In 1998, WSU, in collaboration with NASA, the FAA and the aviation companies, conducted an extensive experimental program to obtain aerodynamic performance data for a range of clean and iced aircraft configurations. The main goal of the effort was the development of a database that can be applied to the study of aerodynamic scaling effects on full-size aircrafts and to assess the effects of ice shape on the aerodynamic performance and penalties. Models tested to date included different airfoil sections with chord lengths ranging from 4 to 57 inches, a full-scale and 25%-scale business jet empennage, a 15%-scale business jet aircraft, a 6.5%-scale commuter aircraft and a 22%-scale swept wing. A large number of airfoils with simulated ice shapes were investigated during these tests for Reynolds numbers in the range of approximately 150,000 to 7.9 million.
Listed below are a number of projects related to aerodynamic testing with iced airfoil:
Ice Accretion Effects on a Swept Wing
Past experimental studies to assess the effects of ice accretions on aircraft aerodynamic performance had been limited mostly to 2-D airfoils. However, the aerodynamic effects on swept wing were largely unknown. Therefore the FAA initiated a research program with the Icing Group at WSU to generate an aerodynamic database specifically for swept wing. It is believed that such as a database would help to develop practical certification guidance material for iced swept wing, and to improve and validate computational tools for aerodynamic analysis and design. In this program, a 5-ft wing model equipped with an aileron was designed and fabricated at WSU. Icing tests were initially conducted with the wing at NASA IRT where ice shape castings were produced. These ice cast were then mounted on the wing and installed into the 7-ft x 10-ft wind tunnel facility at WSU. Aerodynamic performance tests were conducted using a balance capable of measuring hinge moment and six component forces. Surface static pressures were also obtained for a range of angles of attack at a Reynolds number of 1.8 million. Tests were conducted with a total of six ice shape castings and seven LEWICE simulated ice shapes.
NASA/TM2002-211557 Ice Accretions on a Swept GLC-305 Airfoil
Tailplane Icing Program
Aircraft operation in icing conditions can result in ice formation on the tailplane (horizontal tail) leading edge, which in some cases can cause tailplane stall. This phenomenon is known as Ice Contaminated Tailplane Stall or ICTS. At least 139 fatalities have resulted from 16 ICTS related accidents involving primarily turbo propeller-powered transport and commuter category airplanes. In 1998, NASA and Bombardier/Learjet Company funded a research program to develop test methodologies for assessing contaminated tailplane performance and handling qualities. Extensive wind tunnel experiments were conducted with a full-scale, a 25%-scale and 15%-scale models of a business jet aircraft. The full-scale tail tests were conducted at the NASA Ames 40-ft x 80-ft wind tunnel facility while the 25%-scale and 15%-scale models were tested in the WSU 7-ft x 10-ft low speed wind tunnel. Tests parameters included a range of angles of attack, Reynolds numbers between 0.7 and 7.9 million (based on tail mean aerodynamic chord) and elevator deflections between -15° and +15°. A database on the tailplane performance and handling was generated from these experimental tests.
Pilot Simulator Program
Pilots in both the general aviation and commuter airplane categories have little current training support that would provide the necessary knowledge about how to best manage an in-flight icing encounter. Initial and recurrent training are needed to provide awareness of the consequences of an icing encounter, whether it is intentional (with the airplane certified for flight-in-icing) or inadvertent. To address this safety issues, NASA initiated a collaborative research program with WSU in 1998 to develop a ground-based pilot simulator program for training pilot in realistic icing encounters. The program involved the generation of experimental data on the flight characteristics of aircraft with ice contamination, and the development of the software fot pilot interactions. Tests were conducted with a clean and iced 6.5%-scale Twin Otter aircraft model in the vertical tunnel at the Bihrle Applied Research (BAR) Large Amplitude Multi Purpose (LAMP) rotary balance wind tunnel in Germany and 7-ft x 10-ft wind tunnel facility at WSU. Extensive experimental tests were carried out with a range of control and flap deflections. The simulation models were developed by BAR using the experimental data for the clean and iced aircraft configurations, which were verified against flight test results. The outcome of the research program is a desktop simulator that had undergone a series of successful tests by BAR and NASA personnel.
Experimental Investigation of Simulated Ice Shapes on an NLF Airfoil
NASA’s Advanced General Aviation Transport Experiments (AGATE) program has developed a natural laminar flow (NLF) airfoil for the AGATE aircraft. The design incorporates a favorable pressure gradient over a large extent of the wing surface with a short pressure recovery region near the aft region of the airfoil at design condition. However, NLF airfoils present a challenge for the ice protection system due to the requirements for maintaining surface tolerances in order to achieve the desired laminar flow. It is thought that mechanical de-icing system (selected for the AGATE aircraft) can cause residual ice deposits on the airfoil surface during inter-cycle activities hence affect the aerodynamic performance. This research work was conducted to evaluate the sensitivity of the NLF airfoil to surface roughness resulting from the presence of ice on the leading edge of the airfoil. The experimental investigation was performed on a 2-D, 48-inch chord, NLF-0414 airfoil equipped with a 25% chord single element flap. Tests were conducted at the 7-ft x 10-ft wind tunnel at WSU. The lift, drag, pitching moment and hinge moment coefficients were measured at Reynolds numbers of 1.8, 3.0 and 4.5 million and for angles of attack in the range of -8° to +18°. Flap deflections tested were -10°, -5°, 0°, +5° and +10°. The ice shapes used include a 45-minute, 2-minute and 5-minute ice accretions as well as four inter-cycle ice shapes obtained from the use of two pneumatic and two electro-expulsive de-icing systems.