Solar Impulse – How to validate the numerical model of a superlight aircraft with A340 dimensions!

Abstract

"The Solar Impulse project ... aims to have an airplane that can take off and fly autonomously, day and night, propelled uniquely by solar energy, right around the world without fuel or pollution. An unachievable goal without pushing the current technological limits in all fields..."

This citation from the Solar Impulse homepage describes the engineering challenges for the aircraft development. The particular design and the use of novel materials made it possible to produce an aircraft with 63m wing span with only 1.7 t of weight including pilot. This superlight design demands very accurate testing procedures. In addition, the magnitude of the apparent mass of the surrounding air in relation to the structural mass requires a new approach for the model validation process to take these effects into account.

This paper will give insight in a two step model validation strategy. The dynamic characteristics of a) the load carrying structure and b) the full aircraft equipped with solar panels were determined experimentally in two ground vibration test (GVT) campaigns. The modal parameters extracted from GVT were used to update the FE model of the load carrying structure at first and of the aircraft ready for flight afterwards.

In detail, this paper presents the procedure for GVT on an aircraft with eigenfrequencies considerably below 1 Hz. For the model updating strategy, the approach for the analytical determination of eigenfrequencies and mode shapes with the apparent mass effects included is presented.