An overview of a model rotor icing test in the NASA Lewis Icing Research Tunnel

NASA Technical Memorandum 106471 NASA Technical Memorandum 106471 AlAA-94-0716 AlAA-94-0716 An Overview of a Model Rotor Icing Test in the An Overview of a Model Rotor Icing Test in the

NASA Lewis Icing Research Tunnel NASA Lewis Icing Research Tunnel

Randall K. Britton Randall K. Britton Sverdrup Technology, Inc. Sverdrup Technology, Inc.

Lewis Research Center Group Lewis Research Center Group Brook Park, Ohio Brook Park, Ohio Thomas H. Bond Thomas H. Bond Lewis Research Center Lewis Research Center Cleveland, Ohio Cleveland, Ohio and and Robert J. Flemming Robert J. Flemming Sikorsky Aircraft Division, UTC Sikorsky Aircraft Division, UTC Stratford, Connecticut Stratford, Connecticut Prepared for the Prepared for the 32nd Aerospace Sciences Meeting 32nd Aerospace Sciences Meeting sponsored by the American Institute of Aeronautics and Astronautics sponsored by the American Institute of Aeronautics and Astronautics Reno, Nevada, January 10-13, 1994 Reno, Nevada, January 10-13, 1994

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An Overview of a Model Rotor Icing Test in the NASA Lewis Icing Research An Overview of a Model Rotor Icing Test in the NASA Lewis Icing Research Tunnel Tunnel Randall K. Britton Randall K. Britton Sverdrup Technology, Inc. Sverdrup Technology, Inc.

NASA Lewis Research Center Group NASA Lewis Research Center Group Brook Park, Ohio Brook Park, Ohio Thomas H. Bond Thomas H. Bond NASA Lewis Research Center NASA Lewis Research Center Oeveland, Ohio Oeveland, Ohio Robert J. Flemming Robert J. Flemming Sikorsky Aircraft Division, UTC Sikorsky Aircraft Division, UTC Stratford, Connecticut Stratford, Connecticut Abstract Abstract During two entries in late 1989, a heavily instrumented sub-scale model of a helicopter main During two entries in late 1989, a heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center (LeRC) Icing Research Tunnel (IRT). The rotor was tested in the NASA Lewis Research Center (LeRC) Icing Research Tunnel (IRT). The results of this series of tunnel tests have been published previously. After studying the results from results of this series of tunnel tests have been published previously. After studying the results from the 1989 test and comparing them to predictions, it became clear that certain test conditions still the 1989 test and comparing them to predictions, it became clear that certain test conditions still needed investigation. Therefore, a re-entry of the Sikorsky Aircraft Powered Force Model (PFM) needed investigation. Therefore, a re-entry of the Sikorsky Aircraft Powered Force Model (PFM) in the IRT was instituted in order to expand upon the current rotorcraft sub-scale model in the IRT was instituted in order to expand upon the current rotorcraft sub-scale model experimental database. The major areas of interest included expansion of the test matrix to include experimental database. The major areas of interest included expansion of the test matrix to include a larger number of points in the FAA AC 29-2 icing envelope, inclusion of a number of high power a larger number of points in the FAA AC 29-2 icing envelope, inclusion of a number of high power rotor perfonnance points, close examination of wann temperature operations, operation of the rotor perfonnance points, close examination of wann temperature operations, operation of the model in constant lift mode, and testing for conditions for icing test points in the full scale model in constant lift mode, and testing for conditions for icing test points in the full scale helicopter database. The expanded database will allow further and more detailed examination and helicopter database. The expanded database will allow further and more detailed examination and comparison with analytical models. Participants in the test were NASA LeRC, the U.S . Anny comparison with analytical models. Participants in the test were NASA LeRC, the U.S . Anny Vehicle Propulsion Directorate based at LeRC, and Sikorsky Aircraft. The model rotor was Vehicle Propulsion Directorate based at LeRC, and Sikorsky Aircraft. The model rotor was exposed to a range of icing conditions (temperature, liquid water content, median droplet diameter) exposed to a range of icing conditions (temperature, liquid water content, median droplet diameter) and was operated over ranges of shaft angle, rotor tip speed, advance ratio, and rotor lift. The data and was operated over ranges of shaft angle, rotor tip speed, advance ratio, and rotor lift. The data taken included blade strain gage and balance data, as well as still photography, video, ice profile taken included blade strain gage and balance data, as well as still photography, video, ice profile tracings, and ice molds. A discussion of the details of the test is given herein. Also, a brief tracings, and ice molds. A discussion of the details of the test is given herein. Also, a brief examination of a subset of the data taken is also given. examination of a subset of the data taken is also given.

Nomenclature Nomenclature Rotor Lift Coefficient Tunnel Velocity (ft/sec) Rotor Lift Coefficient Tunnel Velocity (ft/sec) CL Veo CL Veo Rotor Torque Coefficient Rotor Torque Coefficient CQ CQ Rotor Solidity Rotor Solidity 3) 3) LWC Liquid Water Content (glm LWC Liquid Water Content (glm Advance Ratio Advance Ratio MVD Droplet Diameter (Il-m) MVD Droplet Diameter (Il-m) T Static Air Temperature CC) T Static Air Temperature CC) Rotor Tip Speed (ft/sec) Rotor Tip Speed (ft/sec) R Rotor Radius (ft) R Rotor Radius (ft) Shaft Angle (deg.) Shaft Angle (deg.)

L Main Rotor Lift (lbs) L Main Rotor Lift (lbs) Icing Time (sec) Icing Time (sec) c Chord (ft) c Chord (ft) b Number of Blades b Number of Blades Air Density (slugs/ft3) Air Density (slugs/ft3) p p 1 1 - --.------ - --- ---"-- - . --- -- - . -~ " ~ -'-- - - - _ ._- - - - --.------ - --- ---"-- - . --- -- - . -~ " ~ -'-- - - - _ ._- - - Introduction Sikorsky Powered Force Model (PFM) in Introduction Sikorsky Powered Force Model (PFM) in 1989. These tests were very successful, as 1989. These tests were very successful, as Icing has historically been a problem documented in References 1,2, and 3. Icing has historically been a problem documented in References 1,2, and 3.

for aircraft, especially helicopters. Rotor Upon completion of the 1989 tests it for aircraft, especially helicopters. Rotor Upon completion of the 1989 tests it systems are very sensitive to icing because of became clear that there were certain test systems are very sensitive to icing because of became clear that there were certain test high accretion rates and vibration associated conditions of interest still missing from the high accretion rates and vibration associated conditions of interest still missing from the with asymmetric shedding. Most U.S. database. Therefore, a re-entry of the PFM in with asymmetric shedding. Most U.S. database. Therefore, a re-entry of the PFM in helicopters (military and civilian) have restricted the IRT was instituted in order to expand the helicopters (military and civilian) have restricted the IRT was instituted in order to expand the database obtained during the previous test database obtained during the previous test or no clearance for operation in forecasted icing or no clearance for operation in forecasted icing program. The major areas of interest were as program. The major areas of interest were as conditions. One of the major reasons for this is conditions. One of the major reasons for this is the prohibitive cost of qualification/certification. follows: the prohibitive cost of qualification/certification. follows: Current procedures for certification place Current procedures for certification place emphasis on full scale flight testing in natural 1) Expansion of the test matrix to include a emphasis on full scale flight testing in natural 1) Expansion of the test matrix to include a icing conditions. Many required test conditions larger number of points in the FAA AC icing conditions. Many required test conditions larger number of points in the FAA AC from the icing envelope do not readily occur in 29 -2 icing envelope. from the icing envelope do not readily occur in 29 -2 icing envelope.

nature. Further, the helicopter's short range nature. Further, the helicopter's short range (relative to its fixed-wing counterparts) 2) Inclusion of a number of high power (relative to its fixed-wing counterparts) 2) Inclusion of a number of high power essentially forces researchers to sit and wait for rotor performance points and other essentially forces researchers to sit and wait for rotor performance points and other the correct weather conditions rather than rotor icing data not available in the 1989 the correct weather conditions rather than rotor icing data not available in the 1989 "chase" icing. This usually results in very test. "chase" icing. This usually results in very test.

long and expensive flight test programs which long and expensive flight test programs which 3) Close examination of warm temperature 3) Close examination of warm temperature span several icing seasons. The French Super span several icing seasons. The French Super (near and slightly above freezing) (near and slightly above freezing) Puma icing flight test program spanned nine Puma icing flight test program spanned nine operations. operations.

years at a very high cost before certification for years at a very high cost before certification for flight into icing was obtained. Most U.S. flight into icing was obtained. Most U.S.

helicopter manufacturers agree that this level of 4) Operation of the model in constant lift helicopter manufacturers agree that this level of 4) Operation of the model in constant lift expenditure for certification is not economically mode to simulate more realistic flight expenditure for certification is not economically mode to simulate more realistic flight feasible for any domestic helicopter program. profiles during an icing encounter. feasible for any domestic helicopter program. profiles during an icing encounter.

There is, however, a market for all weather There is, however, a market for all weather helicopters in the civilian arena. The major 5) Test at conditions corresponding to helicopters in the civilian arena. The major 5) Test at conditions corresponding to roadblock U.S. manufacturers face is the cost available full scale helicopter icing roadblock U.S. manufacturers face is the cost available full scale helicopter icing of certification. Thus, there is a need to develop database. of certification. Thus, there is a need to develop database.

validated, less expensive alternatives to icing validated, less expensive alternatives to icing flight testing. Although flight testing will This expanded database will allow further and flight testing. Although flight testing will This expanded database will allow further and always be required, validated lower cost more detailed examination and comparison with always be required, validated lower cost more detailed examination and comparison with alternatives can alleviate complete dependence analytical models. Participants in the test were alternatives can alleviate complete dependence analytical models. Participants in the test were on it as a means for certification and thereby NASA LeRC , the U.S. Army Vehicle on it as a means for certification and thereby NASA LeRC , the U.S. Army Vehicle reduce certification cost. Propulsion Directorate, and Sikorsky Aircraft. reduce certification cost. Propulsion Directorate, and Sikorsky Aircraft.

A total of 220 runs were completed A total of 220 runs were completed Because of this need, the NASA Lewis Because of this need, the NASA Lewis throughout the test. Of those, 208 were icing throughout the test. Of those, 208 were icing Research Center (LeRC) formed the Helicopter Research Center (LeRC) formed the Helicopter Icing Consortium (HIC) in 1985 . This events, and the others were system check-out, Icing Consortium (HIC) in 1985 . This events, and the others were system check-out, consortium was composed of members from tare, balanci ng, and baseline runs. The program consortium was composed of members from tare, balanci ng, and baseline runs. The program the U.S. helicopter industry, academia, the was funded in two parts. The first was set up the U.S. helicopter industry, academia, the was funded in two parts. The first was set up Army, and NASA. The HIC began an as a contract between NASA and Sikorsk y. Army, and NASA. The HIC began an as a contract between NASA and Sikorsk y.

ambitious test program which was designed to The second part of the test program was a ambitious test program which was designed to The second part of the test program was a demon stra te that a model helicopter could be cooperative Space Act Agreement between demon stra te that a model helicopter could be cooperative Space Act Agreement between successfully tested in the NASA LeRC Icing Sikorsky and NASA. There were 71 icing test successfully tested in the NASA LeRC Icing Sikorsky and NASA. There were 71 icing test Research Tunnel (IR T) and yield useful data. runs performed during the contract portion of Research Tunnel (IR T) and yield useful data. runs performed during the contract portion of the test and the remaining 137 icing points were the test and the remaining 137 icing points were The test program consisted of a single test of a The test program consisted of a single test of a tested under the Space Act Agreement. This tested under the Space Act Agreement. This lightly instrumented OH-58 Tail Rotor Rig in lightly instrumented OH-58 Tail Rotor Rig in 1988 and two tests of the heavily instrumented paper will provide an overview of the test as 1988 and two tests of the heavily instrumented paper will provide an overview of the test as 2 2 well as a few examples of the data obtained. fuselage skins are scaled to 1/5.727 of full well as a few examples of the data obtained. fuselage skins are scaled to 1/5.727 of full The data discussed will be from the contract scale, as are the standard UH-60 blades used The data discussed will be from the contract scale, as are the standard UH-60 blades used portion of the test. for this test apparatus. However, IRT wall portion of the test. for this test apparatus. However, IRT wall constraints dictated that the scaled blades (2.86 constraints dictated that the scaled blades (2.86 Test Apparatus Description m or 9.37 ft diameter) be truncated to a Test Apparatus Description m or 9.37 ft diameter) be truncated to a diameter of 1.86 m (6.09 ft) for this test. diameter of 1.86 m (6.09 ft) for this test.

Icing Research Tunnel The model was driven by two Able 60 Icing Research Tunnel The model was driven by two Able 60 HP 3-phase variable frequency induction HP 3-phase variable frequency induction electric motors, providing a maximum rotor electric motors, providing a maximum rotor The IRT was designed and built in the The IRT was designed and built in the early 1940s. The IRT is a closed-loop speed of 2286 RPM, for a maximum tip speed early 1940s. The IRT is a closed-loop speed of 2286 RPM, for a maximum tip speed refrigerated wind tunnel. A 4100-hp fan of 222 mls (729 ft/s) . Model power was refrigerated wind tunnel. A 4100-hp fan of 222 mls (729 ft/s) . Model power was provided by a variable frequency motor- provided by a variable frequency motor- provides airspeeds up to 134 mls (300 mph) in provides airspeeds up to 134 mls (300 mph) in an empty test section. The 21,OOO-ton-capacity generator set provided by the an empty test section. The 21,OOO-ton-capacity generator set provided by the refrigeration heat exchanger can vary the total Aeroflightdynamics Directorate of ATCOM. refrigeration heat exchanger can vary the total Aeroflightdynamics Directorate of ATCOM.

0 0 temperature from 50 to -42 C (Figure 1). The The motor generator set had a constant rotor temperature from 50 to -42 C (Figure 1). The The motor generator set had a constant rotor spray nozzles provide droplet sizes from 11 to spray nozzles provide droplet sizes from 11 to speed feedback system that maintained a speed feedback system that maintained a constant RPM throughout an icing encounter. constant RPM throughout an icing encounter.

40!lm median volume diameter (MVD) with 40!lm median volume diameter (MVD) with Rotor head forces and moments were Rotor head forces and moments were liquid water contents (L WC) ranging from 0.2 liquid water contents (L WC) ranging from 0.2 measured using a six component balance that measured using a six component balance that 3 3 to 3.0 glm The tunnel is 1.8 m (6 ft) high and to 3.0 glm The tunnel is 1.8 m (6 ft) high and was gimbal mounted to the model frame. The was gimbal mounted to the model frame. The 2.7 m (9 ft) wide. In 1986 it underwent a major 2.7 m (9 ft) wide. In 1986 it underwent a major balance was electrically heated to maintain it at balance was electrically heated to maintain it at rehabilitation which provided faster and more rehabilitation which provided faster and more the calibration temperature of 20°C. Rotor the calibration temperature of 20°C. Rotor accurate control of the tunnel conditions. A accurate control of the tunnel conditions. A torque was measured using a separate load cell torque was measured using a separate load cell similar upgrade to the refrigeration plant and its similar upgrade to the refrigeration plant and its that measured the reaction force between the that measured the reaction force between the controls was completed in 1991. controls was completed in 1991.

gearbox (mounted on a bearing) and the gearbox (mounted on a bearing) and the For this test, armor plates were attached For this test, armor plates were attached gearbox frame. gearbox frame.

to the walls of the tunnel test section covering to the walls of the tunnel test section covering The four-bladed main rotor was fully The four-bladed main rotor was fully the visual access areas to protect personnel in the visual access areas to protect personnel in articulated and was controlled through a articulated and was controlled through a the control room. Video systems were installed the control room. Video systems were installed conventional rotorcraft system of rotating conventional rotorcraft system of rotating to monitor the test area, local rotor blade to monitor the test area, local rotor blade pushrods and scissors, a swashplate, three pushrods and scissors, a swashplate, three positions , and provide blade tracking positions , and provide blade tracking electromechanical actuators, and a stationary electromechanical actuators, and a stationary information. Reference 1 gives a complete information. Reference 1 gives a complete scissors. Control inputs were made at a control scissors. Control inputs were made at a control description of the setup for the 1989 PFM test description of the setup for the 1989 PFM test console that electronically mixed the inputs to console that electronically mixed the inputs to which was very similar to the setup for the which was very similar to the setup for the move the actuators. Rotor blade motions move the actuators. Rotor blade motions current test entry. current test entry.

(flapping, lead-lag, and collective pitch) were (flapping, lead-lag, and collective pitch) were measured and could be used by a feedback measured and could be used by a feedback Model Rotor Test Rig Model Rotor Test Rig controller to maintain the rotor at a constant controller to maintain the rotor at a constant flapping position. The control console also flapping position. The control console also The Sikorsky PFM is a general purpose The Sikorsky PFM is a general purpose included a rotor lift feedback system which included a rotor lift feedback system which rotor test apparatus that has been installed in a rotor test apparatus that has been installed in a could be used to maintain the rotor at a constant could be used to maintain the rotor at a constant number of wind tunnels and hover facilities, number of wind tunnels and hover facilities, CrJa throughout an icing encounter. Rotor CrJa throughout an icing encounter. Rotor including the Icing Research Tunnel (Figure 2). including the Icing Research Tunnel (Figure 2).

shaft angle was set prior to an icing encounter shaft angle was set prior to an icing encounter The model can be configured with a fuselage The model can be configured with a fuselage balance, powered tail rotor, and empennage. and held constant during each run. balance, powered tail rotor, and empennage. and held constant during each run.

However, the installation was simplified for this The articulated rotor head, as configured However, the installation was simplified for this The articulated rotor head, as configured test to a model main rotor mounted on a six for this test, had coincident flap and lag hinges test to a model main rotor mounted on a six for this test, had coincident flap and lag hinges located at the 8.3 % radial station. There was located at the 8.3 % radial station. There was component balance, with UH-60 BLACK component balance, with UH-60 BLACK no pitch-flap coupling. The rotor lead-lag no pitch-flap coupling. The rotor lead-lag HAWK fuselage skins. The main rotor was HAWK fuselage skins. The main rotor was dampers were electrically heated to maintain the dampers were electrically heated to maintain the located in a position 1.02 m (3.33 ft) above the located in a position 1.02 m (3.33 ft) above the fluid at a constant viscosity. The main rotor fluid at a constant viscosity. The main rotor tunnel floor, 0.1 m (0.33 ft) above the tunnel tunnel floor, 0.1 m (0.33 ft) above the tunnel blades were of composite construction with a blades were of composite construction with a centerline. The PFM BLACK HAWK centerline. The PFM BLACK HAWK 3 3 -_.- --- - ~--- - -- -- .--- .. . - -_.- --- - ~--- - -- -- .--- .. . - chord of 10.72 cm (4.22 in). The blades had for formatting into EXCEL spreadsheets for chord of 10.72 cm (4.22 in). The blades had for formatting into EXCEL spreadsheets for the Sikorsky SC2110 airfoil, which is a modern analysis and plotting. the Sikorsky SC2110 airfoil, which is a modern analysis and plotting.

cambered rotorcraft airfoil with a thickness to The video records provided a viewing cambered rotorcraft airfoil with a thickness to The video records provided a viewing chord ratio of 10%. The blades had a linear history of the ice accretion and shedding. chord ratio of 10%. The blades had a linear history of the ice accretion and shedding.

twist of -11.5". The rotor blades were painted There were three separate video systems: one twist of -11.5". The rotor blades were painted There were three separate video systems: one with blade number and spanwise markings to for safety monitoring, one for blade tracking with blade number and spanwise markings to for safety monitoring, one for blade tracking aid in photo documentation. (which also provided good. ice profile shapes aid in photo documentation. (which also provided good. ice profile shapes near the blade tip), and one that allowed near the blade tip), and one that allowed I nstrumentatioD close-up images of the rotor blades. The three I nstrumentatioD close-up images of the rotor blades. The three systems were strobe driven by a signal off the systems were strobe driven by a signal off the The test used an instrumentation system rotor shaft angle encoder. This gave a "frozen" The test used an instrumentation system rotor shaft angle encoder. This gave a "frozen" that acquired data for both research and safety- image of the blade. The close-up data video that acquired data for both research and safety- image of the blade. The close-up data video of-flight use. Research instrumentation, in system for local rotor blade monitoring was of-flight use. Research instrumentation, in system for local rotor blade monitoring was addition to the balance measurements and blade installed on a tilt and pan mechanism along with addition to the balance measurements and blade installed on a tilt and pan mechanism along with motion sensors noted above, included rotor a 35-mm camera that had a 4OO-mm zoom lens. motion sensors noted above, included rotor a 35-mm camera that had a 4OO-mm zoom lens.

RPM, IRT temperatures and pressures, time RPM, IRT temperatures and pressures, time This video system had the capability of This video system had the capability of varying LWC, pushrod loads, and blade strains. traversing the entire diameter of the main rotor varying LWC, pushrod loads, and blade strains. traversing the entire diameter of the main rotor The primary instrumented blade had five while allowing zoom shots of as small a span as The primary instrumented blade had five while allowing zoom shots of as small a span as flatwise, five edgewise, and three torsion strain 0.10 m (0.3283 ft) of the blade leading edge. flatwise, five edgewise, and three torsion strain 0.10 m (0.3283 ft) of the blade leading edge.

gages. The other blades had a root edgewise The 35-mm camera was focused on the same gages. The other blades had a root edgewise The 35-mm camera was focused on the same strain gage to indicate the times of shedding close-up viewing area as the video camera, strain gage to indicate the times of shedding close-up viewing area as the video camera, events. Additional safety-of-flight allowing pictures with greater resolution and events. Additional safety-of-flight allowing pictures with greater resolution and instrumentation included model thermocouples, clarity to be taken. Both the data video and the instrumentation included model thermocouples, clarity to be taken. Both the data video and the accelerometers, flow meters, and limit 35-mm camera were triggered from the same accelerometers, flow meters, and limit 35-mm camera were triggered from the same indicators. indicators.

strobe to provide an accurate replication of the strobe to provide an accurate replication of the video image for the 35-mm camera. video image for the 35-mm camera.

Data Acquisition Liquid water content information (rise Data Acquisition Liquid water content information (rise time, cloud stabilization, and spray bar lag from time, cloud stabilization, and spray bar lag from The total data collection process spray initiation) was recorded from the Control The total data collection process spray initiation) was recorded from the Control included the Sikorsky Aircraft HP 9000 Room console output. A Johnson-Williams included the Sikorsky Aircraft HP 9000 Room console output. A Johnson-Williams portable data acquisition system, IRT (J-W) LWC meter also measured the LWC portable data acquisition system, IRT (J-W) LWC meter also measured the LWC information on velocity, temperature, and liquid within the test section. Spray times, information on velocity, temperature, and liquid within the test section. Spray times, water content, conventional and strobe temperatures, and general comments were water content, conventional and strobe temperatures, and general comments were illuminated imaging, photographic and manual noted. illuminated imaging, photographic and manual noted.

records pertaining to the accreted ice, plus a Several kinds of post-run information records pertaining to the accreted ice, plus a Several kinds of post-run information number of other measurement and cataloguing about the accreted ice were gathered. Still number of other measurement and cataloguing about the accreted ice were gathered. Still techniques. pictures with a 35-mm camera were taken of the techniques. pictures with a 35-mm camera were taken of the The Hewlett Packard 9000 series blade planform, an end profIle, and any unusual The Hewlett Packard 9000 series blade planform, an end profIle, and any unusual portable data acquisition system sampled data ice formations. Close-up shots of ice growths portable data acquisition system sampled data ice formations. Close-up shots of ice growths in the rotor domain reference system at a rate of were taken to record their minute detail. A in the rotor domain reference system at a rate of were taken to record their minute detail. A 16 samples per blade revolution. Simultaneous heated aluminum block with a cut-out contour 16 samples per blade revolution. Simultaneous heated aluminum block with a cut-out contour sample-and-hold amplifiers froze the analog sample-and-hold amplifiers froze the analog of the airfoil shape was used to make a clean of the airfoil shape was used to make a clean channels before digitizing to maintain a channels before digitizing to maintain a slice through the ice formation. A cardboard slice through the ice formation. A cardboard consistent data snapshot. Processing of the template was then held against the ice shape and consistent data snapshot. Processing of the template was then held against the ice shape and data included correction for tunnel blockage, a tracing made. This process also provided ice data included correction for tunnel blockage, a tracing made. This process also provided ice model gimbal motion, shaft torque tare, gravity thickness values along the blade at discrete model gimbal motion, shaft torque tare, gravity thickness values along the blade at discrete tares, and induced angle of attack. The data spanwise and chordwise locations. Visual tares, and induced angle of attack. The data spanwise and chordwise locations. Visual from the first 10 revolutions in each second observations were recorded about the kind of from the first 10 revolutions in each second observations were recorded about the kind of (total of 160 data samples) were then averaged ice, any secondary growth, and frost formation. (total of 160 data samples) were then averaged ice, any secondary growth, and frost formation.

to create a data record. Processed data records Molds were taken of two blades on eight test to create a data record. Processed data records Molds were taken of two blades on eight test were then transmitted to a personal computer were then transmitted to a personal computer runs including two repeat conditions. While runs including two repeat conditions. While 4 4 this documentation was taking place the data leading edge ice shape faced up. Wooden mold this documentation was taking place the data leading edge ice shape faced up. Wooden mold files of the test run were backed up and a copy boxes were secured around the blades (Figure files of the test run were backed up and a copy boxes were secured around the blades (Figure was downloaded to a micro-computer for 3) and the mold materials were poured around was downloaded to a micro-computer for 3) and the mold materials were poured around post-test processing. post-test processing.

the blades. The thenna! mass of the test section the blades. The thenna! mass of the test section assisted in keeping the temperature constant assisted in keeping the temperature constant Run Procedure while the mold materials set up (the hardening Run Procedure while the mold materials set up (the hardening process started approximately 10 minutes after process started approximately 10 minutes after The test techniques used in the IRT the materials were poured into the mold boxes The test techniques used in the IRT the materials were poured into the mold boxes were based on rotorcraft model operating surrounding the blades). The molds were were based on rotorcraft model operating surrounding the blades). The molds were experience and procedures developed during removed the next morning and the rotor blades experience and procedures developed during removed the next morning and the rotor blades earlier entries in the wind tunnel 1.2.3 . At the earlier entries in the wind tunnel 1.2.3 . At the cleaned for the next test run. cleaned for the next test run.

beginning of a test shift, the model was beginning of a test shift, the model was operated while the IRT temperature was Results operated while the IRT temperature was Results stabilized at the first test condition temperature. stabilized at the first test condition temperature.

At the end of the shift, the tunnel was generally Test Conditions At the end of the shift, the tunnel was generally Test Conditions operated (along with the model) to increase the operated (along with the model) to increase the tunnel temperature above freezing and dry out There were 71 icing tests runs during tunnel temperature above freezing and dry out There were 71 icing tests runs during the tunnel. the contract portion of this test; these will be the tunnel. the contract portion of this test; these will be A typical test run began by bringing the discussed here. The test matrix included a A typical test run began by bringing the discussed here. The test matrix included a PFM up to speed to exercise the rotor, then range of rotorcraft performance parameters for PFM up to speed to exercise the rotor, then range of rotorcraft performance parameters for shutting the model down to take static balance varied IRT conditions. The temperature range shutting the model down to take static balance varied IRT conditions. The temperature range and gage readings. The model was then was 5" to -30·C, the LWe range was 0.35 to and gage readings. The model was then was 5" to -30·C, the LWe range was 0.35 to brought up to operating speed and the rotor was 1.75 g/m3, and the MVD range was 11 to 30 brought up to operating speed and the rotor was 1.75 g/m3, and the MVD range was 11 to 30 stabilized. At this time, a dynamic zero (wind Ilm. The nominal condition was -15"C, 0.50 stabilized. At this time, a dynamic zero (wind Ilm. The nominal condition was -15"C, 0.50 off, zero collective) was taken. The rotor speed g/m3 LWe, and 15 !lm MVD. Icing times off, zero collective) was taken. The rotor speed g/m3 LWe, and 15 !lm MVD. Icing times was then dropped to some nominal level while were from 45 to 250 seconds. Thrust, was then dropped to some nominal level while were from 45 to 250 seconds. Thrust, the tunnel controls were set and the tunnel propulsive force, advance ratio, model rpm, and the tunnel controls were set and the tunnel propulsive force, advance ratio, model rpm, and started up. When the tunnel conditions were rotor control setting (constant lift vs. constant started up. When the tunnel conditions were rotor control setting (constant lift vs. constant stable the model operator returned the rotor to collective) were changed within the above tunnel stable the model operator returned the rotor to collective) were changed within the above tunnel the desired speed and set the rotor conditions. conditions to provide a wide scope of the desired speed and set the rotor conditions. conditions to provide a wide scope of The data engineer then initiated data acquisition performance mapping. Figure 4 shows a The data engineer then initiated data acquisition performance mapping. Figure 4 shows a and the tunnel operator initiated the spray mapping of the meteorological conditions of the and the tunnel operator initiated the spray mapping of the meteorological conditions of the sequence. At the end of the run the tunnel rpm test. This is compared to the previous tests in sequence. At the end of the run the tunnel rpm test. This is compared to the previous tests in 2 2 was brought down to idle (taking approximately 1989 and the FAA Ae 29-2 Icing Envelope. It was brought down to idle (taking approximately 1989 and the FAA Ae 29-2 Icing Envelope. It two minutes) while the model operator lowered can be seen that this test filled in a significant two minutes) while the model operator lowered can be seen that this test filled in a significant the rotor speed to a fall back position. When portion of the envelope not acquired during the the rotor speed to a fall back position. When portion of the envelope not acquired during the the tunnel test section speed was below 10 1989 test. the tunnel test section speed was below 10 1989 test.

As stated previously, the spray times As stated previously, the spray times knots the rotor was stopped. After the run the knots the rotor was stopped. After the run the researchers entered the test section and ranged from 45 to 250 seconds for this test. researchers entered the test section and ranged from 45 to 250 seconds for this test.

documented the resulting ice accretion. The Scale rotor testing uses these short icing times documented the resulting ice accretion. The Scale rotor testing uses these short icing times assembly was deiced and conditions set for the in order to simulate full scale conditions 1. assembly was deiced and conditions set for the in order to simulate full scale conditions 1.

next run. These spray times included the spray next run. These spray times included the spray The tests for which ice molds were to be stabilization time. A plot of the J- W L we data The tests for which ice molds were to be stabilization time. A plot of the J- W L we data taken were the last of the day. Prior to the test for a number of runs is given in Figure 5. Note taken were the last of the day. Prior to the test for a number of runs is given in Figure 5. Note that there was some rise time prior to reaching that there was some rise time prior to reaching run mold materials were mixed, degassed, and run mold materials were mixed, degassed, and kept in a freezer. The catalyst was added to the the target L we (with the rise time generally kept in a freezer. The catalyst was added to the the target L we (with the rise time generally mold mixture during the icing spray of the fmal increasing with the higher LWC runs). The mold mixture during the icing spray of the fmal increasing with the higher LWC runs). The run so that mold materials would be ready when spray condition remained relatively close to the run so that mold materials would be ready when spray condition remained relatively close to the the spray was completed. At the end of the run, desired L we after the ramp up. It was found the spray was completed. At the end of the run, desired L we after the ramp up. It was found after the tunnel was shut down, two of the that the cloud reached the model about 10 after the tunnel was shut down, two of the that the cloud reached the model about 10 blades were rotated 90 degrees so that the seconds after spray on was initiated. blades were rotated 90 degrees so that the seconds after spray on was initiated.

5 5 --- -- --- - _. - -- . - ~- - - --- -- --- - _. - -- . - ~- - - 4) Rotor Lift Condition (Constant 4) Rotor Lift Condition (Constant DiscussioD of Data Collective vs. Constant lift) DiscussioD of Data Collective vs. Constant lift) 5) Main Rotor Lift (Cria) 5) Main Rotor Lift (Cria) Analysis of the data has not been Analysis of the data has not been 6) Advance Ratio (J.l) 6) Advance Ratio (J.l) completed; however, an initial assessment of completed; however, an initial assessment of data quality has been made based on three main data quality has been made based on three main 7) Rotor Tip Speed (UR) 7) Rotor Tip Speed (UR) attributes: repeatability, correct trending, and attributes: repeatability, correct trending, and 8) Shaft Angle (a) 8) Shaft Angle (a) comparison with predictions. This paper will comparison with predictions. This paper will present some examples of the data in all three present some examples of the data in all three For the purposes of this report, results showing For the purposes of this report, results showing categories. categories.

the effects of temperature, LWC, rotor lift the effects of temperature, LWC, rotor lift control mode, main rotor lift, and droplet size control mode, main rotor lift, and droplet size Repeatability Repeatability will be presented. will be presented.

Repeatability has traditionally been a Lift Control Mode Repeatability has traditionally been a Lift Control Mode problem in natural icing flight testing because problem in natural icing flight testing because of the lack of control over meteorological The main rotor lift during the icing of the lack of control over meteorological The main rotor lift during the icing conditions. Cloud formations are governed by encounter was controlled. in two ways for this conditions. Cloud formations are governed by encounter was controlled. in two ways for this nonlinear processes and are almost never test; constant collective mode and constant lift nonlinear processes and are almost never test; constant collective mode and constant lift repeated. Indeed, droplet distribution and mode. In the constant collective mode, the repeated. Indeed, droplet distribution and mode. In the constant collective mode, the concentration can vary widely under the same collective pitch of the rotor was set at the concentration can vary widely under the same collective pitch of the rotor was set at the initial conditions. A major advantage of a beginning of the icing spray and held constant initial conditions. A major advantage of a beginning of the icing spray and held constant facility such as the IRT is that cloud conditions during the icing event. While the rotor was iced facility such as the IRT is that cloud conditions during the icing event. While the rotor was iced within the test section can be controlled with a up and the rotor lift degraded, the pilot within the test section can be controlled with a up and the rotor lift degraded, the pilot reasonable repeatability. maintained a trimmed. flying condition but made reasonable repeatability. maintained a trimmed. flying condition but made Figure 6 shows good repeatability for a no effort to keep lift constant. In the constant Figure 6 shows good repeatability for a no effort to keep lift constant. In the constant constant collective condition which was lift mode, the collective pitch of the rotor was constant collective condition which was lift mode, the collective pitch of the rotor was repeated three times. Repeatability was also increased automatically during the icing spray repeated three times. Repeatability was also increased automatically during the icing spray very good for the constant lift condition, as to maintain a constant lift throughout the icing very good for the constant lift condition, as to maintain a constant lift throughout the icing shown in Figure 7. Figure 8 shows a event. Figure 9 shows a torque rise comparison shown in Figure 7. Figure 8 shows a event. Figure 9 shows a torque rise comparison comparison of ice shape tracings taken at the between two runs in which the only difference comparison of ice shape tracings taken at the between two runs in which the only difference same radial location for a repeat condition. It is the lift control mode of the rotor. It can be same radial location for a repeat condition. It is the lift control mode of the rotor. It can be can be seen that the ice shape was repeated seen that the constant lift mode has a higher can be seen that the ice shape was repeated seen that the constant lift mode has a higher reasonably well, with some minor differences. torque rise for the same condition than the reasonably well, with some minor differences. torque rise for the same condition than the Part of the scatter was due to the ice tracing constant collective mode because of the Part of the scatter was due to the ice tracing constant collective mode because of the procedure employed. In general, it is felt that collective pitch being increased.. procedure employed. In general, it is felt that collective pitch being increased..

the repeatability of the test was very good. the repeatability of the test was very good.

Temperature Temperature Trends Trends One of the main areas of concern for One of the main areas of concern for Icing is a function of many variables, this test was that of temperature effects, Icing is a function of many variables, this test was that of temperature effects, such as LWC, MVD, temperature, velocity, etc. particularly near freezing. Tests at various such as LWC, MVD, temperature, velocity, etc. particularly near freezing. Tests at various The performance of helicopter rotors are also temperatures were performed for both the The performance of helicopter rotors are also temperatures were performed for both the dependent on many factors. Thus, a rigorous constant lift and constant collective control dependent on many factors. Thus, a rigorous constant lift and constant collective control test of the effects of icing on the performance modes. Figure 10 shows the torque rise as a test of the effects of icing on the performance modes. Figure 10 shows the torque rise as a of a helicopter main rotor requires the isolation function of icing time for a temperature range of a helicopter main rotor requires the isolation function of icing time for a temperature range of many different parameters. For this test, the of -25°C to -12 °C with the rotor in the of many different parameters. For this test, the of -25°C to -12 °C with the rotor in the main parameters of interest were: constant collective mode. It can be seen that the main parameters of interest were: constant collective mode. It can be seen that the torque rise increases as temperature increases. torque rise increases as temperature increases.

1) Temperature This is because as the temperature increases, the 1) Temperature This is because as the temperature increases, the 2) LWC accreted ice shape on the outer portion of the 2) LWC accreted ice shape on the outer portion of the 3) MVD rotor blades changes from rime to glaze, 3) MVD rotor blades changes from rime to glaze, 6 6 increasing the performance penalties. This is seconds of icing it can be seen that the slope of increasing the performance penalties. This is seconds of icing it can be seen that the slope of the torque rise was greater for the higher the torque rise was greater for the higher supported by Figure 11. Here, the type of ice at supported by Figure 11. Here, the type of ice at various radial locations has been plotted as a LWCs, as would be expected. This plot also various radial locations has been plotted as a LWCs, as would be expected. This plot also function of temperature. The transition location illustrates just how strongly ice shedding from function of temperature. The transition location illustrates just how strongly ice shedding from from rime to glaze along the outer portion of the rotor can dominate the torque rise. After from rime to glaze along the outer portion of the rotor can dominate the torque rise. After the blade moved inboard as temperature about 40 seconds of icing, shedding effects the blade moved inboard as temperature about 40 seconds of icing, shedding effects increases. This is further illustrated in Figure began to come into play. The highest LWC increases. This is further illustrated in Figure began to come into play. The highest LWC 3) 3) 12, which shows ice tracings taken at a (1.5 glm shed fIrst, at about 40 seconds. The 12, which shows ice tracings taken at a (1.5 glm shed fIrst, at about 40 seconds. The 3) 3) spanwise extent of 90% for two different next highestLWe (1.25 glm began to shed at spanwise extent of 90% for two different next highestLWe (1.25 glm began to shed at temperatures. The -25 °e tracing was clearly a about 50 seconds. Finally, the lowest LWC temperatures. The -25 °e tracing was clearly a about 50 seconds. Finally, the lowest LWC 3) 3) rime shape while the -12 °e tracing was glaze. (1.0 glm did not begin to shed until about 65 rime shape while the -12 °e tracing was glaze. (1.0 glm did not begin to shed until about 65 So, for this temperature range the torque rise seconds. The lowest L we actually had the So, for this temperature range the torque rise seconds. The lowest L we actually had the was mainly a function of transition location. highest torque rise for part of the icing was mainly a function of transition location. highest torque rise for part of the icing encounter, because of the effects of shedding. encounter, because of the effects of shedding.

Figure 13 shows the torque rise as a Figure 13 shows the torque rise as a function of time for a temperature ranging from A similar trend is shown in Figure 17 , which function of time for a temperature ranging from A similar trend is shown in Figure 17 , which -12°C to -2°C with the rotor in constant shows the effect of L WC for the constant lift -12°C to -2°C with the rotor in constant shows the effect of L WC for the constant lift collective mode. For this temperature range it mode of operation. Here again, the slope of the collective mode. For this temperature range it mode of operation. Here again, the slope of the can be seen that the torque rise decreases as torque rise increased with L WC. In this case, can be seen that the torque rise decreases as torque rise increased with L WC. In this case, 3) 3) temperature increased, the opposite of Figure the two highest L WCs (1.25 and 1.5 glm temperature increased, the opposite of Figure the two highest L WCs (1.25 and 1.5 glm 10. The torque rise decreased because, in this showed approximately the same rate of torque 10. The torque rise decreased because, in this showed approximately the same rate of torque temperature range, the radial extent of icing rise. Shedding effects began to occur at about temperature range, the radial extent of icing rise. Shedding effects began to occur at about decreased as the temperature approached that 35 seconds of icing, slightly earlier than in the decreased as the temperature approached that 35 seconds of icing, slightly earlier than in the of freezing. Less ice was accreting on the rotor, constant collective case. Again, because of the of freezing. Less ice was accreting on the rotor, constant collective case. Again, because of the reducing the performance penalties. This is delayed shedding, the case with a L WC of 1.0 reducing the performance penalties. This is delayed shedding, the case with a L WC of 1.0 3 3 shown in Figure 11 where the spanwise extent glm actually showed higher torque rise late in shown in Figure 11 where the spanwise extent glm actually showed higher torque rise late in of ice decreases from 96% to 35% as the the run than that of the higher L WC cases. The of ice decreases from 96% to 35% as the the run than that of the higher L WC cases. The 3 3 temperature increased from -12°C to -2°C. slope of the 0.75 glm case was low enough temperature increased from -12°C to -2°C. slope of the 0.75 glm case was low enough So, for this temperature range the torque rise that its torque rise stayed below that of the So, for this temperature range the torque rise that its torque rise stayed below that of the higher LWC cases, even though it did not shed higher LWC cases, even though it did not shed was mainly a function of icing radial extent. was mainly a function of icing radial extent.

until very late in the encounter (about 75 sec). until very late in the encounter (about 75 sec).

Figures 10 and 13 indicate that, for this test Figures 10 and 13 indicate that, for this test configuration the "worst" case temperature in configuration the "worst" case temperature in Main Rotor Lift Main Rotor Lift terms of torque rise was -12°C. This terms of torque rise was -12°C. This corresponds to the 1989 PFM test which corresponds to the 1989 PFM test which All results for main rotor lift have been All results for main rotor lift have been indicated a "worst" case temperature of indicated a "worst" case temperature of between -15°C and -10 0C. Temperature between -15°C and -10 0C. Temperature non-dimensionalized into the term Cva where, non-dimensionalized into the term Cva where, trending was also done for the constant lift trending was also done for the constant lift mode with similar results to those shown for mode with similar results to those shown for the constant collective case. These results are the constant collective case. These results are shown in Figures 14 and 15. shown in Figures 14 and 15.

and and Liquid Water Content be Liquid Water Content be G=- G=- rcR rcR Another major parameter driving the Another major parameter driving the icing process is LWe. For the case where the icing process is LWe. For the case where the Figure 18 shows the torque rise as a function of Figure 18 shows the torque rise as a function of rotor speed is constant in the absence of rotor speed is constant in the absence of icing time for various rotor lift co nditions icing time for various rotor lift co nditions shedding, the general trend is the higher the shedding, the general trend is the higher the L WC, the higher the accretion rate and L WC, the higher the accretion rate and (Cria) in the constant collective mode. It can (Cria) in the constant collective mode. It can associated performance penalties. Figure 16 associated performance penalties. Figure 16 be seen that there was a slight trend of higher be seen that there was a slight trend of higher shows a plot of torque rise as a function of shows a plot of torque rise as a function of torque rise for higher Cva . This is an angle of torque rise for higher Cva . This is an angle of icing time for various LWCs for the rotor in the icing time for various LWCs for the rotor in the attack effect. The higher lifts were obtained by attack effect. The higher lifts were obtained by constant collective mode. In the first 40 constant collective mode. In the first 40 7 7 increasing the collective pitch of the rotor. The analysis to ice accretion only. The second increasing the collective pitch of the rotor. The analysis to ice accretion only. The second power increment is greater for higher angles of regime exists after the onset of rotor shedding. power increment is greater for higher angles of regime exists after the onset of rotor shedding.

attack. Figure 19 shows the same trend for the Shedding is a somewhat random phenomena attack. Figure 19 shows the same trend for the Shedding is a somewhat random phenomena constant lift mode. The effect seems slightly making correlation in this regime difficult constant lift mode. The effect seems slightly making correlation in this regime difficult more pronounced than in the constant collective The correlation predicts (among other more pronounced than in the constant collective The correlation predicts (among other mode. This is because the collective pitch (and mode. This is because the collective pitch (and things) incremental rotor lift (~CrJa) and things) incremental rotor lift (~CrJa) and hence, local angle of attack) increases during hence, local angle of attack) increases during incremental rotor torque (~Qia). Depending incremental rotor torque (~Qia). Depending the icing event in the constant lift mode. the icing event in the constant lift mode.

on the lift control mode the collective pitch was on the lift control mode the collective pitch was Droplet Size either held constant at the predicted clean rotor Droplet Size either held constant at the predicted clean rotor trim solution (constant collective) or allowed to trim solution (constant collective) or allowed to Droplet size affects the icing process in increase so that lift remained constant at the Droplet size affects the icing process in increase so that lift remained constant at the that larger droplets will tend to impinge further predicted clean rotor trim solution (constant that larger droplets will tend to impinge further predicted clean rotor trim solution (constant back on the airfoil, and thus cause more severe lift). The build-up in L WC that occurred back on the airfoil, and thus cause more severe lift). The build-up in L WC that occurred performance penalties. This trend is born out during the start of the icing encounter (Figure performance penalties. This trend is born out during the start of the icing encounter (Figure in Figure 20. Here, the torque rise is shown to 5) has been ignored. in Figure 20. Here, the torque rise is shown to 5) has been ignored.

be higher for the larger droplet size. Figure 21 Figure 23 shows a comparison between be higher for the larger droplet size. Figure 21 Figure 23 shows a comparison between shows ice tracings taken at rJR = 40% for an the experimental and predicted torque rise for shows ice tracings taken at rJR = 40% for an the experimental and predicted torque rise for MVD of 15 and 20 Il m. It can be seen the constant collective nominal condition. It can MVD of 15 and 20 Il m. It can be seen the constant collective nominal condition. It can (particularly on the upper surface) that the be seen that the comparison is excellent early in (particularly on the upper surface) that the be seen that the comparison is excellent early in impingement limits were further back for the 20 the icing encounter «40 sec). As the onset of impingement limits were further back for the 20 the icing encounter «40 sec). As the onset of Ilm case. It was difficult to draw any shedding begins (>40 sec), the correlation Ilm case. It was difficult to draw any shedding begins (>40 sec), the correlation conclusions about the lower impingement slightly overpredicts the torque rise. Figures 24 conclusions about the lower impingement slightly overpredicts the torque rise. Figures 24 limits. The tracings often had arbitrary and 25 compare the predicted temperature limits. The tracings often had arbitrary and 25 compare the predicted temperature stopping points here because frost formations trending to the experiment. The current stopping points here because frost formations trending to the experiment. The current on the lower surface often masked a well correlation slightly overpredicts the warm on the lower surface often masked a well correlation slightly overpredicts the warm defined ending to the ice shape. Figure 22 temperature cases at an icing time of 20 defined ending to the ice shape. Figure 22 temperature cases at an icing time of 20 shows the ice tracings taken for the same two seconds. The correlation is in good agreement shows the ice tracings taken for the same two seconds. The correlation is in good agreement runs at the 70% radial location. Here it can at 40 seconds, but is optimistic at higher icing runs at the 70% radial location. Here it can at 40 seconds, but is optimistic at higher icing been seen that the glaze horn angle was further times. It is possible that the overprediction at been seen that the glaze horn angle was further times. It is possible that the overprediction at back for the higher droplet size. In a similar 20 seconds is partly due to the fact that the back for the higher droplet size. In a similar 20 seconds is partly due to the fact that the fashion, the secondary feather formation was LWC rise time is ignored in the correlation. At fashion, the secondary feather formation was LWC rise time is ignored in the correlation. At further back for the higher droplet size. the colder temperatures, the correlation further back for the higher droplet size. the colder temperatures, the correlation underpredicts slightly at 20 seconds and is underpredicts slightly at 20 seconds and is Comparison With Predictions conservative at 40 seconds. Comparison With Predictions conservative at 40 seconds.

Theoretical models can be used to Summary and Conclusions Theoretical models can be used to Summary and Conclusions predict accretion, shedding, and rotor predict accretion, shedding, and rotor To date, the examination of the data To date, the examination of the data performance. This paper will present a few performance. This paper will present a few representative results in the area of rotor from this test has proven encouraging. representative results in the area of rotor from this test has proven encouraging.

performance prediction. The Sikorsky Aircraft Preliminary assessments indicate that the performance prediction. The Sikorsky Aircraft Preliminary assessments indicate that the Generalized Rotor Performance (GRP) code quality of the data is excellent. The changes in Generalized Rotor Performance (GRP) code quality of the data is excellent. The changes in was used to compute the rotor performance. An torque were very repeatable for both control was used to compute the rotor performance. An torque were very repeatable for both control icing subroutine linked to GRP was used to modes (constant lift and constant collective). icing subroutine linked to GRP was used to modes (constant lift and constant collective).

predict the changes in the rotor performance All of the trending effects of variables such as predict the changes in the rotor performance All of the trending effects of variables such as due to icing. This subroutine makes use of a due to icing. This subroutine makes use of a temperature, LWC, MVD, and CrJa behaved as temperature, LWC, MVD, and CrJa behaved as rotorcraft icing prediction method based on rotorcraft icing prediction method based on expected. Comparison of test results were expected. Comparison of test results were correlation studies as described in Reference 4. correlation studies as described in Reference 4.

made with the Sikorsky Generalized Rotor made with the Sikorsky Generalized Rotor The method can be broken down into two The method can be broken down into two Performance (GRP) code. Good agreement Performance (GRP) code. Good agreement regimes. The first regime exists prior to the regimes. The first regime exists prior to the was generally seen between the experimental was generally seen between the experimental onset of rotor shedding, thus limiting the onset of rotor shedding, thus limiting the 8 8 data and the predictions. data and the predictions.

In the near term the goal is to complete In the near term the goal is to complete a detailed analysis of the whole data set. In a detailed analysis of the whole data set. In depth correlation studies are to be performed in depth correlation studies are to be performed in order to improve the current prediction order to improve the current prediction capabilities. Molds taken during the test will be capabilities. Molds taken during the test will be used to make castings for simulated ice used to make castings for simulated ice experiments in a dry air wind tunnel. These experiments in a dry air wind tunnel. These experiments will involve detailed performance experiments will involve detailed performance mapping of a select few ice shapes in order to mapping of a select few ice shapes in order to determine the fidelity of the simulated icing test determine the fidelity of the simulated icing test method. method.

Long term goals include a coordinated Long term goals include a coordinated program involving further model icing tests in program involving further model icing tests in conjunction with a full-scale rotorcraft icing conjunction with a full-scale rotorcraft icing flight test. This follows a logical progression flight test. This follows a logical progression for development and verification of the model for development and verification of the model rotor test techniques and analytical methods. rotor test techniques and analytical methods.

References References 1 Flemming, R.J., Bond, T.R., and 1 Flemming, R.J., Bond, T.R., and Britton, R.K., "Results of a Sub-Scale Model Britton, R.K., "Results of a Sub-Scale Model Rotor Icing Test," AIAA Paper 91-0660 (Also Rotor Icing Test," AIAA Paper 91-0660 (Also NASA 1M 103709), January 1991. NASA 1M 103709), January 1991.

2 Flemming, R.J. and Saccullo, A., 2 Flemming, R.J. and Saccullo, A., "Tests of a Model Main Rotor in the NASA "Tests of a Model Main Rotor in the NASA Lewis Research Center Icing Research Lewis Research Center Icing Research Tunnel," NASA CR 189071 (Also SER- Tunnel," NASA CR 189071 (Also SER- 510354), December 1991. 510354), December 1991.

3 Britton, R.K. and Bond, T.R., "A 3 Britton, R.K. and Bond, T.R., "A Review of Ice Accretion Data From a Model Review of Ice Accretion Data From a Model Rotor Icing Test and Comparison With Rotor Icing Test and Comparison With Theory," AIAA Paper 91-0661 (Also NASA Theory," AIAA Paper 91-0661 (Also NASA 1M 103712), January 1991. 1M 103712), January 1991.

4 Flemming, R.J. and Lednicer 4 Flemming, R.J. and Lednicer D.A., "High Speed Ice Accretion on Rotorcraft D.A., "High Speed Ice Accretion on Rotorcraft Airfoils," NASA CR 3910, August 1985. Airfoils," NASA CR 3910, August 1985.

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0.00 0.00 -35 -30 -25 -20 -15 -10 -5 0 5 -35 -30 -25 -20 -15 -10 -5 0 5 Temperature (Oe) Temperature (Oe) Figure 4. Icing test points for 1989 and 1993 tests. Figure 4. Icing test points for 1989 and 1993 tests.

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- - -T = -13°C .... - - -T = -13°C ....

... ~.- - . ... ~.- - .

••••••.•• T = -12°C ••••••.•• T = -12°C

. ...., ..-- . ...., ..--

..... ~ ..... ~

.... - .... -

_. ;.,- .. - - - ~ _. ;.,- .. - - - ~

.- .. - .- .. -

-7 ----- _" -7 ----- _"

.-........- ..... .-........- .....

~ --- --- ~ --- ---

..... - ..... - ..... - ..... -

--" .. - -- --" .. - --

",-~ ",-~ ., .,

o 20 40 60 80 100 o 20 40 60 80 100

Icing Time (sec) Icing Time (sec) Figure 10. Torque rise trend with "cold" temperatures (constant collective mode). Figure 10. Torque rise trend with "cold" temperatures (constant collective mode).

14 14 .--- ' - - -~--- - -- ' .' .. - . ---~-.- . . ------ ... - . ~ - .--- ' - - -~--- - -- ' .' .. - . ---~-.- . . ------ ... - . ~ - 1.00 1.00 .,-.. .,-..

0.80 0.80 ~ ~ I.. I..

'-" '-" c c 0.60 0.60 0 0 ::: :::

5 5

0 0 ~ ~ 0.40 0.40 ~ ~ "0 "0 eo:: eo:: ~ ~ 0.20 0.20 0.00 0.00

-30 -25 -20 -15 -10 -5 o 5 -30 -25 -20 -15 -10 -5 o 5

Static Temperature (OC) Static Temperature (OC) Figure 11. Experimental ice type and extent for anchor point conditions (constant Figure 11. Experimental ice type and extent for anchor point conditions (constant collective mode). collective mode).

-122C -122C

r/R = 0.90 r/R = 0.90

, ,

" "

Figure 12. Ice shape tracing comparison at 90% radial location (constant collective mode). Figure 12. Ice shape tracing comparison at 90% radial location (constant collective mode).

15 15

--_ .. _-_ .. - --_ .. _-_ .. -

'-- ----- ---- ----- ---_._ --- -- '-- ----- ---- ----- ---_._ --- -- --T=-12°C --T=-12°C - - -T = -10°C - - -T = -10°C - - .. - - T = -8°C - - .. - - T = -8°C - - -T = -6°C - - -T = -6°C •••••• -. T = -4°C •••••• -. T = -4°C ",' ",'

-----T = -2°C -----T = -2°C

".' ".'

~ ~ .,,_ __ .. a- .,,_ __ .. a- , ..... ' .. , ..... ' ..

,.- ,.-

.. - .. -

.. .,,- - ""... - ~ .. .,,- - ""... - ~

. ,- . ,-

---.--.-- ---.--.--

--- ---

o 20 40 60 80 100 o 20 40 60 80 100

Icing Time (sec) Icing Time (sec) Figure 13. Torque rise trend with ''warmer'' temperatures (constant collective mode). Figure 13. Torque rise trend with ''warmer'' temperatures (constant collective mode).

/ ... / ...

---T=-30 °C ---T=-30 °C

. \ . \

- - -T = -25°C - - -T = -25°C • • /. ".. /. "..

- - - - - T = -20°C - - - - - T = -20°C ----- T = -15°C ----- T = -15°C

~... - ~... -

., ,. , ., ,. ,

. -_.." . -_.."

- , - ,

_/- ,-,' _/- ,-,'

. , . ,

. ,.- . ,.-

-- --

/' , .. /' , ..

• - till" .-.._ ..... ~;... .... - • - till" .-.._ ..... ~;... .... -

. ,.- --- . ,.- ---

~," - ~," -

. ,. . ,.

o 10 20 30 40 50 60 70 80 o 10 20 30 40 50 60 70 80

Icing Time (sec) Icing Time (sec) Figure 14. Torque rise trend with "cold" temperatures (constant lift mode). Figure 14. Torque rise trend with "cold" temperatures (constant lift mode).

16 16

---- ...• _- -_ .... - .- --.- ~~-~- ---- ...• _- -_ .... - .- --.- ~~-~-

--T=-15°C --T=-15°C - - -T = -10°C - - -T = -10°C ----- T = -6°C ----- T = -6°C

-···-T = -2°C -···-T = -2°C

o 10 20 30 40 50 60 70 80 o 10 20 30 40 50 60 70 80

Icing Time (sec) Icing Time (sec) Fig ur e 15. Torqu e rise trend with "warmer" temperatures (constant lift mode). Fig ur e 15. Torqu e rise trend with "warmer" temperatures (constant lift mode).

. ~ . ~

, '. , , '. , • ", t' ", • ", t' ",

,.I ~'''.1 • ,.I ~'''.1 •

,. \·Yr~ ~ ..... ' "" ~ ,. \·Yr~ ~ ..... ' "" ~

, J,.' .,,, , J,.' .,,, " I " I '~ '~ " ,.--- ---------.. " ,.--- ---------..

, , A A

, -- LWC = 1.0 g/m 3 , -- LWC = 1.0 g/m 3

, , A A , , - - - LWC = 1.25 g/m 3 - - - LWC = 1.25 g/m 3 , , A A

----- LWC = 1.5 g/m 3 ----- LWC = 1.5 g/m 3

" "

o 20 40 6 0 80 1 00 o 20 40 6 0 80 1 00

Icing Time (sec) Icing Time (sec) Figure 16. Torque rise trend with L we (constant collective mode). Figure 16. Torque rise trend with L we (constant collective mode).

17 17 ------- ------ - ------------ ----~ - ------- ------ - ------------ ----~ - 1'-', 1'-', ~ • II -. ~ • II -.

,I , 'Il ~'.\, ,I , 'Il ~'.\,

, A.," "-"_1 , A.," "-"_1

• 10 c. "0 • 10 c. "0 .. , 0 .. .. , 0 ..

. ." . ."

~ ~

" I " I

.~I!- - .~I!- -

.. . . .. . .

• • • • .Y'/, .Y'/,

"1 "1

LWC = 0.75 g/m"3 LWC = 0.75 g/m"3

.~ .~

r r

- - - LWC = 1.0 gfm"3 - - - LWC = 1.0 gfm"3

-----LWC = 1.25 g/m"3 -----LWC = 1.25 g/m"3 11"'- ----. LWC = 1.5 gfm"3 11"'- ----. LWC = 1.5 gfm"3

o 20 40 60 80 100 o 20 40 60 80 100

Icing Time .(sec) Icing Time .(sec) Figure 17. Torque rise trend with LWC (constant lift mode ). Figure 17. Torque rise trend with LWC (constant lift mode ).

--CUSigma = 0.062 --CUSigma = 0.062

- - - CUSigma = 0.081 - - - CUSigma = 0.081

- - - - - CUSigma = 0.091 - - - - - CUSigma = 0.091

o 20 40 60 80 100 o 20 40 60 80 100

Icing Time (sec) Icing Time (sec) Figure 18. Torque rise trend with Clla (constant collective mode). Figure 18. Torque rise trend with Clla (constant collective mode).

18 18 ----- ~----------.--~ ----- ~----------.--~ --C USigma = 0.045 --C USigma = 0.045

- - • CUSigma = 0.066 - - • CUSigma = 0.066

-----C USigma = 0.081 -----C USigma = 0.081

_ •• •• CUSigma = 0.089 _ •• •• CUSigma = 0.089

o 20 40 60 80 100 o 20 40 60 80 100

Icing Time (sec) Icing Time (sec) Figure 1 9. Tor que rise trend with CrJa (constant lift mode). Figure 1 9. Tor que rise trend with CrJa (constant lift mode).

--- Condo 28, 15 microns --- Condo 28, 15 microns - - • Condo 28A, 20 microns - - • Condo 28A, 20 microns

o 20 40 60 80 100 120 o 20 40 60 80 100 120

Icing Time, sec Icing Time, sec Figure 20. To rq ue rise trend with MVD (constant lift mode). Figure 20. To rq ue rise trend with MVD (constant lift mode).

19 19

.MVD = 20 1.1 .MVD = 20 1.1

MVD = 15 1.1 MVD = 15 1.1

rlR = 0.40 rlR = 0.40

x/c x/c Figure 21. Comparison of ice shape tracings for radial location of 40% (constant lift Figure 21. Comparison of ice shape tracings for radial location of 40% (constant lift mode). mode).

MVD = 20 1.1 MVD = 20 1.1

~ ~

rlR = 0.70 rlR = 0.70

15 15 MVD= 1.1 MVD= 1.1 x/c x/c Figure 22 . Comparison of ice shape tracings for radial location of 70% (constant lift Figure 22 . Comparison of ice shape tracings for radial location of 70% (constant lift mode). mode).

20 20 - - - - -- -. -~ -~- - - - - -- -. -~ -~- - ------- - - ------- - --- Experiment --- Experiment o Prediction o Prediction o o o o 1st Shed 1st Shed

o 20 40 60 80 100 o 20 40 60 80 100

Icing Time (sec) Icing Time (sec) Figure 23. Comparison between experiment and theory for torque rise (constant collective Figure 23. Comparison between experiment and theory for torque rise (constant collective mode). mode).

Icing Time = 20 sec. Icing Time = 20 sec.

~ ~

= C" = C"

I- I- o o Eo- Eo- <l <l o Experiment o Experiment - - 9 - - Prediction - - 9 - - Prediction -30 -25 -20 - 15 -10 -5 0 -30 -25 -20 - 15 -10 -5 0 Static Temp er a ture (OC) Static Temp er a ture (OC) Figure 24. Comparison between experiment and theory for torque rise as a function of Figure 24. Comparison between experiment and theory for torque rise as a function of temperature for an icing time of 20 seconds (constant collective mode). temperature for an icing time of 20 seconds (constant collective mode).

21 21 Icing Time = 40 sec. Icing Time = 40 sec.

o Experiment o Experiment - -8 - - Prediction - -8 - - Prediction

-30 -25 -20 -15 -10 -5 o -30 -25 -20 -15 -10 -5 o

Static Temperature (OC) Static Temperature (OC) Figure 25. Comparison between experiment and theory for torque rise as a function of Figure 25. Comparison between experiment and theory for torque rise as a function of temperature for an icing time of 40 seconds (constant collective mode). temperature for an icing time of 40 seconds (constant collective mode).

22 22 Form Approved Form Approved REPORT DOCUMENTATION PAGE REPORT DOCUMENTATION PAGE OMB No. 0704-0188 OMB No. 0704-0188

I I

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1. A G ENCY USE ONLY (Lea ve blank) 3 REPORT TYPE AND DATES COVERED 1. A G ENCY USE ONLY (Lea ve blank) 3 REPORT TYPE AND DATES COVERED 12 . REPORT DATE 12 . REPORT DATE 1 . 1 .

J anuary 1994 Tec hn ical Memorand um J anuary 1994 Tec hn ical Memorand um 4. T IT LE AND SUBTITLE 5. FUNDING NUMBERS 4. T IT LE AND SUBTITLE 5. FUNDING NUMBERS An Overview of a Model Rotor Icing Test in the NASA Lewis An Overview of a Model Rotor Icing Test in the NASA Lewis Icing Research Tunnel Icing Research Tunnel WU-505-68-11 WU-505-68-11 A UTHOR (S) A UTHOR (S) 6. 6.

Randall K. Britton, Thomas H. Bond, and Robert J. Flemming Randall K. Britton, Thomas H. Bond, and Robert J. Flemming 7. P ERF ORM ING ORGANIZA TI ON NAME (S) A ND ADDRESS (ES) 7. P ERF ORM ING ORGANIZA TI ON NAME (S) A ND ADDRESS (ES) 8. PERFORMING ORGANIZATION 8. PERFORMING ORGANIZATION REPORT NUMBER REPORT NUMBER National Aeronautics and Space Administration National Aeronautics and Space Administration Lewis Research Center Lewis Research Center E-8340 E-8340 Cleveland, Ohio 44135-3191 Cleveland, Ohio 44135-3191 9. SP ONSOR I NGIMONITORING AGENCY NAME (S) AND ADDRESS(ES ) 10. SPONSORINGIMONITORING 9. SP ONSOR I NGIMONITORING AGENCY NAME (S) AND ADDRESS(ES ) 10. SPONSORINGIMONITORING AGENCY REPORT NUMBER AGENCY REPORT NUMBER National Aeronautics and Space Administration National Aeronautics and Space Administration NASA TM-I06471 NASA TM-I06471 Washington, D.C. 20546-0001 Washington, D.C. 20546-0001 AlAA-94-0716 AlAA-94-0716 11. S UPPLEM E NTARY NOT ES 11. S UPPLEM E NTARY NOT ES Prepared for the 32nd Aerospace Sciences Meeting and Exhibit, sponsored by the American Institute of Aeronautics and Astronautics, Reno, Nevada, Prepared for the 32nd Aerospace Sciences Meeting and Exhibit, sponsored by the American Institute of Aeronautics and Astronautics, Reno, Nevada, January 10-13, 1994. Randall K. Britton, Sverdrup Technology, In c., Lewis Research Center Group, 2001 Aerospace Parkway, Brook Park, Ohio January 10-13, 1994. Randall K. Britton, Sverdrup Technology, In c., Lewis Research Center Group, 2001 Aerospace Parkway, Brook Park, Ohio 44142 (work funded by ASA Contract AS3-25266 ); Thomas H. Bond, NASA Lewis Research Center; Robert J. Flemming, Sikorsky Aircraft 44142 (work funded by ASA Contract AS3-25266 ); Thomas H. Bond, NASA Lewis Research Center; Robert J. Flemming, Sikorsky Aircraft Division. U Te. Stratford . Connecticut. Re~onsible pe!Son . Randall K. Britton. qrganization code 2720. (2 16 ) 433-1064. Division. U Te. Stratford . Connecticut. Re~onsible pe!Son . Randall K. Britton. qrganization code 2720. (2 16 ) 433-1064.

12 a. D ISTRIB UTI ON/AVAILAB ILITY STATEMENT 1 2b. DISTRIBU T ION CODE 12 a. D ISTRIB UTI ON/AVAILAB ILITY STATEMENT 1 2b. DISTRIBU T ION CODE Unclassified - Unlimited Unclassified - Unlimited Subject Category 02 Subject Category 02 13. ABSTRAC T (Maximum 200 words ) 13. ABSTRAC T (Maximum 200 words ) During two entries in late 1989, a heavily instrumented sub-scale model of a helocopter main rotor was tested in the During two entries in late 1989, a heavily instrumented sub-scale model of a helocopter main rotor was tested in the NASA Lewis Research Center (LeRC) Icing Research Tunnel (IRT). The resul ts of this series of tunnel tests have NASA Lewis Research Center (LeRC) Icing Research Tunnel (IRT). The resul ts of this series of tunnel tests have been published previously. After studying the results from the 1989 test and comparing them to predictions, it been published previously. After studying the results from the 1989 test and comparing them to predictions, it became clear that certain test conditions still needed investigation. Therefore, a re-entry of the Sikorsky Aircraft became clear that certain test conditions still needed investigation. Therefore, a re-entry of the Sikorsky Aircraft Powered Force Model (PFM) in the IRT was instituted in order to expand upon the current rotorcraft sub-scale model Powered Force Model (PFM) in the IRT was instituted in order to expand upon the current rotorcraft sub-scale model experimental database. The major areas of interest included expansion of the test matrix to include a larger number of experimental database. The major areas of interest included expansion of the test matrix to include a larger number of points in the FAA AC 29-2 icing envelope, inclusion of a number of high power rotor performance points, close points in the FAA AC 29-2 icing envelope, inclusion of a number of high power rotor performance points, close examination of warm temperature operations, operation of the model in constant lift mode, and testing for conditions examination of warm temperature operations, operation of the model in constant lift mode, and testing for conditions for icing test points in the full scale helicopter database. The expanded database will allow further and more detailed for icing test points in the full scale helicopter database. The expanded database will allow further and more detailed examination and comparison with analytical models. Participants in the test were NASA LeRC, the U.S. Army examination and comparison with analytical models. Participants in the test were NASA LeRC, the U.S. Army Vehicle Propulsion Directorate based at LeRC, and Sikorsky Aircraft. The model rotor was exposed to a range of Vehicle Propulsion Directorate based at LeRC, and Sikorsky Aircraft. The model rotor was exposed to a range of icing conditions (temperature, liq uid water content, median droplet diameter) and was operated over ranges of shaft icing conditions (temperature, liq uid water content, median droplet diameter) and was operated over ranges of shaft angle, rotor tip speed, advance ratio, and rotor lift. The data taken included blade strain gage and balance data, as angle, rotor tip speed, advance ratio, and rotor lift. The data taken included blade strain gage and balance data, as we ll as still photography, video, ice profile tracings, and ice molds. A discussion of the details of the test is given we ll as still photography, video, ice profile tracings, and ice molds. A discussion of the details of the test is given herein. Also, a brief examination of a subset of the data taken is also given. herein. Also, a brief examination of a subset of the data taken is also given.

15 . NUMBER OF PAGES 15 . NUMBER OF PAGES 1 4. SU BJECT T ERMS 1 4. SU BJECT T ERMS 24 24 16 . PRICE CODE 16 . PRICE CODE Icing; Model rotor testing; Icing Research tunnel Icing; Model rotor testing; Icing Research tunnel A03 A03 SE CURITY CLASSIFICATION 18. SECURITY CLASSIFICA TION 19 . SECURITY CLASSIFICATION 20 . LI MIT ATION OF ABSTRACT SE CURITY CLASSIFICATION 18. SECURITY CLASSIFICA TION 19 . SECURITY CLASSIFICATION 20 . LI MIT ATION OF ABSTRACT 17. 17.

OF REPORT OF TH IS PAGE OF ABSTRACT OF REPORT OF TH IS PAGE OF ABSTRACT Unclassified Unclassified Unclassified Unclassified Unclassified Unclassified S tandard Form 2 98 (R e v . 2-89) S tandard Form 2 98 (R e v . 2-89) NSN 7540-01 -280-55 00 NSN 7540-01 -280-55 00 Prescribed by ANSI Std . Z39-18 Prescribed by ANSI Std . Z39-18 298-102 298-102