Global Model Approach for X-31 VECTOR System Identification

Abstract

A global model approach developed on data from the experimental aircraft program X-31 EFM was recently improved during the X-31 VECTOR program. Both programs are briefly presented, focusing on extremely precise ESTOL landings following a slow, thrust-vectored approach at high angle of attack. High-accuracy navigation and inertial sensor systems enable onboard calculation of the height above runway with sufficient accuracy which is also required to identify ground effect. System identification procedure utilizes a global model to cover the entire flight regime including high-lift configuration during power approach and landing. Analysis of specially designed flight test led to aerodynamic increment tables for supplementary update of the original database. The wind-tunnel and computational fluid dynamics (CFD) predicted ground effect was incorporated into the higly accurate identified global model, which was then used for conventional landings resimulation to support the initial extremely short takeoff and landing (ESTOL) to the ground flight clearance process. Recently an incremental ground effect model was implemented to supplement the original data set. First identification results from conventional and ESTOL landings show some improvements compared to the predictions at very low height above ground.