Environautics EN 1
Response to the 2009 2010 AIAA Foundation Undergraduate Team
Aircraft Design Competition
Presented by Virginia Polytechnic Institute and State University
Left to Right: Justin Cox, Julien Fenouil, Jason Henn, Ryan Hofmeister, Michael Caporellie, Justin Camm, August Sarrol, Richie Mohan
Environautics Team Roster
ii Executive Summary
Environautics presents the EN 1 as a solution to the 2009 2010 American Institute of
Aeronautics and Astronautics (AIAA) Undergraduate Aircraft Design Competition Request For
Proposal (RFP). The design will serve as an environmentally friendly and efficient strut braced wing commercial transport to replace the Boeing 737 and Airbus 320. The RFP calls for a medium range, biofuel capable transport aircraft capable of carrying 175 passengers and cargo over a range of up to 3500 nautical miles and entering service by the year 2020. The main drivers for the proposal include maximizing performance capabilities with respect to the given RFP mission and maintaining a competitive commercial advantage while reducing the aircraft’s overall environmental impact through improved efficiency and usage of biofuels. The requirements of the RFP are discussed in Section 2.1.
The proposed design incorporates the strut braced wing design, a design proven in lightweight general aviation aircraft that enables a reduction of the weight of the main wing spar, allowing for efficiency enhancements through reduced wing thickness and sweep angle. The inclusion of advanced biofuels in the design minimizes performance penalties while reducing the aircraft’s environmental impact, further enhancing the competitive capability of the design compared to existing aircraft in areas such as operating costs. Operating costs are reduced further through use of advanced technologies that permit the aircraft to operate at increased efficiency and fewer delays.
The combination of performance, efficiency, advanced technologies and reduced environmental impact make the Environautics EN 1 a first rate choice for future commercial transports.
iii
Table of Contents Executive Summary ...... iii Index of Figures ...... viii Index of Tables ...... ix Nomenclature ...... x 1. Introduction ...... 1 2. Request for Proposal ...... 1 3. Fuels ...... 3 3.1 Fuel Descriptions ...... 3 Fuel Types ...... 3 3.2 Biological Fuel Sources ...... 8 3.3 Sizing Requirements ...... 8 3.4 Fuel Decision ...... 10 4. Concepts ...... 13 4.1 Blended Wing Body (BWB) ...... 13 4.2 Hybrid Blended Conventional ...... 14 4.3 Strut Braced Wing ...... 15 4.4 Design Selection ...... 16 5. Sizing ...... 17 5.1 Initial Weight ...... 17 5.2 Thrust to Weight and Wing Loading ...... 20 6. Aerodynamic Performance ...... 22 6.1 Drag Polar ...... 22 6.2 Lift to Drag Ratio ...... 23 6.3 Airfoil Selection ...... 24 6.4 Airfoil Analysis ...... 27 7. Propulsion ...... 32 7.1 Engine Technologies ...... 32 7.2 Engine Selection ...... 35 7.3 Fuel System ...... 35 7.4 Engine Maintenance ...... 36 8. Performance ...... 37 8.1 Takeoff, Landing, Balanced Field Length Analysis ...... 37 8.2 Mission Profile ...... 39 9. Weights and Structures ...... 40 9.1 Final Weight ...... 40 9.2 Center of Gravity ...... 43 9.3 Materials ...... 44 9.4 V n Diagram ...... 47 9.5 Structural Analysis ...... 48
vi 10. Stability and Control ...... 56 10.1 Longitudinal Stability Analysis ...... 56 10.1.1 JKayVLM Analysis ...... 57 10.1.2 Tornado Analysis ...... 58 10.2 Control Types ...... 60 10.3 Cruise Trim ...... 60 11. Systems ...... 61 11.1 Cabin Layout ...... 61 11.2 In flight Systems ...... 62 11.3 Cockpit Systems ...... 66 11.4 Ground systems ...... 67 11.5 New Advanced Systems ...... 68 11.5.1 NextGen ...... 68 11.5.2 Lidar/Optical sensing Interface ...... 69 11.5.3 GPS Landing...... 69 12. Cost Estimation ...... 70 12.1 Cost of Research, Development, Testing and Evaluation ...... 71 12.2 Cost of Manufacturing – Lifetime and Unit Cost ...... 72 12.3 Direct Operating Cost ...... 74 13. Concluding Remarks ...... 79 12. References ...... 81
vii Index of Figures
Figure 4.1 Blended Wing Body Concept ...... 14 Figure 4.2 Hybrid Blended Conventional ...... 15 Figure 4.3 Strut Braced Wing Concept ...... 16 Figure 5.2.1 T/W vs. W/S ...... 21 Figure 6.1.1 Cruise Drag Polar ...... 23 Figure 6.3.1 C l vs. Sweep Angle for various values of (t/c) and M dd ...... 25 Figure 6.3.2 Main Wing Airfoil Sections ...... 27 Figure 6.4.1 Limits of laminar flow control technologies ...... 29 Figure 6.4.2 Boeing 737 Root Airfoil Boundary Layer ...... 30 Figure 6.4.3 Boeing 737 Midspan Airfoil Boundary Layer...... 31 Figure 6.4.4 NASA SC(2) 0710 Airfoil Boundary Layer ...... 31 Figure 7.3.1 Airfoil Fuel Tank and C.G. Location ...... 36 Figure 7.3.2 Wing Fuel Tank and C.G. Location ...... 36 Figure 7.4.1 Nacelle panels open for maintenance and engine removal ...... 37 Figure 8.2.1 Mission Profile ...... 39 Figure 9.1.1 Component Weight Comparison ...... 42 Figure 9.2.1 Weight C.G. Excursion Diagram ...... 44 Figure 9.3.1 Aircraft Materials’ Cost per Pound ...... 45 Figure 9.3.2 Aircraft Materials’ Relative Density ...... 45 Figure 9.3.3 Aircraft Materials’ Relative Yield Stress ...... 46 Figure 9.3.4 Materials Used In EN 1 Body ...... 47 Figure 9.4.1 V n Diagram for maneuver and gust ...... 48 Figure 9.5.1 Layout of the wing, strut, jury strut, and vertical offset ...... 49 Figure 9.5.2 Overall layout of the strut and wing design ...... 50 Figure 9.5.3 Distributed load with empty wing fuel tanks ...... 51 Figure 9.5.4 Distributed load with full wing fuel tanks ...... 51 Figure 9.5.5 Node placement and structural components ...... 53 Figure 9.5.6 Degrees of freedom for the strut braced wing ...... 53 Figure 9.5.7 Structural layout for the EN 1 ...... 55 Figure 10.1.1 Aircraft Layout ...... 59 Figure 10.2.1 Main wing ailerons, flaps and leading edge slats ...... 60 Figure 11.1.1 Cabin Layout ...... 62 Figure 11.3.1 Cockpit Systems Layout ...... 66
viii Index of Tables
Table 2.1 RFP General Requirements ...... 3 Table 3.3.1 Fuel Data ...... 9 Table 3.3.2 Necessary Boeing 737 800 Data ...... 9 Table 3.3.3 Fuel Sizing Calculation Results ...... 10 Table 3.4 Fuel Trade Study Results ...... 12 Table 4.4.1 Aircraft Decision Matrix ...... 17 Table 5.1.1 Constants from Boeing 737 800 analysis in Nicolai’s Program...... 18 Table 5.1.2 Variables for the different aircraft designs ...... 19 Table 5.1.3 Constants for Nicolai’s sizing program ...... 19 Table 5.1.4 Weights that are determined by using Nicolai’s Program ...... 20 Table 5.2.1 FAR Requirements ...... 21 Table 6.1.1 Cruise Component Drag ...... 22 Table 7.1.1 Pratt and Whitney PW1000G specifications ...... 32 Table 7.1.2 General Electric 1854 specifications ...... 33 GENX Table 7.1.3 Rolls Royce Trent 1000 specifications ...... 34 Table 7.1.4 CFM Leap X specifications ...... 34 Table 8.1.1 Takeoff, Landing, and Balanced Field Length Results ...... 38 Table 8.2.1 Mission Segment Analysis...... 40 Table 9.1.1 Weight Statement ...... 43 Table 9.5.1 Cantilever and strut braced wing comparison ...... 56 Table 10.1.1 Numeric input parameters for the JkayVLM.exe program ...... 57 Table 10.1.2 Output from JkayVLM.exe ...... 57 Table 10.1.3 Stability Derivatives from Tornado Analysis ...... 59 Table 11.2.1a List of the systems on board for the Strut Braced Aircraft ...... 63 Table 11.2.1b List of the systems on board for the Strut Braced Aircraft ...... 64 Table 11.2.1c List of the systems on board for the Strut Braced Aircraft ...... 65 Table 12.1.1 Cost of Research, Development, Testing and Evaluation ...... 72 Table 12.2.1 Total manufacturing cost of the strut braced airplane design ...... 73 Table 12.3.1 Direct Operating Cost of Flight ...... 75 Table 12.3.2 Direct Operating Cost of Maintenance ...... 76 Table 12.3.3 Direct Operating Cost of Depreciation per Nautical Mile ...... 77 Table 12.3.4 Direct Operating Cost of Landing Fees and Registry Taxes ...... 77 Table 12.3.5 Direct Operating Cost of Financing the Airplane ...... 78 Table 12.3.6 Total Direct Operating Cost ...... 78 Table 13.1 RFP Compliance Summary ...... 80
ix Nomenclature
AR Aspect Ratio b Wing Span Cfe Skin Friction Coefficient CD0 Zero Lift Drag Coefficient CLα Lift Coefficient Slope CLmax Max Lift Coefficient CLTO Take Off Lift Coefficient d Fuselage Diameter e Oswald Efficiency Factor g Acceleration Due to Gravity G Climb Gradient Lift to Drag Ratio Q Dynamic Pressure QR Specific Energy Sexposed Exposed Surface Area Sref Wing Reference Area Swetted Wetted Surface Area Thrust to Weight Ratio Vstall Stall Speed VTO Takeoff Speed W1 Takeoff Weight W2 Landing Weight Wing Loading η0 Overall Efficiency Λ Sweep Angle to Max Thickness ρ Density σ Density Ratio
x 1. Introduction
In 2006, Boeing stated their belief that there will be a higher annual increase in passenger air travel – roughly 5% per year – compared to the annual increases in fuel efficiency, making the claim that more fuel would be needed regardless of efficiency advances [1]. Two years later, commercial transport and shipping flights in the United States surpassed 18 billion gallons of jet fuel used annually by airlines. This equates to almost 450 million barrels of crude oil at roughly
100 dollars each, or 45 trillion dollars [2]. The problems of fuel efficiency, production and pollution are more applicable than ever in today’s world. These issues must be resolved in order to maintain the future growth of the world economy.
Along with a demand for alternative fuel capabilities in aircraft, there are requirements stipulating that future aircraft have increased range, higher lift to drag ratio, and an emphasis on sustainability with a rate of fuel consumption equivalent or less than what is seen in the present industry. With these demands, there is a requirement for a new development and implementation of a lighter, more fuel efficient, practical aircraft. The need for a revolution within the airline industry regarding how it impacts society as a whole must be addressed with a cost efficient, environmentally friendly aircraft.
2. Request for Proposal
The Request for Proposal (RFP) of the American Institute of Aeronautics and
Astronautics (AIAA) calls for the design of a commercial aircraft for service in the year 2020.
This design is considered to be a replacement for the Boeing 737NG and Airbus A320 aircraft.
Improvements will be focused on integrating new technologies and alternative fuels in agreement with the National Aeronautics Research and Development Challenges, Goals and Objective [3].
1 This request for design is taking momentum from the need for alternative fuels to create environmentally friendly aircraft. The current methods of replacing petroleum based fuels through direct addition of alternative fuels gives rise to the need for advanced technologies to improve energy efficiencies. Specifications of the alternative fuels will be studied through environmental emissions, noise, and carbon footprint from the aircraft design [3]. The future cost of incorporating these fuels is also a factor that is to be coupled for ensuing ground and service support systems and airport infrastructure [3].
Requested enhancements of design from the RFP state that the aircraft will have a 25% increase in the lift to drag ratio from current aircraft being replaced. Airfoil technology will incorporate laminar flow techniques for improved transition delays on swept wings. Also desired are improved weight fractions and engine efficiency [3]. The structure is expected to be similar to the light weight composites and materials utilized in the Boeing 787 aircraft with specifications taken from manufacturer projections [3]. The general requirements, as stated by the RFP, are presented in Table 2.1.
The engines given for reference in the RFP include CFM International’s CFM56 5 or
Pratt and Whitney’s PW6122A. Engine selection will be based upon improvements projected
from engine manufacturers in accordance with the targeted alternative fuel from biofuels.
The intention of the AIAA’s RFP is geared toward improving aircraft and engine
efficiency for the future use of alternative fuels. Projections are to reduce aviation environmental
impacts of emissions, noise, and fuel burn [3]. The design will be subject to comparison with
current technologies of aircraft such as the Boeing 737NG and Airbus A320 families.
2 Table 2.1 RFP General Requirements [3]
Design Factor Requirement Safety and Airworthiness Regulations FAR 25 Crew 2 Passengers 175 (1 Class) Seating Pitch 32”, Width 17.2” Width > 12.5 ft Cabin Dimensions Height > 7.25 ft Cargo Volume 1,240 ft 3 Takeoff Distance 8,200 ft Landing Speed < 140 KCAS Maximum zero fuel weight plus fuel Maximum Landing Weight reserves for maximum range Cruise: Mach 0.8 Operating Speed Maximum: Mach 0.83/340 KCAS Initial: 35,000 ft Cruise Altitude Maximum: 41,000ft Nominal: 1,200 nm Range Maximum: 3,500 nm Payload Capability 37,000 lb
3. Fuels
3.1 Fuel Descriptions
A critical aspect of the RFP is the requirement that alternative fuels are used for the design of the aircraft. These alternative fuels should be more environmentally friendly than standard Jet A 1. The alternative fuel used must be able to perform efficiently in all flight conditions the aircraft will encounter. When choosing a fuel, the type of fuel and the fuel source must be considered.
Fuel Types
There are a wide range of fuel types to consider. The primary focus of alternative fuel studies for the near term typically centers on biofuels. This report will discuss the advantages and
3 disadvantages of traditional Jet A 1, Fischer Tropsch synthetic fuel, liquid hydrogen, liquid methane, methanol, ethanol, butanol, biodiesel, and synthetic paraffinic kerosene.
Jet A-1
Jet A 1 is the current standard for aviation fuel. Any proposed replacements have to come close to meeting the standards that Jet A 1 has set. Jet A 1 has a relatively high energy density and a low freezing point suitable for the cold temperatures encountered at high altitudes. Current engines are designed to use Jet A 1 and thus current and future engines may need to be redesigned for an alternative fuel. Current Jet A 1 has a major disadvantage in the current aviation industry in that it is a fossil fuel. The fuel is derived from crude oil and is thus highly polluting, particularly in regard to carbon dioxide emissions. In the current industry climate, environmental concerns have taken a larger role in design decisions and have hastened the search for an alternative [4].
Fischer-Tropsch Synthetic Fuel
Fischer Tropsch (F T) synthetic fuel is based on the concept of the Fischer Tropsch process to convert a synthetic gas into liquid hydrocarbons. The fuel produced can have similar properties to Jet A 1, and research has shown that the energy density of the fuel is slightly higher than Jet A 1. F T synfuel is considered a drop in fuel because it can either be blended with Jet A
1 or used on its own with little to no adverse effects on fuel and engine performance. This has made it a leading contender for a short term replacement for Jet A 1. However, the fuel is considerably more environmentally destructive since it is still a fossil fuel derived from coal.
While emissions directly from the aircraft engine are slightly lower than Jet A 1, the process used to create the fuel is more polluting than the process to create Jet A 1, resulting in a net
4 increase in released greenhouse gas emissions of 147%. The price to produce F T synfuel is comparable to current crude oil prices between $80 and $100 per barrel. [8][30]
Liquid Hydrogen
Liquid hydrogen is one of the main contenders for long term aviation fuel solutions. The fuel has a pollution value of nearly zero, and has a large specific energy, but the energy density is the lowest of all the alternative fuels. This means that hydrogen fuel will have a lower mass than any other fuel but require the largest volume to contain it. Liquid hydrogen needs to be cryogenically stored, meaning the tanks need more insulation, which increases the weight and volume. The fuel would also require a completely redesigned infrastructure to accommodate the fuel [4].
Liquid Methane
Liquid methane has many of the same advantages and disadvantages as liquid hydrogen.
In addition, liquid methane, while plentiful around the world in ice deposits on the ocean floor, is difficult and dangerous to acquire and transport [4].
Methanol
Methanol is an alcohol fuel meaning it is mildly corrosive to the current infrastructure used to store aviation fuel. It is, however, a partial drop in fuel because it can be blended with aviation fuel and only requires small modifications to the engine. Methanol has a low specific energy and low energy density compared to other alternatives, which makes it less desirable as a fuel.
5 Ethanol
Ethanol is another alcohol based fuel. It is a popular alternative fuel suggestion in many fields, particularly within the automotive industry. The increased interest in production for other industries would decrease the time it would take for economic viability. In addition, ethanol has been researched extensively as a fuel. While most of these studies are done for automobiles, some of the results are still applicable to aviation propulsion systems. It has less of an environmental impact when burned compared to most fossil fuels, particularly if it is biologically derived. It is also suited for blending with some other fuels to improve performance and minimize problems with the fuel properties. This is useful as a stop gap until a fuel ultimately replaces traditional Jet A 1 [9]. Ethanol has a moderately low specific energy and energy density resulting in a large increase in the fuel’s mass and volume required. Ethanol on its own also has problems with its clouding point. The fuel will start to gel well before the minimum operating temperature standard set by Jet A 1. For ethanol to be a viable alternative, it must be further developed to overcome these problems [4].
Butanol
The third alcohol based fuel is n butanol, referred to as butanol throughout this report.
Butanol’s corrosiveness is significantly less than ethanol, making it the most attractive of the alcohol fuels for storage and transport. The process to create butanol is similar to ethanol, which is attractive as the processes for ethanol production are well documented and widely used. Like ethanol, it can be blended with many other fuels to increase efficiency and help mitigate problems with fuel properties. Butanol’s specific energy and energy density values are typically much higher than ethanol and come close to the values for biodiesel. In addition, as a stand alone fuel it does not have as many issues with freezing and clouding that ethanol and biodiesel have.
6 It also resists contamination by water better than other alcohol based fuels. As an aviation fuel, butanol has potential if it is researched further [10].
Biodiesel
Biodiesel is one of the most favored alternative aviation fuels because of its properties. It has high specific energy and energy density values. Aviation fuels can be mixed with biodiesel, or biodiesel can be used by itself, without a significant performance penalty. The fuel is not corrosive to engine parts like some alcohol based fuels. Biodiesel has a number of disadvantages, however. The foremost is its current inability to withstand the temperatures encountered at high altitudes without clouding or freezing. Blending with Jet A 1 can reduce or eliminate this problem, but this is not a long term solution for a Jet A 1 replacement. It also has a high flash point compared to Jet A 1, which means it is harder to ignite the fuel [9][11].
Synthetic Paraffinic Kerosene
Synthetic paraffinic kerosene (SPK) is a newly developed fuel alternative that can be produced from biological sources. The production process uses the Fischer Tropsch method as discussed earlier, but avoids the pollution caused by coal. This fuel is chemically the same as Jet
A 1 and is not corrosive, preventing the need to change the current infrastructure. Also, the specific energy and energy density are comparable to Jet A 1. SPK has passed all initial certification tests that Jet A 1 must undergo. SPK has been in several 50% by volume flight tests with Jet A 1, and there was no significant change in engine performance. Currently, SPK is capable of using many different biomass sources, allowing the use of the best source available.
More research is necessary to develop a commercial production facility, but BioJet Corporation has recently been under agreement with a major distributor to sell 4 million barrels over the course of 2 years [25].
7 3.2 Biological Fuel Sources
The benefit of using biological fuel sources to reduce the environmental impact of an airliner centers around the consumption of greenhouse gases during the growth of the biomass.
Greenhouse gases are still released during operation, but the consumption of the same gases during growth results in an essentially carbon neutral process. These fuel sources can generally be broken down into three groups for biofuels: first generation, second generation, and third generation biofuels. First generation biofuels are typically made from feedstock such as corn, soybeans and the seeds and grains of wheat. They are widely criticized for diverting world food supplies, particularly in poor areas of the world. These sources also have a low amount of energy produced per acre of land. Soybeans can produce about 60 gallons of biofuel per acre of land.
Second generation biofuels are produced from non food biomass, such as waste biomass from crops and cellulose. However, like first generation fuels, the land required to grow the biomass is high for the amount of fuel produced [11]. Third generation fuel sources require less land to produce the same amount of fuel compared to the first two generations. Currently, algae derived
fuel is the only source to be placed in this category. Predictions suggest that algae could produce
150 to 300 times the fuel that an equivalently sized crop of soybeans could produce in the same
timeframe. Algae can be grown on land not suitable for most other crops, so it can avoid using
land that would be used for producing food or other essential products. In addition, algae are
capable of producing a wide variety of different fuels. These advantages have made it a leading
contender for a future alternative fuel source [4].
3.3 Sizing Requirements
An important consideration in meeting the RFP is the use of biofuels and how they affect the sizing requirements for an aircraft. Using 8 common biofuels and Jet A 1, it was possible to
8 determine the requirements for an aircraft meeting the RFP through the use of the Breguet range equation and knowledge of a Boeing 737 800’s capabilities. Table 3.1 provides information on each fuel studied. The Breguet range equation is