Delft University of Technology and Lightweight Structures B.V. worked on the development of a high performance flight simulator under the name SIMONA. SIMONA is a joint faculty project that will focus on research on SImulation, MOtion and NAvigation of aircraft and other vehicles. Several industrial partners, simulation and non-simulation, participate in this development.
The flight simulator consists of a composite ‘flight deck’ structure (the shuttle) which is directly attached to the hydraulic motion system (see figure 1). As such, the simulator has been in operated and tested for one year.

The second stage of the development includes the design and manufacture of control loading, improved software and the Visual Display System (VDS). The VDS features a 180º outside view, which is projected by means of 3 LCD projectors, a back projection screen and a large mirror in front of the flight deck. Such VDS will complete the system to a full flight simulator, similar to FAA approved level D systems, but at much lower weight and dedicated to research instead of training. The VDS is based on the 10 ft. PANORAMA system by SEOS Displays ltd. The SIMFUSION GP image generator is manufactured by Evans and Sutherland, also a project partner. 
 

Major design requirements of the Research Simulator are:

This is achieved by combining a high performance motion system with low mass and a very stiff structure.

The Visual Display System consists of many, large and heavy components placed at a large distance from the centre of motion, which makes it critical for the performance of the simulator. This paper describes the design and manufacture of the VDS support structure.

The design process was done in two phases. During the first phase a quick FE-analysis was performed on a structure that consists of an all space frame support of carbon fiber tubes, in order to estimate the first natural frequency. This analysis showed:

Below the design process of the second phase is discussed in more detail.

In normal flight, 4 Hz is a reasonable upper limit for the highest bandwidth of the interaction between the pilot and the aircraft. The weight, inertia and flexibility of the shuttle and of the VDS structure will effect motion performance. In order to achieve a 60° phase shift at 4 Hz, the first natural frequency should be at least 2.5 times the 4 Hz

It must be possible to operate the system must be operate the system at high frequencies over 10 Hz. At such high frequencies the structural integrity must be maintained, without phase shift requirement.To assure this, the first natural frequency should be well over 15 Hz.

For all elements of the VDS the specific requirements are listed such as accessibility, light tightening, and effect on image quality and performance of the simulator. Based on the set of requirements, several possible design solutions for the visual display support structure have been generated.

The load transfer of the items of the VDS through the shuttle shell to the gimbals (and the floor) is designed to be as direct as possible. This way a stiff suspension is achieved in the most efficient way, i.e. using as little material as possible. Based on this analysis the possible load paths have been determined for each degree of freedom. It was found that pitching (rotation about y-axis) and rolling (rotation about x-axis) are the most critical modes. Accordingly, essential load paths are:

The structure consists mainly of large spans which need to be light tight. Therefore suitable structures are either a space frame combined with cloth, or sandwich panels. The generated configurations consist of different combinations of these. Two sketches of structural concepts are presented.

The quality of the concepts are judged on the estimated stiffness over weight ratio on functionality and on complexity (costs). Out of the possible solutions, two structural concepts were composed: the canopy-petal concept and the space truss concept. These are modeled in 3D CAD (Pro-engineer) to check geometrical interference with any other parts. In fig. 3-6 the concepts and the denominations for the components of the VDS are shown.

Critical aspects are weight, stiffness, producibility and ease of assembly. Natural frequency and performance of the simulator increase with lower weight and higher stiffness. Manufacturing must be feasible and the cost-performance ratio must be acceptable. The VDS consists of many components that need to be positioned accurately. The ease of assembly influences the accuracy of the positioning of the elements and thus improves the simulation.

These aspects are discussed for the canopy-petal concept and the space truss concept below:

Weight	Stiffness over weight is an important criteria. It is expected that the tubular concepts can be lighter than the sandwich panel concepts, but a large weight penalty is imposed by the joints (aluminium balls). The weight will be derived from the 3D CAD model.
Stiffness	The most effective way of increasing the stiffness of the structure is by creating direct load paths and reducing the panel span. Carbon reinforced epoxy and sandwich material will be used.
Producibility	The composite tubular concept has been elaborated in the first design of the VDS, and a feasible procedure for joining and assembling, though complex, has been found. The sandwich panels require large moulds, but except for the canopy, flat panels can be used. Manufacturing is complicated by the large number of inserts required. The carbon tubes of the lower crown have been produced with carbon prepregs using a blow moulding process.
Ease of assembly	The tubular space frame concept is very sensitive to the accuracy of assembly. It highly depends on craftsmanship and is expected to be more time consuming than the assembly of sandwich panels. With sandwich panels the location of the inserts is critical, but this can be controlled by use of reference points in the mould or on the shuttle.

Based on the above evaluation a choice between the two alternatives could not yet be made. The functional requirement of the natural frequency (‘as light and stiff as possible’) dominates. Using FE-analysis, the eigenmodes of both concepts are compared. A first dimensioning is done analytically, based on the strength and stiffness requirement.