# State of the Art Review about Bio-Inspired Design and Applications: An Aerospace Perspective
## 4 Applications of Bio-Inspiration in the Aerospace Industry
To offset the low density of such an atmosphere that directly impacts the aerodynamic performance and restricts commonly used space-flight techniques, a flapping wing, and a hovering mechanism was devised and studied numerically using the Navier-Stokes equation. It was predicted that a bumblebee's wing shape wouldn't sustain flight in the Martian atmosphere. However, an enlargement of the wing coupled with a flapping-based wing movement could help generate lift to counteract the increased weight on Mars. A flapping wing MAV's noise control capabilities were improved by incorporating a wing design, commonly observed in insects such as bats and butterflies [70]. Dielectric elastomers and other similar materials were used as wings in MAV designs, namely an insect-inspired wing as a reference design, a moth-inspired fabric-based wing design, and an elastic wing design inspired by bats. It was found that the noise per unit thrust decreased with increasing flapping frequency for all the systems and that the rubber flaps provided a better noise reduction than the films. A leading-edge alula inspired device (LEAD), influenced by a set of feathers on each wing of a bird, called the alula (refer Figure 19) was developed and verified for aerodynamic performance [71; 72; 73]. The LEAD provided optimal performance when placed along the wing's semi-span, increasing lift during post and deep stalling. An investigation to improve the aerodynamic performance inspired by a pigeon's discrete wing structure. A continuous wing orientation revealed a better drag reduction with more increased lateral stability than a constant wing structure. This indicated the efficiency in the aerodynamic performance of a discrete wing design [72]. Figure 20 depicts the models developed for testing the discrete and continuous structures. Figure 18: Mechanism for flapping to analyse wing deformations [68]. A corrugated wing designed based on a dragonfly was implemented on panels and verified experimentally, with results indicating an improvement in flow characteristics, with more considerable pressure differences between the upper and lower corrugated surfaces, causing an increase in a lift [73]. Another application of a flapping wing mechanism in a UAV to counter turbulence during the flight was approached [74]. During turbulent flights, birds tend to hover rather than flap their wings, which allow a set of covert feathers beside the primary feathers to deflect gusts of turbulent winds. Figure 21 indicates the natural and synthetic mechanisms for the same. The application of a gust mitigation system (GMS) in flapping wing UAVs served a purpose similar to the covert feathers, helping mitigate gusts of winds only while facing turbulence, and remained integrated with the entire wing at all other times to maintain the wing profile. Figure 19: A deployed alula on the wing of the bird [71]. Figure 20: Models fabricated for wind tunnel testing (**a**) Completely folded, discrete wing design (**b**) Completely folded, continuous wing design [72]. A Bat's wing possesses a very articulated musculoskeletal system, which assists them with multiple degrees of freedom, in addition to a compact and lightweight mechanism [75; 76]. Mimicking this behaviour, Figure 22 depicts an arm wing structure that was modelled and analysed. The design showed successful wing performance during the flapping motion.