SAE Aero East 2017 Mid-Term Report

Transcription

1 Mid-Term Report MAE 435W Project Management Project Advisor: Dr. Drew Landman Team Members: Sarah Arms, Aaron Calkins, David Ewing, Andy Helmann, Stacey LeGrand Mark Michielsen, Jordan Roque, Tonya White HONOR PLEDGE I pledge to support the honor system of Old Dominion University. I will refrain from any form of academic dishonesty or deception, such as cheating or plagiarism. I am aware that as a member of the academic community, it is my responsibility to turn in all suspected violators of the honor system. I will report to Honor Council hearings if I am summoned. By attending Old Dominion University you have accepted the responsibility to abide by this code. This is an institutional policy, approved by the Board of Visitors. 1

2 Table of Contents Table of Contents List of Tables and Figures Abstract....4 Introduction Methods...6 Results Discussion Conclusion References

3 List of Tables and Figures Figure 1: Overview of 2017 Competition Aircraft Figure 2: Completed Empennage.7 Figure3; Fuselage Construction Jig Figure 4: Overview of Fuselage Construction Figure 5: Wing Joiner Detail Figure 6: Completed Wing Panels.12 Figure 7; Completed Winglet.13 Figure 8; Passenger Seating Layout...14 Figure 9; Proposed Landing Gear Design..16 Figure 10; Landing Gear Strut and Wheel.17 Figure 11; Test Aircraft on Final Approach Figure 12; Wing Joiner undergoing Testing Figure 13; Failed Wing Joiner Post Test...19 Figure 14; Fuselage Structural Test...20 Table 1: Passenger Seat Sizing & Stability

4 Abstract The SAE Aero East Design Competition is an international competition of remote-control airplanes with a specific purpose. This year the competitors planes are required to carry a payload of passengers as well as their luggage, represented by tennis balls and steel plates respectively, and perform basic flight maneuvers like takeoffs, landings, and turns. Some restrictions include the use of no more than 1000 watts for all power needs and that the aircraft must take off in 200 feet and land in 400. The specific design challenges for this team were to manufacture the airframe and conduct flight tests. Multiple construction methods for the fuselage frames were considered, and based on testing it was decided that cutting from plywood with the laser cutter affords the best combination of manufacturing efficiency and strength. The multiple piece wing joiners had to be designed then fabricated, and after several tests were conducted, a method was selected and the joiners were manufactured. Completing construction of the wings involved installing leading edge sheeting and multiple detail parts. The empennage was built, covered, and eventually installed on the fuselage. Fuselage construction was delayed due to the manufacturing of jigs which needed to be designed and milled. Fuselage construction has proceeded to an advanced stage, and is still delayed due to an incomplete CAD model of the airframe. The payload prediction has been reduced due to a desire to shift our weight budget towards fuselage structural strength due to a lack of facilities to test a full size fuselage prior to flight. 4

5 Introduction The SAE Aero Design Series competition is an international design competition intended to provide undergraduate and graduate students with a real-life engineering challenge. The SAE Series competition requires students to design, build, and fly a radio control plane which can generate revenue by carrying simulated passengers and their luggage. These passengers are represented in the plane by tennis balls and their luggage by steel plates in a cargo bay. Each team must also provide a written and oral presentation which are graded and contribute to the overall score. (SAE International, 2017) Many universities across the country and the world establish teams to represent them in the competition. ODU became involved in this international competition 3 years ago and has been competing every year since, finishing in sixth place in The chief challenges that the SAE Series intends to provide are a set of mission objectives which in order to achieve require research, problem-solving, and compromise from the competing teams as well as a quality of communication skills which are important to the engineering workplace. (SAE International, 2017) The competition provides valuable, real world experience in the design, manufacture, and test process of a deliverable, to a scheduled timetable. The goal for ODU s 2017 SAE Aero East team has been to finalize the design, build, and test the aircraft by mid-march in order to submit the final report the SAE and to be prepared to compete in April against the other teams. 5

6 Figure 1 Overall view of 2017 Competition Aircraft Methods After taking over from the previous team, the bulk of the work remaining was construction and flight testing. Designs had been established for nearly every portion of the aircraft, leaving only the landing gear, details of the fuselage, wing connections, and fuselage construction to be determined. The wing was designed to separate into three sections, for ease of transportation, and construction, but flight loads need to be transferred from the outer wing panels to the center section of the wing. A removable joiner assembly, which incorporated the dihedral angle for the outer wing panels was designed which would carry the loads without making the assembly process overly complex. The majority of construction remained to be completed for the wing including the D-tube sheeting with 1/32 balsa wood and the installation of other wing detail parts. Ailerons also were designed and 6

7 constructed. The empennage consists of a horizontal stabilizer and a single vertical stabilizer. The movable control surfaces are hinged to the trailing edges of these stabilizers. The construction is a balsa spar, with balsa ribs and a 1/32 sheeted balsa leading edge. The horizontal stabilizers are manufactured on a jig structure and then joined afterwards. The vertical stabilizer is constructed with two vertical members and spaced ribs, and then entirely sheeted in 1/32 balsa. The stabilizer is also constructed on a jig and sheeted afterwards. Figure 2. Completed Empennage The Control surfaces were constructed from balsa sheeting as well. Manufacturing was done without any jigs, instead spacing the frames by hand along a leading edge spar. Hardpoints were 7

8 created for mounting the servo control horns according to the positions of the servos inside the wing and empennage. Figure 3. Fuselage Construction Jig Figure 4. Overview of Fuselage Structure 8

9 The fuselage was constructed of vertical formers and longitudinal members. The fuselage was manufactured in a jig assembly. The jig assembly supported the lower keel assembly in the correct position, and contained side members to position the frames in the correct positions and ensure they remained perpendicular to the longitudinal plane of the aircraft during construction. The jig design was revised during construction to allow for the installation of aft fuselage truss members, which could not be installed in the original configuration due to interference with the side members. Research was conducted to determine the most efficient arrangement of passengers in the fuselage. The rules specify the minimum and maximum distance allowed between passengers.. Due to the tadpole shape of the fuselage, a simple grid arrangement is not possible as the width of the cargo bay changes according to the longitudinal position inside the craft. A truss design is being tested and evaluated for the passenger seating. Servo sizing was accomplished based upon the necessary hinge moment in units of ounce-inches. The Excel aircraft design spreadsheet provided by the previous class was utilized to obtain the hinge moments. Once the hinge moment was converted to ounce-inches, servo specifications were researched and servos were selected which matched the specifications. Aircraft Transportation was discussed as well. The team is constructing PVC carrying cages which will allow transportation of the aircraft components without damage. 9

10 Results The wing is constructed utilizing a main and aft spar constructed of Spruce wood for the center section and balsa for the outer sections, all with a balsa shear web. The ribs are constructed of balsa and are spaced on the spar at even intervals. The wing was built in three sections. The center section is constant chord with zero tape and incorporates spoilers. The center section also supports the luggage compartment as well as the landing gear. The center section will attach to the fuselage with three bolts and will be removable for transportation. The outer wing sections are tapered from root rib to tip and feature 2 degrees of dihedral. They are fitted with winglets to prevent high pressure air from spilling over, and ailerons for roll control. All the wing sections are covered with a commercially available heat shrink type plastic covering. 10

11 Figure 5 Wing Joiner Detail The wing outer sections are complete, the center wing section airfoil structure is complete, and the wing-fuselage attach structure and payload bay support structure are scheduled for completion the first week of March. Manufacture of the wing joiners are complete. Figure 6. Completed Wing Panels 11

12 Figure 7. Completed Winglet The horizontal stabilizer was designed with a backward sweep which required a slight, by-hand modification of the jigs manufactured for their assembly. Otherwise, assembly of the empennage was largely identical to that of the wing sections, except for the fact that the vertical stabilizer was fully sheeted with 1/32 balsa. One complication which required a change in the planned design was a flaw in the construction of the jigs. This necessitated the forming of two half-panels with load bearing, transverse spars which were scarfed together at the center. Servos along with their mounts were installed, the positions of which were determined largely by the proximity to solid structural members. The last step before covering the empennage was the soldering and wiring of the servos which was done in such a way as to minimize the necessary 12

13 length, and therefore weight, of the signal and power wires. After covering, the control surfaces were attached to their associated lifting bodies with tape hinges and then adjustable control linkages were added between the horns and servo arms of each. With the fuselage arrangement determined, prototype passenger seat platforms were built. These prototypes were simple ¼ balsa sheets with holes of varying diameter bored through them in which a tennis balls would be set. A simple test was performed to determine how stable these seats were without the addition of any mechanical restraint which consisted of tilting the passenger plate at an increasing angle and recording at what angle a tennis ball would roll out. Since the passenger plate serves a double purpose as a load bearing member, the passenger seats cannot perforate the material too densely without undermining its strength, so a balance between passenger stability and structural integrity is necessary. Hole Diameter (mm) Angle of Repose ( o ) Table 1. Passenger Seat Sizing and Stability Figure 8. Passenger seating layout (60 passengers) 13

14 The 2016 aircraft utilized a conventional tricycle landing gear, with a single axle mounted below the fuselage with bearing supported wheels outboard. The nose gear was a wire strut unit steerable for ground handling, and had a urethane roller blade wheel. This provided satisfactory service, but for the 2017 aircraft a gear arrangement that offered less drag was required. Several configurations were considered. Retractable gear was briefly considered, but was rejected as the benefits of drag reduction were outweighed by the increased weight and complexity of the system. A tricycle gear arrangement was also considered but offered no advantage over the 2016 design. A bicycle gear arrangement, with fore and aft main gear supporting equal shares of the aircraft weight was selected, as initial impressions were that it would offer a reduction in drag over the tricycle gear arrangement. This was proved by performing a drag force analysis of both systems, showing a reduction of nearly 2 Newtons of drag force with the bicycle gear arrangement. Initially, the design of the gear focused on designing the struts and suspension system. A trailing arm design manufactured out of Aluminum was designed. This gear utilized an elastomeric shock and dampening absorber. The gear was designed in inventor and a stress analysis was performed. The disadvantages identified were difficulty of manufacture, as the gear was composed of several parts, and concern that testing methods were not adequately identifying all the forces which the gear would experience during ground operations. 14

15 Figure 9. Proposed Landing Gear Design Additionally, the weight of the gear became a concern after some re-design resulted in larger members. A wire strut had been utilized on the nose gear of the 2016 aircraft, and a stress analysis was performed to determine if this strut would be adequate to support the greater anticipated weight of the 2017 aircraft. Based on the results it was decided to utilize the wire struts. The wire struts are commercially sourced and modified to meet requirements. Modifications include shortening and bending the lower legs of the struts, and re-locating the axle mounting fixtures. The front strut is shortened and welded to a metal plate, which in turn is mounted to the aircraft structure. The front strut is fixed, and aligned with the aircraft's longitudinal axis. The rear strut is similarly modified, and is mounted in bearings to the aircraft structure. This strut rotated with a servo through a 45 degree arc to allow for steering while 15

16 taxiing, and during takeoff and landing before the rudder becomes effective. Both struts utilize an identical, urethane roller blade wheel. Landing loads and taxing shocks are absorbed with a wire spring which is manufactured as part of the landing gear strut. Figure 10. Landing Gear Strut and Wheel The landing gear is mounted directly to the support structure of the luggage bay, which allows for the most direct transfer of loads to the ground. The wings are supported by outrigger struts, which remain fixed to the aircraft during flight. The struts bear no landing or support loads, and are sized and positioned to keep the fuselage upright during ground operations. Although near completion, some construction on the aircraft remains and must be completed before the bulk of testing may begin. An available test aircraft was used to flight test the bicycle style landing gear arrangement. This test aircraft utilized a forward gear assembly similar to the 16

17 type intended for the competition aircraft. Flight testing proved the soundness of the arrangement, with the caveat that the actual competition aircraft would be utilizing a slightly different geometry, and would be operating off of a paved runway instead of the grass runway used for testing. A structural analysis determined the thickness of the mounting plate and the toe dimensions of the welds required. Figure 11 Test Aircraft on Final Approach When the wing joiner was conceptualized, there was uncertainty as to whether it would be able to handle the expected dynamic flight loads. A static load test was done on a prototype wing joiner. The prototype was clamped to a table and had increased weight applied to it. The joiner did not fail once all of the available weights in the lab had been applied. Thus, a team member applied a significant amount of added weight by pressing down onto the wing joiner. From this 17

18 test, it was determined that the proposed joiner design was sufficient and would hold the aircraft together while subjected to the expected operating loads. Figure 12. Wing Joiner Undergoing Testing Figure 13. Failed Wing Joiner Post Test 18

19 The fuselage s structure is nearing completion as well. Although not all of the structural members have been added, such as the 1/32 balsa sheeting which will be applied to the underside of the fuselage, the passengers seats, or the wing interface, a brief manual assessment of structural integrity was performed by team members. Figure 14. Fuselage Structural Assessment 19

20 Discussion The goal of this project was to design and build an aircraft to enter into the 2017 SAE Aero East Design Series competition capable of carrying at least 50 passengers with their required luggage around the prescribed flight path. A secondary goal is to provide a jumping off point for successive ODU teams to continue performing in SAE competitions. There are several aspects of the plane that could be improved upon for a future iteration. A decision was made to prioritize structural strength over weight savings as this is an unproven construction method, and due to deadlines and scheduling it is not possible to construct and test a representative fuselage prior to flight testing. A decision was also made to simplify fuselage frame construction methods, this caused overall weight to rise but simplified manufacture of the fuselage frames, again this decision was based on time and deadline constraints. The carrying cages for the transport of the aircraft will be built in the coming weeks. These cages will protect the fragile plane structure when traveling to and from airfields for testing and competition. The trailer as well will require modifications to accept the stowages for the aircraft. Final design of the passenger seat plate is as yet unfinished due to an uncertainty as to exactly how many passengers the aircraft will be able to lift. The design will also depend on how much loading the passenger plate can sustain with the various hole diameters, testing which has not yet been performed. 20

21 Conclusion The aircraft is nearly complete at this point: The primary construction tasks which remain are structural interfaces between the empennage, and the wing and the fuselage. The various studies and experiments performed have enabled the team to keep the factor of safety to a minimum, eliminating unnecessary structure and weight. The complexity, weight, and drag of the landing gear system was greatly reduced once it was determined wire-strut outriggers could be used in place of wheels. The current design for the fuselage will serve for initial flight testing, but it is expected that there will be another iteration before the overall design is finalized. Once the construction is complete, test flights will begin in which it will be possible to determine the exact loading the aircraft can sustain. This and other information must be obtained for the technical report due to the SAE Series in order to participate in the competition. The information gathered for the technical report and the standing that this aircraft obtains during the competition will aid future teams in entering a plane with even better performance. 21

22 References [1] SAE Aero Design Competition East and West Rules, S. International, [2] E. V. Laitone, "Fixed-Pitch Propeller Selection for Light Airplanes," Journal of Aircraft, vol. 37, pp , 2000/05/ [3] M. Robert, "Electric Motor Modeling for Conceptual Aircraft Design," in 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, ed: American Institute of Aeronautics and Astronautics, [4] S. Gundmundsson, General Aviation Aircraft Design: Applied Methods and Procedures. Waltham, Ma: Butterworth-Heinemann, [5] B. Patrick, "Sizing the landing gear in the conceptual design phase," in 2000 World Aviation Conference, ed: American Institute of Aeronautics and Astronautics, [6] B. Tugay and T. Halit, "Structural Optimization of the Landing Gear of a Mini-UAV," in 12th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference, ed: American Institute of Aeronautics and Astronautics, [7] O. Michael, Z. Cale, and L. Michael, "Analytical/Experimental Comparison for Small Electric Unmanned Air Vehicle Propellers," in 26th AIAA Applied Aerodynamics Conference, ed: American Institute of Aeronautics and Astronautics, [8] U. A. A. Group. (2016, 3/04/2016). UIUC Airfoil Coordinates Database. Available: [9] D. J. Peery, Aircraft structures: Courier Corporation, [10] R. Hibbler, Mechanics of Materials, Eighth ed. Upper Saddle River, New Jersey: Prentice Hall, [11] J. Pritchard, "Overview of Landing Gear Dynamics," Journal of Aircraft, vol. 38, pp , 2001/01/ [12] J. A. Nairn, "Numerical simulations of transverse compression and densification in wood," Wood and fiber science, vol. 38, pp , [13] B. Toson, P. Viot, and J. J. Pesqué, "Finite element modeling of Balsa wood structures under severe loadings," Engineering Structures, vol. 70, pp ,