X-47B UCAS
PROJECT TIMEFRAME
Fall 2013 - Spring 2014
PROJECT PURPOSE
To test and apply the knowledge gained through my aerospace studies on a complex, real-world project.
TECHNIQUES USED
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Aerodynamic & stability analysis
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Conceptual and detail design
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CAD modeling
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Programming in Arduino
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Wind tunnel testing
SKILLS LEARNED
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Airfoil selection
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Fundamentals of tailless aircraft
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Tooling design and preparation
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Composites manufacturing
While this build wasn't a senior design project, I treated it as such by performing some textbook design processes. I created a constraint diagram to determine the appropriate wing and power loadings for the types of flying this model would perform. I adjusted the airfoils and twist to achieve the right lift distribution for a tailless model. And finally, I built a weight and balance table to ensure that everything would get placed properly to achieve the correct center of gravity.
I used CATIA to perform the CAD work for this project. Despite the simple planform, the blended wing and inlet geometry added complexity to the design. Plus, the serpentine ducting needed to be seamlessly integrated with the inlet, fan unit, and exhaust while maintaining cross section area.
Next I designed the internal structures. Since most of the airframe would be comprised of thin composite skins, the internals were responsible for mounting everything from landing gear to batteries to control surface actuators. Plus, it had to carry the loads from the outer wing spars through the center of the fuselage while working around the fan and inlet ducting.
After the CAD was complete, I used a 5-axis CNC mill to cut tooling from laminated MDF sheets. No fancy mold making materials here - I was a college student after all. Since the equipment couldn't be left unattended, I spent several full weekends in the machine shop.
I finished the tooling with lots of sanding, some automotive primer, and plenty of mold release. Then I laid up the skins using several layers of fiberglass and a thin foam core for added stiffness. The parts were vacuum bagged overnight.
After the skins were cured, I left them inside the mold halves and installed the laser cut plywood internal structure. Then, the halves were joined with thickened resin and homemade clamps.
With the airframe complete, it was time to mount electronics and hardware. The retractable landing gear was among the most tedious elements due to the complex door arrangement. I created a custom landing gear door sequencer using Arduino in order to properly stage the landing gear retraction and door motions.
Once all of the hardware was fitted, I took advantage of a unique opportunity - to mount the model in the largest wind tunnel available at Purdue. This was always the plan - in fact, the test section width was the primary sizing constraint for the aircraft's wingspan.
The wind tunnel data validated the initial aerodynamic modelling, and showed that this tailless aircraft would be stable in normal flight. Plus, it allowed me to determine the pitch trim and angle of attack required for cruise.
I finished the model with some paint, an airbrush, and custom decals to match the real aircraft as best as possible. It looked great!
Time to fly! I fitted the model with some simple vertical stabilizers for passive yaw stability and to make it easier to see in the air.
I need to design a sideslip sensor in order to allow ArduPilot to perform closed-loop yaw stabilization without the vertical stabilizers. That's a project for another time.
This project had a larger effect on my life than most. I was hired by Northrop Grumman after finishing it and having a chance meeting at a trade show and moved to San Diego.
I never worked on the X-47B program during my time at Northrop. Though I did have a chance to visit an aircraft carrier at sea, including an arrested landing and catapult launch. Not a bad trade!
