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  1. AERODYNAMIC ASSESSMENT OF FLIGHT-DETERMINED SUBSONIC LIFT AND DRAG CHARACTERISTICS OF SEVEN LIFTING-BODY AND WING-BODY REENTRY VEHICLE CONFIGURATIONS , Technical Publication
    Authors: Edwin J. Saltzman , K. Charles Wang and Kenneth W. Iliff
    Report Number: NASA-TP-2002-209032
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: This report examines subsonic flight–measured lift and drag characteristics of seven lifting-body and wing-body reentry vehicle configurations with truncated bases. The seven vehicles are the full-scale M2-F1, M2-F2, HL-10, X-24A, X-24B, and X-15 vehicles and the Space Shuttle Enterprise. Subsonic flight lift and drag data of the various vehicles are assembled under aerodynamic performance parameters and presented in several analytical and graphical formats. These formats are intended to unify the data and allow a greater understanding than individually studying the vehicles allows. Lift-curve slope data are studied with respect to aspect ratio and related to generic wind-tunnel model data and to theory for low-aspect-ratio planforms. The definition of reference area is critical for understanding and comparing the lift data. The drag components studied include minimum drag coefficient, lift-related drag, maximum lift-to-drag ratio, and, where available, base pressure coefficients. The influence of forebody drag on afterbody and base drag at low lift is shown to be related to Hoerner’s compilation for body, airfoil, nacelle, and canopy drag. This feature may result in a reduced need of surface smoothness for vehicles with a large ratio of base area to wetted area. These analyses are intended to provide a useful analytical framework with which to compare and evaluate new vehicle configurations of the same generic family.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 02, 15
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    Report Date: November 2002
    No. Pages: 156
    Funding Organization: 529-50-04-00-RR-00-000
    Keywords:      Aerodynamics; Lifting bodies; Reentry vehicles; Reusable launch vehicles


  2. STABILITY AND CONTROL ESTIMATION FLIGHT TEST RESULTS FOR THE SR-71 AIRCRAFT WITH EXTERNALLY MOUNTED EXPERIMENTS , Technical Publication
    Authors: Timothy R. Moes and Kenneth Iliff
    Report Number: NASA-TP-2002-210718
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: A maximum-likelihood output-error parameter estimation technique is used to obtain stability and control derivatives for the NASA Dryden Flight Research Center SR-71A airplane and for configurations that include experiments externally mounted to the top of the fuselage. This research is being done as part of the envelope clearance for the new experiment configurations. Flight data are obtained at speeds ranging from Mach 0.4 to Mach 3.0, with an extensive amount of test points at approximately Mach 1.0. Pilot-input pitch and yaw-roll doublets are used to obtain the data. This report defines the parameter estimation technique used, presents stability and control derivative results, and compares the derivatives for the three configurations tested. The experimental configurations studied generally show acceptable stability, control, trim, and handling qualities throughout the Mach regimes tested. The reduction of directional stability for the experimental configurations is the most significant aerodynamic effect measured and identified as a design constraint for future experimental configurations. This report also shows the significant effects of aircraft flexibility on the stability and control derivatives.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 08
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    Report Date: June 2002
    No. Pages: 93
    Funding Organization: 710-35-14-E8-OM-00-844
    Keywords:      Control derivatives; Maximum likelihood estimates; Parameter identification; SR-71; Stability derivatives


  3. IN-FLIGHT VIBRATION ENVIRONMENT OF THE NASA F-15B FLIGHT TEST FIXTURE , Technical Memorandum
    Authors: Stephen Corda, Russell J. Franz, James N. Blanton, M. Jake Vachon and James B. DeBoer
    Report Number: NASA-TM-2002-210719
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: Flight vibration data are analyzed for the NASA F-15B/Flight Test Fixture II test bed. Understanding the in-flight vibration environment benefits design and integration of experiments on the test bed. The power spectral density (PSD) of accelerometer flight data is analyzed to quantify the in-flight vibration environment from a frequency of 15 Hz to 1325 Hz. These accelerometer data are analyzed for typical flight conditions and maneuvers. The vibration data are compared to flight-qualification random vibration test standards. The PSD levels in the lateral axis generally are greater than in the longitudinal and vertical axes and decrease with increasing frequency. At frequencies less than approximately 40 Hz, the highest PSD levels occur during takeoff and landing. Peaks in the PSD data for the test fixture occur at approximately 65, 85, 105-110, 200, 500, and 1000 Hz. The pitch-pulse and 2-g turn maneuvers produce PSD peaks at 115 Hz. For cruise conditions, the PSD level of the 85-Hz peak is greatest for transonic flight at Mach 0.9. From 400 Hz to 1325 Hz, the takeoff phase has the highest random vibration levels. The flight-measured vibration levels generally are substantially lower than the random vibration test curve.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 05
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    Report Date: February 2002
    No. Pages: 27
    Funding Organization: 710-35-14-M1-00-38-00-S-000
    Keywords:      F-15B flight test fixture; Flight test; Power spectral density; Random vibration;Vibration flight data


  4. GROUND AND FLIGHT EVALUATION OF A SMALL-SCALE INFLATABLE-WINGED AIRCRAFT , Presented at the 40th AIAA Aerospace Sciences Meeting & Exhibit, 14-17 January 2002, Reno, Nevada.
    Authors: James E. Murray, Joseph W. Pahle, Stephen V. Thornton, Shannon Vogus, Tony Frackowiak, Joe Mello, Brook Norton
    Report Number: NASA-TM-2002-210721
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: A small-scale, instrumented research aircraft was flown to investigate the flight characteristics of inflatable wings. Ground tests measured the static structural characteristics of the wing at different inflation pressures, and these results compared favorably with analytical predictions. A research-quality instrumentation system was assembled, largely from commercial off-the-shelf components, and installed in the aircraft. Initial flight operations were conducted with a conventional rigid wing having the same dimensions as the inflatable wing. Subsequent flights were conducted with the inflatable wing. Research maneuvers were executed to identify the trim, aerodynamic performance, and longitudinal stability and control characteristics of the vehicle in its different wing configurations. For the angle-of-attack range spanned in this flight program, measured flight data demonstrated that the rigid wing was an effective simulator of the lift-generating capability of the inflatable wing. In-flight inflation of the wing was demonstrated in three flight operations, and measured flight data illustrated the dynamic characteristics during wing inflation and transition to controlled lifting flight. Wing inflation was rapid and the vehicle dynamics during inflation and transition were benign. The resulting angles of attack and of sideslip were small, and the dynamic response was limited to roll and heave motions.
    Distribution/Availability: Unclassified - Unlimited
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    Report Date: January 2002
    No. Pages: 24
    Funding Organization: 274-00-00E8-RR-00-DDF
    Keywords:      Research aircraft; Inflatable gliders; Aircraft performance; Inflatable structures; Structural analysis


  5. WING TORSIONAL STIFFNESS TESTS OF THE ACTIVE AEROELASTIC WING F/A-18 AIRPLANE , Technical Memorandum
    Authors: William A. Lokos, Candida D. Olney, Natalie D. Crawford, Rick Stauf and Eric Y. Reichenbach
    Report Number: NASA-TM-2002-210723
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: The left wing of the Active Aeroelastic Wing (AAW) F/A-18 airplane has been ground-load-tested to quantify its torsional stiffness. The test has been performed at the NASA Dryden Flight Research Center in November 1996, and again in April 2001 after a wing skin modification was performed. The primary objectives of these tests were to characterize the wing behavior before the first flight, and provide a before-and-after measurement of the torsional stiffness. Two streamwise load couples have been applied. The wing skin modification is shown to have more torsional flexibility than the original configuration has. Additionally, structural hysteresis is shown to be reduced by the skin modification. Data comparisons show good repeatability between the tests.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 05
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    Report Date: May 2002
    No. Pages: 11
    Funding Organization: 706-35-00-E8-14-00-AAW
    Keywords:      Ground load testing; Wing deflection measurement; Wing elastic twist; Wing flexibility; Wing torsional stiffness
    Notes: Presented at the 43rd AIAA/ASME/ASCE/AHS Structures, Structural Dynamics and Materials Conference, Denver, Colorado, April 2002. AIAA-2002-1333.


  6. GROUND AND FLIGHT TEST STRUCTURAL EXCITATION USING PIEZOELECTRIC ACTUATORS , Technical Memorandum
    Authors: David F. Voracek, Mercedes Reaves, Lucas G. Horta and Starr Potter
    Report Number: NASA-TM-2002-210724
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: A flight flutter experiment at the National Aeronautics and Space Administration (NASA) Dryden Flight Research Center, Edwards, California, used an 18-inch half- span composite model called the Aerostructures Test Wing (ATW). The ATW was mounted on a centerline flight test fixture on the NASA F-15B and used distributed piezoelectric strain actuators for in-flight structural excitation. The main focus of this paper is to investigate the performance of the piezoelectric actuators and test their ability to excite the first-bending and first-torsion modes of the ATW on the ground and in-flight. On the ground, wing response resulting from piezoelectric and impact excitation was recorded and compared. The comparison shows less than a 1- percent difference in modal frequency and a 3-percent increase in damping. A comparison of in-flight response resulting from piezoelectric excitation and atmospheric turbulence shows that the piezoelectric excitation consistently created an increased response in the wing throughout the flight envelope tested. The data also showed that to obtain a good correlation between the piezoelectric input and the wing accelerometer response, the input had to be nearly 3.5 times greater than the turbulence excitation on the wing.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 02
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    Report Date: April 2002
    No. Pages: 15
    Funding Organization: 036-00-00-E8-RR-00P-DDF
    Keywords:      Actuators; Flight test; Flutter; Piezoelectrics; Structural excitation
    Notes: Also presented at the 43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, April 22-25, 2002, Denver Colorado. AIAA-2002-1349


  7. STRAIN GAGE LOADS CALIBRATION TESTING OF THE ACITVE AEROELASTIC WING F/A-18 AIRCRAFT , Also presented at the 22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference, St. Louis, Missouri June 24-27, 2002.
    Authors: William A. Lokos, Candida D. Olney, Tony Chen, Natalie D. Crawford, Rick Stauf, Eric Reichenbach
    Report Number: NASA-TM-2002-210726
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Distribution/Availability: Unclassified - Unlimited
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    Report Date: June 2002
    No. Pages: 15
    Funding Organization: 706-35-00-E8-14-00-AAW
    Keywords:      Strain gage calibration; loads testing; load equations; load measurement; load calibration


  8. METEOROLOGICAL SUPPORT OF THE HELIOS WORLD RECORD HIGH ALTITUDE FLIGHT TO 96,863 FEET , Presented at the 10th Conference on Aviation, Range, and Aerospace Meteorology, May 13-16, 2002, Portland, Oregon.
    Authors: Edward H. Teets Jr., Casey J. Donohue, Patrick T. Wright
    Report Number: NASA-TM-2002-210727
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: In characterizing and understanding atmospheric behavior when conducting high altitude solar powered flight research flight planning engineers and meteorologists are able to maximize the use of available airspace and coordinate aircraft maneuvers with pilots to make the best use of changing sun elevation angles. The result of this cooperative research produced a new world record for absolute altitude of a non-rocket powered aircraft of 96,863 ft (29,531.4 m). The Helios prototype solar powered aircraft, with a wingspan of 247 ft (75.0m), reached this altitude on August 13, 2001, off the coast of Kauai, Hawaii. The analyses of the weather characterization, the planning efforts, and the weather-of-the-day summary that led to at record flight are described in this paper.
    Distribution/Availability: Unclassified - Unlimited
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    Report Date: May 2002
    No. Pages: 20
    Funding Organization: 710-61-14-E8-PP-00-SMW
    Keywords:      Helios; climatology; aerodynamics; meteorology; ERAST


  9. COMPARISON OF RELATIVE NAVIGATION SOLUTIONS APPLIED BETWEEN TWO AIRCRAFT , Technical Memorandum
    Authors: Glenn Bever, Peter Urschel, Curtis E. Hanson
    Report Number: NASA-TM-2002-210728
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: Use of global positioning systems (GPS) for guidance and control functions is of increasing interest to the aviation industry. Many levels of solutions exist, from the relatively simple to highly complex integrated systems. This presentation examines three different GPS approaches to determining the relative separation between two aircraft. It presents flight test data showing the errors in each of the three approaches, tradeoffs in selecting from these three approaches, and the simplifying assumptions made for implementing applications that may reduce the requirements and therefore the cost of using them.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 04
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    Report Date: June 2002
    No. Pages: 27
    Funding Organization: WU 706 35 00 E8 28 00 AFF
    Keywords:      aircraft communication; relative aircraft navigation; flight test instrumentation; F/A-18; autonomous air navigation; global positioning system
    Notes: Presented at the AIAA 1st Technical Conference and Workshop on Unmanned Aerospace Vehicles, Systems, Technologies and Operations, May 20-23, 2002, Portsmouth, Virginia.


  10. AN OVERVIEW OF FLIGHT TEST RESULTS FOR A FORMATION FLIGHT AUTOPILOT , Technical Memorandum
    Authors: Curtis E. Hanson, Jack Ryan, Michael J. Allen, Steven R. Jacobson
    Report Number: NASA-TM-2002-210729
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: The first flight test phase of the NASA Dryden Flight Research Center Autonomous Formation Flight project has successfully demonstrated precision autonomous station-keeping of an F/A-18 research airplane with a second F/A-18 airplane. Blended inertial navigation system (INS) and global positioning system (GPS) measurements have been communicated across an air-to-air telemetry link and used to compute relative-position estimates. A precision research formation autopilot onboard the trailing airplane controls lateral and vertical spacing while the leading airplane operates under production autopilot control. Four research autopilot gain sets have been designed and flight-tested, and each exceeds the project design requirement of steady-state tracking accuracy within 1 standard deviation of 10 ft. Performance also has been demonstrated using single- and multiple-axis inputs such as step commands and frequency sweeps. This report briefly describes the experimental formation flight systems employed and discusses the navigation, guidance, and control algorithms that have been flight-tested. An overview of the flight test results of the formation autopilot during steady-state tracking and maneuvering flight is presented.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 08
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    Report Date: August 2002
    No. Pages: 17
    Funding Organization: WU 706 35 00 E8 28 00 AFF
    Keywords:      Formation autopilot; Formation flight; Station keeping
    Notes: Also presented at the AIAA Guidance, Navigation and Control, AIAA Atmospheric Flight Mechanics, AIAA Modeling and Simulation Technologies, and AIAA/AAS Astrodynamics Conferences, Monterey, California, AIAA-2002-4755


  11. FLIGHT TEST TECHNIQUES USED TO EVALUATE PERFORMANCE BENEFITS DURING FORMATION FLIGHT , Technical Publication
    Authors: Ronald J. Ray, Brent R. Cobleigh, M. Jake Vachon, Clinton St. John
    Report Number: NASA-TP-2002-210730
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: Previous investigations into formation flight have shown the possibility for significant fuel savings through drag reduction. Using two F/A-18 aircraft, NASA Dryden Flight Research Center has investigated flying aircraft in autonomous formation. Positioning the trailing airplane for best drag reduction requires investigation of the wingtip vortex effects induced by the leading airplane. A full accounting of the vortex effect on the trailing airplane is desired to validate vortex-effect prediction methods and provide a database for the design of a formation flight autopilot. A recent flight phase has mapped the complete wingtip vortex effects at two flight conditions with the trailing airplane at varying distances behind the leading one. Force and moment data at Mach 0.56 and an altitude of 25,000 ft and Mach 0.86 and an altitude of 36,000 ft have been obtained with 20, 55, 110, and 190 ft of longitudinal distance between the aircraft. The moments induced by the vortex on the trailing airplane were well within the pilot's ability to control. This report discusses the data analysis methods and vortex-induced effects on moments and side force. An assessment of the impact of the nonlinear vortex effects on the design of a formation autopilot is offered.
    Distribution/Availability: Unclassified - Unlimited
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    Report Date: August 2002
    No. Pages: 23
    Funding Organization: 706 35 00 E8 28 00 AFF
    Keywords:      Aircraft performance; drag reduction; drag measurement; performance tests; fuel consumption
    Notes: Also presented at the AIAA Atmospheric Flight Mechanics Conference and Exhibit, Monterey, CA, August 5-8, 2002.


  12. THE ROLE OF AIRCRAFT SIMULATION IN IMPROVING FLIGHT SAFETY THROUGH CONTROL TRAINING , Technical Memorandum
    Authors: Karla S. Shy, Jacob J. Hageman, Jeantette H. Le
    Report Number: NASA-TM-2002-210731
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: NASA Dryden Flight Research Center uses its six-degrees-of-freedom (6-DOF) fixed-base simulations for mission control room training to improve flight safety and operations. This concept is applied to numerous flight projects such as the F-18 High Alpha Research Vehicle (HARV), the F-15 Intelligent Flight Control System (IFCS), the X-38 Actuator Control Test (XACT), and X-43A (Hyper-X). The Dryden 6-DOF simulations are typically used through various stages of a project, from design to ground tests. The roles of these simulations have expanded to support control room training, reinforcing flight safety by building control room staff proficiency. Real-time telemetry, radar, and video data are generated from flight vehicle simulation models. These data are used to drive the control room displays. Nominal static values are used to complete information where appropriate. Audio communication is also an integral part of training sessions. This simulation capability is used to train control room personnel and flight crew for nominal missions and emergency situations. Such training sessions are also opportunities to refine flight cards and control room display pages, exercise emergency procedures, and practice control room setup for the day of flight. This paper describes this technology as it is used in the X-43A and F-15 IFCS and XACT projects.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 05
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    Report Date: August 2002
    No. Pages: 29
    Funding Organization: 706 51 54 T4 56 00 X43
    Keywords:      Computer programs; flight safety; flight training; integrated mission control center; simulation
    Notes: Also presented at the AIAA Modeling and Simlation Technologies conference at Monterey, CA, August 5-8, 2002


  13. INDUCED MOMENT EFFECTS OF FORMATION FLIGHT USING TWO F/A-18 AIRCRAFT , Technical Memorandum
    Authors: Jennifer L. Hansen Brent R. Cobleigh
    Report Number: NASA-TM-2002-210732
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: Previous investigations into formation flight have shown the possibility for significant fuel savings through drag reduction. Using two F/A-18 aircraft, NASA Dryden Flight Research Center has investigated flying aircraft in autonomous formation. Positioning the trailing airplane for best drag reduction requires investigation of the wingtip vortex effects induced by the leading airplane. A full accounting of the vortex effect on the trailing airplane is desired to validate vortex-effect prediction methods and provide a database for the design of a formation flight autopilot. A recent flight phase has mapped the complete wingtip vortex effects at two flight conditions with the trailing airplane at varying distances behind the leading one. Force and moment data at Mach 0.56 and an altitude of 25,000 ft and Mach 0.86 and an altitude of 36,000 ft have been obtained with 20, 55, 110, and 190 ft of longitudinal distance between the aircraft. The moments induced by the vortex on the trailing airplane were well within the pilot's ability to control. This report discusses the data analysis methods and vortex-induced effects on moments and side force. An assessment of the impact of the nonlinear vortex effects on the design of a formation autopilot is offered.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 02
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    Report Date: August 2002
    No. Pages: 22
    Funding Organization: 706 55 00 E8 28 00 AFF
    Keywords:      Formation; vortex; F-18; rolling; yawing
    Notes: Also presented at the AIAA Atmospheric Flight Mechanics Conference and Exhibit, Monterey, CA, August 5-8, 2002.


  14. STRING STABILITY OF A LINEAR FORMATION FLIGHT CONTROL SYSTEM , Technical Memorandum
    Authors: Michael J. Allen, Jack Ryan, James F. Parle, Curtis E. Hanson
    Report Number: NASA-TM-2002-210733
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: String stability analysis of an autonomous formation flight system was performed using linear and nonlinear simulations. String stability is a measure of how position errors propagate from one vehicle to another in a cascaded system. In the formation flight system considered here, each ith aircraft uses information from itself and the preceding ((i-1)th) aircraft to track a commanded relative position. A possible solution for meeting performance requirements with such a system is to allow string instability. This paper explores two results of string instability and outlines analysis techniques for string unstable systems. The three analysis techniques presented here are: linear, nonlinear formation performance, and ride quality. The linear technique was developed from a worst-case scenario and could be applied to the design of a string unstable controller. The nonlinear formation performance and ride quality analysis techniques both use nonlinear formation simulation. Three of the four formation-controller gain-sets analyzed in this paper were limited more by ride quality than by performance. Formations of up to seven aircraft in a cascaded formation could be used in the presence of light gusts with this string unstable system.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 08
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    Report Date: August 2002
    No. Pages: 16
    Funding Organization: WU 706-35-00-E8-20-00-AFF
    Keywords:      Aircraft; formation ; leader-follower; stability; string
    Notes: Also presented at the AIAA Guidance, Navigation, and Control Conference, Monterey, California, August 5-8, 2002.


  15. INITIAL FLIGHT TESTS OF THE NASA F-15B PROPULSION FLIGHT TEST FIXTURE , Technical Memorandum
    Authors: Nathan Palumbo, Timothy R. Moes, M. Jake Vachon
    Report Number: NASA-TM-2002-210736
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: Flights of the F-15B/Propulsion Flight Test Fixture (PFTF) with a Cone Drag Experiment (CDE) attached have been accomplished at NASA Dryden Flight Research Center. Mounted underneath the fuselage of an F-15B airplane, the PFTF provides volume for experiment systems and attachment points for propulsion experiments. A unique feature of the PFTF is the incorporation of a six-degree-of-freedom force balance. The force balance mounts between the PFTF and experiment and measures three forces and moments. The CDE has been attached to the force balance for envelope expansion flights. This experiment spatially and inertially simulates a large propulsion test article. This report briefly describes the F-15B airplane, the PFTF, and the force balance. A detailed description of the CDE is provided. Force-balance ground testing and stiffness modifications are described. Flight profiles and selected flight data from the envelope expansion flights are provided and discussed, including force-balance data, the internal PFTF thermal and vibration environment, a handling qualities assessment, and performance capabilities of the F-15B airplane with the PFTF installed.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 07
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    Report Date: July 2002
    No. Pages: 15
    Funding Organization: WU 710-35-14-00-38-00-F15
    Keywords:      F-15B flight testing; In-flight force balance; Propulsion flight test fixture; Propulsion flight testing; Rocket-based combined cycle propulsion
    Notes: Presented at 38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Indianapolis, Indiana July 7-10, 2002, AIAA-2002-4131.


  16. A GROUND-BASED RESEARCH VEHICLE FOR BASE DRAG STUDIES AT SUBSONIC SPEEDS , Technical Memorandum
    Authors: Corey Diebler and Mark Smith
    Report Number: NASA-TM-2002-210737
    Performing Organization: NASA Dryden Flight Research Center, Edwards, CA
    Abstract: A ground research vehicle (GRV) has been developed to study the base drag on large-scale vehicles at subsonic speeds. Existing models suggest that base drag is dependant upon vehicle forebody drag, and for certain configurations, the total drag of a vehicle can be reduced by increasing its forebody drag. Although these models work well for small projectile shapes, studies have shown that they do not provide accurate predictions when applied to large-scale vehicles. Experiments are underway at the NASA Dryden Flight Research Center to collect data at Reynolds numbers to a maximum of 3 times 10 to the seventh power, and to formulate a new model for predicting the base drag of trucks, buses, motor homes, reentry vehicles, and other large-scale vehicles. Preliminary tests have shown errors as great as 70 percent compared to Hoerner's two-dimensional base drag prediction. This report describes the GRV and its capabilities, details the studies currently underway at NASA Dryden, and presents preliminary results of both the effort to formulate a new base drag model and the investigation into a method of reducing total drag by manipulating forebody drag.
    Distribution/Availability: Unclassified - Unlimited
    Subject Category: 02
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    Report Date: November 2002
    No. Pages: 14
    Funding Organization: 953-50-00-SE-RR-00-000
    Keywords:      Base drag; Coast-down test; Drag bucket; Forebody drag; Ground vehicle
    Notes: Also presented as a slide presentation at the United Engineering Foundation (UEF) conference on the Aerodynamics of Heavy Vehicles Trucks, Buses, and Trains, Dec. 2-6, 2002, Monterey-Pacific Grove, CA
 
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