Overview
In order to improve safety and efficiency of air transport, new composite materials such as carbon fibre reinforced polymer and novel primary structure design architectures are being considered to replace traditional sheeting. Lattice structures used for spacecraft rocket interstages and fairings preserve high strength and safety and are thus an attractive option for composite airframe structures.
The idea behind the ALASCA project was to perform a comprehensive investigation, starting with the beneficial geodesic design well-proven in space technology and transferring it to composite aircraft fuselage designs. The main objectives of this research programme were:
- Maximum weight and cost reduction by using lattice designs for fuselage structures;
- Development of manufacture-optimised lattice designs satisfying airworthiness requirements;
- Verification of airworthiness by manufacture and testing of representative lattice components.
Since structural requirements and boundary conditions in rocket technology are quite different from those in aircraft fuselage design, the scope of this project covered the specific aspects of design, sizing, manufacture and testing of lattice structures that follow from aircraft requirements. The objectives will only be achieved when solutions to the following issues in terms of lay-out, design, sizing, manufacture, and testing are found:
- Pro-lattice aircraft configurations for maximum weight and cost savings;
- Aircraft specific components treated in the lattice fuselage design;
- Lattice elements, i.e. examination in the aircraft-specific detailed design of loads from impact and internal pressure.
Starting with the definition of requirements and specification for civil aircraft fuselages, a number of aeroplane configurations are compared for optimal fuselage barrel design and manufacturing efficiency. Identifying the most suitable aircraft design, the fuselage section loads are provided for the fuselage barrel section design process.
Herein two pro-lattice and two reference barrel design concepts for the barrel section has been developed, sized and compared in terms of weight and manufacturing costs. On component level, design solutions for a lattice structure have been performed for window cut-outs, barrel-floor interfaces and barrel-barrel interfaces.
Despite the design concept development for a suitable pro-lattice barrel section, an important aspect of EU- ALaSCA is the lattice sizing method development, which is done on barrel, component and element level.
Funding
Results
In the level 1 project ALaSCA (Advanced Lattice Structures for Composite Airframes) the potential of novel airframe architecture has been demonstrated. Deriving from a spacecraft well proven structure design, two different pro-lattice barrel concepts has been developed. On the one hand a highly integral airframe concept, which can be produced in automated tape laying or winding process. On the other hand, a differential design concept with load bearing skin and a multifunctional covering of the primary structure.
Innovation aspects
For an investigation of the impact of the weight reduction on aircraft level, a mass reduction of 10% of primary structure weight has been implemented in the airplane configuration calculation only for the ALaSCA barrel section. Due to scaling effects on other aircraft components, the barrel mass reduction results already in 1% overall fuel consumption reduction for the flight mission of such short and middle range aircraft. These significant design improvements for composite geodesic fuselage structures derived from following findings:
- The resulting non-rectangular skin bays between the ribs, which show increased buckling coefficients compared to rectangular skin bays with the same weight.
- The uniaxial loading of the monolithic ribs, with which a strain allowable increase can be pursued, considering an impact protection of the highly oriented ribs.
- Aiming a possibly high axial stiffness for the stiffeners, CFRP-Metal Hybrid shows the potential achieving a high axial stiffness, while also being damage tolerant.
Readiness
Due to the focus of EU-ALaSCA on a global barrel design level, there are open questions on the local level. The successful applied follower project, called EU-PoLaRBEAR, will focus on the above-mentioned investigations, relying on a bottom-up approach on local level to increase the technology readiness level of geodesic structures.