Thomas P. Ratvasky

NASA/FAA TAILPLANE ICING PROGRAM OVERVIEW.

The effects of tailplane icing were investigated in a four-year NASA/FAA Tailplane Icing, Program (TIP). This research program was developed to improve the understanding, of iced tailplane aeroperformance and aircraft aerodynamics, and to develop design and training aides to help reduce the number of incidents and accidents caused by tailplane icing. To do this, the TIP was constructed with elements that included icing, wind tunnel testing, dry-air aerodynamic wind tunnel testing, flight tests, and analytical code development. This paper provides an overview of the entire program demonstrating the interconnectivity of the program elements and reports on current accomplishments.

Envelope Protection for In-Flight Ice Contamination

Abstract Fatal loss-of-control (LOC) accidents have been directly related to in-flight airframe icing. The prototype system presented in this paper directly addresses the need for real-time onboard envelope protection in icing conditions. The combinations of a-priori information and real-time aerodynamic estimations are shown to provide sufficient input for determining safe limits of the flight envelope during in-flight icing encounters. The Icing Contamination Envelope Protection (ICEPro) system has been designed and implemented to identify degradations in airplane performance and flying qualities resulting from ice contamination and provide safe flight-envelope cues to the pilot. Components of ICEPro are described and results from preliminary tests are presented. Nomenclature A stability matrix B control matrix b reference span c mean aerodynamic chord C l β rolling moment due to sideslip angle derivative, ∂ C l ∂β C l δ a rolling moment due to aileron deflection derivative, ∂ C ∂δ l a

Simulation Model Development for Icing Effects Flight Training

ABSTRACT A high-fidelity simulation model for icing effects flight training was developed from wind tunnel data for the DeHavilland DHC-6 Twin Otter aircraft. First, a flight model of the un-iced airplane was developed and then modifications were generated to model the icing conditions. The models were validated against data records from the NASA Twin Otter Icing Research flight test program with only minimal refinements being required. The goals of this program were to demonstrate the effectiveness of such a simulator for training pilots to recognize and recover from icing situations and to establish a process for modeling icing effects to be used for future training devices. INTRODUCTION In response to a 1997 White House Initiative to reduce aviation accidents, NASA formed the Aviation Safety Program (AvSP) in 1999. The seven-year program has been tasked to reduce aviation accident rates by 80% by 2007 and by 90% by 2017. Accident and incident reports were analyzed to focus efforts on areas of highest return. These studies showed that 13% of all weather-related accidents were due to airframe icing. To address the icing hazard, NASA has developed a number of tools to supplement pilot training. To date, these tools consist of educational & training videos and computer-based training CD-ROMs. However, a task within the System Wide Accident Prevention Project of AvSP is currently underway to develop a flight simulator that incorporates icing effects for pilot training applications. The purpose of the Pilot Simulator Training for Aircraft Icing Effects (PSIM) activity is to provide pilots with ground-based training facilities that provide a realistic simulation of in-flight icing encounters. This capability will provide pilots a pre-exposure to the adverse effects of icing on airplane performance, stability and control. It will serve as a tool for initial and recurrent pilot training to provide awareness of the consequences of an icing encounter and the knowledge of how to best manage potential adverse maneuvers that may result from icing-induced loss of control. In order to establish this icing effects flight training capability, NASA Glenn Research Center teamed with Bihrle Applied Research and the Wichita State University in 1998 to develop a flight simulation demonstrator. The work also establishes a methodology for developing flight simulators that incorporate icing effects that can be used by flight training organizations, operators, airframe manufacturers, and pilots in safety training programs. A typical application for such a flight modeling process would be to add the capability to existing flight trainers. In such a case, a baseline flight model would already exist. This effort focuses on the steps needed to augment a baseline model with appropriate data to model the effects of icing. In the case of the Twin Otter, no appropriate baseline simulation was available; therefore, as an additional step, one was developed and validated as part of the effort. It was important to have both baseline and iced simulations from a pilot training standpoint, so that a pilot could be exposed to the juxtaposition of both conditions. Starting from the baseline simulation also allowed researchers to assess, in an incremental fashion, the level of modification and steps required to implement icing effects to an existing baseline. To accomplish this, the PSIM effort was designed to proceed in three phases, a baseline model development and validation (BASELINE), a horizontal tail icing model development and validation (ICE01), and a full aircraft icing model development, assessment, and validation (ICE02). Once a baseline simulation structure was established, each phase of the flight model development focused primarily on the development of aerodynamics models and control system models. The basis for each of the developmental aerodynamics and control models was low speed wind tunnel data. These data were used to populate table driven models of aerodynamics forces, moments, and hinge moments. The models were then validated with flight data. To complete the validation, physics-driven modifications are made to the raw wind-tunnel data and then reintroduced to the simulation. The revised model is then reevaluated against an independent data set until appropriate acceptance criteria are met. In this effort, modifications applied to the

Iced Aircraft Flight Data for Flight Simulator Validation

NASA is developing and validating technology to incorporate aircraft icing effects into a flight training device concept demonstrator. Flight simulation models of a DHC-6 Twin Otter were developed from wind tunnel data using a subscale, complete aircraft model with and without simulated ice, and from previously acquired flight data. The validation of the simulation models required additional aircraft response time histories of the airplane configured with simulated ice similar to the subscale model testing. Therefore, a flight test was conducted using the NASA Twin Otter Icing Research Aircraft. Over 500 maneuvers of various types were conducted in this flight test. The validation data consisted of aircraft state parameters, pilot inputs, propulsion, weight, center of gravity, and moments of inertia with the airplane configured with different amounts of simulated ice. Emphasis was made to acquire data at wing stall and tailplane stall since these events are of primary interest to model accurately in the flight training device. Analyses of several datasets are described regarding wing and tailplane stall. Key findings from these analyses are that the simulated wing ice shapes significantly reduced the C , max, while the simulated tail ice caused elevator control force anomalies and tailplane stall when flaps were deflected 30 deg or greater. This effectively reduced the safe operating margins between iced wing and iced tail stall as flap deflection and thrust were increased. This flight test demonstrated that the critical aspects to be modeled in the icing effects flight training device include: iced wing and tail stall speeds, flap and thrust effects, control forces, and control effectiveness.

Development and Utility of a Piloted Flight Simulator for Icing Effects Training

Abstract A piloted flight simulator called the Ice Contamination Effects Flight Training Device (ICEFTD), which uses low cost desktop components and a generic cockpit replication is being developed. The purpose of this device is to demonstrate the effectiveness of its use for training pilots to recognize and recover from aircraft handling anomalies that result from airframe ice formations. High-fidelity flight simulation models for various baseline (non-iced) and iced configurations were developed from wind tunnel tests of a subscale DeHavilland DHC-6 Twin Otter aircraft model. These simulation models were validated with flight test data from the NASA Twin Otter Icing Research Aircraft, which included the effects of ice on wing and tail stall characteristics. These simulation models are being implemented into an ICEFTD that will provide representative aircraft characteristics due to airframe icing. Scenario-based exercises are being constructed to give an operational-flavor to the simulation. Training pilots will learn to recognize iced aircraft characteristics from the baseline, and will practice and apply appropriate recovery procedures to a handling event.

Isokinetic TWC Evaporator Probe: Development of the IKP2 and Performance Testing for the HAIC-HIWC Darwin 2014 and Cayenne 2015 Field Campaigns

A new Isokinetic Total Water Content Evaporator (IKP2) was downsized from a prototype instrument, specifically to make airborne measurements of hydrometeor total water content (TWC) in deep tropical convective clouds to assess the new ice crystal Appendix D icing envelope. The probe underwent numerous laboratory and wind tunnel investigations to ensure reliable operation under the difficult high altitude/speed/TWC conditions under which other TWC instruments have been known to either fail, or have unknown performance characteristics. The article tracks the testing and modifications of the IKP2 probe to ensure its readiness for three flight campaigns in 2014 and 2015. Comparisons are made between the IKP2 and the NASA Icing Research Tunnel reference values in liquid conditions, and to an exploratory technique estimating ice water content from a bulk ice capture cylinder method in glaciated conditions. These comparisons suggest that the initial target of 20 percent accuracy in TWC has been achieved and likely exceeded for tested TWC values in excess of about 0.5 gm–3. Uncertainties in the ice water content reference method have been identified. Complications are introduced in the necessary subtraction of an independently measured background water vapour concentration, errors of which are small at the colder flight temperatures, but increase rapidly with increasing temperature, and ultimately limit the practical use of the instrument in a tropical convective atmosphere to conditions colder than about 0 C. A companion article in this conference traces the accuracy of the components of the IKP2 to derive estimated system accuracy.

Development and Implementation of a Model- Driven Envelope Protection System for In-Flight Ice Contamination

Abstract Fatal loss-of-control (LOC) accidents have been directly related to in-flight airframe icing . The prototype system presented in this paper directly addresses the need for real-time onboard envelope protection in icing conditions. The combinations of a-priori information and real -time aerodynamic estimations are shown to provide sufficient input for determining safe limits of the flight envelope during in-flight icing encounters. The Icing Contamination Envelope Protection (ICEPro) system has been designed and implemented to identify degradations in airplane performance and flying qualities resulting from ice contamination and provide safe flight-envelope cues to the pilot. Components of ICEPro are described and results from preliminary tests are presented. Introduction The University of Tennessee Space Institute (UTSI) in partnership with Bihrle Applied Research (BAR) has completed a 3-year cooperative research effort with NASA in response to the NASA Research Announcement (NRA) NNH06ZEA001N under Appendix B of the Aviation Safety Program. A prototype Icing Contamination Envelope Protection (ICEPro) system was developed to meet the objectives defined under the Integrated Vehicle Health Management (IVHM) Project, topic IVHM 3. 1, Environmental Hazards, which are caused by the “Effects of Icing on Aircraft State”. This paper presents the results of this research, which focuses on the concept, design, development, implementation, and evaluation of the real-time vehicle state assessment system.

In-Flight Aerodynamic Measurements of an Iced Horizontal Tailplane

The effects of tailplane icing on aircraft dynamics and tailplane aerodynamics were investigated using, NASAs modified DHC-6 Twin Otter icing research aircraft. This flight program was a major element of the four-year NASA/FAA research program that also included icing wind tunnel testing, dry-air aerodynamic wind tunnel testing, and analytical code development. Flight tests were conducted to obtain aircraft dynamics and tailplane aerodynamics of the DHC-6 with four tailplane leading-edge configurations. These configurations included a clean (baseline) and three different artificial ice shapes. Quasi-steady and various dynamic flight maneuvers were performed over the full range of angles of attack and wing flap settings with each iced tailplane configuration. This paper presents results from the quasi-steady state flight conditions and describes the range of flow fields at the horizontal tailplane, the aeroperformance effect of various ice shapes on tailplane lift and elevator hinge moment, and suggests three paths that can lead toward ice-contaminated tailplane stall. It was found that wing, flap deflection was the most significant factor in driving the tailplane angle of attack toward alpha(tail stall). However, within a given flap setting, an increase in airspeed also drove the tailplane angle of attack toward alpha(tail stall). Moreover, increasing engine thrust setting also pushed the tailplane to critical performance limits, which resulted in premature tailplane stall.

Current Methods Modeling and Simulating Icing Effects on Aircraft Performance, Stability, Control

Icing alters the shape and surface characteristics of aircraft components, which results in altered aerodynamic forces and moments caused by air flow over those iced components. The typical effects of icing are increased drag, reduced stall angle of attack, and reduced maximum lift. In addition to the performance changes, icing can also affect control surface effectiveness, hinge moments, and damping. These effects result in altered aircraft stability and control and flying qualities. Over the past 80 years, methods have been developed to understand how icing affects performance, stability, and control. Emphasis has been on wind-tunnel testing of two-dimensional subscale airfoils with various ice shapes to understand their effect on the flowfield and ultimately the aerodynamics. This research has led to wind-tunnel testing of subscale complete aircraft models to identify the integrated effects of icing on the aircraft system in terms of performance, stability, and control. Data sets of this nature enable pilot-in-the-loop simulations to be performed for pilot training or engineering evaluation of system failure impacts or control system design.

Flight Testing an Iced Business Jet for Flight Simulation Model Validation

Abstract A flight test of a business jet aircraft with various ice accretions was performed to obtain data to validate flight simulation models developed through wind tunnel tests. Three types of ice accretions were tested: pre-activation roughness, runback shapes that form downstream of the thermal wing ice protection system, and a wing ice protection system failure shape. The high fidelity flight simulation models of this business jet aircraft were validated using a software tool called “Overdrive.” Through comparisons of flight-extracted aerodynamic forces and moments to simulation-predicted forces and moments, the simulation models were successfully validated. Only minor adjustments in the simulation database were required to obtain adequate match, signifying the process used to develop the simulation models was successful. The simulation models were implemented in the NASA Ice Contamination Effects Flight Training Device (ICEFTD) to enable company pilots to evaluate flight characteristics of the simulation models. By and large, the pilots confirmed good similarities in the flight characteristics when compared to the real airplane. However, pilots noted pitch up tendencies at stall with the flaps extended that were not representative of the airplane and identified some differences in pilot forces. The elevator hinge moment model and implementation of the control forces on the ICEFTD were identified as a driver in the pitch ups and control force issues, and will be an area for future work.