The swerve response of fin- and spin-stabilized projectiles to control mechanism inputs is sometimes not intuitive. This paper seeks to explain the basic parameters that govern the swerve of projectiles excited by control inputs. By modeling the overall effect of a generalized control mechanism as a nonrolling reference frame force applied to a point on the projectile, general expressions for swerve are obtained in terms of basic vehicle parameters. These compact expressions are used to show that maximum swerve response for a fin-stabilized projectile is achieved when the force is applied near the nose of the projectile, whereas maximum swerve response for a spin-stabilized projectile is achieved when the force is applied near the base of the projectile.

Simplified Projectile Swerve Solution for General Control Inputs

Flapping flight has the potential to revolutionize micro air vehicles (MAVs) due to increased aerodynamic performance, improved maneuverability, and hover capabilities. This paper presents the design of a robotic flapping wing mechanism for use in general studies involving flapping flight and laboratory-based experimental optimization of flapping trajectories. The design allows for dynamic adjustment of flapping trajectories in air or liquids with three rotational degrees of freedom on each wing. The design, instrumentation, and control of the mechanism are discussed, and experimental characterization of the mechanism's performance is presented. Preliminary trajectory optimization using a Box-Behnken design approach is used and shows successful parameter optimization. The limitations of the current mechanism are addressed. A survey of flapping mechanisms is presented.

https://journals.sagepub.com/doi/pdf/10.1260/1756-8293.4.1.31

A Differentially Driven Flapping Wing Mechanism for Force Analysis and Trajectory Optimization

Traditional flapping-wing robots (FWRs) obtain lift and thrust by relying on the passive deformation of their wings which cannot actively fold or deform. In contrast, flying creatures such as birds, bats, and insects can maneuver agilely through active folding or deforming their wings. Researchers have developed many bio-inspired foldable or deformable wings (FDWs) imitating the wings of flying creatures. The foldable wings refer to the wings like the creatures’ wings that can fold in an orderly manner close to their bodies. Such wings have scattered feathers or distinct creases that can be stacked and folded to reduce the body envelope, which in nature is beneficial for these animals to prevent wing damage and ensure agility in crossing bushes. The deformable wings refer to the active deformation of the wings using active driving mechanisms and the passive deformation under the aerodynamic force, which functionally imitates the excellent hydrodynamic performance of the deformable body and wings of the creatures. However, the shape and external profile changes of deformable wings tend to be much smaller than that of folding wings. FDWs enable the FWRs to improve flight degree of flexibility, maneuverability, and efficiency and reduce flight energy consumption. However, FDWs still need to be studied, and a comprehensive review of the state-of-the-art progress of FDWs in FWR design is lacking. This paper analyzes the wing folding and deformation mechanisms of the creatures and reviews the latest progress of FWRs with FDWs. Furthermore, we summarize the current limitations and propose future directions in FDW design, which could help researchers to develop better FWRs for safe maneuvering in obstacle-dense environments.

Bio-inspired flapping wing robots with foldable or deformable wings: a review

Pressure measurements over flapping wings are less commonly available due to the difficulties associated with instrumenting them. This represents an important limitation of the aerodynamic data available for the development of self-contained flapping wing vehicle autopilots and for researchers working on the aerodynamics of bio-inspired flapping wings. This paper describes the design, construction, and testing of a customized flap stand, and a distributed pressure sensing system embedded in a set of rigid flapping wings to provide high speed ‘on-board’ flow measurements. While the hovering condition is the main focus, the setup is applicable to forward flight conditions as well. Data processing techniques are described along with the method used to measure pressure distributions over the wings. A series of flap tests were conducted in still air, with pressures measured only in air and force and torque measurements taken both in air and in a vacuum. Comparisons between the pressure-based estimates of aerodynamic loads and direct measurements taken by the force instrumentation are presented. The comparisons suggest the pressure-based system provides reasonable estimates of aerodynamic loads but is limited by the frequency response of the pressure lines used.

/pdf/experimental-investigation-of-the-pressure-force-and-torque-3dg1fjrmb9.pdf

Experimental investigation of the pressure, force, and torque characteristics of a rigid flapping wing

Measurements of aerodynamic forces over flapping wings are challenging due to unsteady flowfields and rapidly changing structural loads. This represents an important limitation to the aerodynamic data currently available to researchers working on the aerodynamics of bioinspired flapping wings. This paper proposes the use of pressure-based instrumentation for flapping-wing testing and documents the comparison of two experimental methods to measure the aerodynamic lift generated during the stroke of a rigid flapping wing. The first approach uses a force transducer to measure the forces in air and vacuum, and the second approach uses pressure measurements taken on the surfaces of the wing. The results from both methods are used to validate each other and provide experimental data for a test case with easily simulated conditions. This paper describes the design of the test hardware required, including a custom flap stand, flap mechanics, and instrumented wing construction techniques. A series of flap tests we...

Experimental Characterization of Lift on a Rigid Flapping Wing

This paper describes a series of experiments using a flapping wing mechanism. Force measurements were combined with high speed photography for two sets of flexible wings. The aerodynamic forces generated by flexible membrane type wings were measured using a two degree of freedom force balance constructed during the course of these experiments which measured the aerodynamic forces of lift and thrust. Lift and thrust measurements were acquired as the mechanism flapped the flexible wings for multiple cases, and the two most interesting conditions were explored in more detail. These two conditions consisted of a zero velocity free stream condition and a forward flight condition of 5 m/s. For these two conditions, high-speed video of the flapping wing was taken. The images from the video were also correlated with cycle averaged aerodynamic forces produced by the mechanism. Several observations were made regarding the behavior of flexible flapping wings that should aid in the design of future flexible flapping ...

https://journals.sagepub.com/doi/pdf/10.1260/175682909789996168

Force measurements and flow visualization for a flexible flapping wing mechanism

Multiple actuator concepts for guiding a subsonic projectile were screened in a series of wind tunnel tests. Both mechanical protrusion type devices and jet based devices were tested at various subsonic Mach numbers. Pressure measurements were made on an instrumented double scale model representative of a 25 mm grenade. Each of the devices changed the flow field around the model projectile in the wind tunnel which in turn changed the surface pressure distribution. The measured surface pressures were used to estimate the forces and moments developed as a result of the actuator. In addition, actuation times for several devices to were measured in a series of bench tests in order to assess their relative utility on an actual round. Particular emphasis was placed on developing fast actuators that could be used for spin stabilized rounds. The results indicate that it is possible to generate forces that can be used to guide subsonic rounds, however, developing actuators with sub millisecond response times remains a challenge.

Mechanical and Jet Actuators for Guiding a Small Caliber Subsonic Projectile

In this paper the use of multiple squib charges as actuators for the guidance of transonic projectiles is explored. A series of experiments were developed to simulate squib explosions and these were compared with a limited set of measurements from actual squibs. The rapid release of high pressure gas was used to both generate thrust directly and to actuate a small guidance pin. The thrust developed, chamber pressure, drain time, as well as the rise and fall time of the pin were studied over a range of several pressures and configurations. Experimental tests were conducted at the Georgia Tech Research Institute and the Army Research Lab. Force and pressure measurements, impact response, and high-speed video captures were acquired for analysis and comparison. The results show that it is both possible to create a sub-millisecond thruster and to actuate a mechanical pin into an oncoming flow in less than a millisecond. However, further experimentation is needed to refine the experimental setup and obtain the smallest possible actuation times.

Investigation of Explosive Charge Driven Actuators for Guided Projectiles

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Papers

Force measurements and flow visualization for a flexible flapping wing mechanism

Mechanical and Jet Actuators for Guiding a Small Caliber Subsonic Projectile

Investigation of Explosive Charge Driven Actuators for Guided Projectiles