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Lecture 2

Lecture 2 - Lecture 2 Ge*ng Started on your Aircra4...

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Unformatted text preview: Lecture 2 Ge*ng Started on your Aircra4 Design Ini8al Weight Es8mate •  Make an ini8al guess on the aircra4’s max gross takeoff weight based on similar aircra4 –  Conduct surveys of exis8ng UAVs Wing Sizing •  Calculate the wing area necessary to meet the wing loading, stall speed, or cruise specifica8ons. –  If sizing by stall, pick a reasonable value for the max li4 coefficient L = W = 1 ρVs2 SCL ,max 2 –  If sizing by range, pick a reasonable L/Dmax € Aircra4 layout •  With the wing area es8mated, sketch a few possible configura8ons for your aircra4. –  Make sure to keep in mind the placement of all the internal components: engine, payload, landing gear, flight computer, etc. –  Es8mate sizes of horizontal and ver8cal surfaces necessary to achieve sta8c stability. –  Inden8fy pros and cons of each configura8on. •  Select the most promising configura8on Drag es8ma8ons •  Calculate the frontal and weSed areas from your sketches to obtain an ini8al es8mate for the parasite drag coefficient. –  Later, you’ll be using the component build ­up method  ­ you can start with that right away if you like. •  Es8mate induced drag coefficient –  Remember that both the wing and tail generate li4 •  Calculate total drag (parasite + induced drag) at important flight condi8ons: –  max speed –  Cruising speed –  Max L/D condi8on, min power condi8on, 0.7VTO, etc. Thrust/Power Es8mates •  Make a reasonable guess for propeller efficiency for your aircra4. –  You can start with ηp ≈ 0.8 For cruise and top speed condi8ons: –  And for takeoff, climbing: η p ≈ 0.65 € –  Later you will be compu8ng these efficiencies more accurately when you design your propeller. € •  Calculate necessary engine power to meet performance specs –  Top speed, takeoff, rate of climb –  Make sure to account for al8tude effects for performance requirements not at sea level. Engine selec8on •  Research available engines •  Select an engine with sufficient power to meet all performance requirements, and obtain its weight and dimensions. Cruise condi8ons •  Calculate the drag under cruise condi8ons. •  Calculate the engine power se*ng at the specified cruise speed. •  Using the Breguet range/endurance equa8ons, calculate the fuel required to sa8sfy range/endurance requirements for your mission. Refine weight es8mate •  Obtain weights –  For the structures (wing, tail, fuselage), you can use the Niccolai or Cessna formulas. –  For flight computer, nav sensors, payload, cameras, etc., you probably will need to do your own research. •  Sum up all components to obtain updated weight es8mate •  Determine center of gravity loca8on for the extreme loading condi8ons Stability check •  Calculate the sta8c stability deriva8ve, Cma, for the extreme loading condi8ons. •  Check that the aircra4 is stable in pitch by verifying that Cma is nega8ve for all possible loading condi8ons. A minimum stability margin of 5% is recommended. •  If the aircra4 is unstable, the aircra4 layout must be revised to shi4 the CG forward with respect to the wing. •  Also check that the aircra4 is trimmable in each loading condi8on. Iterate your design •  You now have a new max gross takeoff weight es8mate. •  Repeat the process to correct any viola8ons of design specs, or to improve the ini8al design. ...
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