The Brittish Model Flying Association (BMFA) annually runs a number of interesting competitions. This UAV was designed following the criteria for the BMFA 2015 Electric Lift Challenge.


My team designed and built a UAV for the Payload Challenge 2 (Quantity) contest. The mission of the aircraft was to transport as many tennis balls as possible around a polygonal flight path, within a maximum of ten minutes.

  • Rules: Details on the rules of the competition can be found here.
     
  • Team
    • Conceptual and preliminary design: H. Shukla, H.T. Nguyen, C.C. Long, L.S. Chung, R. Feng & M. Samuel.
    • Detailed design: H.T. Nguyen, C.C. Long, L.S. Chung & M. Samuel.
       
  • Flight path: The distance between the loading bay and the starting point (indicated by the orange dot) is 10m. The maximum takeoff distance is 61m in either direction of the starting point. The direction in which the aircraft will take off will depend on the wind direction. The aircraft will make a turn and fly 150m to Pylon 1 and then make another turn and fly 300m to Pylon 2. It will then make a final turn and fly back 150m, and then land within 61m. This was taken to be the flight mission of the aircraft.
  • Objectives

The main objectives in this competition are fourfold:

  • Design and build an electrically propelled aircraft to transport the greatest number of tennis balls around a polygonal course within a ten-minute time constraint.
  •  Present their aircraft’s design and construction in a technical report, including design drawings.
  • Deliver a verbal presentation of their aircraft affront a panel of judges.
  • Demonstrate the performance of aircraft at the flight competition.
Competition flight path

Competition flight path


Objectives

The main objectives in this competition are fourfold:

  • Design and build an electrically propelled aircraft to transport the greatest number of tennis balls around a polygonal course within a ten-minute time constraint.
  •  Present their aircraft’s design and construction in a technical report, including design drawings.
  • Deliver a verbal presentation of their aircraft affront a panel of judges.
  • Demonstrate the performance of aircraft at the flight competition.

Design Constraints

  • Aircraft configuration
    • Only fixed wing designs with a wingspan of 1500mm or less.

    • Constituents of the propulsion unit were specified to be one E-flight Power 10 motor and one E-flight 40A speed controller, both of which are available direct from the BMFA office.

    • A 3-cell Lithium Polymer battery with a capacity under 2200 MAh was specified. Only one battery could be used per flight round.

    • Modification of the motor was not allowed but gearboxes and variable pitch propellers, however, were acceptable. A minimum distance of 100mm between the isolator unit and the propeller arc (25° minimum) was allowed.

    • Removal and visibility of the fuse should be aided by affixing a tag to it. A propeller spinner or rounded safety nut must be fitted on forward facing motors.

  • Radio restrictions
    • Radio installations will be examined by organisers and must be deemed fit for the

      intended application. Servos and linkages must be capable of handling anticipated air loads.

    • Computer transmitters are allowed. However, any extra functions, mixing or advanced programming must be explained and demonstrated to judges in the presentations.

    • Gyros/auto stabilisation is allowed but any aids to stable flight must be able to be overridden by pilot command at any flight phase.

    • Radio equipment must be on the 2.4GHz frequency band only and must be UK compliant.


Conceptual Design

The conceptual design employed the following aircraft design process and tools

  • Systems engineering: Systems engineering tools were used during the design of this aircraft. These tools were beneficial to the team in various ways. They helped the team to make good decisions and approach the design of the aircraft in a more holistic and systematic manner. Tools utilised include:
    • Requirements decomposition
    • Matrix of Alternatives
    • Quality Function deployment (QFD)
       
  • Initial weight sizing
  • Centre of gravity excursion
  • Aircraft structures

Preliminary & Detailed Design

In this phase of the design, the following were looked at:

  • Propulsion
  • Aerodynamics
  • Wing planform selection
  • Airfoil selection
  • Velocity-load factor (v-n) diagram
  • Horizontal and vertical tail sizing
  • Detailed structural design (including FEA)
  • Risk assessment
    • Impact on landing
    • Structural strength and stability
    • Spare parts and replacements
    • Ground logistics

Wireframe three-view drawings of configuration chosen