Equipment Bays Research Articles

Scoring Approach to Assess Maintenance Risk for Aircraft Systems in Conceptual Design

Ease of maintenance can significantly contribute to reducing aircraft operational cost. Maintenance risk is defined as the opposite of maintenance ease; it is impacted by many factors, most of which are decided upon during the aircraft’s conceptual design. This paper proposes a novel method to assess the maintainability risks of aircraft systems by combining various aspects on the component level, intercomponent level, bay level, and aircraft level. For each level, all contributing factors to maintenance risk are analyzed and integrated into several scores. These maintenance risk scores can be used to assess the various aspects contributing to maintenance risk, using input parameters available during the conceptual design phase. This paper presents the validation of the scores using different components and aircraft equipment bays, such as avionic racks, the nose cone, and a complex aft equipment bay of a business jet. The proposed maintenance risk scoring method will enhance multidisciplinary tradeoff studies during aircraft conceptual design, considering competing design aspects such as system placement, thermal aspects, impact on aircraft balancing, or even the overall aircraft shape. Therefore, this new conceptual design capability enables designing novel aircraft configurations featuring unconventional system component placement or component bay shapes while considering maintenance aspects upfront.

Influence of Ventilation Flow Rate and Gap Distance on the Radiative Heat Transfer in Aircraft Avionics Bays

The feasibility of the future more-electric, hybrid-electric, and all-electric aircraft configurations will depend on a good understanding of thermal aspects early in the design. However, thermal analysis of aircraft equipment bays is typically performed at later design stages to validate if the design meets the minimal certification requirements rather than to optimize the cooling strategy. The presented work aims to provide new insight into thermal aspects in typical aircraft equipment bays. In particular, system thermal interactions, such as radiation, play a more significant role in tightly packaged bays, such as avionics bays. This paper investigates the influence of radiation on the overall system heat dissipation in two representative avionics bays. Using Computational Fluid Dynamics (CFD) simulation, combined with an analytical approach, the authors analyze the impact of several parameters, such as varying mass flow rates and distances between adjacent systems, on their thermal interaction. The results suggest that the radiative effects must be considered when the gap distance between the systems is larger than 0.1 m, the flow rate between two systems is not strong enough to have high convective heat exchanges, when the systems of interest are hidden by other systems from the ventilation sources, and when the system’s internal heat dissipation is significant. Overall, this paper’s results will contribute enhance conceptual design methods, such as the previously developed Thermal Risk Analysis, and help optimize thermal management strategies for future aircraft.

Ventilation considerations for an enhanced thermal risk prediction in aircraft conceptual design

The capability to assess thermal aspects early in aircraft design is a crucial enabler for unconventional, more-electric, hybrid-electric, or all-electric aircraft configurations. This paper presents an extended version of a so-called thermal risk assessment approach for aircraft conceptual design. The assessment of thermal risk and the definition of a suitable cooling strategy during the conceptual design phase enables the anticipation of changes in the design process within a multidisciplinary design and optimization framework. In a previous paper, the authors propose applying dimensionless numbers to assess the thermal environment of a considered aircraft zone and predict the systems' thermal risk with a limited number of inputs. This research paper investigates the relations between the aircraft systems' locations within an equipment bay and the characteristics of the ventilation sources. The concept of mainstream flow is introduced, and new dimensionless numbers are established. The streamwise and the cross-stream numbers help to assess the closeness of a system to a ventilation source, while the heat removal potential assesses the cooling effectiveness due to the closest ventilation source for a particular system in an equipment bay. Two aircraft equipment bays with different configurations demonstrate the effectiveness of the thermal risk assessment methodology. The results are validated using computational fluid dynamic simulations. The enhanced thermal risk assessment approach will enable a more accurate definition of thermal requirements for aircraft systems within the aircraft conceptual design phase and reduce potential thermal issues later in the design process.

Thermal risk prediction methodology for conceptual design of aircraft equipment bays

Early thermal analysis is becoming increasingly important, in particular for more electric, hybrid electric or all electric aircraft in combination with novel vehicle concepts. Traditionally, aircraft thermal analyses are performed later in the design process, when the aircraft system architecture is already defined, which can lead to costly modifications and delays late in the design process. Thus, assessing thermal risk during the conceptual design phase represents a way to anticipate changes in the design process. This research paper presents an innovative approach using dimensionless numbers to predict system thermal risk for the conceptual design of aircraft equipment bays. The article presents two realistic case studies, a business jet aft equipment bay and a rotorcraft nose equipment bay. The validation with computational fluid dynamic simulations demonstrates novel the capabilities of this thermal risk assessment. In summary, the proposed approach will improve the definition of thermal requirements during the aircraft conceptual design phase and will reduce the risk of potential thermal issues later in the design process.

Polybrominated Diphenyl Ether and Organophosphate Flame Retardants in Canadian Fire Station Dust

Fire fighters are at a high risk for exposure to toxic chemicals during and subsequent to fire suppression activities. In the Canadian Fire Station Dust Study (CFSDS) we measured 19 polybrominated diphenyl ether (PBDE) and six organophosphate flame retardant (OPFR) chemicals in dust collected in 2017–18 by vacuuming the living quarters of 24 Canadian fire stations from four provinces. The predominant flame retardant (FR) was BDE-209, with a median concentration of 7060 ng/g, which was a magnitude higher than medians of the major congeners of the pentaBDE formulation measured at 620 ng/g (Σ5 BDE-47, 99, 100, 153 and 154). OPFR median concentrations exceeded those of pentaBDE and were on the same order of magnitude as BDE-209, with TCIPP, TDCIPP and TPHP as the dominant OPFRs with median concentrations ranging from 2350 to 4780 ng/g. Fire station age and carpeting were significantly correlated with select OPFRs and PBDEs. Furthermore, fire stations that also vacuumed equipment bays and fire truck interiors had median concentrations that were a magnitude higher (BDE-209: 81,700 ng/g) and two to three-fold higher (TCIPP, TDCIPP and TPHP) than fire stations that excluded those areas. FR concentrations in CFSDS dust were higher but on the same order of magnitude as Canadian residential dust and significantly lower than dust collected from Canadian WEEE dismantling. CFSDS FR concentrations were also significantly lower than those we reported in our 2015 U.S. fire station dust. Our data reflect the downward trend of PBDEs following their phase out and a shift toward OPFRs as replacements.

Open systems avionics network to replace MIL-STD-1553

This paper is a proposal for a future method of avionics data communication. The need for this proposal results from the shortcomings in the current avionics architecture, video distribution network, and in the MIL-STD-1553 data communication system. The separately wired video and data communication systems can be combined to save weight, which is especially critical for rotorcraft. Aircraft, once fielded, have limited capacity for modification and improvement due to fixed computer throughput and processing performance, network bandwidth, and space available in the avionics equipment bays. The changes proposed by this paper are to be made in conjunction with the replacement of the redundant computer boxes with open system avionics functions on industry standard circuit cards. This open architecture approach was developed over the last ten years and is now being implemented in many aircraft applications including the F-22 and the RAH-66 programs. The V-22 rotorcraft, which although just entering production, is being modified for joint service customers where modern computer performance and expanded data network bandwidth is needed. The changes of this proposal will fill this need, reduce the weight of upcoming production models, and provide growth or spare capability so that additional video and data components can be added with minimal effect on existing components. This paper examines the current V-22 avionics video and data communication hardware and wiring and propose a new implementation of open system architecture standards with integrated digital video and data communication based on ANSI standard copper fibre channel.

Insights into the Damage Mechanism of Teflon® FEP from the Hubble Space Telescope

Metallized Teflon® FEP (fluorinated ethylene propylene) thermal control material on the Hubble Space Telescope (HST) has been found to be degrading in the space environment. Teflon® FEP thermal control blankets (space-facing FEP) retrieved during the first servicing mission (SM1) were found to be embrittled on solar-facing surfaces and contained microscopic cracks. During the second servicing mission (SM2) astronauts noticed that the FEP outer layer of the multi-layer insulation (MLI) covering the telescope was cracked in many locations around the telescope. Large cracks were observed on the light shield, forward shell and equipment bays. A tightly curled piece of cracked FEP from the light shield was retrieved during SM2 and was severely embrittled, as witnessed by ground testing. A failure review board was organized to determine the mechanism causing the MLI degradation. Density, x-ray crystallinity and solid-state nuclear magnetic resonance (NMR) analyses of the FEP retrieved during SM1 were inconsistent with results of FEP retrieved during SM2. Because the retrieved SM2 material was curled while in space, it experienced a higher temperature extreme during thermal cycling, estimated at 200°C, than the SM1 material, estimated at 50°C. An investigation on the effects of heating pristine FEP and FEP retrieved from the HST was therefore conducted. Samples of pristine, SM1 and SM2 FEP were heated to 200°C and evaluated for changes in density and morphology. Elevated-temperature exposure was found to have a major impact on the density of the retrieved materials. The characterization of the polymer morphology of the as-received and heated FEP by NMR provided results that were consistent with the density results. Differential scanning calorimetry (DSC) was conducted on pristine, SM1 and SM2 FEP. DSC results provided evidence of chain scission and increased crystallinity in the space exposed FEP, which supported the density and NMR results. Samples exposed to simulated solar flare x-rays, thermal cycling and long-term thermal exposure provided information on the environmental contributions to degradation. These findings have provided insight into the damage mechanisms of FEP in the space environment.

Simulation Study of an Aircraft's Environmental Control System Dynamic Response

SIMULATION was made of the environmental control system (ECS) of a high-performance aircraft. The ECS provides temperature control for the cockpit and avionics equipment bays, throughout the flight performance envelope of the aircraft. This is achieved by bleeding hot air from the engine, cooling part of it, and mixing the hot and cold flows. The sensors, controller, and valves of the system were modeled, as well as the heat exchangers and expansion turbine. The simulation was programed in CSMP, on an IBM 370/165 computer and operated over an array of conditions representative of the whole operational envelope of the ECS. Dynamic response was compared to specification s and sensitivity of performance to system parameters was measured. A partial evaluation of the simulation was achieved by using some available laboratory test results and comparing these with simulation results from the same conditions. The rationale, models, program, and results are presented in this paper. Content The environmental control system (ECS) of a highperformance aircraft is required to perform complex tasks. Consequently, it is complex in design. The ECS must supply proper temperature air to the cabin and to the avionics equipment, within the entire performance envelope of the aircraft and within the entire scale of external conditions of temperature and pressure. There are specifications on the dynamic behavior which require the system to stabilize within seconds and to not exceed specific inlet temperatures to the cabin and equipment which would be harmful to the pilot and to the avionics. Proper flow levels must be maintained and it is necessary that no severe pressure changes reach the cockpit, which would be uncomfortable to the pilot. To verify the design of the ECS for a high-performance aircraft, a simulation was made which portrayed the dynamic performance of the system. It was intended to study stability, study sensititivity, identify possible problem areas in the design, and serve as a tool to evaluate the dynamic effects of any future design changes. A discussion of the system follows. System Description. The ECS provides temperature control for the cockpit and avionics equipment bays, throughout the flight performance envelope of the aircraft. This is achieved by bleeding hot air from the engine, cooling part of it, and mixing the hot and cold flows. Transient changes into the ECS occur when the pilot alters the engine throttle setting and/or when altitude changes occur. A functional flow diagram of the ECS system is shown in Fig. 1. The rate of flow of bleed air from the engine is