This preview shows page 1. Sign up to view the full content.
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. ...
View
Full
Document
 Winter '09
 Tooney

Click to edit the document details