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At least 55 records · Page 3

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NASA NTRS1979

Flow visualization studies of a general research fighter model employing a strake-wing concept at subsonic speeds

A systematic wind tunnel study was conducted in the Langley high-speed 7 by 10 foot tunnel to document, by oil-flow photographs, the surface flow patterns for configurations incorporating strake-wing geometries indicative of current and proposed maneuvering aircraft. The configurations employed combinations of strakes with reflexed planforms having exposed spans of 10 percent, 20 percent, and 30 percent of the reference wing span and wings with trapezoidal planforms having leading-edge sweep angles of approximately 30 deg, 44 deg, and 60 deg. Tests were conducted at Mach numbers of 0.3 and 0.5 and at angles of attack ranging from approximately 5 deg to 30 deg in 5 deg increments at 0 deg sideslip. The configurations incorporating the strake-wing geometries exhibited more organized flow patterns with smaller asymmetries to higher angles of attack than the corresponding configurations incorporating the wing-alone geometries did.

Luckring, J. M.↗

NASA NTRS1983

High angle-of-attack aerodynamics of a strake-canard-wing V/STOL fighter configuration

High angle-of-attack aerodynamic data are analyzed for a strake-canard-wing V/STOL fighter configuration. The configuration represents a twin-engine supersonic V/STOL fighter aircraft which uses four longitudinal thrust-augmenting ejectors to provide vertical lift. The data were obtained in tests of a 9.39 percent scale model of the configuration in the NASA Ames 12-Foot Pressure Wind Tunnel, at a Mach number of 0.2. Trimmed aerodynamic characteristics, longitudinal control power, longitudinal and lateral/directional stability, and effects of alternate strake and canard configurations are analyzed. The configuration could not be trimmed (power-off) above 12 deg angle of attack because of the limited pitch control power and the high degree of longitudinal instability (28 percent) at this Mach number. Aerodynamic center location was found to be controllable by varying strake size and canard location without significantly affecting lift and drag. These configuration variations had relatively little effect on the lateral/directional stability up to 10 deg angle of attack.

Durston, D. A.↗

NASA NTRS1990

Aerodynamic Effect of Strakes on Two-Dimensional Tail Boom Models of the OH-58A and the OH-58D Helicopters

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.

Crowell, Cynthia A.↗

NASA NTRS1994

Preparations for flight research to evaluate actuated forebody strakes on the F-18 high-alpha research vehicle

As part of the NASA High-Angle-of-Attack Technology Program (HATP), flight tests are currently being conducted with a multi-axis thrust vectoring system applied to the NASA F-18 High Alpha Research Vehicle (HARV). A follow-on series of flight tests with the NASA F-18 HARV will be focusing on the application of actuated forebody strake controls. These controls are designed to provide increased levels of yaw control at high angles of attack where conventional aerodynamic controls become ineffective. The series of flight tests are collectively referred to as the Actuated Nose Strakes for Enhanced Rolling (ANSER) Flight Experiment. The development of actuated forebody strake controls for the F-18 HARV is discussed and a summary of the ground tests conducted in support of the flight experiment is provided. A summary of the preparations for the flight tests is also provided.

Murri, Daniel G.↗

NASA NTRS1979

Subsonic longitudinal and lateral aerodynamic characteristics for a systematic series of strake-wing configurations

A systematic wind tunnel study was conducted in the Langley 7 by 10 foot high speed tunnel to help establish a parametric data base of the longitudinal and lateral aerodynamic characteristics for configurations incorporating strake-wing geometries indicative of current and proposed maneuvering aircraft. The configurations employed combinations of strakes with reflexed planforms having exposed spans of 10%, 20%, and 30% of the reference wing span and wings with trapezoidal planforms having leading edge sweep angles of approximately 30, 40, 44, 50, and 60 deg. Tests were conducted at Mach numbers ranging from 0.3 to 0.8 and at angles of attack from approximately -4 to 48 deg at zero sideslip.

Luckring, J. M.↗

NASA NTRS1980

Effect of wing location and strakes on stability and control characteristics of a monoplanar circular missile with low-profile tail fins at supersonic speeds

A wind tunnel test was conducted at Mach numbers from 1.70 to 2.86 to extend the aerodynamic data base for wing tail effect on stability and control characteristics of monoplanar missiles. The results are summarized to show the effects of tail fin dihedral angle, wing location, and nose body strakes. The results indicate that an increase in tail fin dihedral angle produces positive increments in directional stability that allow greater trimmed lift coefficient values (maneuver potential) to be obtained. An increase in wing tail gap for the Mach number range reduces the aerodynamic center travel and produces reductions in directional stability at the lower angles of attack. A change in wing height (vertical location) strongly influences the angle of attack at which pitch up and the most directional stability occur. The addition of strakes to the baseline configuration increases directional stability, which allows a significant increase in stable trimmed maneuver capability. The tail fins of the baseline configuration are effective in producing roll and yaw control that are accompanied by favorable yaw and roll, respectively.

Blair, A. B., Jr.↗

NASA NTRS1983

Numerical simulation of the leading-edge separation vortex for a wing and strake-wing configuration

In the present investigation, the 'thin layer' Navier-Stokes equations are used to compute the flow about a delta wing and a strake-delta wing configuration. Both configurations possess blunt noses and rounded leading edges. The computational grid about these configurations is generated using a newly developed three-dimensional grid-generation code which solves a set of Poisson equations with spherical coordinate variables using an alternating direction implicit (ADI) scheme. Computational results are obtained for an isolated wing with 60 deg sweep and a strake-wing configuration with 80-60 deg sweep. Computations for angles of attack in the range from 6 to 30 deg are presented. Attention is given to the effect of the angle of attack, the Mach number, and the Reynolds number. Theoretical results are compared with experimental data.

Fujii, K.↗

NASA NTRS1984

Helicopter Anti-Torque System Using Strakes

A helicopter is disclosed with a system for controlling main-rotor torque which reduces the power and size requirements of conventional anti-torque means. The torque countering forces are generated by disrupting the main rotor downwash flowing around the fuselage. The downwash flow is separated from the fuselage surface by a strake positioned at a specified location on the fuselage. This location is determined by the particular helicopter wash pattern and fuselage configuration, generally being located between 20 deg before top dead center (TDC) and 80 deg from TDC on the fuselage side to which the main rotor blade approaches during rotation. The strake extends along the fuselage from the cabin section to the aft end and can be continuous or separated for aerodynamic surfaces such as a horizontal stabilizer.

Kelley, H. L.↗

NASA NTRS1986

Helicopter Tail-Boom Strakes

Yaw control and overall efficiency increased at hover and low speeds. Wind-tunnel investigation showed strake located on left side of tail boom has potential to reduce high adverse side loads on tail boom in hover and in sideward flight. Test demonstrated addition of single long strake to left side of tail boom most effective configuration for reducing left pedal requirements in right sideward flight.

Kelley, H. L.↗

NASA NTRS1991

Aerodynamic control using forebody strakes

Aerodynamic control using a rotatable, miniature nose-tip strake system was investigated in a water tunnel with a forebody model. Flow visualization and yawing moment measurements were performed. The results show that the system was highly effective in controlling the forebody vortices and producing controlled yawing moments at moderate-to-high angles of attack. In comparison with the forebody strakes used in several previous studies, the system can potentially be substantially smaller in size, simpler in operation, and effective over wide ranges of angles of attack and sideslip.

Ng, T. Terry↗

NASA NTRS1993

The strake - A simple means for directional control improvement

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.

Wilson, John C.↗

NASA NTRS1995

Using the HARV simulation aerodynamic model to determine forebody strake aerodynamic coefficients from flight data

The method described in this report is intended to present an overview of a process developed to extract the forebody aerodynamic increments from flight tests. The process to determine the aerodynamic increments (rolling pitching, and yawing moments, Cl, Cm, Cn, respectively) for the forebody strake controllers added to the F/A - 18 High Alpha Research Vehicle (HARV) aircraft was developed to validate the forebody strake aerodynamic model used in simulation.

Messina, Michael D.↗

NASA NTRS1996

F-18 HARV With Nose Strakes For Forebody Vortex Control

Nose of F-18 High Alpha Research Vehicle (HARV) modified with conformal, mechanically actuated nose strakes for enhanced rolling (ANSER). Forebody vortex control effected by use of actuated strakes and/or other flow-control devices. System provides means to evaluate design tradeoffs.

Bowers, Albion H.↗

NASA NTRS1996

Flight test maneuvers for closed loop lateral-directional modeling of the F-18 High Alpha Research Vehicle (HARV) using forebody strakes

Flight test maneuvers are specified for the F-18 High Alpha Research Vehicle (HARV). The maneuvers were designed for closed loop parameter identification purposes, specifically for lateral linear model parameter estimation at 30, 45, and 60 degrees angle of attack, using the Actuated Nose Strakes for Enhanced Rolling (ANSER) control law in Strake (S) model and Strake/Thrust Vectoring (STV) mode. Each maneuver is to be realized by applying square wave inputs to specific pilot station controls using the On-Board Excitation System (OBES). Maneuver descriptions and complete specification of the time/amplitude points defining each input are included, along with plots of the input time histories.

Morelli, E. A.↗

NASA NTRS1996

Design Specification for a Thrust-Vectoring, Actuated-Nose-Strake Flight Control Law for the High-Alpha Research Vehicle

Specifications for a flight control law are delineated in sufficient detail to support coding the control law in flight software. This control law was designed for implementation and flight test on the High-Alpha Research Vehicle (HARV), which is an F/A-18 aircraft modified to include an experimental multi-axis thrust-vectoring system and actuated nose strakes for enhanced rolling (ANSER). The control law, known as the HARV ANSER Control Law, was designed to utilize a blend of conventional aerodynamic control effectors, thrust vectoring, and actuated nose strakes to provide increased agility and good handling qualities throughout the HARV flight envelope, including angles of attack up to 70 degrees.

Bacon, Barton J.↗

NASA NTRS1998

A Method for Integrating Thrust-Vectoring and Actuated Forebody Strakes with Conventional Aerodynamic Controls on a High-Performance Fighter Airplane

A method, called pseudo controls, of integrating several airplane controls to achieve cooperative operation is presented. The method eliminates conflicting control motions, minimizes the number of feedback control gains, and reduces the complication of feedback gain schedules. The method is applied to the lateral/directional controls of a modified high-performance airplane. The airplane has a conventional set of aerodynamic controls, an experimental set of thrust-vectoring controls, and an experimental set of actuated forebody strakes. The experimental controls give the airplane additional control power for enhanced stability and maneuvering capabilities while flying over an expanded envelope, especially at high angles of attack. The flight controls are scheduled to generate independent body-axis control moments. These control moments are coordinated to produce stability-axis angular accelerations. Inertial coupling moments are compensated. Thrust-vectoring controls are engaged according to their effectiveness relative to that of the aerodynamic controls. Vane-relief logic removes steady and slowly varying commands from the thrust-vectoring controls to alleviate heating of the thrust turning devices. The actuated forebody strakes are engaged at high angles of attack. This report presents the forward-loop elements of a flight control system that positions the flight controls according to the desired stability-axis accelerations. This report does not include the generation of the required angular acceleration commands by means of pilot controls or the feedback of sensed airplane motions.

Lallman, Frederick J.↗

NASA NTRS2005

Aerodynamics of an Axisymmetric Missile Concept Having Cruciform Strakes and In-Line Tail Fins From Mach 0.60 to 4.63

An experimental study has been performed to develop a large force and moment aerodynamic data set on a slender axisymmetric missile configuration having cruciform strakes and in-line control tail fins. The data include six-component balance measurements of the configuration aerodynamics and three-component measurements on all four tail fins. The test variables include angle of attack, roll angle, Mach number, model buildup, strake length, nose size, and tail fin deflection angles to provide pitch, yaw, and roll control. Test Mach numbers ranged from 0.60 to 4.63. The entire data set is presented on a CD-ROM that is attached to this paper. The CD-ROM also includes extensive plots of both the six-component configuration data and the three-component tail fin data. Selected samples of these plots are presented in this paper to illustrate the features of the data and to investigate the effects of the test variables.

Jerry M Allen↗

NASA NTRS2005

Aerodynamics of an Axisymmetric Missile Concept Having Cruciform Strakes and In-Line Tail Fins From Mach 0.60 to 4.63, Supplement

Jerry M Allen↗