OPENROCKET Ground Track Chart

[SuperMoonFire]

Hello guys,

I am currently participating in a project of a hyper-sonic hybrid rocket launch, and I have been given an assignment to estimate the approximation of the rocket's flight trajectory. I have chosen the OpenRocket soft, however, I have encouterd some misunderstandings of the output results.

I am kinda new to this programm, so I have decided to write here, as I did not find any posts related.

Environmental influence on the flight trajectory is the key feature in my research, so I had all of the info on the wind, coordinates and rod orientation filled out, however, and this is what botheres me, when the wind is stated to blow directly from the South direction the output graph in the Ground Track preset shows slight movement of a rocket (apparently just by ~2 metres) to the side. Apart from that, the lateral distance, velocities etc. seems fine.

I have no idea how to interpret those results.

There is another thing may be or not linked to the previous one: I can not allign the launching rod with respect to the wind, or I simply don't understand the relativness algorithm. If someone could explain to me, how to properly adjust the direction of the launch rod, he have my deep gratitude

I enclose the pics of the graph, the options screen and the rocket itself to the thread. If any additional info would be needed, feel free to ask:2::blush:

 

[Buckeye]

The documentation covers the launch rod alignment in detail. See if that helps. I usually don't mess with it.

As for the small side movement, I agree. Even with NO wind and NO launch angle, the rocket will drift to the side a couple meters. Either this is some advanced 6 DOF rocket aerodynamics that I don't understand, there are numerical round off errors during the time stepping, or it is a bug. RockSim and RASAero don't display this behavior.

 

[SuperMoonFire]

The documentation covers the launch rod alignment in detail. See if that helps. I usually don't mess with it.

As for the small side movement, I agree. Even with NO wind and NO launch angle, the rocket will drift to the side a couple meters. Either this is some advanced 6 DOF rocket aerodynamics that I don't understand, there are numerical round off errors during the time stepping, or it is a bug. RockSim and RASAero don't display this behavior.

Thanks for your reply!

I guess I will state it as a software bias, however, what would you propose to do, if I have to state the direction of the launch that differs with the direction of the blowing wind? Would this bias affect the calculation of the resultant trajectory?

The bias is not much, though, but the speed of the rocket is very high, so in the case of the side wind the deviation could be dangerous.

 

[duckhead]

From the Open Rocket release notes of November 2011 (version 1.1.9):
For this version Richard Graham has implemented geodetic computation methods, which take into account the curvature of the Earth and the coriolis effect. The computation method is selected by the Geodetic calculations option in the simulation options. It's not (yet) a full spherical computation model, but should be accurate enough for almost all sub-orbital needs.

Is it possible the slight drift you are seeing is due to the coriolis effect in the simulation?

 

[SpaceManMat]

I have no idea how to interpret those results.

It is less then 3m west compared to 3.25km north. Ignore it, by comparison it is nothing but noise (less than .1%)

Imagine driving over 3km and then complaining that your rocket has come down to the right of your car not the left where you thought it should. The graph is exaggerating the westerly movement, if you set the x and y coordinates to the same scale then it would look like a dead straight line.