Cannot get the plot to work

clear,clc

alt0=0;

altStep=2;

numAlt=5000;

alt=alt0:altStep:(alt0+altStep*(numAlt-1));

p=.7444;

K=.0234;

cD0=.0069;

W=1918.733*9.81;

lapse=(-6.5*10^-3);

S=12.6;

CL32OVCDmax=.25*((3/(K*(cD0^(1/3))))^.75);

Psealevel=11*10^3;

seaLevelrho = 1.225;

seaLevelTemp = 294;

RCmax=zeros;

for i=1:numAlt

altTemp = seaLevelTemp + alt(i)*lapse;

altrho = seaLevelrho*(altTemp/seaLevelTemp)^(((-9.81/lapse)/287)-1);

Palt=Psealevel*((altrho/seaLevelrho)^.7);

vMaxROC=((2/p)*(sqrt((K/(3*cD0)))*W/S))^.5;

maxROC=Palt/W-(sqrt(2*W))/(sqrt(altrho*S)*CL32OVCDmax);

end

plot(alt,maxROC,'.r')

xlabel('Altitude (m)')

ylabel('Maximum achiveable R/C')

Answer 1

[Star Strider]

Subscript ‘maxROC’ —

maxROC(i)=Palt/W-(sqrt(2*W))/(sqrt(altrho*S)*CL32OVCDmax);

The plot then appears.

The problem is that ‘maxROC’ is overwritten in the loop otherwise, so only the last value appears. MATLAB does not plot single points unless a marker is specified.

alt0=0;
altStep=2;
numAlt=5000;
alt=alt0:altStep:(alt0+altStep*(numAlt-1));
p=.7444;
K=.0234;
cD0=.0069;
W=1918.733*9.81;
lapse=(-6.5*10^-3);
S=12.6;
CL32OVCDmax=.25*((3/(K*(cD0^(1/3))))^.75);
Psealevel=11*10^3; 
seaLevelrho = 1.225; 
seaLevelTemp = 294;
RCmax=zeros;
for i=1:numAlt
    altTemp = seaLevelTemp + alt(i)*lapse;
    altrho = seaLevelrho*(altTemp/seaLevelTemp)^(((-9.81/lapse)/287)-1);
    Palt=Psealevel*((altrho/seaLevelrho)^.7);
    vMaxROC=((2/p)*(sqrt((K/(3*cD0)))*W/S))^.5;
    maxROC(i)=Palt/W-(sqrt(2*W))/(sqrt(altrho*S)*CL32OVCDmax);
end 

figure
plot(alt,maxROC,'.r')
xlabel('Altitude (m)')
ylabel('Maximum achiveable R/C')

EDIT — Corrected typographical errors.

.

Answer 2

[Askic V]

Please use " toggle code" option when posting Malab code. It looks better.

The reason you're not getting what you expect is that variable maxROC is a single double number i.e. constant and alt is an array of dimensions (1, 5000).

Perhaps this is what you want:

clear,clc
alt0=0;
altStep=2;
numAlt=5000;
alt=alt0:altStep:(alt0+altStep*(numAlt-1));
p=.7444;
K=.0234;
cD0=.0069;
W=1918.733*9.81;
lapse=(-6.5*10^-3);
S=12.6;
CL32OVCDmax=.25*((3/(K*(cD0^(1/3))))^.75);
Psealevel=11*10^3; 
seaLevelrho = 1.225; 
seaLevelTemp = 294;
RCmax=zeros;
for i=1:numAlt
    altTemp = seaLevelTemp + alt(i)*lapse;
    altrho = seaLevelrho*(altTemp/seaLevelTemp)^(((-9.81/lapse)/287)-1);
    Palt=Psealevel*((altrho/seaLevelrho)^.7);
    vMaxROC=((2/p)*(sqrt((K/(3*cD0)))*W/S))^.5;
    % make maxROC an array
    maxROC(i)=Palt/W-(sqrt(2*W))/(sqrt(altrho*S)*CL32OVCDmax);
end 
plot(alt,maxROC,'.r')
xlabel('Altitude (m)')
ylabel('Maximum achiveable R/C')

BTW, what is the point of vMaxROC and having it inside the loop especially?