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-   -   Question in regards to Ejection Baffles. (http://www.oldrocketforum.com/showthread.php?t=13420)

dvmanning 01-17-2014 09:07 PM

Question in regards to Ejection Baffles.
 
Having never used an Ejection baffle, is it practical to use a baffle in the BT-50 tube, .095 inch I.D. or are the baffles designed more for the larger tubes? Are the sizes in millimeters, as I have seen described as a Series 13, 14, 19 etc. The BT-60 has an inside diameter of 40.52 mm or 1.595 inches 1.6 inches.. What baffles would I order for the BT-50 or the BT-60 tubes, if I decide to use the baffles in the construction of the future models. :)

BEC 01-17-2014 10:16 PM

My favorites for BT-55 and up are the conical ones from Semroc on this page: http://www.semroc.com/Store/scripts...p?idCategory=68

I have seen some baffles from other vendors for BT-50 but don't have any experience with any of them.

tbzep 01-17-2014 10:41 PM

I have used 1/2 moon baffles in BT-20. They are actually in motor mounts of short rockets that don't have room for wadding and chute. They work great, but the rockets have low flight numbers so I don't know how many flights they will last. I suspect less than 50 flights before they burn out.

dvmanning 01-18-2014 07:01 AM

I guess my question should be "How are they sized for the smaller ones? Here is an example on SEMROC, (Featherweight laser-cut fiber ejection baffle ring for #16 tubes. ) What is the #tube that I need for the BT50 tube. I get the sizing for the BT-55, BT-60, BT70, etc.
The Estes Vagabond has the BT-60 tube, so the EBR-60W Baffle will work since it has the 1/4 inch elastic cord. This is the main one I am considering to install the Cone shaped ejection baffle in. Thanks for the link to Semroc , but I'm quite familiar with the website, since all of my components have been purchased from them. over the past two years.

hcmbanjo 01-18-2014 09:28 AM

Here you go!

BT-50 Baffles and above:
http://www.jonrocket.com/index.php?...ndex&cPath=9_36

BT-20 baffles and above:
http://www.unclemikesrocketshack.co...mex_Baffle.html
Scroll down to the "Baffles Made From Letramax"

tbzep 01-18-2014 09:53 AM

Quote:
Originally Posted by dvmanning
What is the #tube that I need for the BT50 tube.

If you are making a home made baffle for a BT50 tube, use a BT50 size tube coupler. Estes/Semroc designation is JT-50C. Balsa Machining Service carries that size tube in 1", 4", and 34" lengths, C50-1, C50-4, C50-34.

dvmanning 01-18-2014 10:30 AM

Thanks, for the great information.

dvmanning 01-18-2014 10:31 AM

Thanks, for the websites. I can use these later.

Joe Wooten 01-18-2014 12:04 PM

I don't remember who made them, probably SEMROC, but I have used the BT50 baffles with good success. ABout 20 flights on both of them so far.

BEC 01-18-2014 12:38 PM

Quote:
Originally Posted by dvmanning
I guess my question should be "How are they sized for the smaller ones? Here is an example on SEMROC, (Featherweight laser-cut fiber ejection baffle ring for #16 tubes. ) What is the #tube that I need for the BT50 tube. I get the sizing for the BT-55, BT-60, BT70, etc.
The Estes Vagabond has the BT-60 tube, so the EBR-60W Baffle will work since it has the 1/4 inch elastic cord. This is the main one I am considering to install the Cone shaped ejection baffle in. Thanks for the link to Semroc , but I'm quite familiar with the website, since all of my components have been purchased from them. over the past two years.


Sorry - I should've caught your SAM number in your post and realized that you were already familiar with Semroc stuff.....

Semroc doesn't have baffles for smaller than BT-55. If they did I'd expect they'd be so marked (though one for ST-9 would also work, if it existed, since it has the same ID).

Others have provided some good alternatives.

FWIW - I use the Semroc EB-60 in all my BT-60-based birds including my Vagabond.

mycrofte 11-03-2019 08:54 AM

1 Attachment(s)
This is an old thread but seemed appropriate.

Suddenly occurred to me there was no need to build a separate baffle when I am already building an engine tube. So, for my last few rockets, I have been designing one right into an extended tube.
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jetlag 11-04-2019 07:50 AM

By your sketch, it looks to me like that baffle will burn up after just a few flights. Not enough room for flame or heat dissipation.

Allen

ghrocketman 11-04-2019 08:53 AM

+1 to what jetlag just said.
That thing will be TORCHED in less than 5 flights.

mycrofte 11-04-2019 09:08 AM

Quote:
Originally Posted by jetlag
By your sketch, it looks to me like that baffle will burn up after just a few flights. Not enough room for flame or heat dissipation.

Allen


The drawing was more for concept than dimensional accuracy. But most baffles seem to be about 2". I have never done a test burn to see how far the flame comes out during ejection.
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tbzep 11-04-2019 09:21 AM

I built a AAA Aviation Fuels Cherokee G with a similar motor tube baffle. Even with heavy wall tubing, the holes in the motor tube directed jets of hot gases and eventually burned the body tube at the location of each motor tube baffle hole.

mycrofte 11-05-2019 05:24 AM

I don't plan on anything that big.

tbzep 11-05-2019 07:03 AM

Quote:
Originally Posted by mycrofte
I don't plan on anything that big.

My point is that it even burned through heavy wall tubes, not the size of the rocket. I've built D powered rockets that were much larger.

The ejection gases need to be contained in a way that they do not get directed toward an outside wall unless it is protected with a heavy coupler, preferably fish paper or something that will take a long time to ablate.

mycrofte 11-06-2019 05:40 AM

Might be a good idea to cut an inch long section of tube and glue in where the holes exhaust. At least doubling the body tube there would last longer.
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vulcanitebill 11-09-2019 10:28 PM

I have buit baffles of that type in 29mm motor mount tubes. I use a longer tube, at least 12" long, glue a 29mm wood disk in the front of the tube and then a solid bulkhead of airframe diameter with big slots or openings cut in the perimeter. I build an eyebolt into this to attach the recovery harness to. Then I cut some rectangular openings in the side of the motor tube just behind the bulkhead, usually a couple of rectangular openings on opposite sides of the tube. The part of the tube that remains gets glassed so it can still resist pull from the recovery harness.

I didn't know how large the openings needed to be but I figured that an Aerotech RMS could blow through a 24mm or 29mm tube so I calculated the area of a 24mm tube and try to make the slots and openings add up to at least that much area.

I've not had a problem with this but my rockets haven't had more than a half dozen flights each. I'm not concerned about burning out the airframe because the openings in the motor tube are far enough in front of the motor that the flames probably won't reach that far.

I don't think a baffle makes sense in a very short rocket. I think the best strategy would be a kevlar chute protector.

ghrocketman 11-10-2019 10:35 AM

The ejection flame front of typical SU BP motors goes at least 8" if not more.

mycrofte 11-11-2019 05:27 AM

I only launch with Estes A-B-C motors. And I have yet to see any baffle that long. So, I am guessing they will all burn out eventually.
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ghrocketman 11-11-2019 11:35 AM

The baffle does not need to be 8" long. It only needs to be 8+" away to not be in contact with any flame.
For example, the baffle on my Semroc Explorer is about 10" away from the top of the motor.

If it is in contact with flame, yes, eventually the tube and baffle will get torched.


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