Felipe Bohorquez

Bio: Felipe Bohorquez is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Rotor (electric) & Blade element momentum theory. The author has an hindex of 7, co-authored 8 publications receiving 810 citations.

Challenges Facing Future Micro-Air-Vehicle Development

Abstract: Nomenclature Ar = rotor disk area CD = sectional drag coefficient CD0 = zero-lift drag coefficient Clα = lift-curve slope CP = power coefficient CPi = induced power coefficient CP0 = profile power coefficient CT = thrust coefficient c = chord length D = drag force D.L . = disk loading L = lift force m = mass P.L . = power loading SF = separated flow T = rotor thrust V = local wind velocity perceived by flap W = weight W f = final weight Wo = gross takeoff weight α = blade section angle of attack η = efficiency μ = dynamic viscosity ρ = air density σ = rotor solidity = flapping amplitude (peak to peak)

Design, Analysis and Hover Performance of a Rotary Wing Micro Air Vehicle

Abstract: An initial design concept for a micro-coaxial rotorcraft using custom manufacturing techniques and commercial off-the-shelf components is discussed in this paper. Issues associated with the feasibility of achieving hover and fully functional flight control at small scale for a coaxial rotor configuration are addressed. Results from this initial feasibility study suggest that it is possible to develop a small scale coaxial micro rotorcraft weighing approximately 100 grams, and that available moments are appropriate for roll, yaw and lateral control. A prototype vehicle was built and its rotors were tested in a custom hover stand used to measure Thrust and power. The radio controlled vehicle was flown untethered with its own power source and exhibited good flight stability and control dynamics. The best achievable rotor performance was measured to be 42%.

Small Rotor Design Optimization Using Blade Element Momentum Theory and Hover Tests

Abstract: The current investigation focuses on the development of a low-cost computational methodology to design and optimize hovering rotors for small-scale vehicles using circular arc airfoils. Rotors for vehicles having a representative Re between 5000 and 60,000 were considered. A detailed experimental study of rectangular and tapered blades generated the data necessary to identify main performance trends and the effect of planform modifications. A blade element momentum theory model coupled with a table lookup scheme was implemented. The database was interpolated along three dimensions (Re, camber, and angle of attack) to obtain the local aerodynamic coefficients used in the calculation of the nonlinear inflow distribution along the blade span. Two methodologies were used in the calculation of the database. First, a purely numerical approach using the two-dimensional flow solver INS2D was evaluated. Second, a reverse method that used the experimental rotor data to refine the original previously generated database was investigated. Validation showed that the model predictive capabilities improved with the empirical corrections. An optimization algorithm was implemented to perform a grid search using power loading as the hover efficiency metric. The methodology proposed is able to optimize blade geometry and operating conditions following imposed constraints within a defined design space.

Hover Performance of Rotor Blades at Low Reynolds Numbers for Rotary Wing Micro Air Vehicles

Abstract: Rotary wing Micro Air Vehicles (MAV’s) are especially well suited for a broad range of missions that fixed wing MAV’s cannot accomplish. An efficient small-scale hovering rotor is required to make this configuration practical. Experimental studies show that for a variety of rotors at low Reynolds numbers (Re<50,000), poor performance was consistently measured. The current investigation explores the influence of a series of parameters such as airfoil shape and tip Reynolds number on the rotor’s performance, as well as the different stall mechanisms present on different rotor blades. Figure of merit was measured experimentally, and surface flow visualization was implemented on the rotor blades with the use of fluorescent oil. A Blade Element Momentum Theory model of the rotor was used to calculate the airfoil characteristics from the hover tests. The model also showed that the profile contributions to the total power requirements are considerably larger than for full-scale rotors, reducing the effect of any blade planform optimization. The ongoing research will bring some insight on the behavior of the flow over the rotor blade at low Re, establishing the basis for an optimized rotor design.

Biomimetic mechanism for micro aircraft

Abstract: A biomimetic pitching and flapping mechanism including a support member, at least two blade joints for holding blades and operatively connected to the support member. An outer shaft member is concentric with the support member, and an inner shaft member is concentric with the outer shaft member. The mechanism allows the blades of a small-scale rotor to be actuated in the flap and pitch degrees of freedom. The pitching and the flapping are completely independent from and uncoupled to each other. As such, the rotor can independently flap, or independently pitch, or flap and pitch simultaneously with different amplitudes and/or frequencies. The mechanism can also be used in a non-rotary wing configuration, such as an ornithopter, in which case the rotational degree of freedom would be suppressed.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Minimum snap trajectory generation and control for quadrotors

Abstract: We address the controller design and the trajectory generation for a quadrotor maneuvering in three dimensions in a tightly constrained setting typical of indoor environments. In such settings, it is necessary to allow for significant excursions of the attitude from the hover state and small angle approximations cannot be justified for the roll and pitch. We develop an algorithm that enables the real-time generation of optimal trajectories through a sequence of 3-D positions and yaw angles, while ensuring safe passage through specified corridors and satisfying constraints on velocities, accelerations and inputs. A nonlinear controller ensures the faithful tracking of these trajectories. Experimental results illustrate the application of the method to fast motion (5–10 body lengths/second) in three-dimensional slalom courses.

Trajectory generation and control for precise aggressive maneuvers with quadrotors

Abstract: We study the problem of designing dynamically feasible trajectories and controllers that drive a quadrotor to a desired state in state space. We focus on the development of a family of trajectories defined as a sequence of segments, each with a controller parameterized by a goal state or region in state space. Each controller is developed from the dynamic model of the robot and then iteratively refined through successive experimental trials in an automated fashion to account for errors in the dynamic model and noise in the actuators and sensors. We show that this approach permits the development of trajectories and controllers enabling such aggressive maneuvers as flying through narrow, vertical gaps and perching on inverted surfaces with high precision and repeatability.

The GRASP Multiple Micro-UAV Testbed

Abstract: In the last five years, advances in materials, electronics, sensors, and batteries have fueled a growth in the development of microunmanned aerial vehicles (MAVs) that are between 0.1 and 0.5 m in length and 0.1-0.5 kg in mass [1]. A few groups have built and analyzed MAVs in the 10-cm range [2], [3]. One of the smallest MAV is the Picoftyer with a 60-mmpropellor diameter and a mass of 3.3 g [4]. Platforms in the 50-cm range are more prevalent with several groups having built and flown systems of this size [5]-[7]. In fact, there are severalcommercially available radiocontrolled (PvC) helicopters and research-grade helicopters in this size range [8].