This paper presents the flight test verification and validation of a novel multi-reference longitudinal and lateral-directional guidance logic across multiple autonomous aircraft with distinctly ...different dynamics. L
N
guidance logic takes advantage of tracking a span of multiple references across the desired track, similar to an insect’s compound eyes, allowing for a much higher temporal resolution and more predictive and anticipatory guidance logic. The stability of L
N
guidance algorithms is investigated using global Lyapunov stability theorems and its stability is proved. Validation and verification flight tests of L
N
lateral-directional guidance logic demonstrate superior tracking performance adaptability of this novel method compared to other methods such as
L
1
or
L
2
+
. The L
N
longitudinal guidance is newly developed in this paper and shows excellent altitude tracking capabilities and similarly scalable. Statistical analysis of multiple flight tests involving varying environmental states with three unique aircraft and different advanced flight controllers are shown to prove the capabilities, robustness, and consistency of L
N
guidance.
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EMUNI, FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This paper presents the flight test verification and validation of a novel multi-reference longitudinal and lateral -directional guidance logic across multiple autonomous aircraft with distinctly ...different dynamics. L.sub.N guidance logic takes advantage of tracking a span of multiple references across the desired track, similar to an insect's compound eyes, allowing for a much higher temporal resolution and more predictive and anticipatory guidance logic. The stability of L.sub.N guidance algorithms is investigated using global Lyapunov stability theorems and its stability is proved. Validation and verification flight tests of L.sub.N lateral-directional guidance logic demonstrate superior tracking performance adaptability of this novel method compared to other methods such as L.sub.1 or L.sub.2.sup.+. The L.sub.N longitudinal guidance is newly developed in this paper and shows excellent altitude tracking capabilities and similarly scalable. Statistical analysis of multiple flight tests involving varying environmental states with three unique aircraft and different advanced flight controllers are shown to prove the capabilities, robustness, and consistency of L.sub.N guidance. Keywords UAS * Flight test * Autonomy * 3D guidance * Predictive and adaptive guidance * UAM * Lyapunov
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EMUNI, FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This research presents dynamic modeling and controllability analysis of a moderately damaged Viking-400 unmanned aerial system. In absence of flight test data, changes in longitudinal and ...lateral-directional dynamic modes of this aircraft due to asymmetric damage are investigated using Athena Vortex Lattice. Dynamic modeling of damaged aircraft has not been studied extensively. The majority of existing works are based on research conducted at NASA Langley, which used wind tunnel experiments on a 5.5%-scale model of generic transport aircraft. Only a few studies have examined onboard adverse impacts on the dynamic model of damaged UASs and most of these studies used extremely simple approaches to reflect changes in the UAS dynamic by manipulating stability and control derivatives based on perceived impact of damage. In this work, two major cases with different extents of damage are considered. Main scenarios are: (1) wing tip loss with partial aileron loss (2) damage to the horizontal tail and elevator. Damages are assumed to be asymmetric, inflicted by man-portable air defense systems. Uniquely, a methodology is created to document the changes in moment of inertia and aircraft geometry. Utilizing AVL, stability and control derivatives were developed at the aircraft's cruise velocity of 60 knots for each damage condition. Modal analyses are conducted for each scenario. Using linear time-invariant system representation of the UAS, a controllability analysis is also conducted for each scenario. The results of this analysis show that the aircraft is controllable for all damage scenario.
In this paper, the propwash phenomenon for pusher configuration unmanned aerial systems (UASs) is studied. The SkyHunter UAS has the propeller placed aft of the fuselage and in front of the ...horizontal tail with no offset from the zero lift plane. Thus, the propeller slipstream directly flows over the horizontal tail affecting its aerodynamics. To validate the physics based model developed for propwash impacts and to quantify the effects of propwash, the SkyHunter UAS was equipped with an extra pitot tube. The first pitot tube was placed at the nose of the aircraft where the air is undisturbed and it was measuring the aircraft's velocity. The second pitot tube was placed at different locations on the horizontal tail and three flight tests were conducted. Flight test data showed that the current configuration of the SkyHunter: (A) has large variations in the horizontal tail dynamic pressure ratio along the span of the horizontal tail. (B) had the dynamic pressure ratio higher than 1.7 in two of the three investigated locations along the span of the horizontal tail. This suggests that the theoretical estimate of the dynamic pressure ratio (which is 0.93) may be an under estimation. (C) The dynamic pressure ratio varied with time during flight. A change in the horizontal tail dynamic pressure ratio directly leads to a shift in the location of the aerodynamic center of an aircraft as well as changes in the stability and control derivatives of an aircraft. The implication of these changes in small UASs can be significant since they affect the aircraft longitudinal stability, trim elevator, and flight characteristics. In order to mitigate such changes during flight, a redesign was made to the original empennage design where is an offset was added between the zero lift plane and the aerodynamic center of the horizontal tail. This redesign intends to move the horizontal tail above (and away from) the propeller slipstream. Manufacturing of the redesigned horizontal tail was completed recently and it was flight tested. Flight test data from the new design show that the new design successfully mitigates the effects of the propwash.
An in-house unmanned aerial system (UAS) is designed, analyzed and manufactured to support high-sensitivity and low-frequency ice penetrating radars to be used for research in the polar region. A 55 ...MHz antenna will be secured onto the wings. The UAS, called Astrid, is designed based on previous research experience that provided information on the significant effects of the polar atmospheric conditions (e.g. wind shear, gusts, etc.) on UAS performance. In addition to the adverse weather conditions, post flight test analysis showed that pusher engines on UASs cause significant changes to the aerodynamic forces and moments generated by the horizontal tail. This is primarily due to the turbulent nature of the propwash slipstreams flowing over the empennage and variation of their turbulency with changes in engine RPM. Based on this information, a wing configuration with a stabilizing polyhedral is selected. Astrid UAS also features a pusher engine with a twin boom, high-horizontal tail offset from the zero-lift plane. A dynamic model for Astrid UAS is developed using Advanced Aircraft Analysis (AAA), a program used to estimate aircraft stability and control derivatives. These derivatives are used to create a linear time-invariant system used for modal analysis. The dynamic model of the aircraft was used to investigate its handling qualities. Astrid's maiden flight test was successfully conducted in October 2019 and the longitudinal dynamic model is validated in subsequent flight tests.
Vertical take-off and landing (VTOL) aircraft leverage the performance and efficiency of fixed-wing aircraft with the operational flexibility of rotary-wing aircraft. However, their complex dynamics ...and the inherent multi-mode of operation often make sufficiently robust controller design difficult, time consuming, and expensive. Transitioning between flight modes (e.g. vertical takeoff to cruise or cruise to landing) risks instability, oscillations, and high-G maneuvers. These challenges have been traditionally solved by relying on multi-modal PID design patterns and gain scheduling, necessitating the development of a different controller for each flight mode. Modern VTOL flight controller methods (e.g. Model Predictive Control) are often heavily model dependent and lack robustness to large uncertainties in the aircraft dynamic model. Such dependency eliminates any opportunity for flight controller to be transferable between different aircraft platforms without labor intensive practices. This paper presents simulation results of a deep learning based model-agnostic quad mode VTOL controller that is trained and optimized with the Proximal Policy Optimization (PPO) algorithm in simulation. Our controller is fully policy based rather than dynamic model dependent (e.g. LQR, H2, MPC, etc.) and thus is fully transferable between models without any retraining. Flight controller performance and robustness against perturbation is shown through a rigorous test suite that leverages data generated from real flight tests and the Dryden wind turbulence model.
With the advent of the unmanned aerial systems (UAS) era, it is important that research be conducted into the reliable and safe operation of UAS in urban areas, where aircraft are flying over people ...and property in spatially constrained environments. A large focus in recent years has been on adaptable collision avoidance systems capable of avoiding fixed and airborne traffic. This paper presents flight test validation of an adaptive collision algorithm known as the morphing potential field algorithm. The morphing potential field algorithm has been modified to allow implementation of more advanced guidance logics such as L_{2}^{+} guidance. The aim is to validate the morphing collision avoidance path planning algorithm in a complex scenario, with multiple aircraft-two fixed wing and two rotary wing-flying the same spatially constrained area. The aircraft were intentionally put in a collision course with each other and other obstacles. Validation flight tests were successfully conducted to assess performance of morphing potential field navigation algorithms and also to quantify the impact of possible communication delays on the safety of collision avoidance methods for high speed and high inertia aircraft.
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