of freedom computation of the F-15E entering a spin

A six-degree-of-freedom computational model is used to calculate the the motion of an F-15E entering a spin. The massively separated flowfield around the aircraft is predicted using Detached-Eddy Simulation (DES). These simulations build on previous calculations of the aircraft at high angle of attack, both at static conditions and with a prescribed rotary motion. Predictions are assessed via comparison to Boeing's stability and control database. Asmall bump is added to the nose of the aircraft that triggers an asymmetric vortex shedding on the forebody, as observed in flight and wind tunnel tests at high angles of attack. The yawing moment produced by the asymmetric vortices drives the spin. Three attempted spin entries are calculated. The first attempt releases the aircraft from rest and in a horizontal attitude. The aircraft drops, the nose rapidly tucks down, and the aircraft recovers. The aircraft passes through the high angle of attack regime too quickly to develop a significant spin rate due to the asymmetric vortex shedding around the forebody. The remaining two attempts prescribe a rotary motion around the center of gravity and the freestream velocity vector with the aircraft at 90° angle of attack and descending vertically at Mach 0.3. The two attempts differ only in the initial direction of rotation. For one case, the asymmetric vortex shedding results in an anti-spin yawing moment. In this case the aircraft rotation rate rapidly decreases, the nose tucks down, and the aircraft recovers. For the second attempt, an oscillatory spin is entered and maintained for over five revolutions. The mean angle of attack, descent rate, and spin rate match well the expected conditions from the stability and control database. However, bank oscillations grow over time, and eventually reduce the effective angle of attack sufficiently to eliminate the asymmetric vortex shedding on the nose, reducing the spin rate. The aircraft then begins a recovery. The calculations were performed on 512 to 1024 processors allowing a rapid turn around despite the very large number of timesteps required.