Baffle ???

[Race58]

I am building a V2 using a Canadian Arrow. I plan to fly it with "E"-"F" motors and carry a Boostervision camera payload section.
Since I am a fairly "New BAR" and have been out for quite awhile I have never used a baffle before but now days it seems that a lot do.
I made one out of a coupler and some centering ring scrap I had laying around. It is 1" long and has 3 baffle plates. I plan to mount it at the top of the BT50H engine mount. All of this is posted in the pics below.
It seems so small so my ?? is will it be enough to handle the ejection gasses or will wadding etc. be needed also??

View attachment V2 MM-Baffle 013.JPG

View attachment PB010009.JPG

View attachment PB010011.JPG

View attachment V2 MM-Baffle 012.JPG

 

[geof]

That looks fine, IMO. It looks like you've got 3-5 inches between the top of the motor and the bottom of the baffle. Fine. 3 plates should work, although I have also gone for 4-5 sometimes. Nice neat work.

One thing I might say is that the baffle plates look a little close together. Maybe 0.5in between them (or more) would be better. Let's see what others say.

G

 

[powderburner]

From the description, it sounds a little on the tight side but I believe it should work.

Sounds like there is plenty of 'space' for the gases to get through the baffle. If the discs are three-in-an-inch and if they are at each end of the inch plus one in the middle, they are essentially a half inch apart. That makes a flow area between discs of something like 1/2 square inch (1/2 inch long by approx 1 inch wide) which is about the same cross-sectional area available for gas flow as the path coming out of the front of the motor. Ought to work fine. Apply a good fillet of glue around the fwd outer edge of the fwd disc to keep it from pushing out of the baffle and out the front end of the rocket.

However, remember the closer you put the baffle to the motor, and the tighter you make the gas path (smaller holes, fewer holes, tighter spacing between baffle discs, etc), the hotter the ejection gas is going to be when it hits and squeezes through the baffle. Hot gas means scorching and erosive flow, which may cause premature burn-through of the baffle. Coating the baffle surfaces with epoxy (via Qtip, as far as you can reach) might help a bit.

Hot gas, in this case, means combustion temp of the blackpowder ejection charge. I don't have that number handy at the moment but IIRC we are at something like 2500 or 2600 degrees? That is inside the front of the motor. As the ejection gas expands it begins to cool (slightly) but it is still going to be pretty warm. More space for expansion means more chance for the gases to expand and cool, and to mix with the air in the chamber and cool. It might be better next time if you could allow a few more inches in front of the motor before you place the baffle?



Edit: Oops. Looked more closely at the pix. Your baffle is not in the BT80, it is in the BT50 MMT. Changed my gas-path numbers. Still looks like it should work.

 

[Race58]

Thanks for the inputs. Since nothing is glued yet I can extend the MT and make the baffle longer. It is on the CA and I have plenty of room since I elected for this V2 version to make a video payload and not cut out the 4+ inches in the BT. I'll just use this baffle on something else.
Getting back into this I have found that I have quite a bit to catch up on or learn for the first time or again (CRS you know:surprisedand this forum is great for that.
Thanks

 

[Ford Prefect]

Might I suggest a portion of Chore Boy stainless steel scrubber as a heat sink.

Cjirate:

 

[jflis]

I would suggest a minor modification that will help more gas pass but should still provide an effective baffle. I notice in your picture that you have a half-moon shape cut from within the ring in your baffle. I am assuming that all 3 rings are cut the same and rotated 180 degrees from each other.

That *border* around the cut out isn't necessary and may result in the hole being too small, especially if you get one of the aggressive ejection charges.

I've attached a figure from our baffle assembly to give you an idea of what I am talking about.

Hope this helps
jim