Search Results

In recent years there has been increasing interest in quantifying the emissions from aircraft in order to generate inventories of emissions for climate models, technology and scenario studies, and inventories of emissions for airline fleets typically presented in environmental reports. The preferred method for calculating aircraft engine emissions of NOx, HC, and CO is the proprietary “P3T3” method. This method relies on proprietary airplane and engine performance models along with proprietary engine emissions characterizations. In response and in order to provide a transparent method for calculating aircraft engine emissions non proprietary fuel flow based methods 1,2,3 have been developed. This paper presents derivation, updates, and clarifications of the fuel flow method methodology known as “Fuel Flow Method 2”.

The 98,000 lb. thrust Pratt & Whitney PW4098 high-bypass turbofan engine recently completed a flying test-bed program on the Boeing 777-300 airplane. The purpose of the one-month program was to validate engine operability and to gather data that can be used for upcoming engine certification to the standards of Federal Aviation Regulations part 33. Testing included engine transient operation, steady-state performance, in-flight starting, component cooling, and inlet compatibility. When engine certification is complete, an airplane certification program will be conducted for the 777-300/PW4098, a combination of the world's largest twin engine airplane and the world's largest turbofan engine yet to fly.

As part of NASA’s Aviation Safety and Security Program, a simulation study of a twin-jet transport aircraft crew training simulation was conducted to address fidelity for upset or loss-of-control flight conditions. Piloted simulation studies were conducted to compare the baseline crew training simulation model with an enhanced aerodynamic model that was developed for high-angle-of-attack conditions. These studies were conducted in a flaps-up configuration and covered the approach-to-stall, stall and post-stall flight regimes. Qualitative pilot comments and preliminary comparison with flight test data indicate that the enhanced model is a significant improvement over the baseline. Some of the significant unrepresentative characteristics that are predicted by the baseline crew training simulation for flight in the post-stall regime have been identified.

Power quality has become a subject of increased attention for electrical power systems on both commercial and military aircraft. Several power quality guidelines and specification documents exist that govern today's power system operation and the contributing characteristics of electrical load equipment. This paper presents power quality requirements for future Boeing commercial airplanes, driven by advances in aerospace applications of power electronic equipment, increased load demand and complexity, as well as new power system architectures. The influence of new equipment types on electrical system power quality is described including the effects of motor controllers, AC power converters, and large dynamic loads. The impact of power type classifications such as variable frequency AC power and multiple DC voltage levels is also discussed. Simulation results are presented to develop and validate these power quality requirements.

This paper is an explanation of some of the Flight Test Safety (FTS) methods used to reduce the risk associated with military rotorcraft development. Two flight test programs are addressed, the V-22 Osprey tiltrotor and the RAH-66 Comanche helicopter. A short history of the development of each program is provided as background information. Some of the challenges and strengths of joint ventures are also identified and discussed. Four critical elements of an FTS program are identified: 1) Organizational Risk Management (ORM), 2) issue/anomaly resolution, 3) incident recording and corrective action documentation and 4) interface between FTS and other organizations. Methods used in the two programs to address these elements are reviewed and can be applied to other flight test programs.

As aircraft continue to increase their power and thermal demands, transient operation of the power and propulsion subsystems can no longer be neglected at the aircraft system level. The performance of the whole aircraft must be considered by examining the dynamic interactions between the power, propulsion, and airframe subsystems. Larger loading demands placed on the power and propulsion subsystems result in thrust, speed, and altitude transients that affect the aircraft performance and capability. This results in different operating and control parameters for the engine that can be properly captured only in an integrated system-level test. While it is possible to capture the dynamic interactions between these aircraft subsystems by using simulations alone, the complexity of the resulting system model has a high computational cost.

Modern military engines desire both the fuel efficiency of high-bypass turbofans and the high specific thrust of a low-bypass turbofan. Using traditional engine architectures, performance and efficiency are in conflict, so an engine is usually designed to best meet requirements for its primary mission. While the concept of a variable cycle engine is not new, recent advances in engine architecture technology suggest that adding a second bypass stream to a traditional turbofan can provide significant benefits. This “third stream” (the core flow being the primary stream and the inner bypass being the second stream) airflow can be independently modulated so that engine airflow demand can be matched with the available inlet flow at a variety of operating points, thereby reducing spillage drag. Additionally, the third stream air provides a valuable heat sink for cooling turbine cooling air or dissipating other aircraft heat loads.

The aircraft lifecycle involves thousands of transactions and an enormous amount of data being exchanged across the stakeholders in the aircraft ecosystem. This data pertains to various aircraft life cycle stages such as design, manufacturing, certification, operations, maintenance, and disposal of the aircraft. All participants in the aerospace ecosystem want to leverage the data to deliver insight and add value to their customers through existing and new services while protecting their own intellectual property. The exchange of data between stakeholders in the ecosystem is involved and growing exponentially. This necessitates the need for standards on data interoperability to support efficient maintenance, logistics, operations, and design improvements for both commercial and military aircraft ecosystems. A digital thread defines an approach and a system which connects the data flows and represents a holistic view of an asset data across its lifecycle.

The desire to operate rotorcraft in icing conditions has renewed the interest in developing high-fidelity analysis methods to predict ice accumulation and the ensuing rotor performance degradation. A subset of providing solutions for rotorcraft icing problems is predicting two-dimensional ice accumulation on rotor airfoils. While much has been done to predict ice for fixed-wing airfoil sections, the rotorcraft problem has two additional challenges: first, rotor airfoils tend to experience flows in higher Mach number regimes, often creating glaze ice which is harder to predict; second, rotor airfoils oscillate in pitch to produce balance across the rotor disk. A methodology and validation test cases are presented to solve the rotor airfoil problem as an important step to solving the larger rotorcraft icing problem. The process couples Navier-Stokes CFD analysis with the ice accretion analysis code, LEWICE3D.

A highly modified F/A-18 aircraft is being used to demonstrate that aeroelastic wing twist can be used to roll a high performance aircraft. A production F/A-18A/B/C/D aircraft uses a combination of aileron deflection, differential horizontal tail deflection and differential leading edge flap deflection to roll the aircraft at various Mach numbers and altitudes. The Active Aeroelastic Wing program is demonstrating that aeroelastic wing twist can be used in lieu of the horizontal tail to provide autonomous roll control at high dynamic pressures. Aerodynamic and loads data have been gathered from the Phase I AAW flight test program. Now control laws have been developed to exploit aeroelastic wing twist and provide autonomous flight control of the AAW aircraft during Phase II. Wing control surfaces are being deflected in non-standard ways to create aeroelastic wing twist and develop the required rolling moments without use of the horizontal tail.

As the cost and complexity of modern aircraft systems increases, emphasis has been placed on model-based design as a means for reducing development cost and optimizing performance. To facilitate this, an appropriate modeling environment is required that allows developers to rapidly explore a wider design space than can cost effectively be considered through hardware construction and testing. This wide design space can then yield solutions that are far more energy efficient than previous generation designs. In addition, non-intuitive cross-coupled subsystem behavior can also be explored to ensure integrated system stability prior to hardware fabrication and testing. In recent years, optimization of control strategies between coupled subsystems has necessitated the understanding of the integrated system dynamics.