That was the “Red Bull Tunnel Pass” project

That was the “Red Bull Tunnel Pass” project

More than a year of preparation, over 40 people involved and a distance of around 2.26km in just around 44 seconds: on September 4th, Italian stunt pilot Dario Costa broke not just one, but four world records at the “Red Bull Tunnel Pass Flight”. The technical expertise and the products of bionic surface technologies were also involved.

Istanbul, Turkey. On September 4th, Dario Costa launched his flying machine with the sunrise inside the Çatalca tunnels on the Marmara Highway. Around 2.26km had to be covered with high precision: the start of the route was in a tunnel, then passed through a short open stretch of highway before entering, passing through and also exiting the next tunnel.
The Italian stunt pilot needed 43.44 seconds for this incredible masterly performance, the average speed was 303.08 km/h (188.07 mph) in the second tunnel. In addition to intensive physical and mental training for the pilot to master the difficulties inside and outside the tunnels, extensive calculations and analysis had to be carried out in advance. This made it possible to ensure whether his plan was at all possible and when or where critical situations might occur.

Italian stunt pilot Dario Costa flies to four world records in his Zivko Edge 540 V4 with Riblets from BST

Flight through the tunnel using CFD

It all started in 2020 when Dario Costa, who had already spend more than 5.000 hours in the air in around 20 years of flying experience, had been harboring a dream for years and approached bionic surface technologies with the Words “Can you tell me, using your CFD calculations, how risky a high-speed flight through a long tunnel with a flying machine is?”. It was an undertaking that no one before him had ever dared to undertake. As experts in aerodynamics and long-time companions of many Red Bull Air Race pilots – including Dario himself and his mentor Peter Besenyei – we did not want to miss this opportunity. For a year, we searched and simulated at BST and also locally the perfect conditions that would make a stunt of such magnitude possible. For this purpose, the mammoth project was divided into five different episodes.

Episode 1 – Basic Simulation | Stationary

To get a feel for the situation, three calculations were initially done with different speeds and wind conditions. These assumed an unmoved, i.e. practically ‘stationary’ in the air, aircraft one in free flight, on the viaduct and once inside tunnel T2. The latter two calculations had a flight altitude of 1m due to the tunnel dimensions. The special feature of these simulations was that a scanned geometry of the racing plane was used for them. Due to the fact that there were no examples for such a flight, the difficulty was that the angle of attack and pitch of the aircraft were unknown – these were necessary for the further calculations. Both could be estimated and finally calculated. Finally, the output was how the attitude of the airplane varied inn the three different scenarios when the three different acting forces were changed.
Sketch of the tunnel including drawn height and width, as well as inclination angle

Episode 2 – Simulation Tunnel Flight | Transient

After the aircraft was simulated stationary during the first calculations on the one hand, a piece of tunnel and open track, i.e. the entrance from the viaduct into the second tunnel, was selected for the moved analysis – for the best possible results – on the other hand. This made it possible to better visualize the changes in forces and moment on the aircraft and to finally clarify whether such a risky stunt could even be within the realm of possibility. Also crucial was the definition of a reaction time. This was the time the pilot had to react to external conditions, such as crosswinds. This was 0.25 seconds and was important for the mental coaching of Dario Costa in the further course.
A short sensitivity analysis, i.e. how sensitive the aircraft responds to certain parameters, was also done. This 2D analysis, which again looked more closely at altitude, speed and temperature, revealed three so-called “Bumps” in the air pressure. These were passed on to the pilot so that he could prepare himself optimally.

Lead engineer Lucas Garcia de Albeniz explains the simulation as he enters the tunnel

Episode 3 – Location Check

In April 2021, the important technical location check too place to get an idea of the actual situation. On site, the track and the tunnel were examined again in detail, and wind conditions, solar radiation, and outside and inside temperatures were measured at several times of the day. Because the temperature inside and outside the tunnel was more constant, the wind calmer and Dario had the sun at his back while flying – thus less potential to be blinded when exiting the tunnel – it could be determined with high probability at this point, that the flight would take place in the early morning. In addition, the route was completed several times with a test vehicle at the same speed as Dario would then fly. During these runs, a camera was mounted at the eye level of the flight pilot to serve him in the form of film sequences during later training.
Lead engineer Lucas Garcia de Albeniz at the location check in the Çatalca tunnel

Episode 4 – Modifications

At the same time, further simulations were run to make Dario Costa’s project as safe as possible. For this purpose, further modifications were made to his flying machine, a Zivko Edge 540 V2, such as rudder tips.
As a further highlight, the Riblet surfaces developed by BST were also used on the aircraft. For the first time in aviation history, Riblets were used to absorb and compensate ground-level turbulences in the air – also a world premiere. The special structure of the Riblets and the specially designed rudder tips, which had a larger contact surface, increased the maneuverability of the entire aircraft.
This was confirmed by Dario Costa, as well as the fact of having more control at low speeds.

BST engineer Lucas Garcia de Albeniz uses a picture to explain Dario Costa the possible areas for Riblets (orange)

Episode 5 – Weather Stations

The final phase included comprehensive weather monitoring for which BST was also responsible in addition to the modifications and simulations. For this, five weather stations were installed in and around the tunnels, measuring the speed and direction of wind, temperature, humidity and pressure every minute between 4 and 8 a.m. Based on this plan and BST’s CFD calculations, engineers created a plan of action for which weather conditions would be safe to launch. For example, there were no-go criteria in which a flight could not take place under any circumstances: when the temperature would have changed by more than 10°C or an absolute wind speed of more than 7 m/s.
Sharkskin Technology as a safety aspect on the wings

Four world records for Dario and a personal one for BST

A year of planning. Over forty people involved. One dream. It was a challenging project, but thanks to the create cooperation it went smoothly. Dario Costa was not only to able to realize his dream, but also set four world records in just on flight:

  • First flight with an airplane through a tunnel
  • Longest flight under a obstacle (1.730 m)
  • First flight through two tunnels
  • First aircraft take off in a tunnel

However, it was not only the Italian who was able to break records, but also bionic surface technologies. In addition to increasing efficiency, BST’s Riblets served as an important safety aspect in this project. We couldn’t have imagined a better project for demonstrating how important Riblets / Shark Skin technology is in flight!