SYSTEM REQUIREMENTS REVIEW - Purdue University



SYSTEM REQUIREMENTS REVIEWChad Carmack Aaron Martin Ryan Mayer Jake Schaefer Abhi Murty Shane Mooney Ben Goldman Russell Hammer Donnie Goepper Phil Mazurek John Tegah Chris Simpson Spring 2010Table of contents TOC \o "1-3" \h \z \u INTRODUCTION PAGEREF _Toc253672065 \h 1Mission statement PAGEREF _Toc253672066 \h 1Outline PAGEREF _Toc253672067 \h 2MARKET AND CUSTOMERS PAGEREF _Toc253672068 \h 3Projected Business Market PAGEREF _Toc253672069 \h 3Cabin Model PAGEREF _Toc253672070 \h 5Mission Sketch PAGEREF _Toc253672071 \h 12Design Mission PAGEREF _Toc253672072 \h 13Operating Mission PAGEREF _Toc253672073 \h 14SYSTEM DESIGN REQUIREMENTS PAGEREF _Toc253672074 \h 15The House of Quality PAGEREF _Toc253672075 \h 15Compliance Matrix PAGEREF _Toc253672076 \h 18Benchmark Aircrafts and New Technology PAGEREF _Toc253672077 \h 20INITIAL SIZING ESTIMATES PAGEREF _Toc253672078 \h 23Database PAGEREF _Toc253672079 \h 23Constraint Diagram PAGEREF _Toc253672080 \h 25Initial Estimates PAGEREF _Toc253672081 \h 26Summary PAGEREF _Toc253672082 \h 32Next Steps PAGEREF _Toc253672083 \h 32REFERENCES PAGEREF _Toc253672084 \h 33APPENDIX A PAGEREF _Toc253672085 \h 34INTRODUCTIONThe past decade has seen a considerable amount of economic advancement take place in the international markets, where countries such as China and India have become industrial leaders. Due to such rapid growth, many fortune 500 companies seek to take advantage of this situation by expanding their businesses in these countries. Keeping this in mind, designing a long range aircraft with time saving capabilities is promising.The team will target multinational corporations as their main clients, for whom time is money. Providing an aircraft which will save clients time and help increase revenue is a crucial design objective. The proposed aircraft will also be designed to meet and exceed all of the environmental N+2 standards set forth by NASA. Research, use of historical data, and other tools such as computational packages, are being used to design the aircraft. The team has taken into consideration every customer requirement and has developed an aircraft catered to meet these requirements. The goal of the project is to design an aircraft that gives its customer a truly elite ownership experience. Mission statementThe main goal of this project is to design a cost effective aircraft with high speed capabilities, which is able to transport its customers to their desired locations in the least amount of time possible. The project’s secondary goal is to meet NASA’s N+2 criteria, reducing the environmental impact of the aircraft. The proposed aircraft will be able to compete with other aircraft in the ultra long range category. OutlineThis report is comprised of five sections. The first section will give the reader a brief market overview discussing customer needs and benefits. It will also discuss current market sizes and address competitor’s aircraft. The next section is the concept of operations section, also referred to as the CONOPS. In this part of the paper, the team will address crucial components of the project’s goals such as customer satisfaction and its affect its influence on the aircraft. The CONOPS section will also cover expected flight ranges and required runway lengths, the aircraft’s payload and passenger capability, mission sketches, and segment descriptions.The system design requirements section follows the CONOPS section, and contains the house of quality in detail. It also explains how the team intends on meeting NASA’s N+2 goals, and introduces new technologies that might be integrated to assist the design in meeting these goals. Following system design requirements, initial sizing estimations will be computed. These estimates contain values such as; lift to drag ratios, Specific Fuel Consumption (SFC), and empty weight fractions. The final section discusses the projects future design goals. This includes the future steps which will need to be taken in order to accomplish the objective of the project. MARKET AND CUSTOMERSPrimary customersPrior to starting the design process, a market analysis study was conducted to find the ideal market niche to accommodate. Identifying the primary client was the first step. In the past 2 years there has been a substantial plummet in the financial market. The only groups of people that have not changed their outlook as a result of this downfall are the wealthier side of society, including CEO’s of multinational corporations and celebrities. This elite class of passenger prefers a luxurious, fast, and private travel experience. Using a public airport is usually a very inconvenient and time consuming endeavor. Historically this side of society has a proven financial stability track record and was deemed to be the primary customer. With this historically stable clientele, the outlook for expected aircraft sales in this class has remained and is expect to stay stable and maintain steady growth. Other possible clientele include fractional air services.Projected Business Market According to the Research firm Frost & Sullivan, the Middle East and Asia are one of the few world regions where the long haul business jet market has registered growth. The air-taxi segment is also expected to be a major driver for this market. According to the Frost & Sullivan’s data, the Middle East logged 93,000 business jet movements in 2008, this number was projected to reach 103,000 last year. Growth is expected to continue, reaching 160,000 jets in 2018. Frost & Sullivan projected the compound annual growth rate of business jet movements in the Middle East will be about 6.21 percent from 2008 to 2018. Figure 1 depicts markets in various regions of the world.1Figure SEQ Figure \* ARABIC 1: Business Aircraft Expansion Percentage.As the economy recovers from the current downturn, orders for business aircraft are expected to increase, which should sustain sales for new business jets over the next 10 years. The sharp contraction of the U.S. economy and ensuing worldwide recession during 2008-2009 is expected to cause a significant reduction in the near term demand for business jets. Many original equipment manufacturers (OEMs) have and will likely continue to receive order cancelations in early 2009 . Order intake is forecast to fall as low as 375 units in 2009, and is expected to improve by the end of the year, reaching 2008 levels of approximately 1,400 units per year by 2013. 2 Figure SEQ Figure \* ARABIC 2: Purchase Plan Analysis.Figure 2 depicts a pie chart which breaks down intended purchases by aircraft type. The chart clearly shows that the bulk of jets to be purchased are of the large cabin class. The following pages discuss the technical details of our design, which is believed to offer the best possible solution for the customers. 2Cabin Model The aircraft was conceived as a 16-passenger business class jet. Accordingly, the initial sizing of the aircraft was directly dependent on an efficient and attractive layout capable of comfortably seating 16 passengers. Design began by choosing the general shape of the cabin, and a cylindrically-shaped cabin was found to be of the greatest benefit due to its association with reduced manufacturing costs. Additionally, this design would simplify the pressurization of the cabin. Once the shape of the cabin was determined, the next step was to scale the aircraft. The two major dimensions requiring attention in the sizing of the cabin were its length and interior diameter. The aircraft that is most similar (currently in certification testing) is the Gulftsream G650. Therefore, when determining the cabin’s diameter (and length), figures were checked against Gulfstream’s to ensure an additional level of realism. Numerous layouts were considered before settling on one which offers the client a wide variety of seating arraignments and ample personal space. The cabin currently accommodates seating for up to 16 passengers and a resting area for 2 crew members. The cabin is furnished with 2 sofas, 6 individual seats, and conference seating for 4. It is also equipped with a large galley and two lavatories, one at the front of the cabin and one positioned aft of the main cabin where the tail meets the fuselage. The main entrance and exit is positioned between the forward lavatory and the nose of the aircraft. Even with all of the aforementioned amenities, the cabin still boasts a personal volume of 81.5 cubic feet. Note that this volume is calculated for a full cabin of 16 passengers, which means that any flights carrying fewer than 16 passengers (which is expected to be quite often) will allow for even more personal space. The graph in REF _Ref253670720 \h Figure 3 shows a correlation between trip duration and cabin space. This graph was provided from Torenbeek, synthesis of subsonic aircraft design. From this graph, it is possible to see that with a volume of 81.5 cubic feet per passenger, our aircraft will allow 16 passengers to fly in “plush” comfort for up to a four hour trip. As the number of passengers decreases, each passenger will have more room and the amount of time for the “plush” category will be increased. The trend lines for this plot are linear, so it is also possible to continue them out to a max flight time of 12 hours. Even with a full cabin of 16 passengers, the aircraft boasts comfortable accommodations for a full length flight.3 Figure SEQ Figure \* ARABIC 3: Comfort vs. Duration.However, this number is low in comparison to the G650, due to two main factors: the G650’s greater cabin length and elliptical cabin shape. This style of cross section has a flatter lower section to make better use of internal volume. Still, the team’s design is both attractive and efficient, and therefore its general shape will not be changed at this point. By affording accurate sizing and spacing to the cabin layout, an estimate of its initial length was found to be an even 50 feet. The cabin’s inner diameter was chosen after careful consideration of current similarly scaled business jets and the client’s needs.The length of the nose and tail are usually sized according to a fineness ratio, calculated to be the ratio of the length of the section divided by the cabin diameter. Sizing began by investigating the range of fineness ratios currently in use and it was found that the nose of current aircraft usually have a fineness ratio between 1.5 and 2, while the tail of current aircraft usually have a fineness ratio of between 2.5 and 3. At this point in the design, no consideration for the aerodynamic impact from fineness ratio has been made; aside from staying within current ranges. It is however recognized that, particularly for a transonic aircraft, the fineness ratio of the aircraft plays a critical role in drag production. The nose and tail were designed with fineness ratios of 1.6 and 2.7, respectively, based upon visual cues from current high performance business jets. However, these lengths are by no means finalized and changes are anticipated further into the design process. Because the fineness ratio is a comparison of section length to cabin diameter, the resolution of these ratios also means that the first estimates for the lengths of the nose and tail. These estimates are 1.6*(8.83 feet) = 14.17 feet for the nose and 2.7*(8.83 feet) = 23.9 feet for the tail. This provided the first practical approximation of the aircraft’s total length at 88 feet.The aircraft’s total fineness ratio was found by dividing the aircrafts total length by the cabin diameter. Currently the aircraft boasts a fineness ratio of 9.96. Comparing this to the G650’s ratio of 11.08, this aircraft’s fineness ratio is certainly well within realistic range. This is based on the fact that this aircraft is designed to compete with the G650 at its own transonic flight regime. Also, while the fineness ratio is not the ultimate choice when it comes to performance, it is a very important characteristic to consider and likely one whose impact will have to be weighed against other necessary performance characteristics in the future. Comparing the nose and tail to the main cabin visually, the chosen fineness ratio set the aircraft’s lines in terms of length ratios, visually depicted in Figure 4 below.Figure SEQ Figure \* ARABIC 4: Effect of Overall Fineness Ratio on Aircraft Length.Resulting from the interior sizing is an aircraft cross-section with two rows of outboard seating, and a center aisle from the fore end of the cabin until the conference area. Primary dimensions for the interior cross sectional area are shown in Figure 5, and a dimensioned top-view of the main cabin is provided in Figure 6, with a detailed drawing showing seating dimensions in Figure 7.Figure SEQ Figure \* ARABIC 5: Interior Main Cabin Cross Section.Figure SEQ Figure \* ARABIC 6: Top View of Interior Cabin Dimensions.Figure SEQ Figure \* ARABIC 7: Detail of Cabin Amenity Dimensions.While the specifications of the aforementioned cabin layout can provide passengers with a plush flight experience for a set duration, a cabin re-design is currently underway to further heighten passenger comfort. The incorporation of an industry-competitive quantity of windows placed in a manner to provide ample passenger view while retaining cabin flexibility is currently being incorporated in the cabin layout. A “designing from the cup holders”, comfort first, interior design mentality is shaping the next generation of cabin interior. The incorporation of minor amenities such as the very cup holders, individual ventilation outputs, the infringement of chair reclining on other passengers, aisle widths and personal privacy concerns are also under current refinement. In addition to the chair and sofa design, passenger comfort was addressed in regards to lavatory size and placement. The rear lavatory’s location aft of the rear bulkhead provides a visual separation from the passengers in the main cabin, but maintains a close proximity to the conference area and galley. Emergency exit placement was chosen from both safety, as well as spatially contributing perspectives. The emergency exit was placed approximately mid-length in the cabin, and on the opposite outboard wall of the main cabin door. This location provided both an easily accessible location for exit from the conference and mid-cabin seating areas, and further ensured a wide aisle width through the conference seating, providing a spatial break from the non-conference seating. Location of the emergency exit and other key features of the aircraft interior are visible in Figure 8 below. Figure SEQ Figure \* ARABIC 8: Aircraft Interior Key FeaturesFocusing not only on passenger comfort, crew comfort on extended flights is currently under design refinement. While the two crew seats can be fully reclined, a crew rest area containing two stacked bunks is under development, though its isolation from the main cabin without infringement upon aisle width requires further assessment. The expanded crew rest will provide a bunk for an additional pilot and a current crew member during extended flights. Cabin adjustment with the incorporation of the crew rest area will necessitate a re-arrangement of interior cabin space, incorporating the currently unused space along the right outboard wall at the rear of the main cabin. A rendered image of the current cabin layout is provided in Figure 9 below for visual reference.Figure SEQ Figure \* ARABIC 9: Rendered Image of Current Cabin MockupCONCEPT OF OPERTATIONSMission Sketch25482551105535Figure SEQ Figure \* ARABIC 10: Representative City Pairs 4It is understood that with businesses time is money so the need to move people quickly and efficiently to and from meetings is of utmost importance. In today’s economy, businesses are not necessarily tied down to one country but instead are spread across several locations around the world. This makes personal meetings substantially more difficult. Flying conventional commercial flights to and from meetings, while seemingly cheaper than taking a business jet, actually incurs larger costs due to the major losses in time. It is this dilemma of unnecessary and costly wasted time that this project looks to address. A key component of this aircraft is to provide a long range business jet that enables truly global transportation. With a still-air range of 6350 nautical miles, this aircraft is capable of making non-stop international flights; eliminating the costly layovers associated with commercial flights and shorter ranged business jets. As seen in the following table, the range of 6350 nautical miles puts several desirable destinations well within reach.Table SEQ Table \* ARABIC 1: Distances between City Pairs.Los AngelestoSeoulDallastoMoscowLos AngelestoBeijingNew YorktoDubaiChicagotoTokyoLos AngelestoHong Kong5209 nm5035 nm5432 nm5949 nm5452 nm6309 nmDesign MissionThe design mission was developed and optimized with the city pair of Los Angeles and Hong Kong in mind. The design mission consists of eight mission legs between nine points as illustrated in the following figure.Figure SEQ Figure \* ARABIC 11: Design Mission Flight Plan.The first leg of the mission, from points 0 to 1, is taxi and takeoff to an altitude of 50 feet. From points 1 to 2 is the climb portion of the mission where the aircraft climbs at best rate to an altitude of 42,000 feet. From there the aircraft enters the cruise leg of the mission, between points 2 and 3, and begins cruising at a Mach number of 0.85 for 6350 nautical miles. Cruise is then followed directly by a no range credit descent to land where the aircraft will attempt a landing, from points 4 to 5, climb to an altitude of 5000 feet at best rate climb, points 5 to 6, and commence cruise to an alternate airport 200 nautical miles away. Once at the alternate airport, the aircraft will enter a holding pattern for 45 minutes, from points 7 to 8, and then begin a no range credit descent to land. Finally, the aircraft lands at the alternate airport and completes the last mission leg at point 9 when it comes to a stop.Operating MissionWhile the design mission is the optimal, most efficient use of this aircraft, several other operating missions can be made by this aircraft as well. One such operating mission would be flying from New York to Los Angeles. The distance between the two cities, which is 2146 nautical miles, falls well within the maximum still-air range of 6350 miles. To compensate for the largely unused range, the aircraft can then be flown at its maximum Mach number of 0.9 at a maximum capacity of 16 passengers. This range tradeoff allows for tremendous flexibility in speed and capacity for shorter ranged flights.SYSTEM DESIGN REQUIREMENTSThe House of QualityA house of quality was constructed as the primary tool of Quality Function Deployment (QFD) for this project. The house of quality is shown in REF _Ref253672181 \h Figure 12. The house was built in the traditional order, starting with an analysis of customer needs. Eleven customer needs were identified, and organized into 4 groups. The importance of each need was then ranked on a scale of one to ten. Since no customers were available, these tasks were completed using the design team’s beliefs of how customers would perceive the product. The customer attributes of a relatively fast aircraft, having a long range, were considered the most important. After the importance of the attributes was assessed, competing products were compared in terms of these needs. Two competing products were selected from the ultra-long range jet market. These aircraft were the Gulfstream G650, and the Bombardier Global Express XRS. For both competing aircraft, the same two areas contained the greatest room for improvement. These were the nitrous oxide emissions of the aircraft (desired to be lower), and the ability of the aircraft to fly out of small airports. Note that certain benchmark values in Figure 12 are highlighted to indicate that there was not enough information available to make a firm conclusion. After these benchmarks were determined, the engineering characteristics for the design were determined. These engineering characteristics were measurable specifications that would control the design’s ability to meet customer needs. Threshold values were also identified as these requirements were drafted. Twelve engineering requirements were listed, created a matrix of 132 cells.Each of the cells was evaluated in terms of the strength of the relationship between a customer attribute and its corresponding engineering characteristic. There was a strong relationship between the aircraft’s need to be “fast” (one of the most important customer attributes) and the aircraft’s cruise mach, which had a threshold value set at 0.8. This value was established based on the idea that the aircraft could not be considered fast by any customer if it cruised at a speed noticeably slower than most modern jet transports. The other customer attribute judged to be particularly important, a long flight range, was most strongly affected by the fuel consumption of the aircraft and its design range. A threshold value of 6000 nautical miles was set for the design range at this phase, as a result of studying historical ultra-long range jet specifications and market segmentation. After all of the relationships between the customer attributes and the engineering requirements were determined, the importance of each engineering characteristic was calculated from the strength of its relationships with the customer needs. There were three engineering characteristics which came out to be in the highest range of importance. These characteristics were cruise mach, takeoff distance, and fuel consumption. After the house of quality’s matrix was complete, the interactions between the various engineering characteristics were assessed. Multiple strong relationships were observed with both fuel consumption and passenger capacity. It was determined that fuel consumption had a strongly positive relationship with both nitrous oxide emissions and range. It was also determined that passenger capacity had a strongly negative relationship with takeoff distance, range, and variable cost. While the positive relationships associated with fuel consumption are worth noting as opportunities to easily improve the design; the negative relationships associated with the aircraft’s capacity are particularly important because they are indicative of potential future tradeoffs.Figure SEQ Figure \* ARABIC 12: House of pliance MatrixThe compliance matrix is a key component of the design process. The compliance matrix helps keep track of goals and aids in determining the current status of the design. A compliance matrix lists the important engineering parameters and assigns target and threshold values for each of those parameters, along with an estimate of each value in the current design.The engineering characteristics in the compliance matrix are the same as those in the house of quality that address the needs of the customer. The target values are the values of the engineering parameters that are thought to best fit the customer needs. These target values are the ultimate goals of the aircraft design. The threshold values are the values of each of the parameters that were determined to be the minimum requirements of the final product. Some threshold values are determined by laws and regulations, while others are determined by the design team in order to establish a baseline for the design.The target and threshold values of each of the engineering parameters in the compliance matrix were chosen for different reasons. Both the threshold and target values of the still air range were chosen based on distances between major destinations and specifications of similar existing aircraft. A still air range of 6350 nautical miles provides a route between many of the world’s most popular business travel destinations.The cruise altitude is an important parameter because if the aircraft can climb above the traffic, it can fly more quickly to the destination. For this reason, the target value of cruise altitude is 45000 ft, and the threshold is 40000 ft.The target value for the LTO NOx emissions is 75% below the levels in CAEP 6. This is a number that is taken directly from the N+2 goal set by NASA. The threshold value is 60% below the levels in CAEP 6, which corresponds to the NASA’s N+1 goal. Similarly, the cumulative certification noise level target corresponds to the N+2 goal of 42 dB below the stage 4 level, and the threshold value corresponds to the stage 4 level.5The N+2 goal set by NASA also includes a 40% reduction in fuel burn. The target value for fuel burn was determined by deducting 40% from the fuel burn of a similar aircraft, the Gulfstream G650. Similarly, the threshold value was determined by the 33% reduction for the N+1 goal. The fuel burn of the G650 was determined by dividing the maximum fuel capacity by the maximum range due to the lack of published data regarding the fuel burn for the G650. Inverting these numbers gives the specific range.5The sill height is an important parameter because the passengers need to be able to enter and exit the aircraft without necessarily requiring special services from the airport. This means that the door to the aircraft needs to be reasonably close to the ground to make it easier to incorporate stairs into the aircraft. The target and threshold values were chosen as 4 feet and 5 feet, respectively.Table SEQ Table \* ARABIC 2: Requirement Compliance MatrixPerformance CharacteristicTargetThresholdCurrentHeadwind Range6300 nmi6000 nmi6300 nmiTakeoff Distance Field Length6000 ft7000 ft6000 ftMaximum Passengers17816Cruise Mach.85.8.85Cruise Altitude45000 ft40000 ft45000 ftCabin Noise60 dB70 dB65 dBLTO NOx EmissionsCAEP 6 -75%CAEP 6 -60%CAEP 6 -70%Cumulative Certification Noise Level232 dB274 dB274 dBSpecific Range0.263 nmi/lb0.208 nmi/lb0.161 nmi/lbLoading Door Sill Height4 ft5 ft4 ftVariable Costs$4100/hr$4300/hr$4100/hrBenchmark Aircrafts and New TechnologyOne of the major goals of the project is to reduce fuel consumption. Green technology will be used to reduce emissions, but the most effective method to reduce carbon dioxide and NOx output is by reducing overall fuel consumption. An aircraft had to be selected for a fuel consumption benchmark. The Gulfstream G650 currently performs a similar design mission with a fuel consumption rate of 0.158 nm/lbs. This figure was calculated by dividing the maximum range by the maximum fuel weight. The design mission was to reduce current fuel burn by as much as 40%. A reduction of 40% in fuel consumption based upon the G650 would be a fuel burn of .265 nm/lbs. A modern aircraft that has a similar fuel consumption is the Gulfstream G150 with a current fuel consumption of .287 nm/lbs. The G150 is considerably smaller than the current aircraft proposed in the design; therefore such a large reduction in fuel burn will require extensive use of advanced technology and engineering. 6The reduction in fuel consumption is just one of the many goals proposed by NASA’s subsonic fixed wing program. NASA has set four fundamental goals referred to as N+2 for a subsonic fixed wing business aircraft set for production in the 2020 timeframe. The four goals are 42 dB below stage 4 certification, 75% reduction in NOx emissions, 40% reduction in fuel consumption, and a performance field length reduction of 50%. The first three design goals will be met by using an innovative propulsion system. Due to the long range and high capacity of the current design mission, the reduction in field length will most likely not be met. 5The team currently proposes to use advanced technologies that are currently under research to achieve NASA’s N+2 goals. The first design component will be the use of composite materials. Aircraft such as the Boeing 787 have achieved a significant empty weight reduction by utilizing composite materials in the majority of the airframe. A reduction in aircraft weight will allow for reduced fuel consumption and a reduction in take off length. Another advanced technology that is being explored is the use of an unducted propfan for a propulsion system. An unducted propfan is an advanced engine design that would incorporate two counter rotating fans that would be directly connected to the engine’s turbines. General Electric explored the unducted propfan concept in the 1980s and 1990s and even flew a design named the GE36 on a Boeing 727 test aircraft. The project had problems with noise levels and vibration due to the wave drag created by the high speed fans. The noise levels and plummeting fuel costs of the 1990s caused the cancellation of the project. Currently, Rolls-Royce, General Electric, and NASA are working together to achieve a noise reduction level in the unducted propfan concept. “The outcome of this work is that we are now confident that open-rotor-powered aircraft will be quieter than any equivalent aircraft flying today and that it will comfortably meet Stage 4 noise legislation,” says Robert Nuttal, Rolls-Royce’s vice president of future programs strategic marketing (Norris 54). The unducted propfan technology is currently the only possible solution to meet NASA’s N+2 goals within the specified time frame.7In fact, NASA’s environmentally responsible aviation program (ERA) is devoting much of its research in the subsonic fixed wing project to the unducted propfan technology. “ERA is focused on the goals of NASA’s N+2, a notional aircraft with technology primed for development in the 2020 time frame as part of the agency’s subosonic fixed-wing program,” Guy Norris. Nuttal was quoted in Aviation Week’s December 14, 2009 issue as saying, “So far the GE-NASA experience seems to echo that of Rolls-Royce. We are able to confirm that the fuel burn will be 25-30% better than today’s products. And, because of the engine cycle of the open rotor; the nitrous oxide will be 20% lower than another engine with an equivalent combustor technology. We are now preparing for the next tranche with the next build of the rig taking place in Q2 2010”. Because of the current development being made on the concept and NASA’s faith in the technology, the team feels it is an appropriate decision to anticipate using unducted propfans as a propulsion system for the design project. 7INITIAL SIZING ESTIMATESDatabaseA database of aircraft was developed to be used in sizing the aircraft to meet the requirements for achieving the design mission. Other aircraft with similar weights, ranges, number of passengers, and purposes were included. The aircraft in the database are shown in Table 3 below, as well as some of the important specifications associated with each aircraft. All of these aircraft are business jets that carry between 8 and 18 passengers.Table SEQ Table \* ARABIC 3: Aircraft DatabaseAircraftW0 (lb)We/WoARTsl/W0Range (nmi)W0/SLong range cruise MGulfstream G550910000.5307697.6888740.338132675080.035180.8Gulfstream G650996000.5421696.8503990.323293700077.6305530.85Bombardier Global Express XRS980000.5076538.6457930.30102615095.8904110.85Bombardier Global 5000925000.5621628.6457930.318919528090.5088060.85Gulfstream G500851000.5640427.6888740.361575580074.8460860.8Citation X36,1000.599037.7722960.374737307068.5009490.82Bombardier Challenger 30038,8500.5855867.805920.351403310074.4252870.75Bombardier Challenger 85051,0000.5058828.2470440.361569312086.8676550.74Bombardier Learjet23,5000.6247237.2365310.391489240588.8468810.74Bombardier Learjet 8533,5000.6298519.4384870.364179270083.5411470.78Cessna Citation Sovereign30,3000.5762387.774970.380858280058.7323120.76Gulfstream G15026,1000.5632187.7237670.338697295065.250.75Hawker 400039,5000.5772157.1809090.34957285574.3879470.78Hawker 75027,0000.67.0457510.345185217072.1925130.76Hawker 850XP28,0000.5832147.7483140.332857260073.4908140.76Hawker 900XP28,0000.5864297.7483140.339286290473.4908140.76There is a large range in weight within the aircraft in the database, from a low of 23,500 lbs to a high of 99,600 lbs. It was initially desired to only include heavier planes similar to the size of the plane our group is designing. However, there are a limited number of planes that exist with size and performance characteristics similar to ours. This places several limitations on our sizing methods, which caused us to include more dissimilar planes into the database. Because of this, there are clearly two different classes within our database. The first group focused on the larger aircraft with longer ranges which more closely match the design mission. The second group includes mostly smaller business jets. REF _Ref253672240 \h Figure 13 shows the division of these two groups and graphically illustrates the difference in size between them. The large group, called “Class 1,” has aircraft with gross weights greater than 80,000 lbs while the smaller group, called “Class 2,” has aircraft with gross weights less than 52,000 lbs. Also REF _Ref253672240 \h Figure 13 shows the variation even within each group for We/Wo as a function of Wo. This will potentially cause uncertainty in the initial sizing estimates as the trends have large R2 values.Figure SEQ Figure \* ARABIC 13: Aircraft Database Groups.Constraint DiagramA constraint diagram was used to find initial estimates for the wing loading and thrust to weight ratio of our aircraft. These numbers were found by plotting various flight conditions and maneuvers to graphically asses the plane’s performance. The constraint diagram associated with our initial design is shown below in Figure 14. The aircraft must operate in the upper left part of the diagram, above the second segment climb, and left of the landing ground roll. This means that the wing loading is limited primarily by landing ground roll and the thrust to weight ratio is limited primarily by second segment climb. It is important to note that the landing ground roll appears as a vertical line because there is no reverse thrust included in the calculations. Reverse thrust was not included because the engine we plan to use, an unducted fan, is not capable of producing reverse thrust. If the wing loading of our design is lowered enough, top of climb could become a limiting factor. Also if the takeoff ground roll is reduced much below 4700 ft, it will become a constraining factor. A subsonic 2.5g maneuver at 250 knots is not a design-limiting constraint at this time.Figure SEQ Figure \* ARABIC 14: Constraint Diagram.The constraint diagram shows that the aircraft must have a wing loading of less than 101 lbs/ft2 due to the landing ground roll of 3500 feet or less and the landing CL max of 2 which corresponds to the slotted flaps that our plane is using. The aircraft must also have a TSL/W0 of greater than .33 because of the second segment climb. If the wing loading goes below 65, then the TSL/W0 must increase in order to meet the top of climb requirements.Initial EstimatesInitial sizing estimates were based primarily on trends calculated from our database as well as some historical estimates. First, an estimated aspect ratio of 8.0 was chosen based on the similarly sized “Class 1” aircraft in our database. From this estimate, the corresponding cruise lift to drag ratio can be calculated through a combination of equations presented by Raymer, Nicolai, and Carte.8 Using the equation listed as equation 1, a cruise lift to drag ratio for our plane can be found to be 15.56. The specific fuel consumption was also estimated based on existing business jets; our calculations assumed that SFCcruise is 0.5 and SFCloiter is 0.6.Eq. 1 With these values, the weight of the aircraft can be estimated. Two methods were used, the first of which was to simply create a curve fit from similar aircraft relating the gross weight (W0) to the empty weight fraction (We/W0). The curve fit through Group 1 aircraft produced equation 2.Eq. 2This equation was then used inside of a sizing loop to converge upon a final weight estimate. The full MATLAB code used in this process can be found in Appendix A. This curve-fit method yielded a gross weight of 92,000 lbs. While this method provided a reasonable gross weight estimate, there were some reasons to be skeptical. REF _Ref253672339 \h Figure 15 shows that there is a large variation in the data and that the trend line may not be a good estimate as there are only 5 data points with a large variance. Because of the lack of similarly sized planes and the large variation in data, a second sizing method was also used.Figure SEQ Figure \* ARABIC 15: Curve Fit of Similar Aircraft.In order to improve our weight estimate, a least squares regression was used. This method was appealing because it included much more than just the empty weight fraction in its calculation. The second method used equation 3 below.Eq. 3The challenge in using this method is that each additional unknown exponent requires an additional aircraft in the database in order to solve the equation. Our own database only contains five aircraft in the similarly sized “Class 1” genre. Because of this, the entire database of aircraft was used. Solving for the unknown constants in equation 3 provided the complete equation shown in equation 4 below. Eq. 4This method again uses a loop to converge on a final gross weight, and also includes other design variables where the first method did not. This method gave a gross weight of 108,000 lbs which is 18,000 lbs greater than the previous estimate and 8,000 lbs greater than even the largest business jet in the database, the G650. These estimates are, however, still based on a database of aircraft with a large variation amongst them. This could result in a large error when attempting to make trends amongst the data. One clue that the approximations may not be perfect can be found in examining the signs of the exponents. For example, one might intuitively conclude that as the aspect ratio increases, so does the empty weight fraction. This should produce a positive exponent for the aspect ratio variable, but the solution from our database produces a negative exponent. Likewise, as the wing loading increases, the size of the wing decreases, and therefore the empty weight fraction should also decrease. This should produce a negative exponent for the wing loading variable, but the solution from our database produces a positive exponent. As the design moves forward, the challenge will be to improve upon the database and find planes that better relate to the one we are designing. A better, more representative database should resolve the inaccuracies present in the sizing methods.Both weight estimation methods will continue to be developed until they either converge upon the same solution, or until one becomes clearly better than the other. The method of the least squares regression is more desirable, however, since it includes many more design variables in its calculation and therefore characterizes many traits simultaneously. Table 4 below summarizes the current weight prediction values produced by the two sizing methods.Table SEQ Table \* ARABIC 4: Estimated Weights?Curve Fit Weights (lbs)LSR Weights (lbs)Wo92,100108,200We50,10059,300Wf39,50046,300While the sizing code was used primarily to find an initial estimate for the gross weight of the aircraft, it could be adjusted slightly to predict the performance of the plane under various loading conditions. This was desirable in assessing how the plane would perform for typical operating missions that differ greatly from the design mission. In particular, it was important to know how the range would be affected by flying at faster or slower Mach numbers. This information would be useful in determining whether or not our plane could carry a certain amount of people over a particular distance at a desired speed. Using a fixed initial gross weight, Figure 16 was generated, which predicts the performance of the plane under various conditions.Figure SEQ Figure \* ARABIC 16: Range vs. Mach Number.This plot shows that the plane can travel at Mach 0.9 for any range less than 5500 nmi for any number of passengers. A longer distance, or a strong headwind, could require a slower cruise speed. This plot also shows the tradeoff between range and cruise Mach number. While business jet owners often want to fly as fast possible, doing so will reduce the range of the plane. For short missions, this is not an issue. But for longer missions, such as the design mission, the pilot must be very aware of this tradeoff.CONCLUSIONSummaryThe initial phase of the project consisted of indentifying customer needs and target markets. After this was completed, customer needs were translated into system requirements using Quality Function Deployment methods. Various mission sketches and design missions were then computed and analyzed using target performance values, such as range. In addition, with the use of advanced technologies such as unducted propfans and composites, NASA’s N+2 goals should be attainable within the given time frame. Aircraft weight was determined through the application of iterative sizing methods using both a least squares regression and generic curve fits of historical aircraft data. Next StepsThis System Requirements Review completes the initial step in the design process, and will serve as a stepping stone for the remainder of the project. The next step is to go into further detail. More accurate L/D equations will need to acquired. Technology factors will also need to be included in the sizing code. Aircraft configurations will need to be taken into consideration, such as the propulsion system, wing design and placement, control surfaces, cabin layout and amenities as well as landing gear. Lastly, attitude dynamics of the aircraft will need to be researched. REFERENCES1 "Avionics Magazine :: Outlook: High Hopes for General Aviation." Breaking News and Analysis on Aviation Today. Web. 11 Feb. 2010. < "Honeywell Aerospace Business Aviation Outlook Forecasts $200 Billion inGlobal Business Jet Sales Through 2019." Web. 11 Feb. 2010. <, Egbert. Synthesis of subsonic airplane design an introduction to the preliminary design, of subsonic general aviation and transport aircraft, with emphasis on layout, aerodynamic design, propulsion, and performance. Delft: Delft UP, Nijhoff, Sold and distributed in the U.S. and Canada by Kluwer Boston, 1982. Print.4Great Circle Mapper. Web. 11 Feb. 2010. <“Subsonic Fixed Wing Project”. NASA. 08 February 2010. 's All The World's Aircraft. Web. 11 Feb. 2010. < Norris, Guy. “Rotor Revival”. Aviation Week & Space Technology. 14 December 2009. pages 54-57. 8 Raymer, Daniel P. Aircraft Design A Conceptual Approach (Aiaa Education Series). New York: AIAA American Institute of Aeronautics & Ast, 2006. Print.APPENDIX AMatlab Sizing Code%% Enter Input Values num_pass = 8; %number of passengersnum_crew = 4; %number of flight crewrange_design = 6350; %nmirange_aa = 200; %"aa" = "alternate airport", units = nmiloiter = 0.5; %hours AR = 8.0; %aspect ratioSFC_cruise = 0.5; %1/hourSFC_loiter = 0.4; %1/hourM_cruise = .85; %cruise mach Passenger_weight = 220; %lbs/personFlightCrew_weight = 200; %lbs/person Wo_guess = 10000; %lbs %Some variables from constraint diagramTW = 0.33;WS = 100; %choose weight estimation method (1=curve fit, 2= LSR)Wo_eqn = 2; %% Design Mission (find Wf/Wo) V_cruise = M_cruise*968.1/1.689; %ktsLD_cruise = 0.85*(1.4*AR+7.1); %L/D at cruiseLD_loiter = 1.4*AR+7.1; %L/D during loiter w1w0 = 0.97; %takeoffw2w1 = 0.991-.007*M_cruise-.01*M_cruise^2; %climb - Raymer Curve Fit eqn.w3w2 = exp((-range_design*SFC_cruise)/(V_cruise*LD_cruise)); %cruise - Breguet Range eqn.w4w3 = 0.995; %landingw5w4 = 0.97; %missed approach (TO)w6w5 = 0.985; %climbw7w6 = exp((-range_aa*SFC_cruise)/(V_cruise*LD_cruise)); %divert to alternate airport - cruise Breguetw8w7 = exp((-loiter*SFC_loiter)/LD_loiter); %hold at 2nd airport - Endurance eqn.w9w8 = 0.995; %landing Wf_Wo = 1.01*(1-w1w0*w2w1*w3w2*w4w3*w5w4*w6w5*w7w6*w8w7*w9w8); %fuel weight fraction %% Loop to find Wo for n = 1:1:100 if Wo_eqn == 1 %We_Wo = 1.02*Wo_guess^(-0.06); %From Raymer general jet transport %We_Wo = 1.3783*Wo_guess^(-0.082); %From Raymer - database with all planes We_Wo = 67.69*Wo_guess^(-0.422); %From Raymer - database with only the big planes else if exist('a','var') == 0 a = GetLSRcoeffs('aircraft_database_updated.xlsx'); end We_Wo = exp(a(1))*Wo_guess^a(2)*AR^a(3)*TW^a(4)*WS^a(5)*M_cruise^a(6)*range_design^a(7); end % Other CalcsWpayload = Passenger_weight*num_pass;Wcrew = FlightCrew_weight*num_crew; We = We_Wo * Wo_guess;Wf = Wf_Wo * Wo_guess;Wo_guess = We+Wf+Wpayload+Wcrew;end Wo_guess function coeffs = GetLSRcoeffs(filename) % We_Wo estimate - Least Squares regression% we/wo = b*wo*AR*(T/W)*(W/S)*Mmax*range % Columns in order are:% Aircraft (doesn't read this one in, so Wo is column 1)% W0, We, We/Wo, AR, T/W, Mmax, Range, W/S, Mcruise data = xlsread(filename);WeWo_vect = data(:,3);Wo_vect = data(:,1);AR_vect = data(:,4);TW_vect = data(:,5);WS_vect = data(:,8);Mmax_vect = data(:,9); %sometimes use cruise instead of maxRange_vect = data(:,7); Fbar = log(WeWo_vect);temp1 = [log(Wo_vect), log(AR_vect), log(TW_vect), log(WS_vect), log(Mmax_vect), log(Range_vect)];temp2 = ones(length(Wo_vect),1); Xbar = [temp2 temp1];coeffs=Xbar\Fbar; ................
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