I have issues calculating lift coefficient (CL), drag coefficient (CD), and thrust (T)

Hello everyone,

I am having some issues with my MATLAB code for calculating lift coefficient (CL), drag coefficient (CD), and thrust (T). The values I am getting are not close to the ones that my professor calculated by hand for CL (0.76 0.74 0.69 0.61 0.54 0.49 0.47 0.49 0.54 0.61 0.69 0.74 0.76), and I am not sure where the issue might be. Additionally, the graphs for CL, CD, and T do not look like they should. I have included my code below for reference. Can anyone help me figure out what might be causing the discrepancies?

clc;
clear;
close all;
syms CL CD T CDzero K gamma V R g m rho S
V = 202;
R = 1000;
g = 9.8;
rho = 1.058;
S = 24;
m = 7800;
gamma = [0 30 60 90 120 150 180 210 240 270 300 330 360];

%Initialize vectors for CL, CD, and T
CL_vector = zeros(size(gamma));
CD_vector = zeros(size(gamma));
T_vector = zeros(size(gamma));

%Calculate CL, CD, and T for each gamma value
for i = 1:length(gamma)
    %Calculate CL
    CL = (2*cosd(gamma(i)) + (V^2/(R*g))*m*g)/(rho*V^2*S);

    CL_vector(i) = CL;
    
    %Calculate CD
    CDzero = 0.02;
    K = 0.05;
    CD = CDzero + K*CL^2;
    CD_vector(i) = CD;
    
    %Calculate T
    T = m*g*sin(gamma(i)) + (rho*V^2*S*CD)/2;
    T_vector(i) = T;
end

%Plot graphs
figure;
plot(gamma,CL_vector);
xlabel('gamma');
ylabel('CL');
grid on;

figure;
plot(gamma,CD_vector);
xlabel('gamma');
ylabel('CD');
grid on;

figure;
plot(gamma,T_vector);
xlabel('gamma');
ylabel('T');
grid on;

disp(CL_vector)

    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072    0.3072

Thank you in advance!

Answer 1

[VBBV]

clc;
clear;
close all;
% syms CL CD T CDzero K gamma V R g m rho S
V = 202;
R = 1000;
g = 9.8;
rho = 1.058;
S = 24;
m = 7800;
gamma = [0 30 60 90 120 150 180 210 240 270 300 330 360];
CDzero = 0.02;
K = 0.05;

%Initialize vectors for CL, CD, and T
CL_vector = zeros(size(gamma));
CD_vector = zeros(size(gamma));
T_vector = zeros(size(gamma));

%Calculate CL, CD, and T for each gamma value
for i = 1:length(gamma)
    %Calculate CL
    CL = 2*(m*g*cosd(gamma(i)) + (m*V^2/(R*g))*g)/(rho*V^2*S);

    CL_vector(i) = CL;
    
    %Calculate CD
   
    CD = CDzero + K*CL^2;
    CD_vector(i) = CD;
    
    %Calculate T
    T = m*g*sind(gamma(i)) + (rho*V^2*S*CD)/2;
    T_vector(i) = T;
end

%Plot graphs
figure;
plot(gamma,CL_vector);
xlabel('gamma');
ylabel('CL');
grid on;

figure;
plot(gamma,CD_vector);
xlabel('gamma');
ylabel('CD');
grid on;

figure;
plot(gamma,T_vector);
xlabel('gamma');
ylabel('T');
grid on;

disp(CL_vector)

    0.7619    0.7422    0.6881    0.6144    0.5406    0.4866    0.4668    0.4866    0.5406    0.6144    0.6881    0.7422    0.7619

[VBBV]

CL = 2*(m*g*cosd(gamma(i)) + (m*V^2/(R*g))*g)/(rho*V^2*S);  % the parenthesis was not placed correctly

the parenthesis was not placed correctly, additionally the equation also seems to be slightly incorrect, where the mass term is not multiplied in the numerator for calculating lift force term. Also, the below line

 T = m*g*sind(gamma(i)) + (rho*V^2*S*CD)/2;

seems to be incorrect where the sind needs to be used instead of sin

[VBBV]

can you attach the graphs how they look like ?

[Agache Mihai]

Thanks a lot!!

[Othman Jasim]

Hello sir What’s that (i) terms for?