Matplotlib，Python中的图比例缩放

我编写了下面的程序来绘制形状，如代码后所示：

length = 100
a = 50
b = 0
n = 2
alpha = np.radians(25.)
d = 18

x_nose = np.linspace(0,a,50)

r_nose = (0.5*d*(1. - ((x_nose-a)/a)**2.)**(1./n))

x_mid = np.linspace(a,(a+b),2)

r_mid = (((d/2) * np.ones(2)))

x_tail = np.linspace((a+b),length,50)

l_tail = (length - a - b)

r_tail = (0.5*d - ((3*d)/(2*l_tail**2) - np.tan(alpha)/l_tail)*(x_tail-a-b)**2 + (d/l_tail**3 - np.tan(alpha)/l_tail**2)*(x_tail-a-b)**3)

line1 = plt.plot(x_nose,r_nose,'k',x_mid,r_mid,'k',x_tail,r_tail,'k')
line2 = plt.plot(x_nose,-r_nose,'k',x_mid,-r_mid,'k',x_tail,-r_tail,'k')
plt.axis('equal')
plt.setp([line1,line2], linewidth=2)  
plt.show()

但是，用于定义用于计算形状的公式length = 100。如何缩放变量的整个数字length？