Simulation software assists in a bid to create an iconic flying car

Key points

  • The Transition roadable aircraft has a flight range of up to 490 miles
  • It is able to transform from aircraft to car in less than 30 seconds
  • ANSYS software was key in advancing the vehicle to the prototype stage

Since the earliest days of the aviation industry, inventors and entrepreneurs from motorcycle racers to home-built aircraft enthusiasts and the largest auto makers have sought to develop the iconic mash-up of future transportation technology known as the ’flying car’. Some of their attempts did manage to test successfully and even reside in museums. Sporting names such as Autoplane, Aerobile and Airphibian, these machines were impressive but they never lived up to the mythological pedigrees conjured up by science-fiction authors and film makers.

The concept is a proven one but, due to the engineering challenges involved in combining a lightweight, aerodynamic aircraft with the stability needed for long-distance driving, to date none of these vehicles have been successfully brought to market.

Recently, however, Boston company Terrafugia revealed a production prototype for a street-legal aircraft that it hopes to begin manufacturing this year. Terrafugia Latin for ’escape from land’ used simulation tools from ANSYS to arrive at a production prototype of its innovative Transition roadable aircraft.

After earning global attention following successful test flights in early 2009, the prototype was revealed to the industry in 2010 at the annual experimental Aircraft Association (eAA) AirVenture Oshkosh national airshow. With a flight range of up to 490 miles (790km) and a cruising speed of 105mph, the Transition can also drive up to 65mph on the road. It is capable of transforming from aircraft to car in less than 30 seconds. The sophisticated design features foldable wings that span more than 26ft (8m), a rear-wheel-drive system for the road and a rear pusher propeller for flight.

While the Transition is not designed to replace anyone’s car, it is intended to drive at normal highway speeds so owners can easily access local airports. This required Terrafugia’s engineering team to simultaneously consider the aerodynamics of flying and driving activities that exert very different forces on the vehicle. While physical tests in a wind tunnel helped to validate the initial concept design, they were both time and cost intensive.

The Transition is intended to drive at normal highway speeds so owners can easily access local airports

For this reason, the engineering team turned to ANSYS Fluent software to make and verify design modifications for the new production prototype, working in a virtual simulation environment that saved time and money while enabling engineers to assess a complex range of design considerations. Unlike a typical car or aircraft, the Transition has a host of extra components to consider when analysing airflows around the vehicle, as wheels, propellers, foldable wings and other shapes affect dynamic flows whether it is driving or flying. Using the software’s modelling capabilities, the team conducted whole-vehicle airflow tests to study the effects of the slightest design change on overall performance.

It addressed issues such as maximising wing lift in the air while minimising the effects of crosswinds along the road. Without an ability to work in a virtual environment, Terrafugia’s team would have had to construct complicated physical models, modify or rebuild them and conduct hours of real-world testing.

Simulations powered by fluid dynamics software from ANSYS enabled the rapid testing and verification of some modifications to the transition design, based on the physical performance of the initial proof-of-concept vehicle.

Wind-tunnel tests revealed an adverse interaction between the vehicle’s front suspension and its canard. Rather than relying on more physical testing, Terrafugia used ANSYS technology to further explore this interaction as well as potential solutions. As the work progressed, it became clear that while the canard configuration had initially been integral to the design, it was undesirable from a number of standpoints.

With the Transition receiving classification as a multipurpose passenger vehicle, the full-width bumper requirement for passenger cars was no longer applicable.

Simulation software verified that lighter weight, better flight characteristics and improved looks were all potential benefits of a canard-free design. Another challenging aerodynamic design aspect was attaining a wing stall speed of less than 52mph, which is a requirement for the light sport category of aircraft.

As slower in-air speeds generally create safer flying conditions, it was important for the Terrafugia engineers to design the vehicle to operate at a low speed for safety and stability without stalling. With support from ANSYS experts, the team developed a detailed engineering approach to obtain accurate predictions, including the use of a virtual blade modeller (Vbm) that plugged in to the fluid dynamics software and created further capabilities to model the transition’s propeller. After deploying the Vbm tool, the team reshaped the wing and the rest of the body as needed to match the weight and centre-of-gravity requirements of the vehicle.

The new design improves the in-air and on-road performance of the Transition and ensures that the vehicle lends itself to full-scale manufacturing. Terrafugia found that ANSYS simulation software was critical in advancing it to the production prototype stage.