Physical Prototype - Drag Reduction System (DRS)

Working Mechanism

Design Process 

The requirements of the build prototype are:

• Low cost
• Simple and quick fabrication method
• Demonstrate feasibility with variable tolerances and model compliance
• Demonstrate functionality and accuracy to the linkage model

Build Process

We started off with prototyping the morphing wing, the novel portion of this design. We initially started with a flexure prototype to add flexibility to the wing. However, this proved difficult because the flexure buckled the high-pressure inwards, likely inducing turbulence.

We fixed and adjusted this by splitting the high-pressure surface and sliding the two surfaces together. This fixed our overconstraint problem and added flexibility to reduce the force required by the driving link.

Next, we moved onto the linkage design. We had two states that drove the linkage design: the down state with camber and angle of attack of zero, and the up state with 13 degrees and 28 degree wing element with a positive camber angle on the second element.

These wing spacing and driving requirements were simulated and iterated to minimize the spacing between elements and maximize angle of attack without flow separation.

For the down configuration, we referenced the BL145 airfoil specification¹ and concluded that the optimal angle for lowest drag was an angle of attack of zero.

After finalizing the linkage geometry, we moved to creating links and revolute joints. Because one of our requirements is to be low-cost and quick to fabricate, we decided to print plastic bushings, caps, and revolute bosses. After iterating on cap press-fit fitment, we found that the optimal press-fit interference is 0.025mm of radial clearance.

Additionally, after printing the intial wing element parts, we realized that it was difficult to simulate the deformation of the wing. We also realized that the since the trailing edge camber link moved inwards slightly, we needed to add a prismatic slot to prevent overconstraint.

Ultimately, we only needed two prototypes to create our initial model. This was due to us having prior experience in fabrication and linkage design, which greatly facilitated making this project efficiently and on-time.

Reflection

This prototype was successful at demonstrating functionality for our DRS mechanism. We learned a lot about building functional plastic joints, designing linkages that are toleranced well, and preventing overconstraint.

For the final project, we plan on finalizing the wing morphing flexure, establishing requirements for structural loading, and building struts and linkages out of a more durable and reliable material. Our full-size model will need to be fully functional and will need to be reliable for a demonstration.  

Bill of Materials

¹DEFIANT CANARD BL145 AIRFOIL (defcnd3-il). Defiant canard BL145 airfoil (DEFCND3-il). (n.d.). http://airfoiltools.com/airfoil/details?airfoil=defcnd3-il