Baffle Unit Build Thread

I wanted to try to build a better baffle. I like them because they do help to trap the larger ejection debris that can wreak havoc on the recovery system. But on this one I wanted to integrate the recovery system anchor along with this.

The design criteria was primarily centered on making it 1) heat durable, 2) shock-load durable, and 3) relative light.

The parts are relatively simple. A coupler of 2.31/32" length for a 2.60" airframe (I think I got it from Uncle Mike's Rocket Shack), 3 x 1/8" thick plywood bulkplates (Hobby Lobby), and 6 x 0.65" wooden dowels (Home Depot). The 3 dowels will serve as column between the bulkplates, with each bulkplate having 3 pockets (a depth of only 0.0125") each to make locating them a bit easier.

A 1/8" line of braided Kevlar, about 12" in length" will be placed 180 degrees from each other and anchored to the sides of the coupler with laminating epoxy and ~6 oz fiberglass. I plan to use Aeropoxy adhesive for the remainder of the joins and avoid the 5-minute stuff, mostly because I wanted a bit more working time. I am hoping for an assembly time of about 30 minutes to an hour.



Greg

Very cool Greg. I used the poor man's approach in my Partizon:



The holes are near the outer edge, the hot materials tend to hit the center and get blocked, and the gasses make their way through the holes - works well but I still use a blanket around the chute. Looking forward to your finished result.

GregGleason said:

I wanted to try to build a better baffle. I like them because they do help to trap the larger ejection debris that can wreak havoc on the recovery system. But on this one I wanted to integrate the recovery system anchor along with this.

The design criteria was primarily centered on making it 1) heat durable, 2) shock-load durable, and 3) relative light.

The parts are relatively simple. A coupler of 2.31/32" length for a 2.60" airframe (I think I got it from Uncle Mike's Rocket Shack), 3 x 1/8" thick plywood bulkplates (Hobby Lobby), and 6 x 0.65" wooden dowels (Home Depot). The 3 dowels will serve as column between the bulkplates, with each bulkplate having 3 pockets (a depth of only 0.0125") each to make locating them a bit easier.

A 1/8" line of braided Kevlar, about 12" in length" will be placed 180 degrees from each other and anchored to the sides of the coupler with laminating epoxy and ~6 oz fiberglass. I plan to use Aeropoxy adhesive for the remainder of the joins and avoid the 5-minute stuff, mostly because I wanted a bit more working time. I am hoping for an assembly time of about 30 minutes to an hour.

View attachment 185833

Greg

Click to expand...

Greg:
Very Nicely cut plywood pieces
One of the main reasons I do not use baffles more often is primarily because the Ware (burn-out) way to quickly. The first couple I build I did exactly what your doing 1/8" birch Plywood baffle plates inside a 2.6 (BT-80) coupling. Coated actually Double coated with Good quality 30minute epoxy. Coated EVERYTHING including the inside of the couplers after each baffle plate was installed. I used this particular baffle in an Upscale 3-D12 Clustered model. I believe my flight log shows it lasted 7 flights. SEVEN Flights before the core was burned completely thru requiring either replacing or switching back to Wadding. I chose wadding.
My next Baffle was in a smaller BT-60 model flying with a single D12. This time I not only Epoxy coated everything but also installed a double layer of thick Aluminum Duct sealing metal tape to the exposed aft end of each plate. This Baffle lasted a good bit longer 15 flights. but still burned thru both Aluminum and epoxy.
That's when I started digging into what our BP Motor after burns actually looked like. I was shocked to find my beloved D12's produce an After propellant burning jet of FLAME for Over 2 seconds with Some Test motors even longer. It's no wonder our Epoxy and poor old aluminum metal tape didn't stand up longer.

I said Self; lets look for a stainless steel Thin Sheet or tape that can handle more heat.
What I've found are two things. I either cut 26ga (.018") 304 stainless steel sheet discs or two layers of 2" wide .002" adhesive backed Stainless steel tape set in and coated with 30minute epoxy. So far they are holding up to the heat and flames from my 2 to 5 motor D12 clustered models well.

As for the Shock-cord Anchor; I've gone to using a series of different multi stranded Stainless Steel wire rope or Stainless Fishing leaders to move the Kevlar (Kevlar degrades every time it's subjected to temps 900°f and above) at least a foot to 18" above the motor mount. Since making that change I haven't lost a Shock-Cord on my standard or Larger models
Hope these suggestions help a little.

matthewdlaudato said:

Very cool Greg. I used the poor man's approach in my Partizon:

Click to expand...

Thanks.

Have you flown it yet? If so, did it work ok?

Micromeister said:

Greg:
Very Nicely cut plywood pieces
One of the main reasons I do not use baffles more often is primarily because the Ware (burn-out) way to quickly ...

Click to expand...

John, I might try that.

Out of curiosity, what was the distance between the bottom end of your baffle and the tops of your motor mounts?

Greg

GregGleason said:

I wanted to try to build a better baffle. I like them because they do help to trap the larger ejection debris that can wreak havoc on the recovery system. But on this one I wanted to integrate the recovery system anchor along with this.

The design criteria was primarily centered on making it 1) heat durable, 2) shock-load durable, and 3) relative light.

The parts are relatively simple. A coupler of 2.31/32" length for a 2.60" airframe (I think I got it from Uncle Mike's Rocket Shack), 3 x 1/8" thick plywood bulkplates (Hobby Lobby), and 6 x 0.65" wooden dowels (Home Depot). The 3 dowels will serve as column between the bulkplates, with each bulkplate having 3 pockets (a depth of only 0.0125") each to make locating them a bit easier.

A 1/8" line of braided Kevlar, about 12" in length" will be placed 180 degrees from each other and anchored to the sides of the coupler with laminating epoxy and ~6 oz fiberglass. I plan to use Aeropoxy adhesive for the remainder of the joins and avoid the 5-minute stuff, mostly because I wanted a bit more working time. I am hoping for an assembly time of about 30 minutes to an hour.

View attachment 185833

Greg

Click to expand...

What did you use to cut the bulkheads?

Bat-mite said:

What did you use to cut the bulkheads?

Click to expand...

CNC mill.

Greg

Sweet. Do you ever do custom work for other forum members?

Bat-mite said:

Sweet. Do you ever do custom work for other forum members?

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Ha!

I don't know, since no one has ever asked. I suppose I would consider it though.

Greg

GregGleason said:

Thanks.

Have you flown it yet? If so, did it work ok?



John, I might try that.

Out of curiosity, what was the distance between the bottom end of your baffle and the tops of your motor mounts?

Greg

Click to expand...

It varies quite a bit depending on the overall size & Length of the model. That said in most of the 2.6" diameter models the aft end of the baffle was never closer then 10" from the forward end of the MMT, with the furthest 15.5" separation.
Somewhere I have a few super-8 movies of test motors inside clear glass tubing showing the after flames reaching as much as 5"+/- after burn-out. Almost looks like a blow-torch flame, really quite striking.

GregGleason said:

Thanks.

Have you flown it yet? If so, did it work ok?

Greg

Click to expand...

Yes, several times. Works fine.

I'd love to see those movies. I've been experimenting with baffles myself.

The ejection charge going off may still leave delay grain behind to continue burning. Check out the two pics attached. I beleive the fireballs are the ejection charge blowing out chunks of delay grain.

The baffles I'm making are disks cut in half slightly off center so the halves overlap and each lip has a verticle lip on the lower side to catch the heavier particles. Not enought flights to determine its effectiveness yet.

Having giving this some more thought, I'm going forward with the initial design but I plan to add some screws so that I can make this a replaceable item. That way the rocket can still be used if the baffle gets toasted beyond use.

Or I may not.

Regardless, like many engineering choices, there is an upside/downside to any design. And the "right answer" in one application may not work in another scenario.

Greg

First to Greg -
Looks like a great design. The CNC cuts and dowel recesses are well thought out.

To Micromeister,
Your baffle may have lasted only seven flights with (combined) three D engine ejections hitting it at once.

Check this out:
https://modelrocketbuilding.blogspot.com/2013/01/centurion-autopsy.html



I wouldn't have cut open the Centurion, but it was so banged up and beyond repair.
After fifteen single engine flights on it I was surprised how the baffle end plates held up.
No burn through or thinning of the heavy card stock ends.
During construction they were just coated with white glue. No epoxy, no metal tape.
The ejection crud just kept coating the flat plates and probably protected it from any damage.
This baffle could have gone through many, many more flights.