Ejection Baffle

[OldAir]

I see in some old plans that certain models include an "ejection baffle" device where you can preclude the use of wadding to protect the 'chute, etc.
These seem to be a stage coupler ring with a perforated "plate" on both ends - if I understand their function right (?) - It will spin out ejection charge particles and "dilute" the hot gases so that they cool down so that the recovery device won't melt, etc...

Is there more to it - and how would I go about making one from scratch for say a BT-70 body tube size - on a 2-motor cluster? Any critical dimensions to follow - distance from the motors, distance from first in to last out plate, hole size ratio??? Am I making this too complicated?

Thanks to all - this is a great site and your experience is greatly appreciated.. :D

[sandman]

Don't reinvent the wheel?

Just go here. On the far left side pull down "components" then click on "misc",. they are at the bottom of that page.:D

http://fliskits.com/products/01prod_fs.htm

[barone]

I see in some old plans that certain models include an "ejection baffle" device where you can preclude the use of wadding to protect the 'chute, etc.
These seem to be a stage coupler ring with a perforated "plate" on both ends - if I understand their function right (?) - It will spin out ejection charge particles and "dilute" the hot gases so that they cool down so that the recovery device won't melt, etc...

Is there more to it - and how would I go about making one from scratch for say a BT-70 body tube size - on a 2-motor cluster? Any critical dimensions to follow - distance from the motors, distance from first in to last out plate, hole size ratio??? Am I making this too complicated?

Thanks to all - this is a great site and your experience is greatly appreciated.. :D

You can also go to Semroc (http://www.semroc.com/Store/scripts/prodList.asp?idCategory=68) and get some manufactured differently. But they all serve the same purpose. What Gordon is trying to tell you, why waste your time and energy trying to manufacture something someone has already made. It most cases, you probably come out cheaper buying the kit. But, if you're like alot of us who have scraps and pieces laying about, buy a kit, see how it's put together, then build your own. :D

[snaquin]

I really like the Semroc baffles and I try to remember to order a few with every parts order I place.

Links to the ST-13 version I used in a scratch built.

http://forums.rocketshoppe.com/attachment.php?attachmentid=3372

http://forums.rocketshoppe.com/attachment.php?attachmentid=3373

.

[jflis]

Don't reinvent the wheel?

Just go here. On the far left side pull down "components" then click on "misc",. they are at the bottom of that page.:D

http://fliskits.com/products/01prod_fs.htm

Here are some direct links to the FlisKits baffle pages to help you out:

BAF-70 for the BT-70 tube (http://fliskits.com/products/components/prod_pages/baf70.htm)

BAF-60 (http://fliskits.com/products/components/prod_pages/baf60.htm)

BAF-55 (http://fliskits.com/products/components/prod_pages/baf55.htm)

BAF-50 (http://fliskits.com/products/components/prod_pages/baf50.htm)

We hope to have a BAF-20 out soon too

hope this helps!
jim

[maricopasem]

How much weight does a baffle add as compared to wadding? Is the difference negligible even in LPR rocketry?

[CPMcGraw]

How much weight does a baffle add as compared to wadding? Is the difference negligible even in LPR rocketry?

Think about the components used in a (typical) baffle -- a coupler, two thin bulkheads, and air... :rolleyes:

The baffle might weigh a fraction more than a handful of wadding, but not much more. In the case of larger-diameter models (BT-55/ST-13 and up), the overall weight might even be less, since it takes more wadding to fill the tube. Probably not enough of a weight difference to notice in reality. RockSim might tell you if the weight is measurable, but that's only if you know already how much the wadding weighs.

[snaquin]

How much weight does a baffle add as compared to wadding? Is the difference negligible even in LPR rocketry?

I popped the three components from the sheet of my Semroc EB-13 shown in the link I posted and it barely tipped my scale at just over 3 grams, unassembled. It's light weight but very strong when assembled.

I also consider a baffle a nice retro-fit item to replace an aging recovery system or to upgrade an existing recovery system to anchor kevlar to. The forward ring has a small hole already punched in it for that reason.

For the reasons Craig mentioned I would consider using a baffle even more in the case of larger-diameter models.

Last EB-13 baffle I flew in a minimum diameter scratch built had to be located a mere 6" in front of the motor tube and ejection charge from a G40 single use motor. That's about 0.7 g of black powder and it worked flawlessly. I'm pretty much sold on using a baffle in all my scratch builts as well as kits that don't include them.

.

[barone]

Another great reason for the baffle......it keeps your parachute/recovery system from sliding back into the rocket, changing the CG. Some designs don't allow for much error in CG so keeping the recovery system from sliding back keeps your rocket stable.....

Just my couple of pennies.....

[Eagle3]

FYI - Semroc just added baffles for BT-55/60/70 tubes.

[dwmzmm]

I've made simple Centuri style baffles using sturdy cardboard stock, sissors and a paper
hole puncher. Used it on my MaxiAlphax4 model (now lost), which was a four engined
(24 mm) cluster. Didn't want to waste recovery wadding in that BT-80 size bodytube.
The baffle worked perfectly for the two flights I wa able to fly before losing it at NSL - 2006
last May...

[RenegadeIV]

The attached pictures show a scratch built medium power rocket that I had put together last year with a homemade ejection baffle in it. I used a tubing coupler and some bulkheads made from aircraft plywood with 4 holes drilled in the to make the baffle. There is a bulkhead that looks the same as the one shown on the end mounted in the middle of the tubing coupler with the 4 holes rotated 90 degrees to help stop the hot particles from coming out the top. For extra measure, I installed a Chore Boy stainless steel cleaning pad (look like the ones in the Aerotech motor mount assemblies) into the gap. This design also acts as an anti-zipper baffle. I have launched this rocket on several motors up to a G and it works great every time. The main thing to keep in mind when building the baffle yourself is that you need to stop the hot particles in the ejection charge from reaching the parachutes. If you put 2-3 bulk heads with holes mis-aligned, that should trap all of the particles in the baffle, but allow the pressure to build and deploy the recovery device in the rocket.