Tech Briefs

Inflation of the aircraft

Release from mooring position and aircraft take off

Flow field around the aircraft during take off

FSI Analysis of a Lighter than Air (LTA) Aircraft

Lighter than air aircraft and other aerostats such as free balloons, tethered balloons, airships, etc. use "aerostatic" lift (i.e., a buoyant force that does not require movement through or of the surrounding air masses to act) rather than aerodynamic lift as in winged aircraft. Helium, and in some cases also hydrogen, enclosed in a gas-tight partition of the craft are used as buoyancy gases to provide the aerostatic lift. Although aerostats and especially airships have attracted people for over a hundred years now, the development of lighter than air aircraft was overshadowed and abandoned due to spectacular accidents such as the well known Hindenburg disaster.

Figure 1  Lighter Than Air in history*

In recent years, since advanced materials (e.g., light-weight gas-tight fabrics, composites) and modern production and safety technologies have become available, several companies worldwide started to design new lighter than air aircraft for missions such as transportation, rescue, downward-looking radar coverage, tourism, recreation, and advertising.

Figure 2  Proposal for a modern aerial cruiser

Lighter than air aircraft can be either rigid, semi-rigid or fully flexible. The development of new, more advanced designs requires expertise far beyond the classical, either structural or fluid dynamics, engineering and simulation disciplines. In fact, fluid-structure interaction (FSI) simulation techniques together with dedicated adaptive meshing capabilities among others are needed to successfully model these designs. ADINA, with its structural, fluid dynamics and loss-free FSI capabilities, together with the steered (either manual or automatic) adaptive meshing (SAM) techniques, provides a seamless development environment for realizing lighter than air aircraft projects quickly and reliably, thereby minimizing the need to build and test expensive prototypes.

The figures below and the movies above show a set of results obtained by Dr. Thomas Chatzikonstantinou, Aachen, Germany, using ADINA for the modeling of a lighter than air aircraft configuration from SkyLifter, Perth, Australia (see Figure 3). The structure of the fully flexible, medium size aircraft (25m diameter) was modeled using membrane elements (with the orthotropic material model and contact) for the gas chambers and using truss elements for the suspension line system. While ADINA can be used to model also the gondola, engine installation etc., in detail, in this project the payload was modeled as a single mass point for simplicity. The implicit dynamic, fully unsteady FSI simulation using SAM of a wind tunnel model was performed in two successive FSI runs. In the first FSI run, only the inflation of the aircraft was simulated. In the second FSI run, a restart run, the aircraft was released from its low-mooring position and a directed propulsion force put the aircraft in motion. Since implicit time integration was used throughout the analysis, in each time step full equilibrium was established leading to a reliable solution. ADINA of course not only simulates any maneuver of the aircraft, as needed, but records and outputs also strains, stresses, velocities, accelerations, pressures, etc. at every individual point of the aircraft and its environment over time.

Figure 3  Lighter than air aircraft configuration by Skylifter, Perth, Australia

Figure 4  ADINA FSI model with contact

Figure 5  Gas-tight fabric structure of orthotropic material

Figure 6  Stress distribution in fabric after inflation

This FSI simulation showed that the SkyLifter's lighter than air aircraft configuration met the design objectives. The simulation is also a demonstration as to how ADINA can be used successfully in advanced analyses including FSI to study complex problems in engineering and the sciences.

For more information on the ADINA FSI capabilities, refer to our page fluid-structure interaction capabilities of ADINA.

LTA, lighter than air aircraft, airship, aerostat, buoyancy, fluid-structure interaction, FSI, adaptive meshing

* This image comes from the Brockhaus and Efron Encyclopedic Dictionary (1890-1907). The copyrights for that book have expired and this image is in the public domain.

Courtesy of Dr. Thomas Chatzikonstantinou, Aachen, Germany and SkyLifter, Perth, Australia