# Basic Geometry and Initial Guesses

Almost by definition, the early part of the conceptual design process is the only part of the product development where we do not yet have a geometry model to refer to. Thus, some of the all-important aerodynamic figures have to be guessed at this point, largely on the basis of high level geometrical parameters like the aspect ratio.

In [30]: AspectRatio_ = 9

In [31]: CDmin = 0.0418

In [32]: WSmax_kgm2 = 20

In [33]: TWmax = 0.6

In [34]: Pmax_kW = 4

Estimated take-off parameters

In [35]: CLTO = 0.97

CDTO = 0.0898 muTO = 0.17

# Preamble

Some of the computations and visualizations performed in this document may require additional Python modules; these need to be loaded first as follows:

In [36]: %**matplotlib **inline

In [37]: **from __future_ import **division

**import math**

**from aerocalc import **std_atm **as **ISA **import numpy as np**

In [38]: **import matplotlib**

**import matplotlib.pylab as pylab import matplotlib.pyplot as plt**

In the interest of conciseness and modularity, it is often useful to define repeated operations as functions. Let us first define a function for coloring in the unfeasible area underneath a constraint boundary:

In [39]: **def **ConstraintPoly(WSl,TWl,Col,al):

WSl.append(WSl[-1])

TWl.append(0)

WSl.append(WSl[0])

TWl.append(0)

WSl.append(0)

TWl.append(TWl[-2 ]) zp = zip (WSl,TWl)

pa = matplotlib.patches.Polygon(zp,closed = True

, color=Col, alpha = al)

**return **pa

Next, we define a method for setting the appropriate bounds on each constraint diagram:

In [40]: **def **PlotSetUp(Xmin, Xmax, Ymin, Ymax, Xlabel, Ylabel): pylab.ylim([Ymin,Ymax]) pylab.xlim([Xmin,Xmax]) pylab.ylabel(Ylabel) pylab.xlabel(Xlabel)

In [41]: Resolution = 2000 Start_Pa = 0.1