Understanding and Evaluating Aviation Radio Connectivity using Virtual-Flight Tests (VFT)
Understanding and Evaluating Aviation Radio Connectivity using Virtual-Flight Tests (VFT)
Simulating Installed Antenna Performance and Radio Coverage in Aerospace
Virtual flight tests allow for the design, testing and validation of aircraft antenna configurations in a simulated environment, without the need for costly physical prototypes. This enables designers and engineers to assess the antenna performance and the communication reliability of an aircraft before committing to physical testing. The usage of VFT keeps growing, mainly because of several reasons:
- Cost-effective: Conducting physical flight tests can be very costly, as it involves setting up aircraft, equipment, and personnel for the test. Virtual flight tests reduce the need for physical testing, thus lowering costs significantly.
- Flexibility: Virtual flight tests allow for more flexibility in testing various scenarios and configurations. It is easier and much more efficient to make adjustments and changes in a virtual environment compared to physical flight tests, which involves preparing aircraft and equipment.
- Accuracy: Virtual flight tests can provide more accurate results, as they allow for precise control over the environment, test parameters and conditions.
Overall, virtual flight tests for testing the installed antenna performance, the connectivity and reliability, and also the radar sensor performance, offer a cost-effective, flexible, efficient, and accurate alternative to physical flight tests.
Altair Feko, including WinProp and WRAP technologies, provides the solution and capabilities to address the challenges for the Ground-to-Air and Air-to-Air communication, considering challenging terrain profiles, dynamic objects, variable flight paths and a wide range of antenna constellations. This involves the handling of 3D map data including topography, vegetation, buildings, and other obstacles. For the simulation of the radio channel sophisticated wave propagation models including ray tracing solvers are utilized and a wide range of empirical methods for the aeronautical radio channel, also according to ITU standards. Overall the Feko suite is a complete tool set for aerospace applications both in defense and civilian domains as it delivers essential modules to meet the antenna design, the frequency and radio network planning requirements for radar and radio communications, regardless of the challenging conditions.
We are now showing below several cases as examples, also covering real cases on digital twin technology applied to virtual flight tests.
Import Maps of the Scenario
In advance the environment of interest can be set-up by downloading and converting topographical maps e.g. from USGS or other sources - you can have a look at the corresponding part of the WinProp intermediate level training or by downloading and converting map data from openstreetmap for building vectors including vegetation - see the video tutorial How to Convert Open Steet Map file in WinProp (youtube.com).
Case 1: Aircraft-to-Drone Communication over the Grand Canyon
An aircraft and a drone communicate while flying near and over the Grand Canyon as a function of time. At each instant, the radio channel between the two flying objects is simulated and the connectivity in terms of received power, feasible data rate and throughput analyzed. For this purpose the antenna patterns computed in Feko using full wave solvers and considering the effects of the mounting at the aircraft/drone geometry plus the corresponding materials can be imported in WinProp and attached to the flying objects.
The aircraft antenna is defined as transmitter flying along one trajectory over time, including also the changing orientation in terms of yaw / pitch / roll angles. The drone antenna is considered as prediction point moving along other trajectory over time, see the picture above. Depending on the situation either a ray-optical wave propagation model, the parabolic equation (PE) method or one of the ITU-R propagation models can be applied. The attached sample project includes the topo map of the Grand Canyon area, the antenna patterns of aircraft and drone and uses the deterministic two-ray propagation model incl. direct ray and ground reflection in the rural scenario mode, see the picture below. Further demo projects in the domain of virtual-flight tests can be provided on request.
The slide deck with step-by-step instructions as well as corresponding sample data can be downloaded here.
Case 2: Virtual Flight Test with Drone over City
In another tutorial under the above link a virtual flight test scenario in WinProp is demonstrated. In this demo, a drone follows a 3D flight path in an urban environment while the connectivity between the ground station and the drone is simulated. There is also a step-by-step video tutorial and the corresponding sample project included in the linked article.
Case 3: Virtual Flight Tests in Larger Scenarios
For larger terrain scenarios covering tens or even hundreds of kilometers, the WRAP technology provides all the required modules and functionalities. The picture shows the obtained received power on the ground for various positions along the flight path, i.e. when the aircraft takes off, flies the trajectory over the Alpes and lands again. For the aircraft antenna constellations 3D patterns from Feko can be imported including the effect of the aircraft geometry and mounting. The aircraft antenna is automatically oriented according to the defined flight path e.g. here looking forward with a downtilt of 30 degrees.
Case 4: Virtual Flight Test on a Different Atmosphere (Mars)
NASA JPL successfully used the Altair solution for their MARS mission regarding the prediction of the radio connectivity between their Mars Perseverance Rover and Mars Ingenuity Helicopter. WinProp technology was used to plan safe flight routes to avoid losing their precious assets and the simulation results were validated with 14 real flight tests. 
Source and more information at: https://www.linkedin.com/posts/nacer-chahat-1133054b_telecom-marshelicopter-activity-6957998487007371264-jgPi
Case 5: Air Traffic Control
German DFS and Swiss Skyguide verified the Ground Based Augmentation System (GBAS) radio coverage at different heights on and around the airports of Frankfurt, Munich, and Zurich. Altair’s tools allowed the air traffic control agencies to calculate the GBAS signal levels without the need to simplify the environment, resulting in an accurate signal propagation model. Additionally, the agencies can use this simulation strategy to evaluate how future structures, such as airport towers and docks, might affect the radio coverage. 
Please read the full story under: https://altair.com/resource/enabling-aviation-safety-altair-solutions-enable-precision-auto-landing-at-complex-airports?lang=en
Case 6: Digital Twin To Capture In-Flight Behavior of Helicopter Radar
Leonardo needed to correct a helicopter radar transmission loss caused by in-flight vibration to the helicopter's radome. Leonardo deployed Altair's digital twin solution to solve the problem. Using a multiphysics approach, the team created a digital twin of the radar antenna's structural and electromagnetic systems. They then correlated the deformation to the antenna's design, tracked changes based on vibration, and calculated the antenna's electromagnetic signature. With these findings, Leonardo could optimize its next antenna build version without using expensive prototypes. The full story can be found on https://altair.com/resource/getting-the-signal-with-digital-twin-leonardo-deploys-digital-twin-to-capture-in-flight-behavior-of-helicopter-radar?lang=en