Ejection Baffle - To Use or Not To Use

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lcorinth

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I'm building my first non-kit (it's from plans from a book, so not, I guess, scratchbuilt - maybe semi-scratch??), and I was thinking of building an ejection baffle into it. I haven't used one yet, but it's a 1.64 inch tube, 18 inches long, so it seems plenty big enough. I like the idea of not having to load up wadding each time I launch it.

Is there some kind of minimum size of rocket you'd want before considering to install a baffle? Are there reasons you would not want to have a baffle in a rocket? And when would you definitely need a baffle?

When I was building my Big Bertha, I almost considered putting one in there, but decided to stick with the instructions.
 

K'Tesh

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I'm building my first non-kit (it's from plans from a book, so not, I guess, scratchbuilt - maybe semi-scratch??), and I was thinking of building an ejection baffle into it. I haven't used one yet, but it's a 1.64 inch tube, 18 inches long, so it seems plenty big enough. I like the idea of n ot having to load up wadding each time I launch it.

Is there some kind of minimum size of rocket you'd want before considering to install a baffle? Are there reasons you would not want to have a baffle in a rocket? And when would you definitely need a baffle?

When I was building my Big Bertha, I almost considered putting one in there, but decided to stick with the instructions.
Generally speaking, in my fleet everything that is a 1.637" (BT-60) or larger gets a baffle if it has the length to allow for a gap between the top of the motor and the bottom of the baffle, as well as enough space for the laundry. As such, presuming you're not building something that uses a long 29mm motor, or a 38mm motor, you should have enough space in an 18" long BT-60 body tube.

BTW My smallest diameter rocket w/a baffle is the BT-55 (1.33") based Estes Bandit.
 
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rharshberger

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Im with K'Tesh on baffles, most of my new builds use them. I just modify a 4 inch coupler with the half-moon style disks (4 of them). So far my Mean Machine Clone does great, in the two flights so far the ejection is so low pressure (i guess thats a good way to describe it) that the 3 sheets of recovery wadding i used are still in the tube yet the laundry is depoloyed.
 

lcorinth

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Im with K'Tesh on baffles, most of my new builds use them. I just modify a 4 inch coupler with the half-moon style disks (4 of them). So far my Mean Machine Clone does great, in the two flights so far the ejection is so low pressure (i guess thats a good way to describe it) that the 3 sheets of recovery wadding i used are still in the tube yet the laundry is depoloyed.
I was thinking of building one of those. Seems like pretty simple construction.

What do you use for the halfmoons? Basswood?
 

K'Tesh

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I was thinking of building one of those. Seems like pretty simple construction.

What do you use for the halfmoons? Basswood?
1/8" thick balsa, JB Weld, CA glue, and the cardboard core of a toilet paper roll for the smaller (no tube coupler) ones (such as what you've got going). 1/8" birch ply remnants for the larger ones.



If the rocket has a tube coupler I'll try to use that instead of the TP core (unless it'd end up being right on top of the MMT). I also like to use Semroc's baffle to cap off the the assembly, and keep the shock cord (typically teabag mount) and parachute from falling too far back.
 
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g zilla

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I vote no. Used them a couple times If you want to fly high gotta step up if you are flying mid ok
 

Handeman

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I got a bale of dog barf 8 - 10 years ago and have about 3/4 left. I just bring a big pretzel container of that along and don't bother with baffles.
 

cjp

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Im with K'Tesh on baffles, most of my new builds use them. I just modify a 4 inch coupler with the half-moon style disks (4 of them). So far my Mean Machine Clone does great, in the two flights so far the ejection is so low pressure (i guess thats a good way to describe it) that the 3 sheets of recovery wadding i used are still in the tube yet the laundry is depoloyed.
With 4 half moons why would you need wadding?I use 3 half moons,no wadding and have no issues and a clean parachute.
 

cjp

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1/8" thick balsa, JB Weld, CA glue, and the cardboard core of a toilet paper roll for the smaller (no tube coupler) ones (such as what you've got going). 1/8" birch ply remnants for the larger ones.



If the rocket has a tube coupler I'll try to use that instead of the TP core (unless it'd end up being right on top of the MMT). I also like to use Semroc's baffle to cap off the the assembly, and keep the shock cord (typically teabag mount) and parachute from falling too far back.
Make sure you coat the motor side of the discs with epoxy so the wood does not burn.With this setup you can't replace the baffle after it's glued in.
 

lcorinth

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1/8" thick balsa, JB Weld, CA glue, and the cardboard core of a toilet paper roll for the smaller (no tube coupler) ones (such as what you've got going). 1/8" birch ply remnants for the larger ones.



If the rocket has a tube coupler I'll try to use that instead of the TP core (unless it'd end up being right on top of the MMT). I also like to use Semroc's baffle to cap off the the assembly, and keep the shock cord (typically teabag mount) and parachute from falling too far back.
Nice!

BTW, what is a teabag mount?

Also, I've recently bought centering rings from JonRocket.com that are made from some kind of black fiber. What is that stuff made of, and can you buy sheets of it? Is it flame retardent? Seems kind of easy to cut. I was wondering if it would make good baffle material. Using balsa makes me nervous, and basswood is hard to cut (I'd be doing this freehand with a hobby knife, as I have no idea what kind of tool I'd use to cut it otherwise - though I'd like to be able to machine cut perfect circles somehow).
 

cjp

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Nice!

BTW, what is a teabag mount?

Also, I've recently bought centering rings from JonRocket.com that are made from some kind of black fiber. What is that stuff made of, and can you buy sheets of it? Is it flame retardent? Seems kind of easy to cut. I was wondering if it would make good baffle material. Using balsa makes me nervous, and basswood is hard to cut (I'd be doing this freehand with a hobby knife, as I have no idea what kind of tool I'd use to cut it otherwise - though I'd like to be able to machine cut perfect circles somehow).
You get good results making discs out of birch plywood.I use that for centering rings and discs.I cut mine out using a wheel and circle cutter on my drill press.You could use hole saw cutters also.Those could be used in a drill press or hand held drill.Basswood is soft and does not cut well for me.With birch plywood you could use 1/8 inch thichness.That is what I also make my fins from.Balsa again is to soft.
 

K'Tesh

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A teabag mount is what Estes uses to attach the shockcord to the rocket.
 

g zilla

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Just wait after 10 or more launches that baffle can get jammed up with disks, caps,wadding and other crap and fail.
 

lcorinth

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I got a bale of dog barf 8 - 10 years ago and have about 3/4 left. I just bring a big pretzel container of that along and don't bother with baffles.
I have a bale of dog barf - I couldn't believe how cheap it was! A bale for about the same price as a packet of Estes wadding!

But I'd like to try baffles to see what they're like. I figure a simple half moon type might also be easier to shake the crap out of it after launch. I'm building a simple scratch rocket, so my first time I'm going to try it on something that's not expensive, and that I could easily rebuild if I needed to.
 

Woody's Workshop

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Has a jammed up baffle ever caused a major malfunction? Such as blown out engine mount, side of the air frame under the baffle?
I know they are a permanent mount item. This may change several rockets in the build quere.
 

gregkdc

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I will give a vote up for the baffle. I have used both dog barf and baffles and like baffles better especially in mid and high power. It kind of depends on what you like to do with your rocket, I prefer a low and slow flight over a screamer that you can't see so the added weight is not an issue. I also like the fact that once it is installed I never have to worry about dog barf while out in the field, it simplifies things just a little. I know it isn't that much but the bails of dog barf are big and messy and I would rather not deal with them. I like to use a half moon or more like a 2/3 moon for the baffles and then a disk with holes drilled in it around an eye bolt to tie the shock cord to. I make this last disk thicker and sometime reinforce it with a coupler tube above it to resist being pulled out. Let us know what you end up doing it never hurts to try, maybe you will like them.
 

gregkdc

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Has a jammed up baffle ever caused a major malfunction? Such as blown out engine mount, side of the air frame under the baffle?
I know they are a permanent mount item. This may change several rockets in the build quere.
I have never had a problem with them getting to the point they caused a problem. Yes sometimes on the smaller ones they can rattle a little from paper chunks but even then the garbage usually finds it way out.
 

Woody's Workshop

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I'll say one thing for baffles, it's a "Greener" end result from not having dog barf or other materials left behind.
I've never used dog barf, but I know Estes Recovery Wading comes down glowing red and may start fires.
 

Micromeister

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I'll say one thing for baffles, it's a "Greener" end result from not having dog barf or other materials left behind.
I've never used dog barf, but I know Estes Recovery Wading comes down glowing red and may start fires.
Woody:
Have to disagree with both of your above statements.
First and foremost: Dogbarf (blow in insulation) it TOTALLY biodegradable outdoors. It's even SAFE around Livestock.

Second: Estes flameproof wadding may show signs of ignition while falling though the air, but the solution the stuff is soaked in is self-extinguishing. You might see on occasion tiny bit of red as the wadding is returning through the air but the second the airflow stops so does the charring. In more then 45 years of flying with large groups to individually, I have never seen or heard of a single grass fire being started by the use of Flameproof wadding even in the driest of Grass conditions. Estes FP wadding is also totally biodegradable.
I have seen several numbskulls use ordinary untreated Toilet Tissue as wadding that HAS caused a few concerns.

Personally I'm not a big fan of baffles as they wear out far too soon for my liking. I do use them occasionally but for the most part still use a combination of FP tissue and Dog Barf in my LPR and MPR models.
 
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Micromeister

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Has a jammed up baffle ever caused a major malfunction? Such as blown out engine mount, side of the air frame under the baffle?
I know they are a permanent mount item. This may change several rockets in the build quere.
You bet they have:
There are several different types of Baffle builds out there a few use copper or stainless scrubbing pads as the filtering element. These scrubbies fill up with cap clay and other debris very quickly. If not replaced regularly or are forgotten to be cleaned out they will cause NO Deploy conditions that will end the flying life of the model.
even the simple 2 or three layer off-set hole baffle catches and hold Trash from previous flights. most of the time this can be shaken out but if left to collect can also clog the ports with the same result as the scrubbie described above.

My big objection is whatever style or method of construction the super hot gases and motor After burn Flame (that can reach 4-6inches long) erode the baffle plates and eventually fail damaging the recovery system and/or make the use of standard ejection wadding necessary for it's next flight or scrapping the model.

I think most everyone should try at least one Baffled model just so you can see what the differences are and how long the model will last. I'm still flying rockets build back in the early 70's without baffles. Every single ejection baffled model I've every had lasted no more the 10-15 flights. There is a very good reason the ejection baffle is not a universal standard building practice.
 
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matthewdlaudato

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I would suggest making the baffle modular and thus removable. In a small rocket, 2 2-56 nylon or metal screws into the bulkhead, or even right into the cardboard coupler will do it. That way you can clean or replace as needed.
 

lcorinth

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I would suggest making the baffle modular and thus removable. In a small rocket, 2 2-56 nylon or metal screws into the bulkhead, or even right into the cardboard coupler will do it. That way you can clean or replace as needed.
How do you actually get to it to remove it? Do you have any photos? Because I'm having trouble picturing how I'd get it out of there.
 

K'Tesh

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How do you actually get to it to remove it? Do you have any photos? Because I'm having trouble picturing how I'd get it out of there.
I discovered how to make one of my baffles removable with my PSII 2.5" Cherokee D upscale, use a rail button to anchor it in place. Remove the rail button, and it comes out.


unfinished baffle showing how I mount the t-nut inside the coupler

I mount a t-nut to a piece of scrap 1/8" aircraft ply (and a layer of balsa over that), sand the curve into the balsa and glue it inside the coupler. With the screw in place, the coupler seems to be pretty stable, and if I ever need to remove it (say inspecting for flame erosion), all I have to do is unscrew it.
 
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matthewdlaudato

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How do you actually get to it to remove it? Do you have any photos? Because I'm having trouble picturing how I'd get it out of there.
See for example:

http://www.rocketryforum.com/showthread.php?t=69837

This build of mine didn't use it as a baffle, but the short answer to your question is, tug on the Kevlar cord; or, push a dowel up through the motor mount, or, hook a bent coat hanger wire through one of the baffle holes.
 
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Woody's Workshop

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If it was me, and I have a rocket in the build process that I installed a Sunward Baffle Kit, I'd cut the body tube just above and below the baffle and put in a coupler.
You'd loose a few inchs and need a repaint & decals if in that area.
But that's just me. I've got a few rockets shorter than should be due to crinkles, zipper, etc.
But they still fly!
 

matthewdlaudato

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I like WW's idea - we use couplers all the time to turn basic birds into DD, using the coupler to mount a baffle could work nicely.
 

o1d_dude

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Not a fan of baffles although I know they can be useful in preventing body tube zippers and burnt parchutes.

Just something about being able to look down the open end of the body tube and see daylight through the motor tube. It's all great for pushing out seized motor cases.

The removable baffle idea is worth further study.
 

jadebox

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Also, I've recently bought centering rings from JonRocket.com that are made from some kind of black fiber. What is that stuff made of, and can you buy sheets of it? Is it flame retardent?
The material is a fiberboard marketed as "art board." Artists use it as a backing for various kinds of projects. It makes for stiffer, stronger centering rings than the coated cardboard that Estes uses for most of their centering rings. You buy sheets at craft and art stores.

It's not treated to be fire resistant or flame retardant, but it doesn't burn very easily. We use it for the baffle plates in our smaller-size baffles and it probably would work okay for larger diameter baffles.

-- Roger
jonrocket.com LLC
 
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