Homemade ejection baffles

[CatServant]

Is there a rule of thumb for the total area of baffle plate holes? I have a laser cutter and would like to start making my own baffles but I want to make sure there’s enough airflow to provide sufficient pressure for a successful parachute deployment. I’m already assuming that total area in must be less than or equal to total area out.

 

[86mustang408w]

Yes an no. You can get pretty creative especially if you have a laser cutter. I started making some years ago but never finished them. I bought couplers, and wood to make by "hand". But it would be the equal amount of holes in one as the other. But you could do a few more smaller holes in the aft piece, then bigger but less holes in the forward pc. They are just staggered so they don't line up. I'm hoping to get a laser cutter soon. I could dig up some info? I'm going to be making them also again for certain BT sizes and hopefully by this fall after that cutter gets here. What sizes are you making?

 

[SolarYellow]

The "half moon" style is well proven. On that basis, half the body tube cross section being open should be adequate, although flow is restricted with many smaller holes vs. one large one. Another reasonable rule of thumb (at least for BP motors) is to have as much open cross section as the ID of the motor casing.

Either way, the focus should be on the "labyrinth" effect rather than reducing the area. Make the stuff change direction at least a couple times.

 

[CatServant]

What sizes are you making?

Just BT-80 for now. Yes, I have a laser cutter. I’m putting the baffle in a Super Big Bertha.

 

[86mustang408w]

Ok, awesome. I have one too that has a baffle in it. I got it from Rocketarium years back. I'm actually working on it right now, heres the top of that one. The bottom of the coupler and the aft baffle, the holes are around the outer diameter and there's about 10 or so. They are the same size(diameter hole) as these tops ones. I might add a few holes as I'm going from a D motor to 29mm composites. The ejection charge might be too much for the baffle setup like that. It flies and ejects on the 24mm fine. It may be fine but its on my mind, and mines extended which gives it a little extra room. Ill try to get a picture of the bottom if you like I have one somewhere. Every baffle is different depending on the rocket and body tube size. Some guys will make chute stops too, like like a half moon shape and its a little odd looking but it works. Ill have some more here shortly as Rocketyworks is making a ejection baffle his way for another project I have going. So that should be Interesting to see.

 

[CatServant]

I also added a stainless steel scrubber (half of one actually) to really stop the hot particles.

 

[86mustang408w]

I also added a stainless steel scrubber (half of one actually) to really stop the hot particles.

Cool man! You can get pretty creative with these, in many areas. That's what I love about this Hobby..

 

[ep29030]

There are lots of variations on baffles that work well. I’ve used a half dozen different designs that all work. Anything that prevents the flame front from directly reaching the recovery train works. Of course, I still suggest a small amount of wadding or a nomex pad as a backup.

 

[shanejohnson2002]

I got a cheap laser cutter not too long ago, and ejection baffles are one of the main things I cut with it. What I've found is, while there's no hard/fast 'rule of thumb' to dictate the design, there are basically 2 limiting factors:

1) The amount of resistance it creates inside the tube needs to be minimized.

Too much resistance is bad for a multitude of reasons, but the simplest are that it's less rearward force on the motor / less stress on the retention, and it allows the ejecta to leave the body tube more quickly, which cools it off more quickly, and reduces the likelihood of burnt/torched/damaged body tubes, shock cords, laundry, etc.

2) The ability of the baffle to redirect the hot particles so they are not impacting the parachute directly.

What I've found is that a simple zig-zag design is usually the easiest. On higher-powered rockets, I add a small brace across the center of the open area to allow for some strength. My strongest design yet is on my 38mm 3" Crossfire ISX upscale....it's simple zig-zag plates with 1/4" holes in the middle, with a 1/4" x 3" eye bolt through the center of them all. Each plate is actually 2 1/8" pieces glued together to make 1/4" pieces.

Side note, I always treat the side of the baffles that face the ejection charge with a thin layer of JB weld. Might be overkill but it makes me feel better.

 

[Sooner Boomer]

Sounds good. Here's what I did. Similar idea. Made to fit inside a BT-80 coupler.

 

[Jimbooregon]

Sounds good. Here's what I did. Similar idea. Made to fit inside a BT-80 coupler.

View attachment 602568

View attachment 602569

Nice simple design! I like it.