Flexible-wing-based micro air vehicles

Ifju, Peter; Jenkins, David; Ettinger, Scott; Lian, Yongsheng; Shyy, Wei; Waszak, Martin R.

doi:10.2495/978-1-85312-941-4/08

Cited by 46 publications

(41 citation statements)

References 23 publications

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“…They also revealed that the platform is capable of other styles of flight: flight using the propellers as the sole propulsion mode after reaching a critical velocity (either by a launch or by use of both modes initially), intermittent flapping, and gliding. The propeller only and gliding is possible because the wings passively balloon into a suitable airfoil shape in flight (using flexible wings with propeller propulsion has been studied in other works 38,40 ). Notably, gliding via the use of gravity to generate velocity is viable.…”

Section: Mixed Mode Flight Performancementioning

confidence: 99%

“…19,30,[32][33][34][35][36][37] One such approach is the usage of flexible membranes which provides performance with passive deformation (with benefits not limited to flapping flight only). 35,[38][39][40] Additionally, it was noted that usage of a single actuator to drive both wings saves weight, but limits the flapping gait. This is because only fixed amplitudes can be achieved and wing gait characteristics are tied to a single source, 41 unless a complex mechanism is designed to overcome it.…”

Section: Introductionmentioning

confidence: 99%

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Characterizing and modeling the enhancement of lift and payload capacity resulting from thrust augmentation in a propeller-assisted flapping wing air vehicle

Holness

Bruck

Gupta

2017

International Journal of Micro Air Vehicles

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Biologically-inspired flapping wing flight is attractive at low Reynolds numbers and at high angles of attack, where fixed wing flight performance declines precipitously. While the merits of flapping propulsion have been intensely investigated, enhancing flapping propulsion has proven challenging because of hardware constraints and the complexity of the design space. For example, increasing the size of wings generates aerodynamic forces that exceed the limits of actuators used to drive the wings, reducing flapping amplitude at higher frequencies and causing thrust to taper off. Therefore, augmentation of aerodynamic force production from alternative propulsion modes can potentially enhance biologicallyinspired flight. In this paper, we explore the use of auxiliary propellers on Robo Raven, an existing flapping wing air vehicle (FWAV), to augment thrust without altering wing design or flapping mechanics. Designing such a platform poses two major challenges. First, potential for negative interaction between the flapping and propeller airflow reducing thrust generation. Second, adding propellers to an existing platform increases platform weight and requires additional power from heavier energy sources for comparable flight time. In this paper, three major findings are reported addressing these challenges. First, locating the propellers behind the flapping wings (i.e. in the wake) exhibits minimal coupling without positional sensitivity for the propeller placement at or below the platform centerline. Second, the additional thrust generated by the platform does increase aerodynamic lift. Third, the increase in aerodynamic lift offsets the higher weight of the platform, significantly improving payload capacity. The effect of varying operational payload and flight time for different mixed mode operating conditions was predicted, and the trade-off between the operational payload and operating conditions for mixed mode propulsion was characterized. Flight tests revealed the improved agility of the platform when used with static placement of the wings for various aerobatic maneuvers, such as gliding, diving, or loops.

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Section: Mixed Mode Flight Performancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterizing and modeling the enhancement of lift and payload capacity resulting from thrust augmentation in a propeller-assisted flapping wing air vehicle

Holness

Bruck

Gupta

2017

International Journal of Micro Air Vehicles

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“…= aspect ratio b = wing span, cm c = chord, cm C L = lift coefficient C L max = maximum lift coefficient (at stall) C SF = side force coefficient C l = roll moment coefficient C l;β = roll-stability derivative, rad −1 C n = yaw moment coefficient C n;β = yaw stiffness derivative, rad −1 f s = data-sampling frequency, Hz Re = Reynolds number U 0 = freestream velocity, m∕s I N RECENT years, the capabilities of micro aerial vehicles (MAVs) have improved so dramatically that several different institutions have designed and flown a wide variety of vehicles for a multitude of applications [1][2][3][4][5]. These designs typically rely heavily on iterative testing procedures because no readily accessible analytic tools are available for MAV development.…”

Section: Armentioning

confidence: 99%

Roll Stall for Low-Aspect-Ratio Wings

Linehan

Mohseni

2016

Journal of Aircraft

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The longitudinal aerodynamics of micro aerial vehicles, although not fully understood, have been the subject of several studies in recent years; however, little work has been done to investigate the lateral loading. In this experiment, flat-plate wings with rectangular planforms of aspect ratios AR 0.75, 1, 1.5, and 3 and tapered planforms of λ 0.75, 0.5, and 0.25 were placed in the wind tunnel at a Reynolds numbers of 7.5 × 10 4 . Angle-of-attack sweeps were performed at sideslip angles of β 0, −5, −10, −15, 20 and −35 deg, and the side force, yaw moment, and roll moment were measured. Although the side force and yaw moment coefficients (C SF and C n ) were typically negligible, the roll moment coefficient C l was found to increase linearly with angle of attack before stalling in a manner reminiscent of a lift curve. This "roll stall", which has not previously been observed for micro-aerial-vehicle-type wings, is attributed to the upstream tip vortex creating an additional lift component due to its impact on the spanwise variation of effective angle of attack in addition to the force generated by its own low-pressure core. As the downstream tip vortex is convected away from the wing, a net moment is created. Computations of the roll-stability derivative indicate that a micro aerial vehicle in equilibrium flight conditions may experience magnitudes of C l;β at the upper limit of, or even above, the range of −0.10 ≤ C l;β ≤ 0 considered to represent good handling qualities in aircraft.

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“…Note that, one of the least understood aspect of small-scale flight is its aerodynamic performance, which is the focus of the current study.From an aerodynamics perspective, a key challenge for a MAV designer is the low lift-to-drag ratio of even the most optimized airfoil geometries at low Reynolds numbers. Several fixed-wing MAVs have already been successfully tested [2][3][4][5][6]. One particular example [5,6] has a weight of 80 grams and a flight endurance of about 30 minutes.…”

mentioning

confidence: 99%

Experimental Investigation of Micro Air Vehicle Scale Helicopter Rotor in Hover

Benedict

Winslow

Hasnain

et al. 2015

International Journal of Micro Air Vehicles

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This paper describes a fundamental experimental study, which involved systematic performance and flowfield measurements (PIV) to understand and optimize the hover performance of a MAV-scale helicopter rotor operating at Reynolds numbers lower than 30,000. The rotor parameters that were varied include blade airfoil profile, blade chord, number of blades, blade twist, planform taper and winglets at blade tip. Blade airfoil section had a significant impact on the hover efficiency and among the large number of airfoil sections tested, the ones with the lower thickness to chord ratios and moderate camber (4.5% to 6.5%) produced the highest rotor hover figure of merit. Increasing the solidity of the rotor by increasing the number blades (with constant blade chord) had minimal effect on efficiency; whereas, increasing the solidity by increasing blade chord for a 2-bladed rotor, significantly improved hover efficiency. Moderate blade twist (-10t o -20˚) and large planform taper (larger than 0.5) marginally improved rotor efficiency. Rotor blades with small winglets (height ≈ 6% of rotor radius) at the tip also improved hover performance. While using winglets, the flowfield measurements showed a diffused tip vortex, which could reduce the induced aerodynamic losses. Spanwise lift distribution obtained using sectional bound circulation computed from the measured flowfield correlated well with the load cell measurements. The optimal rotor designed based on the understanding gained from the present study produced a figure of merit of 0.67, which is the highest value of FM ever reported in the literature for micro-rotors operating at these low Reynolds numbers. INTRODUCTIONMicro Air Vehicles (MAVs) are small-scale aerial platforms, which are envisioned to have a wide range of both military and civilian applications. Being small and compact systems, MAVs offer several advantages such as portability, rapid deployment, real-time data acquisition capability, low radar cross section, low noise signatures and low production cost. The micro air vehicle concept was first proposed by DARPA back in 1997 [1] and according to DARPA's original definition, the size of these vehicles has to be within 6 inches (0.154 m) with a gross weight of 100 grams (including 20 grams payload) and a flight endurance of 60 minutes. However, even after substantial progress in the last two decades, the fact that none of the current MAVs are even close to achieving this endurance goal (60 mins), is a true testament to the difficulty of this problem. The key reasons for this are the inefficiencies associated with the low Reynolds number aerodynamic regime at which these vehicles operate and challenges in smallscale power generation and storage. Note that, one of the least understood aspect of small-scale flight is its aerodynamic performance, which is the focus of the current study.From an aerodynamics perspective, a key challenge for a MAV designer is the low lift-to-drag ratio of even the most optimized airfoil geometries at low Reynolds numbers. Several fi...

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Flexible-wing-based micro air vehicles

Cited by 46 publications

References 23 publications

Characterizing and modeling the enhancement of lift and payload capacity resulting from thrust augmentation in a propeller-assisted flapping wing air vehicle

Characterizing and modeling the enhancement of lift and payload capacity resulting from thrust augmentation in a propeller-assisted flapping wing air vehicle

Roll Stall for Low-Aspect-Ratio Wings

Experimental Investigation of Micro Air Vehicle Scale Helicopter Rotor in Hover

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