Emergency Flight Control Based on the Fan Wing

FanWing has been taken to the visual field because of its performance combination of fixed-wing aircraft and helicopter. Its flight mode is currently limited mainly by a remote control, while the research of automated flight control is on the rise. The fan wing could offer lift, thrust, and the additional pitch moment for longitudinal control. At the same time, the roll moment and the yaw moment can be generated by the differential rotation of the cross-flow fan to realize the lateral control. It provides the possibility for its emergency flight control when the aerodynamic control becomes inefficient at a low speed. The difficulties in designing the emergency control system in both the longitudinal and lateral controls are analyzed. And it emphasizes the importance of selecting its center of gravity and the emergency control method of longitudinal control in engineering. The simulation results show that as an emergency flight control system, fan wing control is feasible. The study of the fan wing control will provide a reference solution for its further engineering applications.

An Experimental Analysis of Active Pitch Control for an Assault Amphibious Vehicle Considering Waterjet-Hydrofoil Interaction Effect

The present study aims to reduce the pitch motion of an assault amphibious vehicle system in seaways by waterjet impeller revolution rate control. A series of seakeeping tests were performed in a towing tank with a 1/4.5-scale model. This vehicle is manufactured as a box-shaped hull, and since an appendage that generates lift force is attached, the amount of change in pitch motion is large according to the forward speed. For pitch motion reduction, the impeller revolution rate and resultant pitch moment were controlled through a proportional-integral-derivative controller. Improvements in seakeeping performance were examined in both regular and irregular conditions by the model tests in terms of root mean square of pitch motion. The tuned controller decreased pitch motion by more than 60%.

Analysis on controllability and stability of quad-tilt-rotor aircraft in helicopter mode

The controllability and stability of quad-tilt-rotor aircraft in helicopter mode are modeled and analyzed, which will provide a theoretical guidance for the subsequent control system design. First of all, the flight dynamics model is established considering rotor-wing interference and verified with relevant experiments. Then, a control strategy for helicopter mode is proposed with trim characteristic analysis. Finally, corresponding control efficiency and cross coupling are calculated and analyzed along with characteristics of the stability derivatives and eigenvalues. The results show that the value of heading control efficiency is much smaller than that of other channels. The longitudinal force and pitch moment caused by vertical control input increase with the increase of the velocity. Yawing moment caused by lateral control input shows similar variations. The velocity stability becomes worse with the increase of the velocity. The stability of all other modes is augmented as velocity increases except the spiral mode.

Motion Analysis of Butterfly-Style Flapping Robot Using CFD Based on 3D-CAD Model and Experimental Flight Data

In this paper, a computational fluid dynamics (CFD) analysis system based on a 3D-CAD model of a butterfly-style flapping robot using its experimental flight data is proposed. The butterfly-style flapping robot can control its attitude by changing its flapping and lead-lag angles; however, measuring the lift, thrust, and body pitch moment directly during flight is difficult. In the case of the flight motion analysis of insects, the state of flight has been photographed, and numerical analysis has been performed to obtain the flow field around the wings. However, when performing the motion analysis of hardware, it is difficult to reflect the shape of the body accurately using this method. In this study, a CFD analysis system considered the shape of the developed butterfly-style flapping robot as 3D-CAD data and analyzed the flow field around the wings using the experimental flight data of the hardware. The results of motion analysis showed that the attitude during flight differs due to the difference in lifts and body pitch moments in the flight experiment data of the hardware with different neutral angles of the flapping wings.

Analysis of the Magnus Moment Aerodynamic Characteristics of Rotating Missiles at High Altitudes

The Magnus moment characteristics of rotating missiles with Mach numbers of 1.3 and 1.5 at different altitudes and angles of attack were numerically simulated based on the transition SST model. It was found that the Magnus moment direction of the missiles changed with the increase of the angle of attack. At a low altitude, with the increase of the angle of attack, the Magnus moment direction changed from positive to negative; however, at high altitudes, with the increase of the angle of attack, the Magnus moment direction changed from positive to negative and then again to positive. The Magnus force direction did not change with the change of the altitude and the angle of attack at low angles of attack; however, it changed with altitude at an angle of attack of 30°. When the angle of attack was 20°, the interference of the tail fin to the lateral force of the missile body was different from that for other angles of attack, leading to an increase of the lateral force of the rear part of the missile body. With the increasing altitude, the position of the boundary layer with a larger thickness of the missile body moved forward, making the lateral force distribution of the missile body even. Consequently, Magnus moments generated by different boundary layer thicknesses at the front and rear of the missile body decreased and the Magnus moment generated by the tail fin became larger. As lateral force directions of the missile body and the tail were opposite, the Magnus moment direction changed noticeably. Under a high angle of attack, the Magnus moment direction of the missile body changed with the increasing altitude. The absolute value of the pitch moment coefficient of the missile body decreased with the increasing altitude.

Effect of passenger uncertainty on the inertial properties of a railway coach

The rotation transformation matrix and translation transformation matrix are derived. They are combined to study the variation of inertial properties of the loaded coach with seating and standing passengers. After that, a CRH2 (China Railway Highspeed) motor coach and Chinese adults in statistical terms are illustrated for precise modelling. It is indicated that CG (Center of Gravity) positions and moments of inertia are all close to linear varying with passenger numbers but at different slopes before and after full-load. It is also found that yaw moment of inertia and pitch moment of inertia are highly correlated. The mass has larger correlation on CG z than CG x and CG y, and larger correlation on roll moment of inertia than yaw and pitch moment of inertia. It may offer some instructions and reference for more realistic simulation of railway vehicle dynamics and measure experiments.

Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

The Murphy number: how pitch moment of inertia dictates quadrupedal walking and running energetics

Many quadrupedal mammals transition from a four-beat walk to a two-beat run (e.g. trot), but some transition to a four-beat run (e.g. amble). Recent analysis shows that a two-beat run minimizes work only for animals with a small pitch moment of inertia (MOI), though empirical MOI were not reported. It also remains unclear whether MOI affects gait energetics at slow speeds. Here I show that a particular normalization of the pitch moment of inertia (the Murphy number) has opposite effects on walking and running energetics. During walking, simultaneous fore and hindlimb contacts dampen pitching energy, favouring a four-beat gait that can distribute expensive transfer of support. However, the required pitching of a four-beat walk becomes more expensive as Murphy number increases. Using trajectory optimization of a simple model, I show that both the walking and slow running strategies used by dogs, horses, giraffes and elephants can be explained by work optimization under their specific Murphy numbers. Rotational dynamics have been largely ignored in quadrupedal locomotion, but appear to be a central factor in gait selection.

On the Accuracy of an Analytical Solution to Model Wave-Induced Loads on an Underwater Vehicle in Real-Time

The accuracy of an existing analytical solution for modeling the linear, first-order wave- induced loads on a fully submerged body is investigated. The accuracy is assessed for the situation where the underlying theoretical assumptions are met and the sensitivity of the accuracy to these assumptions is also explored. The accuracy was quantified by comparing the analytical solutions to experimental measurements from a tow tank with wave generation capability. The assessment showed that when all the assumptions are met, the heave and surge forces are predicted quite accurately but the pitch moment is over predicted. The results also showed that the deeply submerged assumption is met as long as the body does not cause a disruption of the passing wave on the free surface. The slenderness and end face curvature assumptions are also quite relaxed and the curvature assumption only affects the pitch moment accuracy. The most stringent assumption appears to be the body-of revolution assumption which can cause all three loads to be predicted poorly. The analytical solution appears to be accurate over a large parameter space and could be incorporated as a wave disturbance model into a virtual environment used to develop control and autonomy of unmanned underwater vehicles.