What effect do the walls of the tunnel have on tests like these? I recall that the NACA* guys had some way to compensate when testing airfoils, but I don't know what it was. *Before NASA. Lots of great info dug up by them.
Yes, the stability test must be done with the rocket in the launch configuration. The fuel in the rocket motor adds weight to the back of the rocket and will move the CG aft - making the rocket less stable. You want to make sure the rocket is stable in the "worst case" configuration...
For a model rocket the fuel tends to be at the back of the rocket. As the fuel is burned the back end of the rocket gets lighter. This causes the CG of the rocket to move forward. The CP stays constant, and since the CG is moving forward during the burn the stability of the rocket increases (i.e. more distance between the CP and CG). This might not be the case for a liquid fueled rocket since the fuel load may be more towards the center or front of the rocket. It al depends on there the fuel is located.
Do you really want it to fly into the wind? Or have a rocket that will fly straight up? I thought having a rocket that can lay perfectly sideways in the wind tunnel is best.
There is no precise answer to your question. If the rocket flies "straight up" is will actually drift with the wind and thus not stay directly overhead. If the rocket weather cocks into the wind, it can actually compensate for the wind drift affect - i.e. fly into the wind then drift back. An unguided rocket needs to have some stability (a.k.a. static margin), usually between 1 and 2 calibers (a.k.a. body diameters). This means rocket will tend to point into the wind to some degree due to its stability. A neutrally stable rocket wont weather cock, but it will also likely become unstable as it hits wind layers. You want to avoid rockets that are over-stable, because they will really point into the wind which is also undesirable. Also, from a safety perspective you don't want your rockets to fly straight up, because what goes up will come down. If you have a recovery system problem you could have a hazardous dart coning down. I have seen this at more than one high-power rocketry meet and luckily no one got hit (but there have been close calls...). Hope this helps.
No. The center of pressure depends on the fins and aerodynamics, etc. The center of mass will change if you add weights, however, which can impact the stability of the rocket. Hope this helped :D
Outstanding analysis and video quality ! Your serious about this hobby, terrific explanation 😊
Nice video! I'd love to see more about your wind tunnel and how it's built. Any chance you could give us a video tour?
Man your explanation is OP
Very good explanation
Getting back into rocketry and enjoying your video. A question. How did you change the CG for the tests? Clay in a hole, Water with a plug?
Agree with another viewer's request to see and understand how the wind tunnel works ?
This was a great video 👍please keep them coming
What effect do the walls of the tunnel have on tests like these? I recall that the NACA* guys had some way to compensate when testing airfoils, but I don't know what it was.
*Before NASA. Lots of great info dug up by them.
Do we have to do the final rocket stability test with the rocket motor and parachute in place?
Yes, the stability test must be done with the rocket in the launch configuration. The fuel in the rocket motor adds weight to the back of the rocket and will move the CG aft - making the rocket less stable. You want to make sure the rocket is stable in the "worst case" configuration...
Does this software compute the stability with the motor, too?
sir i have a question after burning the full in the rocket where CG
For a model rocket the fuel tends to be at the back of the rocket. As the fuel is burned the back end of the rocket gets lighter. This causes the CG of the rocket to move forward. The CP stays constant, and since the CG is moving forward during the burn the stability of the rocket increases (i.e. more distance between the CP and CG). This might not be the case for a liquid fueled rocket since the fuel load may be more towards the center or front of the rocket. It al depends on there the fuel is located.
Do you really want it to fly into the wind? Or have a rocket that will fly straight up? I thought having a rocket that can lay perfectly sideways in the wind tunnel is best.
There is no precise answer to your question. If the rocket flies "straight up" is will actually drift with the wind and thus not stay directly overhead. If the rocket weather cocks into the wind, it can actually compensate for the wind drift affect - i.e. fly into the wind then drift back. An unguided rocket needs to have some stability (a.k.a. static margin), usually between 1 and 2 calibers (a.k.a. body diameters). This means rocket will tend to point into the wind to some degree due to its stability. A neutrally stable rocket wont weather cock, but it will also likely become unstable as it hits wind layers. You want to avoid rockets that are over-stable, because they will really point into the wind which is also undesirable. Also, from a safety perspective you don't want your rockets to fly straight up, because what goes up will come down. If you have a recovery system problem you could have a hazardous dart coning down. I have seen this at more than one high-power rocketry meet and luckily no one got hit (but there have been close calls...). Hope this helps.
what is the software is called.
As mentioned on the video, the software is known as OpenRocket. Do an internet search and you should find the download site.
The center of pressure will change if i ad weights ?
No. The center of pressure depends on the fins and aerodynamics, etc. The center of mass will change if you add weights, however, which can impact the stability of the rocket. Hope this helped :D
@@user-tk8cz3ry8l شكرا 😀