Advanced Rotor Aerodynamics Concepts with Application to Large Rotorcraft Matthew W Floros Raytheon ITSS Moffett Field California Wayne Johnson Army NASA Rotorcraft Division NASA Ames Research Center Moffett Field California Michael P Scully Aeroflightdynamics Directorate AMRDEC US Army Aviation and Missile Command Ames Research Center Moffett Field California A study was conducted using the comprehensive analysis CAMRAD II to explore performance enhancements to large rotorcraft The aircraft considered were a 125 foot diameter six bladed rotor helicopter and an 85 foot diameter fourbladed rotor tilt rotor The objectives were to reduce power required and increase maximum lift The effects of improved airfoils and active controls were investigated Airfoils with higher maximum lift and with reduced drag were investigated Results showed a moderate improvement in the maximum lift capability for the helicopter and a large improvement for the tilt rotor For the helicopter 2 rev individual blade control resulted in modest power savings in cruise flight which increased with control amplitude and forward speed The optimum phase for the individual blade control was relatively insensitive to both amplitude and forward speed The influences of active twist increased chord increments in airfoil properties and tilt rotor tip extensions were also investigated The purpose of the current study was to examine possibilities for rotor aeromechanics performance improvements and gain understanding of how these blade element level technologies One of the challenges likely to face the rotorcraft industry in interact to produce integrated rotor performance This underthe future is designing a new generation of transport rotorcraft standing will be used to guide future research that are significantly larger than current models As rotor size increases the scaling issues become more severe and the fraction of gross weight required for rotor and rotor controls increases As a result large rotorcraft use high disk loading to Approach reduce rotor size and weight However high disk loading impacts both performance high induced power and operational suitability high downwash velocity The technology chal The approach taken in this investigation was to design large lenge is to enable large low disk loading rotors with afford rotorcraft both helicopter and tilt rotor versions based on advanced technology goals and determine the rotor performance able weight fractions for these designs The U S Army Rotary Wing Vehicle RWV One or several enabling rotor technologies will likely be re Technology Development Approach TDA goals for FY05 quired to produce the performance gains and weight savings were used for all rotorcraft components This established tarnecessary for a cost effective large rotorcraft Such technolo gets for rotor performance using advanced technology The gies must provide greater maximum thrust from a given blade second phase was to examine what performance enhancements area and reduce the power required to achieve a given level of might be achieved using specific advanced rotor concepts thrust These performance improvements must be attained for the same or less weight for a given blade and disk area This The design mission profile for these rotorcraft was a 20 ton will result in less rotor and rotor controls weight to attain a load 500 km mission radius on an Army hot day 4000 MSL and 95 F The vertical takeoff requirement was Hover given maximum thrust capability Out of Ground Effect HOGE at 95 of Maximum Rated Presented at the American Helicopter Society Aerodynamics Acoustics and Power MRP on an Army hot day The cargo compartment Test and Evaluation Technical Specialists Meeting San Francisco CA January 23 25 2002 Copyright c 2002 by the American Helicopter Society of these rotorcraft had to be the same as that of a C 130 transInternational Inc All rights reserved port 10 x 9 x 40 feet Advanced technology rotorcraft designs Introduction 1 were created to satisfy these requirements The basic parameters of these designs are given in Table 1 The rotorcraft design synthesis which produced the information for Table 1 was also used to calculate the rotor trim conditions This trim included the effects of airframe wing fuselage and empennage aerodynamics and engine mass flow jet thrust and momentum drag The resulting rotor trim parameters are given in Table 2 Table 1 Helicopter and tilt rotor configurations Property Gross Weight Disk Loading psf Empty Weight GW Fuel Weight GW Engine Power shp Rotor Radius R ft Geometric Solidity Number of Blades NB Blade Twist T deg Precone P deg Articulation First Flap Natural Frequency Cyclic Mode per rev Collective Mode per rev Tip Speed VT ft sec Versions of these designs were also created using baseline rotor technology The dimensions and gross weights of these baseline versions remained the same as the advanced technology designs to avoid scaling effects The engines were scaled up to retain the same hover capability with less efficient rotors The greater weight and greater power required by these baseline technology rotors resulted in reduced payload less than the 20 ton design requirement The baselines for RWV TDA rotor technology were RAH 66 for helicopters and MV 22 for tilt rotors Baseline rotor technology means here the same airfoils twist and planform as RAH 66 and MV 22 Rotor size disk loading design blade loading blade aspect ratio number of blades and hub concept were design parameters used to select the designs for this application Note that although the starting points for the designs were existing successful designs and design variables such as disk loading and radius were chosen for a specific mission the baseline designs were not necessarily optimal Given these designs and the predicted gap between baseline technology and FY05 technology the next step was to determine if the FY05 goals could be realized and what rotor technologies were likely to be able to bridge the gap Helicopter 121 000 9 9 53 9 11 8 2 x 11 960 62 5 0 1065 6 11 0 Hinged Tilt Rotor 129 600 11 4 60 2 7 7 2 x 12 640 42 5 0 0752 4 47 3 2 Gimbaled 1 07 1 07 725 1 02 1 07 750 626 Table 2 Typical helicopter and tilt rotor trim conditions at 1 g The design points for the helicopter and tilt rotor were based on typical modes of operation for the two vehicles For the tilt rotor hover performance airplane mode performance 180300 kts and maximum helicopter mode lift at 80 kts were design points For the