Make to Innovate Cardinal Flight Aerodynamics Team

Transcription

1 Make to Innovate Cardinal Flight Aerodynamics Team Group Members: Alexander Scott Benjamin Vanduyne Brandon Ganey Joseph Cairo Lyle Sorensen 1

2 Abstract The purpose for this milestone was to construct an accurate physics simulation model using RealFlight RC Simulator and explain the analysis involved. This model simulation allows Cardinal Flight to estimate the handling capabilities by creating an aircraft with similar physics to that of Arrow (Cardinal Flight s latest design). The Cooper-Harper rating scale was used in the analysis of the simulation. In addition to this evaluation, this simulation will be used to provide a few recommendations to improve the aircraft. Methodology RealFlight Simulator is a program created to allow pilots to practice flying Radio Controlled (RC) aircraft using a USB controller and a computer (Figure 1). The program allows for the selection of pre-made aircraft or the selection of user designed aircraft. With the option of user designed aircraft, pilots are able to practice flying a custom aircraft design prior to building it. RealFlight uses accurate physics of flight to create a simulation which creates a correct representation of flying the real RC aircraft. By accounting for wind, air density, and many other variables, RealFlight helps create a seamless transition from flying on the computer to flying in real life as seen in Figure 2. While RealFlight is not a perfect simulation, it is extremely close to flying a real RC aircraft. Figure 1. RealFlight 7.5 Interlink Elite Controller Edition 2

3 Figure 2. RealFlight 7.5 Simulation Example Generating a model in the RealFlight simulator requires the user to select from a list of base models, then the user may adjust geometry, physical characteristics, and equipment. The Calypso model (Figure 3) met requirements that made it possible to edit the model in Arrow s likeness; the model was capable of powered flight and had a two-phase dihedral, as it was goal was to minimize editing in general. Once a sufficient aircraft was selected, in this case the Calypso base model, dimensions were adjusted to match the planned Arrow model in its current form, which can be viewed in Table 1. Figure 3: Calypso Visual Representation Model (Left) and Calypso Physics Wireframe Model (Right) Table 1: General Arrow Aircraft Dimensions Chord Span Main Wing Horizontal Tail ¼ Vertical Tail Fuselage length 9 3 3

4 Figure 4 shows the progression of RealFlight s default model toward an aircraft that resembles Arrow. Figure 4 is the skeletonized physics frame of Arrow in comparison to Calypso s frame. Note the difference in size between the two, as well as difference in tail configuration and extended dihedral on Arrow. It is worth mentioning that RealFlight allows the user to input the airfoil of the tail sections and main wing, a NACA 0012 and Selig S7075 respectively, as well as a dihedral of 3 degrees. Figure 4: Original Calypso Physics Wireframe (Left) vs. Edited Arrow Physics Wireframe (Right) In addition to adjusting the geometry of the physics models, the weights and exact drive system equipment installed were selected. The total weight of the aircraft was selected to be 15lbs (estimated weight, per Mechanical Team design). Then the exact drive system was selected for the model. The exact battery configuration was selected: 6S12P Lithium-Ion battery pack. Next a custom motor was created to match the one purchased for the aircraft, Tiger Motor U The following parameters were chosen to model the motor: 170KV, 1.1A no load current,.089 Ohm resistance, and 42 Magnetic Poles. Next a folding Carbon Fiber propeller was selected with the dimensions of 28 diameter with 12 pitch. Discussion In order to evaluate Arrow, the team utilized the Cooper-Harper rating scale to access the handling characteristics of the aircraft. The rating scale is a set of criteria used by test pilots and engineers to evaluate an aircraft performing a specific maneuver. The rating scale ranges from 1 (indicating the best handling characteristics) to 10 (representing the lowest quality of handling characteristics). The grading criteria is outlined in Figure 5. 4

5 Figure 5. Cooper Harper Handling Qualities Rating Scale Cardinal Flight is designing the aircraft to meet a rating of 3 or lower. The rating of 1-3 is regarded as satisfactory performance without required improvement. Cardinal Flight has elected to evaluate the aircraft on 4 basic maneuvers: Powered Climb, Level Flight, Gliding Decent, and Coordinated Turns. Immediately the aircraft was deemed to be extremely stable; however, Arrow as designed by the Mechanical Team was shown to possess a very low degree of control. The aircraft was unable to recover from unusual attitudes so the flight control areas were increased till appropriate control responses were deemed acceptable. The testing could not continue with the original flight controls, so all ratings were accessed with the increased size of flight controls. The size increases are noted later in the Recommendation section of the report. The various ratings assigned to each maneuver can be seen in Table 2. 5

6 Table 2. Cardinal Flight Arrow Cooper Harper Ratings Evaluated Maneuver Rating 1 (Best) 10 (Worst) Powered Climb 1 Level Flight 1 Gliding Decent 1 Coordinated Turns 4 Powered Climb: this maneuver consisted of throttling to 75% power and climbing at the maximum stable attitude in a straight flight path. The aircraft was able to climb at 500 feet per min (FPM). This climb rate was deemed excessive but available during flight. The aircraft remained level in roll and maintained a stable climb attitude automatically with minimal elevator trim. There was no pilot compensation required to maintain course, so the Cooper-Harper Rating for the maneuver was deemed a 1. Level Flight: this maneuver consisted of maintaining level flight in regards to both pitch and roll while holding the throttle at 50% power. The aircraft was quickly trimmed to maintain level flight with zero pilot input to hold the maneuver. Additionally, any control impulse was quickly dampened out with the aircraft returning to un-accelerated flight. There was no pilot compensation required to maintain course, so the Cooper-Harper Rating for the maneuver was deemed a 1. Gliding Decent: this maneuver consisted of maintaining level bank angle while holding the throttle at 0% power. The maneuver was performed after the Level Flight trial so that aircraft was trimmed to maintain attitude. Once a stable glide path was established at a decent of 50 FPM, zero pilot input was required to hold the maneuver. There was no pilot compensation required to maintain course, so the Cooper-Harper Rating for the maneuver was deemed a 1. Coordinated Turn: this maneuver consisted of maintaining a level turn at 20deg holding the throttle at 50% power. During the turns a large amount of rudder input was required to maintain proper coordination. The rudder input varied pending bank angle and was required to prevent departure from a stable flight path. Moderate pilot compensation was required to maintain course. The required compensation was not extreme, only annoying. The so the Cooper-Harper Rating for the maneuver was deemed a 4. Aside from the additional pilot input required for the coordinated turns, the aircraft was extremely stable and easy to fly. The simulator performance yielded great feedback to the pilots of the group, so that improvements to the design could be recommended by the Aero team. The Aero team plans to use this method of evaluation on future aircraft designs. 6

7 Recommendations After reviewing the Cooper-Harper rating scale, the Aerodynamics team came to a consensus on two major points from the simulation; the first regarding the sizing of the control surfaces of Arrow, and the second surrounding the controllability of the aircraft. For the first recommendation, the Aerodynamic Team advises adding more area to the ailerons, elevators, and rudder. The Aero team s recommendations are listed in Table 3 in order increase response to pilot control input. Table 3. Original Flight Control Dimensions vs. Recommended Flight Control Dimensions Original Recommended Chord Span Chord Span Aileron Elevator Rudder The second area of concern dealt with a physics phenomenon that occurs for larger aircraft, which is called adverse yaw. This phenomenon occurs when the control surfaces are large enough that when deflected down, the drag and resulting moment created on the side of the aircraft in question causes a noticeable yaw opposite the direction of the roll. To account for this, the Aero team suggests mixing rudder and aileron commands such that there is a linear relation between pilot input for aileron deflection and resulting rudder compensation, in the neighborhood of 30% to 50%. One other remedy is to have differential throws for the ailerons such that a deflection down is a fraction of the deflection upward on the opposite side to equalize drag. Conclusion Using RealFlight RC Simulator was a great way to evaluate the handling capabilities of Arrow. By utilizing the quantifications given by the Cooper-Harper rating scale and the model of Arrow created in RealFlight, the Aero Team was able to provide recommendations to improve the aircraft. This milestone has reassured Cardinal Flight of Arrow s flight performance and helped to minimize potential problems with the flight control system. Furthermore, the data collected from the simulator will help Cardinal Flight perfect the overall design of the aircraft. 7