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  • 11
    Publication Date: 2019-07-10
    Description: In at least one embodiment, the apparatus of the invention is a flight vehicle tail assembly having an exterior surface, at least one first vent in the exterior surface, at least one second vent in the exterior surface, and an air passage connecting the at least one first vent to the at least one second vent allowing air to flow there between. Where the at least one first vent is located near a high air pressure area acting on the exterior surface during a range of predefined flight conditions, Further, the at least one second vent is located near a low air pressure area acting on the exterior surface during the predefined flight conditions. So that at the predefined flight conditions adverse loads on the tail assembly are reduced by venting air from the high pressure area, through the tail assembly, to the low pressure area. The method of the present invention includes the steps of: receiving air through the at least one first vent in the exterior surface, passing the air through the tail assembly from the at least one first vent to at least one second vent in the exterior surface. and ejecting the air out of the tail assembly at the at least one second vent.
    Keywords: Aircraft Design, Testing and Performance
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  • 12
    Publication Date: 2019-07-12
    Description: Spoilers on tail boom significantly improve yaw control in both right and left sidewinds. Spoilers are two thin plates extending outward, perpendicular to curvature of boom, distance of about 6 percent of total depth of tail boom. Along-the-boom dimensions of spoilers are as long as possible without interfering with such existing critical parts as tail rotor. Further enhancement, spoilers made retractable and automatically deployable as required. Concept applicable to all single-rotor helicopters. Applied as simple economical addition to existing helicopters or incorporated into new helicopter designs.
    Keywords: MECHANICS
    Type: LAR-13630 , NASA Tech Briefs (ISSN 0145-319X); 16; 10; P. 84
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  • 13
    Publication Date: 2019-07-13
    Description: The use of a strake or spoiler on a helicopter tail boom to beneficially change helicopter tail boom air loads was suggested in the United States in 1975. The anticipated benefits were a change of tail boom loads to reduce required tail rotor thrust and power and improve directional control. High tail boom air loads experienced by the YAH-64 and described in 1978 led to a wind tunnel investigation of the usefullness of strakes in altering such loads on the AH-64, UH-60, and UH-1 helicopters. The wind tunnel tests of 2-D cross sections of the tail boom of each demonstrated that a strake or strakes would be effective. Several limited test programs with the U.S. Army's OH-58A, AH-64, and UH-60A were conducted which showed the effects of strakes were modest for those helicopters. The most recent flight test program, with a Bell 204B, disclosed that for the 204B the tail boom strake or strakes would provide more than a modest improvement in directional control and reduction in tail rotor power.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TM-101496 , NAS 1.15:101496 , AVSCOM-TM-88-B-014 , International Conference on Helicopter Handling Qualities and Control; Nov 15, 1988 - Nov 17, 1988; London
    Format: application/pdf
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  • 14
    Publication Date: 2019-07-13
    Description: Two documents discuss results of additional investigations of concept introduced in "Helicopter Tail-Boom Strakes" (LAR-13233). Essence of concept that strake or pair of strakes on side of tail boom facing retreating side of main rotor of helicopter perturbs flow in such way to increase aerodynamic pressure on that side, contributing force to thrust from tail rotor. Because of force, thrust required of tail rotor for yaw control reduced. Important advantage in low-speed flight, especially in sideward flight, in which tail-rotor thrust in absence of strake sometimes insufficient.
    Keywords: MECHANICS
    Type: LAR-14219 , NASA Tech Briefs (ISSN 0145-319X); 18; 12; P. 83
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  • 15
    Publication Date: 2019-07-13
    Description: A joint U.S. Army/NASA flight investigation was conducted utilizing an instrumented Bell 240B single-rotor helicopter to determine the effectiveness of horizontally-mounted tail boom strakes on directional controllability and tail rotor power required during low-speed, crosswind operating conditions. The purpose of the strakes was to separate airflow over the tail boom and change fuselage yawing moments in a direction to improve the yaw control margin and reduce tail rotor power required. Low-speed crosswind data were obtained in 5-knot increments at airspeeds of 0 knots to 35 knots and for 30 deg increments in wind azimuth from 0 to 330 deg. In right sideward flight at the most critical wind azimuth and airspeed (60 deg azimuth measured from the nose of the aircraft and 20 knots airspeed), the strakes improved the pedal margin by about 6 percent of total travel and reduced the tail rotor power required by 17 percent. The increase in yaw control and reduction in tail rotor power offered by the strakes can expand the operating envelope in terms of gross weight and altitude capability. No effects in forward flight were noted.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AHS, Annual Forum; May 21, 1990 - May 23, 1990; Washington, DC; United States
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  • 16
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2019-07-13
    Description: Variable-tilt helicopter rotor mast proposed to improve helicopter performance and reduce vibration, especially at upper end of forward-speed range of helicopters. Achieved by use of universal coupling in main rotor mast or by tilting entire engine-and-transmission platform. Performance, energy efficiency, and safety enhanced.
    Keywords: MACHINERY
    Type: LAR-13779 , NASA Tech Briefs (ISSN 0145-319X); 19; 11; P. 82
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  • 17
    Publication Date: 2019-07-10
    Description: Two large-scale, two-dimensional helicopter tail boom models were used to determine the effects of passive venting on boom down loads and side forces in hovering crosswind conditions. The models were oval shaped and trapezoidal shaped. Completely porous and solid configurations, partial venting in various symmetric and asymmetric configurations, and strakes were tested. Calculations were made to evaluate the trends of venting and strakes on power required when applied to a UH-60 class helicopter. Compared with the UH-60 baseline, passive venting reduced side force but increased down load at flow conditions representing right sideward flight. Selective asymmetric venting resulted in side force benefits close to the fully porous case. Calculated trends on the effects of venting on power required indicated that the high asymmetric oval configuration was the most effective venting configuration for side force reduction, and the high asymmetric with a single strake was the most effective for overall power reduction. Also, curves of side force versus flow angle were noticeable smoother for the vented configurations compared with the solid baseline configuration; this indicated a potential for smoother flight in low-speed crosswind conditions.
    Keywords: Aerodynamics
    Type: NASA/TP-2000-210083 , NAS 1.60:210083 , AMCOM-AFDD/TR-00-A-007 , L-17770
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  • 18
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2019-07-12
    Description: Improved, economical method for bonding elastomers to metals prevents failures caused by debonding. In new technique, vulcanization and curing occur simultaneously in specially designed mold that acts as form for desired shape of elastomer and as container that positions and supports metal parts. Increases interface adhesion between metal, adhesive, and elastomer.
    Keywords: FABRICATION TECHNOLOGY
    Type: LAR-13645 , NASA Tech Briefs (ISSN 0145-319X); 14; 7; P. 82
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  • 19
    Publication Date: 2019-08-15
    Description: Flight records are presented from an early flight test of a wing-tip mounted tilting-ducted-fan, vertical-take-off and landing (VTOL) aircraft configuration. Time histories of the aircraft motions, control positions, and duct pitching-moment variation are presented to illustrate the characteristics of the aircraft in hovering, in conversion from hovering to forward flight, and in conversion from forward flight to hovering. The results indicate that during essentially continuous slow level- flight conversions, this aircraft experiences excessive longitudinal trim changes. Studies have shown that the large trim changes are caused primarily by the variation of aerodynamic moments acting on the duct units. Action of the duct-induced downwash on the horizontal stabilizer during the conversion also contributes to the longitudinal trim variations. Time histories of hovering and slow vertical descent in the final stages of landing in calm air show angular motions of the aircraft as great as +/- 10 deg. about all axes. Stick and pedal displacements required to control the aircraft during the landing maneuver were on the order of 50 to 60 percent of the total travel available.
    Keywords: Aircraft Design, Testing and Performance
    Type: NASA-TN-D-372 , L-891
    Format: application/pdf
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