Model Aircraft Modifications
The model airplane is based on the Flite Test Bushwacker and is constructed primarily out of foam board and hot glue, and is powered using a LiPo and a brushless motor. The stock design is already very high-performing and extremely robust.
However, with modifications, I was able to increase its low-speed flight characteristics, aerobatic maneuverability, and improve its landing performance.
The largest modification is the alteration of the horizontal stabilizer from a conventional 'stabilizer-and-elevator' configuration into a full-flying stabilator. The increased area reduces the angle of attack required by the elevator, resulting in improved pitch-up authority, especially at low speeds.
The second large modification to enhance low-speed flight is the addition of leading-edge slats. Slats have proven to be very effective as a high-lift device on scale aircraft. However, I wasn't sure how effective they would be at low Reynolds numbers. I found helpful information on a paper written by Traub and Kaula, Effect of Leading-Edge Slats at Low Reynolds Numbers that showed that although slats didn't perform the same way they did on large-scale aircraft, they still effectively moderated stall onset. In addition, the paper was helpful in determining the optimum geometry for the slats.
Effect of Leading-Edge Slats at Low Reynolds Numbers, Lance W. Traub, and Mashaan P. Kaula.
My model airplane wing with slats augmented
Another modification is the enhancement of the main landing gear. The original design had a bent steel wire support two 4"⌀ wheels. It was very light and strong but wasn't very effective in absorbing impacts.
I upgraded the landing gear with a custom 3D printed mechanism that used rubber bands as shock cords to reduce the impact loads that would transfer into the airframe. The mechanism is one piece, utilizing living hinges. The new landing gear had almost four times the suspension travel, allowing me to fly steeper and slower approaches without worrying about damaging the aircraft.
Also, the area of the control surfaces was increased. Aforementioned, the elevator had a dramatic increase in area when the stabilizer and elevator were combined to form the full-flying stabilator.
Instead of split ailerons+flaps, I combined them to form full-span flaperons, doubling the effective flap area while also doubling the aileron area. The ailerons are wired on separate channels, enabling me to program in aileron differential to reduce adverse yaw. Additionally, the ailerons are now partially in the propwash, providing greater authority especially at very low speeds.
The rudder servo horns were rigged to provide as much deflection as geometrically possible.
High-alpha descent demonstrating low-speed maneuverability
Linear carbon fiber rods were hot glued to the aileron trailing edge, stabilator leading edge, stabilator trailing edge, and rudder trailing edge to add rigidity and protect the edges of foam from being damaged with a minimal weight penalty.