50 tons for weightlessness

The world's largest wind tunnel fan provides optimum lift for indoor skydiving

The feeling of weightlessness is no longer just reserved for astronauts and professional parachutists: there has been an increase in the number of so-called indoor skydiving centres in many cities, in which amateur athletes can also experience the feeling of weightlessness for a short period of time without having to encounter increased accident risks. Such a leisure facility was opened in Katowice (Poland) just in the spring of 2017, which was planned and designed by the Indoor Skydiving Germany Group (ISG). The wind tunnel fan posed a particular challenge: instead of using several small fans as is customary, the skydiving system was intended to be operated with just one single large model. ISG brought the fan experts from TLT-Turbo GmbH on board since such a fan for such a purpose had not yet been realized. Their research and development department was able to carry out the assignment as required thanks to their many years of experience in the design of large fans for industry. Both companies are already working on further joint projects.

Parachute jumps can pose health risks for the jumper, especially due to unexpected air movements and the difficult landing. A single jump can also prove to be quite expensive. This isn't the case with indoor skydiving: fans generate a controlled air flow with only minimal turbulence, so that athletes are not exposed to any danger and training conditions are especially realistic. It is because of this – and due to the low costs compared to parachuting – that the new trend sport is suitable for almost every age group and enjoys increasing popularity.

There are now numerous possibilities for indoor skydiving activities across Europe – including the “Flyspot” in Katowice, Poland. However, the facility clearly stands out from most others of this type: instead of installing several fans to generate the air flow, only one large fan is intended for the same purpose. The enormous dimensions (the outer diameter is six meters), however, represented a novelty in the field of skydiving systems. This is why the Indoor Skydiving Germany Group (ISG), which had taken over the planning for the facility in Katowice, commissioned the industrial fan manufacturer TLT-Turbo GmbH to design the fan.

Large fan reduces energy consumption and risk of accidents

ISG initially developed a new concept prior to concrete planning for the system. Instead of the usual four smaller fans, this involved the use of only one single model. “On the one hand, this has the advantage that a single fan achieves a comparatively high degree of efficiency and thus consumes less energy than several small fans. Operating costs can be significantly reduced as a result,” explains Andreas Kuhn, project manager at TLT-Turbo GmbH. “On the other hand, the air flow is more uniform and makes skydiving even safer for the athlete.”

The research and development department of TLT-Turbo initially used a feasibility study to clarify whether and to what extent the concept was feasible. “In August 2016, we were finally commissioned to come up with a corresponding fan with an outer diameter of six meters,” explains Kuhn. “Based on ISG's new concept, the main requirement was that the air speed should be infinitely variable. It was also important that the air should be distributed as uniformly as possible over the entire cross-section of the flight chamber – and free of vibrations and disturbing turbulences in the optimum case”.

Fan generates maximum flow speed of over 300 km/h in the air chamber

It was the first order of this kind for TLT-Turbo: indoor skydiving was completely new territory for the experienced fan manufacturers. Nevertheless, the company has been successfully planning, designing and producing wind tunnel fans and the like for well-known companies, for example from the automotive and aviation industries, for many years. “The main difference between a standard wind tunnel fan and a model used in skydiving is the vertical orientation,” Kuhn explains. “The loads on the motor shaft are especially different due to this arrangement. Here bending can be disregarded, but high axial loads occur.”

In this case, there is also the special feature that the motor is situated in front of the impeller when viewed in the flow direction at the request of the motor manufacturer and not in the shadow of the impeller as usual. In addition, the blades have been designed to be as long and narrow as possible in order to achieve turbulence-free flow characteristics. The fan now achieves an installed capacity of 1,350 kW and generates a maximum flow speed of over 300 km/h in the flight chamber.

Installation via the roof at 15 m in height

The fan was delivered in Katowice from the production site in Bad Hersfeld and assembled there in March 2017. The motor had to be brought into the building via the roof due to the difficult local conditions. The components could only be assembled there. This placed high demands on occupational safety, since a fall protection system and 15 m high scaffolding were required for lifting the component. TLT-Turbo supplied a mounting support system specially designed for the installation here.

The installation was carried out in two steps. “First, the guide vanes consisting of four parts, which in turn comprise three ring segments as well as an outflow body, were installed. This was followed by the installation of the active part,” reports Kuhn. The second step especially required a great deal of intuition and sensitivity from the assembly team: “The assembly of the active part with built-in motor and impeller hub had to be performed with particular care and precision. While the motor was brought in from above, the sensitive cables had to be drawn into the housing of the hollow guide blades at the same time.” During this action, it was imperative that the motor and signal cables directly connected to the motor must not be kinked. Otherwise, damage would have resulted in the complete motor having to be sent to the manufacturer for inspection, which would have completely disrupted the schedule.

Project facilitates entry into new business fields

In contrast, the 50 t active part was transported to the installation position laterally through an opening in the building via a supporting structure with rails. Finally, the six carbon fibre blades could be added. At the same time, the commissioning tasks as well as the implementation of the first checks and adjustments began. The flight instructors were able to commence test flights in the newly built skydiving channel within a very short period. Since the tight schedules could be adhered to despite the difficult circumstances and changes in customer requirements at short notice, all participants were very satisfied with how the project went in the end.

All in all, the assignment presented TLT-Turbo engineers with great challenges, since many new developments that are not used for standard industrial fans were necessary for the skydiving fan. This project also helped the company secure entry into new business fields. Thanks to the outstanding cooperation with ISG in the first joint project, the fan experts have already received further orders - including two engineering assignments for a total of three machine types as well as two production orders for two large fans, also with a diameter of six meters. “Of course, the new field of activity also presents our engineers with special incentives to be able to demonstrate our extensive expertise in unconventional areas,” Kuhn concludes.