Ejection Baffle - To Use or Not To Use

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Roger Smith
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BTW, I don't really have a preference for using baffles or not. I don't fly low-power enough to really consider whether I should include baffles in my rockets.

But, while designing and testing a kit (which may make it to market some day) we decided to include a baffle. We were already planning to use a coupler in the rocket, so turning it into a baffle with a couple of plates won't add much cost to the kit. And the baffle will keep the parachute and rest of the recovery system higher up the rocket so not as much nose weight will be required to ensure stability.

-- Roger
 

lcorinth

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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
Oh, thank you! By the way, thanks for the free parachute in my last order!
 

Solomoriah

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I do baffles in everything BT-60 and bigger. Right now I still have a couple of Semroc baffles lying around, but I also build bypass baffles sometimes:



Just coat the lower off-centering (TM) ring with epoxy to protect it from fire and you're good.
 

BEC

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I'm in a similar spot - I prefer baffles in anything bigger than BT-55. For my PS-II birds I had custom ply discs so I could make something similar to what's in the post above for them. I hope BMS gets back in the semi-custom cutting again to facilitate making more.

My favorite baffles were the Semroc cup-shaped ones and I still have some on hand, but have begun using the coupler/perforated disc types from UMRS and JonRocket in some builds.

I've never had any clogging issues. I do shake the loose bits out after a flight if I can.
 

rharshberger

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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?

I prefer 1/8th aircraft plywood and then coat it with epoxy on the bottoms of the two lowest baffles that are exposed to the ejection charge. I build the baffle into a coupler and put a 1/4 oak dowel through the middle lengthwise to attach the screw eyes for my shock cord. Usually the screw eye has a 30lb steel fishing leader attached that reachs just above the seperation point, that way I dont have to tear the rocket apart latter to put in a new shock core I just replace the section above the body tube.

Also with the Half or 2/3rds Moon baffles I dont get junk piling up in them, and the motor mounts I always add a centering ring to the very top so it sits flush that way the red caps from my Aerotech ejection charges dont ge stuck beside the MMT tube, a little side to side shake and they fall out.
 
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HeavyBurdon

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What's the standard for baffle placement -- in other words...what is the min distance between the top of the engine mount and bottom of the baffle? Looking to put one in a 18 inch BT-60 scratch build chambered for D and E motors. I put one in my previous build (made of 2 BT-60 tubes), but I used the baffle as a coupler between the two tubes, and the rocket is lonnnnng, so I didnt worry about min placement distance.
 

rharshberger

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I'm in a similar spot - I prefer baffles in anything bigger than BT-55. For my PS-II birds I had custom ply discs so I could make something similar to what's in the post above for them. I hope BMS gets back in the semi-custom cutting again to facilitate making more.

My favorite baffles were the Semroc cup-shaped ones and I still have some on hand, but have begun using the coupler/perforated disc types from UMRS and JonRocket in some builds.

I've never had any clogging issues. I do shake the loose bits out after a flight if I can.
Bernard have you looked at the ones Qualman rocketry makes for the BT series airframes?
 

Cape Byron

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Bernard have you looked at the ones Qualman rocketry makes for the BT series airframes?
+1 on the Qualman Baffles.


I use them on scratch builds and anything that gets turned into a kit has a baffle included (BT-50 and over).

Simple, reliable and cheap. Cannot recommend them highly enough. David Qualman is also a great person to deal with.

If any of you are in Australia we have Qualman BT50, BT55 and BT60 baffles for our kits in stock. Message me!
 

neil_w

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The Qualman designs look clever but the lack of a coupler sleeve makes them look hard to glue into a tube. Also, some of them look like they have rather small vent area.
 

Cape Byron

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@neil_w, I've only used the BT50 through BT60 sizes but have never had any dramas glueing them in. similar to a motor mount, just in a different place. :)

Never had an ejection problem with them either; the crossover vent moves a lot of gas through it.

I really like the fact that all the ejection debris just shakes out after each flight. I've had probs in the past with baffles stuffed with something like a Chore Boy. They trap a lot of gubbins and are harder, for me, to keep clear.

As always, different strokes for different folks. One solution never fits all problems. ;)
 

rharshberger

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The Qualman designs look clever but the lack of a coupler sleeve makes them look hard to glue into a tube. Also, some of them look like they have rather small vent area.
They seem to work and have been around for a while, David Qualman has been a sponsor of SodBlaster since its beginning a couple of years ago.
 

BEC

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What's the standard for baffle placement -- in other words...what is the min distance between the top of the engine mount and bottom of the baffle? Looking to put one in a 18 inch BT-60 scratch build chambered for D and E motors. I put one in my previous build (made of 2 BT-60 tubes), but I used the baffle as a coupler between the two tubes, and the rocket is lonnnnng, so I didnt worry about min placement distance.
My personal rule of thumb in a situation like this is to put the baffle as high as I can while still being able to comfortably accommodate the recovery system. In practice this leads to me using a ruler to push a Semroc cup-style baffle into a BT-60 bird about 6 1/2 inches or so down from the top. This works for things like Big Bertha, QCC Explorer, Solar Warrior....basically anything that uses BT-60 at its full length or close to it.

Bernard have you looked at the ones Qualman rocketry makes for the BT series airframes?
Rich, that post was about getting custom-cut bulkheads from BMS for bypass-style baffles (see Solomoriah's post just above mine) for the original PSII builders' kits. That's still an open need since Bill Saindon doesn't do the semi-custom stuff any more and every time I ask him about it he just deflects my question. I don't think it was worth it to him to do those things.

For BT-sized I am sure I have a couple of David's baffles to hand....but I can't remember if I've used them yet. Being 1/8 inch plywood they are kind of heavy (well, at least relative to fiberboard Semroc baffles). I'm sure I'll give one a try at some point. I do like the stuff David makes.
 

rharshberger

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My personal rule of thumb in a situation like this is to put the baffle as high as I can while still being able to comfortably accommodate the recovery system. In practice this leads to me using a ruler to push a Semroc cup-style baffle into a BT-60 bird about 6 1/2 inches or so down from the top. This works for things like Big Bertha, QCC Explorer, Solar Warrior....basically anything that uses BT-60 at its full length or close to it.


Rich, that post was about getting custom-cut bulkheads from BMS for bypass-style baffles (see Solomoriah's post just above mine) for the original PSII builders' kits. That's still an open need since Bill Saindon doesn't do the semi-custom stuff any more and every time I ask him about it he just deflects my question. I don't think it was worth it to him to do those things.
I agree the non-standard size PSII tubes and the discontinuing of the kits is probably a good reason for Bill to stop offering that kind of stuff. I have heard that Bill is also a behind the scenes supplier/manufacturer for parts for other vendors kits. He also has Mercury Engineering Rockets too iirc.
 

BEC

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You used to be able to basically order any sort of centering ring or bulkhead you wanted...you had to send a 2D CAD file and he'd laser-cut it for you. He discontinued doing that when he moved to Nevada, and is less-than-enthusiastic when asked about it since then (as I have on a couple of occasions, even in person at NARAMs). Oh well.....I just need to find a maker-space with a laser that will cut 1/8 inch ply.
 

Senior Space Cadet

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I just received several baffles, in different sizes (29mm being the smallest), from Apogee. I've got one in my BT-80 build right now.
I guess I'll see which side I fall on, after some launches.
Just seemed like a clean, hassle free solution to protecting the parachute and chord, plus it gives me something solid to attach my shock chord to.
I hadn't really thought about them burning up. I might try spraying them with stove paint.
 

JoePfeiffer

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I haven't seen a reason for there to be any minimum distance between the motor and the baffle. Before I discovered Nomex I put baffles in dual deploy rockets, with the ejection charge canister inserted into the baffle itself.

So, just plan on using your baffle to manage how far your chute can shift in flight if you want, but don't worry about distance from motor.
 

beeblebrox

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I do baffles in everything BT-60 and bigger. Right now I still have a couple of Semroc baffles lying around, but I also build bypass baffles sometimes:



Just coat the lower off-centering (TM) ring with epoxy to protect it from fire and you're good.
That baffle design works perfect, I even use it BT-50 rockets...hate wadding. MY basic mod to that is to 3D print the adapter rings, making the top one a bit thicker with a hole sideways in it for the screw attaching a rail button... For small tubes, I place the inside tube and the coupler (Glued together) on a piece of wide masking tape and flood the moon shaped space where you would put a coupler with a 1/8" thick layer of 30 min epoxy instead. The below pics are for BT-55. The small tube is a LOC 1/2" launch lug. Nice and thick to withstand the abuse of ejection charges.

IMG_20190619_124508248.jpg
IMG_20190619_131809480.jpg
IMG_20190619_165031887.jpg
 

Senior Space Cadet

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If you are a perfectionist, which seems to be the case with many on this forum, you might want to cover your eyes. I was reluctant to say this before because I know it won't be popular.
What I'm doing is making an extra long body, even using two uncut tubes, since I can't seem to cut them perfect, and using an Apogee baffle as the coupler.
This accomplishes, or potentially accomplishes, a few things.
By getting the baffle away from the motor it is less likely to get burned or for the recovery system to burn.
It moves the mass forward.
You still have plenty of room for your recovery system.
If you have a chute failure and your rocket lawn darts, crumpling the end of your rocket, you have a way of fixing it.
 

Antares JS

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What I'm doing is making an extra long body, even using two uncut tubes, since I can't seem to cut them perfect,
Senior Space Cadet, I started cutting tubes for the first time when I built some Boyce models. This item I've linked is a huge help for that and it's cheap. It takes some fanangling to use with the bigger tubes, but I did use it to cut BT-80 tubes for my Gemini-Titan.

To post on topic I just don't see what the big deal is about stuffing some tissue wadding or dog barf down your tube. I have never once considered bothering with a baffle.

 

beeblebrox

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Senior Space Cadet, I started cutting tubes for the first time when I built some Boyce models. This item I've linked is a huge help for that and it's cheap. It takes some fanangling to use with the bigger tubes, but I did use it to cut BT-80 tubes for my Gemini-Titan.

To post on topic I just don't see what the big deal is about stuffing some tissue wadding or dog barf down your tube. I have never once considered bothering with a baffle.

Cut tubes the old fashioned way, with an exact knife... Wrap masking tape around the tube, about 3-4 layers. Use the edge as a guide for the knife, the trick is to not try to cut all the way through in one pass. You can get a very nice clean cut this way.
 

Antares JS

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Cut tubes the old fashioned way, with an exact knife... Wrap masking tape around the tube, about 3-4 layers. Use the edge as a guide for the knife, the trick is to not try to cut all the way through in one pass. You can get a very nice clean cut this way.
Masking tape wraps can still end up being crooked. The Kuhn tube cutter stabilizes the tube really well and ensures a square cut. Though yes, do not try to cut all the way through in one pass. I usually take three or four passes before the blade starts going all the way through.
 

o1d_dude

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I always start with a sheet of paper wrapped around the tube to be cut. Any skew or wonkiness is immediately apparent.

Mark the cut with a sharp pencil and cut s-l-o-w-l-y with a razor saw. Shallow cuts and going arounfd the tube 2-5 times will give a nice cut edge. Any irregularities can be removed with and sanding bar or a sheet of sandpaper on the the FLAT benchtop will work. Use a triangle to verify squareness.

I keep a sheet of plate glass (18”X30”) on my benchtop. Usually covered with three layers of waxed paper. Balsa and tissue modeling habits die hard.
 

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