# Homework Help: Form drag of aerofoil?

1. Oct 18, 2015

### AstroSM

1. The problem statement, all variables and given/known data
I have a question about a symmetrical aerofoil at zero incidence in uniform flow. I a graph Cp against (y/c), but I don't understand why it has to be against y/c. The most negative value of m is -0.69. And h=0.38 where h is ration of maximum height to chord length c. The coefficient of the profile drag Cd is 0.3

2. Relevant equations
The question says drag coefficient is given Cd=closed loop integral { Cp d(y/c)} sorry, I can't use LaTex

3. The attempt at a solution
First I inverted the graph, because it's just confusing this way.
So what I did what I separated the graphs into four curves, and did line integral on each of them.
I let u=y/c, so it's easier to integrate with respect to u.
Curve 1: integral{ (2+2m)u/h +1 } , u from -h/2 to 0
Curve 2: integral{ -(2+2m)u/h +1 } , u from 0 to h/2
Curve 3: integral{ -4mu/h +m } , u from h/2 to h/(2+2m)
Curve 4: integral{ 4mu/h +m } , u from -h/(2+2m) to -h/2

Then I added all of them, but I didn't get the correct answer. What should I do actually?

Regards,