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EFFECT OF CONTROL SYSTEM AUGMENTATION ON HANDLING QUALITIES AND TASK PERFORMANCE IN GOOD AND DEGRADED VISUAL ENVIRONMENTS Colin R. Theodore Ben Lawrence Carlos A. Malpica San Jose State Foundation (SJSUF) Aeromechanics Office NASA Ames Research Center NASA Ames Research Center Moffett Field, CA Moffett Field, CA James E. Lindsey Christopher L. Blanken Monterey Technologies, Inc.
Mark B. Tischler NASA Ames Research Center U.S. Aviation Development Directorate-AFDD Moffett Field, CA Aviation & Missile Research, Development & Engineering Center (AMRDEC) Tom Berger Research, Development and Engineering Command University Affiliated Research Center (UCSC) Ames Research Center NASA Ames Research Center Moffett Field, CA Moffett Field, CA In June 2013, NASA and the U.S. Army jointly conducted a simulation experiment in the NASA-Ames Vertical Motion Simulator that examined and quantified the effect s of limited-authority contro l system augmentation on handling qualities and task performance in both good a nd degraded visual environments. The vehicle model used for the experiment was the OH-58D with similar size, weight and performance, and the same 4-blade rotor system as the Bell 407 civilian helicopter that is commonl y used for medical evacuation and emergency medical services. The control systems investigated as part of this study included the baseline aircraft Rate Command system, a short-term Attitude Command/A ttitude Hold system that uses lagge d-rate feedback to provide a short- term attitude response, Modernized Control Laws that provide an Attitude Command/Attitude Hold control response type, and Modernized Control Laws with an a dditional Position Hold f unction. Evaluation tasks included the ADS-33 Hover, Sidestep , Acceleration/Deceleration, and Pirouette Mission Task Elements, as well as a new proposed Emergency Medical Services task that includes an approach and landing at a minimally prepared remote landing site. Degraded visual enviro nments were simulated with night vision goggles and an unaided night scene. A total of nine experimental te st pilots participated in the four-week simulation experiment. Data recorded during the evaluation in cluded Cooper-Harper handling qualities ratings, Bedford Workload scale ratings, and task performance. The Usable Cue Environment (UCE) was measured for this simulation experiment, and found to be UCE=1 in good visual environments and UCE =2 in degraded visual environments with night vision goggles . Results showed that handling qualities ratings were improved with a control system providing short-term attitude respons e over a rate command system, although the improvements were not sufficient to produce Level 1 handling qualities in degraded visu al environments. Results for an Attitude Command/Attitude Hold control system showed that borderline Level 1 handling qualities could be achieved in degraded visual environments, and the 10% authority stability augmentation system was adequate to obtain these handling qualities ratings.
Introduction flying in IMC and DVE. The Aeronautical Design Standard-33 (ADS-33) Handling Qualities Requirements The hazards associated with he licopter flight in Degraded for Military Rotorcraft (Ref. 3) defines control system Visual Environments (DVE) have led to a number of response type requirements as a function of Usable Cue accidents, both in military operations, particularly in Environment (UCE), or the “quality” of the visual brownout conditions (Ref. 1), and in civilian operations conditions. In degraded visual conditions (UCE>1), with inadvertent flight into Instrument Meteorological ADS-33 requires a minimum Attitude Command/Attitude Conditions (IMC) and loss of situational awareness Hold (ACAH) response type, along with Rate resulting from degraded visual conditions (Ref. 2) being Command/Direction Hold (RCDH) and Rate significant contributors. Fo r small helicopters, a major Command/Height Hold (RCHH) depending on the contributor to the high accident rate is their inherent specific Mission Task Element (MTE), in order to obtain instability without advanced control modes. This Level 1 handling qualities.
instability can lead to excessive pilot workload when ___________________________________ Presented at the American Helicopter Society 70th Annual Forum, Montreal, Canada, May 20-22, 2014. This is work of the U.S.
Government and is not subject to copyright protection in the U.S.
The mitigation of DVE has received increased attention unsatisfactory for stability and control characteristics of recently with many research efforts typically focusing on the current fleet, and recommends that handling qualities one or more of the following areas: 1. improved sensors standards for all future helicopters be at a level consistent to better detect the terrain and obstacles around the with available modern technologies, and that certification rotorcraft, including the ability to see at night and in low criteria be reviewed and modified to ensure undesirable light conditions, and through fog, rain, dust, sand, etc.; 2. flying characteristics encounter ed in real world use be improved heads-up and heads-down displays to provide identified in pre-certification testing and corrected.
the pilot with improved situational awareness; and, 3.
improved flight controls through advanced control modes A study by the United Kingdom Civilian Aviation to reduce pilot workload and improve flight precision. Authority, Safety Regulati on Group (Ref. 7) looked at The combination of these three key technologies to accident data from 1975 to 2004 in order to identify provide for safe and effective operations in the DVE handling qualities related causes of accidents. The single comprise what has been commonly referred to as the largest cause of accidents (excluding mechanical failures) “three legged DVE stool” (Ref. 4). for small helicopters was identified as loss of control due to spatial disorientation resu lting from degraded visual Many studies have looked at the cause of helicopter conditions such as ‘inadvertent IMC’ (IIMC). Ref. 7 accidents and have concluded that handling qualities concluded that when DVE was encountered, the primary aspects contribute to many acci dents in both Good Visual cause of accidents was poor pilot situational awareness Environments (GVE) and DVE, and that accident rates and spatial disorientation in which poor or inappropriate can be reduced by making helicopters easier to fly with mechanical flight control characteristics resulted in additional augmentation. The study by Dugan and degraded handling qualities; increased pilot workload that Delamer (Ref. 5) examined civilian mishaps between further exacerbated the problem. Ref. 7 also suggested 1993 and 2004 and found that most incidents occurred in that serious consideration mu st be given to improvements GVE, especially single main rotor helicopters, and in in regulations, operating procedures and requirements for particular helicopters with teetering rotors that were not pilot training.
augmented or had only “limited” rate stabilization. Ref. 5 proposes that even small improvements to helicopters On the military side, Ref. 1 from 2009 states that DVE stability and control could dramatically reduce accident caused by brownout and whiteout account for almost half rates and recommends helicopter airframe manufacturers of the Air Force rotorcraft airframe losses, and are the study the feasibility of designing or incorporating low leading cause of airframe losses for the Army. In addition cost, lightweight stability augmentation systems. Where a to the safety impact, DVE creates impediments to hydraulic system is not practical for inclusion in the operations where these conditions occur. Ref. 1 also design, the technology currently exists to provide the mentions that numerous tec hnologies are being developed secondary or automatic flight control system functions to mitigate DVE, and that a systems approach that with small electric actuators. Ref. 5 also states that if includes increased ability to “see through” or “see and stability augmentation systems are implemented, along remember,” improved handling qualities at low speeds in with other safety investment strategies, a reduction in the landing zone, improved display symbology for accident rate of as much as 50% may be achievable. aircrew situational awareness, and auto-land capabilities for rotorcraft are all potentia l elements to the total DVE An earlier study by Harris, Kasper and Iseler (Ref. 6), solution. With respect to handling qualities, Ref. 1 examining NTSB narrative summary data for 8,346 mentions that one of the major causes of rotorcraft low- rotorcraft accidents from 1963 to 1997, found that the two speed mishaps in DVE is undetected drift resulting in largest piloting related causes of accidents were collision dynamic aircraft rollover and/or contact with structures or with obstacles (15.7%) and loss of control (13.2%). Ref. other aircraft. The leading types of hover mishaps for 6 notes that a major source of difficulty was the coupling military rotorcraft are main-rotor and tail-rotor strikes.
between the application of power and the yaw response of Ref. 1 proposes that low-speed handling qualities be single main rotor helicopters making them inordinately improved through the use of appropriate flight controls difficult to fly, particular ly during divided attention response types which meet the requirements of ADS-33 operations, and mentions that the addition of an automatic (Ref. 3). These response types include Attitude stability and control system generally reduced overall loss Command/Attitude Hold and hover-position hold so that of control situations. To combat these handling qualities the rotorcraft will not enter an undetected drift while in deficiencies, Ref. 6 recommended that low-priced hover, and translational rate command to allow the pilot stability augmentation systems, at a minimum for yaw, be to precisely maneuver the airc raft with reduced workload.
developed and certified at least with 10% authority. Ref.
6 also mentions that civilian handling qualities design An earlier study by Key (Ref. 8) examined rotorcraft standards date back to the 1950s and are now accidents due to pilot error over a period from 1986 to 1998 and characterized these into groups related to task specific MTE, in order to obtain Level 1 handling difficulty, situational awarene ss and visual environment. qualities. For UCE=3 or IMC operations, additional The outcome of this study is that poor handling qualities augmentation in the form of Translational Rate Command can exist while performing hover and low speed tasks, (TRC), Rate Command/Direction Hold (RCDH), Rate especially in DVE, and that handling qualities research Command/Height Hold (RCHH) and Position Hold (PH) showed that control laws optimized for daytime are required to obtain Level 1 handling qualities.
operations typically result in poor handling qualities in DVE and at night. Ref. 8 concluded that handling The background for the requirements specified in the qualities improvements are possible with flight control ADS-33 handling qualities requirements guide is augmentation that provides ACAH, and that this can be presented in Ref. 9, and includes results from a number of achieved even with limited authority systems that studies that examined the effects of control system currently exist in the helicopter fleet. Ref. 8 also pointed augmentation on helicopter handling qualities in both out that average pilot experience reduced from 1324 hours GVE and DVE. Ref. 10 includes results of a study on the in 1992 to 536 hours in 1997 and suggests that this National Research Council of Canada variable stability reduced experience contributed to an increase in observed Bell 206 aircraft using NVGs and daylight filters to accident rate over that time. This study concluded that simulate various levels of DVE. This work identified two reduced pilot experience may be revealing existing critical issues when operating helicopters at night and/or handling qualities issues, and since flight time and in poor weather conditions, namely, the basic problem of proficiency are likely to decrease further, the importance avoiding collisions with fixed or moving objects, and the of achieving good handling qualities becomes key so as to loss of ability by the pilot to adequately stabilize the demand less skill from the pilot.
aircraft. Ref. 10 investigates the hypothesis that loss of control caused by DVE can be compensated for with The studies just mentioned have established a link increased aircraft stability, and the specification between accidents in both GVE and DVE associated with methodology behind the UCE definition attempts to inadequate handling qualities in hover and low speed quantify this. Ref. 11 examines the effects of handling flight, and suggest that the accident rate would be reduced qualities and displays in hover and low-speed flight in with increased levels of flight control augmentation. reduced visibility conditions. The results of this study Some of these studies also suggested that current indicate that rate and attitude command may be used for certification requirements are inadequate to eliminate varying levels of partial IMC, but that TRC is required for configurations with poor handling qualities, particularly low speed and hover operations in zero visibility. Ref. 11 in DVE and in high pilot workload situations. Ref. 7 concludes that the addition of displays, such as flight provides a survey of civil regulations most pertinent to directors, were not a substitute for control system civil helicopter operations in degraded visual conditions augmentation.
with the objective of identifying gaps and shortfalls in the current set of regulations and making recommendations For the OH-58D, a recent study by Berger, et al in Ref.
on how these might be addressed. Ref. 7 notes that civil 12, looked at the effect of optimizing and augmenting the regulations divide operations into either visual flight rules current OH-58D Rate Command stability and control or instrument flight rules with no particular consideration augmentation system, which was developed by hand given to DVE operations, and that the regulations do not tuning the control law gains duri ng flight testing. Results clearly address DVE and divided attention operations. compared flight test handling qualities ratings for the Ref. 7 concludes from a review of civil handling qualities baseline OH-58D Rare Command control system and an requirements that the many requirements are too optimized short-term ACAH control system with select subjective and open to interpretation by manufacturers ADS-33 Mission Task Elements (MTEs) in both GVE and qualification test pilots, and that the criteria for DVE and DVE. Ref. 12 concluded that the optimized short- and divided attention operations described in ADS-33 term ACAH control system provided better handling (Ref. 3) are similarly applicable to civil helicopter qualities in both GVE and DVE, but mentions that the operations. short-term ACAH control syst em did not meet the ADS- 33 requirement for an ACAH response type in DVE for From a military perspective, flight control augmentation the short-term response only due to the lack of pure requirements are presented in ADS-33 (Ref. 3), which attitude feedback. A further conclusion from Ref. 12 is indicates that Rate Command is sufficient to obtain Level that pilots did not notice a significant difference between 1 handling qualities in GVE (UCE=1) for near earth hover the baseline and short-term ACAH designs for more and low speed operations. In UCE=2 (DVE), Ref. 3 dynamic maneuvers, such as the Sidestep MTE, requires, an ACAH response type, along with Rate Acceleration/Deceleration MTE and the run-in to the Command/Direction Hold (RCDH) and Rate Hover MTE, confirming that the benefits associated with Command/Height Hold (RCHH) depending on the short-term ACAH are most observed in high-bandwidth tasks, such as the deceleration and station keeping The anticipated outcomes of this experiment include: portions of the Hover MTE. The handling qualities - Assessment and quantification of the benefits of ratings for the RC and short-term ACAH control systems increased control augmentation with a partial used in the current simulation experiment will be authority flight control architecture for missions in validated against the flight test results for both GVE and GVE and DVE.
DVE shown in Ref. 12. - Initial development of mission task elements and evaluation metrics appropriate for civil missions in In June 2013, NASA and the U.S. Army jointly conducted DVE, including Medevac and EMS operations.
a simulation experiment fo cused on improved flight - Refinement of control syst em and handling qualities requirements for civilian Medevac/EMS and military control to evaluate the effect s of limited-authority control system augmentation on handling qualities and task scout helicopters.
performance in both GVE and DVE. The vehicle model Approach used for this experiment was the OH-58D with similar size, weight and performance, and the same 4-bladed rotor system as the Bell 407 air ambulance helicopter that A pilot-in-the-loop handling qualities simulation experiment of the OH-58D was conducted in the NASA- is commonly used for Medical Evacuation (Medevac) and Ames Vertical Motion Simulator (VMS) to address the Emergency Medical Services (EMS). The OH-58D includes a standard partial authority (±10%) Stability and above objectives. The OH-58D aircraft model was configured with a number of different flight control Control Augmentation System (SCAS), while for the Bell systems to provide different levels of control 407 a SCAS is available as an aftermarket option, such as the Cobham HeliSAS analog autopilot and stability augmentation. Tests were conducted in both GVE and DVE, with DVE simulated primarily with the pilots augmentation system (Ref. 13 ). The control systems wearing Night-Vision Goggles (NVGs) in a simulated investigated during this si mulation experiment include: night scene, but also with an unaided night scene. The the baseline aircraft Rate Command (RC) system; a short- test maneuvers included Mission Task Elements (MTEs) term Attitude Command/Attitude Hold (st-ACAH) system from ADS-33 for the scout/attack class rotorcraft (Ref. 3), that uses lagged-rate feedback rather than attitude including: Hover, Pirouette, Sidestep, and feedback to provide a short-term attitude response; Acceleration/Deceleration maneuvers. A civilian EMS Modernized Control Laws (MCLAWS) that provide an type mission/task of landing at a remote, minimally Attitude Command/Attitude Hold (ACAH) control prepared site in the presence of obstacles (EMS Approach response type; and, MCLAWS with an additional Position MTE) was developed and also included in this Hold function (MCLAWS+PH). No altitude hold mode experiment.
was implemented in the control systems.
A total of nine experimental test pilots (XPs) from NASA, This paper begins with the objectives and approach of the U.S. Army, U.S. Navy, Fede ral Aviation Administration current simulation experiment. The description of the (FAA), and the U.S. rotorcraft industry participated in the simulation experiment includes an overview of the OH- experiment along with three non-XPs with extensive OH- 58D flight dynamics model and the flight control systems 58, DVE and/or EMS operational experience. All of the used in the experiment, a description of the VMS facility pilots had extensive rotorcra ft experience in light utility and pilot controls and displays, the experimental single main rotor helicopters and in other helicopter sizes evaluation tasks and procedures, and finishes with the and configurations. The diverse breadth of backgrounds overall test matrix. Next, results are presented for the and control techniques by the different pilots provided a different ADS-33 MTEs used during the experiment and widely representative sampling group. The evaluation the EMS Approach MTE developed for this experiment.
pilots were asked to provide comments and handling Results shown include the performance for the individual qualities ratings (HQRs) using the Cooper-Harper rating tasks and the Cooper-Harper handling qualities (Ref. 14) scale (Ref. 14), step through a questionnaire tailored and Bedford Workload ratings (Ref. 15). Results are also specifically for this experiment, and were also asked to included for an evaluation of the usable cue environment estimate their spare pilot workload capacity on the provided in the simulation in both GVE and DVE Bedford Workload scale (Ref. 15). For the MTEs used in conditions. Finally a summary and the conclusions of the this experiment, Visual Cu e Ratings (VCR) (Ref. 16) experiment are presented.
were collected to evaluate the UCE in simulated GVE and DVE. The data collected during this experiment also Objectives included the task performance data for the ADS-33 MTEs and the new EMS Approach MTE proposed and The objective of this study is to investigate and quantify investigated as part of this study. The following section the effect of control system augmentation on handling describes the experiment design and methodology in more qualities and pilot task performance in GVE and DVE.
detail, including the simulation model and experiment test feedback, are used to achieve a st-ACAH response type in procedures. pitch and roll. The st-ACAH concept could be implemented for any aircraft with an existing rate- Description of Simulation Experiment response type SCAS using the same control hardware architecture, reducing the cost of any potential upgrades.
Aircraft Model and Flight Control Systems The st-ACAH response type is provided in hover up to 40 knots, and is blended to RC from 40 to 60 knots with RC The experiment was conducted using the OH-58D aircraft beyond 60 knots.
that has a maximum gross wei ght of about 5,500 lbs. and includes a three-axis (pitch, roll, and yaw) partial The control system characteristics are provided in Table authority (±10%) Stability Control Augmentation System 1, which shows that this concept meets ADS-33 Level 1 (SCAS). The state-space fli ght dynamics models of the requirements with improved damping over the rate aircraft were extracted usi ng system identification (Ref. command system. As presented in Ref. 12, the st-ACAH 17) from flight test data. Models, which were identified control system rendered Level 1 handling qualities ratings at hover and 80 knots from previous research (Ref. 12), in a GVE. However, the lack of a long-term attitude hold were ‘stitched’ together along with trim data to develop a capability, RCDH and RCHH resulted in Level 2 (HQR continuous dynamics model (Ref. 17) that is valid up to 4) handling qualities in the DVE.
about 100 knots. The Control Equivalent Turbulence Input (CETI) model (Ref. 18) was configured for the OH- Modernized Control Laws (MCLAWS) The MCLAWS 58D and incorporated into the analysis model to provide system was developed to expand on the st-ACAH work realistic turbulence for the simulation. Four different that was done. The design objectives were to build on the control system concepts were implemented as part of this good short-term response characteristics of the st-ACAH experiment, which are described in the following sections. control laws, but extend the attitude hold capabilities to steady-state using a direct attitude measurement that is Rate Command (RC) The RC system is the baseline available on most modern helicopters. Originally control system of the OH -58D. It provides a rate developed for the AH-64 Apache (Ref. 19), MCLAWS command response type that in cludes rate stabilization via achieves an ACAH response type in pitch and roll using an angular rate feedback loop and a control input feed- existing partial-authority SCAS actuators with special forward loop for control augmentation. As described in attention paid to minimizing the saturation of the SCAS Ref. 12, these control laws were hand-tuned in flight, and servos. Figure 1b shows a block diagram schematic of are not optimized to meet the handling qualities MCLAWS, which replaces the simple SCAS block in requirements as are the other three control system Figure 1a. MCLAWS subtract s out the mechanical stick concepts. However, this RC control system is to actuator path, and replaces it with an explicit model representative of the OH-58D as well as many of the following control system, which consists of an attitude helicopters that are used for civil EMS type missions response command model, an inverse plant, and a today, and so it was picked for this study.
feedback loop. These control laws were adapted and ® optimized using CONDUIT (Ref. 20) for the OH-58D Figure 1a shows a block diagram schematic of the RC for this experiment to ensure that within the SCAS authority, the aircraft response will track the command control system. Pilot stick inputs are fed into both a mechanical mixer and the SCAS. The SCAS outputs drive model. In the yaw axis, MCLAWS includes a Rate the limited-authority SCAS actuators, which are summed Command/Direction Hold (RCDH) mode, which captures with the mixed pilot stick commands, and used to drive and maintains a heading once the pilot releases the pedals.
the boost actuators. Finally, the rates from the bare- As with the st-ACAH control systems, MCLAWS are airframe are fed back to the SCAS. blended to rate command from 40 to 60 knots. It should be noted that a sensor package providing attitude Table 1 shows the control system characteristics of the measurements would need to be added to the aircraft to rate command system. The rate command control system achieve an MCLAWS control system.
exhibits Level 2 performance for closed-loop damping and pitch axis phase margin. Table 1 shows the control system characteristics of the MCLAWS design. The command models in the Short-term Attitude Command/Attitude Hold (st- MCLAWS design were tuned to achieve the same Level 1 ACAH) The st-ACAH control system was developed and piloted bandwidths as the st-ACAH design, as seen in the table. The feedback gains were optimized to give the test flown in 2011 as a possible upgrade to the OH-58D SCAS (Ref. 12). This system uses the same hardware as same crossover frequencies and disturbance rejection the rate command system shown in Figure 1a, however bandwidths as the st-ACAH design, while achieving lagged-rate gains, equivalent to washed-out attitude better closed-loop damping.
a UH-60 collective stick and was deemed to be sufficient MCLAWS plus Position Hold (MCLAWS+PH) A for this particular simulation experiment. Note that none position hold functionality was added to MCLAWS that of the button or switches on the collective inceptor were engages when the center stick is in detent and the speed is used during this experiment.
below 5 knots. Below 5 knots, a deceleration to hover is initiated with position hold engaging when the ground The primary flight display and the horizontal situation speed is below 0.5 knots. The system allows the pilot to (hover) display, similar to the Army’s Common Avionics ‘adjust’ the hover position with a ‘hat’ switch on the Architecture System (CAAS) displays, were provided on cyclic control inceptor. No altitude hold mode was the instrument panel. The Ho rizontal Situation Indicator (HSI) display provides the pilot with some cueing implemented in the MCLAWS+PH control system.
information regarding the current mode when the Figure 1c shows the block diagram schematic for the MCLAWS+PH flight control mode is engaged. Figure 6(a) shows the display in a transition mode with the stick velocity and position outer-loops wrapped around the ACAH inner-loop. Since thes e loops are only active with out of detent, or with the speed above 5 knots. Below 5 the stick in the detent position, subtracting out the direct knots and with the stick in detent, a deceleration to hover is initiated, indicated in Figure 6(b) with a green dot stick to actuator path using the mechanical mixing model is not needed. inside the green acceleration circle near the center of the HSI display. When the speed drops below 0.5 knots, position hold is engaged, indi cated in Figure 6(c) where Table 1 shows the control system characteristics of the MCLAWS+PH design. The inne r-loop is identical to the the green circle is filled grey. The pilot can ‘adjust’ the MCLAWS design, as seen in the table. Also shown are hover position with the ‘coolie hat’ switch on the cyclic control inceptor. A single “click” of the ‘coolie hat’ is 1- the additional velocity and position hold loop characteristics. These loops were optimized in foot translation, while hol ding the deflection of the ® CONDUIT using a nested optimization approach as ‘coolie hat’ is a translational rate of 4 ft/sec.
presented in Ref 21. Table 1 shows that the stability margins are disturbance rejection bandwidths for the outer Carefully tailored visual scenes of the ADS-33 and EMS velocity and position loops all meet the Level 1 type evaluation tasks were developed with attention to requirements. The table also shows the 3 σ variations in task cueing and visual text ures in both GVE and DVE the position of the helicopter during simulated moderate conditions. For this experiment, DVE was simulated primarily with the pilots wearing Night-Vision Goggles turbulence. These values are within the ±3 ft requirements of the ADS-33 Hover MTE. (NVGs) in a simulated night scene, but also with an unaided night scene. Figure 7 shows a photo of the NVGs Facility mounted to the pilots’ helmet. The goggles used were ITT Exelis Aviator’s Night Vision Imaging System The experiment was conducted in the Vertical Motion (ANVIS) AN/AVS-6 goggles.
Simulator at NASA-Ames Research Center, described in Ref. 22 (Figure 2). The Transport Cab (T-Cab) was used. Evaluation Tasks and Procedures This cab provides the pilot with 205-degree field of view, as well as a chin window, as shown in Figure 3. The The test maneuvers flown as part of this experiment simulation facility provides six-degree-of-freedom motion included Mission Task Elements (MTEs) from ADS-33 with 60-feet of vertical and 80-feet of lateral travel, which for the scout/attack class ro torcraft, including: Hover, Pirouette, Sidestep, and Acceleration/Deceleration is a unique facility for rotorcraft handling qualities work.
Helicopter center stick, collective stick and pedal pilot maneuvers. These maneuvers were flown in accordance control inceptors were selected to closely match those of with the procedures and performance targets outlined in ADS-33 (Ref. 3), with the excep tion of the Sidestep MTE.
the OH-58D and were installed for the right cockpit seat, the evaluation pilot position. The center stick used for For this experiment, the Sidestep MTE was performed this experiment is shown in Figure 4 and is a cyclic using a translation to the right only rather than the right then left translation described in ADS-33. The reason for inceptor from a Seahawk, which was judged by a current OH-58 pilot to be the closest available cyclic inceptor to this change is that the VMS visual system does not the OH-58D inceptor. The Trim Release button is in the provide enough visual cueing out the left side window to enable the aggressive lateral bank and motion to the left.
center of the upper panel of the cyclic stick, and the position hold ‘coolie hat’ switch is to the left of the Trim Release button. The Trim Release button removes and re- A civilian EMS type mission/task of landing at a remote, minimally prepared site in the presence of obstacles (EMS centers the stick forces when it is pressed in any of the flight control modes. The collective stick used in this Approach MTE) was developed and also used in this experiment is shown in Figure 5. This is representative of experiment. The EMS task had the pilot start at 65-knots level flight at 250-feet AGL on a heading 90-degrees ability to track the desired glideslope, and their landing from the final approach path to the landing zone. Figure 8 performance in-terms of distance to the center of the shows a picture of the general EMS Approach MTE with landing zone and their ground speed and attitudes at the landing zone just to the left of the middle of the landing.
picture, centered among the simulated buildings and water tower. The pilot would then make a 90-degree right Pilots were required to complete initial training sessions descending, decelerating turn to an altitude of 200 feet to familiarize themselves with the OH-58D flight and a speed of 15 knots to prepare to begin the descent. dynamics and the control systems evaluated during this The descent starts when the aircraft was positioned along experiment, the ADS-33 MTEs and the EMS Approach a nominal 12-degree glideslope to landing in the center of MTE, the particulars of the motion and visual cueing a defined landing zone. The pilot was required to provided in the VMS in both GVE and DVE, and maintain a ground speed of 15 knots during the descent, operation of the NVGs in DVE. Prior to evaluation runs, which translates into about 325 ft/min of descent rate. the pilots flew each configuration for practice purposes as Figure 9 shows a screenshot fr om the simulation with the many times as required until the pilots felt consistent aircraft in the vicinity of the landing zone. The landing performance could be achieved. The task displays were zone is marked with cones spaced in a 100x100-foot box, available for the pilot to look at in the cab following each with the desired landing point in the middle of the landing practice run so that they could see their performance for zone. that particular run. For the formal evaluation runs, pilots were required to perform a minimum of three runs prior to Figure 10 shows an unaided night scene from the pilot the collection of pilot comments and ratings. If pilots felt perspective of the landing zone during final approach. that a run was anomalous, or they felt that they needed This night scene would be viewed by the pilot through additional runs to fully evaluate the configuration, they NVGs and unaided to simulate DVE conditions. For the were free to execute additional runs as desired. For the night scene, the cones marking the extent of the landing evaluation runs, the information on the task performance zone are replaced by simulated flashlights positioned on displays was read back to the pilot as to their performance the ground pointing towards the center of the landing in terms of desired and adequate standards for each MTE.
zone. The headlights of two vehicles are used to also cross illuminate the center of the landing zone, and an The data recorded during the experiment included the ownship mounted spotlight also helps to illuminate the pilot control inputs, aircraft state data and the task landing zone. Figure 11 shows a view of the landing zone performance for each of the MTEs evaluated, as well as through the NVGs. The NVG scene eliminates the pilot comments and ratings. The pilot would first run vehicle headlights and the ownship spotlight. The pilot through a questionnaire specifically tailored for this terminated the approach in a hover for 5 seconds over the experiment, shown in A ppendix A, providing their center of the landing zone before descending to a landing. comments and impressions for each of the questions During the approach and descent, the pilots ‘call out’ listed. This questionnaire includes the pilot providing when they have acquired the glideslope and are Cooper-Harper Handling Qualities ratings in accordance descending towards the landing zone, and a second call with Figure 13 (Ref. 14), and an estimate of their spare when they are initiating the deceleration to the hover workload capacity on the Bedford Workload scale shown position. Table 2 contains the performance standards for in Figure 14 (Ref. 15). Pilots were also asked to assign the EMS Approach MTE. It should be noted that the numerical scores from one to nine rating the level of performance standards listed in Table 2 are considered to precision obtainable, their ability to be aggressive, the be notional at this stage since this is a proposed new MTE ride quality during the maneuver, and the predictability of and precise and meaningful performance standards are yet the aircraft response to pilot inputs. These questions were to be established. The performance standards were developed by Lusardi, et al in Ref. 23, and the application chosen based on pilot feedback and were aimed at of a numerical rating scale allowed for quantitative achieving a balance between providing a realistic analysis of the otherwise qualitative comments.
operational flying task and making the task repeatable across pilots. Test Matrix Figure 12 shows an example of the test engineer displays The full matrix of configurations evaluated during this used to monitor pilot performance metrics for the task, experiment is shown in Table 3. The goal was to have based on the ability of the pilot to maintain speed and each of the nine experimental test pilots run through this glideslope, and their ability to land in the center of the entire test matrix, however this was not possible for all of landing zone with minimal ground speed. Following each the pilots. Table 3 also lists the number of test pilots who run, feedback was provided to the pilot on their ability to provided evaluations for each of the configurations. A maintain speed though the approach and landing, their couple of notes for this test matrix are: - One level of turbulence was used throughout the UCE Evaluations: entire simulation experiment. This turbulence level was set as a trade-off to provide adequate The UCE was evaluated as part of this experiment in both disturbances to increase pilot workload for task GVE and DVE with NVGs using the procedures outlined performed in GVE, while not providing unnecessarily in ADS-33 test guide (Ref. 16). As required in ADS-33, high workload in more difficult tasks, such as the the evaluation was conducted using the RC control system Hover MTE in DVE with the Rate Command control for the Hover MTE using the DVE performance system. standards. The UCE for DVE with an unaided night - All of the maneuvers were flown with no steady scene was not evaluated since the simulated ADS-33 winds. Various wind speeds and directions were Hover MTE course could not be used in DVE unaided examined for the Pirouette and EMS Approach tasks, conditions. A total of three pilots provided Visual Cue but it was felt that the inclusion of turbulence, Ratings (VCRs) with the ratings summarized in Table 4.
particularly in DVE, was sufficient to provide a Figure 15 shows average attitude and translational rate representative level of pilot workload. VCRs plotted on the UCE Criterion Boundary (Ref. 3).
- The MCLAWS+PH control system was evaluated Two sets of VCRs for GVE and DVE are plotted on only with the Hover MTE. In initial testing, the Figure 15, one (labeled as ‘A ll Pilots’) with the average Hover MTE proved to be the best MTE at VCRs for all of the pilots, a nd the other (labeled as ‘No differentiating between the MCLAWS configurations Pilot C’) is the average VCRs from the pilots who with and without Position Hold activated. The provided the worst VCR ratings. The VCR results shown addition of Position Hold for the other ADS-33 in Figure 15 indicate that GVE provides UCE=1 and DVE MTEs and the EMS Approach MTE did not provide with NVGs provides UCE=2. These UCE ratings for any additional information beyond the MCLAWS GVE and DVE with NVGs are consistent with the OH- control systems. 58D flight test results (Ref. 12), which also had UCE=1 in - The EMS Approach task was set-up in the simulation GVE and UCE=2 in DVE with NVGs.
to be flown from any direction to the landing zone, where the fixed locations of the buildings and terrain The translational rate VCR ra tings shown in Table 4 show would provide different visual cues to the pilots that there is no significant di fferent in GVE longitudinal during their descent and landing. Initially it was and lateral cueing. However the ratings in DVE are proposed to have the pilots fly familiarization or higher for longitudinal translation than lateral, indicating practice runs at a particular approach angle, and then that longitudinal translationa l rate cueing is poorer than use different approach angles for the evaluation runs. lateral in DVE with NVGs.
However, in order to be consistent, it was decided that all of the familiarization and evaluation runs be Hover MTE Results: flown at the same approach angle to the landing zone for all of the pilots. The effect of control augmentation on Cooper-Harper - The EMS Approach MTE was flown in DVE unaided handling qualities ratings for the ADS-33 Hover MTE in as well as DVE with NVGs since the illuminated GVE and DVE with NVGs is shown in Figure 16. This landing zone provided sufficient cueing for the figure also shows the flight test data for the OH-58D for approach and landing to be flown in DVE unaided. GVE and DVE flight with the legacy or baseline rate The ADS-33 MTEs that included simulated hover response control system (for si mplicity, this is referred to and cueing boards, and lines and cones on the as the RC control system flight test data in this paper) and ground, did not provide enough cueing to the pilot st-ACAH control system as presented in Ref. 12.
when flown in DVE unaided; therefore, they were in DVE with NVGs only. In GVE, all of the pilots provided handling qualities ratings of 4-5 for the RC control system, indicating that Results this is a solidly Level 2 aircraft for this task in GVE. This is comparable with the OH-58D flight test results with the same RC control architecture, where the two pilots both Over 1400 data runs were performed as part of this provided handling qualities ratings of 4. ADS-33 experiment with 12 different evaluation pilots, including indicates that a RC system is the minimum response type nine experimental test pilo ts (XPs) from NASA, U.S.
required for Level 1 Handling Qualities in GVE Army, U.S. Navy and FAA, and 3 non-XPs that had (UCE=1), however for this particular aircraft in the Hover extensive OH-58, DVE and/or EMS operational MTE, the RC system produced Level 2 handling qualities.
experience.
For the st-ACAH control system the average handling qualities rating is 3.5, which is borderline Level 1, and is an improvement of about 1. 0 HQR when compared with the RC control system. This indicates that with a and stick motion Root Mean Squared (RMS) for the moderate augmentation to th e RC control system, Level 1 Hover MTE are shown in Figures 17 and 18. The cut-off handling qualities can be achieved in GVE for the Hover frequency is defined by Tischler and Remple (Ref. 17) MTE. These results are comparable with the flight test and is a good measure of the piloted operating frequency results for the OH-58, where both flight test pilots gave a and crossover frequency. For longitudinal stick cutoff HQR 3 for the st-ACAH in GVE. frequency and RMS shown in Figure 17, there is no substantial difference between the results from the GVE Further augmentation with the MCLAWS and and DVE cases for any of the control systems examined.
MCLAWS+PH response types produces a Level 1 aircraft The longitudinal stick data also shows that both the cut- with average HQR ratings of about 3.0 for both ACAH off frequency and RMS decrease with additional control control systems, with 5 out of 9 pilots providing ratings of augmentation, which indicates a reduction in pilot 3 or better for MCLAWS, and 8 out of 9 pilots providing workload to obtain the improved handling qualities shown ratings of 3 or better for MCLAWS+PH. These results in Figure 16.
also show that the addition of Position Hold does not significantly improve the handling qualities ratings for For lateral stick (Figure 18), the cut-off frequency is this particular task in GVE. There are no flight test slightly higher for each control system in GVE as results for comparison for the MCLAWS and compared with DVE. This is possibly due to the MCLAWS+PH response types since the OH-58D is increased precision required in the vertical axis (that may currently not equipped to fly with an ACAH response influence the other axes) for the Hover MTE in GVE that type, even though the 10% authority SCAS actuators increases the pilot workload to maintain the desired task simulated in this experiment show that the current OH- performance.
58D SCAS hardware would be sufficient to provide ACAH with MCLAWS in the hover and low speed flight An interesting result in Figure 18 is that the cut-off regime. frequency increases significantly from RC to st-ACAH for both the GVE and DVE cases. This is likely due to For DVE, an average handling qualities rating of 5.5 was the additional lateral axis bandw idth available with the st- obtained with the RC control system, which is again ACAH control system that the pilot is using to improve comparable with the flight test data where the two pilots the task performance and handling qualities rating with provided ratings of 5 and 6. For st-ACAH, the the st-ACAH control system, as shown in Figure 16. The improvement is only about 0.5 HQR with the best pilot same is not true for the longitudinal stick (Figure 17), rating being a 4.5. This is slightly degraded from the where the cut-off frequency consistently decreases with flight test results where both pilots provided a HQR of 4 additional augmentation.
for the Hover MTE in DVE. In comparing all of the Hover MTE simulation results with the flight test data, it Sidestep MTE Results: is seen that the flight test handling qualities ratings are consistently at the better HQR range obtained from the Figure 19 shows the handling qualities ratings for the simulation experiment. ADS-33 Sidestep MTE in GVE and DVE for the RC, st- ACAH and MCLAWS control systems. It should be A more substantial improvement in handling qualities noted that Sidestep MTE pe rformed in this simulation ratings in DVE is seen with the MCLAWS response type experiment differed from the Sidestep MTE described in where the improvement is more than 1 rating point as ADS-33 in that the translation was performed only to the compared with st-ACAH to an average HQR better than right whereas ADS-33 requires a right then left 4, and that 3 out of 9 pilots rated this control translation. The handling qualities data shown in Figure configuration Level 1 with HQR=3. The addition of 19 show a lot of variation in the individual ratings as Position Hold in DVE improves the ratings by an average indicated by the size of the error bars for the different of 0.5 to be borderline Level 1, and with 4 out of 9 pilots control systems and visual conditions. This wide range in rating this a Level 1 aircraft with a handling qualities pilot ratings is due to the lack of visual cueing provided in rating of 3. These simulati on results are not directly the VMS for this particular MTE. With this in mind, the comparable to the ADS-33 requirements for Level 1 results shown in Figure 19 indicate a progression of handling qualities in DVE (UCE=2) since the MCLAWS improved handling qualities from the RC control system control system down not include RCHH. However it is to the st-ACAH and MCLAWS control systems, with the expected that the addition of RCHH to MCLAWS would average handling qualities rating being borderline Level 1 reduce the workload in the vertical axis and confer Level with the MCLAWS control system.
1 handling qualities.
Another interesting trend to note from Figure 19 is that The pilot longitudinal and lateral stick cut-off frequencies the Sidestep MTE performed in DVE has better or equal average HQRs as when performed in GVE. This is bandwidth of the Pirouette MTE compared with the because the DVE standards for this MTE are significantly Hover MTE, and results in a lower improvement in less aggressive. Performing this task to GVE standards, handling qualities ratings when compared with the Hover especially with the least amount of augmentation (RC) MTE. It is also worth noting that one pilot provided a was very difficult in the aircraft, and the task performance HQR of 7 for st-ACAH in DVE, and that this pilot had standards dominate over the available cues. only limited experience in flying with NVGs. This particular result shows the effect of a “low-time” pilot and Acceleration / Deceleration MTE Results: supports the assertion of Ref. 8 that lack of flight time and proficiency (in this case with NVGs) can significantly The limitations of the visual cueing in the VMS were increase workload and degrade handing qualities ratings.
even more apparent for the Acceleration/Deceleration MTE than they were for the Sidestep MTE. The main EMS Approach MTE Results: issues with the Acceleration/Deceleration MTE is the forward out-of-the-window visuals in the nose-down Figure 21 shows handling qualities ratings for the EMS acceleration portion and nose-up deceleration portions of Approach MTE developed for this experiment and the MTE were not sufficient to provide the pilot with described earlier in this paper. This figure shows results adequate ground references during these key portions of for GVE and DVE with the RC, st-ACAH and MCLAWS the MTE. Due to the extreme pitch attitudes and lack of control systems. For GVE, the aircraft is borderline Level cues in the simulation, the Acceleration/Deceleration 1 with an average handling qualities rating of about 3.5 MTE was evaluated by only 2 pilots during the for the RC control system and improves to Level 1 with experiment, and the results are not being reported in this the st-ACAH and MCLAWS control systems. A similar paper. trend or improvement is obtained with DVE unaided and DVE with NVGs for all of the control systems shown.
Pirouette Results: The handling qualities ratings are Level 2 with an average rating of 4.5 for the RC and st-ACAH control system, and Figure 20 shows the handling qualities ratings for the improving to borderline Level 1 with MCLAWS with an Pirouette MTE in GVE and DVE for the RC, st-ACAH average rating of 3.5. With the descending-approach in and MCLAWS control systems. For GVE, the RC this MTE, the potential benefits of adding altitude hold control system produces a Level 2 response with an (RCHH) to the MCLAWS control system maybe less for average handling qualities rating of about 4, which is the EMS Approach MTE than for the Hover and Pirouette consistent with the average handling qualities rating of MTEs. Pilots commented that in DVE they could not 4.5 achieved for the Hover MTE (Figure 16). The pick up speed and vertical velocity changes as quickly or handling qualities rating improves to borderline Level 1 as accurately as in GVE, particularly during the initiation with an average rating of 3. 5 with the st-ACAH control and tracking of the glideslope, which was a key factor in system, and solidly Level 1 w ith an average rating of 2.5 the degraded handling qualities ratings in DVE.
for the MCLAWS control system; all pilots rated MCLAWS as Level 1 for the Pirouette MTE. It is worth noting that saturation of the actuators of the 10% authority SCAS was not a factor in the handling The DVE results in Figure 20 shows that the handling qualities shown in Figure 18 for the EMS Approach MTE.
qualities ratings degrade by between 1 and 1.5 HQR when This indicates that a 10% authority SCAS would compared to the individual GVE results with the same generally be sufficient to provide good handling qualities control system response types. The average rating with from st-ACAH response type with software upgrades, or the MCLAWS control system in DVE is less than 4, and 3 an ACAH response type with attitude feedback for this out of 8 pilots rated this as Level 1. It is expected that the particular MTE.
addition of RCHH for the Pirouette MTE would further reduce the workload in the vertical axis and confer Level In comparing the st-ACAH and RC control systems, 1 handling qualities, and is consistent with the ADS-33 pilots commented that the helicopter response was requirements for Level 1 in DVE.
“smoother” with st-ACAH, particularly during the 90- degree turn, and was “more controllable” during the It is worth noting that the improvement in handling deceleration and landing phase of the task.
qualities rating from RC to st-ACAH control systems for the Pirouette MTE is about 0.5 whereas the improvement The improvement in HQRs from RC to st-ACAH for the is about 1.0 for the Hover MTE (Figure 16). This is EMS Approach MTE (Figure 21) is smaller than the primarily due to the st-ACAH improving the short-term improvement seen for the Hover MTE (Figure 16). This response characteristics, which is less important for the is consistent with the comparison between the Hover and Pirouette MTE than the Hover MTE due to the lower task Pirouette MTEs, where a smaller HQR improvement is seen with the Pirouette MTE (Figure 20) than with the Summary and Conclusions Hover MTE. This is due to the fact that the st-ACAH control system primarily improving the short-term A piloted simulation experiment was in the NASA-Ames response characteristics, which are less important for the Vertical Motion Simulator that examined and quantified EMS Approach MTE and the Pirouette MTE than for the the effects of limited authority control system Hover MTE. The Hover MTE also requires the pilot to be augmentation on handling qualities and task performance more aggressive to attain the level of precision required in both good and degraded visual environments. The by the task, and is a higher bandwidth task than the vehicle model used for the experiment was the OH-58D Pirouette and EMS Approach MTEs. with similar size, weight and performance, and the same 4-bladed rotor system as the Bell 407 civilian helicopter Figure 22 shows the Bedford Workload rating versus that is commonly used for medical evacuation and control system response type for the same cases shown in emergency medical services. The control systems Figure 21. The Bedford Workload ratings scale requires investigated as part of this study include the baseline the pilot to rate the level of workload associated with a aircraft Rate Command system, a short-term Attitude task, based on the amount of spare capacity they feel they Command/Attitude Hold system that uses lagged-rate have to perform additional tasks, with lower ratings feedback rather than attitude feedback to provide a short- indicating lower workload and higher spare capacity. For term attitude response, Modernized Control Laws that the current experiment, pilots are required to maintain provide an Attitude Command/Attitude Hold control situational awareness in order to fly the EMS Approach response type, and Modernized Control Laws with an MTE in accordance with the requirements listed in Table additional Position Hold function. Evaluation tasks 2. The results shown in Figure 22 indicate that the pilots’ included the ADS-33 Hover, Sidestep, workload is significantly increased when performing the Acceleration/Deceleration, and Pirouette Mission Task task in DVE compared with GVE since flying the task in Elements, as well as a new proposed EMS task that DVE requires addition pilot workload to maintain includes a remote landing at a minimally prepared landing situational awareness in order to achieve required mission site. DVE was simulated with NVGs and a night scene performance. Figure 22 also shows that there is little unaided. A total of nine experimental test pilots difference in workload in DVE unaided versus DVE with participated in the four-week simulation experiment.
NVGs. The trends in workload shown in Figure 22 are Data recorded included handling qualities ratings, consistent with the handling qualities ratings shown in workload using the Bedford Workload scale, and task Figure 21 in that increased levels of control system performance. The Usable Cue Environment for this augmentation improve the handling qualities ratings while experiment in the VMS was found to be UCE=1 in GVE at the same time reduce the pilot workload required. It is and UCE=2 in DVE with NVGs. This is consistent with worth noting that one pilot provided a HQR of 6 for st- the flight tests on the OH-58D and allows for a direct ACAH and a HQR of 8 in DVE with NVGs. This pilot comparison between the current simulation results and had limited experience with NVGs and these results flight test data.
highlight that using NVGs without sufficient flight time and proficiency can significantly degrade handing The following conclusions can be drawn from this qualities. experiment: The pilot longitudinal and lateral stick cut-off frequencies - The handling qualities ratings for the Hover and stick RMS for the EMS Approach MTE are shown in MTE in this simulation experiment are consistent Figures 23 and 24. The pilot cutoff frequencies decrease with those from the OH-58D flight test for the with additional control augmentation, which is seen for RC and st-ACAH contro l systems, providing both the longitudinal and lateral stick inputs, and is important anchor points for the results of the consistent with the improvement in handling qualities simulation experiment.
ratings with control augmenta tion shown in Figure 21.
Comparing the cut-off frequencies for the EMS Approach - The st-ACAH control system, that can be MTE (Figures 23 and 24) with the cutoff frequencies for achieved with software upgrades only on the the Hover MTE (Figures 17 and 18), shows that the OH-58D and other helicopters that have rate frequencies for the EMS Approach MTE are significantly stabilization, improves the handling qualities for less than those for the Hover MTE. The reason for this is all of the MTEs examined in this experiment, that the Hover MTE has a significantly higher task particularly those that have a high task bandwidth than the EMS Approach MTE requiring a bandwidth, such as the ADS-33 Hover MTE.
higher pilot workload to obtain the required task performance. - The MCLAWS control system that provides an ACAH response type produces Level 1 handling qualities for all of the MTEs examined in this (ADS-33E-PRF), US Army Aviation and Missile experiment in GVE, and borderline Level 1 Command, March 21, 2000.
handling qualities for the MTEs in DVE. The addition of Position Hold improves the average 4. Brown, K., “Surviving DVE: Q&A with Tony Pots,” HQR only by about 0.5 for the Hover MTE. It is Rotor & Wing, Vol. 46, No. 9, September 2012, pp. 34- likely that the addition of altitude hold with 37.
RCHH (as required by ADS-33 for some MTEs) would result in Level 1 handling qualities in 5. Dugan, D., Delamer, K. J., “The implications of DVE. Handling Qualities in Civi l Helicopter Accidents Involving Hover and Low Speed Flight”, NASA/TM— - The 10% authority stability augmentation system 2005-213473, November, 2005.
was sufficient to achieve an ACAH response type with the MCLAWS control system up to the 6. Harris F. D., Kasper, E. F., Iseler, L. E., ”US Civil transition speed of 40 knots, and actuator Rotorcraft Accidents, 1963 Through 1997”, NASA/TM- saturation was not a factor in the handling 2000-209597, USAAMCOM-TR-00-A-006, December qualities ratings for any of the MTEs examined 2000.
during this simulation experiment.
7. Anon., ”Helicopter Fli ght in Degraded Visual - The results for the EMS Approach MTE were Conditions”, CAA Paper 2007/ 03, Safety Regulation consistent with those obtained for the Hover Group, CAA, September 2007.
MTE where handling qualities improved with increased augmentation, and borderline Level 1 8. Key, D. L., “Analysis of Army Helicopter Pilot Error handing qualities were achieved with MCLAWS Mishap Data and the Implications for Handling in DVE. Pilots commented that the EMS Qualities”, 25th European Rotorcraft Forum, Rome, Italy, Approach MTE, developed for this experiment, September 14-16th, 1999.
is representative of civilian operations and was a good task to highlight the differences in pilot 9. Hoh, R. H., Mitchell, D. G., Aponso, B. L., Key, D.
workload and handling qualities between the L., and Blanken C. L., “Background Information and different control systems tested. User’s Guide for Handling Qualities Requirements for Military Rotorcraft,” USAAVSCOM TR 89-A-008, - The results highlighted the importance of flight December 1989.
time and proficiency when using NVGs. One pilot, who had limited experience with NVGs, 10. Hoh, R. H., “Handling Qu alities Criterion for Very provided significantly degraded handling Low Visibility Rotorcraft NOE Operations,” Presented at qualities ratings (Level 3 for some MTEs), which the AGARD Flight Mechanics Panel Meeting, Rotorcraft illustrated that NVGs alone are not sufficient to Design for Operations, Amsterdam, The Netherlands, improve handing qualities without adequate October 1986.
training.
11. Hoh, R. H., Baillie, S. W., Morgan, J. M., “Flight References Investigation of the Tradeoff between Augmentation and Displays for NOE Flight in Low Visibility,” Presented at 1. Anon., “Aviation Safety Technologies Report,” the Midwest Regional National Specialist’s Meeting on Acquisition and Technology Programs Task Force (ATP Rotorcraft Flight Controls and Avionics, American TF), Department of Defense Aviation Safety Helicopter Society, Cherry Hill, New Jersey, October 13- Technologies Report, Washi ngton, DC: Defense Safety 15, 1987.
Oversight Council, Office of the Under Secretary of Defense for Personnel and Readiness, Program Budget 12. Berger, T., Tischler, M. B., Blanken, C. B., Fujizawa, Request 10-15, Program Decision Memorandum, April B. T., Harding, J. W., Borden, C. C., Cothren, L. E., 30, 2009. Wright, J. J., Arterburn, D. R., and Pfrommer, M. R., “Improved Handling Qualities for the OH-58D Kiowa 2. Anon., US Joint Helicopter Safety Analysis Team: Warrior in the Degraded Visu al Environment,” presented th Year 2000 Report to the International Helicopter Safety at the American Helicopter Society 67 Annual Forum, Virginia Beach, Virginia, May 3-5, 2011.
Team, September 2007.
3. Anon., "Handling Qualities Requirements for 13. Stephens, Ernie, “Cobham Displays HeliSAS on Bell 407,” Rotor & Wing, Military Rotorcraft", Aeronautical Design Standard-33 http://www.aviationtoday.com/rw/topstories/Cobham- Flight,” presented at the American Helicopter Society Displays-HeliSAS-on-Be ll-407_78885.html, April 1, 62nd Annual Forum, Phoenix, AZ, May 2006.
2013.
20. Tischler, M. B., Ivler, C. M., Mansur, M. H., Cheung, 14. Cooper, G. E. and Harper, R. P., “The Use of Pilot K. K., Berger, T., and Berrios, M., “Handling-Qualities Rating in the Evaluation of Ai rcraft Handling Qualities,” Optimization and Trade-offs in Rotorcraft Flight Control NASA TN D-5153, April 1969. Design," presented at the Ro torcraft Handling Qualities Conference, University of Liverpool, UK, Novebmer 15. Roscoe, A. H., and Ellis, G. A., “A Subjective Rating 2008.
Scale for Assessing Pilot Work load in Flight: A Decade of Practical Use,” Royal Aerospace Establishment, 21. Mansur, M. H. and Tischler, M. B., “Flight Test Technical Report TR 90019, March 1990. Comparison of Alternate Strategies for Multi-Loop Control Law Optimization,” presented at the American 16. Blanken, C. L., Hoh, R. H., Mitchell, D. G., and Key, Helicopter Society 69th Annual Forum, Phoenix, AZ, D. L., "Test Guide for ADS-33E-PRF", Special Report May 2013.
AMR-AF-08-07, July 2008.
22. Aponso, B. L., Tran, D. T., and Schroeder, J. A., 17. Tischler, M. B. and Remple, R. K., Aircraft and “Rotorcraft Research at the NASA Vertical Motion Rotorcraft System Identification: Engineering Methods Simulator,” presented at the American Helicopter Society and Flight Test Examples Second Edition , AIAA, 2012. 64th Annual Forum, Montreal, Canada, April 29 - May 1, 2008.
18. Lusardi, J. A., von Gruenhagen, W., Seher-Weiss, S., "Parametric Turbulence Modeling for Rotorcraft 23. Lusardi, J. A., Blanken, C. L., Ott, C. R., Malpica, C.
Applications, Approach, Fli ght Tests and Verification," A., and von Grunhagen, W., “In Flight Evaluation of presented at the Rotorcraft Handling Qualities Active Inceptor Force-Feel Characteristics and Handling Conference, University of Liverpool, UK, Nov 2008. Qualities,” presented at the American Helicopter Society 68th Annual Forum, Fort Wort h, Texas, May 1 – 3, 2012.
19. Harding, J. W., Moody, S. J., Jeram, G. J., Mansur, M. H., and Tischler, M. B ., “Development of Modern Control Laws for the AH-64D in Hover/Low Speed APPENDIX A – Pilot Questionnaire This pilot questionnaire is below. The pilot would run thr ough this questionnaire each time they were to give a rating.
Task Performance 1. Describe ability to meet DESIRED / ADEQUATE performance standards.
2. Describe aggressiveness / precision with which task is performed.
3. If trying for DESIRED performance resulted in unacceptable oscillations, did decreasing your goal to ADEQUATE performance alleviate the problem?
Aircraft Characteristics 4. Describe any objectionable controller force characteristics.
5. Describe predictability of initial aircraft response.
6. Describe any mid- to l ong-term response problems.
7. Describe any objectionable oscillations or tendency to overshoot.
8. Describe any non-linearity of response.
9. Describe any problems with harmony of pitch and roll, sp eed control, with height control, and with heading hold/turn coordination.
Demands on the Pilot 10. Describe overall control strategy in performing the task (cues used, scan, etc.).
11. Describe any control compensation you had to make you to account for deficiencies in the aircraft.
12. Describe any modifications you had to make to what you w ould consider “normal” control technique in order to make the aircraft behave the way you wanted.
13. Describe utility of Position Hold feature a nd impact on ability to perform the task.
14. Describe impact of DVE on performing the assigned task.
Assign WORKLOAD Ratings for overall task.
15. Provide a numerical rating for level of precision obtainable (one = low pr ecision, and nine = high precision).
16. Provide a numerical rating for ability to be aggressive (one = limited, nine = unlimited).
17. Provide a numerical rating for ride quality duri ng the maneuver (one = smooth, nine = jerky).
18. Provide a numerical rating for predictability of aircraft response to pilot inputs (one = predictable, nine = unpredictable).
19. Provide estimate of spare pilot workload capacity on the Bedford Workload Scale.
MISC.
20. Please comment on anything else th at may have influenced you.
Assign HANDLING QUALITIES RAT ING for overall task.
21. Using the Cooper-Harper rating scale, please highlight your decision-making pr ocess and adjectives that are best suited in the context of the task. If assigned HQR is Leve l 2, briefly summarize any deficiencies that make this configuration unsuitable for normal accomplishment of this task, i.e., justify why the procuring activity should reject this configuration as a means to accomplish this task.
22. What was the critical sub-phase of the task (e.g., entry, st eady-state, exit) or major determining factor in the overall Handling Quality Rating (HQR).
Table 1. Control system characteristics of the four control concepts.
RC st-ACAH MCLAWS MCLAWS+PH Inner-loop Roll 51.3, 4.17 65.7, 8. 88 63.7, 12.1 63.7, 12.1 Phase, Gain Margin Pitch 40.8, 6.56 59.5, 14.8 73.9, 17.1 73.9, 17.1 [deg], [dB] Yaw 82.6, 5,52 73.0, 10. 6 94.5, 15.3 94.5, 15.3 Roll 4.94 2.46 2.50 2.50 Crossover Frequency Pitch 3.58 1.65 1.65 1.65 [rad/sec] Yaw 4.15 3.09 3.0 3.0 Roll 3.81, 0.14 3.73, 0. 14 3.66, 0.10 3.66, 0.10 Bandwidth, Phase Delay Pitch 2.65, 0.17 1.97, 0. 11 2.02, 0.09 2.02, 0.09 [rad/sec], [sec] Yaw 2.08, 0.10 2.05, 0. 10 2.22, 0.06 2.22, 0.06 Roll - 1.05 1.05 1.05 DRB [rad/sec] Pitch - 0.50 0.52 0.52 Roll - 3.07 3.18 3.18 DRP [dB] Pitch - 3.30 2.54 2.54 ( ω < BW) -0.06 0.44 0.64 0.64 Min. ζ [-] ( ω > BW) 0.17 0.47 0.5 0.5 Outer-loop: Heading Hold Phase, Gain Margin Yaw - - 54.3, 13.2 54.3, 13.2 [deg], [dB] Crossover Frequency Yaw - - 4.0 4.0 [rad/sec] DRB [rad/sec] Yaw - - 1.18 1.18 DRP [dB] Yaw - - 2.61 2.61 Min. ζ [-] All - - 0.47 0.47 Outer-loop: Velocity Hold Vx - - - 56.1, 13.4 Phase, Gain Margin [deg], [dB] Vy - - - 48.8, 11.7 Vx - - - 0.78 Crossover Frequency [rad/sec] Vy - - - 0.82 Vx - - - 0.6 DRB [rad/sec] Vy - - - 0.69 Vx - - - 2.07 DRP [dB] Vy - - - 2.16 Min. ζ [-] All - - - 0.5 Outer-loop: Position Hold x - - - 54.1, 9.53 Phase, Gain Margin [deg], [dB] y - - - 48.1, 11.6 x - - - 0.2 DRB [rad/sec] y - - - 0.2 x - - - 2.32 DRP [dB] 1.83 y - - - 0.5 Min. ζ [-] All - - - 2.15 CETI 3 σ [ft] x - - - 1.32 CETI 3 σ [ft] y - - - Table 2. EMS Approach MTE task performance metrics.
Scout/Attack GVE DVE DESIRED PERFORMANCE • Maintain speed within: ± 3 kts ± 4 kts • Maintain lateral track within: ± 9 deg ± 9 deg • Maintain rate of descent within ± 300 ft/min ± 300 ft/min • Maintain heading within: ± 5 deg ± 5 deg • Achieve stable hover or land within box within lateral ± 8 ft ± 8 ft dimensions: • Achieve stable hover or land within box within longitudinal ± 8 ft ± 8 ft dimensions: • Attain roll attitude at touchdown below: ± 3 deg ± 3 deg • Attain pitch attitude at touchdown below: ± 3 deg ± 3 deg • Attain longitudinal velocity at t ouchdown within: ± 0.5 kts ± 0.5 kts • Attain lateral velocity at touc hdown within: ± 0.5 kts ± 0.5 kts • Attain vertical velocity at t ouchdown within: ±1.0 kts ± 1.0 kts ADEQUATE PERFORMANCE • Maintain speed within: ± 6 kts ± 8 kts • Maintain lateral track within: ± 16 deg ± 16 deg • Maintain rate of descent within ± 500 ft/min ± 500 ft/min • Maintain heading within: ± 10 deg ± 10 deg • Achieve stable hover or land within box within lateral ± 15 ft ± 15 ft dimensions: • Achieve stable hover or land within box within longitudinal ± 15 ft ± 15 ft dimensions: • Attain roll attitude at touchdown below: ± 5 deg ± 5 deg • Attain pitch attitude at touchdown below: ± 5 deg ± 5 deg • Attain longitudinal velocity at t ouchdown within: ± 1.0 kts ± 1.0 kts • Attain lateral velocity at touc hdown within: ± 1.0 kts ± 1.0 kts • Attain vertical velocity at t ouchdown within: ±2.0 kts ±2.0 kts Table 3. Complete test matrix (ADS-33 MTEs for OH-58D).
Response Visual Number of XPs Task Type Conditions Providing Ratings Hover MTE RC GVE 9 Hover MTE st-ACAH GVE 9 Hover MTE MCLAWS GVE 9 Hover MTE MCLAWS+PH GVE 9 Hover MTE RC DVE with NVGs 9 Hover MTE st-ACAH DVE with NVGs 9 Hover MTE MCLAWS DVE with NVGs 9 Hover MTE MCLAWS+PH DVE with NVGs 9 Accel / Decel RC GVE 1 Accel / Decel st-ACAH GVE 1 Accel / Decel MCLAWS GVE 1 Accel / Decel RC DVE with NVGs 1 Accel / Decel st-ACAH DVE with NVGs 1 Accel / Decel MCLAWS DVE with NVGs 1 Sidestep RC GVE 7 Sidestep st-ACAH GVE 7 Sidestep MCLAWS GVE 7 Sidestep RC DVE with NVGs 7 Sidestep st-ACAH DVE with NVGs 7 Sidestep MCLAWS DVE with NVGs 7 Pirouette RC GVE 8 Pirouette st-ACAH GVE 8 Pirouette MCLAWS GVE 8 Pirouette RC DVE with NVGs 8 Pirouette st-ACAH DVE with NVGs 8 Pirouette MCLAWS DVE with NVGs 8 EMS Approach MTE RC GVE 8 EMS Approach MTE st-ACAH GVE 8 EMS Approach MTE MCLAWS GVE 8 EMS Approach MTE RC DVE with NVGs 8 EMS Approach MTE st-A CAH DVE with NVGs 8 EMS Approach MTE MCLAWS DVE with NVGs 8 EMS Approach MTE RC DVE unaided 8 EMS Approach MTE st-ACAH DVE unaided 8 EMS Approach MTE MCLAWS DVE unaided 8 Table 4. Visual Cue Ratings (VCRs) for the Hover MTE in GVE and DVE with NVGs.
Attitude Translational Rate Pitch/Roll Longitudianal/Lateral GVE DVE GVE DVE Pilot A 1 / 1 3 / 2 2 / 1 4 / 3 Pilot B 2 / 2.5 4 / 3.5 2 / 2.5 4.5 / 3.8 Pilot C 1 / 1 1.5 / 1.5 2.5 / 2.5 4 / 3.5 Attitude VCR Translational Rate VCR Avg / Std Dev Avg / Std Dev Avg / Std Dev Avg / Std Dev All Pilots 1.5 / 0.87 2.83 / 1.26 2.33 / 0.29 4.17 / 0.29 Without Pilot C 1.75 / 1.06 3.5 / 0.71 2.5 / 0.0 4.25 / 0.35 (a)
(b)
(c) Figure 1. Block diagram schematic of the (a) rate co mmand and short-term ACAH control laws, (b) MCLAWS, and (c) MCLAWS with position hold.
Figure 2. NASA-Ames Vertical Motion Simulator Figure 3. NASA-Ames Vertical Motion Simulator (VMS). cockpit and displays layout.
Figure 4. Center stick inceptor representative of OH- Figure 5. Collective stick inceptor. Note: None of the 58D center stick. buttons or switches on the collective inceptor will be used during this experiment.
(a). Translation HSI display. (b). Deceleration to hover HSI display.
(c). Position hold HSI display.
Figure 6. NASA-Ames VMS em ulation of the Army’s Common Avionics Architecture System (CAAS) Horizontal Situation Indicator (HSI).
Figure 7. Night Vision Goggles (N VGs) mounted to pilots’ helmet.
Figure 8. Day-time scene from the start of the EMS Approach MTE. Landing zone is to the left of the center of this picture. Initial helicopter direction is at 90 degrees to the final approach path to the landing zone.
Figure 9: Screenshot showing the vicinity of the landing zone for EMS A pproach task, helicopter descending to the landing point and cones making the intended landing zone.
Figure 10: Screenshot showing night scene from the pilot perspective of th e landing zone during final approach. This night scene would be viewed by the pilo t unaided to simulate DVE conditions.
Figure 11: View of landing zone during final approach taken though the NVGs used during the experiment.
(a). EMS descent performance display. (b). EMS landing performance display.
Figure 12: Task performance displays for EMS task, (a) focuses on the performance during descent for speed and glideslope tracking, and (b) focuses on the landing performance.
Figure 13. Cooper-Harper handli ng qualities rating scale (Ref. 14).
Figure 14. Bedford pilot workload rating scale (Ref. 15).
Figure 15: Visual Cue Ratings plotted on UCE criteri on boundary for Hover MTE for GVE and DVE with NVGs.
Figure 16: Hover MTE handling qualities ratings from VMS simulation and flight test (Ref. 13).
Figure 17: Hover MTE cut-off frequenc y and RMS for longitudinal stick.
Figure 18: Hover MTE cut-off frequency and RMS for lateral stick.
Figure 19: Sidestep MTE handling qualities ratings fr om VMS simulation and flight test (Ref. 13).
Figure 20: Pirouette MTE handling qua lities ratings from VMS simulation.
Figure 21: EMS Approach task showing Cooper-Harper handli ng qualities ratings versus control system response type for GVE and DVE.
Figure 22: EMS Approach task showing Bedford Workload rating versus control system response type for GVE and DVE.
Figure 23: EMS Approach MTE cut-off fre quency and RMS for longitudinal stick.
Figure 24: EMS Approach MTE cut-off frequency and RMS for lateral stick.