why isn't my code iterating?

the problem i am having is that my velocity while loop is not ending. it just iterates forever and never changes in value for any of the parameters within the loop.

I know there is a lot of but the problem is specifically within the while loop, just wanted to add it all so all variables are known.

%problem 1

%given parameters----------------------------------------------------------

g=9.81; %m/s^2

mT0=190854;%kg

WT0=mT0*g; %N

SLG=.887; %m^2

u_roll=.023;

Sw=367.7; %m^2

CLmax=1.84;

b=50.4; %m

CDflap=.02;

CLG=.65*CLmax;

Hobst_given=50; %ft

H_obst=Hobst_given*.3048;%m <-------feet to meters

Hw=4.072; %m

CDpara=.018;

gammaCL=15;

T0=178000*3; %N

%density conversions-------------------------------------------------------

denisty1=.002106; %slugs/ft^3

density=1.085; %kg/m^3

densitysl1=.002377; %slugs/ft^3

densitysl=1.2251; %kg/m^3

sigma=density/densitysl;

%aspect ratio and effiective AR--------------------------------------------

AR=b^2/Sw;

AReff=AR*sqrt(b/(2*Hw));

%e value-------------------------------------------------------------------

e=2/(2-AReff+sqrt(4+AReff^2));

%drag coefficients---------------------------------------------------------

CD_ig=CLG^2/(pi*e*AReff);

CD0LG=((3.23*WT0)/1000)*(SLG/Sw);

%CD flap is given as .02

Cdg=CD_ig+CDflap+CDpara+CD0LG;

%a)

%ground roll for a jet-----------------------------------------------------

SG=(WT0/(sigma*Sw*CLG))*((T0/WT0)^-1)*((g*density)^-1);

%iteration for velocity----------------------------------------------------

n=1;

V(n)=0;

q(n)=.5*V(n)^2*density;

Daero(n)=Cdg*q(n)*Sw;

L(n)=CLG*q(n)*Sw;

Droll(n)=u_roll*(WT0-L(n));

Fx(n)=T0-Daero(n)-Droll(n);

ax(n)=g*(Fx(n)/WT0);

t(n)=0;

delt=.01; %sec

while V(n)<1.2*120

n=n+1;

t(n)=t(n-1)+delt;

V(n)=V(n-1)+ax(n-1)*delt;

q(n)=.5*V(n)^2*density;

Daero(n)=Cdg*q(n)*Sw;

L(n)=CLG*q(n)*Sw;

Droll(n)=u_roll*(WT0-L(n));

Fx(n)=T0-Daero(n)-Droll(n);

ax(n)=g*(Fx(n)/WT0);

end

%velocity------------------------------------------------------------------

V=V(end);

Answer 1

[Jeremy]

Your while loop is converging on a value that is less than 1.2*120.

Consider adding an additional parameter that breaks the loop when the solution has converged.

error = 1;
while V(n)<1.2*120 && error > 1e-10
    n=n+1;
    t(n)=t(n-1)+delt;
    V(n)=V(n-1)+ax(n-1)*delt;
    q(n)=.5*V(n)^2*density;
    Daero(n)=Cdg*q(n)*Sw;
    L(n)=CLG*q(n)*Sw;
    Droll(n)=u_roll*(WT0-L(n));
    Fx(n)=T0-Daero(n)-Droll(n);
    ax(n)=g*(Fx(n)/WT0);
    if n < 2
        error = 1;
    else
        error = abs(V(n) - V(n-1));
    end
end

[Jared Wheeler]

thanks!