Rocket Question

[jy2370]

Hi, I am relatively new to rocketry, and I have done a recent launch, which I have uploaded a video of in the link below. The problem is that right after the rocket left the launch rail, it immediately turned. I used spin tabs on the rocket, so I am confused what caused this to happen. Any suggestions?

https://drive.google.com/file/d/0B34KvGCO1A6MWnlIQnpxeWRYVlU/view?usp=sharing
https://drive.google.com/file/d/0B34KvGCO1A6MRzZ2eU5ZQzJIVGc/view?usp=sharing

Thank you all for you responses!

 

[dhbarr]

At a guess, the fore button cleared the rail, the spin tabs turned the nose a bit, the aft button cleared the rail, and it then rapidly spun up.

 

[rharshberger]

How many calibers of stability did the rocket have? Looks like the rocket is "overstable" and as such weathercocked into the wind, if that is the case next time angle the rod in the direction is blowing to (with the wind, its kind of counter-intuitive) and the weather cocking will correct to a more vertical flight. Winds appear to be around 5 mph to maybe as high as 10mph.

dhbarr also has a viable scenario.

 

[markkoelsch]

Was there any wind? If so, I would say you have a classic case of what is called weather cocking.

 

[dhbarr]

I didn't guess wind only because I couldn't hear it on the mic. The correct answer is, of course, m04r flights!

 

[BuiltFromTrash]

Sounds like weather cocking. Adding spin tabs will change your cp/cg relationship a lot.

 

[Woody's Workshop]

Watched the video several times. From what I can tell, there was torque and when it cleared the rod it went in the direction of the torque.
This could have been from the spin fins, but it didn't look like to me the speed was enough to cause such torque from the fins.
I would be more inclined to say it was on the launch lugs themselves. Noticing an immediate speed increase once it left the rail.
If it has 2 launch lugs, they may not be exactly aligned, or from painting there could be excess inside the lug.
Also if the launch rod was heavily used before you, there could have been a BP build up.
This is where I would start to look, and of coarse, more launches.

 

[jy2370]

Yes, there was not much wind during the launch. Either day, I will try weighing down the bottom of the rocket for the next launch. If I look at the video closely, I can see that it turned immediately afterwards, then went relative straight. I think this may be more due to the torque problem. By the way, the launch lug was new and I launched the rocket twice with the same results, which I uploaded now. Do you have any suggestions on how to fix the torque problem?

 

[Woody's Workshop]

Not if the torque is from the spin fins.
Try it on a shorter rod, give it less time to build torque.
If it gets worse, go with a longer rod.

 

[tomsteve]

location of the LL on the rocket can cause this. too far aft and the rocket binds on the rod. rule of thumb ( for me) is to have 2/3rds of the LL ahead of the CG. personally I use 2- one at aft of BT and one at CG.
I don't think adding weight to the bottom of the rocket is necessary.

 

[jy2370]

Hi, thank you for your suggestion. We are using two rail buttons. One is above the CG and one is below. Should I get rid of one of them?

 

[rharshberger]

Hi, thank you for your suggestion. We are using two rail buttons. One is above the CG and one is below. Should I get rid of one of them?

No, you need two rail buttons, launch lugs on the other hand you can use one longer one in place of two shorter ones if necessary.