Rotorcraft

This thesis describes a dynamic height estimator and controller for rotorcraft landing and hovering in ground effect based on flowfield sensing and modeling. The rotor downwash in ground effect is represented using a ring-source potential flow model selected for real-time use. Experimental verification of the flow model and an augmented flow model for tilt are presented. A nonlinear dynamic model of a compound pendulum heave test stand that reduces to the dynamics of a rotorcraft in ground effect is presented with open-loop analysis and closed-loop control simulation. Equations of motion and stability characterization of of a heaving rotor IGE are derived for external perturbations and it is shown that a uniform sideward wind does not cause instability and uniform axial wind from the top can cause instability. Flowfield velocity measurements are assimilated into a grid-based recursive Bayesian filter to estimate height above ground in both simulation and experiment. Height tracking in ground effect and landing using the estimated height are implemented with a dynamic linear controller in both simulation and experiment. Mean estimation and motion errors are found to b e no greater than 5% and 9% respectively, demonstrating that height estimation and control is possible with only flow sensing and modeling.

At 14:46 JST on March 11, 2011, a massive earthquake hit the northeastern coast of Japan. The magnitude of the earthquake was 9.0 (Mw). It was the most powerful earthquake ever recorded in Japanese history. The earthquake triggered a deadly tsunami and swept away thousands of houses and lives. At the same time, the Fukushima Dai-ichi (No1) nuclear power plant was struck by the tsunami and the reactor took serious damage. This caused reactors to have a core meltdown and explode. There had been a radiation leak in the nuclear power plant. On March 15, the Japanese government set the restricted area within 30 km from the Fukushima nuclear power plant due to the radiation leakage. On March 17, two Japan Self Defense Force (JSDF) CH-47J helicopters dropped water to cool the failing reactor. The mission was successful, and the radiation around the reactor was gradually decreased, allowing for further operations. On April 14, one month after the disaster, the Japanese government requested the dispatchment of the Japan Coast Guard (JCG) for a search and rescue mission within the restricted area. This was the first search and rescue mission held at sea within a radioactive-contaminated environment in Japan, for which nine patrol boats, two airplanes, and three helicopters were sent for the mission. This paper describes the general outline about the cooling, thermo-monitoring, and the search and rescue missions as well as the equipment used, maximum permissible dose of radiation, and the mission environment. Then it compares this data with the helicopter operations during the Chernobyl accident. The purpose of this paper is to expand readers’ knowledge about helicopter operations during nuclear disasters with the hopes for it to be a useful material for future missions. The story of this paper is based on the author’s experience as a dispatched Japanese Coast Guard helicopter pilot.

This AGARDograph presents a general summary of suggested Night Vision Goggle (NVG) testing methods and should be used as a framework for developing airborne and laboratory based experiments to evaluate equipment. While there may be basic NVG test methods that can be applied regardless of the eventual use of the NVGs, some organizations will require specific tests of the equipment representative of the operational environment. An evaluation that involves ground and flight tests is desirable to address specific questions and general use issues, respectively. This approach is important because it extends measurements of device characteristics to real vision and flight performance. The objective of this document is to provide an inventory of rules, standards, procedures, methods and means needed to test and evaluate night vision systems. It identifies best practice methods from each of the participating countries. This is the first step in synthesizing a standardized test methodology. In order to meet its objective, the scope of this AGARDograph is limited to the testing of night vision devices based on image intensification technology. It does not cover other systems such as thermal imaging, infra-red (IR), millimetre wave radar and low light level television (LLTV). It extensively covers the test methodologies currently used by NATO countries to evaluate night vision systems. It also discusses specific system test methodologies relating to rotary wing aircraft. This AGARDograph includes sections covering the basic theory of the systems in use today, human vision and its relationship to the technology, general flight test methodology and an inventory of flight test techniques from NATO countries. Some consideration is given to the testing required as a precursor to flight test such as mock-up trials, simulation and aircraft ground trials. However, tests focused on health hazards, ballistic protection, acoustic protection, laser protection and the fitting and wearing of the helmet are not covered. The AGARDograph addresses the influence of NVGs on human visual perception and does not consider other sensor modalities (e.g. auditory or tactile) or aeromedical factors (e.g., neck strain, visual adaptation, eye strain, fatigue, etc.).

This aim of this work is to practice the conceptual and preliminary design phases for a rotorcraft that complies with a specific mission profile as a course project for the UUM527E Rotorcraft Design Course at the Istanbul Technical University. The rotorcraft in question is expected to hover for at least 24 hours which is a very demanding requirement in terms of fuel consumption, weight empty fraction and aerodynamic efficiency. The objective of this project simply pushes the limits of today’s technological boundaries in aerospace. Moreover, only a few rotorcrafts can handle such long endurance missions and most of them are still in development. Consequently, the design has to be innovative considering the possibilities of near future.

This research focuses on the development of an active rotor system capable of primary control and vibration reduction for rotorcraft.  The objective is to investigate the feasibility of a novel Trailing Edge Flap (TEF) actuation system driven by Pneumatic Artificial Muscles (PAMs).  A significant design effort led to a series of experimental apparatuses which tested various aspects of the performance of the actuators themselves and of TEF systems driven by them.  Analytical models were developed in parallel to predict the quasistatic and dynamic behavior of these systems.
Initial testing of a prototype blade section with an integrated PAM driven TEF proved the viability of the concept through successful benchtop testing under simulated M = 0.3 loading and open jet wind tunnel tests under airspeeds up to M = 0.13.  This prototype showed the ability of PAM actuators to generate significant flap deflections over the bandwidth of interest for primary control and vibration reduction on a rotorcraft.  It also identified the importance of high pneumatic system mass flow rate for maintaining performance at higher operating frequencies.
Research into the development and improvement of PAM actuators centered around a new manufacturing technique which was invented to directly address the weaknesses of previous designs.  Detailed finite element model (FEM) analysis of the design allowed for the mitigation of stress concentrations, leading to increased strength.  Tensile testing of the swaged actuators showed a factor of safety over 5, and burst pressure testing showed a factor of safety of 3.  Over 120,000,000 load cycles were applied to the actuators without failure.  Characterization testing before, during, and after the fatigue tests showed no reduction in PAM performance.
Wind tunnel testing of a full scale Bell 407 blade retrofitted with a PAM TEF system showed excellent control authority.  At the maximum wind tunnel test speed of M  = 0.3 and a derated PAM operating pressure of 28 psi, 18.8° half-peak-to-peak flap deflections were achieved at 1/rev (7 Hz), and 17.1° of half-peak-to-peak flap deflection was still available at 5/rev (35 Hz).  A quasistatic system model was developed which combined PAM forces, kinematics and flap aerodynamics to predict flap deflection amplitudes.  This model agreed well with experimental data.
Whirl testing of a sub-span whirl rig under full scale loading conditions showed the ability of PAM TEF systems to operate under full scale levels of centrifugal (CF), aerodynamic, and inertia loading.  A commercial pneumatic rotary union was used to provide air in the rotating frame.  Extrapolation of the results to 100% of CF acceleration predicts 15.4° of half-peak-to-peak flap deflection at 1/rev (7 Hz), and 7.7° of half-peak-to-peak flap deflection at 5/rev (35 Hz).
A dynamic model was developed which successfully predicted the time domain behavior of the PAM actuators and PAM TEF system.  This model includes control valve dynamics, frictional tubing losses, pressure dynamics, PAM forces, mechanism kinematics, aerodynamic hinge moments, system stiffness, damping, and inertia to solve for the rotational dynamics of the flap.
Control system development led to a closed loop control system for PAM TEF systems capable of tracking complex, multi-sinusoid flap deflections representative of a combined primary control and vibration reduction flap actuation scheme.
This research shows the promise that PAM actuators have as drivers for trailing edge flaps on active helicopter rotors.  The robustness, ease of integration, control authority and tracking accuracy of these actuators have been established, thereby motivating further research.

The future armed reconnaissance aircraft (FARA) program seeks to enable the development of new, highly capable vertical/short takeoff or landing (VSTOL) vehicles. The preliminary design of one air vehicle for a conventional rotorcraft is developed. The design process for this aircraft is detailed, and the advantages and disadvantages of the aircraft are discussed. Future efforts for the enhancement of the design are presented. The aircraft’s design is found to meet the FARA thresholds for forward flight, geometry, and hover.

This paper details the aerodynamic design and wind tunnel testing of the nacelle-mounted sails for the V-22 Osprey tiltrotor aircraft. Several Boeing wind tunnel tests dating back to the early 80's have shown great potential for improving the tiltrotor aerodynamic efficiency in cruise using nacelle-mounted sails. In 2008, a Boeing wind tunnel test of a 15%-scale model V-22 provided data on the effects of various sail design parameters. These included incidence, dihedral, and position on the nacelle. The goal of the test was to demonstrate that a set of full-scale representative sails would provide the target level of drag reduction on a flight test aircraft. The test also provided the opportunity to optimize a configuration that provided the best lift-to-drag ratio in cruise flight, therefore reducing the amount of flight testing that would be needed. The optimum design tested in the wind tunnel was a set of three sails per nacelle that provided an 8 percent increase in the cruise lift-to-drag ratio. On an aircraft, this improvement would yield a cruise drag reduction of approximately 10 percent. This improvement would amount to a nearly 5 percent increase in the performance margin for the Marine and the Air Force Self Deployment range capability. Data from the flight test is expected to provide design guidance for production implementation.

Financial support for helicopter operators to implement safety systems and equipment is essential to sustain the European Union (EU) rotorcraft community, and to prevent incidents and accidents from occurring because of a lack of the proper technologies. We delineate in our research the possibilities of obtaining funding to bring explicit benefits and give better information to European operators. This paper shows the current EU funding programmes for the aviation industry that are accessible.

Artykuł jest poświęcony weryfikacji jakości sterowania typu Active Disturbance Rejection Control (ADRC) dla zadania regulacji pozycji dwuwirnikowego systemu aerodynamicznego (TRAS). Technika ADRC nie wymaga od użytkownika znajomości dokładnego modelu matematycznego rozważanego obiektu. Jej ideą jest redukcja wszystkich nieznanych lub trudnych do zamodelowania zjawisk w obiekcie do wypadkowego zaburzenia estymowanego i kompensowanego w zamkniętym układzie sterowania. Wykorzystany w pracy system laboratoryjny TRAS to nieliniowy, wielowejściowy-wielowyjściowy obiekt
o dwóch stopniach swobody, z występującymi silnymi sprzężeniami skrośnymi. Otrzymane wyniki eksperymentalne pokazują przewagę metody ADRC nad klasycznym sterownikiem proporcjonalno-całkująco-rózniczkującym (PID) w kontekście odporności algorytmu na parametryczną i strukturalną niepewność modelu obiektu sterowania.

The aim of the article is to propose a robust and reliable engineering method for identifying and characterizing vortical structures within a flow field measured with a classic two-component PIV measurement system. Some of the most popular vortex-detection criteria are briefly presented for comparison purposes. Many of these fail if spurious vectors are present within the flow field due to poor PIV image quality. The proposed method was tested both on synthetic images of ideal vortices, having different spatial resolutions and different noise levels in order to perform a parametric assessment, and on real PIV images of a four-bladed rotor wake.

This paper presents a robustness study of an Active Disturbance Rejection Control (ADRC) framework. An experimental verification is carried out on a Two Rotor Aerodynamical System (TRAS). The cross-couplings and highly nonlinear behavior of this complex system limit the performance of classical and linear controllers, widely-used in industrial practice. Additionally, the obtainment of a reliable mathematical model of TRAS is a challenging and tedious job. In ADRC, the unmeasured dynamics and external disturbance, associated with the 2-DOF motion of TRAS, are treated as an additional state variable. It is then estimated by a Nonlinear Extended State Observer (NESO) and compensated in the control signal. The obtained results showed the effectiveness of proposed ADRC-based controller in coping with dynamic and nonlinear variations, commonly seen in aerodynamical systems. It was noticed that due to disturbance estimation and its further cancellation a precise mathematical model of the plant is not required. The ADRC robustness was compared through experiment with other model-free method, i.e. the proportional-integral-derivative controller (PID). Better outcomes in terms of disturbance rejection have been reported for the ADRC approach.

This paper discusses the Modern Technology Rotors Program at NASA Ames Research Center. This program is a joint NASA/Army effort, with extensive participation by industry. The program ideology and also current and future rotor systems which are to be included in this program are presented.

This aim of this work is to practice the conceptual and preliminary design phases for a rotorcraft that complies with a specific mission profile as a course project for the UUM527E Rotorcraft Design Course at the Istanbul Technical University. The rotorcraft in question is expected to hover for at least 24 hours which is a very demanding requirement in terms of fuel consumption, weight empty fraction and aerodynamic efficiency. The objective of this project simply pushes the limits of today’s technological boundaries in aerospace. Moreover, only a few rotorcrafts can handle such long endurance missions and most of them are still in development. Consequently, the design has to be innovative considering the possibilities of near future.

The aim of the article is to propose a robust and reliable engineering method for identifying and characterizing vortical structures within a flow field measured with a classic two-component PIV measurement system. Some of the most popular vortex-detection criteria are briefly presented for comparison purposes. Many of these fail if spurious vectors are present within the flow field due to poor PIV image quality. The proposed method was tested both on synthetic images of ideal vortices, having different spatial resolutions and different noise levels in order to perform a parametric assessment, and on real PIV images of a four-bladed rotor wake.

The paper illustrates a research activity carried out at CIRA with the aim to characterize experimentally and numerically the blade tip vortices of a small scale four-bladed isolated rotor in hover flight and to evaluate their decay process during the convection of the wake downstream. 2C-2D PIV measurements were carried out below the rotor disk down to a distance of one radius. The numerical simulations were aimed at assessing the modelling capabilities and the accuracy of a free-wake Boundary Element Methodology. Several detection criteria were investigated in order to identify a suitable one for the analysis of PIV data. The Γ 2 vortex was selected as the most robust and reliable criterion and was applied to both experimental and numerical results. The tip vortices were characterised in terms of vorticity, circulation, swirl velocity, core radius and trajectory. The rotor wake mean velocity field and the instantaneous vortex characteristics were investigated. The experimental/num...