Rudder Surface Research Articles

Examination of F/A-18 honeycomb composite rudders for disbond due to water using through-transmission ultrasonics

The flight control surfaces of F/A-18 aircraft are composed of carbon/epoxy skin and aluminum honeycomb core composite material that has a known susceptibility to water ingress. The rudder has failed in flight due to moisture induced bond degradation between skin and core. Manual through-transmission Ultrasonic Testing (UT), applied to the rudder surface, currently identifies disbond as a reduction in received signal amplitude. However, water within the honeycomb cells provides significant sound transmission, which may mask disbond. In this study, water was first identified within two in-service rudders using thermography. Precise water locations were then mapped by neutron radiography. Time-base analysis of through-transmission A-scans, obtained using squirter technology, permitted discrimination of cell wall signals from signals that had passed through water within the cells. Examination of received cell wall signal intensities, modeled for disbond in the presence of water, demonstrated potential for identification of disbond even when water was present.http://dx.doi.org/10.5755/j01.u.66.2.529

혼-타의 수평틈새가 캐비테이션에 미치는 영향에 관한 수치적 연구

AbstractRecently, as container ships become larger and faster, rudder cavitations are more frequently observed near the gap between the horn and rudder pl ates of the ships to cause serious damages to the rudder surface of the ship. The authors already have suggested through a series of model experiments and numerical computation s that employment of an appropriate blocking device for gap flow may retard the gap cav itation. For examples, a cam device installed near the outer edges of the vertical gap or a water-injection device combined with a pair of half-round bars installed inside the gap can considerably reduce the gap cavitation. However, it is also found that effective bl ocking of the flow through the vertical gap results in growth of the cavitation near the horiz ontal gap instead. In the present study, effectiveness of the simultaneous blocking of th e flow through the horizontal and vertical gaps of a horn type rudder in minimizing the damag e by gap cavitation is studied. Additional blocking disks are inserted inside the hori zontal gaps on the top and bottom of the pintle block and numerical computations are carri ed out to confirm the combined effect of the blocking devices.

유체 공급장치를 활용한 간극유동 제어에 관한 수치적 연구

Recently, horn-type rudders are generally being used at high speed container ships and are frequently suffering from the cavitation occurs on the rudder surface in the vicinity of the gap between the horn and rudder plate. In the present study, a fluid supplying device is employed as to decrease the gap cavitation of the horn-type rudder. The device is devised to inject the water against the pressure side through the nozzle installed inside of the gap to control the gap flow. Numerical calculations are performed to investigate the effectiveness of the device and the results show that the device can noticeably reduce the gap cavitation. The rates of water injection for achievement of the maximum retardations of gap flow are also sought.

Experimental study on the gap entrance profile affecting rudder gap cavitation

The unsteady cavity patterns around the gap of the conventional and newly developed semi-spade rudders for marine ships are visualized qualitatively using a high-speed CCD camera. Time-resolved PIV analysis is also performed with the bubble tracers to study the flow behavior over the rudder surface. In addition, pressure measurements are conducted on the rudder surface and inside the gap to find out the flow characteristics around the gap entrance of the rudder. Both the rudders are tested without a propeller wake at the various cavitation numbers and at the rudder deflection angle of −8°⩽ θ⩽10°. The strong cavitation patterns around the conventional rudder gap are significantly reduced by adopting a newly developed entrance profile, and a time-resolved velocity field is found to be very effective in catching the vortical cavity flow around the rudder gap. The stagnation point near the gap entrance of the conventional rudder can cause unsteady cavity flow. However, the developed rudder has very stable pressure distribution along the horn surface and decreases the pressure inside the gap because of the modification of the gap entrance. The pressure distribution around the gap of the suction side is closely related to the variation of the rudder deflection angle. The cavitation inception speed is delayed by about 4 knots in the angle range of −5°⩽ θ⩽5° by employing the developed profile of the gap entrance.

Simulation of flow-over processes and calculation of strength characteristics of controls for vehicles with ring-propeller propulsors

The results of experimental investigations of the flow of aerodynamic controls for aerosleds in a subsonic flow are presented. The basic flow structures are revealed, and the aerodynamic characteristics of the rudder surface and the ring-rudder system under shading conditions are obtained. Recommendations for the calculating the aerodynamic coefficients of rudder surfaces in a vortex wake are given.

Semi-spade 타의 간극 캐비테이션에 대한 실험적 연구

The horn and movable parts around the gap of the conventional semi-spade rudder are visualized by high speed CCD camera with the frame rate of 4000 fps (frame per second) to study the unsteady cavity pattern on the rudder surface and gap. In addition, the pressure measurements are conducted on the rudder surface and inside the gap to find out the characteristics of the flow behavior. The rudder without propeller wake is tested at the range of <TEX>$1.0{\leq}{\sigma}_v\;1.6$</TEX> and at the rudder deflection angle of <TEX>$-8{\leq}{\theta}{\leq}10^{\circ}$</TEX>. The time resolved cavity images are captured and show strong cavitation around the rudder gap in all deflection angles. As the deflection angle gets larger, the flow separated from the horn surface increases the strength of cavitation. The accelerated flow along the horn decreases its pressure and the separated flow from the horn increases the pressure abruptly. The pressure distribution inside the gap reveals the flow moving from the pressure to suction side. In the negative deflection angle, the turning area on the movable part initiates the flow separation and cavitation on it.

History of In-Flight Simulationat General Dynamics

General Dynamics‐Advanced Information Systems (GDAIS) (formerly Veridian) has been the primary innovator, developer, and operator of in-flight simulators in the United States, as well as the rest of the world, since 1947. Though other agencies and countries have developed their own in-flight simulators, the focus is on GDAIS accomplishments in this field. In-flight simulation puts the pilot in the real flight environment and has been used in the development of new aircraft, research of flying qualities and flight-control systems, and training of pilots and engineers in these areas. More recent uses have been in the field of display systems and as avionics test beds. Early technologies that led to the development of variable stability aircraft and their earlier applications, are described first, followed by GDAIS’s history in the development and utilization of in-flight simulation, starting in 1949 with the first flight of the F4U-5 and its auxiliary rudder surface, up to the present with the five-degree-of-freedom F-16 Variable Stability In-Flight Simulator and Test Aircraft. Specific case studies are presented that describe the development and distinctive features of each of the GDAIS in-flight simulators and some of the more significant applications of these unique tools are highlighted.

선미 후류에서 작동하는 혼타의 압력분포에 관한 연구

Hull-propeller-rudder interactions are studied by the iterative computational procedures. Hull effects on the propeller are reflected through the effective velocities computed by the vortex ring method which used the measured nominal wake as input data. A potential based panel method has been developed to solve the propeller-rudder interactions using the obtained effective velocities. Steady flow characteristics around the rudder surface can be obtained by computing the induced velocities on the rudder by the propeller and vice versa are computed by the iterative manner until the converged solutions are obtained. Flow characteristics around the propeller and the rudder are measured by Laser Doppler Velocimetry(L.D.V.) in large cavitation tunnel at Samsung Heavy industries. The gap flow model is adopted to solve the characteristics of the horn rudder. Numerical results are compared with the experimental values and the computed velocity fields and pressure distributions with rudder angle on the horn rudder surface show good agreement with measured ones in large cavitation tunnel.

A Twisted Rudder for Reduced Cavitation

A rudder operating behind a propeller can experience large onset flow angles along the rudder span. At a given speed, the maximum rudder angle before cavitation is substantially higher in turning to one direction than to the opposite side. At high speeds, rudders can experience severe surface cavitation, even at zero degree rudder deflection angle. Observation from full-scale trials and dry dock inspection of a surface ship combatant show that rudder cavitation is a real problem in terms of ship operation and maintenance. It is shown in this paper that cavitation inception and erosion problems associated with the existing fleet rudders can be avoided or reduced by using the concept of a twisted rudder. A fleet rudder can be twisted along its span to align the incoming flow. The twisted rudder model has been designed, fabricated, and tested in the Navy's Large Cavitation Channel (LCC). Two-component Laser Doppler Velocimetry (LDV) was used to measure the field velocity and inflow angles in the propeller slipstream. A dynamometer and a series of pressure taps were used to measure rudder lift, drag and pressure distributions on the rudder surface. To evaluate the effect of twist angles on rudder performances, a full-scale rudder, designated the non-twisted rudder, has also been fabricated and tested back-to-back in the LCC with the twisted rudder for direct comparison. The advantages of using a twisted rudder to improve cavitation performance are presented in this paper.