Carlos Montalvo

Use of Microspoilers for Control of Finned Projectiles

Relative to other air vehicles, the physical control mechanism on a smart projectile plays much more of a central role in the overall system design. Many different smart projectile control mechanisms have been created, including aerodynamic based mechanisms such as movable canards, propellant based mechanisms such as squibs, and inertia based mechanisms such as internal moving masses. The work reported here considers small micro spoilers located between rear fins to create aerodynamic force changes to enable projectile control. In particular, boundary layer shock interaction between the projectile body, fins, and micro spoilers provides a multiplicative effect on controllable forces and moments. A parametric study varying the micro spoiler configuration is conducted to examine the level of control authority possible for this control mechanism concept. Results indicate that relatively small micro spoilers located between fins generate substantial control authority that is capable of eliminating impact errors caused by muzzle jump, aerodynamic uncertainty, and atmospheric winds. These conclusions are based on CFD predictions of the effect of micro spoilers on air loads coupled to a rigid 6-degree-of-freedom projectile trajectory simulation.

Effect of canard stall on projectile roll and pitch damping

A computational and mathematical approach is used to investigate the effect of canard stall on projectile roll and pitch damping. For spinning projectiles with dithering canards, large angles of attack can be achieved by these canards. These large angles of attack can lead to stall that causes abnormal loads on the projectile. Because of these abnormalities, it is important to include the effects of stall on the projectile. First, the total roll and pitch moments of two canards is derived. These equations are then analysed to show that the effects of canard stall can produce a decrease in roll damping, causing roll rate to increase, and an increase in pitch damping, causing the no roll frame pitch rate to decrease. To validate this analysis, simulation is performed using a fully non-linear six-degree-of-freedom dynamic model with canard aerodynamics. The results from the simulation agree with the equations derived; thus, for projectiles that use dithering canards for control, it is important to include these non-linear effects in the projectile dynamic model.

Performance Characteristics of an Autonomous Airdrop System in Realistic Wind Environments

For airdrop systems, there is normally a large gap between the landing accuracy predicted in simulation and the accuracy observed in flight test. Even with mature systems, the landing accuracies observed in flight test are typically worse by a factor of two to three compared to the accuracy expected from simulation. The current work explores the possibility that this discrepancy can be mitigated by incorporating more realistic models of atmospheric wind into airdrop system simulations. To this end, realistic wind environments are generated by implementing a standard atmospheric wind model from the weather community. A six degree of freedom parafoil and payload model representing a real system is then flown in the wind environment using guidance, navigation, and control algorithms that represent the current state of the art in the airdrop community. Through Monte Carlo simulation, predicted landing accuracies are generated using both the realistic wind environment and simplified wind models common among current airdrop simulations. Results indicate that simulated landing accuracy is decreased by nearly a factor of two when using a realistic wind environment, which may explain the current difference between simulated and flight test accuracy of autonomous airdrop systems.

Estimation of Projectile Aerodynamic Coefficients Using Coupled CFD/RBD Simulation Results

A method to compute aerodynamic coefficients for a projectile is described. The core data used by the algorithm is so called virtual fly out results where an unsteady time accurate computational fluid dynamics simulation is tightly coupled to a rigid projectile flight dynamic simulation. The output of the overall simulation is time history data of the motion of the projectile along with all loads on the body. With time synchronized air loads and projectile motion information, aerodynamic coefficients are estimated using a 2 step procedure. First, projectile motion data is fit to the projectile linear theory analytic solution using the aerodynamic coefficients as fitting parameters. The results from the projectile linear theory fitting procedure are fed as initial conditions to an output error parameter identification algorithm. During numerical experiments it was found that local minima exist for this problem. This problem was remedied by using a grid of initial conditions for the parameters and running them through the projectile linear theory equations. Then the best overall result was selected as the initial condition for the output error method algorithm. With this algorithm modification, the technique is shown to work for synthetic data and virtual fly out data.

Avoiding Lockout Instability for Towed Parafoil Systems

Many towed systems consist of a parent platform moving along the ground, air, or water surface connected to a towed vehicle via a tether line. Motion of a towed parafoil system can be complex and is driven by motion of the parent platform, canopy control inputs, and wind disturbances. A particularly problematic flight dynamic instability for this system is canopy lockout, in which the canopy attains a large lateral offset and bank angle resulting in high line tension. It is possible to use left and right brakes to return the system to its nominal position; however, if the lateral offset and bank angle are too large, it is not possible to restore the system to a nominal position, and the lateral offset and bank angle grows until impact with a ground surface. This paper explores the lockout phenomena using a multibody simulation and identifies passive means to avoid the instability by locating the tether connection point forward on the cradle in combination with sufficiently high cradle–canopy yaw stiffness...

Meta Aircraft Flight Dynamics

A meta aircraft is an air vehicle composed of a set of independent aircraft that are connected together in flight to form a larger composite aircraft. This paper explores the dynamics of meta aircraft systems with a focus on the changes in the aircraft flight dynamic modes and flexible modes of the system. Specifically, when aircraft are connected, basic flight dynamic modes such as the phugoid, short period, dutch roll, spiral, and roll modes change as a function of the number of connected aircraft. For aircraft connected in a wing-tip-to-wing-tip configuration, the longitudinal modes remain largely invariant with respect to the number of aircraft, whereas lateral modes are variable for both tip-to-tail and wing-tip-to-wing-tip connection configurations. In addition, connected aircraft exhibit complex flexible modes that change based on the characteristics of the connection joint and the number of connected aircraft. These conclusions are reached using a rigid six-degree-of-freedom representation for a s...

Green’s function–based surrogate model for windfields using limited samples:

There exists many applications for which wind-velocity is desired over a three-dimensional space. The vector field associated with these wind velocities is known as a “windfield” or “velocity-windfield.” The present work provides a fast method to characterize windfields. The approach uses the free-space Green’s function for potential theory as an inexpensive surrogate model in lieu of either complicated physics-based models or other types of surrogate models, both of which require volumetric discretizations for the three-dimensional case. Using the gradient of the third Green’s identity, the wind-velocity in the interior of a domain is entirely characterized by a surface discretization while still providing a three-dimensional model. The unknown densities on the surface are determined from enforcement of the interior form of the identity at arbitrary points coinciding with wind measurements taken by unmanned aerial vehicles. Numerical results support the feasibility of the method.

Design, Simulation, and Experimental Testing of Humanitarian Aid Airdrop Micro Packages

Conventional airdrop methods for humanitarian aid and emergency relief require dropping heavy payloads far away from the intended recipients. Currently, there are a number of issues with this method of delivery. Because supplies are distributed by just a few large crates dropped on or near the location of those requiring relief, there is not only risk of injury upon being struck by one of these large crates, but it is also common for the distribution of supplies to be inhibited by adversaries. Thus, in an effort to reduce or eliminate the occurrence of such difficulties, a safer, more effective means of dropping and distributing humanitarian aid is necessary. The development of small sized packages of supplies that can be dispersed directly above a populated area with minimal risk of human injury is essential to ensure safe, timely, and effective distribution of aid. The research reported here explores several proposed packaging designs of individual food and water rations to identify possible methods to deploy emergency relief in a manner consistent with the previously stated requirements. With a combination of flight dynamic simulation, wind tunnel testing, and flight testing, promising package designs that meet impact requirements are identified.

Characterization of a two-dimensional static wind field using Radial Basis Functions:

Radial Basis Functions are a modern way of creating a regression model of a multivariate function when sampled data points are not uniformly distributed in a perfect grid. Radial Basis Functions are well suited to atmospheric characterization when unmanned aerial vehicles (UAVs) are used to sample the given space. Multiple UAVs reduce the time for the Radial Basis Functions to yield a suitable solution to the measured data while data from all aircraft are aggregated and sent to Radial Basis Functions to fit the data. The research presented here focuses on the requirements for a high correlation value between the sampled data and the actual data. It is found that the number of centers is a large driver of the goodness of fit in the Radial Basis Function routine, much like aliasing is an issue in sampling a sinusoidal function. These centers act like a sampling rate for the spatially varying wind field. If the centers are dense enough to fully capture the spatial frequency of the wind field, the Radial Basis Functions will produce a suitable fit. This also requires the number of data points to be larger than the number of centers. The ratio between the number of centers and number of sampled data points declines as the number of centers increases. The results presented here are revealed using a two-dimensional Fourier series analysis coupled to a spatially varying atmospheric wind model and a Radial Basis Function regression model.

Measured and simulated analysis of a model rocket

A comparison between two types of sensors and two types of simulation software are investigated here for a student built rocket. Many students use an open source software package called OpenRocket which uses empirical aerodynamics based on the shape of the rocket. This software is compared to the standard set of rigid body dynamic equations using coefficients for the aerodynamics based on windtunnel and computational fluid dynamics tests. During experimentation two sensors are used and price and resolution is compared. The first sensor is a turn-key sensor called the TeleMega which has many features such as telemetry and on board data logging. In an effort to reduce costs, the Arduino Mega platform has been augmented with a custom made shield capable of measuring Global Positioning System (GPS), angular velocity, and attitude information with on board data logging as well. Although this sensor has limited functionality, the cost is substantially reduced. It is shown that all sensors and simulation software have their strengths and weaknesses with appropriate usage for each.