Loads Kernel User Guide

The Loads Kernel Software allows for the calculation of quasi-steady and dynamic maneuver loads, unsteady gust loads in the time and frequency domain as well as dynamic landing loads based on a generic landing gear module. This report is a published of the Loads Kernel User Guide, version 1.0 as of 7. October 2020

Gust Encounter of a Supersonic Fighter Aircraft using CFD Methods

The gust encounter of a supersonic fighter aircraft is investigated with the CFD code SU2 and the aerodynamic panel methods VLM and ZONA51. The interaction of the elastic aircraft, the flight controller and the gust is captured in a closed-loop time domain simulation. The comparisons show a moderate agreement between aerodynamic panel methods and CFD in terms of section loads, which has multiple reasons: first, the two aerodynamic methods yield different pitching moment characteristics, which have an influence on the flight mechanical reaction of the aircraft and the reaction of the flight controller. Second, due to the increase of the effective angle of attack during the gust encounter, vortices develop, which are not present in the horizontal level flight condition. Because of the large suction peaks due to the vortices, the surface pressure distribution changes significantly, an effect that is missed completely by the aerodynamic panel methods. The section loads predicted by the CFD based approach are higher, which eventually influences the structural sizing of the aircraft. Also, there is a significant structural dynamic reaction, which shows that for fighter aircraft, a transient gust analysis including structural elasticity is essential for the aircraft design

Loads Kernel User Guide

The Loads Kernel Software allows for the calculation of quasi-steady and dynamic maneuver loads, unsteady gust loads in the time and frequency domain as well as dynamic landing loads based on a generic landing gear module. This report is a published copy of the Loads Kernel User Guide, Version 1.01 as of 11. January 2021

Preparation of Loads and Aeroelastic Analyses of a High Altitude, Long Endurance, Solar Electric Aircraft

High altitude, long endurance aircraft can serve as platform for scientists to make observations of the earth over a long period of time. Staying airborne only by solar electric energy is, as of today, a challenge for the aircraft design and requires an extremely light weight structure at the edge of the physically possible. This paper focuses on the loads and aeroelastic aspects of such a configuration, discusses the selected strategies and presents the applied methods and tools, including the resulting models prepared for the HAPomega configuration currently under development at the DLR. Because of the structural flexibility and the slow speed of the aircraft, flight mechanical and flight control aspects interact with aeroelastics e.g. during a gust encounter, making a non-linear time domain simulation necessary. Both maneuver and gust loads are used for the structural sizing and result in a very light and slender airframe with very low eigenfrequencies

Aeroelastic Modeling, Loads Analysis and Structural Design of a Fighter Aircraft

The DLR Future Fighter Demonstrator (FFD) is a highly agile, two-seated aircraft with twin-engines with reheat and a design flight speed extending into the supersonic regime up to Ma=2.0. Based on a given conceptual design, this work focuses on the aeroelastic modeling, including structures, masses and aerodynamics. With these models, a comprehensive loads analysis with 688 maneuver load cases, covering the whole flight envelope, is performed. Based on the resulting section and nodal loads, the structural model is subject to a structural optimization resulting in a preliminary, total primary structural mass of ~3.3t. To confirm the results, the aerodynamic panel methods (VLM and ZONA51) are compared to higher fidelity results obtained from CFD, showing a moderate agreement in terms of surface pressure distribution

Design and Sizing on a Parametric Structural Model for a UCAV Configuration for Loads and Aeroelastic Analysis

The authors present the setup of a parametric structural finite element model for the loads and aeroelastic analysis of an unmanned combat air vehicle (UCAV). The DLR-F19 is a “flying wing” configuration with a geometry based on previous research conducted in the scope of the “Mephisto” project and its predecessors “FaUSST” and “UCAV2010”. While a considerable body of knowledge exists regarding conventional configurations, unconventional configurations lack that same level of experience, and data for comparison is rarely available. Using an adequate structural model, the conceptual design stage becomes more sophisticated and already allows for the investigation of physical effects at an early stage of the design process. Strategies for structural modeling and proper condensation, aero-structural coupling, loads integration, control surface attachment, and the use of composite materials are addressed in this paper. The resulting model is sized for minimum structural weight, taking into account 216 load cases. In addition, a comprehensive loads analysis campaign is conducted and the resulting loads are evaluated at defined monitoring stations. In addition to maneuver loads, quasi-static gust loads are calculated using the Pratt formula and compared to results obtained from a dynamic 1-cosine gust simulation. The reasons for higher loads of the Pratt formula based method are discussed. The conclusion is that the Pratt formula is suitable for the preliminary sizing of “flying wing” configurations

Parametric aeroelastic modeling, maneuver loads analysis using CFD methods and structural design of a fighter aircraft

The DLR Future Fighter Demonstrator (FFD) is a highly agile, two-seated aircraft with twin-engines equipped, a reheat and a design flight speed extending into the supersonic regime (up to Ma=2.0). Based on a given conceptual design, the presented work focuses on the aeroelastic modeling, including structures, masses and aerodynamics. Using the models, a comprehensive loads analysis with 688 maneuver load cases, covering the whole flight envelope, is performed. Comparing the results obtained from aerodynamic panel methods (VLM and ZONA51) with higher fidelity results obtained from CFD, the necessity of CFD based maneuver loads analysis in preliminary design of such fighter configuration is shown, as it leads to physically different as well as higher loads. The rigorous application of CFD is a heavy burden during the preliminary design, but this work demonstrates that it is doable as of today. Finally, the model is subject to structural optimization, demonstrating that the differences in loads result in a heavier primary structural net mass with ≈ 3.3t for the approach based on aerodynamic panel methods and ≈ 4.1t for the CFD based approach. Because all remaining models are unchanged, this difference in mass can be clearly attributed to the physical differences in the flow solutions obtained from the panel methods and CFD

Design and sizing of a parametric structural model for a UCAV configuration for loads and aeroelastic analysis

The authors present the setup of a parametric structural finite element model for the loads and aeroelastic analysis of an unmanned combat air vehicle (UCAV). The DLR-F19 is a “flying wing” configuration with a geometry based on previous research conducted in the scope of the “Mephisto” project and its predecessors “FaUSST” and “UCAV2010”. While a considerable body of knowledge exists regarding conventional configurations, unconventional configurations lack that same level of experience, and data for comparison is rarely available. Using an adequate structural model, the conceptual design stage becomes more sophisticated and already allows for the investigation of physical effects at an early stage of the design process. Strategies for structural modeling and proper condensation, aero-structural coupling, loads integration, control surface attachment, and the use of composite materials are addressed in this paper. The resulting model is sized for minimum structural weight, taking into account 216 load cases. In addition, a comprehensive loads analysis campaign is conducted and the resulting loads are evaluated at defined monitoring stations. In addition to maneuver loads, quasi-static gust loads are calculated using the Pratt formula and compared to results obtained from a dynamic 1-cosine gust simulation. The reasons for higher loads of the Pratt formula based method are discussed. The conclusion is that the Pratt formula is suitable for the preliminary sizing of “flying wing” configurations

Identifizierung dimensionierender Lastfälle auf Ebene finiter Elemente an einer Nurflügelstruktur im Vergleich zur Schnittlastmethode

Diese Arbeit entwickelt, implementiert und testet eine auf der Finite-Elemente-Analyse aufbauende Methode zur Identifizierung dimensionierender Lastfälle und vergleicht diese mit der klassischen Identifizierung durch die Schnittlastmethode. Für den Vergleich werden beide Methoden in den Vorentwurfsprozess des Nurflügels MULDICON implementiert. Es wird vermutet, dass die Schnittlastmethode an der unbestimmten, flächigen Struktur eines Nurflügels nicht alle dimensionierenden Lastfälle erkennt. Dies konnte nicht bestätigt werden, beide Methoden identifizieren alle dimensionierenden Lastfälle. Jedoch wertet die neue Methode die Lastfälle detaillierter aus und ist dabei unabhängig von der Form der Struktur. Außerdem bietet sie weitreichende Visualisierungs- und Interpretationsmöglichkeiten, die es beispielsweise möglich machen, im Vorentwurfsprozess Lastpfade darzustellen und hochbelastete Strukturbereiche zu erkennen

Results from Loads and Aeroelastic Analyses of a High Altitude, Long Endurance, Solar Electric Aircraft

This work presents the results of comprehensive loads and aeroelastic analyses for the design of the high altitude, long endurance, solar electric aircraft HAP. To ensure a sophisticated design, a large number of maneuver, gust, gyroscopic and landing loads cases are considered. The structural sizing results in a total primary structural mass of 38.4 kg, which is very low considering the wing span of ~28.0 m. The extreme light-weight construction (wing loading ~4.0 kg/m^2) leads to a highly flexible aircraft, making aeroelastic analyses mandatory. Results of static and dynamic aeroelastic analyses are presented, showing that the resulting design is plausible from an aeroelastic point of view