Facility for Outdoor Rotor Testing (FORT)

The aerodynamics around a rotorcraft body is extremely complex and difficult to simulate both computationally and experimentally. Scaled experimental testing using wind tunnels can reliably provide insight into the flow characteristics around a three-dimensional object and can provide decent simulations to real world scenarios.

However, this kind of testing has two disadvantages: these tunnels are expensive to operate and they often have difficulty simulating turbulence and the random nature of wind gusts. To truly incorporate a real world environment, an outdoor facility should also be used. Researchers, Gerald Angle and John Ruth, have designed and are in the process of constructing a Facility for Outdoor Rotor Testing (FORT) for tilt and helicopter rotors that can capture some of these random effects.

The basic configuration of the Facility for Outdoor Rotor Testing consists of a single prop-rotor on a simple steel structure driven by an electric motor. A major concern in the design of this facility was the sizing of the facility to ensure adequate flow similarity to a full scale aircraft. This was done based on an acceptable Reynolds number of around half of that predicted for a tilt-rotor aircraft. The prop-rotor used in this facility will be an 88-inch diameter propeller that drives airflow over a model, approximating the rotor wash.

The Facility for Outdoor Rotor Testing has several advantages over traditional wind tunnel testing. The inherent rotation, which is present in vertical take-off and landing aircraft, is difficult to simulate in a wind tunnel. Another advantage is the exposure to the random but measurable nature of the real world which can easily be neglected in wind tunnel testing. The Facility for Outdoor Rotor Testing will have the ability to allow for the differences in atmospheric conditions, including wind speed/direction, temperature, pressure and humidity. The facility will have the capability of testing moderately large (15-20%) scaled fuselage models in an environment that incorporates both the rotational and axial velocities that exist in the wake of a main rotor. It is hoped that this facility will help in the evolution of new helicopter technologies and will provide for a new testing capability that will be used by several helicopter companies.