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| Mr. Meadth teaching aircraft stability via Zoom |
The first step for our skillful students was to learn the ins and outs of classic aerodynamics. In January, February, and March, the eight juniors and seniors studied airfoil behavior, lift and drag equations, and learned how to use weighted averages to find the center of gravity of a complex system. Our team learned the different parameters of airfoil design, and used virtual wind tunnel tests to predict just how those airfoils would respond in real life.
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| The virtual wind tunnel program XFoil: a classic historical aerospace simulation! Note the cambered airfoil shape at the bottom, with the yellow boundary layer on top and the blue one below |
Even more important was the notion of stability. What makes some physical systems stable, and others unstable? The incredible hexacopter drone that emerged in the first semester was inherently unstable, which means that it will rapidly flip and roll and fall out of the sky if the onboard computer-controlled gyroscopes were to stop doing their job. The gyroscopes sample the position and orientation of the drone dozens of times per second, and send minor corrections to the six motors, all without the pilot on the ground ever knowing it. Stable drone flight is an astounding human accomplishment, powered by calculus and implemented by technology, but it is not inherently physically stable.
On the other hand, the powered fixed-wing aircraft in this project must be physically stable. Tethered to a central post and flying continual circles, the aircraft will have only one remote-control channel controlling the power to the motor. There are no ailerons, elevators, rudder, or flaps. Without moveable control surfaces, the aircraft must be designed to constantly self-correct all by itself. If the nose dips down a little because of a gust of wind, it must automatically seek to find level again. If it rolls a little too much to one side, it needs to roll back again. The principles involved hold true for most common vehicles: cars, bicycles, even the caster wheels on supermarket carts.
Having mastered the physics involved, the students set about the difficult task of starting their design. No kits, no instructions, no fixed starting point! In teams of two, the students created a complicated spreadsheet filled with graphs and tables and physics equations, listing masses and locations and forces and moments. The students also designed a multi-part CAD model according to those numbers using the professional-grade online platform Onshape; ideally, the CAD model, the spreadsheet design, and the manufactured plane itself will end up as three matching representations of the same reality.
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| Pedro's and Nolan's aircraft in its complete form |
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| The same aircraft in an exploded view |
Mr. Meadth ordered in the necessary tools and materials for construction: carbon fiber bars and tubes, balsa wood, lithium-ion batteries, electronic speed controllers for the advanced motors, propellers, wheels, and filament for the 3D printer. These materials were fully paid for by a generous grant from AIAA, the American Institute of Aeronautics and Astronautics. AIAA believes strongly in encouraging the work done by K-12 schools in advancing aerospace education, and Providence School has received similar grants in the past.
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| The delivery of the critical components arrives! |
Through the COVID-19 distance learning experience, the four teams produced their designs without ever meeting in person with each other or the teacher. Because of Zoom lessons, shared spreadsheets, and the powerful collaborative nature of Onshape, this project didn't skip a beat. Mr. Meadth set up a manufacturing station in his own garage, and busily set to work producing what the students had designed. The CNC (computer numerical control) machine carved out flat balsawood ribs with exact length, thickness and camber dimensions, and the Raise3D 3D printer produced the three-dimensional components such as fuselages and tail.
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| The Providence Engineering Academy manufacturing facility! |
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| A completed wing rib from Ben and Todd, with carbon fiber spar inserted |
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| The vertical tail for Nolan's and Pedro's aircraft, over nine hours in the making! |
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| The huge 30-hour print of the fuselage/ wing box (lots of temporary support material can still be seen |
Where to from here? The Advanced Engineering II students will receive deliveries of their manufactured pieces, to be assembled at home. Test flights, possible redesigns, and the final maiden voyages are scheduled to happen in late May—stay posted for the culmination of this exciting story!
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