1、AEROSPACE INFORMATION REPORTAIR1812REV.AIssued 1985-10Revised 1997-10Superseding AIR1812Environmental Control Systems Life Cycle CostFOREWORDChanges in this revision are format/editorial only.TABLE OF CONTENTS1. SCOPE .31.1 Purpose .32. REFERENCES .33. BACKGROUND - IMPORTANCE OF ECS LIFE CYCLE COST
2、44. LIFE CYCLE COST CATEGORIES44.1 Research, Development, Test and Evaluation (RDT Kosfeld, O.; Short, R.; Moyich, G.: “Advanced Environmental Control System,” Technical Report AFFDL-TR-77-68 Air Force Dynamics Laboratory.5. Campbell, S., Taylor, K., “Aircraft Avionics Environmental Control Design a
3、nd Analysis Procedures for Optimized Life Cycle Cost,” General Dynamics Corporation, Convair Aerospace Div. Report GDCA-PDB-71-002, July 1971.6. Berger, R., “A Systems Approach - Minimizing Avionics Life Cycles Cost,” SAE TechnicalPaper 831107.7. Dieckmann, R.; Watson, A.; Glover, S., “Development o
4、f Integrated Environmental Control System Designs for Aircraft,” Technical Report AFFDL-TR-72-9 Volume I Air Force Flight Dynamics Laboratory.8. Rachowitz, B., Pulito, V.; and Izzi, M.: “Modular Life Cycle Cost Model,” Volume I, Rev. 1,AFFDL-TR-78-40, Air Force Systems Command.9. Anon.: “Logistics S
5、upport Cost Model Users Handbook,” U.S. Air Force, August 1976.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1812 Revision A- 4 -2. (Continued):10. Anon: “USAF Cost and Planning Factors,” AF
6、 Regulation 173-13 Department of the Air Force, February 1982.11. Hilbert, W.; and Bruno, A.: “Environmental Control System Concept Study for a Type A V/STOL Aircraft,” Report No. NADC-78039-60, Naval Air Development Center.12. Anon: “SAE Aerospace Applied Thermodynamics Manual,” ARP1168, Society of
7、 Automotive Engineers, Inc.3. BACKGROUND - IMPORTANCE OF ECS LIFE CYCLE COST:An important part of initial ECS development is to compare alternate ECS designs and the total cost impact of these designs over the life of the aircraft in which it is used (i.e., ECS life cycle cost). In the past, ECS wer
8、e designed to maximize the thermodynamic performance, with compromises to minimize size, weight and initial cost. Since many ECS costs are fixed by early design choices, it is imperative that implications of ECS design decisions on costs be identified. For example, a 1980 estimate (100 production un
9、its) for ECS operational and support costs is 2/3 of ECS life cycle costs, while development and procurement costs comprise the remaining 1/3 (Reference 1). Therefore it is important to determine the impact of ECS design decisions on the operational and support cost part of LCC early in an ECS devel
10、opment program. In order to minimize overall aircraft LCC, it is also important to be aware of and to assess the impact that ECS has on other aircraft systems when evaluating candidate ECS approaches.4. LIFE CYCLE COST CATEGORIES:Life cycle costs for ECS, and for other aerospace systems and structur
11、e, are divided into three categories which occur sequentially, but which generally overlap. These costs may be for “one-time” efforts or hardware (non-recurring costs), or for repetitive efforts or multiple items of hardware (recurring costs). The three life cycle cost categories are: 1) research, d
12、evelopment, testing and evaluation; 2) procurement; 3) operations and support. These are outlined in the following sections. More detail about these cost elements is found in References 2 and 3.4.1 Research, Development, Test and Evaluation (RDT cabin air recirculation; shaft power; use of fuel as a
13、 heat sink. The benefits of these approaches is dependent on the aircraft configuration and mission.5.2.3 Avionics Systems: The degree to which an ECS thermally conditions avionics impacts their reliability. Avionics reliability is strongly related to junction temperatures of solid state electronic
14、devices in the avionics. Components operated at low junction temperatures have low failure rates. Junction temperatures are dependent on internal thermal design and on external cooling. For forced cooled avionic units, the coolant flow rate and temperature are major factors affecting reliability. In
15、formation in Reference 4 relates avionics reliability to coolant temperatures. Industry and service data indicate that lower junction temperatures result in reduced component failure rates and consequently lower maintenance costs. Reducing temperature fluctuations of avionic environments or the cool
16、ant also improves avionics reliability. (See Reference 5.) Avionics coolant types, their flow rates and their temperatures significantly impact ECS penalties and overall aircraft costs. Reference 6 further discusses the need for integration of ECS and avionics during early design stages to minimize
17、overall LCC.5.2.4 Structure: An aircraft must be large enough to accommodate the environmental control system and additional fuel used by the engine to provide power for the ECS. Aircraft structure must be strong enough to maintain pressure differential in occupied compartments and equipment compart
18、ments. Structural weight increases occur as compartment pressure differential is increased above a minimum value. Structural size and weight to provide the ECS capability directly affect overall aircraft costs.5.2.5 Secondary Power: The size and performance requirements of secondary (also referred t
19、o as auxiliary) power systems may be affected by the ECS. These include the hydraulic, accessory drive, and electrical systems. Hydraulic power may be required for fans and compressors. The accessory drive may be required to provide shaft power (e.g. for compressors) and electrical power (e.g. for v
20、alves, fans, compressors). The resultant increase in size, weight, and complexity of these systems to provide power to the ECS has a direct impact and their costs and overall aircraft costs.6. ECS COST FACTORS AND COST DISTRIBUTIONS:The purpose of this section is to discuss factors which have major
21、impacts on ECS costs, and to relate these to cost distributions among the three cost categories of section 4.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1812 Revision A- 9 -6.1 Primary ECS
22、 Cost Factors:Primary ECS design factors that affect cost are the size and type of the heat load to be cooled and the type of airborne application for the ECS. These key design factors influence the type of ECS, the size (weight) of the ECS, and the power it uses. These factors also impact the cost
23、of fuel to lift the ECS and the fuel cost to provide power to the ECS. ECS application and types of ECS heat loads influence complexity of the ECS. ECS complexity directly affects ECS reliability, which impact ECS operational and support costs. These effects are shown in Figure 2 and discussed furth
24、er in the following subsections.6.1.1 ECS Design: A key design factor affecting ECS life cycle cost is the size of the heat load being cooled by the ECS. Simply stated, ECS life cycle cost increases as the size of the heat load increases. However, variations in the flow rate and temperature requirem
25、ents of the heat load, auxiliary functions provided by the ECS, and the airborne system or aircraft in which the ECS is used also have significant impact on the size and cost of an ECS.The type of airborne application affects ECS costs in several ways. The speed and altitude (i.e. flight envelope) d
26、etermine the maximum temperature of the ECS heat sink (nominally air) as well as the aerodynamic heat load, and hence influence ECS size.The location of ECS equipment in the aircraft, relative to the power source and cooling loads, determines ECS ducting size and complexity which in turn impact cost
27、.6.1.2 ECS Weight: ECS weight affects life cycle cost in several ways. Production costs increase as weight increases because more material is used, and more labor is needed to fabricate and handle larger components. Similar factors affect support costs. Another important factor is the cost of fuel r
28、equired by the engines to carry the ECS.Production costs can be related to the weight of ECS components. Cost algorithms differ among components (e.g. see Ref. 7). Ducting has the lowest cost per unit weight. Refrigeration components have a higher cost per unit weight than ducting. Control related c
29、omponents have the highest cost per unit weight. Ducting relative weight and cost (for open air cycle ECS) increase as engine bleed conditions increase and as the distance from the refrigeration package to the engine increases. Relative costs of controls are determined more by complexity than by wei
30、ght.ECS weight effect on fuel costs is determined by the aircraft application (i.e., mission and type of engine). If the mission nominally includes significant flight time at efficient engine operation (i.e., low specific fuel consumption), ECS weight impact on fuel cost will be lower per flight hou
31、r than for more variable missions.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1812 Revision A- 10 -FIGURE 2 - Primary ECS Cost FactorsCopyright SAE International Provided by IHS under lice
32、nse with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1812 Revision A- 11 -6.1.3 ECS Power Requirements: ECS power requirements affect life cycle costs primarily via the effect on engine specific fuel consumption, hence fuel costs. Section 5.2.1 discus
33、ses the impact of ECS on the engine.Engine bleed air is the most common source of power for the ECS, and the source of pressurized air which is conditioned by the ECS. Use of engine bleed air is a convenient means to obtain pressurized air. However, as a power source, bleed air use is generally not
34、as efficient as other alternates. This is partially because bleed air power often is dissipated by regulation to acceptable pressure levels. Electrical and hydraulic power can be provided at relatively high efficiencies. Direct mechanical power use is restrictive on ECS location, but is usually the
35、most efficient.Efficiency and weight of alternate power systems have differing impacts on ECS life cycle costs. Bleed air powered ECS use high speed components to reduce weight, but require heavy high temperature ducting to transfer power from the engine to the ECS. Electrical and hydraulic power is
36、 obtained by first converting engine mechanical power via generators or pumps, but the power transfer lines are small. Electrical motors used are nominally heavier than hydraulic motors, but they may be cheaper. These and other factors affect weight and fuel to provide the power.6.1.4 ECS Reliabilit
37、y: The reliability of an ECS affects the operational and support costs. ECS with fewer parts will generally have higher reliability resulting in lower unscheduled maintenance costs. Dynamic ECS components (e.g., turbines, compressors, and fans) and control related components (e.g., valves and contro
38、llers) are normally the ECS reliability drivers. Overall ECS reliability basically is a function of the number and complexity of these types of components used. Higher RDT&E costs, to increase reliability and to reduce maintenance tasks, can have significant positive effects in reducing O&S costs of
39、 ECS.6.2 Cost Distributions:The relative importance of the three cost categories of Section 4 may vary depending on the type of aircraft and ECS. One reason is that the operational uses of ECS are quite varied (i.e., contrast the long subsonic cruise of a passenger or cargo transport aircraft to the
40、 relatively short duration flight of a military fighter). Another reason is that fuel costs have become a more significant factor, hence generalized historical information is not valid (when fuel costs are considered part of operations cost). A third reason is that new ECS designs are being consider
41、ed that reduce the significance of fuel costs.6.2.1 RDT&E Cost Distributions: ECS RDT&E costs are largely dependent on system size, complexity, prior development and operational requirements. ECS RDT&E costs relative to total ECS life cycle costs, decrease as the number of units procured increase. A
42、 representative estimate for RDT&E costs for current types of ECS is 5% to 10% of ECS life cycle costs (200 aircraft, References 1 and 4). Relative to production costs, a nominal estimate for ECS RDT&E cost is 100 times the ECS unit production cost.Copyright SAE International Provided by IHS under l
43、icense with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AIR1812 Revision A- 12 -6.2.2 Procurement Cost Distributions: ECS procurement costs are basically dependent on the quantity of units produced. Production cost per unit is dependent on system complex
44、ity and size, and on the quantity produced. As the number of systems produced increases, the cost per unit decreases. This reduction of unit cost is termed a “learning curve”. A percentage factor is applied to the learning curve definition. The percentage defines a lower unit cost if the number of u
45、nits to be produced is doubled. A typical percentage value is 95%.ECS procurement costs vary considerably, relative to life cycle costs, because operational and support cost variations are dependent on aircraft mission requirements (e.g., from References 1, 4 and 7 production costs are from 1/8 of l
46、ife cycle costs to more than 1/2 of life cycle costs).An approach for consideration of procurement costs is to classify ECS components according to general function or use. For example, (1) basic refrigeration components (including heat exchangers, turbomachines and fans), (2) ducting, for fluid dis
47、tribution to and from the refrigeration components and (3) control components, including valves.With this approach, a comparison of two air cycle ECS, in two aircraft having very different missions, indicates that basic refrigeration components are about 1/6 of production costs, ducting is about 1/2
48、, and control related components are about 1/3.6.2.3 Operational and Support Cost Distributions: Operational and Support costs are the largest element of ECS life cycle costs, and they are the most variable. The reason for this is the varied applications of the ECS. Three prime factors affecting O&S
49、 costs are deployment, the rate of use and the mission of the aircraft. Some support costs increase as deployment increases (i.e., locations at which aircraft are used). Support costs affected by deployment include the cost of additional maintenance personnel, and general administrative support. (The cost of setting up the additional support bases comes under the heading of Procurement-Support Investment Costs). Aircraft use rate, mission
