Bottom body tube ripped during recovery deploy

[rsingh]

Please advise my rocket was ripped apart during parachute deploy. Please see the attached picture.

Is it that my bottom body tube was of poor quality?

Top was carrying EGG and altimeter, thus I have too much weight and should use more thick body tube?

 

[Art Upton]

Please advise my rocket was ripped apart during parachute deploy. Please see the attached picture.

Is it that my bottom body tube was of poor quality?

Top was carrying EGG and altimeter, thus I have too much weight and should use more thick body tube?

looks like a "Zipper" from too long of a deployment delay causing too much speed at time of chute opening.

 

[rsingh]

I used an F15-6, and the OpenRocket simulation said the parachute deploy velocity was good. What can I do next time to prevent this issue?

 

[Voyager1]

I used an F15-6, and the OpenRocket simulation said the parachute deploy velocity was good. What can I do next time to prevent this issue?

Yes, that does look like a zipper!

How accurately did you enter the model parameters into OpenRocket. Masses, surface finishes, materials, axial positions, etc, of installed objects.

Also, did you confirm that the actual measured loaded rocket total mass was similar to the simulation mass? Was your shock cord long enough? Was the recommended delay in the simulation close to the 6 second delay of the motor?

Post your simulation file for others to review.

 

[kuririn]

I used an F15-6, and the OpenRocket simulation said the parachute deploy velocity was good. What can I do next time to prevent this issue?

Did you mod the sim to take into effect the added weight of the extra hardware?
What was the optimum delay?
You can prevent zippering by several methods:
1. Swab thin CA on the end of the airframe where the shock cord contacts the tube. Sand to fit.
2. Put a foam bumper on the kevlar line in that area.
3. Use a wider shock cord where it comes into contact with that area.
4. Use elastic or nylon instead of kevlar in that area. So the kevlar leader ends BELOW the end of the tube and the shock cord connects to it.
5. Use a motor with the optimum delay for that rocket. Optimum means the ejection charge fires at or near the apogee of the motor used.
6. Any combination of the above.

 

[Wrightme43]

Did the rocket fly vertical, or fly horizontally?

Sometimes they carry alot of speed because the energy wasn't used up, going up.

Sometimes the delays run longer than expected sometimes much shorter.

Sometimes a very long shock cord can help.

Giant leap Rocketry makes a zipper preventor that is a foam ball attached to the shock cord at the tube end.

Some people CA glue the tube ends.

Was it trucking when the ejection charge went off.

I had a Aspire take off like a cruise missle, completely lost it visually, heard it eject, stretched the swivel to oval shape, shredded the streamer, and landed. It had a very long shock cord, I believe thats the only thing that saved the tube.

 

[Art Upton]

I used an F15-6, and the OpenRocket simulation said the parachute deploy velocity was good. What can I do next time to prevent this issue?

Just looking at that rocket an F15-6 seems like too long of a delay. -6 can sometimes be too long in 2.1" diameter rockets and then you added an Egg and other stuff in it. Next time use a F15-4, or a bigger punch AeroTech AP motor.

 

[Bob Yanecek]

Obviously a very high velocity deployment event.
Re-enforcing the BT will help but that means you are still experiencing high forces at ejection.
A longer shock cord with stretch (I use Kevlar with taped Z-folds to 'simulate' stretching).
If all Z-folds pull out during deployment, you need to add more length or increase the tear force for the z-folds.
Sewing the Z-folds allows for more control over the amount of force it takes to break the Z-fold.

 

[Handeman]

You didn't describe the flight profile. What happened? Did the chute eject well before apogee, at apogee, or long after apogee? How vertical was the overall flight? Straight up, weathercocked into the wind? What was the angle. What do you estimate the speed of the rocket was when the deployment occurred. You asked if your tube was poor quality, but you didn't tell us the type, manufacturer, etc. of the tube.

It's really hard to tell which of the excellent suggestion you got will help the most if we don't know what happened on the flight.

 

[AlfaBrewer]

I'm guessing this was a TARC test flight or attempted qualification flight. If so, have a chat with your mentor.

You do have a mentor, right? If not, find one close to you in the mentor directory.

 

[Hobie1dog]

I think he's still working on trying to answer all the questions we posed to him.