21st Applied Aerodynamics Conference AIAA 2003-3952
AIAA 2003-395221st Applied Aerodynamics Conference23-26 June 2003, Orlando, FloridaDESIGN OF 1/48th-SCALE MODELS FOR SHIP/ROTORCRAFT INTERACTION STUDIESMichael R. DerbyAerospace Computing, Inc.Moffett Field, CA 94035AbstractIn support of NASA and Navy sponsored research, theArmy/NASA Rotorcraft Division at Ames ResearchCenter has designed and fabricated 1/48th-scalerotorcraft models and an amphibious assault shipmodel. The model scale was selected primarily toaccommodate testing in the Army 7- by 10-Foot WindTunnel at NASA Ames. In addition to ship/rotorcraftinteraction studies, the models are used to investigatethe aerodynamic interaction of rotorcraft with otheraircraft, with large structures, and with the ground. Fourrotorcraft models representing three configurationswere built: a tiltrotor aircraft, a tandem rotor helicopter,and a single main rotor helicopter. The design of thesemodels is described and example results from severaltest configurations are presented.NotationAbcCMxCTDDWMxNRsTUWxyzaircraft total rotor disk areatiltrotor wingspanblade chord lengthaircraft roll moment coefficient,Mx /(ρ(ΩR)2(πR2)R), positive right wing downaircraft thrust coefficient,T/(ρ(ΩR)2A)rotor diameterdownwindaircraft roll momentnumber of bladesrotor blade radiustiltrotor wing semispan, b/2aircraft total thrustupwindstreamwise location of UW aircraft relative toDW aircraft, positive in drag directionlateral location of UW aircraft relative to DWaircraft, positive to right (pilot’s view)vertical location of UW aircraft relative to DWaircraft, positive upPresented at the 21st Applied Aerodynamics Conference, Orlando,Florida, 23 – 26 Jun 2003. Copyright 2003 by the AmericanInstitute of Aeronautics and Astronautics, Inc. The U.S. Governmenthas a royalty-free license to exercise all rights under the copy-rightclaimed herein for Governmental purposes. All other rights arereserved by the copyright owner.Gloria K. YamauchiNASA Ames Research CenterMoffett Field, CA 94035µΩρσadvance ratio, tunnel speed/(ΩR)rotor rotational speedair densityrotor geometric solidity, Nc/(πR)IntroductionThe Army/NASA Rotorcraft Division at NASAAmes Research Center has initiated an experimentalprogram to study the aerodynamic interaction ofrotorcraft with other aircraft, with large structures suchas buildings and ships, and with the ground. DuringOctober 2001-June 2002, a series of experiments wasconducted in the Army 7- by 10-Foot Wind Tunnel atNASA Ames investigating the aforementionedscenarios. The primary experiments completed were theshipboard operations of rotorcraft and terminal areaoperations of tiltrotors.1, 2 The experimental results areproviding valuable guidance in determining the effectof upwind aircraft location on a downwind on-deckaircraft, characterizing the airwake of a ship,characterizing the combined ship/rotorcraft airwake,and determining safe formation flight configurations fortiltrotors in- and out-of-ground effect for terminal areaoperations. In addition, the database is a valuablesource for validating analyses.1The primary driver for the model scale selectionwas to accommodate the ship/rotorcraft interactionstudy undertaken for the Navy. A 1/48th-scale ship wasdetermined to be the largest size that could be tested inthe 7- by 10-Foot Wind Tunnel given the test sectionlength of 15 ft and the ship yaw angle requirements. Inaddition, commercial plastic fuselage kits for some ofthe aircraft were available at 1/48 t h -scale thusminimizing fabrication effort and cost.For the ship/rotorcraft and formation flight studiesaddressed in this paper, correctly simulating the trailedrotor wake strength and position is key. The parametersthat govern the strength and position of the trailed wakeare rotor thrust and forward speed, not the details of therotor geometry. If key nondimensional parameters suchas rotor thrust coefficient and advance ratio can bematched between model and full-scale results, themodel scale data should provide a good representationof full-scale events. Hence, the general aerodynamicinteraction characteristics should be captured using the1American Institute of Aeronautics and AstronauticsCopyright 2003 by the American Institute of Aeronautics and Astronautics, Inc.The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes.All other rights are reserved by the copyright owner.
1/48th-scale models. Previous work at Ames using small(approximately 1/40th -scale) tiltrotor aircraft haveproven the viability of using models of this size foraerodynamic investigations.3, 4This paper describes the design and fabrication ofthe ship and rotorcraft models and the installation of themodels in the wind tunnel. The different phases of theexperimental program together with the testingprocedures are described. Sample results are shown.Model DescriptionMost of the hardware for this experimentalprogram was designed and fabricated by NASA Ames.For the ship/rotorcraft aerodynamic study, 1/48th-scalemodels of an amphibious assault ship, a tiltrotor (two),a tandem rotor helicopter, and a single main rotorhelicopter were designed and fabricated. The twotiltrotors were subsequently used during the terminalarea operations investigations. The following sectionsprovide details on the ship and aircraft geometries.Model mounting is also discussed.ShipThe ship was a low fidelity, 1/48th-scale model ofan LHA amphibious assault ship. The ship geometrywas scaled from the shipyard drawings of an LHA; keydimensions are provided in Table 1. The radio masts,cranes, radar antennae and other smaller features werenot modeled. The ship superstructure was modeled asslab sided blocks, and includes representations of thefunnels. The flight deck edge and catwalks weremodeled together as a single rectangular extrusionalong the port and starboard sides of the ship. The hullof the model extended down to the nominal waterline.The model bow geometry was representative of theactual ship through two removable, fiberglass skinnedfoam panels. All other components of the ship wereconstructed from 1/2 inch-thick aluminum honeycombcore panels. The deck edge elevator and the aft aircraftelevator were modeled flush with the deck. The shipwas split near the midpoint into forward and aftsections that bolt together, allowing easier storage andhandling. Sub-components were bolted to the mainstructure.The ship was mounted internally to an aluminumrail that extends nearly the entire length of the ship. Therail was mounted to linear bearings that were welded tothe tunnel turntable, which provides model yaw. Thelinear bearings allowed longitudinal freedom forlocating the ship in the tunnel. The linear bearings wereequipped with brakes to lock the ship in position. Thebrakes were accessible through panels located on thestarboard side of the hull. The aft end of the mountingrail was supported by two castering, spring loadedwheels that prevent drooping of the aft end of the shipwhich was cantilevered off the end of the turntable. Thewheels also allowed the model to be yawed over thesloped floor of the diffuser section of the tunnel. Brushbristles, approximately 2 in long, were attached to thebottom of the ship perimeter. The brushes served asseals to prevent unwanted airflow between the shipbottom and the tunnel floor. The pliable brushesconformed to the different size gaps between the tunnelfloor and ship as the ship was translated and yawed inthe tunnel. Figure 1 shows the ship mounted in the windtunnel.Aircraft ModelsFour aircraft models were fabricated, representing3 types of aircraft: tiltrotor, tandem rotor helicopter andsingle main rotor helicopter. Full-scale V-22, CH-46,and CH-53E dimensions guided the designs. Key fullscale geometric properties, provided by the Navy, areshown in Table 2. The primary modeling parameterswere rotor diameter, solidity, rotor-rotor position andrelative tip speed. Additionally, for the tiltrotor, therotor-wing separation was modeled accurately. All ofthe models used rigid hubs and had collective controlonly (no cyclic). The hub and control systems werecommercially available radio-control (R/C) modelhelicopter tail-rotor assemblies. The rotor blade pitchcases were redesigned to minimize the blade rootcutout. The models were mounted on 0.75-inchdiameter, six-component balances.High-power-density R/C model motors wereselected with physical dimensions compatible with thescale of the models. Each aircraft used a single AstroCobalt-40 sport motor (AstroFlight, Inc, Model #640)mounted within the aircraft to power the rotor(s). Theaircraft power requirements were estimated using afigure of merit of 0.40, which is appropriate for lowReynolds number rotors ( 50,000). Gear ratios foreach transmission were chosen to provide nearoptimum motor operation at the selected rotor rpm.Rotor rpm was selected based on the available power,with some design margin (25%) on the estimated powerrequirement. The most critical power requirement wasfor the single main rotor helicopter model. Theavailable motor power limited the maximum tip speedof the models to approximately 33% of full-scale.Commercially available R/C radio transmitters,receivers, speed controllers, governors and controlservos were used to remotely control rotor rpm andcollective pitch. Two identical DC power suppliesrated for 30 Amps at 25 Volts, powered the modelmotors. Batteries were used to power the collectivecontrol servo motors and speed controller. Table 3provides a summary of the physical dimensions andproperties of each model aircraft.2American Institute of Aeronautics and Astronautics
Tiltrotor Major components of the tiltrotor modelare shown in Figure 2a. The model is shown mountedon the upwind, traversing sting in Figure 2b. The motorprotruded from the nose of the aircraft, and the nacelleswere not modeled. The wing was made from machinedaluminum. The wing sweep and dihedral were modeled.The flaperons were set at zero degrees deflection. Therotor shafts were oriented vertically; outboard cant ofthe rotors was not modeled. The shafts were fixed at 90deg for helicopter mode flight. The fuselage was a1/48th -scale plastic model by Italeri, kit #825. Thelanding gear was not modeled. The rotor bladeplanform and twist were similar to a full-scale tiltrotorblade. The rotor blade airfoils were a blend of a lowReynolds number airfoil and a tiltrotor airfoil.The tiltrotor model used a 2-stage gear reduction.The first stage, a 1.63:1 helical transmission, was bolteddirectly to the motor. The second stage was a 1.19:1right angle gearbox that also served as the balancemounting block. The transmission output shaftsupported a magnet providing a 1/rev pulse used togovern the motor speed and provide rpm. The wingswere bolted to the sides of the transmission housing.The rotor driveshafts protruded beneath the lowersurface of the wing. The nacelle transmissions were 1:1RC helicopter tail rotor transmissions. The collectivecontrol linkage ran under the wing planform to servosmounted on the sides of the transmission housing. Therotor hubs were rigid with remote control of collectivepitch only. Hence the rotors operated with some non zero hub moment in helicopter mode forward flight.Differential collective pitch could be introduced to trimrolling moment. The balance moment center waslocated mid-way between the two rotors in the rotorrotor plane.the chassis. The skin was made from 0.020-inch plasticsheet shaped to provide a more realistic profile. Theskin included stub wings and the lower portion of therear pylon and was wrapped over the chassis top andsides and secured to the chassis using Velcro strips.Single Main Rotor Helicopter Figure 4a shows themajor components of the single main rotor helicopter.Figure 4b shows the model installed on the upwind,traversing sting; the ship is seen in the background.Since a 7-bladed hub was not commercially available, a5-bladed hub was used. The intent was to match thefull-scale CH-53E (7-bladed hub) solidity. The bladeswere fabricated assuming an identical root cutout as the3-bladed tandem rotor hub. Unfortunately, the rootcutout of the 5-bladed hub proved to be larger; hence,the rotor radius was closer to 1/46th-scale than 1/48th.The low Reynolds number airfoil used for the tandemrotor helicopter was also used for the single main rotorhelicopter blade. The blade planform and twist wererepresentative of the full-scale helicopter. Thehelicopter was designed with a two-stage 4:1 gearreduction.A 1/48th -scale plastic model kit of a CH-53G(Revell Germany) was modified to serve as thefuselage. Cut-outs were made in the kit fuselage asappropriate to ensure a snug fit around the modelchassis. As shown in Fig. 4, the motor protruded fromthe front of the fuselage. The fuselage was secured tothe chassis using small hex screws. The kit's stubwings, external auxiliary tanks, and cowling weremodified to simulate the planform area of the 3-enginedCH-53 variant. The tail assembly was not modeled inorder to provide clearance for the sting mount.Aircraft MountingTandem Rotor Helicopter The tandem helicoptermajor components are shown in Figure 3a. Figure 3bshows the model mounted on the upwind, traversingsting. The relative height and shaft angles of the rotorhubs were modeled correctly. The aft transmission washigher than the forward transmission, and the forwardtransmission was canted 2.50 degrees forward. Themain transmission provided direct coupling to theforward transmission and a 1:1 ratio to the afttransmission. The helicopter transmission ratio was setat 1:1 in order to reduce the complexity and size of thegearbox. Although this did not provide the optimummotor rpm, the power required was still well within thepower capability of the motor. A six-componentbalance was located under the aft rotor.The rotor blade planform and twist were similar tothe equivalent full-scale blade. A low Reynolds numberairfoil was used instead of the full-scale airfoil.A removable skin was fashioned for the model toaccommodate protrusions in the body contour due toFor the ship/rotorcraft aerodynamic interactionstudy, a tiltrotor was mounted to a ship-supported stingthat was manually adjustable axially, in yaw, and inheight above deck. The sting was bolted to a hard pointbeneath the deck in the interior of the ship, thusminimizing protrusions above deck. The tiltrotor wasfixed at a height corresponding to wheels on-deck fullscale. Two mounting positions were provided for thesting near the port edge of the ship, downstream of thesuperstructure. To simulate an aircraft operatingupwind of the on-deck tiltrotor, a second aircraft(tandem rotor helicopter, single main rotor helicopter ortiltrotor) was sting-mounted and suspended from astreamlined strut attached to the tunnel traverse system.A two-piece sting was used to offset the modelsvertically and horizontally from the traverse. Thehorizontal sting could be manually yawed in fixedincrements of 5 degrees up to 15 degrees (to starboard).3American Institute of Aeronautics and Astronautics
The upwind model could be traversed in the lateral,vertical, and streamwise directions.For the formation flight studies, the downwind orfollowing aircraft was mounted on a fixed pedestalmount. The mount permitted manual adjustment ofmodel yaw, pitch, and height.Aircraft Force and Moment MeasurementsA maximum of two aircraft were testedsimultaneously. Each aircraft was mounted on a sixcomponent (5 forces, 1 moment), 0.75-inch diameterinternal balance. The six components were comprisedof two normal force elements providing normal forceand pitching moment, two side force elementsproviding side force and yaw moment, an axial forceelement pair, and a roll moment element pair. Table 4provides the maximum allowable load for eachcomponent.Both balances were calibrated in the laboratoryimmediately before they were installed in the aircraft.For each balance, the calibration consisted of 12 singlecomponent loading runs. The data from the 12 runswere then used to compute a calibration matrix for thebalance. The normal force and rolling momentresponses were accurate within approximately 0.5% ofthe applied load.landing spots and four yaw angles (representing portside winds) over a range of velocities. Figure 6 showsseveral planes of PIV data superimposed on the ship.The reverse flow region behind the ship superstructureis clearly shown. Vortical regions locatedapproximately at the same location from the deck edgeas the oil line in Fig. 5 are also seen.The majority of the ship/rotorcraft interaction testconcentrated on acquiring aircraft force and momentdata for different arrangements of aircraft on or near theship. Figure 7 shows the installation of the primaryconfiguration tested: a tiltrotor on the ship deck with atandem rotor helicopter operating upwind. The tiltrotoraircraft was set to an initial low thrust level without theinfluence of the upwind aircraft. The upwind aircraftwas then set at a desired thrust and traversed in a pre programmed grid in the x-y plane (Fig. 8) at a givenheight above deck, z, while the tiltrotor forces andmoments were allowed to vary. At each position, theupwind aircraft was trimmed to the desired thrustbefore recording a data point. Using this procedure, theforces and moments of the on-deck tiltrotor weremapped as a function of upwind aircraft position. Thesemappings were acquired for several wind speeds at shipyaw angles of 0 and 15 degrees (to starboard). The testresults provide guidance in establishing safe shipboardoperational limits of the corresponding full-scalerotorcraft.ResultsExample results from the ship/rotorcraft interactiontest and the tiltrotor formation flight test are presented.The procedures for the different test configurations arealso discussed.Ship/Rotorcraft Interaction StudiesOne of the objectives of this interaction study wasto characterize the airwake of the ship alone. These datacould then be used to validate analyses without theadded complexity of including the effects of one ormore rotorcraft. Some limited surface flowvisualization was acquired by applying an oil mixture tothe surface of the ship deck. The oil mixture consistedof motor oil, olive oil, mineral spirits, and titaniumdioxide. Figure 5 shows the resulting oil pattern for ayaw angle of 15 deg and an approximate freestreamvelocity of 36 ft/s. The oil required about 20 minutes toreach a stable pattern. A line of oil build-up is seen inthe figure originating from the port leading edge andextending the length of the deck. Subsequent velocityfield measurements acquired using Particle ImageVelocimetry (PIV) suggest the oil line represents thepath of a vortex originating from the port leading edge.PIV was used to acquire three components ofvelocity in a 3-ft by 6-ft (H x W) plane orientedperpendicular to the freestream. Data were acquired at 4Formation FlightThe aerodynamic interaction of two modeltiltrotors in helicopter-mode formation flight wasinvestigated as part of the NASA Runway IndependentAircraft Program. The thrust and the roll moment of thedownwind aircraft were the primary measures of theaerodynamic interaction between the two aircraft. Threescenarios representing tandem level flight, tandemoperations near the ground, and a single tiltrotoroperating above the ground for varying winds wereexamined and the results reported.2Figure 9 shows the two tiltrotors installed in theArmy 7- by 10-Foot Wind Tunnel. The pitch attitude ofboth aircraft was fixed at zero; therefore, both rotor tippath planes were horizontal. The upwind model wastraversed in the lateral, vertical, and streamwisedirections upstream of the downwind stationary aircraft.Figure 10 shows the two aircraft with a ground planeinstalled. The ground plane is 4-ft by 8-ft andapproximately 1.25 inches thick with a rounded leadingedge.Based on limited velocity field measurementsacquired downstream of one of the tiltrotors (without aground plane
-scale plastic model by Italeri, kit #825. The landing gear was not modeled. The rotor blade planform and twist were similar to a full-scale tiltrotor blade. The rotor blade airfoils were a blend of a low Reynolds number airfoil and a tiltrotor ai
Aerodynamics is the study of the dynamics of gases, or the interaction between moving object and atmosphere causing an airflow around a body. As first a movement of a body (ship) in a water was studies, it is not a surprise that some aviation terms are the same as naval ones rudder, water line, –File Size: 942KBPage Count: 16Explore furtherIntroduction to Aerodynamics - Aerospace Lectures for .www.aerospacelectures.comBeginner's Guide to Aerodynamicswww.grc.nasa.govA basic introduction to aerodynamics - SlideSharewww.slideshare.netBASIC AERODYNAMICS - MilitaryNewbie.comwww.militarynewbie.comBasic aerodynamics - [PPT Powerpoint] - VDOCUMENTSvdocuments.netRecommended to you b
For permission to copy or to republish, contact the copyright owner named on the first page. For AIAA-held copyright, write to AIAA Permissions Department, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344 AIAA 2005 - 1042 COMPUTATIONAL FLUID DYNAMICS STUDY OF TURBULANCE MODELING FOR AN OGIVE USING COBALT FLOW SOLVER AND A 2N TREE-BASED
For permission to copy or to republish, contact the copyright owner named on the first page. For AIAA-held copyright, write to AIAA Permissions Department, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344 AIAA 2005 - 1042 COMPUTATIONAL FLUID DYNAMICS STUDY OF TURBULANCE MODELING FOR AN OGIVE USING COBALT FLOW SOLVER AND A 2N TREE-BASED
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