Free-Wing Unmanned Aerial Vehicle as a Microgravity Facility

Abstract

A conceptual study is presented on the dynamics of a proposed unmanned aerial vehicle (UAV), which is designed as a testbed for studying the influence of micro-(or partial) gravity on various biological or physical phenomena. The design option of a torque-controlled wing, free to rotate about a spanwise axis, is evaluated in terms of gust sensitivity and automatic settling at a certain g-setpoint. The complete set of nonlinear equations of motion of such a free-wing UAV are derived using Lagrange's equations. A linear aerodynamic model of the UAV is used to investigate its flight dynamics, gust sensitivity, and ability to fly micro-and partial gravity flights. Comparison to a similar fixed-wing UAV shows considerably decreased gust sensitivity. NomenclatureC m = dimensionless moment coefficient about the center of gravity of the fuselage c = cosinē c = mean aerodynamic chord F = generalized force f = position of the fuselage center of mass g = Earth's gravitational acceleration H = transfer function h = position of the intersection of the hinge lines of both wing halves L = Lagrangian function lw = position of the left wing half center of mass M = moment m = mass n = load factor p = angular velocity component of the fuselage along the x f axis q = angular velocity component of the fuselage along the y f axis q = column vector of generalized coordinates R = transformation matrix between two reference frames r = angular velocity component of the fuselage along the z f axis rw = position of the right wing half center of mass S = power spectral density s = angular velocity component of the wing halves along their hinge axes s = sine T = kinetic energy t = tangent t = time u = geodetic velocity component of the center of mass of the fuselage along the x f axis V = potential energy v = geodetic velocity component of the center of mass of the fuselage along the y f axis v = velocity ; A.M.Kraeger@lr.tudelft.nl. w = geodetic velocity component of the center of mass of the fuselage along the z f axis w = column vector denoting the center of mass of the wing halves in wing fixed axes x = in combination with index: x coordinate of the element indicated by the index; without index: x-position coordinate of the fuselage center of mass in geodetic reference frame y = in combination with index: y coordinate of the element indicated by the index; without index: y-position coordinate of the fuselage center of mass in geodetic reference frame z = in combination with index: z coordinate of the element indicated by the index; without index: z position coordinate of the fuselage center of mass in geodetic reference frame α = angle of attack = hinge axis dihedral angle γ = flight path angle δ e = elevator deflection δW = increment in virtual work δq = incremental virtual displacement δ w = angular deflection of the wing halves ζ = damping θ = pitch angle = hinge axis sweepback angle σ = standard deviation ϕ = roll angle ψ = heading angle Ω = skew symmetric matrix ω = column vector of (angular) velocity components ω 0 = undamped natura...

Acceleration control of a multi-rotor UAV towards achieving microgravity

“…In practice, if the sampling time is small enough, then for every small time interval in which the velocity can be assumed to remain constant, there will be sufficient number of time steps for the convergence of Eq. (19) to happen.…”

“…Owing to a d being constant and the quasi-steady velocity assumption, the quantities P and Q are constants, and therefore, the difference equation in Eq. (19)…”

“…However, a few applications exist for which these performance measures do not form part of the UAV design requirements. An example is the use of UAVs as research platforms to enable microgravity for an on-board payload [1,15,18,19]. For such UAVs, the main performance criterion is the ability to maintain a desired constant acceleration-free-fall-so that the payload experiences microgravity for a specified duration.…”

“…Consequently, the low cost involved in setting up and conducting microgravity experiments using small UAVs led the research community to use them as microgravity enabling platforms in spite of their low payload capacity. Multiple conceptual and simulation studies that were carried out indicated the feasibility of using a fixed-wing UAV as a microgravity enabling platform [15,19,23]. However, the corresponding flight tests did not yield satisfactory g-quality-the fluctuations in the experienced gravity were of the order of 0.4 g [15,18].…”

A Segmented Freewing Concept for UAS Gust Alleviation in Adverse Environments

“…Unmanned aerial vehicles have become increasingly popular for use in long endurance missions, experimentation, and surveillance. Kraeger [19] studied the use of a freewing UAV for a microgravity facility where the UAV could fly exact mission profiles at a lower cost compared to larger microgravity facilities operated by manned aircraft. A fixed wing UAV microgravity facility was more sensitive to gusts compared to the much larger manned microgravity facility.…”