Stability and Control Characteristics of High Performance Aircraft

A-10 aircraft with centerline fuel tank used in System Identification (SID) of CFD.

A-10 aircraft with centerline fuel tank used in System Identification (SID) of CFD. Isosurface of vorticity.

The motivation for this work is to initially use CFD so that flight test and wind tunnel resources can be applied where they are needed the most.  The combination of Cobalt with the resources of High Performance Computation program of the DoD allow for more in-depth simulations and quick turnaround.  This work is a good step toward the end goal of ‘flying’ an aircraft using Cobalt.

During this work, the A-10 with centerline fuel tank was simulated in order to compare CFD and SID of CFD versus wind tunnel.  Developing a SID model can be done in minutes and once validated, it can calculate stability derivatives for a small portion of an aircraft’s aerodynamic database.  A dynamic, time-accurate simulation of a maneuver developed to produce a SID of the A-10 is shown below.

Modeling moving control surfaces on a full-scale aircraft is the next step in capability development. Two simulations for the same maneuver were conducted. Full-scale, dynamic, time-accurate analysis of the F-16 in the clean aircraft configuration, with moving horizontal tails, and with moving horizontal tails and moving leading edge flaps (LEF) was accomplished using Cobalt and the overset grid method. The aircraft and control surfaces motions are accomplished by reading in time histories computed using ATLAS and forcing the aircraft and control surfaces through a prescribed motion. By doing this, more accurate results can be obtained and a more realistic simulation is achieved.  In the animation below, the F-16 is put through a flight maneuver as the control surfaces deflect according to a schedule.  The automatic overset grid assembly is shown near the end of the animation.

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