I have trouble getting MATLAB to increase altitude or plot tail height upward when I use a positive number. I have to use a negative number. Why is this???

Code:

pn=0;
pe=0;
pd=0;
phi=0;
theta=0;
psi=0;
handle=[];
%Simulation parameters
dpn=0.5; %Change in position.
dpsi=0.01; %Change in yaw angle.
simlength=150;%Number of Sim Steps
%Draw and update the plane's position.
for k = 1:simlength
    pn = pn+dpn;
    pe = pe+dpn;
    %THE CODE THAT PRODUCES A PROBLEM IS BELOW
    pd = pd - 0.1;

There's also a problem with the tail fin. I have to designate it as being oriented "downward"...in the negative direction, to produce a vertical tail oriented upward. This is similar to the increment for the vertical height scale above, being increased with a negative number.

[Pat Gipper]

That is because a positive pitch always causes the tail of the plane to drop relative to the nose.

Answer 1

[Pat Gipper]

The NED (North East Down) coordinate system is positive in the plane crashing direction. That's why it is good to use a negative dpd to avoid a descent. The Roll-Pitch-Yaw (phi theta psi) system is shown in the figure below, with credits to the citation shown. Positive change in the pitch angle (theta) have a standard change in the orientation of the plane to bring the nose up. Note that NED zero position is located at the nose of your aircraft as opposed to the typical center of gravity of an airplane that might be about mid-wing. As a result, when you pitch up then the entire aircraft will drop below the nose, very unusual.

E., J.R. (2016). Runway detection from map, video and aircraft navigational data. 10.13140/RG.2.2.26415.79525.