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  • 1
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    The strake - A simple means for directional control improvement (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: On the basis of several flight test programs conducted to date, a directional control margin improvement of at least 5 percent is obtainable for right-sideward flight throught the use of flow pattern separation-controlling tail-boom strakes. The enhanced directional control margin is critically important in low speed maneuvers, where high airloads are experienced by the tailboom. Numerous European helicopters have incorporated the strake on their tailbooms.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Vertiflite (ISSN 0042-4455); 39; 2; p. 29-31.
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Two-dimensional aerodynamic characteristics of several polygon-shaped cross-sectional models applicable to helicopter fuselages (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A wind-tunnel investigation was conducted to determine 2-D aerodynamic characteristics of nine polygon-shaped models applicable to helicopter fuselages. The models varied from 1/2 to 1/5 scale and were nominally triangular, diamond, and rectangular in shape. Side force and normal force were obtained at increments of angle of flow incidence from -45 to 90 degrees. The data were compared with results from a baseline UH-60 tail-boom cross-section model. The results indicate that the overall shapes of the plots of normal force and side force were similar to the characteristic shape of the baseline data; however, there were important differences in magnitude. At a flow incidence of 0 degrees, larger values of normal force for the polygon models indicate an increase in fuselage down load of 1 to 2.5 percent of main-rotor thrust compared with the baseline value. Also, potential was indicated among some of the configurations to produce high fuselage side forces and yawing moments compared with the baseline model.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3233 , L-16951 , NAS 1.60:3233 , AVSCOM-TR-92-B-002 , AD-A254938
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Effect of planform taper on hover performance of an advanced AH-64 model rotor (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The hover performance of a 27 percent scale model baseline rotor and advanced rotor with a 3:1 tapered tip (TR3) for the AH-64 attack helicopter was investigated and compared. Hover results from a previously tested advanced rotor with a 5:1 tapered tip (TR5) were also compared. Rotor thrust was varied over a range for two tip Mach numbers. The results indicated that the TR3 blades had improved performance compared with the TR5 blades, and both the TR3 and TR5 blades were superior to the baseline rotor. The additional margin in performance for the TR3 blades was likely due to an increase in blade area and Reynolds number in the tip region of the blades.
    Keywords: AERODYNAMICS
    Type: NASA-TM-89145 , L-16267 , NAS 1.15:89145 , AVSCOM-TM-87-B-10 , AD-A184287
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Aerodynamic Performance of a 0.27-Scale Model of an AH-64 Helicopter with Baseline and Alternate Rotor Blade Sets (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Performance of a 27 percent scale model rotor designed for the AH-64 helicopter (alternate rotor) was measured in hover and forward flight and compared against and AH-64 baseline rotor model. Thrust, rotor tip Mach number, advance ratio, and ground proximity were varied. In hover, at a nominal thrust coefficient of 0.0064, the power savings was about 6.4 percent for the alternate rotor compared to the baseline. The corresponding thrust increase at this condition was approx. 4.5 percent which represents an equivalent full scale increase in lift capability of about 660 lbs. Comparable results were noted in forward flight except for the high thrust, high speed cases investigated where the baseline rotor was slightly superior. Reduced performance at the higher thrusts and speeds was likely due to Reynolds number effects and blade elasticity differences.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4201 , L-16725 , NAS 1.15:4201 , AVSCOM-TM-90-B-015 , AD-A224493
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Process for bonding elastomers to metals (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A process for bonding elastomeric material to a metal part includes coating a heat curable adhesive on the surfaces of the metal part to be bonded. The metal part is placed in a mold, a bottom plate and an upper transfer pot of a transfer molding machine is preheated to a predetermined cure temperature. A predetermined quantity of uncured elastomeric material is loaded into the transfer pot. The mold containing the adhesive coated metal part is clamped to the bottom plate, and almost contemporaneously, the uncured elastomeric material is pressed into the mold while maintaining heat and pressure in the mold for a time sufficient to vulcanize and thereby cure the elastomeric material simultaneously with the adhesive, whereby contacting surfaces of the metal part are strongly bonded to the vulcanized elastomeric material.
    Keywords: NONMETALLIC MATERIALS
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Helicopter low-speed yaw control (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A system for improving yaw control at low speeds consists of one strake placed on the upper portion of the fuselage facing the retreating rotor blade and another strake placed on the lower portion of the fuselage facing the advancing rotor blade. These strakes spoil the airflow on the helicopter tail boom during hover, low speed flight, and right or left sidewards flight so that less side thrust is required from the tail rotor.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Flow visualization of mast-mounted-sight/main rotor aerodynamic interactions (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Flow visualization tests were conducted on a 27 percent-scale AH-64 attack helicopter model fitted with various mast-mounted-sight configurations in an attempt to identify the cause of adverse vibration encountered during full-scale flight tests of an Apache/Longbow configuration. The tests were conducted at the NASA Langley Research Center in the 14- by 22-Foot Subsonic Tunnel. A symmetric and an asymmetric mast-mounted-sight oriented at several skew angles were tested at forward and rearward flight speeds of 30 and 45 knots. A laser light sheet seeded with vaporized propylene glycol was used to visualize the wake of the sight in planes parallel and perpendicular to the freestream flow. Analysis of the flow visualization data identified the frequency of the wake shed from the sight, the angle-of-attack at the sight, and the location where the sight wake crossed the rotor plane. Differences in wake structure were observed between the various sight configurations and slew angles. Postulations into the cause of the adverse vibration found in flight test are given along with considerations for future tests.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 93-3517 , In: AIAA Applied Aerodynamics Conference, 11th, Monterey, CA, Aug. 9-11, 1993, Technical Papers. Pt. 2 (A93-47201 19-02); p. 903-920.
    Format: text
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  • 8
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    Exploratory flow visualization investigation of mast-mounted sights in presence of a rotor (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A flow visualization investigation with a laser light sheet system was conducted on a 27-percent-scale AH-64 attack helicopter model fitted with two mast-mounted sights in the langley 14- by 22-foot subsonic tunnel. The investigation was conducted to identify aerodynamic phenomena that may have contributed to adverse vibration encountered during full-scale flight of the AH-64D apache/longbow helicopter with an asymmetric mast-mounted sight. Symmetric and asymmetric mast-mounted sights oriented at several skew angles were tested at simulated forward and rearward flight speeds of 30 and 45 knots. A laser light sheet system was used to visualize the flow in planes parallel to and perpendicular to the free-stream flow. Analysis of these flow visualization data identified frequencies of flow patterns in the wake shed from the sight, the streamline angle at the sight, and the location where the shed wake crossed the rotor plane. Differences in wake structure were observed between the sight configurations and various skew angles. Analysis of lateral light sheet plane data implied significant vortex structure in the wake of the asymmetric mast-mounted sight in the configuration that produced maximum in-flight vibration. The data showed no significant vortex structure in the wake of the asymmetric and symmetric configurations that produced no increase in in-flight adverse vibration.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4634 , L-17409 , NAS 1.15:4634 , ATCOM-TR-95-A-001
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Helicopter anti-torque system using fuselage strakes (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The improvement of the helicopter torque control system is discussed. At low to medium forward speeds helicopter performance is limited by the effectiveness of the means for counteracting main rotor torque and controlling sideslip airloads. These problems may be overcome by mounting strakes on the aft fuselage section. For single rotor helicopters whose main rotor rotates counter-clockwise as viewed from above, one of the strakes would be mounted in the upper lefthand quadrant and the second in the lower left hand quadrant. The strakes alter the air flow around the fuselage by separating the flow so as to produce lateral airloads on the tail boom which oppose main-rotor torque. The upper strake operates in a right crosswind to oppose main rotor torque, and the lower strake has effect in left crosswinds. The novelty of this invention resides in the simple and economical manner in which the helicopter tail boom may be modified by the addition of strakes in order to increase torque control, and reduce the need for supplemental mechanical means of torque control.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Aerodynamic Effect of Strakes on Two-Dimensional Tail Boom Models of the OH-58A and the OH-58D Helicopters (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: During hover and low speed flight, helicopters experience significant aerodynamic forces on the tail boom caused by the wake from the main and tail rotors and by crosswinds. These effects were simulated during a study conducted in the Langley 14 by 22 Foot Subsonic Tunnel on a 136 percent scaled 2-D tail boom model with cross sections representative of those on the U.S. Army OH-58A and the OH-58D helicopters. The effects of longitudinal strakes attached to the cross sections were studied. To obtain the aerodynamic forces acting on the cross sections, the flow incidence range on the scaled models was varied from -45 to 90 degrees and the models were tested through a dynamic pressure range of 5 to 15 psf. The results of the OH-58A and the OH-58D configurations show a significant improvement at conditions which represent right sideward flight by reducing the adverse aerodynamic side force when the strakes are installed. These data were used to calculate a change in tail rotor power for the full scale flight vehicle and indicated approx. a 5 to 6 percent average savings in right sideward flight for the critical velocity range of 0 to 30 knots. Increases in the tail boom normal force were noted due to the strakes. The results indicate a potential for reducing the directional control and tail rotor thrust required in the critical hover and right sideward flight speed range with a calculated minimum increase to main rotor power required and an overall net improvement in power of 0.5 percent for both the OH-58A and OH-58D.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4248 , L-16842 , NAS 1.15:4248 , AVSCOM-TR-90-B-010 , AD-A230876
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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