During my senior year of mechanical engineering at Purdue University, I joined the Purdue Aero SAE club. The purpose of the club is to compete in the global Aero SAE challenge held in Florida for our region. The competition consists of designing a remote-controlled airplane within certain restrictions; namely, the plane must use a certain battery and must carry tennis balls to represent passengers. The team that can carry the most number of tennis balls wins the competition. The key to winning is utilizing the most aerodynamic wings and getting the most amount of thrust from the battery. This was my first year on the team, however, I was given the role of controls engineer lead. I lead a team of 10 younger engineers. Prior to the club, I knew very little about controls for aircraft, but I am glad to say that I’ve learned a lot.
This is the CAD model of the aircraft we designed.
The controls department for this aircraft design process was broken down into two main subsections. The first was the design of the control surfaces. For this aircraft, the team determined that two ailerons, an elevator, and a rudder were sufficient to control the aircraft during takeoff, cruising, and landing. The ailerons were the first control surfaces designed. The design process for the ailerons started by doing significant research on typical ratios used by other aircraft designers. Typical deflections ranged from +/- 30 degrees to +/- 12 degrees, and so the team analyzed the pros and cons to each. The obvious plus of a large deflection is that the aircraft will have a tighter roll radius and faster roll rate. Although with this large deflection comes higher forces associated with pressure build-up in front of the control surface. In addition, there are significant challenges for this particular aircraft concept. The largest is, of course, the weight allowances. So, for this reason, the team determined that a deflection of +/- 20 degrees would be sufficient middle ground for all control surfaces.
The foam plane, used for proof of concept
The next object of the design process was to determine the span of the aileron compared to the wingspan. Typical values for this were in the range of 0.2 to 0.5. The team again went with a middle ground approach of 0.3. The meaning behind this is that 30% of the wing length will be used for the aileron. The team then created a Matlab code to determine the roll rate and exact sizing for the chord and area of the control surfaces.
The final product, 14 feet in width!
In the end, the team created a working aircraft. The team and I included were very proud of our accomplishment for creating an operational aircraft. Unfortunately, due to a particularly windy test day, our model crashed beyond repair. The real problem was that it crashed too near the competition that only a scrambled effort could allow a new plane to be produced. With exams lingering, many people decided to study rather than stay up all night building an airplane, and I am sad to say that I was a part of that group. I can say, however, that I learned a tremendous amount and found a new love: flying aircraft. Joining this club was one of the greatest choices I made during college.
The plane was truly a beauty! (Before it crashed)
Want to see more? Here is the Matlab code used to size the Ailerons
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