High fidelity ground effect model based on DGPS data

A global model approach developed on the X-31 EFM data was recently improved during the experimental aircraft program X-31 VECTOR. The VECTOR program is briefly presented, focusing on extremely precise ESTOL (Extremely Short Take-Off and Landing) manoeuvre 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 utilises a global model to cover the entire flight regime including high lift configuration during power approach and landing. Analysis of specially designed flight tests led to aerodynamic increment tables for supplementary update of the original database. The wind-tunnel and CFD-predicted ground effect was incorporated into the highly accurate identified global model which was then used for conventional landings re-simulation to support the initial 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 shortly before touch down.