Design of a Slowed-Rotor Compound Helicopter for Future Joint Service Missions

A slowed-rotor compound helicopter has been synthesized using the NASA Design and Analysis of Rotorcraft (NDARC) conceptual design software. An overview of the design process and the capabilities ofNDARC are presented. The benefits of trading rotor speed, wing-rotor lift share, and trim strategies are presented for an example set of sizing conditions and missions. NOMENCLATURE Acronyms DGW Design Gross Weight GW Gross Weight HOGE Hover out of Ground Effect IRP Intermediate rated power ISA International Standard Atmosphere MCP Maximum continuous power MRP Maximum rated power MTOW Maximum Takeoff Weight NDARC NASA Design and Analysis of Rotorcraft SFC Specific fuel consumption SRC Slowed-Rotor Compound Symbols 6 Rotor solidity (geometric) CD Drag coefficient CL Lift Coefficient CT Rotor thrust coefficient Cu, Weight coefficient k 1,000 feet of elevation INTRODUCTION A compound helicopter is a helicopter that incorporates an auxiliary propulsor for forward thrust and/or a wing for auxiliary lift. By compounding the rotor, the rotor may be offloaded at higher speeds, with advantages in reduced power and potentially reduced loading on the rotor dynamic components. A compound helicopter typically Presented at the American Helicopter Society Aeromechanics Specialist's Conference, San Francisco, CA, January 20-22, 2010. This is a work of the U.S. Government and is not subject to copyright protection. achieves higher speed, better cruise efficiency, and can operate at higher altitudes. The wing can also provide a convenient mounting location for external stores and improve the maneuver performance in forward flight. Typically, compound helicopters pay penalties in hover performance due to increased download and power losses associated with the auxiliary propulsor, plus the extra weight of the propulsor and main wing. Operationally, the wing can be an issue for storage and transport, and can impede the egress of passengers in some circumstances. For attack helicopter missions, compound helicopters such as the AH-56A Cheyenne (propulsor and wing) and S-67 Blackhawk (wing) have been developed in response to the perceived need for greater speed and range. For utility and troop transport missions, compounds such as the X-49A Speedhawk (propulsor and wing) have been developed. Other recent studies, such as Sikorsky's X2 demo (propulsor) have also centered on the compound helicopter configuration as potentially desirable. For traditional helicopters, as true airspeed increases, advancing tip mach numbers become large and retreating blade stall occurs, leading to performance degradation and increased vibration. Slowing the rotor speed can alleviate this, albeit at the cost of reduced lifting capability and retreating blade stall. By unloading the rotor with a wing, the loss of rotor lifting capability is mitigated. A study was undertaken to explore the factors affecting design of a slowed-rotor compound helicopter using a new rotorcraft design code, NASA Design and Analysis of Rotorcraft (NDARC, Ref. 1). A single main-rotor layout, with an anti-torque rotor, a pusher propeller and a wing, was synthesized and sized against a design mission and four design conditions. https://ntrs.nasa.gov/search.jsp?R=20100024364 2018-03-25T19:04:58+00:00Z