# MATLAB Drag Calculation from Matlab

1. Sep 22, 2011

### Thusithatck

I am trying to estimate the Thrust and Torque generated by a propeller blade by utilising the Blade Element Theory. I was able to get Lift but not Drag. Below is the code generated by Matlab.

The calculation procedure is,

T1 = twist pitch ratio
RTheta = root pitch angle
Phi = atan(V/(Omega*r))
ro = 1.225 (density)
C = 0.15 m
Cdo = 0.008 (zero lift drag)

Alpha = RTheta + T1*r - Phi

Here the twist is negative which makes the tip to have a small pitch angle.

for i = 1:3:132 % Forward Speed of the A/C
for j = 1:3:39 % rps (rpm/60)

syms r

omega(j) = 2*pi*j;
W2(i,j) = i^2 + (omega(j)*r)^2;
CD(i,j) = Cdo + K*(a*Alpha(i,j))^2;

W2CD(i,j) = expand (W2(i,j)*CD(i,j));

Drag(i,j) = double(0.5*ro*Cr*int(W2CD(i,j),r,Hr,D/2));
end
end

As the calculation is run, I always gets a message saying below details,

??? Error using ==> sym.maple at 87
Error, (in IntegrationTools:-Utils:-Simplify) too many levels of recursion

Error in ==> sym.int at 51
r = reshape(maple('map','int',f(:),[x.s '=(' a.s ')..(' b.s ')']),size(f));

Error in ==> New at 74
Drag(i,j) = double(0.5*ro*Cr*int(W2CD(i,j),r,Hr,D/2));

I would like to know how to get the drag values. I have tried every possible method, but I still get this message.

Furthermore, independent to the above question, is it OK to get the real part of a complex number to calculations?

Say if,

R = 2*D

where,
D = 0.45 + 09i

and if you take only the real number then,

R = 0.90

Is it correct? or possible? if so or not, is there is an exception where you can take R=0.90?