Wing Configurations

Conventional & Biplane

Seventeen aircraft from the selection in the historic data are a conventional configuration. The general opinion of designers is that the simplicity of conventional set-ups outweighs any drawbacks; this is due to their wide use in industry and similar missions. The manufacture can also be split into the wings, fuselage, and tail components with the fuselage providing a perfect location for the payload to be stored while not complicating its installation. It is also not essential to implement features such as taper or sweep which is advantageous as a means of simplifying manufacture. The main problem is the increased drag due to the presence of the fuselage as a body that doesn’t also provide its own lift. The biplane configuration is also present in the selection of aircraft researched; the two aircraft that used a biplane set up are commercial UAVs which is telling 3of the disadvantages of using them. The main criticisms of the biplane set-up from competition teams is the added complication of the structural components required for construction, with little added benefit to the aerodynamic performance. Another option is to employ a delta wing, though none of the examples researched had done. The most notable benefits are the reduced effects of shock waves and the improved manoeuvrability. This suggests why a delta wing configuration was not seen as these strengths are not necessary for the BMFA project as the UAV will be operating at low speeds. Additionally, the high sweep angles and taper of a delta wing make them unnecessarily difficult to construct considering their lack of suitability to the BMFA payload challenge.

Flying Wing

Some aircraft adopt the flying wing configuration. Five of the selected aircraft, including one of the highest performing aircraft when considering MTOW/OWE, the WSU sUAVe, use the flying wing as the entire body produces lift, holding the potential to significantly reduce OWE. The main problem with the design of a flying wing is the difficulty in making it stable; the lack of a tail plane adds complications when considering the flight dynamics. There are means to maintain stability such as winglets and rear mounted elevons, but these will require additional knowledge and consideration. Construction of a flying wing could also be challenging as sweep is essential for stability, however, there are many ways to simplify the manufacturing as individual sections can be printed, reducing the need for complicated internal structures.

Wing Features

Sweep is beneficial as a means of reducing the incident speed normal to the leading edge. This is mostly useful for higher speed applications, hence why most similar competition style UAVs do not implement it. Sweep is also avoided for aircraft with similar missions and manufacturing situations as it is more difficult to produce. However, sweep is essential for a f lying wing as it varies the location of lift along the span, helping maintain longitudinal stability and thus reducing the risk of an uncontrollable flip about the wing axis. Most examples from literature incorporate some degree of taper; this is mainly due to the savings on weight that can be achieved. Taper can be used to take advantage of the nature of lift distribution along the span, whereby the outboard section can be made with a shorter chord, reducing the respective weight. This is desirable for the BMFA challenge as any means of reducing weight will lead to an increase in the ratio of MTOW/OWE, making the design more competitive. A key disadvantage of taper is an increased risk of stall at the wing tips. Twist can be used to partially mitigate this problem. Twist can vary the angle of incidence along the span ensuring that the wing tips are the last part of the wing span to stall, however, it is extremely difficult to achieve in a handmade aircraft which is evidenced by the fact that no aircraft in the study used twist.