The Technical University of Munich (TUM) is developing flight-simulation software that better mimics the effects of turbulent obstacle and terrain winds on helicopters and thus better prepares pilots for dealing with these challenging conditions.
"Until now, flight simulators have not adequately reflected the reality of flying in close proximity to large objects," said TUM's Dr. Juergen Rauleder. "When it comes to wind conditions and the response of the helicopter, existing programs follow a rigid pattern. That means that local variations and changing conditions are not taken into account—unless the entire flow environment is known in advance." Researchers working at TUM's Chair of Helicopter Technology are employing real-time computational analysis for both fluid mechanics and flight dynamics to replicate more accurately the conditions encountered in mountainous regions or close to skyscrapers or near oil rigs, ships and cliffs.
TUM notes that unforeseen air flows can be the most treacherous. For example, a moving ship causes air turbulence and sudden local shifts in wind speed known by specialists as "ship airwake flow." It changes continually through wave action and fluctuating inflow conditions. In addition, turbulence occurs near the deck, the bridge and other ship structures. As a helicopter approaches the ship, there is interference between these air currents and the flow produced by the rotors. Conditions near a mountain slope or next to high buildings are similarly complicated. In all of these cases, the helicopter's flight characteristics are influenced by complex and overlapping aerodynamic effects.
Dealing with those situations takes a lot of skill and practice, both of which can currently be acquired only through on-the-job training. To become adept at landing on a ship in heavy seas, for example, a student pilot has to repeat this tricky feat dozens of times with an experienced flight instructor. That's the only way to gain the necessary experience to compensate for the complex interplay of air flows through perfectly timed adjustments to the pitch of the rotor blades.
"Conventional training is expensive, risky and stressful for student pilots. It also imposes heavy demands on the aircraft: because the first attempts usually result in rather hard landings, the dampers and landing gear take quite a beating," said Rauleder.
The TUM team has developed a simulation program that combines flow mechanics and flight dynamics in real time. "The numerical model is extremely flexible and does not depend on stored flow data. We only have to enter the external conditions such as topography, wind speeds and the helicopter type. During the simulation, our algorithms use that data to continuously compute the interacting flow field at the virtual helicopter's current location," Rauleder said.
The new program also lets pilots instantly "feel" the impact of the local air flows on the helicopter. This allows them to try out the effects of their control movements in a stress-free setting: perfect preparation for a soft landing that is easy on the aircraft, Rauleder said. The potential of this method has attracted interest from the U.S. Office of Naval Research, which is contributing funding under the auspices of its basic research program. Virtual models are being tested against actual conditions at sea in cooperation with researchers at the U.S. Naval Academy, George Washington University and the University of Maryland. Air flows on a ship are being measured using hundreds of sensors.
The TUM team will also be using in-flight data collected by the German Aerospace Center (DLR) to validate the flight dynamics. "The validation of the models and testing of our simulation environment by experienced pilots in our research simulator is enormously important for our developments," said Rauleder. "That's the only way we can ensure that the simulator training prepares student pilots for tough missions."
