„SAGITTA – Unmanned Aerial Vehicle with�innovative CFRP airframe “�

Abstract

The age of Unmanned Aerial Vehicles (UAV) has already begun and will grow substantially in the next few years. Besides small size drones below 5kg there are various ongoing developments that focus on significantly larger aerostructures.

The SAGITTA UAV has been developed in an “Open Innovation” Initiative lead by Airbus Defense and Space. The strategic approach behind SAGITTA was to investigate a VLO (Very Low Observability) concept that is based on an invertedly flying UAV with an undisturbed and clean surface on the ground facing side. The UAV itself has a span of 3m, a MTOW (Maximum Take off Weight) of 150kg. The UAV is equipped with two jet engines (2x300N) and shall be able to fly without vertical stabilizers. The MTOW limit of 150kg and the parachute based termination system were hard requirements form certification side.

DLR as one of the partners was mainly involved in flight simulation concepts, system aspects and in the realization of the landing gear and the composite airframe structure. Even though the flight hardware itself was not the major challenge of the project when it started, structural complexity as well as certification and weight requirements soon reached a level where conventional approaches where no longer applicable. In the final stage of the project the only chance to meet the demands was an approach based on extremely low areal weight thin ply prepreg/micro-sandwich structures that were assembled by structural bonding.

Even more challenging were the extreme forces that had to be dealt with. The dominating and critical load cases were activation of the termination system and hard landing because these highly concentrated loads had to be gently introduced into the highly filigree airframe structure. Surface requirements were also very high especially on the “clean side”. The complete leading edge had to be integrated into the wing skin in order to avoid any seems and dedicated impedance variations. Above all the complete bonding based assembly procedure had to be “First Time Right” because there was no “Fall Back” solution foreseen within the limited budget and timeframe of the project.

Taking all the above mentioned challenges into account the successful flight test in July 2017 was the final prove that cooperation between Industry and research institutions can be extremely fruitful especially when the target is as ambitious as it was in the SAGITTA project.