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J A C Kentfield - One of the best experts on this subject based on the ideXlab platform.

  • quantitative prediction of the idealized performance of aircraft with outboard Horizontal Stabilizers
    Journal of Aircraft, 2012
    Co-Authors: J A C Kentfield
    Abstract:

    An outboard-Horizontal-stabilizer aircraft configuration is one in which the Horizontal and vertical tail surfaces are supported by booms projecting downwind from each wing tip of a monoplane such that these surfaces lie within the upwash and inwash flow generated by each wing tip. The Horizontal surfaces project, therefore, outboard of each wing tip, with a vertical surface mounted above each boom. A description is given of the inherent advantage of an outboard-Horizontal-stabilizer configuration. A theoretical treatment, closely based on fundamental concepts, is presented that is designed to facilitate the evaluation of the net drag of an outboard-Horizontal-stabilizer configuration in terms of the wing-lift coefficient of an equivalent conventional configuration of equal lift. The theoretical treatment is applied to several outboard-Horizontal-stabilizer-type configurations to evaluate flight performance in terms of lift/drag versus wing-lift coefficient. These performances are compared with the idealized performances of equivalent conventional configurations. It was found that, depending upon the details of the basis of the comparison, the outboard-Horizontal-stabilizer configurations were from 30 to 50 % more efficient in terms of lift/ drag than their conventional alternatives.

  • aircraft with outboard Horizontal Stabilizers history current status development potential
    Progress in Aerospace Sciences, 2009
    Co-Authors: J A C Kentfield
    Abstract:

    Abstract The potential of using outboard Horizontal Stabilizers (OHS) to reduce aircraft drag, and hence improve fuel economy, was investigated historically, experimentally and theoretically. The feasibility of OHS configurations on the basis of the structural stress levels expected was also studied. The findings of the work showed that from simple, low Reynolds number, wind-tunnel tests, at a wing-chord-based Reynolds number of approximately 6×104 and also from theoretical analyses for a higher Reynolds number of 9×106, lift/drag (L/D) value increases in the region of 40–50% for wing and tail surfaces can be expected relative to corresponding values for conventional aircraft. When account is taken of fuselage and tail-support boom drag, the expected overall L/D increase is in the region of 30–35%. The analytical stress-level work showed that contrary to what, on a first thought basis, might be expected, there were no major stress problems. Flight tests at the University of Calgary, and by others elsewhere, employing radio-controlled, powered, model aircraft (i.e. UAVs) showed that aircraft of the OHS type were easily controlled in flight and were stable. An examination was made of additional areas that may contribute yet further to the development of the OHS concept.

  • lift drag ratios of aircraft with outboard Horizontal Stabilizers
    46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
    Co-Authors: J A C Kentfield
    Abstract:

    Predictions are presented of the performances, in terms of lift/drag (L/D) ratios, of aircraft with outboard Horizontal Stabilizers. The predicted performances show significant increases in L/D ratios ranging from approximately 30% to more than 50% when compared with otherwise comparable conventional configurations. The performance prediction range covered wing aspect ratios from 4 to 10. A prime reason for the L/D improvements included profiting from a lift contribution from the Horizontal stabilizer the two sections of which lie in the wing-tip upwash flows thereby offsetting, for a prescribed aircraft gross weight, some of the lift otherwise required from the wing and yet leaving a sufficient lift coefficient margin available for pitch control. Also the position of the vertical Stabilizers, downwind of the wing, attached to the Horizontal stabilizer support booms involved the generation of an aerodynamic lift type force, acting in the Horizontal plane, which helps to offset the skin friction and induced drag of the twin vertical surfaces. The force acting on the vertical Stabilizers is a consequence of these surfaces lying, when mounted above the booms, in an inwash flow generated by the combined action of the wing-tip flow field and the mainplane downwash. Lastly, due to the directions of the flows impinging upon their surfaces, the Stabilizers also generate a thrust component helping to further cancel their drags.

  • aerodynamic loading and stability of an aircraft with outboard Horizontal Stabilizers
    45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
    Co-Authors: J A C Kentfield
    Abstract:

    An application is studied of the outboard Horizontal stabilizer (OHS) aircraft design concept to a high-altitude, long endurance (HALE) mission, uninhabited air vehicle (UAV). It was found that the OHS concept appears to be very well suited for the suggested mission because of the relative advantage, compared with a conventional UAV design, of an improved lift/drag ratio over a wide range of lift coefficients implying that the benefits of improved performance, in lift/drag terms, would be available during both cruise to and from the surveillance site and during the loiter phase of the mission. A simplified, approximate, design process is presented that allows the expected lift/drag ratio of the aerodynamic surfaces to be estimated in an elementary manner. A correspondingly simplified wing-root bending moment and wing-root stress analysis showed that wing bending moments and resultant structural stresses were not, despite intuitive suspicions to the contrary, major problems. The overall results of the analysis showed that the OHS concept, even when analyzed only in the most basic and elementary manner, offered compared with otherwise comparable conventional aircraft designs, an improved lift/drag ratio and did not reveal any insoluble, or major, stress related problems. These results were found to be consistent, in general, with prior, more detailed, analyses and supportive experiments.

  • flow fields around the tails of aircraft with outboard Horizontal Stabilizers
    44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
    Co-Authors: J A C Kentfield, Bernard Wong
    Abstract:

    An application is studied of the outboard Horizontal stabilizer (OHS) aircraft design concept to a high-altitude, long endurance (HALE) mission, uninhabited air vehicle (UAV). It was found that the OHS concept appears to be very well suited for the suggested mission because of the relative advantage, compared with a conventional UAV design, due to an improved lift/drag ratio over a wide range of lift coefficients implying that the benefits of improved performance, in lift/drag terms, would be available during both cruise to and from the surveillance site and during the loiter phase of the mission. A simplified, approximate, design process is presented that allows the expected lift/drag ratio of the aerodynamic surfaces to be estimated in an elementary manner. The all-important flow fields around the tail surfaces of a wind-tunnel model of the suggested OHS vehicle were explored using twodimensional PIV equipment. It was shown by this means, that the flows around the Horizontal stabilizer surfaces generated by the wing-tip vortices, made it possible for the Horizontal Stabilizers to generate lift and, due to the upwash approaching these surfaces, this lift was obtained efficiently with offset of both the fictional and induced drags of the Horizontal tails. In-flows about the vertical stabilizer surfaces generated, in a Horizontal plane, lift forces acting primarily towards the vehicle vertical plane of symmetry but also inclined upwind. As a direct consequence of this a thrust component of the Horizontally directed lift force also served to counteract the drag forces associated with the vertical tails.

Saeed Farokhi - One of the best experts on this subject based on the ideXlab platform.

  • prediction of antisymmetric buffet loads on Horizontal Stabilizers in massively separated flows phase ii
    1999
    Co-Authors: Saeed Farokhi, Saeid Mirsafian, Tom Sherwood, Mark Ewing
    Abstract:

    Abstract : The Federal Aviation Administration (FAA) has a continuing program to collect data and develop predictive methods for aircraft flight loads. Some of the most severe and potentially catastrophic flight loads are produced by separated flows. Structural response to the aerodynamic excitation produced by separated flows is defined as buffeting. A low-cost technique for the prediction of full-scale buffet loads on Horizontal Stabilizers of aircraft is described. A 1/13-scale rigid generic wind tunnel model with a t-tail configuration (based on the Beech Super King Air 200) was constructed and tested at the Wichita State University 7x10 ft. subsonic wind tunnel. The test matrix included a dynamic pressure range of 25 to 45 psf; an angle-of-attack range of -5 to 20 degrees, and a sideslip range of 0 to 20 degrees. The stabilizer was instrumented with differential pressure transducers and strain gages. The measured pressure power spectra and cross-spectral densities were scaled and used to excite a full-scale aeroelastic finite element model which included the tail structure and aft tail cone. The computed Horizontal stabilizer rolling moment power spectra are used to determine the number of exceedences (within a known probability) of a specified rolling moment level per a given maneuver (e.g., stall). Representative pressure, strain gage, and rolling moment power spectra are discussed as is a selected exceedence estimate.

  • stochastic modeling of antisymmetric buffet loads on Horizontal Stabilizers in massively separated flows
    1996
    Co-Authors: Saeed Farokhi, Clay S Mauk, James E Locke
    Abstract:

    Abstract : Federal Aviation Regulation (FAR) 25 has been revised to clearly identify buffet loading as a structural design load. A modem method was developed to model antisymmetric buffet design loads on Horizontal Stabilizers with a known probability, utilizing a rigid wind tunnel model. The surface pressure was measured for a large number of test conditions, including the most severe buffeting environment for this type of aircraft: the tail immersed in the massively separated wake of the wing. Modifications to the Beech King Air 200 one-sixth scale wind tunnel model included the construction of a new Horizontal stabilizer instrumented with 12 miniature pressure transducers. Structural characteristics of the full-scale aircraft were estimated using the Automated STRuctural Optimization System (ASTROS) program. ASTROS, while not directly supporting buffet calculations, is written in a flexible high-level language and thus easily adaptable. Motion-dependent aerodynamics (stiffness and damping) were computed using the proven doublet lattice method, which is incorporated into ASTROS. Due to difficulties with the data acquisition system, the current approach was validated with buffet pressure power spectral densities from an existing reference. Based on the results, the methodology is sound. Future work would include more detailed investigations of the buffet phenomenon and integration of software programs to build a multidisciplinary design tool. This would allow aircraft manufacturers to predict the Horizontal stabilizer antisymmetric buffet loads early in the certification program.

James E Locke - One of the best experts on this subject based on the ideXlab platform.

  • stochastic modeling of antisymmetric buffet loads on Horizontal Stabilizers in massively separated flows
    1996
    Co-Authors: Saeed Farokhi, Clay S Mauk, James E Locke
    Abstract:

    Abstract : Federal Aviation Regulation (FAR) 25 has been revised to clearly identify buffet loading as a structural design load. A modem method was developed to model antisymmetric buffet design loads on Horizontal Stabilizers with a known probability, utilizing a rigid wind tunnel model. The surface pressure was measured for a large number of test conditions, including the most severe buffeting environment for this type of aircraft: the tail immersed in the massively separated wake of the wing. Modifications to the Beech King Air 200 one-sixth scale wind tunnel model included the construction of a new Horizontal stabilizer instrumented with 12 miniature pressure transducers. Structural characteristics of the full-scale aircraft were estimated using the Automated STRuctural Optimization System (ASTROS) program. ASTROS, while not directly supporting buffet calculations, is written in a flexible high-level language and thus easily adaptable. Motion-dependent aerodynamics (stiffness and damping) were computed using the proven doublet lattice method, which is incorporated into ASTROS. Due to difficulties with the data acquisition system, the current approach was validated with buffet pressure power spectral densities from an existing reference. Based on the results, the methodology is sound. Future work would include more detailed investigations of the buffet phenomenon and integration of software programs to build a multidisciplinary design tool. This would allow aircraft manufacturers to predict the Horizontal stabilizer antisymmetric buffet loads early in the certification program.

Shoop, Brian P - One of the best experts on this subject based on the ideXlab platform.

  • Structural design analysis of the Tail Landing Gear Bay and the vertical/Horizontal Stabilizers of the RAH-66 comanche helicopter
    Monterey California. Naval Postgraduate School, 1997
    Co-Authors: Shoop, Brian P
    Abstract:

    The RAH-66 Comanche's stealth design requires the use of radar- absorbing material (RAM) on the outer skin of the aircraft. The reduced stiffness properties of RAM produce insufficient tail torsional stiffness, necessitating the use of non-radar-absorbing graphite on the outer skin of the tail section. This thesis investigates structural design modifications to increase the tail section's stiffness to allow the use of RAM on the outer skin and still meet all structural requirements. An original model represents the prototype aircraft at first flight. The goal is to create a model using RAM on the outer skin that watches the structural stiffness of the original model. This thesis builds on earlier work conducted at the Naval Postgraduate School (NPS). Two new design modifications to the tailbone are developed. The best modification increases the torsional stiffness of a baseline model by six percent. Integrating earlier NPS modifications increases torsional stiffness by 12 percent. When RAM is applied to the outer skin of the modified model, torsional stiffness is reduced by only six percent from the baseline as compared to a 24 percent reduction with no modifications. Additional modifications to the vertical and Horizontal Stabilizers further increase structural stiffness and reduce weighthttp://archive.org/details/structuraldesign00shooMajor, United States ArmyApproved for public release; distribution is unlimited

Brian P Shoop - One of the best experts on this subject based on the ideXlab platform.

  • structural design analysis of the tail landing gear bay and the vertical Horizontal Stabilizers of the rah 66 comanche helicopter
    1997
    Co-Authors: Brian P Shoop
    Abstract:

    Abstract : The RAH-66 Comanche's stealth design requires the use of radar-absorbing material (RAM) on the outer skin of the aircraft. The reduced stiffness properties of RAM produce insufficient tail torsional stiffness, necessitating the use of non-radar-absorbing graphite on the outer skin of the tail section. This thesis investigates structural design modifications to increase the tail section's stiffness to allow the use of RAM on the outer skin and still meet all structural requirements. An original model represents the prototype aircraft at first flight. The goal is to create a model using RAM on the outer skin that watches the structural stiffness of the original model. This thesis builds on earlier work conducted at the Naval Postgraduate School (NPS). Two new design modifications to the tailbone are developed. The best modification increases the torsional stiffness of a baseline model by six percent. Integrating earlier NPS modifications increases torsional stiffness by 12 percent. When RAM is applied to the outer skin of the modified model, torsional stiffness is reduced by only six percent from the baseline as compared to a 24 percent reduction with no modifications. Additional modifications to the vertical and Horizontal Stabilizers further increase structural stiffness and reduce weight.