Concept generation and selection

For our concept selection, several criteria are assessed to select our concept. 

First, landing and takeoff flexibility is crucial for our design to allow landing on compact spaces with shorter landing distances due to reduced impact of ground effect. This is considered along with the ground clearance needed for our landing.

The amount of thrust required is also taken into account for our selection. This criterion is chosen as it helps us determine the number of engines needed for our design to generate the necessary amount of thrust as well as increase airspeed throughout the duration of the flight. This also serves with the lift needed for takeoff and climb of our aircraft. Because of the shorter takeoff conditions, the amount of thrust is crucial to ensure faster terrain clearance.

Ground and air stability and maneuverability are also parts of the important criteria as they are necessary to maintain safety during landings on non-airport runways. For non-ideal landing locations, our design will need a sufficient level of maneuverability and stability as it will be necessary to control the aircraft for stable landings. In accordance with our criteria, concept 2 (Two engines placed below the cantilevered overwing, with tricycle type landing gear attached to the fuselage) fits best with the required criteria. The two engines will provide a sufficient amount of thrust while the overwing design gives more ground clearance and shorter landing distance for our mission. The tricycle-type landing gear also provides good balance required for our landing condition. Moreover, the design will also implement a turbo propeller engine as it provides maximum efficiency at lower speed and altitude when compared to that of a jet engine. This type of engine is also lighter for ease in takeoff and landing with limited runway distance. This type of engine also significantly lowers the cost of both the engines themselves and the maintenance costs. Turboprop engines are lighter in weight which make take-off and landing easier; moreover, they are more efficient at lower speeds and easier to maintain.

CONCEPT REFINEMENT

Airfoil Selection: We chose NACA 4415, switched from NACA 0009. We choose this airfoil type based on the camber we have chosen. Also, the coefficient of lift per angle of attack is higher compared to other airfoils. This allows our design to have the highest lift possible per angle of attack changed. From Nicolai, the stalling angle is 8 degrees. Furthermore, we chose a 4 digit airfoil as it has good stall characteristics which are beneficial for landing in remote areas.

Turbo Propeller Engine: We chose Pratt & Whitney Canada PT6 because it is designed for the best performance in a low-altitude mid-speed flight. It also generates enough power to satisfy the requirement we have for our mission.

Landing Gear:

We have chosen to go with a non-retractable tricycle arrangement for our landing gear. The non-retractable ones allow for lower weight not needing the retracting mechanism and reduce the possibility of failure in the system. Also, for our flight speed, with a well designed support, the non-retractable system is not going to drastically affect the aerodynamics thus having minimal effect on factors such as top speed or drag.

Wing Shape: We chose a straight tapered wing. This wing shape increases the aspect ratio which helps to increase lift, and the smaller wingtips lower the drag by reducing the wing-tip vortices. This wing shape is also cost-efficient and easier to manufacture compared to that of a curved wing making it a suitable choice.