Baffle blowout

[Zeus-cat]

I installed a Semroc BT-60 baffle in a Semroc Vega kit. I extensively modified the kit externally, but the baffle was the only internal change to the stock kit. The bottom of the baffle was about 11.75 inches from the top of the motor. I made 5 launches using Estes B6 and C6 motors. On the fifth launch the baffle completely blew out. I didn't notice the damage until I got home.

Here are two photos. The first is what is left of the baffle. The second is a heavily cropped photo of the rocket shortly after ejection. In the upper right corner you can see the cone portion of the baffle floating away.

I don't have a lot of experience with baffles, but having a baffle blow out after 5 launches doesn't seem right. I built the baffle according to the instructions. Do you think I just had a very aggresive ejection charge that blew out the baffle?

 

[jj94]

How well did you glue the components together?

And by the way, I love the way you laid out the wood for the Vega's finish.

 

[Zeus-cat]

jj94,

I glued the baffle together using yellow glue. It should have been very strong. I ran a Kevlar shock cord up through the holes, but it did not tie off to the baffle so there should have been no strain from that.

I call the rocket Ye Olde Amish Rocket. I designed it as if the Amish built a rocket to go to the moon. The launch lug is the outhouse that hangs off the side of the rocket. Opposite the outhouse is the door. If I ever get around to it I would like to add some decals. One decal that I will post next to the outhouse is "Thou must bring thine own recovery wadding."

 

[sylvie369]

I call the rocket Ye Olde Amish Rocket. I designed it as if the Amish built a rocket to go to the moon.

You'll enjoy the rocket in this photo, then:

https://www.collegefund.org/news/thinkindian_dan.html

and my attachment.

It was built by a group at the College of the Menominee Nation for a collegiate rocketry contest here, using almost entirely recycled natural parts. That's leather you see holding on the nose cone, and a woodburned design in the side. There are some non-natural parts where necessary, notably the camera in the nose cone, but very few.

Dan flew it about three years ago, on a K550, successfully. I'm told that it's currently on display at the Smithsonian.

 

[chanstevens]

That looks very much like glue joint failure, since most of the upper and lower plates are intact. I think the fact that you allow the baffle to slide in/out freely rather than glue it in the body tube will also contribute to this, since you've got a little rubbing going on against the outer seam.

One construction tip--glue the aft plate on first, and then circle back with a decent fillet on the internal seam. After that's dried, flip it over and glue on the forward plate. The forward plate won't tend to take much stress, as it's getting pushed back on as it slides out, but the aft plate is the one that wants to come apart during deployment.

 

[MarkII]

I always use slow-curing epoxy to assemble baffles and to glue them into the rocket. I also put a thin coat of epoxy over all of the surfaces of the baffle to help extend its life. No baffle is immortal; they all give out eventually. Another good idea is to add a section of tube coupler between the top and bottom plates in order to completely enclose the baffle's interior, and to add a section of coupler tubing to cover either all or at least the first several inches of the inner wall of the airframe above the motor mount. The reason for adding these liners is that the baffle traps and holds the burning particles from the ejection charge rather than allowing them to be blown up and out of the rocket. Those particles remain permanently inside the rocket and they continue to burn for awhile after ejection until they eventually burn out. Adding couplers as tube liners provides some extra protection against burn-through of the airframe walls within the baffle and just above the motor mount. I don't know what anyone else experiences, but whenever I retrieve my baffle-equipped rockets after they have flown, I find that the section of the airframe that is contiguous with the baffle is extraordinarily HOT to the touch and it stays that way for a worrisome length of time. The motor casing often cools down faster than that section of the rocket. I can only imagine what is happening to the inner wall of the body tube during that interval.

MarkII

 

[DAllen]

Do you think I just had a very aggresive ejection charge that blew out the baffle?

Could be. I've noticed that some Estes motors seem to have more pop (sometimes KAH-BOOM) than others. This is why I have never installed baffles. I find the lure of baffles baffling.

If you are worried about frying your recovery gear buy a nomex chute protector and a $7 bag of cellulose insulation - a.k.a. dog barf. Use lots of dog barf. Easy to clean up and when you consider just how long that bag is going to last the cost per flight is waaaaay less than a penny.

-Dave

 

[Zeus-cat]

Could be. I've noticed that some Estes motors seem to have more pop (sometimes KAH-BOOM) than others. This is why I have never installed baffles. I find the lure of baffles baffling.

If you are worried about frying your recovery gear buy a nomex chute protector and a $7 bag of cellulose insulation - a.k.a. dog barf. Use lots of dog barf. Easy to clean up and when you consider just how long that bag is going to last the cost per flight is waaaaay less than a penny.

-Dave

I have played with both the baffles and the Nomex sheets. I do like the Nomex and don't think I will be getting any more baffles.

 

[MarkII]

I have never gotten even as much as a soot mark on the chutes that I have used in any of my baffle-equipped rockets, and I have never needed to augment any baffle with dog barf, wadding or a chute protector. Baffles do indeed work. None of my baffles have ever blown out, either. As I mentioned before, I always use epoxy for their construction and installation. Yes, it is true that baffles are not appropriate for every rocket, and yes, they will eventually wear out. Whether a baffle wears out after 20 flights or after 220 flights depends to a great extent on how well it has been assembled and how well it has been installed. (I'm sure that the size probably makes a difference, too. All other things being equal, large diameter baffles probably outlast small diameter units.) There are ways, though, to make a baffle removable for service or replacement.

MarkII

 

[talkin Monkey]

Maybe use JB Weld at permanent adhesion points?