Analytical Aerodynamic Model of Spanwise Flexible Flapping Wings in Forward Flight

Dynamic load due to gust for helicopter rotors directly affects the structural stress and flight performance. In case of gust, it may cause the loss of trust force or the increase of deflection for rotors. In current work, an effective coupled aeroelastic model based on a medium-deflection beam theory and a nonlinear unsteady aerodynamic model in the time domain were constructed. Three types of gust in vertical direction were added in the model. The dynamic response and structural load for helicopter rotors under three types of gust were calculated, respectively. Results indicated that when rotors suffer a gust in hover at downward direction, the thrust force on rotor disk would decrease significantly when the gust amplitude increases, which should be paid attention in the design. Among the three gust types with the same gust strength, the maximum instantaneous shear force due to impulse shape gust is the largest. When the rotors suffer a gust in a forward flight, the shear force at the root of rotors would increase with the gust strength first but then it decreases. More attention should be paid to the decrease of thrust force and the increase of structural load in a forward flight.

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Stable hovering of a jellyfish-like flying machine

Journal of The Royal Society Interface ◽

10.1098/rsif.2013.0992 ◽

2014 ◽

Vol 11 (92) ◽

pp. 20130992 ◽

Cited By ~ 37

Author(s):

Leif Ristroph ◽

Stephen Childress

Keyword(s):

High Speed ◽

Motion Tracking ◽

The Body ◽

Flapping Wings ◽

Wing Size ◽

Centre Of Mass ◽

Hovering Flight ◽

High Speed Video ◽

Aerodynamic Model ◽

Aerodynamic Surfaces

Ornithopters, or flapping-wing aircraft, offer an alternative to helicopters in achieving manoeuvrability at small scales, although stabilizing such aerial vehicles remains a key challenge. Here, we present a hovering machine that achieves self-righting flight using flapping wings alone, without relying on additional aerodynamic surfaces and without feedback control. We design, construct and test-fly a prototype that opens and closes four wings, resembling the motions of swimming jellyfish more so than any insect or bird. Measurements of lift show the benefits of wing flexing and the importance of selecting a wing size appropriate to the motor. Furthermore, we use high-speed video and motion tracking to show that the body orientation is stable during ascending, forward and hovering flight modes. Our experimental measurements are used to inform an aerodynamic model of stability that reveals the importance of centre-of-mass location and the coupling of body translation and rotation. These results show the promise of flapping-flight strategies beyond those that directly mimic the wing motions of flying animals.

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Non-linear unsteady aerodynamic model for insect-like flapping wings in the hover. Part 1: Methodology and analysis

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1243/09544100jaero49 ◽

2006 ◽

Vol 220 (2) ◽

pp. 61-83 ◽

Cited By ~ 82

Author(s):

S A Ansari ◽

R Żbikowski ◽

K Knowles

Keyword(s):

Flapping Wings ◽

Unsteady Aerodynamic ◽

Aerodynamic Model ◽

Non Linear

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Numerical study of the sound generated by two tandem arranged wings in forward flight

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406220924460 ◽

2020 ◽

pp. 095440622092446

Author(s):

Nathan A Widdup ◽

Li Wang ◽

Fang-Bao Tian

Keyword(s):

Sound Pressure ◽

Numerical Study ◽

High Mass ◽

Flapping Wings ◽

Sound Generation ◽

Mass Ratio ◽

Forward Flight ◽

Flexible Wings ◽

Fluid Mass ◽

Mass Ratios

The sound generated by two tandem arranged flexible wings in forward flight is numerically studied by using an immersed boundary method, at a Reynolds number of 100 and Mach number of 0.1. Three distinct cases are studied, encompassing a single wing and two tandem wings flapping in phase and out of phase. The sound generation of flapping wings is systematically studied by varying the wing flexibility (represented by the frequency ratio [Formula: see text]), structure-to-fluid mass ratio ([Formula: see text]), the phase difference (φ), and the gap ([Formula: see text]) between the two flapping wings. The results show that there is a direct correlation between the wing flexibility and sound generation for all cases considered. Specifically, for wings of low mass ratios ([Formula: see text]), an increase in flexibility resulted in a decrease in sound generation. For wings of high mass ratios ([Formula: see text]), an increase in flexibility resulted in higher sound output. The introduction of a second wing flapping in-phase resulted in an increase in aerodynamic features and sound generation, while the introduction of a second wing flapping out-of-phase experiences a decrease in sound output when compared to the in-phase case. In both cases, the effect of the wing flexibility on the sound production is similar to that of the single wing. An increase in flexibility is also found to have an impact on the plane of maximum sound pressure. For example, increasing flexibility resulted in a rotation of the plane of maximum sound pressure counter-clockwise relative to those at lower frequency ratios. Flexible wings with a structure-to-fluid mass ratio of unity and medium flexibility (i.e. [Formula: see text] and [Formula: see text]) are found to generate lower sound with high aerodynamic performance conserved.

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