Aircraft Design Proposal 2016

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  1. Ember Aviation Presents the LAT-1 In response to the 2015 – 2016 AIAA Foundation Undergraduate Team Aircraft Design Competition Presented by California Polytechnic…
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  • 1. Ember Aviation Presents the LAT-1 In response to the 2015 – 2016 AIAA Foundation Undergraduate Team Aircraft Design Competition Presented by California Polytechnic State University, Pomona Aerospace Engineering Department Aircraft Design 2015 – 2016
  • 2. i Ember Aviation Team Team AIAA Member Numbers Arutyunyan, Sipanah Aerodynamics 688353 Benitez, Omar Team Deputy, Systems 688415 Davila, Francisco Structures 688424
  • 3. ii Ghadimian, Ani Controls 481732 Hunt, Kelly Aerodynamics 688649 Kieu, Tai Chi Team Lead, Structures 605712 Kuhl, Ethan Propulsion 688654 Sanchez, Victor Systems Engineering 688422 Yin, Teddy Controls 665617 Dr. Don Edberg Design Advisor 022972-00
  • 4. iii Executive Summary In response to the 2015-2016 American Institute of Aeronautics and Astronautics (AIAA) Graduate Team Aircraft Design Competition Request for Proposal, Ember Aviation would like to present the LAT-1. The Ember Aviation team which consists of Aerospace Engineering undergraduate students currently attending California Polytechnic State University, Pomona received the RFP on September 2015. The RFP states that Researchers at NASA have predicted an increase in wildfires during the next 50-100 years due to the increase in global temperatures. In result, the need for a purpose built aircraft to fight wildfires is more apparent. The RFP requested a design of a Large Air Tanker with an Entry into Service date of 2022 with a lifetime of no less than 20 years. This purposely built Large Air Tanker will replace current retrofitted aircraft that are in service today. According to the RFP, one of the mission that this design should perform is that the aircraft shall be able to carry a payload of 5,000 gallons of water or retardant that is equivalent to a max weight of 45,000 lbs. to perform 3 drops per sortie (assumed 4 sorties per the RFP) on a 200 nm radius from base. Another mission the design shall be able to perform is to perform a Ferry Range of 2,500 nm. During the drop mission, the LAT-1 will cruise when flying to the fire site, and it will drop the retardant below 300 ft. above ground level at a speed less than 150 knots to have retardant shear minimized and accuracy increased. The bases at which the aircraft will be taking off and landing have a Balanced Field Length of 5,000 ft. with an assumption of +35F standard atmosphere at an altitude of 5,000 ft. above mean sea-level. The aircraft shall minimize total ownership cost and shall be equipped with sensors, cameras, communication equipment, etc., all to provide a forward observer function for other firefighting aircraft in the area. The LAT-1 aircraft design submitted by Ember Aviation, features a retardant tank fuselage shape with two engines mounted on top of the wings.
  • 5. iv
  • 6. v Table of Contents Team AIAA Member Numbers i Executive Summary iii List of Figures vii List of Table xi List of Acronyms xii 1. Requirement Overview 1 2. Configuration Overview 2 2.1 Configuration Concept 2 2.2 Twin Boom Tail 2 3. Material Selection 4 4. Mission Analysis 6 5. Design Approach 9 5.1 Initial Sizing 9 5.2 Iteration and Refinement 11 6. Wing Selection 14 6.1 Wing Plantform 14 6.2 Airfoil Selection 16 7. Aerodynamic Analysis 18 7.1 Aerodynamic Lift 18 7.1.1 Low Speed Lift Curves 18 7.1.2 Spanwise Lift Distribution 20 7.2 Drag Build-Up 21 7.2.1 Parasite Drag 21 7.2.2 Compressibility Drag 23 7.2.3 Induced Drag 24 7.2.4 Drag Polar 25 7.2.5 Lift to Drag Ratios 26
  • 7. vi 8. Stability & Control 27 8.1 Horizontal Tail Sizing (Notch Chart) 27 8.2 Vertical Tail Sizing (Minimum Control Speed) 30 8.3 Tail Configuration 32 9. Aircraft Engine 33 9.1 Engine Selection 33 9.2 Engine Mapping 34 9.3 Engine Placement 35 10. Performance Analysis 37 10.1 Payload-Range Calculation 37 10.2 Takeoff, Landing, and Balanced Field Lengths 39 10.3 Operational Envelope 42 11. Weight Breakdown 44 11.1 CG Travel 46 12. Structural Analysis 48 12.1 Wing Structure 49 12.2 Fuselage Analysis 54 13. Landing Gear 55 13.1 Landing Gear Placement 55 13.2 Oleo Strut Sizing & Tire Selection 57 13.3 Landing Gear Analysis 59 14. Fuselage Layout 60 14.1 Interior Fuselage Layout 60 14.2 Built-In Retardant Tank 61 14.3 Fuel 61 15. Maintenance 63 15.1 Airframe Maintenance 63 15.2 Engine Maintenance 63
  • 8. vii 15.3 Retardant Tank Maintenance 64 16. Subsystems 66 16.1 Water/Retardant Filling Methods 66 16.2 Auxiliary Power Unit 67 16.3 Supplemental Oxygen 68 16.4 Situational Awareness 69 17. Cost Analysis 70 17.1 Research, Test, Development and Evaluation Cost 70 17.2 Flyaway Cost 71 17.3 Direct Operating Cost 72 18. Manufacturing Concepts 74 19. Acoustics & Environment 75 20. Program Lifecycle 76 21. Compliance Matrix 78 22. Conclusion 79 References 80
  • 9. viii List of Figures Figure 3-1: A preliminary of materials for the LAT-1 structure was determined 4 Figure 4-1: Mission Profile 1 of the LAT-1 will perform 1 sortie and 3 retardant drops 6 Figure 4-2: Mission Profile 2 of the LAT-1 will not drop payload and return to base 7 Figure 4-3: Mission Profile 3 of the LAT-1 will perform a 2,500 nm ferry range empty 8 Figure 5.1-1: Constraint Diagram 10 Figure 5.2-1: Carpet Plot showing Balanced Field Length Data 12 Figure 5.2-2: Carpet Plot showing Maximum Takeoff Weight 13 Figure 6.1-1: Semi span planform of the wing (all dimensions are in feet) 15 Figure 6.2-1: Drag Polars for the NACA 632-415 and NACA 63-209 airfoils from Abbott and Von Doenhoff’s Theory of Wing Sections 17 Figure 7.1.1-1: Low speed lift curves at landing, takeoff, and clean conditions 19 Figure 7.1.2-1: Normalized section lift coefficient across the semi span of the wing 20 Figure 7.2.1-1: Parasite drag build-up at cruise speed 22 Figure 7.2.4-1: Drag polar curves for various flap extension configurations 25 Figure 7.2.5-1: CL vs L/D at Mach numbers of 0.2, 0.3 and 0.382 26 Figure 8.1-1: Notch Chart 28 Figure 8.1-2: Horizontal tail planform 29 Figure 8.2-1: Vertical tail planform 32
  • 10. ix Figure 9.2-1: CF34-8E thrust mapping 35 Figure 10.1-1: Payload range curve 38 Figure 10.2-1: Balanced Field Length, CF34-8E 41 Figure 10.2-2: Balanced Field Length, CF34-10A 41 Figure 10.2-3: Balanced Field Length, CF34-10E 42 Figure 10.3-1: Operational enveloped of the LAT-1 43 Figure 11-1: Percentage weight breakdown comparison between different methods 45 Figure 11-2: Detail weight percentage breakdown 46 Figure 11.1-1: The CG shown when the aircraft is loaded with full fuel and full payload 46 Figure 11.1-2: Balance Diagram 47 Figure 12-1: Combined V-n Diagram of LAT-1 48 Figure 12.1-1: Spanwise Shear Loading of LAT-1 wing 49 Figure 12.1-2: Spanwise bending moment in x direction of LAT-1 wing 50 Figure 12.1-3: Spars Mass Calculation 51 Figure 12.1-4: Front spar and rear spar dimension 52 Figure 12.1-5 Spars with lightening holes 53 Figures 12.1-6: The internal wing structure includes front spar, rear spar and ribs 53 Figure 12.2-1: Structural layout of fuselage LAT-1 54
  • 11. x Figure 13.1-1: The angle between the AFT CG and the LG location is 15° 55 Figure 13.1-2: The tip-back angle was found to be 16° 56 Figure 13.1-3: Over-turn calculations 57 Figure 13.2-1: Chosen tires with its diameter 58 Figure 13.2-2: Front view and side view of oleo struts 59 Figure 13.3-1: Finite Element Analysis of the landing gear 59 Figure 14.1-1: Interior cabin layout 60 Figure 14.2-1: Retardant tank 61 Figure 14.3-1: Fuel tanks located on the top of the fuselage 62 Figure 16.1-1: Rakord TODO-Matic® 119mm Dry-Brake® Fitting 67 Figure 16.2-2: UTC APS-500R APU Dimensions 68 Figure 17.1-1: RTD&E cost breakdown 71 Figure 17.2-1: Production breakeven point using Nicolai & Carichner’s method 72 Figure 17.2-2: Production breakeven point using Raymer’s method 72 Figure 17.3-1: Operational cost breakdown 73 Figure 20-1: LAT-1 Program Lifecycle 76
  • 12. xi List of Tables Table 5.2-1: Results from the 12 Iterations 11 Table 6.1-1: Important wing parameters and dimensions 15 Table 6.2-1: Airfoil characteristics of top preforming airfoils in Cl max, Cl0, Cd0, and Cd (ClMax). With Re = 9 million 16 Table 7.1.1-1: CLmax at various configurations 20 Table 7.2.1-1 Parasite drag build-up at cruise speed 23 Table 8.1-1: Important tail parameters and dimensions 29 Table 8.2-1: Important vertical tail parameters and dimensions 31 Table 9.1-1: Turbofan engine specifications 33 Table 10.1-1: Payload, Fuel, and Range Calculated 38 Table 10.2-1: Balanced Field Lengths for possible combinations 40 Table 11-1: Dry weight breakdown of the LAT-1 45 Table 12.1-1: Material Selection 52
  • 13. xii List of Acronyms AIAA: American Institute of Aeronautics and Astronautics CG: center of gravity BFL: balanced field length D.O.C: direct operating cost ECS: environmental control system EIS: entry into service FEA: finite element analysis MAC: mean aerodynamic chord MTOW: max takeoff weight ROC: rate of climb SFC: specific fuel consumption SSL: standard sea level VS1: 1 g stall speed VSneg: negative stall speed VA: design maneuvering speed VB: design max gust intensity speed VC: design cruising speed VD: design diving speed
  • 14. 1 1. Requirement Overview The LAT-1 will enter into service in the year 2022 with a lifetime of no less than 20 years. Perhaps the most important requirement by the RFP from AIAA is the ability of carrying a payload of 45,000 lbs. for an operational radius of 200 nm. The aircraft shall be able to have a crew of 2 pilots. The ground support equipment shall have the capability of reloading retardant in less than 10 minutes. It shall be equipped with sensors, communication systems, etc., all to provide communication with any firefighting aircraft nearby. When performing the drops, the LAT-1 will drop the retardant below 300 ft. above ground level at a speed less than 150 knots but no less than 90 knots because of a stall speed requirement. When the aircraft drops and is now empty, it shall dash back to base at a speed greater than 300 knots. It is asked to look into both a turboprop and turbofan engines with the preference of choosing an off-the-shelf engine. There is a ferry range requirement of 2,500 nm to provide the aircraft to any state within the United States that is experiencing a wildfire. The balanced field length is 5,000 ft. with an assumption of +35F standard atmosphere at an altitude of 5,000 ft. above mean sea-level. It shall minimize total ownership cost with justification of the acquisition of the greater capability instead of having a retrofitted aircraft. Finally, the aircraft shall be FAA approved with certification of transfer aircraft (Part 25) with an emphasis on fatigue.
  • 15. 2 2. Configuration Overview 2.1 Configuration Concept The key driving concept for our aircraft, was a mindset we called, Size Zero. The idea behind this was to eliminate any and all wasted space within the aircraft. The goal for our team was to utilize every inch within the aircraft, hence the size zero name for this design concept, in which there was zero wasted space within the airframe. One obvious downfall with all of the current retrofit aircraft currently in operation as firefighting aircraft, is that the payload tanks and drop mechanisms are often attached underneath the fuselage of the aircraft, or occupy very little space within the aircraft. This leads to excess wasted space, wasted space that the aircraft operators are paying for on every flight. By keeping wasted space within the aircraft to minimum, we can prevent excess structural weight and wetted area on the aircraft. Our team stayed focused on making sure that every component installed on the aircraft, earned its way on to the aircraft structure. This size zero mindset heavily influenced the manner in which the payload tank and cockpit were integrated into the aircraft. The aft section of the fuselage is nothing more than the payload tank itself, hung from the primary wing spars. The cockpit, similarly, is attached onto the front of the payload tank with no wasted surface area on the aircraft. 2.2 Twin Boom Tail Given our effort to eliminate wasted space, more specifically the aft fuselage that must be in place to support the vertical and horizontal tails, a different kind of tail must be designed. In the case of our aircraft, a twin-boom tail was deemed to be an ideal solution to this problem. A twin
  • 16. 3 boom tail not only allows for the elevator to place up high in free-stream clean air, thus increasing the efficiency of the horizontal stabilizer, but also allows for a smaller overall vertical tail area, given that there are two vertical surfaces, as opposed to a single tail surface. Given the heavy payload, the larger the elevator, generally the better the aircraft takeoff performance is. By utilizing this twin-boom design, a significantly larger horizontal stabilizer can be design, without creating a difficult structures problem for supporting a tail that large and heavy on a conventional “cigar tube” aircraft. Our aircraft also is unlikely to be ever be reconfigured for any duty, other than that of a fire fighting, thus eliminating the necessity for reconfigurable aft fuselage space.
  • 17. 4 3. Material Selection One of the main requirements mentioned in the RFP is special attention to FFA certification for transport aircraft (Part 25) fatigue. Failure by fatigue is perhaps the biggest concern for structural failure for aircraft components, and it occurs when exposed to frequent applied load. These critical areas can be found on different structural paths and they should be carefully monitored to prevent cracks from stress concentration. Structural Health Monitoring (SHM) is considered one of the most reliable technologies that can be used for early detection of the cracks. Figure 3-1: A preliminary of materials for the LAT-1 structure was determined Therefore, to begin the material selection process, different aircraft materials were examined. DC-10 which is an operating air-tanker, capable of carrying 12,000 gallon of retardant, uses aluminum 2024-T3. This material is widely used in aerospace application due to its excellent fatigue strength, fracture toughness and notch sensitivity. Some of the properties of Aluminum 2024-T3 include fatigue strength of 140 MPa, fracture toughness of 25 MPa-m1/2 , tensile strength of 483 MPa, and high tensile yield strength of 345 MPa. This material will be used in the areas
  • 18. 5 with the highest tension such as the lower wing skin, and pressure critical fuselage skins where fatigue is an important driver. There is a study done on aluminum alloy 2024-T3 for airbus A320 slat-track. The result shows that using SHM technology and electrical conductivity due to the crack growth, the fatigue failure can be easily monitored.
  • 19. 6 4. Mission Analysis The RFA requested that the Large Air Taker being designed shall be able to carry 5,000 gallons of water or retardant (retardant weighing 9 pounds per gallon). This makes the payload weight come out to be a total of 45,000 lbs. When attacking a wildfire, the aircraft will be taking off from an altitude of 5,000 ft. and shall be able to perform 4 sorties on a 200 nm radius (from base) per sortie with the capability of performing 3 retardant or water drops during each sortie while it is establishing the best fire line to prevent the fire from expanding. In addition to this mission, the RFA also required that the aircraft shall be able to perform a ferry range of 2,500 nm in order to lend the aircraft to any state in the United States if that states was experiencing a wildfire. The mission profiles of this Large Air Tanker can be seen in Figure 4-1, Figure 4-2, and Figure 4-3. Also, the fuel burned during this mission is listed in Table 5-1 below. Figure 4-1: Mission Profile 1 of the LAT-1 will perform 1 sortie and 3 retardant drops In Mission Profile 1, the aircraft will fly out to the fire site on a 200 nm radius from the airport it is taking off from. It is estimated that the aircraft will climb 10,000 ft., cruise at a speed of 250 kts for 200 nm to the fire site, descend and perform 3 drops of retardant and all 3 drops
  • 20. 7 must be dropped below 300 ft. above ground level and a speed lower than 150 knots for accuracy. After the drops have been performed, the aircraft will climb 10,000 ft. and dash with a speed greater than 300 kts back to base for a reload of retardant that will be performed in 4 minutes while the engines are idling. Once the aircraft is reloaded with retardant, it will takeoff once again to the fire site. It is assumed from the RFP that 4 sorties can establish a fire line to prevent the fire from expanding. Figure 4-2: Mission Profile 2 of the LAT-1 will not drop payload and return to base In Mission Profile 2, the aircraft will takeoff from base just like in Mission Profile 1 and cruise to the fire site on a 200 nm radius from which the aircraft takes off from. The only difference with this mission compared to the first mission is that there will be no retardant drop. The reason why there will be no retardant drop is that perhaps there was a malfunction with the hydraulic doors, or there was no need for dropping retardant anymore. If this scenario occurs, the aircraft will return to base with its full payload of 45,000 lbs. It is this scenario that resulted in our aircraft being the heaviest.
  • 21. 8 Figure 4-3: Mission Profile 3 of the LAT-1 will perform a 2,500 nm ferry range empty In Mission Profile 3, the aircraft will be performing its ferry range distance of 2,500 nm. The aircraft shall be able to be dispatched quickly anywhere to the continental United States if there is need of a fire fighting aircraft. During this mission, the aircraft will be flying empty (no retardant) because there is no need to fly the aircraft loaded; it will only result in unnecessary fuel burning, thus causing our aircraft to be even heavier. That being said, the aircraft will climb to 30,000 ft. for the turbofan engines to fly at their best efficiency. The aircraft will not be pressurized; however, we will have oxygen masks provided to the pilots in order for them to breathe oxygen with ease. Once the aircraft reaches its altitude, the ferry range mission of 2,500 nm will be performed as the aircraft cruises at 250 nm. Once the aircraft arrives to its destination, it will loiter before landing if necessary.
  • 22. 9 5. Design Approach In designing the LAT-1, much attention was paid to minimizing the cost. The ultimate objective was for the design to meet all of the requirements described in section 1.0 in the most cost effective way. It was well noted that greatly exceeding the requirements would likely drive up the cost. Therefore, careful and detailed analysis was done to ensure that the requirements are met without being greatly exceeded. In order to ensure that the requirements are being met, a constraint diagram was constructed to indicate the optimal thrust-to-weight and wing loading. In order to ensure that the requirements are not being greatly exceeded, a carpet plot was constructed illustrating the results of the design process from multiple iterations, which was used to determine the optimal wing aspect ratio and engine for the aircraft. 5.1 Initial Sizing The initial size of the aircraft was determined based on the performance requirements specified by the RFP. The dash speed, balanced field length, and stall speed requirements were all addressed in determining the optimal thrust-to-weight and wing loading of the aircraft. The constraint diagram, shown in Figure 5.1-1, was constructed with curves representing the boundaries of the possible desig
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