Bewertung von CFK-Strukturen in einem multidisziplinären Entwurfsansatz für Verkehrsflugzeuge (English shop)

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Brief description

The present work deals with the representation of fiber-reinforced plastics (FRPs) within an existing overall design process for commercial aircraft and exploits the new design possibilities arising from this.

To this end, their anisotropic properties are specifically exploited for the design of the wing, taking static aeroelastic effects into account and applying aeroelastic tailoring. Representing these effects in an early phase of aircraft design can help to make future aircraft designs more economical and thus meet market requirements. To classify the work, an overview of programs for determining the structural masses of aircraft designs is first given, and it is highlighted to what extent the present work fills a gap in the field of mass estimation of structures made of FRPs. The aim of the work is therefore, on the one hand, the mass estimation of FRPs and, on the other hand, the feedback of the results into the integrated overall design. Subsequently, the present overall design process and important representatives of overall design methods for aircraft are compared in order to highlight the level of detail of the extended process.

The necessary extensions to the process are described together with a presentation of the theoretical approaches used, and solutions to the resulting problems are derived. The extensions are validated at the overall design level using the example of a medium-range and a long-range aircraft. Parameter studies are then carried out on these example aircraft in order to demonstrate the new capabilities of the overall design and the sensitivities of classically isotropic wings and those made of FRPs to changes in the circulation distribution. For both the medium-range and the long-range aircraft investigated, slightly triangular circulation distributions prove to be advantageous. The CFRP wing shows an optimum closer to the ideal elliptical distribution and leads to generally lighter designs. The influence of static aeroelasticity is small for the medium-range aircraft, but not negligible for the long-range aircraft.

Finally, the influence of aeroelastic tailoring was investigated for a forward-swept and a backward-swept wing on a medium-range aircraft. Through aeroelastic tailoring, a slight reduction in structural mass resulting from passive load alleviation can generally be observed, without drastically affecting control surface effectiveness in a negative way. However, the investigations also show that aeroelastic tailoring alone is not the key technology to compensate for the structural weight disadvantages of a forward-swept wing, which could be of interest for future commercial aircraft from an aerodynamic point of view.

Description

The present thesis covers the representation of fiber reinforced plastics within an existing preliminary aircraft design tool and makes use of the new degrees of freedom through this material. Therefore the anisotropic properties under consideration of static aeroelastic effects are used systematically on the wing design by implementing aeroelastic tailoring. The representation of these effects in an early stage of the aircraft design can help to make future aircraft designs more economic and by this to fulfill the market requirements. For the classification of the thesis first an overview over codes for mass estimation of aircrafts structures will be given. Further it will be highlighted, to which extent this theses fills a gap in the field of mass estimation codes for fiber reinforced plastics. The thesis’ ambition is on the one hand the mass estimation of fiber reinforced plastics and the feedback on the integrated overall design process. Following this, the existing preliminary design process and important representatives of overall preliminary design processes for aircrafts are opposed, to emphasize the degree of details of the extended process.

The necessary changes in the process are described within the presentation of applied theoretical approaches and solutions for the resulting problems are derived. Using the example of a mid and long range aircraft the extensions are validated at preliminary overall aircraft design level. The new features of the design process and the sensitivity to different circulations of classic isotropic built wing and wings out of fiber reinforced plastics are shown within parametric studies for both mid and long range aircraft. Both types gathering benefits out of a slightly ‘triangular’ circulation in spite of an ideal elliptic circulation. A CFRP wing has an optimum closer to the elliptic circulation and makes the designs in general lighter as a wing out of isotropic material. The impact of static aeroelastics are minor to the mid range aircraft but must not be neglected on long range aircraft. Concluding, the impact of aeroelastic tailoring is analyzed for a forward swept wing and a backward swept wing at the example of a mid range aircraft. Through aeroelastic tailoring in general a slightly reduction of structure masse can be observed.

The impact on rudder effectiveness is present but brings no reduction of the design space. As another result the mass disadvantage of the forward swept wing cannot be reduced to zero by aeroelastic tailoring. However, the results make obvious, that aeroelastic tailoring brings only minor advantages and that further studies of non balanced laminates in detail level are necessary.