Initial Weight Estimate
Based on the aerofoil selection, the included technical drawings were generated. The current conceptual design have a span of 1.684 m with a lifting surface area of approximately 0.46 m.
The CG location of an aircraft and it's relation to the aircraft's aerodynamic centre (AC) is largely reliable for its stability and manoeuvrability. Conventionally, the AC location relative to the CG is balanced by the aircraft tail. The lack of tail on this design requires additional careful consideration during the sizing and design process.
With the main aircraft section being thin compared to a conventional cargo plane fuselage design, the position of the electronic components and payload is limited. The CG of each aircraft component is estimated with the assumption that the majority of the usable space is in the forward section of the aircraft. The table below displays the initial CG estimates with distances being measured from the leading edge in the centre of the aircraft.
| Component | Mass [g] | Distance [m] | %MAC |
|---|---|---|---|
| Front Wheel | 23 | 0.05 | |
| Rear Wheels | 46 | 0.63 | |
| Powerplant | 368 | 0.05 | |
| Propeller | 24 | -0.01 | |
| Wing | 1107.2 | 0.386 | |
| OWE | 1568.2 | 0.3033 | 25.37 |
| Payload | 4000 | 0.206 | |
| MTOW | 5568.2 | 0.2336 | 4.36 |
The CG at OWE is placed at 0.3033 m from the nose, or approximately 1 mm behind the aircraft AC. In terms of stability, this would result in a very sensitive aircraft when flying with no payload. The CG at full payload capacity however is located 0.2336 m from the nose. The recommended CG position for optimal in-flight stability is between 5% and 18% MAC. In this case, the condition is met, and therefore when carrying the required payload, the aircraft controls will be sensitive enough for flight without being dangerous. Locations of different CG positions on the aircraft can be seen in the attached technical drawings.
Materials and the CG#
This flying wing design is planned to be manufactured from carbon fibre. The outer skin of the aircraft is a woven carbon fibre shell and acts as the lifting surface as well as a key structural component of the aircraft. Therefore, the number of ribs and spars intended to be used is minimal, maximising usable space within the shell and minimising the operational weight.
The material used for the initial weight estimate was 210gm twill-woven CFRP. A wet-layered carbon fibre component is assumed to have a 50:60 fibre-to-resin weight ratio. Therefore, assuming that three layers of carbon fibre cloth are used for the main shell, with a total area of approximately 0.9 m, the main structural weight is 1.107 kg. The CG of the wing itself is approximated by assuming a uniform distribution of weight throughout the planform, putting the CG at 0.386 m from the tip.