SAE Aero Design Presentation Oct. 30 th 2012

Wind Tunnel Testing and Modification Why use wind tunnels? They’re cheaper than most computational fluid dynamics (CFD) software packages. They generate more realistic data than CFD, since CFD must make assumtions and model simplifications. Small-scale models are much less expensive to build and test. The small-scale results can be extrapolated to the full-scale prototype according to the principles of dimensional analysis and similtude. AeroDesign Team’s Wind Tunnel Goals Modify the wind tunnel at Crosby to: Validate/Invalidate XFLR5 data Accurately predict the lift on the full scale aircraft And select the airfoil and wing configuration that performs optimally

Current Setup Flow is too unsteady to get any usable data Too slow to obtain required Reynolds Numbers with reasonable model sizes Problems:

Proposed Modifications Flow Straightener Converging duct (Sheet Metal) Brace Frame (Wood) Test Section (Plexiglass) DiffuserSupport (Wood)

Duct Sizing Considerations Test section flow must not exceed Mach 0.3 to avoid compressible flow effects Test section area must accommodate wide bodies, 8-9 times the max chord Test section must be tall enough so the walls don’t interfere with the flow, requiring the height to be at least 3 times the max chord Velocity in the test section must allow Reynolds numbers from 50,000 to 500,000 to be achieved with “reasonably sized” scale models. Designing the Mods Brace Frame Design All of the above requirements are met by a 36”x10” rectangular duct The frame must be strong enough to withstand the aerodynamic force on the bottom surface of the converging duct. CFD Results suggest a force of nearly 1300 lbf on the bottom surface of the converging duct.

Analysis & Results Preliminary “back-of-the-envelope” analysis for sizing used elementary fluid mechanics principles from MEE360 and Aeronautics. Continuity: ρAV = constant Mach Number: M² = V²/kRT The flow just past the fan was mapped to estimate the mass flow rate which is assumed constant.

More advanced computational techniques (CFD) were employed to conduct a detailed analysis of the design. Analysis & Results ctd. Streamlines and Outlet Velocity Contours Pressure Contours and Outlet Velocity Contours

Analysis & Results ctd. A structural analysis of the brace frame followed to determine whether our design could support the aerodynamic loading.

What’s Next? To move forward with wind tunnel testing, several things need to be done. Construction of the modifications to the wind tunnel Construction of the scale models Calibration of the sting upon which the models are mounted Design and construction of the model mount

Fabricated Test Rig Made from Scrap Metal and Tubing Points for recycling and Green thinking?! This set up will need to be modified in order to get testing done due to equipment issues.

Data Acquisition Systems

Wing Configuration The wing section (airfoil) has section properties and coefficients which are desirable relative to others, but must still be build into a workable physical configuration for flight. The configuration of the wing on the plane and the wing planform will primarily define the efficiency of the wing, the loads on the aircraft structure, and several stability tendencies. Thus, choosing an appropriate arrangement is key. Many parameters are involved in the configuration, including: – Wing Span – Chord Length – Aspect Ratio – Wing Mount Style – Dihedral Angle / Anhedral Angle – Wing Taper – Wing Twist – Overall Planform – Construction Style and Method – Wing Sweep – Wing Tip Devices – Wing Edge Style – Wing Area – Wing Loading – External Additives (Turbulators, Stall Fences, etc.) – Airfoil Section – Multiple Wings Some of these are closely related to one another, and some do not apply to our design to a large extent.

Aspect Ratio A larger aspect ratio is an inherently more efficient design due to the amount of air in contact with the lifting body Slow speed, low Re flow dominated by induced drag With high AR, AOAs can be smaller, minimizing lift induced drag A high AR may be harder to support structurally due to larger bending moments Lowering chord length lowers Re in an already low energy flow. Long wings tend to be harder to trim out for flight and are sensitive to disturbances Poor roll rate, more rotational inertia

Taper and Twist The wing tip can be unloaded by tapering This will also bring the lift distribution closer to theoretical ideal Strongly tapered wings may reduce tip vortex drag but lead to downwash distribution such that the tips are overly loaded and will stall first. (Wash-in) To avoid this, use moderate taper and/or design wing twist The purpose of twisting is to change the AOA such that the root will tend to stall first, reducing loss of control (outwash) This may be difficult to manufacture and hard to predict

Utilizing XFLR5 XFLR5 has a wing and plane design function which allows the import of airfoils Nearly unlimited configurations can be modeled quickly, with or without a mock fuselage and subjected to aerodynamic forces Animate function allows us to see the values change over range of angles of attack Allows for rough comparison of closely configurations, which will help eliminate some Once a configuration is chosen, it will be paired with the airfoil selected based on physical testing Maintain a goal of testing a scale version of the wing we wish to implement.

Building of Wing

Top Side Front

Wing Building

Monokote

Breaking in the Engine Engine Break-In

Immediate Future Plans Thrust Testing Wind Tunnel Nozzling 3D Models of 4 select Airfoils Sting Modification and Calibration Wind-Tunnel Testing

Hard at Work