arXiv subjects

Xiaozhou Fan

Publications and source records attributed to Xiaozhou Fan.

4 recordsLinked to original sources

arXiv2025

A Narwhal-Inspired Sensing-to-Control Framework for Small Fixed-Wing Aircraft

Fixed-wing unmanned aerial vehicles (UAVs) offer endurance and efficiency but lack low-speed agility due to highly coupled dynamics. We present an end-to-end sensing-to-control pipeline that combines bio-inspired hardware, physics-informed dynamics learning, and convex control allocation. Measuring airflow on a small airframe is difficult because near-body aerodynamics, propeller slipstream, control-surface actuation, and ambient gusts distort pressure signals. Inspired by the narwhal's protruding tusk, we mount in-house multi-hole probes far upstream and complement them with sparse, carefully placed wing pressure sensors for local flow measurement. A data-driven calibration maps probe pressures to airspeed and flow angles. We then learn a control-affine dynamics model using the estimated airspeed/angles and sparse sensors. A soft left/right symmetry regularizer improves identifiability under partial observability and limits confounding between wing pressures and flaperon inputs. Desired wrenches (forces and moments) are realized by a regularized least-squares allocator that yields smooth, trimmed actuation. Wind-tunnel studies across a wide operating range show that adding wing pressures reduces force-estimation error by 25-30%, the proposed model degrades less under distribution shift (about 12% versus 44% for an unstructured baseline), and force tracking improves with smoother inputs, including a 27% reduction in normal-force RMSE versus a plain affine model and 34% versus an unstructured baseline.

cs.RO↗

arXiv2024

Upstroke wing clapping in bats and bat-inspired robots improves both lift generation and power economy

Wing articulation is critical for efficient flight of bird- and bat-sized animals. Inspired by the flight of $\textit{Cynopterus brachyotis}$, the lesser short-nosed fruit bat, we built a two-degree-of-freedom flapping wing platform with variable wing folding capability. In late upstroke, the wings "clap" and produce an air jet that significantly increases lift production, with a positive peak matched to that produced in downstroke. Though ventral clapping has been observed in avian flight, potential aerodynamic benefit of this behavior has yet to be rigorously assessed. We used multiple approaches -- quasi-steady modeling, direct force/power measurement, and PIV experiments in a wind tunnel -- to understand critical aspects of lift/power variation in relation to wing folding magnitude over Strouhal numbers between $St = 0.2 - 0.4$. While lift increases monotonically with folding amplitude in that range, power economy (ratio of lift/power) is more nuanced. At $St = 0.2 - 0.3$, it increase with wing folding amplitude monotonically. At $St = 0.3 - 0.4$, it features two maxima -- one at medium folding amplitude ($\sim 30^\circ$), and the other at maximum folding. These findings illuminate two strategies available to flapping wing animals and robots -- symmetry-breaking lift augmentation and appendage-based jet propulsion.

physics.flu-dyn↗

arXiv2024

Wing twist and folding work in synergy to propel flapping wing animals and robots

We designed and built a three degrees-of-freedom (DOF) flapping wing robot, Flapperoo, to study the aerodynamic benefits of wing folding and twisting. Forces and moments of this physical model are measured in wind tunnel tests over a Strouhal number range of St = 0.2 - 0.4, typical for animal flight. We perform particle image velocimetry (PIV) measurements to visualize the air jet produced by wing clapping under the ventral side of the body when wing folding is at the extreme. The results show that this jet can be directed by controlling the wing twist at the moment of clapping, which leads to greatly enhanced cycle-averaged thrust, especially at high St or low flight speeds. Additional benefits of more thrust and less negative lift are gained during upstroke using wing twist. Remarkably, less total actuating force, or less total power, is required during upstroke with wing twist. These findings emphasize the benefits of critical wing articulation for the future flapping wing/fin robots and for an accurate test platform to study natural flapping wing flight or underwater vehicles.

physics.flu-dyn↗

arXiv2023

An improved aerodynamic model for quasi-steady simulations of animal flight at moderate Reynolds numbers

We report on experimental and numerical studies aimed at developing an improved paradigm to model animal flight at moderate Reynolds numbers ($ 20 k - 50k $). A series of experiments were performed to characterize the behaviors of aerodynamic forces and moment associated with a quasi-steady rectangular wing over a range of angle of attack, $\alpha$. We demonstrate that, while the drag coefficient curve, $C_D(\alpha)$, can be accurately modeled solely by a simple trigonometric function, the evolution of lift coefficient curve, $C_L(\alpha)$, is governed by the sum of trigonometric and exponential functions, where the latter captures the linear variation in lift coefficient within the small-angle regime, as predicted by the linear inviscid theory. In addition, we establish an empirical relation between the location of the center of pressure and $\alpha$, which can be used in conjunction with the proposed aerodynamic formulas (i.e., $C_L$ and $C_D$) to evaluate the pitching moment coefficient, $C_M(\alpha)$, about any arbitrary axis. These quasi-steady formulations are then utilized within a previously tested flapping-wing code to simulate the forward flight of a pigeon and a bat at various flight speeds, and the results are compared against previously reported experimental data. We successfully demonstrate that the proposed formulas yield much better agreement with wingbeat frequency for both animals, especially at higher flight speeds. In addition, the small-angle regime proves critical in offering higher $C_L/C_D$, leading to solutions with lower power consumption and body pitching variation, both of which are important aspects in designing future flapping wing robots.

physics.flu-dyn↗