spl4 - Design Variable Concepts 4 Mar 06 Lab 4 Lecture...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Design Variable Concepts 4 Mar 06 Lab 4 Lecture Notes Nomenclature I W aircraft weight S reference area (wing area) b wing span c average wing chord c r root wing chord c t tip wing chord λ taper ratio (= c t /c r ) AR wing aspect ratio o wing root bending inertia E Young’s modulus M C C η η P ρ air density elec electric power m electric motor efficiency p overall propeller efficiency L lift coefficient D drag coefficient c d wing profile drag coefficient CDA 0 drag area of non-wing components δ tip deflection o wing root bending moment Design Space Design Variables are numbers whose values can be freely varied by the designer to define a designed object. As a very simple example, consider a rectangular wing with a pre-defined airfoil. It can be defined by deciding on the values of the following two design variables: { b, c } (1) Placing these variables along orthogonal axes defines a design space , or set of all possible design options. Each point in the design space corresponds to a chosen design, as illustrated in Figure 1. c 3 2 1 b 4 8 12 Figure 1: Two-variable design space of a rectangular wing. 1 Variable Set Choice Frequently, an alternative variable set can be defined in terms of the starting variable set. For example, we can define the same design space using the variable set { AR , S } (2) with the following relations translating between the two alternative variable sets: AR = b/c b = √ S × AR radicalBig (3) S = bc c = S/AR Figure 2 compares the two design spaces. Other variable sets are possible for this case, such as { AR, b } , { S, b } , etc. The best variable set is usually the one which gives the simplest or clearest means to evaluate the objective function , or performance of the design, so that the best point in the design space can be selected. For example, a possible design objective for the wing will be to minimize flight power for an electric aircraft. Therefore, the objective...
View Full Document

This note was uploaded on 01/28/2012 for the course AERO 16.01 taught by Professor Markdrela during the Fall '05 term at MIT.

Page1 / 6

spl4 - Design Variable Concepts 4 Mar 06 Lab 4 Lecture...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online