Overview
Hobby flying has several plans that allow several enthusiasts to build their own planes. However, an aircraft meant to perform, Chotee possessed a unique design. Chotee was meant to remain stable when loaded with a 100 gram payload, needed a thrust to weight ratio of 0.75, and was required to be agile enough to pass through gates. Such requirements were set by the Boeing National Aeromodelling Competition. Therefore, for this use case, I developed an optimised model leveraging two of the most popular techniques for different parts of the airplane. I used depron (foamboard) for a fuselage and empennage (labelled in diagrams below) and balsa wood for the wing.
Full Prototype Breakdown
Wing Design
Creating a hollow light weight wing with an airfoil shape designed to maximise lift and performance is the most ideal arrangement possible for the given brief. The hollow balsa wood frame is covered by monokote - a heat-shrinking poly compound sheet. The balsa wing contains spars focused around the Center of Lift line to facilitate sturdiness in the critical force points. I developed this on a CAD software (Autodesk Fusion 360), creating the camber on the airfoil after considering the cost of fabrication and the positive return on performance.
The full wing frame is broken into two half-components. This arrangement allows for the formation of a dihedral: an upward angled orientation of the two sections for flight stability. The frame is so designed to keep raw-materials simple as well.
Two half-wing sections as shown in the image above are constructed. The grid render of the 3D CAD design was used to simplify construction using the trace-place method - plans were printed and the relevant pieces were traced with adhesives to develop a precise design towards the end.
The adjacent image shwos the constructed wing. The airfoil ribs were cut from a 2mm balsa sheet, the spars were cut from a 5mm sheet. The internal spar placement was shifted based on an analysis of the ribs’ weakest points.
Electronics
The circuit diagram below represents the connections required to run the airplane using a radio-based remote system. The bank manouvre requires the left aileron to move opposite to the right. This requires an electronic configuration called a Y-Connection. It was an extremely simple configuration that resulted in this desired effect.
The above diagram shows the simple construction of a Y Connector: I soldered these together such that one side receives a negative current when the other is receiving a positive. This ensures that the opposite aileron moves opposite to the other’s orientation.
Gallery
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