Inspired by the high performance of rotary and insect flapping wings capable of vertical take-off and landing and hovering (VTOLH), a novel flapping wing rotor (FWR) has been developed by combining the above two types of wing motions. The FWR offers an alternative configuration for micro air vehicles (MAV) of such high flight performance. Unlike the well-studied aerodynamics of rotary and insect-like flapping wing with prescribed wing motion, the aerodynamic lift and efficiency of the FWR associated with optimal kinematics of motion has not been studied in a systematic manner before. This investigation is therefore focused on the FWR optimal kinematic motion in terms of aerodynamic lift and efficiency. Aerodynamic analysis is conducted for a FWR model of aspect ratio 3.6 and wing span 200 mm in a range of kinematic parameters. The analysis is based on a quasi-steady aerodynamic model with empirical coefficients and validated by CFD results at Re∼3500. For comparison purpose, the analysis includes rotary and insect-like flapping wings in hovering status with the FWR at an equilibrium rotation speed when the thrust equals to drag. The results show that the rotary wing has the greatest power efficiency but the smallest lift coefficient. Whereas the FWR can produce the greatest aerodynamic lift with power efficiency between rotary and insect-like flapping wings. The results provide a quantified guidance for design option of the three types of high performance MAVs together with the optimal kinematics of motion according to flight performance requirement

The effectiveness of a passive gust alleviation device (PGAD) mounted at the wingtip of aircraft in conventional and flying-wing configurations have been studied in previous research. However the PGAD influence on the aeroelastic stability in particular the body freedom flutter (BFF) of a flying-wing aircraft remains as a concern. This present investigation is focused on evaluating the beneficial effect of PGAD on both gust load alleviation and BFF of a small flying-wing aircraft of high aspect ratio wing made of composite. A small range of (1-cos) type of gust load has been considered to select a representative critical gust load case for the study. A parametric study indicates that there is a narrow band of optimal key parameters for the PGAD design. Subsequently a set of optimal parameters is selected to further the analysis of the PGAD mechanism. The case study results show that the PGAD can make the bending moment at the wing root due to gust reduced by 16%. In addition, the BFF speed of the flying-wing aircraft is increased by 4.2%. The investigation reveals that the PGAD mode and its interaction with the wing bending mode and short period oscillation of the aircraft can have beneficial aeroelastic effect on both gust alleviation and flutter suppression

This study investigates the aerodynamic efficiency of a bioinspired flapping wing rotor kinematics which combines an active vertical flapping motion and a passive horizontal rotation induced by aerodynamic thrust. The aerodynamic efficiencies for producing both vertical lift and horizontal thrust of the wing are obtained using a quasi-steady aerodynamic model and two-dimensional (2D) CFD analysis at Reynolds number of 2500. The calculated efficiency data show that both efficiencies (propulsive efficiency-η_p, and efficiency for producing lift-P_f) of the wing are optimized at Strouhal number (St) between 0.1 and 0.5 for a range of wing pitch angles (upstroke angle of attackα_uless than 45°); theStfor highP_f(St = 0.1 ∼ 0.3) is generally lower than for highη_p(St = 0.2 ∼ 0.5), while theStfor equilibrium rotation states lies between the two. Further systematic calculations show that the natural equilibrium of the passive rotating wing automatically converges to high-efficiency states: above 85% of maximumP_fcan be obtained for a wide range of prescribed wing kinematics. This study provides insight into the aerodynamic efficiency of biological flyers in cruising flight, as well as practical applications for micro air vehicle design.

In this paper, the effects of stroke amplitude and wing planform on the aerodynamics of hovering flapping wings are considered by numerically solving the incompressible Navier–Stokes equations. The wing planform geometry is represented using a beta-function distribution for an aspect ratio range of 3–6 and a dimensionless radial centroid location range of 0.4–0.6. Typical normal hovering kinematics has been employed while allowing both translational and rotational durations to be equally represented. The combined effects of stroke amplitude with wing aspect ratio and radial centroid location on the aerodynamic force coefficients and flow structures are studied at a Reynolds number of 100. It is shown that increasing the stroke amplitude increases the translational lift for either small aspect ratio or large radial centroid location wings. However, for high aspect ratio or low radial centroid location wings, increasing the stroke amplitude leads to higher lift coefficients during the translational phase only up to a stroke amplitude of 160°. Further increase in stroke amplitude results in reduced translational lift due to the increased wingtip stall effect. For all the cases considered, the lift and drag coefficients of the rotational phase decrease with the increase of stroke amplitude leading to decreased cycle-averaged force coefficients. Furthermore, it is found that the significant reduction in the rotational drag as the stroke amplitude increases leads to a consistently increasing aerodynamic efficiency against stroke amplitude for all aspect ratio and radial centroid location cases.