Lift Force Measurements Research Articles

Reconstruction of Unsteady Lift Force Measurements Using Non-Dimensional Scaling Optimization

Reconstruction of Unsteady Lift Force Measurements Using Non-Dimensional Scaling Optimization

The effect of variable rotary motion of a flapping wing rotor on its aerodynamic performance based on an improved unsteady vortex ring method

In the previous aerodynamic analysis using a potential flow-based unsteady aerodynamic model for the flapping wing rotor (FWR), the average rotary velocity and flapping frequency together with the flapping and twist angles are usually taken as the FWR kinematics of motion. In the present study, an unsteady vortex ring method (UVRM) is developed to take the rotary velocity variation of the FWR during the flapping motion into account based on 3D unsteady potential flow theory. The UVRM is validated by comparing with the published results of a flapping wing and an FWR model. An FWR test model and the corresponding experimental platforms including a wing motion tracking system and a force measurement system are built to measure the FWR motion and associated forces. Three FWR test cases of different input voltages and kinematics of flapping motion are considered to measure the aerodynamic forces and compare with the UVRM results. The results show that the differences between the measured and pre-set flapping angles (-50°∼ 20°) for the FWR are negligible for all the cases, but the differences in the variation amplitudes of the measured twist angle and the corresponding pre-set rigid twist angles can be as much as about 15°. Also, the FWR rotary velocity varies dramatically during a flapping cycle. For one of the cases with the -10°∼30° pre-set twist angle and 4 V input voltage, the difference between the maximum and minimum rotary speed is about 1451°/s, which makes a significant effect on the FWR aerodynamic performance. The results also show that the calculated lift forces using the UVRM and the measured real-time rotary speeds during a flapping motion are very close to the experimental results. While the calculated results by taking the FWR's average rotary speeds show apparent differences (up to about 25%) from the measured lift forces in most of the cases. Overall, the UVRM provides an efficient method for the FWR aerodynamic analysis with higher accuracy by taking the effect of variable rotary motion and twist angle of the FWR during a flapping cycle into account.

Neural Partial Differentiation for Parameter Estimation of Flexible Aircraft Dynamics

Although the parameter estimation methodologies had been successfully applied for the rigid aircraft dynamics, the aircraft with high degree of flexibility poses challenges to determine the appropriate aeroelastic models for inclusion in the parameter estimation algorithms. Application of the neural networks for the aerodynamic modeling and parameter estimation of an aeroelastic aircraft (or flexible aircraft) is addressed in this paper. A neural network with the scaled conjugate gradient learning algorithm is used for modeling lift and pitching moment coefficients. The partial differentiation of the neural network output is carried out for the estimation of equivalent parameters of an aeroelastic aircraft. It is demonstrated that a reasonable model and estimates of the equivalent parameters for the aeroelastic aircraft are possible with the neural partial differential method by using the measured motion and control variables, without any need for postulating the coupled equations of motion or initialization of the parameters to be estimated. The proposed approach reduces the large number of parameters for aeroelastic aircraft dynamics into fewer equivalent parameters, and this methodology does not require the measurements of the elastic deflections or their derivatives. The neural partial differential method is applied to the simulated flight data of an aeroelastic aircraft for the longitudinal dynamics. The performance of the neural partial differential approach is compared with the estimates obtained from the other methods like classical estimation methods, analytical computation, and values given in the literature for rigid body modeling. The performance is also validated by comparing the measured lift force and pitching moment coefficients with the neural predicted and neural reconstructed coefficients using the estimates obtained through the neural partial differential approach.

Generalized lift force model under vortex shedding

This paper proposes a generalized model for vortex shedding around a static cylinder. This model is a first step to bridge the gap between two existing families of Vortex Induced Vibration (VIV) models , namely (1) stochastic spectral models and (2) wake-oscillator models with coupled fluid and structural equations. The first family is experimentally-based while the models of the second family typically rely on theoretical and phenomenological concepts. These models use a Van der Pol, Rayleigh or a combination of both oscillators for the lift equation. The proposed model generalizes these models by combining all third degree terms in the case of a static model, i.e. by considering the equation of the fluid oscillator only. It is possible to enrich existing models with a more complex parametric model because its parameters are identified from experimental data. A second specificity of the proposed model stems from the observation that, for a static cylinder in low turbulence flow, the envelope of the measured lift force is not perfectly mono-harmonic, nor deterministic. Turbulence in the wake is expected to create fluctuations in the lift envelope. In the proposed model, stochasticity is consequently introduced to reproduce these fluctuations. It is based as an additive exogenous noise as an input to the generalized shedding model, using a Von Karman spectrum. Its coefficients are adjusted so that the model reproduces the probability density function of the measured lift envelope (and its power spectral density). The methodology is applied to Wind Tunnel data of a static circular cylinder in subcritical and postcritical regimes. This set of data is used to identify the coefficients of non-linear terms and Von Karman spectrum. The lift fluctuation coefficient generated with the model matches results available in the literature for the considered regimes. This work focuses on a methodology to obtain a generalized vortex shedding model from experimental data measured on a static body. It can be applied to other cylinder cross-sections or even extended to cylinders arranged in tandem.

Pad Correction Estimation around 5 Belt Wind Tunnel Wheel Belts Using Pressure Tap Measurement and Mathematical Pressure Distribution Model

<div class="section abstract"><div class="htmlview paragraph">5 belt wind tunnels are the most common facility to conduct the experimental aerodynamics development for production cars. Among aerodynamic properties, usually drag is the most important development target, but lift force and its front/rear balance is also important for vehicle dynamics. Related to the lift measurement, it is known that the “pad correction”, the correction in the lift measurement values for the undesirable aerodynamic force acting on wheel belt surface around the tire contact patch, must be accounted.</div><div class="htmlview paragraph">Due to the pad correction measurement difficulties, it is common to simply subtract a fixed amount of lift values from measured lift force. However, this method is obviously not perfect as the pad corrections are different for differing vehicle body shapes, aerodynamic configurations, tire sizes and shapes. As an alternative, CFD is a possible solution to estimate pad correction, but it is still not practical to calculate all cases of the development due to the calculation cost and time.</div><div class="htmlview paragraph">One existing wind tunnel test measurement procedure is to utilize special arrangements in the car restraint apparatus. But this method requires a preparation test apart from the actual aerodynamic test run, which is not ideal in terms of wind tunnel test productivity.</div><div class="htmlview paragraph">In this paper, a new method to estimate the pad correction for 5 belt wind tunnel is proposed, introducing a newly developed mathematical model of pressure distribution on the belt surface. With this model, it is possible to estimate pad correction values without any other preparation test.</div><div class="htmlview paragraph">In order to develop this method, CFD analysis with tire rotation condition was made for 10 cases/6 vehicles. For the validation of CFD itself, these CFD results were compared with the pressure distribution data measured in a single belt wind tunnel.</div><div class="htmlview paragraph">The pressure distribution model was created ensuring its mathematically generated distribution can reproduce 10 cases of CFD results with a unified expression, by changing its 68 parameters. Also, these parameters were reduced to 7, in order to enable parameters estimation by multiple linear regression (MLR) from 42 pressure tap point data around the 5 belt wind tunnel wheel belt.</div><div class="htmlview paragraph">For the verification of the method, CFD results were used. The pad correction values were estimated from 42 pressure tap point data taken from the CFD results, and compared with directly calculated pad correction values from the same CFD results.</div><div class="htmlview paragraph">The verification of the estimation accuracy showed within error variation widths of 0.007 ~ 0.008 (widths between maximum and minimum errors) of pad correction for <i>CL<sub>front</sub></i> or <i>CL<sub>rear</sub></i> correction values. Also, the error variation widths for the same car were 0.001 ~ 0.003 for <i>CL<sub>front</sub></i> pad correction, which is enough to predict its configuration difference trend.</div></div>

PRESSURE DISTRIBUTION DUE TO STERN TAB DEFLECTION AT MODEL SCALE

Trim tabs form an important part of motion control systems on high-speed watercraft. By altering the pitch angle, significant improvements in propulsion efficiency can be achieved by reducing overall resistance. For a ship in heavy seas, trim tabs can also be used to reduce structural loads by changing the vessel orientation in response to encountered waves. In this study, trials have been conducted in the University of Tasmania hydraulics laboratory using a closed- circuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the full- scale INCAT Tasmania 112 m high-speed wave-piercer catamaran. The model was designed for total lift force measurement and pressure tappings allowed for pressures to be measured at fixed locations on the underside of the hull and tab. This investigation examines the pressures at various flow velocities and tab deflection angles for the case of horizontal vessel trim. A simplified two-dimensional CFD model of the hull and tab has also been analysed using ANSYS CFX software. The results of model tests and CFD indicate that the maximum pressure occurs in the vicinity of the tab hinge and that the pressure distribution is long-tailed in the direction forward of the hinge. This accounts for the location of the resultant lift force, which is found to act forward of the tab hinge.

Lift Force Measurement in Landing Gears Dynamic Tests

Abstract As one of the key components of the aircraft in terms of both operation and safety landing gears are of special interest of the aviation regulations. During the touch down landing gears need to dissipate as much of the energy as possible maintaining the lowest volume and weight as required by the aviation design restrictions. According to the aviation regulations landing gears have to be tested in order to prove the dissipation of the calculated landing energy and to evaluate actual loads acting on the fuselage via the mounting nodes of the landing gears. The tests need to replicate the real landing conditions as closely as possible – including the lift force (or lift) acting on the aircraft during landing. The lift force during landing is not sufficient to maintain the aircraft in flight but acts as the relief force to the aircraft weight resulting in lowering loads applied to the fuselage and decreasing landing energy needed to be dissipated. The lift force or lift has to be taken into account during laboratory tests of landing gears. The lift force needs to be simulated in all of the landing gears dynamic tests: performance optimization, proof of the operation for the certification, and the fatigue evaluation. There are two main methods of applying the lift during the tests: equivalent/effective mass or direct lift application. The latter is used at the Landing Gear Laboratory of the Lukasiewicz Research Network – Institute of Aviation (where author works on daily basis). The lift is applied by the pneumatic cylinders built in the test stand. Until recently the control of the lift force value was performed indirectly by the measurement of the pressure inside the pneumatic system. Recently the experimental direct measurement system using force transducers was introduced in order to directly measure the lift force during every test. In the presented paper, the author gives an overview of the lift force measurement system including its design and the results of the preliminary use evaluation.

Aerodynamic effects on an emulated hovering passerine with different wing-folding amplitudes

Bird flight involves complicated wing kinematics, especially during hovering flight. The detailed aerodynamic effects of wings with higher degrees of freedom (DOFs) remain to be further investigated. Therefore, we designed a novel multiarticulate flapping-wing robot with five DOFs on each wing. Using this robot we aimed to investigate the more complicated wing kinematics of birds, which are usually difficult to test and analyze. In this study the robot was programmed to mimic the previously observed hovering motion of passerines, and force measurements and particle image velocimetry experiments. We experimented with two different wing-folding amplitudes: one with a larger folding amplitude, similar to that of real passerines, and one with only half the amplitude. The robot kinematics were verified utilizing direct linear transformation, which confirmed that the wing trajectories had an acceptable correlation with the desired motion. According to the lift force measurements, four phases of the wingbeat cycle were characterized and elaborated through camera images and flow visualization. We found that the reduction in folding amplitude caused a higher negative force during upstrokes and also induced a greater positive force at the initial downstroke through ‘wake capture’. This could increase the vertical oscillation while hovering despite a minor increase in average force production. This phenomenon was not observed during forward flight in previous studies. Our results provide a critical understanding of the effect of wing folding which is required for designing the wing kinematics of future advanced flapping-wing micro aerial vehicles.

Lift forces on three-dimensional elastic and viscoelastic lubricated contacts

When an object suspended in fluid moves past a soft substrate it experiences a lift force due to the deformability of the substrate. Here, we find this lift force analytically for a general elastic or viscoelastic substrate. For oscillatory relative motion, the lift force is time-dependent and its temporal Fourier modes carry signatures of the viscous and elastic components of the substrate response. The theory may be useful to characterize the mechanical properties of soft materials without solid-to-solid contact via lift force measurements.

Unsteady aerodynamics of a wing in a novel small-amplitude transverse gust generator

A novel small-amplitude high-frequency gust generator has been developed that works by oscillating a small fence on the wind tunnel wall. The gust generator produces approximately constant local angle of attack in the chordwise direction. Due to the challenges of measuring small and slightly non-uniform gust angles the gust generator was calibrated using direct lift measurements on a symmetric wing set at zero geometric angle of attack. Unsteady lift force measurements and the Theodorsen's theory were used for the dynamic calibration of the gust angle. At nonzero geometric angles of attack, if the wing’s effective angle of attack remains below the stall angle, unsteady lift closely follows the static lift curve with very small hysteresis. Beyond the stall angle, dynamic stall and larger lift hysteresis are observed. Interestingly, in this regime, if flow is separated and a separation bubble is maintained on the wing throughout the cycle then increasing frequency reduces lift hysteresis. The slope of the lift curve, averaged over the cycle, may be greater than that of attached flow. The gust response is more sensitive to maximum effective angle of attack than the reduced frequency or the reduced pitch rate. The normalized lift change is much larger for separated flows than for attached flows.Graphic abstract

Lift Equivalence and Cancellation for Airfoil Surge–Pitch–Plunge Oscillations

A NACA 0018 airfoil in freestream velocity is oscillated in longitudinal, transverse, and angle-of-attack directions with respect to the freestream velocity, known as surge, plunge, and pitch. The lift-based equivalence method introduces phase shifts between these three motions to construct in-phase sinusoidal components for maximum lift, waveform construction. Lift cancellation is also determined with the exact negative pitch and plunge motion amplitudes found from the equivalence method to achieve out-of-phase wave destruction. Lift cancellation occurs when a combination of these motions is sought to obtain a constant lift magnitude throughout the oscillation cycle. To achieve both equivalence and cancellation of lift, a prescribed pure pitch amplitude through the Theodorsen theory equates the corresponding equivalent plunge amplitude and pitch–plunge phase shift. These Theodorsen, linear superposition findings of pitch–plunge are leveraged toward the Greenberg theory to determine a closed-form, surge–pitch–plunge solution through the addition of a surge–plunge phase shift and optimal surge amplitude for lift cancellation. The lift cancellation surge–pitch–plunge amplitudes define the equivalence amplitude investigated here and theoretically limit the experiment to combinations of the first lift harmonic of the Greenberg theory. The analytical results are then compared with experimental lift force measurements and dye visualization. The normalized lift differences due to unsteady wake and boundary-layer behavior are examined to explore the extents of the Greenberg theory for these cases of lift-based equivalence and cancellation.

Experimental Analysis of the Lift Force Discontinuity of a Spring-Loaded Pressure Safety Valve Working in Pneumatic Service

Abstract Pressure safety valves (PSVs) are designed to provide ultimate protection for pressure systems. For design or optimization purpose, it is necessary to study the lift force exerted on the valve disk. Under special valve configuration, the lift force shows discontinuity with the increment of valve opening, which is an undesirable phenomenon because it may be the cause of some serious problems, such as unstable valve operations. To study their characteristics in depth, experimental investigations are conducted in this paper. For lift force measurement, an experimental rig was specially designed and built. A series of force tests were carried out, and the result indicates that two variables, namely, the position of the adjustment ring and the thickness of the valve nozzle, have great influence on lift force; under certain valve configurations, the lift force has a discontinuous performance; for different configurations, degrees and positions of force discontinuities are very different; lift forces are linear functions of the inlet pressures, and the slopes of the force changes are similar for different valve openings.

Bioinspired Flapping-Wing Robot With Direct-Driven Piezoelectric Actuation and Its Takeoff Demonstration

In this letter, we present the design and the performance of a prototype bioinspired flapping-wing micro aerial vehicle with piezoelectric direct-driven actuation. This type of actuation is superior in terms of structural simplicity because it does not include any transmission mechanism. Instead, a unimorph piezoelectric actuator directly drives the wing. We designed and fabricated a two-wing prototype with a wingspan of 114 mm and successfully demonstrated takeoff using an external power source under a one-degree-of-freedom constraint. The total mass of the prototype was 598 mg, and the maximum measured lift force was 6.52 mN (665 mgf) at a driving voltage of 100 V. We achieved tethered flight using the proposed direct-driven piezoelectric actuator considering the constraint.

Assisting hand function after spinal cord injury with a fabric-based soft robotic glove

BackgroundSpinal cord injury is a devastating condition that can dramatically impact hand motor function. Passive and active assistive devices are becoming more commonly used to enhance lost hand strength and dexterity. Soft robotics is an emerging discipline that combines the classical principles of robotics with soft materials and could provide a new class of active assistive devices. Soft robotic assistive devices enable a human-robot interaction facilitated by compliant and light-weight structures. The scope of this work was to demonstrate that a fabric-based soft robotic glove can effectively assist participants affected by spinal cord injury in manipulating objects encountered in daily living.MethodsThe Toronto Rehabilitation Institute Hand Function Test was administered to 9 participants with C4-C7 spinal cord injuries to assess the functionality of the soft robotic glove. The test included object manipulation tasks commonly encountered during activities of daily living (ADL) and lift force measurements. The test was administered to each participant twice; once without the assistive glove to provide baseline data and once while wearing the assistive glove. The object manipulation subtests were evaluated using a linear mixed model, including interaction effects of variables such as time since injury. The lift force measures were separately evaluated using the Wilcoxon signed-rank test.ResultsThe soft robotic glove improved object manipulation in ADL tasks. The difference in mean scores between baseline and assisted conditions was significant across all participants and for all manipulated objects. An improvement of 33.42 ± 15.43% relative to the maximal test score indicates that the glove sufficiently enhances hand function during ADL tasks. Moreover, lift force also increased when using the assistive soft robotic glove, further demonstrating the effectiveness of the device in assisting hand function.ConclusionsThe results gathered in this study validate our fabric-based soft robotic glove as an effective device to assist hand function in individuals who have suffered upper limb paralysis following a spinal cord injury.

Two modes resonant combined motion for insect wings kinematics reproduction and lift generation

This paper presents an original concept using a two resonant vibration modes combined motion to reproduce insect wings kinematics and generate lift. The key issue is to design the geometry and the elastic characteristics of artificial wings such that a combination of flapping and twisting motions in a quadrature phase shift could be obtained. This qualitatively implies to bring the frequencies of the two resonant modes closer. For this purpose, a polymeric prototype was micromachined with a wingspan of 3 cm, flexible wings and a single actuator. An optimal wings configuration was determined with a modeling and validated through experimental modal analyses to verify the proximity of the two modes frequencies. A dedicated lift force measurement bench was developed and used to demonstrate a lift force equivalent to the prototype weight. Finally, at the maximum lift frequency, high-speed camera measurements confirmed a kinematics of the flexible wings with flapping and twisting motions in phase quadrature as expected.

An experimental study of an airfoil with a bio-inspired leading edge device at high angles of attack

Robust and predictable aerodynamic performance of unmanned aerial vehicles at the limits of their design envelope is critical for safety and mission adaptability. Deployable aerodynamic surfaces from the wing leading or trailing edges are often used to extend the aerodynamic envelope (e.g. slats and flaps). Birds have also evolved feathers at the leading edge (LE) of their wings, known as the alula, which enables them to perform high angles of attack maneuvers. In this study, a series of wind tunnel experiments are performed to quantify the effect of various deployment parameters of an alula-like LE device on the aerodynamic performance of a cambered airfoil (S1223) at stall and post stall conditions. The alula relative angle of attack, measured from the mean chord of the airfoil, is varied to modulate tip-vortex strength, while the alula deflection angle is varied to modulate the distance between the tip vortex and the wing surface. Integrated lift force measurements were collected at various alula-inspired device configurations. The effect of the alula-inspired device on the boundary layer velocity profile and turbulence intensity were investigated through hot-wire anemometer measurements. Results show that as alula deflection angle increases, the lift coefficient also increase especially at lower alula relative angles of attack. Moreover, at post stall wing angles of attack, the wake velocity deficit is reduced in the presence of alula device, confirming the mitigation of the wing adverse pressure gradient. The results are in strong agreement with measurements taken on bird wings showing delayed flow reversal and extended range of operational angles of attack. An engineered alula-inspired device has the potential to improve mission adaptability in small unmanned air vehicles during low Reynolds number flight.

Distinct contributions of explicit and implicit memory processes to weight prediction when lifting objects and judging their weights: an aging study.

Weight predictions used to scale lifting forces adapt quickly when repeatedly lifting unusually weighted objects and are readily updated by explicit information provided about weight. In contrast, weight predictions used when making perceptual judgments about weight are more resistant to change and are largely unaffected by explicit information about weight. These observations suggest that distinct memory systems underlie weight prediction when lifting objects and judging their weights. Here we examined whether these weight predictions differ in their reliance on declarative and nondeclarative memory resources by comparing the adaptability of these predictions in older adults, who exhibit relatively impaired declarative memory processes, to those in younger adults. In the size condition, we measured lift forces as participants repeatedly lifted a pair of size-weight inverted objects in alternation. To assess weight judgments, we measured the size-weight illusion every 10 lifts. The material condition was similar, except that we used material-weight inverted objects and measured the material-weight illusion. The strengths of these illusions prior to lifting, and the attenuation of the illusions that arise when lifting inverted objects, were similar for both groups. The magnitude of the change in the illusions was positively correlated with implicit memory performance in both groups, suggesting that predictions used when judging weight rely on nondeclarative memory resources. Updating of lifting forces also did not differ between groups. However, within the older group the success with which lifting forces were updated was positively correlated with working memory performance, suggesting that weight predictions used when lifting rely on declarative memory resources.

Instantaneous wing kinematics tracking and force control of a high-frequency flapping wing insect MAV

The superior maneuverability of insect flight is enabled by rapid and significant changes in aerodynamic forces, a result of subtle and precise change of wing kinematics. The high sensitivity of aerodynamic force to wing kinematic change demands precise and instantaneous feedback control of the wing motion trajectory, especially in the presence of various parameter uncertainties and environmental disturbances. Current work on flapping wing robots was limited to open-loop averaged wing kinematics control. Here we present instantaneous closed-loop wing trajectory tracking of a DC motor direct driven wing-thorax system under resonant flapping. A dynamic model with parameter uncertainties and disturbances was developed and validated through system identification. For wing trajectory generation, we designed a Hopf oscillator based central pattern generator with smooth convergence. Using the linearized model while treating the nonlinearity as disturbance, we designed a proportional-integral-derivative (PID) controller and a linear quadratic regulator (LQR) for instantaneous wing trajectory tracking at 24 Hz; Using the original nonlinear model, we designed a nonlinear controller to achieve robust performance at over 30 Hz. The control algorithms were implemented and compared experimentally on a 7.5 g Flapping Wing Micro Air Vehicle (MAV). The experiments showed that the PID and nonlinear controls resulted in precise trajectory tracking; while LQR controller tracked with less precision but with smaller input effort. In addition, the nonlinear control algorithm achieved better tracking of wing trajectories with varying amplitude, bias, frequency, and split-cycles while adapting to the variations on wing morphological parameters such as wing geometry and stiffness. Furthermore, the lift force measurements of the nonlinear control results were compared with those of open-loop average wing kinematics control commonly adopted in current designs.

Control of leading edge separation on airfoil using DBD plasma actuator with signal amplitude modulation

In this study, the separation control of an airfoil when a dielectric barrier discharge (DBD) plasma actuator is mounted on its leading edge was examined. Experiments were performed at a Reynolds number of approximately 67,000 with an external airflow of 10 m/s. The DBD plasma actuator was installed on an NACA 0015 airfoil with a 100 mm chord and 150 mm width at x/c = 0.025, where x was the vertical distance measured from the leading edge and c was the chord length. Lift force measurements, flow visualization and velocity measurements were conducted to investigate the performance of the DBD plasma actuator, which was driven by either pulse modulation with amplitude modulation (PM + AM) or pulse modulation only (PM). The PM + AM case was designed to consume the same amount of power as the PM case. The result showed that the PM + AM case improved the lift coefficient compared to the PM case for both St = 0.6 and St = 4.0. Under the stall control condition (angle of attack, α = 16°) and high angle of attack condition (α = 18°), the PM + AM case always demonstrated improved lift over the PM case; the improvement in lift was greater at α = 18° than at α = 16°. Flow visualization confirmed larger and stronger vortex shedding for the PM + AM case over the PM case.

Pressure Distribution due to Stern Tab Deflection at Model Scale

"Trim tabs form an important part of motion control systems on high-speed watercraft. By altering the pitch angle, significant improvements in propulsion efficiency can be achieved by reducing overall resistance. For a ship in heavy seas, trim tabs can also be used to reduce structural loads by changing the vessel orientation in response to encountered waves. In this study, trials have been conducted in the University of Tasmania hydraulics laboratory using a closedcircuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the fullscale INCAT Tasmania 112 m high-speed wave-piercer catamaran. The model was designed for total lift force measurement and pressure tappings allowed for pressures to be measured at fixed locations on the underside of the hull and tab. This investigation examines the pressures at various flow velocities and tab deflection angles for the case of horizontal vessel trim. A simplified two-dimensional CFD model of the hull and tab has also been analysed using ANSYS CFX software. The results of model tests and CFD indicate that the maximum pressure occurs in the vicinity of the tab hinge and that the pressure distribution is long-tailed in the direction forward of the hinge. This accounts for the location of the resultant lift force, which is found to act forward of the tab hinge."